Low-Temperature Processing of Food Products [1 ed.] 0128187336, 9780128187333

Citation preview

Low-Temperature Processing of Food Products

This page intentionally left blank

Low-Temperature Processing of Food Products Unit Operations and Processing Equipment in the Food Industry

Edited by

Seid Mahdi Jafari Faculty of Food Science and Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

Hadis Rostamabadi Department of Food Science and Technology, School of Nutrition and Food Science, Nutrition and Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

Woodhead Publishing is an imprint of Elsevier 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States 125 London Wall, London EC2Y 5AS, United Kingdom Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies. Publisher’s note: Elsevier takes a neutral position with respect to territorial disputes or jurisdictional claims in its published content, including in maps and institutional affiliations. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-12-818733-3 For information on all Woodhead Publishing publications visit our website at https://www.elsevier.com/books-and-journals Publisher: Nikki Levy Acquisitions Editor: Nina Bandeira Editorial Project Manager: Andrea Dulberger Production Project Manager: Fizza Fathima Cover Designer: Christian Bilbow Typeset by TNQ Technologies

Contents

List of contributors

xi

Section One

1

1

2

Basics of low-temperature processing

Fundamentals of chilling/cooling processes M.C. Ndukwu, O.S. Onwuka, Lyes Bennamoun, Fidelis Abam and Godwin Akpan 1.1 Introduction 1.2 Role of cooling/chilling in food preservation 1.3 Mechanism of chilling/cooling processes 1.4 Chilling/cooling curve or phases 1.5 Classification of the cooling/chilling process 1.6 Cooling/chilling stages 1.7 Methods of chilling/cooling 1.8 Chilling/cooling capacity 1.9 Cooling/chilling rate 1.10 Modeling of the chilling and cooling process 1.11 Conclusion References Further reading Fundamentals of freezing processes Seid Reza Falsafi, Asli Can Karaca, Ozgur Tarhan, Rosana Colussi, Bengi Hakg€ uder-Taze, Yogesh Kumar and Hadis Rostamabadi 2.1 Introduction 2.2 Thermochemistry of freezing process 2.3 Freezing approaches 2.4 Impact of freezing on microbial and physicochemical aspects of foods 2.5 Postfreezing events 2.6 Novel freezing system and future trends 2.7 Conclusion References

3

3 4 6 7 8 11 11 14 15 18 20 21 23 25

25 26 30 35 38 42 46 46

vi

3

Contents

Elements of a low-temperature processing system Busra Gultekin Subasi and Esra Capanoglu 3.1 Introduction 3.2 Basics of heat and mass transfer for refrigeration technology 3.3 Main elements of mechanical refrigeration 3.4 Mechanical equipment 3.5 Refrigerants 3.6 Chilling and freezing systems 3.7 Conclusion References

Section Two 4

5

Different types of cooling and freezing systems

Refrigerated rooms and industrial systems for quick chilling and freezing Chinglen Leishangthem, Charis K. Ripnar, Ribhahun Khonglah, Macdonald Ropmay, Tanya Luva Swer and P. Mariadon Shanlang Pathaw 4.1 Introduction 4.2 Present scenario of cold storage in India and global 4.3 Certain measures for the proper functioning of cold storage 4.4 Refrigerated rooms 4.5 Thermal bridges 4.6 Conclusion References Still cooling in air and surface top icing Mohammad Alipour Shotlou, Nader Pourmahmoud and Paria Sarvaree 5.1 Introduction of still cooling in air and surface top icing 5.2 Definition 5.3 Comparison of different types of cooling 5.4 History of using still cooling in air and surface top icing 5.5 Governing equations in cooling systems 5.6 Advantages and disadvantages of cooling methods 5.7 Different cooling devices 5.8 Costs of still air cooling and top-icing 5.9 Factors affecting the effectiveness of still air cooling and top icing in food products 5.10 Comparison 5.11 Effectiveness in food preservation 5.12 Challenges and limitations 5.13 Conclusion References

53 53 54 57 62 70 71 72 72

77 79

79 80 80 81 87 87 87 89 89 89 92 93 94 96 98 107 108 112 113 113 114 115

Contents

6

7

8

Air blast freezing in the food industry Duy K. Hoang and James K. Carson 6.1 Introduction 6.2 Types of air blast freezers 6.3 Air blast freezer design and operation 6.4 Mathematical modeling of refrigeration processes 6.5 Blast freezing and food quality 6.6 Energy usage in air blast freezing 6.7 Conclusion Nomenclature References

117

Spray freezing and single/double-contact freezing systems Bengi Hakg€ uder-Taze, Seid Reza Falsafi and Hadis Rostamabadi 7.1 Introduction 7.2 Principles and mechanism of spray freezing 7.3 Different spray freezing approaches 7.4 Single/double-contact freezing 7.5 Different single/double-contact freezers 7.6 Conclusion References

147

Direct or indirect immersion freezing systems Rogelio S anchez-Vega, Ingrid Aguil o-Aguayo and María Janeth Rodríguez-Roque 8.1 Introduction to immersion freezing systems 8.2 Principles of immersion freezing 8.3 Direct immersion freezing 8.4 Indirect immersion freezing 8.5 Immersion freezing systems 8.6 Innovations in immersion freezing technologies 8.7 Conclusion References

167

Section Three 9

vii

Application of freezing in the food industry

Freezing of fruits and vegetables Marcello Alinovi, Maria Paciulli, Massimiliano Rinaldi, Seid Reza Falsafi and Emma Chiavaro 9.1 Introduction 9.2 Market trends and consumers’ demand for frozen fruits/vegetables 9.3 Freezing 9.4 Quality variations in frozen fruits/vegetables

117 118 124 130 137 139 141 141 142

147 147 150 153 156 163 163

167 170 171 174 176 179 189 190

197 199

199 200 201 211

viii

Contents

9.5

10

Conclusions References

Freezing of meat, poultry, and seafoods Gizem Sevval Tomar, Meryem Seri, Rukiye Gundogan, Humeyra Cavdar and Asli Can Karaca 10.1 Introduction 10.2 Methods used for freezing meat, poultry and seafoods 10.3 Thawing 10.4 Effect of freezing on the quality of meat, poultry and seafood products 10.5 Packaging and storage of frozen meat, poultry, and seafood products 10.6 Recent advances in freezing of meat, poultry, and seafoods 10.7 Conclusion and future perspectives References

218 218 225

225 227 231 234 244 246 251 252

11

Freezing of baked goods and prepared foods 259 Perla G. Armenta-Aispuro, Ofelia Rouzaud-S andez, Yolanda L. L opez-Franco, Jaime Lizardi-Mendoza, José L. C ardenas-L opez and Cristina M. Rosell 11.1 Introduction 259 11.2 Frozen bakery goods 261 11.3 Frozen dough 267 11.4 Freezing technologies 271 11.5 Impact of the freezing on the constituents of different baked goods 274 11.6 Addition of cryo-protectant additives 278 11.7 Conclusions and future perspectives 281 References 281 Further reading 287

12

Quality kinetics and shelf life prediction and management in the frozen foods chain Maria C. Giannakourou and Efimia Dermesonlouoglou 12.1 Introduction 12.2 Modes of deterioration of frozen foods 12.3 Principles of reaction kinetics for frozen foods’ degradation 12.4 Shelf-life determinationdCase studies applying conventional and stochastic mathematical/statistical tools 12.5 Application of TimeeTemperature Integrators for postprocessing cold chain monitoring and optimization 12.6 Concluding remarks References Further reading

289 289 290 296 306 314 318 318 327

Contents

Section Four Design, control, and efficiency of freezers 13

14

ix

329

Design and simulation of freezing processes Narjes Malekjani and Mina Homayoonfal 13.1 Introduction 13.2 An introduction to physical and transport phenomena involved in the freezing process 13.3 Definitions of physical properties and coefficients involved in modeling the freezing process 13.4 Analytical methods 13.5 Empirical solutions 13.6 Numerical solutions 13.7 Modeling coupled heat and mass transfer phenomena 13.8 Supercooling and nucleation effects 13.9 CFD modeling of freezing 13.10 Conclusion References

331

Different parameters affecting the efficiency of freezing systems Małgorzata Nowacka, Agnieszka Ciurzy nska, Magdalena Trusinska and Emilia Janiszewska-Turak 14.1 Introduction 14.2 Freezing processdgeneral factors affecting freezing 14.3 Parameters influence the freezing time and freezing rate/speed 14.4 Conclusion References

373

Index

331 331 334 340 342 346 359 364 366 367 368

373 374 377 393 394 399

This page intentionally left blank

List of contributors

Fidelis Abam Department of Mechanical Engineering, University of Calabar, Calabar, Cross River, Nigeria Ingrid Aguil
o-Aguayo Institut de Recerca i Tecnologia Agroalimentaries (IRTA), Postharvest Programme, Processed Fruits and Vegetable, Parc Agrobiotech, Lleida, Spain Godwin Akpan Department of Agricultural Engineering, Akwa Ibom State University, Mkpat Enin, Akwa Ibom, Nigeria Marcello Alinovi

Department of Food and Drug, University of Parma, Parma, Italy

Mohammad Alipour Shotlou University, Urmia, Iran

Mechanical Engineering Department, Urmia

Perla G. Armenta-Aispuro Departamento de Investigaci
on y Posgrado en Alimentos, Universidad de Sonora, Hermosillo, Sonora, México; Grupo de Investigaci
on en Biopolímeros, Centro de Investigaci
on en Alimentaci
on y Desarrollo, Hermosillo, Sonora, México Lyes Bennamoun Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada Asli Can Karaca Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Esra Capanoglu Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey James K. Carson Zealand

School of Engineering, University of Waikato, Hamilton, New

Humeyra Cavdar Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Emma Chiavaro

Department of Food and Drug, University of Parma, Parma, Italy

Agnieszka Ciurzy
nska Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences e SGGW, Warsaw, Poland

xii

List of contributors

Rosana Colussi Center for Chemical, Pharmaceutical and Food Sciences, Federal University of Pelotas, Pelotas, Brazil José L. C
ardenas-L
opez Departamento de Investigaci
on y Posgrado en Alimentos, Universidad de Sonora, Hermosillo, Sonora, México Efimia Dermesonlouoglou National Technical University of Athens, School of Chemical Engineering, Laboratory of Food Chemistry and Technology, Athens, Greece Seid Reza Falsafi Safiabad Agricultural Research and Education and Natural Resources Center, Agricultural Research, Education and Extension Organization (AREEO), Dezful, Iran Maria C. Giannakourou National Technical University of Athens, School of Chemical Engineering, Laboratory of Food Chemistry and Technology, Athens, Greece Busra Gultekin Subasi Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Rukiye Gundogan Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Bengi Hakg€ uder-Taze Department of Food Engineering, Faculty of Engineering, Usak University, Usak, Turkey Duy K. Hoang Zealand

School of Engineering, University of Waikato, Hamilton, New

Mina Homayoonfal Research Center for Biochemistry and Nutrition in Metabolic Diseases, Institute for Basic Sciences, Kashan University of Medical Sciences, Kashan, Iran; Nutrition Department, School of Medicine, Kashan University of Medical Science, Kashan, Iran Emilia Janiszewska-Turak Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences e SGGW, Warsaw, Poland Ribhahun Khonglah India

Food Processing, Govt. of Meghalaya, Shillong, Meghalaya,

Yogesh Kumar Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Longowal, Punjab, India Chinglen Leishangthem

National Institute of Technology, Rourkela, Odisha, India

Jaime Lizardi-Mendoza Grupo de Investigaci
on en Biopolímeros, Centro de Investigaci
on en Alimentaci
on y Desarrollo, Hermosillo, Sonora, México

List of contributors

xiii

Yolanda L. L
opez-Franco Grupo de Investigaci
on en Biopolímeros, Centro de Investigaci
on en Alimentaci
on y Desarrollo, Hermosillo, Sonora, México Narjes Malekjani Alexander von Humboldt Research Fellow, Otto von Guericke University Magdeburg, Magdeburg, Germany P. Mariadon Shanlang Pathaw North East Centre for Technology Application and Reach, Shillong, Meghalaya, India M.C. Ndukwu Department of Agricultural and Bio-Resources Engineering, Michael Okpara University of Agriculture Umudike, Umuahia, Abia, Nigeria Małgorzata Nowacka Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences e SGGW, Warsaw, Poland O.S. Onwuka Department of Mechanical Engineering, Michael Okpara University of Agriculture Umudike, Umuahia, Abia, Nigeria Maria Paciulli

Department of Food and Drug, University of Parma, Parma, Italy

Nader Pourmahmoud Urmia, Iran

Mechanical Engineering Department, Urmia University,

Massimiliano Rinaldi Italy

Department of Food and Drug, University of Parma, Parma,

Charis K. Ripnar Food Processing, Govt. of Meghalaya, Shillong, Meghalaya, India María Janeth Rodríguez-Roque Autonomous University of Chihuahua, Faculty of Agrotechnological Science, Chihuahua, Mexico Macdonald Ropmay India

Food Processing, Govt. of Meghalaya, Shillong, Meghalaya,

Cristina M. Rosell Food and Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada; Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC), Valencia, Espa~ na Hadis Rostamabadi Department of Food Science and Technology, School of Nutrition and Food Science, Nutrition and Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran Ofelia Rouzaud-S
andez Departamento de Investigaci
on y Posgrado en Alimentos, Universidad de Sonora, Hermosillo, Sonora, México Paria Sarvaree Iran

Mechanical Engineering Department, Urmia University, Urmia,

xiv

List of contributors

Meryem Seri Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Rogelio S
anchez-Vega Autonomous University of Chihuahua, Faculty of Zootechnics and Ecology, Chihuahua, Mexico Tanya Luva Swer National Institute of Food Technology Entrepreneurship and Management (NIFTEM), Sonipat, Haryana, India Ozgur Tarhan

Food Engineering Department, Us¸ak University, Us¸ak, Turkey

Gizem Sevval Tomar Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey Magdalena Trusi
nska Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences e SGGW, Warsaw, Poland

Section One Basics of low-temperature processing

This page intentionally left blank

Fundamentals of chilling/cooling processes

1

M.C. Ndukwu 1 , O.S. Onwuka 2 , Lyes Bennamoun 3 , Fidelis Abam 4 and Godwin Akpan 5 1 Department of Agricultural and Bio-Resources Engineering, Michael Okpara University of Agriculture Umudike, Umuahia, Abia, Nigeria; 2Department of Mechanical Engineering, Michael Okpara University of Agriculture Umudike, Umuahia, Abia, Nigeria; 3Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada; 4 Department of Mechanical Engineering, University of Calabar, Calabar, Cross River, Nigeria; 5Department of Agricultural Engineering, Akwa Ibom State University, Mkpat Enin, Akwa Ibom, Nigeria

1.1

Introduction

Globally food preservation is a major issue, as still greater amount of produced foods can be deteriorated due to the application of inadequate food preservation methods (Kumar & Kumar, 2023; Ndukwu et al., 2015). One of the applied methods to preserve food products for some period is by lowering the temperature of the food and increasing its surrounding humidity so that the initial nutritional, color, and texture characteristics are kept preserved before its consumption. This is the general goal of refrigerated preservation of foods and agricultural products (Chopra et al., 2023). Accordingly, an efficient cold chain is designed to effectively maintain the stability of the food within its system as long as possible without adverse effects on the quality of the food (Becker et al., 2011). For preliminary preservation or precooling for a short duration, which is a primary step, chilling or cooling of the food is adopted, while freezing is implemented for a long period of storage in a cold chain while the food is stored, displayed in the storage cabinet, or even transported. However, whether it is the primary chilling/cooling of the food or the secondary freezing operation of the food in a cold chain, the goal is lowering the temperature or maintaining the food temperature at an optimal level to prevent a microbial attack. Nevertheless, for the chilling or cooling process, the product’s temperature reduction does not reach the freezing temperature where ice is formed on the food, or the food becomes iced solids. Both are processes that exchange thermal energy from one product at a lower temperature with the other at a higher temperature. In cooling, the temperature of the food product is reduced from one level of temperature to another lower level; for chilling, the temperature of the product is reduced and stabilized (James, 2003) such that the mobility of free liquid water in the food is greatly retarded where microbes will be inactive to metabolize. Thus,

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00013-8 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

4

Low-Temperature Processing of Food Products

chilling occurs at a temperature range of
1.0e8.0 C. Chilling is cooling a product close to the temperature of melting ice. This is done within a cold chamber with a lot of air draught or movement at relative humidity ranging from 90% to 95%. Nonetheless, when the temperature of the product is decreased to 1e2 C below the freezing point where we have water ice mixture, it is termed superchilling. However, both processes are deployed to reduce biochemical decomposition in food to extend the product’s shelf life or to serve the product at a particular temperature to consumers. They can also be used to initiate a change of state like crystallization. In the cooling or chilling process, the product is passed through a cooling medium, which could be air, ice, gaseous refrigerants, water, or water mixed with glycol inside a cooling chamber (FAO, 2003). The cooling medium can be recirculated through a mechanical compression or ice-water refrigerating system including evaporative cooling. Other new technologies like adsorption cooling are in existence where certain materials like silica gel are used to absorb water from the food surface, and the adsorbed water is separated by heating. Waste heat from other thermal systems can be used, making the process cost-effective. Additionally, cryogenic cooling exists, which expels the spent vapor directly into the atmosphere. Other newly advocated technologies for cooling include magneto and electro-calorific materials. Generally, cooling/chilling methods can be classified based on the total loss or the mechanical refrigeration systems. However, the same equipment deployed for cooling can also be deployed for chilling. The difference is the operating temperature of the cooling medium and its stability plus other operating variables like heat transfer rate, which determines the temperature gradient that will be experienced by the product and the speed at which it is achieved. The basic criteria are very important, and the chilling operation must be satisfied, including: • • • •

the regulatory demand for the process operations, energy saving by minimizing the time of chilling to increase the operation throughput minimizing the mass loss of the product (especially in meat products), and hampering the toughening of muscles in the case of meat products due to the cold shortening.

1.2

Role of cooling/chilling in food preservation

Different organisms thrive at different levels of temperature. The capacity of these organisms to thrive has been linked to the composition and architecture of the plasma membrane (Acharya, 2023). When heat is extracted from the material with the consequential decrease in temperature, this plasma membrane undergoes a phase transition from liquid crystalline to form a rigid gel. Hence, the transportation of solute is highly impeded. These transition temperatures vary from one material to another. For example, organisms like psychrotrophs and psychrophiles thrive at low temperatures (5e7 C), while mesophiles can thrive at 10 C. This is due to the high presence of unsaturated fats in the lipid membrane (Acharya,

Fundamentals of chilling/cooling processes

5

Table 1.1 Food pathogens and minimal operating temperatures (James & James, 2014).

s/n

Food pathogen

Minimum operating temperature (8C)

1 2 3 4 5 6 7 8 9 10 11 12

Campylobacter spp. 30 Pathogenic Escherichia coli strains Escherichia coli O157:H7 6e7 Salmonella spp. 5 Aeromonas hydrophila Listeria monocytogenes Yersinia enterocolitica Toxigenic Clostridium perfringens Clostridium botulinum proteolytic Staphylococcus aureus Bacillus cereus Clostridium botulinum nonproteolytic

30 7 6e7 5
0.1e1.2
1e0
2 12 10 7 4 3

2023). Several organisms can adapt at low temperatures as shown in Table 1.1; hence, they are not restricted or inactivated at low temperatures, and the lipid membrane can multiply especially in yeast, Gram-negative or Gram-positive bacteria, and molds. Some reasons adduced for these include: • •

low thermal stability of the core enzymes and functional proteins and membrane fluidity at high temperatures

Therefore, organisms that overcome cooling (>8 C) will continue to thrive even in an injured state. Nevertheless, the decreasing temperature lowers the regeneration time of microorganisms. The lower the temperature is, the higher the regeneration time. The implication is that cooling or chilling will impede microbial growth in food and reduce spoilage (James & James, 2014). However, chilling produces cold shock, which can injure or kill the organisms and prevent them from thriving. Though, this depends on the rate of cooling, the type of organism, the growth medium, and the phases of growth. The process of cold shock in chilling damages the membrane lipids that assist in regenerating hydro-pores by which the cytoplasmic contents can leak out. Therefore, the chilling process can limit low-temperature operating pathogens like mesophils, psychrophiles, and psychrotrophs, nonetheless might not kill them completely. Hence, some pathogens can continue to thrive at chilled temperatures with increased health risks as the storage duration increases. Usually, chilling creates an adverse condition that modifies the metabolism process, such as photosynthetic electron transport in fruits and vegetables, the synthesis of pigments to maintain their initial color, and light energy absorption, which alters the photosynthetic redox state. It is then important that products are initially safe before chilling/cooling as chilling/ cooling will not make an unsafe product safe. Several foods have different chilling temperatures as stated in Table 1.2. Thus, this temperature range can be used to categorize the chilled food products.

6

Low-Temperature Processing of Food Products

Table 1.2 Chill temperature range of some products (Rosca et al., 2017). Temperature

Product


1 to þ1 C 0 to þ5 C

Fresh fish, meats, sausages, ground meats, smoked meats, and breaded fish Pasteurized canned meat, milk, cream, yogurt, prepared salads, sandwiches, baked goods, fresh pasta, fresh soups and sauces, pizzas, pastries, and unbaked dough Fully cooked meats, fish pies, cooked or uncooked cured meats, butter, margarine, hard cheese, cooked rice, fruit juices, and soft fruits

0 to þ8 C

1.3

Mechanism of chilling/cooling processes

Any process that removes heat from a material to maintain the temperature of the material below that of the environment is termed refrigeration. Therefore, chilling and cooling are a form of refrigeration. The heat removed from the refrigerated body is transferred to another body, usually the refrigerant or cooling medium whose temperature is below the refrigerated material as shown in Fig. 1.1. Thus, the three heat transfer modes are: conduction, convection/evaporation, and radiation are involved in the process depending on the type of product. The degree of involvement of the various heat transfer modes depends on: • •

position of the chilled/cooled product relative to the cooling medium (conduction heat transfer and the number of products to be chilled/cooled at a time (radiation).

Any mode of heat transfer process can initiate the process, while other modes can complete the process. However, convective movement of the air (convective heat transfer as shown in Fig. 1.1) is the major heat transfer method involved in the chilling/cooling of products.

Insulated wall

Baffles

Ice

Refrigerated Space

Conventional current

Cooled/chilled food

Drain

Figure 1.1 A typical ice-cooling process.

Fundamentals of chilling/cooling processes

7

Heat is carried from the walls and the food through the heat transfer medium to the refrigerant or cooling medium. The rate of heat extraction from cooled/chilled product is affected by the velocity and temperature of the cooling/chilling medium, the mass or thickness of the product, and the nutritional composition of the product, especially the fat content. In the case of weight loss, the rate of moisture loss (evaporation) varies linearly with weight loss. Consequently, the factors affecting the moisture loss of chilled products are the surface area for heat transfer, the vapor pressure deficit, and the mass transfer coefficient. For a system housing the material, the process requires an adequately insulated space to minimize outside heat inflow into the refrigerated space, make optimum use of the capacity of the cooling medium, and reduce the energy requirement of the refrigerated space (FAO, 2003). In general, the thermal insulators must fulfill: • • • •

good mechanical strength, poor moisture absorption/low moisture-vapor permeability, low thermal conductivity, and safety.

Thus, available insulation materials that can be used at cool/chilling temperatures are listed in Table 1.3. The total heat load or refrigeration load to be removed includes: • • • •

heat transmitted through the walls of the refrigerated space, the heat content of the refrigerated material, heat infiltration from warm air, and miscellaneous heat from the equipment.

1.4

Chilling/cooling curve or phases

Conventionally, ice is not formed during chilling/cooling. According to some researchers, this implies a low internal heat driving force, which prolongs the process when the layer of chilled product is very thick. Therefore, chilling takes longer hours. Table 1.3 Some insulation materials at cool/chilling temperatures (FAO, 2003). Type

Density (kg/m3)

Thermal conductivity (W mL18CL1)

Polyurethane foam Expanded polystyrene Expanded perlite Fiberglass Cork (various types) Rock wool bats Sawdust Straw Air space

30e40 kg/m3 10e33 kg/m3 130 kg/m3 10e144 115e250 e e e

0.026e0.0198 at 20e25 C 0.057e0.028 at 0 C 0.047 0.044e0.031 at 0 C 0.052e0.041 at 20e25 C e e e

8

Low-Temperature Processing of Food Products

Temperature (oC)

20

10

Liquid moisture (Cooling/chilling)

Liquid + Solid mixture

0 (Super chilling) Solidificaon -10

[Sensible Heat evoluon]

(Freezing)

[Latent Heat evoluon]

[Sensible heat evoluon] -20 0

5

10

15

20

25

30

Time (min.) Figure 1.2 The cooling curve of moisture depicting the cooling/chilling-super-chilling phases.

For a product consisting of more than one component like food and agricultural materials where the liquid contains dissolved substances, instead of a single melting temperature, the products have two different temperatures, that is, the liquid and solid temperature. The liquid temperature is the temperature above which the moisture is liquid, while the solid temperature is the temperature at which the moisture in the product solidifies, that is, the product freezes. Thus, chilling/cooling occurs in the liquid phase, and the process undergoes a sensible cooling phase with a sloping cooling rate with time as shown in Fig. 1.2. However, at the interphase between the liquid and solid phase occurs the super chilling phase where we have a mixture of solid and liquid moisture at 0 C. Within this phase, the liquid moisture and solid moisture (ice) are in equilibrium, and the cooling rate decreases and remains constant as the water crystallizes with the consequent evolution of the latent heat of fusion. The reason is that at this point, the liquid moisture has greater internal energy than the solid ice.

1.5

Classification of the cooling/chilling process

Cooling/chilling process can be classified as a sensible or latent cooling process. • •

Sensible cooling process: Heat absorbed by the refrigerants or cooling medium resulted in only a change in its temperature Latent cooling process: Heat absorbed by the refrigerants or cooling medium results in a change in state

Fundamentals of chilling/cooling processes

9

Further classification of chilling/cooling methods can be direct or indirect. For a direct method, the heat transfer medium comes in direct contact with the product chilled/cooled to extract the thermal energy from it like ice chilling/cooling (Fig. 1.1). While, in indirect methods, the chilling/cooling of the cooling medium is generated externally like in mechanical compression refrigeration using heat exchangers (Fig. 1.3) before applying the cooling to the product. However, for the direct contact methods, two methods are widely involved based on the heat transfer medium or the cooling medium. These are the spray/immersion/ hydro-cooling methods and the dry air methods. Air chilling employs a flow of controlled chilled air to lower the temperature of the product to the chill temperature. Air chilling is more suitable for fresh produce, and the risk of cross-contamination is low. Sometimes, this air blast is done in a chilling tunnel. Spray chilling employs intermittent water spray jets on the product during the initial period of chilling. Spray/immersion/hydro-cooling offers the following advantages: • • •

higher rates of heat transfer between the cooling medium and the product because of direct contact, reduction of dehydration due to the liquid cooling medium, and reduction of the frosting of the coil.

The choice of cooling medium in spray/immersion/hydro-cooling depends on the freezing temperature, although an iceewater mixture has been used because of the large refrigeration time of ice at a short duration at a constant temperature. Additional cryogenic substances like liquid nitrogen can also be used.

1.5.1

Super-chilling

As described earlier when the chilled temperature falls to about 1.0e2.0 C below the freezing temperature or ice formation partly occurs, it is termed super-chilling. In this process, some water is converted into ice at the surface of the product (Kaale et al.,

Hot water out

Chiller

Chilled water

Heat Exchanger

Hot Air

Storage space Chilled/ cooled Air Pump

Figure 1.3 Indirect chilling/cooling method.

10

Low-Temperature Processing of Food Products

2011). This formed ice will gain heat from the internal heat generated within the product until it reaches equilibrium. By accumulating cold within the product, the superchilling product functions as a heat sink for the ambient heat load. This produces an ice buffer for the product when transported and the need for ice replenishment is avoided. This is because the ice formed beneath the surface of the product absorbs heat from the inside of the product after the equipment is withdrawn, thus the holding period inside the chilling equipment is reduced in comparison to conventional chilling. As the temperature decreases rapidly below freezing temperature, more heat is removed as shown in Fig. 1.4. Super-chilling is described as the interphase between conventional chilling and freezing. Researchers have reported extended storage life of fish with better quality when super-chilled (Duun & Rustad, 2008). However, the major challenges in the super-chilling process are: •

• •

The control or the amount of ice crystal formation that will be optimum. Higher ice crystals have been reported to damage the structure and integrity of fish and can increase drip loss during thawing and product shrinkage. Thus, there is a need to have stable temperatures that will prevent excessive ice crystal formation (Dunn, 2008). The amount of heat to be removed increases, creating complications in the determination of holding time, temperature distribution, and the required heat load (Kaale et al., 2011) The phase change of water creates a problem calculating the chilling time due to discontinuity in enthalpy, which results in an infinite increase in the specific heat capacity. Thus, using the conventional equation for heat load calculation in traditional chilling might pose a problem (Kaale et al., 2011).

Figure 1.4 Heat removal and temperature relationship during chilling and super-chilling (Magnussen et al., 2008).

Fundamentals of chilling/cooling processes

1.6

11

Cooling/chilling stages

Food refrigeration can be classified as either chilled or frozen. The design of equipment to effectively carry out this cooling function requires not only the knowledge of the thermal properties (thermal diffusivity and conductivity, specific heat capacity) of food but also process steps and legislation around the product processing. However, the steps to achieve this passes through the cooling/chilling phase. For cooling food, time is of the essence to prevent bacteria growth on the food. Within the first 20 min, bacterial growth is rapid in cooked food and can double within this period. Therefore rapid cooling can suppress this bacterial growth. Aside from the objective of inhibiting rapid bacterial growth, rapid cooling or chilling minimizes evaporative loss, reduces the cooling period, and increases turnover. It also decreases shrinkage, drip loss, and surface color variation of the product. Nevertheless, rapid chilling or cooling to a temperature less than 10 C can result in toughening in meat due to cold shortening of carcasses before PH reduction to 17 >18 >5 2


1.1
1.1
1.0
1.0
0.6
0.6 0 to 1 þ0.2 to
1.5

Fundamentals of chilling/cooling processes

•

•

• •

•

13

Air chilling: In this case, air at the chill temperature is circulated through a fan/blower or finned evaporator, positioned at one end of the storage space at a relatively high speed. Batches or continuous processes can be used in the air chilling of products. Batch chilling can be done in the cold room while chilling tunnels are adopted for continuous chilling. The air circulation can be performed in longitudinal, transverse, or perpendicular direction. The tunnel continuous air chilling can be counter-current to increase the chilling rate. Air chilling has the advantage of keeping the product surface dry without much exudation as moisture pick is avoided. The report has also stated that air chilling has lower microbial development compared to water immersion. Water immersion chilling: This can occur in batches or continuous flow. In continuous flow, the process involves the use of cold water, which flows in the counter-current direction, while the product flows in the opposite direction. The essence of the flow direction is to maximize the chilling rate (Naghiu & Apostu, 2006). Continuous clean water is provided by this method, which constantly cleans the product and reduces the microbial load. This process achieves a chilling state faster than air chilling due to the higher convective heat transfer coefficient. However, constant water flow from one product to another can increase the rate of pathogen cross-transfer from one product to the other (Barbut, 2002; Bailey et al., 1987). Again, the process can allow the product to retain some water due to the temperature gradient. Though the amount of water retained must be clearly stated as required by food regulators in some countries. Refrigerated seawater: Usually used for chilling fish, in fish trolleys Dry ice: This is solidified carbon dioxide with a temperature in the range of
79 C. However, this method is not used in direct contact with food especially fruits; vegetables and meat because it can cause cold burns and damage to the product. This method is adopted under strict guidelines especially during the transportation of cold products because it can remove oxygen from the environment as it changes to gaseous form. Thus, it can lead to an environmental safety concern (FAO, 2003). Gel ice mat: This is forming an ice by freezing a water based-gel, thus preventing the water from leakage during the thawing of products like meat or fish.

The same equipment and method used for chilling can be used for cooling, but not in all cases due to temperature variations for both processes. However, typical cooling/ chilling methods are as follows: •

•

Air cooling: This is refrigerated cooling whereby unsaturated air at cooling temperature is cooled to the desired temperature and transferred to the product location in the cooling room. This process dehumidifies the storage space and does not need circulation. However, just like all mechanical compression systems, they are not energy efficient, and the refrigerant used might be harmful to the environment. Evaporative cooling: This method relies on the latent heat of the evaporation of water. The minimum temperature the product can be cooled is the wet bulb temperature of the inlet air (Ndukwu et al., 2018). However, two methods are adopted in evaporative cooling: the direct and indirect evaporative cooling system (Ndukwu, 2011; Ndukwu & Manuwa, 2014). In direct cooling, the air passes through the porous evaporative cooling pad/material, which is already humidified with water before entering the storage space. While, for the indirect method, the humidity is first dehumidified with a heat exchanger before passing it through the humidifier (Ndukwu, Ibeh, et al., 2023; Ndukwu et al., 2015). The direct method

14

•

Low-Temperature Processing of Food Products

increases the humidity of the inlet air, which is useful in keeping products like fruits and vegetables fresh (Ndukwu et al., 2022, 2023). The evaporative cooling method is energyefficient and environmentally friendly (Ndukwu & Manuwa, 2015). Nevertheless, it requires a constant water supply and is less efficient, especially in highly humid areas. It requires constant recirculation of air, though not in all designs. Hydro/water cooling: Water can directly be used to draw heat away from a product when it is in indirect contact with the product aside from using its latent heat of vaporization to cool air as in evaporative cooling. This can operate in a closed loop or in cooling towers, which is an open loop compared to air cooling. This method is more energy efficient; however, the water should be treated to prevent microbial growth. Additionally, water is absorbed by the product. Therefore, it is not all products that can tolerate hydro or immersion cooling (Kumer & Kumar, 2023).

1.8

Chilling/cooling capacity

The refrigeration system or equipment extracts heat from the product to reduce the product to the desired temperature. The unit of the heat extracting capacity by the equipment is “tons of refrigeration,” which is the amount of heat required to melt ice in 24 h (FAO, 2003). The calculation of the cooling/chilling load depends on the design or methods of cooling/chilling. For a mechanical chiller illustrated in Fig. 1.2, which uses water to chill the product, the heat load is often premised on the assumption that the air is completely dry and the system is well insulated. Thus, in the process, heat is extracted from the air (Qair) and heat is also added by the pump (Qpump). Where heat extracted (Kcal/hr) is calculated with Eq. (1.1). Qair ¼ Vair Cp;air DTair

(1.1)

where, Vair is the air flow rate, CP is the specific heat capacity and T is the temperature. Thus, the actual heat capacity in tons of refrigeration (1 TR ¼ 3.157 kW) is given in Eq. (1.2) as follow: Qcapacity ¼

Qair þ Qpump 3024

(1.2)

However, if the air is saturated, the condensation heat load should also be added to the chiller capacity. For a system with solid ice as the cooling medium, the container or the storage space is completely sealed. The ice absorbs heat from the stored material and melts. In the design of such a system of importance is the rate at which the ice melts. This can be deduced with Eq. (1.3) as follow: K1 ¼

AU L

(1.3)

Fundamentals of chilling/cooling processes

15

where, A is the heat transfer area, L is the latent heat of fusion of ice, and U is the heat transmission coefficient, which is the rate at which external heat penetrates the storage space given in Eq. (1.4) as follow: U¼

1 1 P xn 1 þ þ a1 k n a2

(1.4)

where, a1 and a2 are the heat transmission coefficient of the outer and inner walls, respectively, x is the thickness of the walls, k is the thermal conductivity of the wall layers, and n is individual wall layers. The heat transfer rate through the storage space can be deduced with Eq. (1.5) (FAO, 2003), while the cooling rate (energy flux) can be deduced with Newton’s law of cooling using Eq. (1.6) (Landerslev et al., 2018) Q ¼ A  U  DT

(1.5)

where, DT is the temperature difference between the outer and inner space.   q ¼ h:A. Ts
Tp

(1.6)

where, h is the heat transfer coefficient and A is the surface area of the product. The mass of ice required to chill/cool the product to the desired temperature can be determined with Eq. (1.6).   Mi L ¼ Mp  Cp;p  Tp;i
Tp;o

(1.7)

where, Mi is the initial mass of the ice (kg), L is the latent heat of fusion of ice (kJ/kg), Mp is the mass of the product (kg), Cp,p is the specific heat capacity of the fresh product, Tp,i is the initial temperature of the product, and Tp,o is the chilled or cooled temperature of the product.

1.9

Cooling/chilling rate

The cooling/chilling rate is a measure of the time required to bring the product to the desired temperature. This parameter is very important in the designing of cost-effective cooling/chilling equipment (Elansari et al., 2016; Tan et al., 2012). For fruits, the initial temperature can be cooled down below 5 C. Fig. 1.5 depicts the cooling rate curve for a product cooled to 7/8 of the initial temperature (Elansari et al., 2020). This cooling time is important because it is believed that at this period to product is close to the storage temperature.

16

Low-Temperature Processing of Food Products

Figure 1.5 An example of cooling a product to the 7/8 cooling time in 9 h (Elansari et al., 2020; open access).

The rate of heat removal from chilled/cooled products is a function of the: • • • •

heat transfer coefficient of the food and the cooling medium, which depends on the physicthermal properties of the product and the food sample, the product surface area, the temperature gradient between the coolant and the product, and air velocity for a forced air cooling/chilling.

Although, increasing air velocity increases the cooling rate it has to be managed to balance the energy cost and the cooling rate (Elansari et al., 2020). The cooling/chilling rate is deduced as a slope of the cooling temperature (T) with time duration (t) as shown in Fig. 1.5. It can be presented mathematically as follow (Rosca et al., 2017): W¼

dT dt

(1.8)

where, T can be deduced kinetically with Eq. (1.9) with the assumption that the product is homogenous, there is no mass movement between the cooling medium and the product, the cooling medium has a constant temperature and the product temperature is the same across the matrix of the product.

Fundamentals of chilling/cooling processes



 T ¼ To þ ðTi
To Þ:e

17

h:S m:Cp

t

(1.9)

where, Cp is the specific heat capacity of the product, m is the product mass (kg), S is the product surface area (m2), Ti and Tf are the initial and final temperature of the product ( C), and To is the cooling medium temperature ( C). Thus the time duration (tr) for cooling or chilling can be deduced as follow: tr ¼

m:Cp Ti
To In h:S Tf
To

(1.10)

To compare the cooling rate at an equal level it is known that initial cooling of most products is analogous in behavior. Thus, they exhibit a “lag period” before an exponential temperature decreases due to the rapid decrease of the core temperature (Elansari et al., 2020). This introduces the J factor which is the initial lag period between the initial cooling and the subsequent exponential decrease as depicted in Fig. 1.6. This factor can be used to calculate the cooling coefficient in Eq. (1.11), which is the slope of the straight line showing the lag period with the rate of change of the

Figure 1.6 A precooling curve (Elsaneri et al., 2020: Open access).

18

Low-Temperature Processing of Food Products

unaccomplished temperature variation of the cooled product per unit difference in temperature of the cooling medium and the fruit (Y). Y ¼ e
Ct

(1.11)

where, C is given as: C¼

ðlnYÞ t

(1.12)

where, Y is given as: Y¼

1.10

Ti
To Tt
To

(1.13)

Modeling of the chilling and cooling process

Modeling to estimate the sensible and latent heat load of a refrigerated system is important to precisely control the refrigerated environment. For every product, this requires knowledge of the thermophysical properties of the product, which includes convective heat and mass transfer (Becker et al., 2011). For a fresh product like fruits, modeling parameters will include the airflow, transpiration, and respiration parameters. The modeling processes enable equipment designers to understand the chilling/cooling characteristics of the products (Kumar & Kumar, 2023). It can be based on analytical, empirical, or numerical methods. However, the approach follows either modeling the cooling curve or heat and energy balances in the cooling system to deduce the temperature propagation in the system using numerical simulation methods. The cooling kinetics predict the chilling or cooling time, and the modeling equations can be solved assuming a definite shape (infinite cylinder, sphere, or slab) for the cooled/chilled products using Fourier’s law (Chuntranuluck et al., 1998). Most modeling of the cooling/chilling process focused on forced air cooling. The chilling/cooling rate is propelled by the loss of moisture from the product surface due to the high air flow rate, which accelerates the removal of latent heat of vaporization. This airflow distribution dynamics through a pack of cooled/chilled products is complex in understanding and information is required to understand the heat transfer at various air distribution points in the packed product. This can be solved using computer algorithms or numerical simulation of the fluid flow using CFD where the storage space can be presented in three dimensions (Han et al., 2015; Kumar & Kumar, 2023). The CFD approach can be direct where the 3D stacks of cooled/chilled product are visualized or converting the stack into porous media. Due to this airflow, the surface heat transfer is the major driving force for temperature decrease from the product, but because most food products have low thermal conductivity and considerable thickness,

Fundamentals of chilling/cooling processes

19

conduction heat transfer from the product core to the surface is also considered (Chuntranuluck et al., 1998). Thus, considering thermal energy flux occurs due to the combined effect of heat and mass transfer the solution of the Fourier’s equation can be used to predict the chilling/cooling characteristics. However, most cases consider the airflow through the stacks as turbulent; therefore, NaviereStokes equations are used to solve the flow equations (Ngcobo et al., 2012). The conduction equation through the core is given as follow: rp Cp

dT ¼ l p V 2 T p þ Se dt

(1.14)

where, rp is the product density (kg m
3), Cp is the specific heat capacity of the product (J kg
1 K
1), ʎp is the thermal conductivity of the product (W m
1 K
1), and Tp is the product temperature (K). The various heat loads which include, evaporation (Qe), respiration (Qr), convection (Qconv), and condensation (Qcond) are accounted for in the sink term (Se) depending on the type of product. For fruits and vegetables, this sink term (Se) can be determined as follow: Se ¼

Qr
Qconv
Qe þ Qcond Vp

(1.15)

where, Vp is product volume (m3). Wang et al. (2021) accounted for only respiratory (Qres) heat load (W/kg) in the cooling of lettuce ice bags, thus they resolved Eq. (1.14) as follow:

PL ¼ j

  ( j
1 j n Mi Cp;i Ti;M
Ti:M X Dt

i¼1

þ Mi

Qjres;i þ Qj
1 res;i 2

) (1.16)

where, M is the mass of the product (kg), Dt is the time step of cooling. The average volume temperature of the product (Tm) is deduced as Eq. (1.17). j j ¼ Ti:c
Ti:M

qjv;i 10li

R2i

(1.17)

where, R is the radius of the product (m), ʎ is the thermal conductivity, and q is the heat generated by the product and subscripts i, M, and c indicate the number, average volume, and center of the product, while the superscript j indicated the number of an individual time step. By selecting the appropriate domain and defining food geometry within the stacks through meshing with the various parametric components of various terms in equations accounted for, the temperature distribution on the product, as it cools, can be visualized as shown in Fig. 1.7.

20

Low-Temperature Processing of Food Products

Figure 1.7 A typical 3D temperature distribution in ice bags as it cools at various air velocity (a, b, c, and d) (Wang et al., 2021).

1.11

Conclusion

Knowing the fundamentals of the chilling/cooling process is important, to have an optimum and efficient process. According to the chilling/cooling curve, the process passes mainly by three phases: the first phase where the temperature of the product decreases from ambient temperature until 0 C and uses the sensible heat. This is followed by the so called: “super-chilling” phase. During this phase, the temperature of the product is kept constant at 0 C. The last phase is the freezing phase, and during this phase, the temperature of the product decreases to negative temperatures. The duration of these phases may vary by product and by the required temperature. In terms of mechanisms, these processes may involve conductive, convective, and heat transfer by radiation, which are fundamental to perform adequate modeling. The transfer of heat can be conducted through gaseous or liquid media, such as air or water. To complete the mathematical modeling of chilling/cooling processes, it is necessary to know about the rate of the process as well as the capacity, those parameters are important for the design of the processing system. Using simulation tools, such as CFD can give an accurate idea about the design and performances of the studied systems.

Fundamentals of chilling/cooling processes

21

References Acharya, S. (2023). Low-temperature storage: Chiling and freezing. Downloaded 25th May, 2023 https://www.biologydiscussion.com/food-microbiology/low-temperaturestorage-chiling-and-freezing/59275. Bailey, J. S., Thompson, J. E., & Cox, N. A. (1987). Contamination of poultry during processing. In F. E. Cunningham, & N. A. Cox (Eds.), The microbiology of poultry meat products (pp. 193e211). New York: Acad. Press. Barbut, S. (2002). Poultry products processing. Boca Raton, FL: CRC Press. Becker, Bryan R., Misra, Anil, & Fricke, Brian A. (2011). Bulk refrigeration of fruits and vegetables part I: Theoretical considerations of heat and mass transfer. HVAC and Research, 2(2), 122e134. https://doi.org/10.1080/10789669.1996.10391338 Carroll, C. D., & Alvarado, C. Z. (2008). Comparison of air and immersion chilling on meat quality and shelf life of marinated broiler breast fillets. Poultry Science, 87(2), 368e372. https://doi.org/10.3382/ps.2007-00213 Chopra, S., Norbert, M., Devinder, D., Pranav, P., Tushar, K., Ankit, K., & Randolph, B. (2023). Design and performance of solar-refrigerated, evaporatively-cooled structure for off-grid storage of perishables. Postharvest Biology and Technology, 197, 112212. Chuntranuluck, S., Well, C. M., & Cleland, A. C. (1998). Prediction of chilling times of foods in situations where evaporative cooling is significant-Part 1. Method development. Journal of Food Engineering, 37, 111e125. Dickens, J. A., & Whittemore, A. D. (1995). The effects of extended chilling times with acetic acid on the temperature and microbiological quality of processed poultry carcasses. Poultry Science, 74(6), 1044e1048. Duun, A. S., Hemmingsen, A. K. T., Haugland, A., & Rustad, T. (2008). Quality changes during superchilled storage of pork roast. LWT - Food Science and Technology, 41(10), 2136e2143. Duun, A. S., & Rustad, T. (2008). Quality of superchilled vacuum packed atlantic salmon (salmo salar) fillets stored at 1.4 and 3.6 C. Food Chemistry, 106(1), 122e131. Elansari, A. M., & Mostafa, Yehia S. (2020). Vertical forced air pre-cooling of orange fruits on bin: Effect of fruit size, air direction, and air velocity. Journal of the Saudi Society of Agricultural Sciences, 19(1), 92e98. https://doi.org/10.1016/j.jssas.2018.06.006 Elansari, A. M., & Siddiqui, M. W. (2016). Recent advances in postharvest cooling of horticultural produce. In M. W. Wasim, & A. Asgar (Eds.), Postharvest management of horticultural crops practices for quality preservation. Apple Academic Press. FAO. (2003). The use of ice on small fishing vessels. Rome: Food and Agriculture Organization of the United Nations. Gill, C. O. (2002). Primary chilling of red meat. In S. J. James, & C. James (Eds.), Meat refrigeration (pp. 99e136). Boca Raton, FL: CRC Press. Woodhead. Han, J. W., Zhao, C. J., Yang, X. T., Qian, J. P., & Fan, B. L. (2015). Computational modeling of airflow and heat transfer in a vented box during cooling: Optimal package design. Applied Thermal Engineering, 91, 883e893. James, S. J. (2003). Chilled storage-attainment of chilled conditions. In A. Press (Ed.), Encyclopedia of food sciences and nutrition (2nd ed., pp. 1169e1175). Amsterdam: Elsevier. James, S. J., & James, C. (2014). Chilling and freezing. In Food safety management, A practical guide for the food industry. Academic Press. https://doi.org/10.1016/B978-0-12-3815040.00020-2

22

Low-Temperature Processing of Food Products

Kaale, L. D., Eikevik, Trygve Magne, Rustad, Turid, & Kolsaker, Kjell (2011). Superchilling of food: A review. Journal of Food Engineering, 107(2), 141e146. https://doi.org/10.1016/ j.jfoodeng.2011.06.004 Kumar, A. R., & Kumar, S. Subudhi (2023). Numerical modeling of forced-air pre-cooling of fruits and vegetables: A review. International Journal of Refrigeration, 145, 217e232. Landerslev, M. G., Araya-Morice, Adriana, Pomponio, Luigi, & Ruiz-Carrascal, Jorge (2018). Weight loss in superchilled pork as affected by cooling rate. Journal of Food Engineering, 219, 25e28. https://doi.org/10.1016/j.jfoodeng.2017.09.012 Ledward, D. A. (2003). Meat preservation (2nd ed., pp. 3772e3777). Encyclopedia of Food Sciences and Nutrition. https://doi.org/10.1016/b0-12-227055-x/00752-5 Magnussen, O. M., Anders, H., Torstveit Hemmingsen, A. K., Johansen, S., & Nordtvedt, T. S. (2008). Advances in Superchilling of Food e Process Characteristics and Product Quality, 19(8), 0e424. https://doi.org/10.1016/j.tifs.2008.04.005 Naghiu, Al, & Apostu, S. (2006). Refrigeration and air conditioning techniques in food industry (in Romanian) (p. 536). Cluj-Napoca. Ndukwu, M. C., & Manuwa, S. I. (2014). Review of research and application of evaporative cooling in the preservation of fresh agricultural produce. International Journal of Agricultural and Biological Engineering, 7(5), 85e102, 2014. Ndukwu, M. C. (2011). Development of clay evaporative cooler for fruits and vegetable preservation. Agricultural Engineering International: the CIGR Journal, 13(1), 1e8. Ndukwu, M. C., & Manuwa, S. I. (2015). A techno-economic assessment for the viability of some waste as cooling pads in evaporative cooling system. International Journal of Agricultural and Biological Engineering, 8(2), 151e158. Ndukwu, M. C., Manuwa, S. I., Bennamoun, L., Olukunle, O. J., & Abam, F. I. (2018). In-situ evolution of heat and mass transfer phenomena and evaporative water losses of three agrowaste evaporative cooling pads: An experimental and modeling study. Waste and Biomass Valorization, 10, 3185e3195. https://doi.org/10.1007/s12649-018-0315-9 Ndukwu, M. C., Ibeh, M. I., Ugwu, E. C., Igbojionu, D. O., Ahiakwo, A. A., & Wu, H. (2022). Evaluating coefficient of performance and rate of moisture loss of some biomass humidifiers materials with a developed simple direct stand-alone evaporative cooling system for farmers. Energy Nexus, 8, 100146. Ndukwu, M. C., Ibeh, M. I., Akpan, G. E., Ugwu, E., Akuwueke, L., Oriaku, L., Ihediwa, VictorE., Abam, F. I., Wu, H., Kalu, C. A., Ben, A. E., & Mbanasor, J. (2023). Analysis of the influence of outdoor surface heat flux on the inlet water and the exhaust air temperature of the wetting pad of a direct evaporative cooling system. Applied Thermal Engineering, 226, 120292. https://doi.org/10.1016/j.applthermaleng.2023.120292 Ndukwu, M. C., Akani, O. A., & Simonyan, K. J. (2015). Nigeria’s grain resource structure and government sustainable policy: A review. Agriculture Engineering International: CIGR Journal, 17(3), 441e457. Ndukwu, M. C., Simo-Tagne, M., Inemesit, E., Akpan, G. E., Ibeh, M. I., Igbojionu, D. O., & Tagne Tagne, A. (2023). The dynamics of respiratory heat load produced by orange using different biomass fibres as wetting materials in a direct evaporative cooling system. Biomass Conversion and Biorefinery. https://doi.org/10.1007/s13399-022-03694-5 Ngcobo, M. E. K., Delele, M. A., Opara, U. L., Zietsman, C. J., & Meyer, C. J. (2012). Resistance to airflow and cooling patterns through multi-scale packaging of table grapes. International Journal of Refrigeration, 35(2), 445e452. https://doi.org/10.1016/j.ijrefrig. 2011.11.008

Fundamentals of chilling/cooling processes

23

Ros¸ca, R., T¸enu, Ioan, & C^arlescu, Petru (2017). Food chilling methods and CFD analysis of a refrigeration cabinet as a case study. Refrigeration. InTech. https://doi.org/10.5772/intech open.69136 Stopforth, J. D., & Sofos, J. N. (2005). 18 - carcass chilling. In Improving the safety of fresh meat (pp. 364e387). Woodhead Publishing Series in Food Science, Technology and Nutrition. https://doi.org/10.1533/9781845691028.2.364 Tamcold. (2019). Why primary chilling is important for the meat industry?. Downloaded 25th May 2023 https://www.tamcold.com/blog/why-primary-chilling-is-important-formeat-industry. Tan, J., Li, S., & Wang, Q. (2012). Experimental study on forced-air pre-cooling of Dutch the three types of cooling methods used in industrial chillers. https://1cold.com/blogs/threetypes-cooling-methods-used-industrial-chillers/. Wang, Xi-Fang, Fan, Zhong-Yang, Li, Bao-Guo, & Liu, En-Hai (2021). Variable air supply velocity of forced-air precooling of iceberg lettuces: Optimal cooling strategies. Applied Thermal Engineering, 187, 116484. https://doi.org/10.1016/j.applthermaleng.2020.116484

Further reading Becker, B. R., Misra, Anil, & Fricke, Brian A. (1996). Bulk refrigeration of fruits and vegetables part I: Theoretical considerations of heat and mass transfer. HVAC and Research, 2(2), 122e134. Chilling and freezing of foods. https://quizlet.com/282207366/chilling-and-freezing-of-foodsflashcards. Cooling, chilling and cold stabilization in food industry. http://wiki.zero-emissions.at/index. php?title¼Cooling,_chilling_and_cold_stabilization_in_food_industry. Duun, A. S., & Rustad, T. (2007). Quality changes during superchilled storage of cod (Gadus morhua) fillets. Food Chemistry, 105(3), 1067e1107. Duun, A. S. (2008). Superchilling of muscle food storage stability and quality aspects of salmon (Salmo salar), cod (Gadus morhua) and pork. Doctoral Theses. Trondheim: Department of Biotechnology, NTNU. Poultry Science, 74, (1995), 1044e1048. Tan, Jingying, Shi, Li, & Wang, Qing (2011). Experimental study on forced-air precooling of Dutch cucumbers. In D. Li, & Y. Chen (Eds.), Computer and computing technologies in agriculture V. CCTA. IFIP advances in information and communication technology (Vol. 369). Berlin, Heidelberg: Springer.

This page intentionally left blank

Fundamentals of freezing processes

2

Seid Reza Falsafi 1 , Asli Can Karaca 2 , Ozgur Tarhan 3 , Rosana Colussi 4 , €der-Taze 5 , Yogesh Kumar 6 and Hadis Rostamabadi 7 Bengi Hakgu 1 Safiabad Agricultural Research and Education and Natural Resources Center, Agricultural Research, Education and Extension Organization (AREEO), Dezful, Iran; 2Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey; 3Food Engineering Department, Us¸ak University, Us¸ak, Turkey; 4 Center for Chemical, Pharmaceutical and Food Sciences, Federal University of Pelotas, Pelotas, Brazil; 5Department of Food Engineering, Faculty of Engineering, Usak University, Usak, Turkey; 6Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Longowal, Punjab, India; 7Department of Food Science and Technology, School of Nutrition and Food Science, Nutrition and Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

2.1

Introduction

Within recent decades, freezing has been widely utilized as a valuable method for processing of food products. Owing to the application of subzero temperatures and restricting the activity of water through its transformation to crystals of ice, freezing could offer a condition that diminishes the rate of unfavorable chemical reactions and physical phenomenon leading to the enhanced shelf life of perishable food products (Ando et al., 2016). Nevertheless, a vast variety of preservation methods have been applied to enhance the shelf life of food products where each one of them follows basic technical rules. There are two key factors that offer freezing as a proper approach for food preservation. The initial parameter is based on the role of temperature on chemical/physical reactions occurring in a food system. Generally, the higher the temperature of the system, the greater the reaction rate. In this line, freezing plays a great role in enhancing the storage stability of products by reducing the rate of biochemical reactions. On the other hand, the transformation of free water molecules into icy structures within the food system reduces the available water needed for most of biological/ chemical reactions (Bilbao-Sainz et al., 2019; Lu et al., 2022). This means that the development of ice structures within a food system not only limits the unfavorable chemical reactions but also restricts the deteriorative microbial activities leading to a remarkable improvement in the storage stability of perishable food products. In general, the decrement of available water along with the reduction of product temperature are two determinant factors which play the main role in preserving the food product from deterioration during storage (Evans, 2016a, 2016b).

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00006-0 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

26

Low-Temperature Processing of Food Products

In one hand, through a slow cooling approach, the crystals of ice are generated beyond the cell walls. In this case, the higher concentration of ions outside the cells increases the osmotic pressure, which acts as a driven force to push the water molecules toward the outside of the cells. This will result in a drastic shrinkage in affected cells and also some irreversible impairment to their cell walls. It is worth to mention that the migrated water will not move back to the original cells through defrosting due to the damages occurred to the cell walls. This concentrated water would be lost through a drip loss during thawing. In addition, the growth of crystals is another phenomenon, which occurs during the storage through development of primary ice crystals by absorption of water molecules on their superficial fractions. The development of polygonal crystalline structures with sharp edges created following a slow freezing approach and a further storage time intensify the damages to the frozen food structure (Cartagena et al., 2021). On the other hand, through a rapid freezing, less cell dehydration would be occurred as less time is available for water molecules to defuse out from the cells leading to less damage to the cell walls and fewer drip loss during thawing. Generally, the faster the freezing process, the smaller the sizes of ice crystals, which are more spherical in shape. This will result in less mechanical damages to the integrity of the cell walls. Attaining a deep insight into the thermochemical mechanism of freezing offers the opportunity to realize the mechanisms of unfavorable changes for each specific food. Given this information, it would be possible to designate an appropriate freezing system for each specific food with the least damage to the final structure of the frozen food. This chapter mainly aims to provide a thorough summary of fundamentals of freezing processes. The thermal and chemical phenomena occurring through freezing is first discussed. Then, the freezing instrument commonplace in food applications was introduced together with their pros and cons (Evans, 2016a, 2016b).

2.2

Thermochemistry of freezing process

Freezing entails the elimination of heat from a substance, which is along with a transformation in its physical state from water to ice. In this regard, the rate of heat elimination is principally influenced by two classes of factors. The first group is relevant to the inherent attributes of the material comprising its size, superficial area, moisture content, density, etc. The second group of factors is related to the freezing medium including the temperature of the system and the rate of heat transfer among the substance and freezing medium (Cheng et al., 2021). The transformation in physical state of water within a substance is not only influenced by the rate of heat elimination but also by the rate at which its internal temperature is altering. In order to reduce the temperature of the system, heat should be omitted through a heat transfer process. Heat transfer basically measures the extent of heat that flows over a pathway between

Fundamentals of freezing processes

27

two points with recognized temperatures gradient. Accordingly, the amount of heat flow in a simple system has a straight relationship with its temperature as shown in below Eq. (2.1): q ¼ CDT

(2.1)

of which, q refers to the heat transferred to system (J), C is the specific heat (J/kg. K), and DT is the temperature gradient (K). In this regard, transferring the heat into a system through three well-known processes, that is, conduction, convection, and radiation, will result in an alteration in the temperature of the system. The conductivity and convection are the dominant methods that modulate the heat transfer within a frozen system and perhaps occurring at internal and external fractions of the freezing system, respectively (Evans, 2016a, 2016b). However, a more important phenomenon in a frozen system is the phase change (Chen et al., 2022). When a liquid containing medium is cooling, the release of heat occurs by two dominant phenomena. (I) Sensible heat, where the temperature of the system is reduced and (II) Latent heat that is associated with the change in the phase of the system, while no change is occurring to the system temperature and reflects the structural rearrangement of the cooling specimen. In this regard, when calculating the heat transfer of the medium, both of aforementioned phenomena should be considered of which, the sensible heat is simply measured by tracking the alterations of the temperature, and the latent heat could be estimated by determining the amount of phase change of the medium. The phase change process principally comprises three steps vis. undercooling, nucleation, and propagation, which are described in detail elsewhere (Evans, 2016a, 2016b).

2.2.1

Determination of freezing time

In a freezing system, the heat load (DH) is the amount of heat that must be removed to reduce the product initial temperature (Ti) from some level above the freezing point (Tf) to some desired final temperature (T). DH ¼ sensible heat removed from the product solids (DHS) þ sensible heat removed from unfrozen water (DHuw) þ enthalpy change due to latent heat (DHL) þ sensible heat removed from the frozen water (DHI) (2.2) These terms can be determined using the equations given below.

DHS ¼ MS CPS Ti  Tf þ MS CPS Tf  T

(2.3)



0 DHuw ¼ Muw CPuw Ti  Tf þ Muw CPuw Tf  T

(2.4)

28

Low-Temperature Processing of Food Products

DHL ¼ MI CPI

(2.5)

DHfw ¼ MI CPI Tf  T




(2.6)

where, MS is the mass of solids in food, Muf, the mass of unfrozen water, CPS, the 0 specific heat of solids and CPuf, the specific heat of unfrozen water, CPuw , the specific heat of unfrozen water below Tf, MI, the mass of ice or unfrozen water, Lv, the latent heat of freezing, and CPI, the specific heat of ice. Heat load is used to determine the refrigeration time using Eq. (2.6). Freezing time ðsÞ ¼

2.2.2

Freezing load ðJÞ Freezing capacity ðWÞ

(2.7)

Determination of the freezing time

Efficient and controlled freezing times help preserve food quality by minimizing the formation of damaging ice crystals and maintaining its taste, texture, and appearance. Moreover, quickly freezing food can minimize the degradation of sensitive nutrients. Therefore, optimizing freezing times reduces energy consumption, enhances distribution efficiency, and reduces storage requirements for frozen foods. Some of the methods for determining freezing time are offered below.

2.2.2.1

Plank’s method (Ede, 1949)

Fundamentals of freezing processes

tF ¼

29

  P$a R$a2  TF  Ta h kf rf Lf

(2.8)

where, tF is the freezing time (s), rf is the density of the frozen material, Lf is the change in the latent heat of the food (kJ/kg), TF is the freezing temperature ( C), Ta is the freezing air temperature ( C), h is the convective heat transfer coefficient at the surface of the material (W/[m2 C]), a is the thickness/diameter of the object (m), kf is the thermal conductivity of the frozen material (W/[m C]), and the constants P and R are used to account for the influence of product shape.

P R

2.2.2.2

Infinite slab

Infinite cylinder

Sphere

1/2 1/8

1/4 1/16

1/6 1/24

Modified Plank’s equations

2.2.2.2.1 Nagaoka et al. equation (Nagaoka et al., 1956)   0 DH rf P$a R$a2  tF ¼ TF  Ta h kf   0 DH ¼ ð1 þ 0:008Ti Þ Cpu ðTi  TF Þ þ Lv þ CPI ðTF  TÞ

(2.9) (2.10)

where, Ti is the initial food temperature, T the final frozen food temperature, Cpu the specific heat of unfrozen food, and CPI the specific heat of frozen food.

2.2.2.2.2 Levy equation (Levy, 1958) Levy (1958) uses Eq. (2.8) to determine the freezing time. However, it considers Eq. (2.10) for enthalpy.   0 DH ¼ ð1 þ 0:008ðTi  TF Þ Cpu ðTi  TF Þ þ Lv þ CPI ðTF  TÞ

2.2.2.3

(2.11)

Pham method (Pham, 1986)

   V DH 1 DH 2 Bis tF ¼  1þ hA DT 1 DT 2 4

(2.12)

30

Low-Temperature Processing of Food Products

where, V is volume of body, h is surface heat transfer coefficient, A is surface area, Bis is Biot number of simple shapes, and other quantities are determined as given below. DH 1 ¼ Cu Ti  Tfm




(2.13)

where, Cu is the specific heat for the unfrozen phase, Ti is the initial temperature, and Tfm is mean freezing temperature ¼ 1:8 þ 0:263 Tc þ 0:105Ta . Tc is final center temperature, and Ta is freezing medium temperature DH 2 ¼ L þ Cs Tfm  Tc




(2.14)

where, L is volumetric latent heat of freezing, and Cs is the specific heat for the frozen phase
Ti  Tfm DT 1 ¼  Ta 2 DT 2 ¼ Tfm  Ta

2.3

(2.15) (2.16)

Freezing approaches

Quality attributes of frozen foods are directly influenced by freezing methods applied since physical and chemical changes can be encountered during freezing and thawing processes (Attrey, 2017). Freezer burn, recrystallization, weight loss, starch retrogradation, protein denaturation, oxidative rancidity, modification of textural and functional properties, loss of color, flavor, and nutritional value are critical problems revealed through freezing (Zaritzky, 2010, pp. 561e607). Successful freezing procedures aim to lower these issues and protect the quality characteristics of initial food material as possible but not promise for improving the quality. Freezing rate and the size, shape, number, and distribution of ice crystals formed during freezing are significant parameters to be considered and vary due freezing methods (Zhu et al., 2019). Fluctuations in temperature during freezing process are effective on ice nucleation and crystal formation. Slow freezing leading to large and irregularly distributed ice crystals is mostly associated with lowered food quality, whereas rapid freezing producing small and uniformly distributed crystals are desirable for preserved quality of frozen foods (Dempsey & Bansal, 2012; Kiani & Sun, 2011). Currently, very well-recognized freezing approaches including plate contact, immersion, air blast, and cryogenic freezing have been used for conventional production in food industry. All these methods have particular procedures, advantages, and disadvantages discussed in the following sections.

Fundamentals of freezing processes

2.3.1

31

Plate freezing

Plate freezing, so-called contact freezing involves firmly squeezing of food product between two refrigerated plates under pressure to facilitate maximum contact. Plate freezers consist of a refrigeration system using refrigerants, such as NH3 and CO2, circulated through channels inside the plates (Fernandez-Seara et al., 2012). Horizontally or vertically stacked a number of plates are comprised by horizontal plate freezers and vertical plate freezers, respectively. Both systems are used for freezing of foods desirably. During operation, target food product is placed properly between the plates which are compressed to sandwich the product ensuring optimal thermal contact between the food and plates, resulted in homogenously shaped frozen product. Plates of any size specific for particular industrial production are available. Freezing time can vary due to type of food product and operation conditions (Fig. 2.1). Plate freezing systems offer a high heat transfer rate due to the large surface contact between plates and products, enabling fast freezing with maximum economy (George, 1993; Visser, 1986). Although the plate freezers are fast, efficient, and easy to use, they have some limitations such as the need of a defined geometry and thickness of the food to be frozen. Flat surfaced food materials should fit to the metal plate chamber for maximum freezing efficiency. High investment costs are considerable as well (Visser, 1986). Meat, fish fillets, pastries, and leafy vegetables are some foods to be frozen by plate freezer rapidly and efficiently (Hessami, 2004; LeBail & Goff, 2008, p. 184; Lv et al., 2021; Parreno & Torres, 2006). Single- and multiplate freezing systems have some benefits for freeze concentration of some extracts and juices as well (Hernandez et al., 2009; Moreno et al., 2014). With the application of freeze concentration, removal of water from juices can be achieved at temperatures below freezing point

Figure 2.1 Schematic of plate freezing.

32

Low-Temperature Processing of Food Products

of water, and thus, better product quality can be obtained since adverse effects of thermal treatments (i.e., evaporation) such as destruction of nutritional constituents and nonenzymatic browning could be eliminated.

2.3.2

Immersion freezing

Immersion freezing, so-called surface freezing and crust freezing, occupies a liquid refrigerant to be used for direct immersion of food material in it or spraying of food product with it as remains liquid along with the freezing process (Lucas & RaoultWack, 1998). Ice nucleation of particles immersed in supercooled water results in formation of mixed-phase clouds. A large number of small-sized ice crystals are formed and thus contributed to the preserved and/or improved quality of frozen foods (Diao et al., 2021; Galetto et al., 2010; Zhu et al., 2005). Rapid cooling and freezing of packed and unpacked foods are achieved via immersion freezing on the basis of direct heat exchange. However, the process requires special refrigerant, and choosing the proper one is difficult for desired purpose. Commonly employed freezing agents are propylene, glycerol, salt, sugar, and alcohol solutions. Immersion freezing is a feasible process able to offer a balance in cost and freezing rate, thus promising for food freezing (Yang et al., 2020). This technique is used for canned foods (i.e., juices), fruits and vegetables, poultry and fish products, commercially (Diao et al., 2021) (Fig. 2.2).

2.3.3

Air blast freezing

In air blast freezing, relatively high speed cold air flows around food material and results in cooling and freezing of product. Packaged or unpackaged food products are placed on trays keeping over freezing coils in a cold air circulating room. Air velocity is critical since it affects the freezing rate and quality of the frozen product (Rahman & Velez-Ruiz, 2007a, 2007b, pp. 653e684). However, high cost is associated with the high air velocity. Besides, smaller and numerous ice crystals can be generated desirably. Since the bacterial growth is suppressed effectively, air blast freezers are widely used for preserving dairy products, meat, poultry, fish, fruits, and vegetables (Dempsey & Bansal, 2012; Kaale et al., 2013) (Fig. 2.3).

Figure 2.2 Schematic of the immersion freezing.

Fundamentals of freezing processes

33

Figure 2.3 Schematic of a batch air blast freezer (Dempsey & Bansal, 2012).

Air blast freezing is economical and applicable to foods possessing different size and shapes. However, the need of frequent defrosting of system and undesirable dehydration of unpacked products are some disadvantages in this freezing technique. Due to application approach, fluidized bed, belt, and tunnel freezing methods are considered as different types of this method. In fluidized bed freezing system, small food particles like pea and berries are fluidized in a bed over a mesh tray by subjecting to vertically blowing cold air (Rahman & Velez-Ruiz, 2007a, 2007b, pp. 653e684). Proper application and rate of cold air giving rise to fluidization; uniformity, size, and shape of the food particles are important parameters in this method. Efficient heat transfer with a high freezing rate, and thus short freezing time is achieved based on relatively small and uniform size of food particles. Besides, lowered dehydration of unpacked food product and defrosting frequency of system is provided. Since they cannot be fluidized properly, large and nonuniform particles are not appropriate for a desirable freezing with this method, which is the main limitation in fluidized bed freezing. Tunnel freezing is one of the most common techniques used in industry for freezing of food materials (Svendsen et al., 2022). Especially, fish processing industry occupies a variety of tunnel freezers according to the volume of process with required handling and hygeneic conditions. Products placed on trays slowly moving along with the long tunnels with circulating cold air surrounding food product in it. In case of belt freezing, food products are loaded on moving single and multiple conveyor belts, and vertical or horizontal air flow is forced through the products, ensuring maximum contact (Dempsey & Bansal, 2012). Multibelt freezers consisting several conveyor systems aligned layer by layer. Besides, spiral belt freezers and impingement jet freezers are other forms of the belt freezers with different positioning.

34

2.3.4

Low-Temperature Processing of Food Products

Cryogenic freezing

In cryogenic freezing, food materials are subjected to extremely cold atmosphere (at or below 60 C) with the direct contact of liqufied gases (Hung, 1996; Truonghuynh et al., 2020). Food product placed on conveyor belts is forwarded through food grade cryogenic environment with continuous counter-current flow. Liquid nitrogen and carbon dioxide are used as cryogens for removing heat quickly from the food to be frozen. Freezing temperature/rate is the key to be considered for desirable freezing process (Truonghuynh et al., 2020). Rapidly occurring freezing reveals rapidly formed relatively small ice crystals resulted in significantly lowered cellular damage in food microstructure (Qian et al., 2018; Zhu et al., 2019). This highly contributes to preserved quality mainly in texture and also color, flavor, and nutritional value of food product. Remarkably lowered dehydration loss, high process efficiency, and capability of adaptation to different production rates with minimal space need due to relatively small size of the freezer are benefits of this system (Kaale et al., 2011; Tan et al., 2021). Thus, cryogenic cooling and freezing provide increased processing rate and economy with improved product quality and properly extended shelf life (Fig. 2.4). Cryogenic freezing is achieved in three ways including spraying, immersion, and spiral freezing (Rahman & Velez-Ruiz, 2007a, 2007b, pp. 653e684). In case of spray freezing, cryogenic liquid is directly sprayed on food material moving in a tunnel. In immersion freezing, food product is immersed in the cryogenic liquid. In case of spiral freezing, vaporized cryogenic liquid is blown over the food product. Cryogenic freezing is conventionally used for freezing of food items including seafoods, vegetables, and bakery products (Meziani et al., 2012; Parreno & Torres, 2006; Truonghuynh et al., 2020).

Figure 2.4 Schematic of a cryogenic freezer (Zhao et al., 2019).

Fundamentals of freezing processes

2.4 2.4.1

35

Impact of freezing on microbial and physicochemical aspects of foods Impact of freezing on microbial attributes of food

Freezing process is applied to foods to maintain food quality and safety. Various meat and poultry products, seafoods, dairy products, fruit, and vegetable products can be listed among the products in which freezing is commonly applied for the control of microbial growth. Majority of the studies investigating the effect of freezing process on microbial attributes of food focus on meat and poultry products. For example, Bollman et al. (2001) investigated the effect of cold shocking on the survival of Escherichia coli O157:H7 in frozen foods. Freezing process was conducted at 20 C, and frozen food samples were stored at 20  1 C for 7 days, whereas cold shocking was applied at 10 C for 1.5 h. No significant difference was reported between the survival levels of cold shocked and noncold shocked E. coli in ground beef or pork. On the other hand, cold shocking was reported to result in a significant enhancement in survival of E. coli in milk, egg, or sausage. Enhanced protection due to cold shocking was related with the presence of a novel protein, which was attributed to an alteration of protein synthesis (Bollman et al., 2001). Szymczak et al. (2020) investigated the effects of various temperature conditions during frozen storage on the quality of marinated Atlantic herring fillets. The fillets were frozen (19 C) and stored for 2 days up to 5 months at constant temperature (19  1 C) or fluctuating temperatures of 19 to 23  1 C. Frozen storage was found to have no significant effect on psychrophilic contamination. On the other hand, application of fluctuating temperatures was reported to have a minimal effect on mesophilic bacteria (0.06e0.07 log (cfu$g1) reduction, which was attributed to recrystallization and destroying of bacterial membranes. The authors concluded that microbial quality of frozen foods is rather affected by raw material quality (Szymczak et al., 2020). In another recent study, the effects of repeated freeze-thaw cycles on microbial quality of beef and chicken meats were investigated. Freeze-thaw cycles were reported to increase the total bacterial counts in both meat types. Moreover, relaxation times measured by low-field nuclear magnetic resonance (NMR), indicating the mobility of water, were reported to be affected by bacteria (Mohammed et al., 2021). The effect of frozen storage on microbial growth in “coconut neera,” the sweet sap of the coconut palm tree, was investigated. Neera samples were frozen and stored at 6 and 20 C. The highest reduction was observed at 20 C in lactic acid bacteria, yeast, and total microorganism count. Therefore, storage at 20 C was recommended for preserving the physicochemical and microbial quality of the product (Sukumaran & Radhakrishnan, 2021).

2.4.2

Transformations in free and bound water during freezing

During the freezing process, free water present in the foods is converted into ice crystals, which results in a decrease in water activity, and hence alterations in reaction rates (Miyawaki, 2018). Sanchez-Alonso et al. (2012) studied the water status in hake fish

36

Low-Temperature Processing of Food Products

with low-field NMR during frozen storage. Hake fillets were frozen at 40 C and stored at 10 C for up to 6 months. Low-field was NMR indicated to be an effective tool for detection of bound water, trapped water, and free water. Increased durations of frozen storage were reported to result in an increase in the free water and a decrease in the trapped water along with a decrease in water holding capacity and apparent viscosity that were associated with the loss of juiciness and development of tougher texture during frozen storage (Sanchez-Alonso et al., 2012). Tan et al. (2018) investigated the effect of freeze-thaw cycles on the quality and water status of instant sea cucumber by low-field NMR and magnetic resonance image (MRI) techniques. Sea cucumber samples were heat-treated, cooled, and then stored at 20 C for 12 h before the thawing treatment, which was conducted at 25 C for 1.5 h up to 25 cycles. The authors reported that increased number of freeze-thaw cycles resulted in increased the mobility of water and also increased the peak area of immobile water (Tan et al., 2018). Cheng et al. (2019) also used low-field NMR for investigating the effect of multiple freeze-thaw cycles on the quality of beef muscle and proportions of bound, immobilized, and free water. Proportion of immobilized water was observed to decrease significantly with increased freeze-thaw cycles. Reformation of ice crystals during freeze-thaw cycles was indicated to result in formation of enlarged holes in muscle fibers (Cheng et al., 2019). Moreover, Lan et al. (2021) investigated the effects of different thawing methods on the physicochemical characteristics and water migration in frozen pompano fish. Pompano samples were frozen and stored at 25 C and then thawed with ultrasonic, radiofrequency, water immersion, microwave, and cold storage thawing methods. The authors observed no significant difference in bound water in fresh and thawed samples. Besides, samples thawed with cold storage and water immersion thawing methods were reported to have less immobilized water compared to the other samples. This finding was associated with significantly increased water loss in slow thawing speed. The content of immobilized water in the sample thawed with radiofrequency method was observed to be similar to that of the fresh sample, suggesting that the radiofrequency thawing had minimal effect on water migration and content. However, the proportion of immobilized water was reported to be higher in microwave-thawed sample compared to the fresh sample, which was associated with an increase in immobilized water by the back-flowing of free water in the microwave thawing process (Lan et al., 2021).

2.4.3

Food weight loss during freezing

During freezing and frozen storage of foods, dehydration occurs due to sublimation of the surface ice. Dehydration related weight loss and changes in the appearance, color, texture, and taste of the product are indicated as in important factor, which lead to not only losses in product quality but also economic loss (Campa~none et al., 2001). Phimolsiripol et al. (2011) studied weight loss in frozen bread dough under various temperature conditions. Dough samples were frozen at 25 C and stored at a temperature range of 8 to 25 C with fluctuations of 0.1, 1, 3 or 5 C. The rate of weight loss in frozen dough samples was observed to be

Fundamentals of freezing processes

37

constant irrespective of the temperature and fluctuation amplitude. On the other hand, weight loss was reported to increase with the amplitude of temperature fluctuations (Phimolsiripol et al., 2011). Mulot et al. (2019) developed a lab scale freezer, which provided uniform freezing conditions and studied food dehydration under mechanical and cryogenic freezing conditions. Tylose plates used in the study as a model food consisted of methylcellulose, water, and sodium chloride. The weight loss due to freezing was reported to be up to 6%. Freezing conditions and product characteristics including surface state and porosity were indicated to have significant effects on weight loss during freezing. The authors suggested that the surface temperature of the product has to be decreased as quickly as possible in order to minimize weight loss (Mulot et al., 2019).

2.4.4

Impact of freezing on food constituents

Freezing process can also affect the macro-constituents of foods. Depending on the processing and storage conditions, freezing and frozen storage can lead to undesired changes in macronutrients such as denaturation of proteins and oxidation of lipids and proteins (Bao et al., 2021). Tejada et al. (2002) investigated the changes in proximate composition of sheep milk cheese during frozen storage. Ripened cheese samples were either slow-frozen at 20 C or quick-frozen at 82 C and stored at 20 C for 3, 6, and 9 months. No significant differences were observed in proximate composition of the control and frozen samples. On the other hand, significantly higher rates of nonprotein nitrogen and amino acid nitrogen observed at the end of the storage period were associated with proteolysis during frozen storage (Tejada et al., 2002). In a recent study, Zhang, Mao, et al. (2020) and Zhang, Li, et al. (2020) employed labelfree proteomics analysis to study protein variations in frozen whiteleg shrimp. Shrimp samples were presoaked with distilled water or sodium trimetaphosphate (STMP), frozen at 30 C and stored at 18 C for 30 days. The authors observed that 163 differentially abundant proteins were down-regulated in distilled water-soaked samples compared to the fresh samples. Soaking in STMP was indicated to up-regulate several differentially abundant proteins and delayed their degradation compared to distilled water-soaked samples. Incorporation of STMP into muscle tissues was associated with decreased protein degradation and better protection against ice-crystal growth (Zhang, Mao, et al., 2020). In case of lipid oxidation, extent of oxidation depends on many different factors including the composition of the product, use of antioxidants, freezing temperature and rate, frozen storage temperature and duration, packaging, and the number of freezeethaw cycles (Bao et al., 2021). In a recent study, Al-Dalali et al. (2022) investigated the effects of frozen storage on the lipid oxidation in marinated raw beef. Freezing and frozen storage were conducted at 18 C for up to 6 months. The authors observed lipid oxidation during the first 2 months of frozen storage. The thiobarbituric acid reactive substances (TBARS) value increased during the first 2 months and then slightly decreased during extended storage. Carbonyl content was also observed to increase linearly during frozen storage. Lipid degradation was found to be the main factor affecting the aroma profile of raw beef (Al-Dalali et al., 2022).

38

2.4.5

Low-Temperature Processing of Food Products

Chemical changes of minor food constituents during freezing

Although freezing is applied to inhibit microbial growth and extend the shelf life of foods, it has been indicated that most foods of plant and animal origin are sensitive to low temperature, and freezing process can result in alterations in nutritional and sensory quality depending on freezing method, freezing conditions, duration, and temperature of frozen storage. Santarelli et al. (2020) investigated the effects of freezing pretreatments, freezing, and frozen storage on total polyphenol content and antioxidant activity of organic and conventional apples. Washed, peeled, and sliced apple samples were pretreated by dipping or vacuum impregnation into organic lemon juice solution at 20 C. After freezing at 40 C, frozen storage was conducted at the same temperature for 10 months. Although free and conjugated polyphenols profile of organic and conventional apples was observed to be different, total phenolic content and antioxidant activity were reported to be similar. Vacuum impregnation pretreatment was reported to enrich the bioactive components in both samples. Freezing and frozen storage were indicated to have different effects on the polyphenol profile of samples (Falsafi et al., 2020a, 2020b; Rostamabadi et al., 2019). Organic and conventional apples were reported to show different responses to freezing-induced physical stress, which were attributed to the differences in cell wall composition and mechanical resistance of tissues (Santarelli et al., 2020). Tejada et al. (2020) recently studied the effect of freezing on nutritional composition, bioactive compounds, and sensory properties of zucchini. Freezing conducted at 18 C after cutting and blanching pretreatments was not reported to have a significant effect on the nutritional composition of zucchini. However, a significant decrease in antioxidant activity, phenolic compounds, and significant losses in adhesiveness and hardness were observed. The sensory characteristics of previously frozen and fresh samples were found to be similar after steaming and stir-frying treatments (Tejada et al., 2020). In another study, the effects of blanching and long-term frozen storage on bioactive components and antioxidant properties of baby mustard were investigated (Zhang et al., 2021). Blanching (96 C, 30 s) was followed by freezing at 20 C and storage at the same temperature for 8 months. The glucosinolates in baby mustard were reported to be preserved in the unblanched sample during frozen storage with a retention of 72.5% of total glucosinolate content. Chlorophylls, carotenoids, ascorbic acid, total phenolics, and antioxidant capacity were reported to be preserved as well. Therefore, the authors suggested freezing without blanching for long-term frozen storage to preserve the nutritional quality of the product (Zhang et al., 2021).

2.5

Postfreezing events

The most significant effect of freezing on food quality is the damage done to cells by the growth of ice crystals. However, freezing causes negligible damage to important

Fundamentals of freezing processes

39

pigments, flavors, and nutritional components. Also, freezing can promote emulsions destabilization, protein precipitation, lipid oxidation, and starch retrogradation (Fellows, 2000, p. 928). Although low temperatures significantly reduce chemical and enzymatic reactions, it must be considered that in foods frozen at 18 C, not all of the water is frozen. The enzymes are not entirely inactive, and the solutes present in this unfrozen aqueous phase are significantly concentrated, which can change the characteristics of the medium, such as pH, redox potential, and ionic strength. Thus, the chemical and physical reactions can advance even if very slowly during frozen storage. Also, the ice crystals formed are not stable and can alter. These physical changes, known as recrystallization, sublimation, and chemical changes, are the leading causes of food quality loss during frozen storage (Fennema, 1975). When postfreezing events are compared between animal and vegetable origin products, it is possible to see substantial differences. For example, meats are less damaged as they have a more flexible fibrous structure that separates during freezing rather than being broken down. For another hand, products of plant origin, mainly fruits and vegetables have a more rigid cellular structure, and ice crystals can damage this. The extent of damage depends on the size of the crystals and the heat transfer rate (Fellows, 2000, p. 928; Fennema, 1975). Among the most common postfreezing events, recrystallization, freezer burn, rancidity, and retrogradation are the most mentioned by literature.

2.5.1

Recrystallization

The physical changes in ice crystals are known as recrystallization, and it is a more significant cause of food quality loss. According to Fellows (2000, p. 928), ice recrystallization during frozen storage influences product quality. There are three types of recrystallizations in food: I. Isomassic recrystallization: is the change in surface shape or internal structure, usually resulting in a lower surface-area-to-volume ratio. II. Combined recrystallization: Two adjacent ice crystals join together to form a larger crystal, causing the number of crystals in the food to decrease. III. Migratory recrystallization: An increase in average size and reduction in crystal number are caused by larger crystals growing at the expense of smaller crystals.

Migratory crystallization is the most important in most foods and is caused mainly by fluctuating storage temperatures (Tan et al., 2021). A typical example of this fluctuation can be given when the door of a freezer is opened, where the surface of the food next to the heat is slightly heated, causing the partial melting of ice crystals, thus increasing the size of larger crystals and disappearing smaller crystals. The molten crystals increase the vapor pressure of the water, and moisture moves to regions of lower vapor pressure, causing areas close to the heat source to dehydratedthe loss of moisture results in toughening of animal tissue and greater exposure to the present oxygen.

40

2.5.2

Low-Temperature Processing of Food Products

Freezer burn

In cold rooms, they have low humidity, as water is removed from the air by the cooling coils. Moisture leaves the surface of the food into the atmosphere and produces visible areas of damage known as freezer burn. The freezer burns result in an ugly white coloration that can be mistaken for mold and result from microscopic cavities previously occupied by ice crystals, which alter the wavelength of the reflected light (Norwig & Thompson, 1984). In nonserious cases, freezer burn can be resolved by rehydration during cooking; in severe cases, it is irreversible and causes chemical and sensory alterations (Rahman & Velez-Ruiz, 2007a, 2007b, pp. 653e684). Dehydration can be controlled by humidification, lower storage temperatures, glazing, or better packaging conditions. One technique used to prevent freezer burn is glazing, generally used in fish and chicken. In this process, a film protects the product from freezer burn. Industrial glazing is usually done by spraying the product surfaces or short dipping the products in a water solution. Choosing the proper packaging can also be crucial in reducing the freezer burn (Rahman & Velez-Ruiz, 2007a, 2007b, pp. 653e684).

2.5.3

Rancidity

The auto-oxidation of lipids, responsible for the appearance of flavors and aromas typical of rancidity, is one of the most relevant chemical reactions in frozen products because, although slowly, it occurs at 18 C. It sharply affects foods with high content of unsaturated fats, such as fish and pork with high-fat content, thus reducing their shelf life. Lipids can also be hydrolyzed, and the increase in free fatty acids produces unpleasant flavors and favors the denaturation of proteins, forming complexes that affect the texture and digestibility (Zaritzky, 2008). The mechanism of lipid oxidation is described as a chain reaction consisting of three distinct steps: initiation, propagation, and termination. During the initiation stage, a hydrogen atom is removed from a fatty acid, leaving a fatty acid alkyl radical converted in the presence of oxygen to a fatty acid peroxyl radicals. In the second step, the peroxyl radical subtracts hydrogen from an adjacent fatty acid forming a hydroperoxide molecule and a new fatty acid alkyl radical. The breakdown of hydroperoxide is responsible for the propagation of the free-radical process. The decomposition of fatty acid hydroperoxides into aldehydes and ketones is responsible for the characteristic rancid flavor and aroma (Fellows, 2000, p. 928; Fennema, 1975). For rancidity development, the presence of catalysts, such as visible light, ultraviolet radiation, metals (copper, iron, nickel, cobalt, and manganese), or metalloproteins (heme group). Both enzymatic and nonenzymatic pathways can initiate lipid oxidation. One of the enzymes considered important in lipid oxidation is lipoxygenase, which is present in many plants and animals and can generate strong flavors and color loss of pigments (Fellows, 2000, p. 928). Oxidative flavor deterioration is produced in both plant and animal products. However, it is identified more in frozen muscle than in frozen vegetable products because blanching is usually applied to vegetables before freezing. Pretreatments such as

Fundamentals of freezing processes

41

blanching are of paramount importance to the food industry, as successful freezing will only maintain the inherent quality initially present in the food and will not improve the quality characteristics; thus, the quality level before freezing is an essential item to consider (Magnussen et al., 2008). The development of oxidative rancidity in frozen muscles is caused by the accumulation of carbonyl compounds formed during the autooxidation of muscle lipids. Enzymatic hydrolysis of lipids, with the release of free fatty acids, occurs during frozen meat storage. Fish and swine, which contain a higher proportion of more reactive polyunsaturated fatty acids, are thus more susceptible to rancidity development (Magnussen et al., 2008). Ready-to-eat foods are also prone to rancidity, as these are complex multicomponent products with a wide variety of ingredients that are cooked and then frozen (Creed, 2006). In these products, the leading cause of rancidity is meat. In addition, lipid oxidation leads to flavor deterioration, and color changes can also result from pigment degradation in meat and vegetables. Some alternatives aim to reduce rancidity; among them are antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), or tocopherols; and metal chelators such as pyrophosphates, tripolyphosphates or hexametaphosphates (Sebranek, 1996). In addition to antioxidants, pretreatments can be carried out to reduce rancidity and other postfreezing events. Bleaching, heat treatment, pretreatment by immersion, osmotic concentration, bacterial ice nucleators or antifreeze proteins, cryoprotectants, and irradiation among the procedures can be highlighted.

2.5.4

Retrogradation

Food systems based on gelatinized starch may undergo texture changes related to the retrogradation of amylose and amylopectin. They can show syneresis and a spongy texture due to slow freezing and frozen storage at relatively high temperatures. These changes may make these products unacceptable to the consumer (Miles, 1985). As starch retrogradation is a recrystallization process, it is diffusion-controlled and depends on solute mobility in the system. The rate of starch retrogradation is influenced by the rate of cooling before storage at temperatures for frozen foods. The rapid cooling rate contributed to greater retrogradation of starch than the slow cooling rate during storage (Hsu & Heldman, 2005); thus, temperature and storage time also significantly affect the quality of starchy foods. The enthalpy of the retrogradation of bread increases during frozen storage, and the rate of bread hardening depends on the time of frozen storage during aging (Barcenas & Rosell, 2006). Thus, freezing rate, temperature, and storage time significantly affect starch retrogradation and the texture properties of starchy foods. Freezing rates and storage temperatures significantly affect starch retrogradation. The textural properties (hardness and stickiness) of cooked rice were correlated with the freezing and retrogradation rates of the starch. Cooked rice processed with higher freezing rates has lower hardness and more prominent adhesiveness (Yu et al., 2010). The addition of hydrocolloids such as xanthan gum helps maintain the rheological characteristics of thawed starch pastes, even under low freezing conditions. However,

42

Low-Temperature Processing of Food Products

not all hydrocolloids are efficient, as they can make rubbery systems more viscous, decreasing molecular mobility and preventing retrogradation related to sponge formation (Ferrero et al., 2000). Ribotta et al. (2003) observed that guar gum and the diacetyl tartaric acid ester of mono- and diglycerides improved bread volume and texture and reduced the aging rate. However, they could not counterbalance the negative effect of frozen storage on dough microstructure. Hydrocolloids are, therefore, primarily designed to interact with the water distribution in the dough and with the rheology of the dough, offering, in principle, better tolerance to frozen storage.

2.6

Novel freezing system and future trends

Conventional freezing methods result in formation of large ice crystals due to low freezing rate of the processes (Cheng et al., 2017; James et al., 2015). Food tissue is subjected to textural damage by these ice crystals, which may also provoke quality deteriorations related to color, flavor, and nutritional characteristics (Lu et al., 2022). Consumers’ trend to reach less processed products with more nutritious properties forced researchers to develop alternative freezing methods (Xu et al., 2017). Hence, novel freezing technologies which can reduce the freezing time and yield small ice crystals are emerged to preserve frozen food quality. These are dehydrofreezing (DF), hydrofluidization (HF) freezing, impingement freezing (IF), ultrasoundassisted immersion freezing (UIF), high-pressure freezing (HPF), electromagnetic fieldeassisted freezing (EMF), isochoric freezing, application of ice structuring proteins (ISPs), and ice nucleation proteins (INPs) (Baskaran et al., 2021; Cheng et al., 2017; Evans, 2016a, 2016b; Mahato et al., 2019). Some of these new methods, such as UIF, HPF and EMF, are used as a complement to conventional freezing systems to control the ice formation. However, other techniques, such as application of ISPs and dehydrofreezing, generate modifications in the structure of the food material (James et al., 2015) (Fig. 2.5). DF, indeed, dates back to 1940s (James et al., 2015; Schudel et al., 2021). It is a two-phased process which includes dehydration pretreatment and freezing stage. It has been principally applied to fruit and vegetables, such as carrot, apple, kiwifruit, apricot, strawberry, pineapple, melon, quince, eggplant, cucumber, and bell pepper, owing to their high water content (Ando et al., 2016; Ramallo & Mascheroni, 2010; Schudel et al., 2021; Wu et al., 2009). The process aims at reducing freezing time and freezing point by decreasing the amount of water in the cellular region either by means of osmotic solutions (osmo-dehydrofreezing), air (convective dehydrofreezing), vacuum, or electromagnetic fields (Cheng et al., 2017; Hu et al., 2022; James et al., 2015; Mahato et al., 2019; Schudel et al., 2021; Wu et al., 2009). By this way, food material can tolerate textural changes related to ice formation. In IF technology, impinging air jets are directed to the food surface in order to reduce the thermal resistance exerted by the surrounding layer of the food material (James et al., 2015; Marazani et al., 2017). Thereby, the process speeds up the heat transfer and decreases the freezing time while preserving the food quality (Marazani

Fundamentals of freezing processes

43

Figure 2.5 Schematic of some novel freezing method: (a) Impingement freezing (Curtsey: Albrecht Machinery, South Africa); (b) electromagnetic fields assisted freezing (Otero et al., 2017); (c) ultrasound-assisted freezing; (d) isochoric freezing (Powell-Palm et al., 2018); and (e) antifreezing protein (Naing & Kim, 2019).

44

Low-Temperature Processing of Food Products

et al., 2017). IF is applicable especially for thin products, such as burgers and fish fillets. HF freezing system basically designed to develop a turbulent flow and create a fluidized bed in order to improve heat transfer during freezing process (Evans, 2016a, 2016b; James et al., 2015; Stebel et al., 2022). This method uses the advantages of both immersion freezing and IF and suitable especially for small-sized food products (Palacz et al., 2019, 2021; Stebel et al., 2022). UIF utilizes low-frequency and high-intensity ultrasound wave which is also known as “power ultrasound” (Cheng et al., 2017; James et al., 2015). The mechanism of UIF is based on ice nucleation by generation of cavitation bubbles, formation of fine ice crystals by collapse of cavitation bubbles, and creation of turbulence by movement of cavitation bubbles (Chen et al., 2022; Jiang et al., 2022; Qui et al., 2022; Zhang, Mao, et al., 2020; Zhang, Li, et al., 2020). Literature studies indicate that UIF technology is mainly applied to fruit and vegetables, dough, meat products, and also liquid samples (Chen et al., 2022; Cheng et al., 2017; Lu et al., 2022; Mahato et al., 2019; Zhang, Mao, et al., 2020; Zhang, Li, et al., 2020). Like UIF, HPF can also be regarded as an adjunct to immersion freezing in order to enhance the process (Cheng et al., 2017). There are three forms of HPF: (a) high pressureeassisted freezing (PAF), (b) high pressureeshifted freezing (PSF), and (c) high pressureeinduced freezing (PIF) (James et al., 2015; Lu et al., 2022). In HPF technology, a constant pressure is applied to change the type of ice crystals and to generate small and evenly distributed ice crystals throughout the food matrix (Cheng et al., 2017, 2021; Evans, 2016a, 2016b; Wu et al., 2017). Fruit, vegetables, meat, fish, and sugar-rich dairy-based products are some of the examples of food matrices which were used in HPF studies (Cheng et al., 2017; James et al., 2015; Mahato et al., 2019). Furthermore, Cartagena et al. (2021) used high-pressure processing as a pretreatment before freezing of albacore to improve frozen fish quality. Contrary to HPF, isochoric freezing occurs at constant volume instead of constant pressure. The principle behind preserving the frozen food quality in isochoric freezing depends on keeping the food material unfrozen at temperatures below its freezing point (Bilbao-Sainz et al., 2021). Thereby, food material is placed in a process chamber in which an isotonic solution exists and the temperature is reduced to allow ice formation in the solution. As a result, formation of ice crystals increases the pressure inside the process chamber (Bilbao-Sainz et al., 2019). Eventually, this ensures keeping the food product unfrozen at subfreezing temperatures. Bilbao-Sainz et al. (2019) and BilbaoSainz et al. (2021) reported the successful applications of isochoric freezing technology to sweet cherry, spinach leaves, and potatoes. EMF technology uses radiofrequency, microwave, electric fields, or magnetic fields in order to control formation and size of ice crystals in frozen foods (Lu et al., 2022; Sadot, Curet, Le-Bail, et al., 2020; Zhan et al., 2019). Underlying mechanism for EMF is rotation of water molecules and modification of hydrogen bonds, which result in smaller ice crystals (Mahato et al., 2019; Mok et al., 2015; Sadot, Curet, Chevallier, et al., 2020; Zhan et al., 2019). Hamzeh-Atani et al. (2022) found that microwaveassisted freezing better preserved the color and reduced drip loss of lamb meat via formation of a number of small ice crystals.

Fundamentals of freezing processes

45

Another novel freezing technology is the use of ice structuring proteins (ISP), also known as antifreeze proteins (AFP). They control ice formation by lowering freezing temperature and prevent recrystallization via adsorbing the ice crystal surface (Baskaran et al., 2021; Evans, 2016a, 2016b). ISPs are naturally found in fish, some plants, microorganisms, and invertebrates in order to protect the organism from being frozen under cold conditions (Baskaran et al., 2021; Evans, 2016a, 2016b; James et al., 2015; Lu et al., 2022). On the other hand, INPs, of which producers are bacteria, are used to accelerate freezing process via initiating ice nucleation at elevated temperatures (Evans, 2016a, 2016b; James et al., 2015). There are also some studies on the combined use of different emerging technologies to improve the freezing process and the quality of the product. For instance, Jiang et al. (2022) made use of CO2 bubbles to pressurize fresh-cut honeydew melon before UIF so as to enhance the effect of ultrasound. In another study, ultrasound is applied to speed up mass transfer in osmotic dehydrofreezing (Fan et al., 2020). Furthermore, Hu et al. (2022) utilized infrared and microwave heating prior to ultra-low-temperature freezing of pork loin. On the other hand, combined use of pulsed electric field with static magnetic field was also tested for its freezing performance (Mok et al., 2015). In conclusion, integration of emerging technologies with freezing processes can be considered to reduce the freezing time and to preserve food quality attributes (Table 2.1).

Table 2.1 Summary table of novel freezing methods. Novel freezing method Dehydrofreezing Hydrofluidization freezing Impingement freezing Ultrasoundassisted immersion freezing High pressure freezing

Working

Application

Removal of moisture prior to freezing Immersion in a hydrofluidized bed for rapid heat transfer High-velocity jets of cold air rapidly freeze the product

Preservation of dried fruits, vegetables, and meats products Quick freezing of small foods like seafood, meatballs, berries, and diced fruits and vegetables Rapid freezing of flat or thin food products, such as pizza, patties, battered chicken breasts and strips Improved freezing of fruits, vegetables, seafood, and meat, by enhancing heat transfer and ice crystal formation Cryopreservation of biological samples like cells, tissues, and organs; production of high-quality frozen food products with better texture and appearance

Application of ultrasound waves during immersion in a freezing medium Rapid freezing under high pressures to preserve cell structure

Continued

46

Low-Temperature Processing of Food Products

Table 2.1 Continued Novel freezing method

Working

Application

Electromagnetic fields assisted freezing

Application of electromagnetic fields to accelerate freezing

Isochoric freezing

Freezing at constant volume to minimize cell damage

Application of ice structuring proteins

Addition of proteins that modify ice crystal formation

Application of ice nucleation proteins

Addition of proteins that induce ice crystal formation

Faster freezing of fruits, vegetables, meat, and seafood, resulting in improved quality and reduced energy consumption Cryopreservation of delicate biological samples like stem cells, embryos, and sensitive biological materials Improve the quality and texture of frozen products like ice cream, by controlling ice crystal growth and reducing ice recrystallization Control the formation of ice crystal and improve the freezing efficiency in freezing of fruits and vegetables

2.7

Conclusion

In this chapter, the principal features of the freezing process of foods along with thermochemistry of freezing process were described. Moreover, the common methods applying for food freezing including, plate freezing, immersion freezing, air-blast freezing, and cryogenic freezing were discussed, and their further influences on microbial and quality attributes of frozen food were investigated. It was also described that how freezing could be followed by postfreezing events such as recrystallization, freezer burn, rancidity, and retrogradation. Finally, the novel freezing techniques and the future of food freezing were discussed.

References Al-Dalali, S., Li, C., & Xu, B. (2022). Effect of frozen storage on the lipid oxidation, protein oxidation, and flavor profile of marinated raw beef meat. Food Chemistry, 376, 131881. https://doi.org/10.1016/j.foodchem.2021.131881 Ando, Y., Maeda, Y., Mizutani, K., Wakatsuki, N., Hagiwara, S., & Nabetani, H. (2016). Effect of air-dehydration pretreatment before freezing on the electrical impedance characteristics and texture of carrots. Journal of Food Engineering, 169, 114e121. https://doi.org/ 10.1016/j.jfoodeng.2015.08.026 Attrey, D. (2017). Chapter 44dSafety and quality of frozen foods. Elsevier.

Fundamentals of freezing processes

47

Bao, Y., Ertbjerg, P., Estévez, M., Yuan, L., & Gao, R. (2021). Freezing of meat and aquatic food: Underlying mechanisms and implications on protein oxidation. Comprehensive Reviews in Food Science and Food Safety, 20(6), 5548e5569. https://doi.org/10.1111/15414337.12841 Baskaran, A., Kaari, M., Venugopal, G., Manikkam, R., Joseph, J., & Bhaskar, P. V. (2021). Anti freeze proteins (Afp): Properties, sources and applicationsdA review. International Journal of Biological Macromolecules, 189, 292e305. Bilbao-Sainz, C., Sinrod, A. J. G., Dao, L., Takeoka, G., Williams, T., Wood, D., Chiou, B.-S., Bridges, D. F., Wu, V. C. H., Lyu, C., Powell-Palm, M. J., Rubinsky, B., & McHugh, T. (2021). Preservation of grape tomato by isochoric freezing. Food Research International, 143, 110228. Bilbao-Sainz, C., Sinrod, A. J. G., Powell-Palm, M. J., Dao, L., Takeoka, G., Williams, T., Wood, D., Ukpai, G., Aruda, J., Bridges, D. F., Wu, V. C. H., Rubinsky, B., & McHugh, T. (2019). Preservation of sweet cherry by isochoric (constant volume) freezing. Innovative Food Science and Emerging Technologies, 52, 108e115. Barcenas, M. E., & Rosell, C. M. (2006). Effect of frozen storage time on the bread crumb and aging of par-baked bread. Food Chemistry, 95, 438e445. Bollman, J., Ismond, A., & Blank, G. (2001). Survival of Escherichia coli O157:H7 in frozen foods: Impact of the cold shock response. International Journal of Food Microbiology, 64(1), 127e138. https://doi.org/10.1016/S0168-1605(00)00463-3 Campa~none, L. A., Salvadori, V. O., & Mascheroni, R. H. (2001). Weight loss during freezing and storage of unpackaged foods. Journal of Food Engineering, 47(2), 69e79. https:// doi.org/10.1016/S0260-8774(00)00101-1 Cartagena, L., Puertolas, E., & de Mar~anon, I. M. (2021). Impact of different air blast freezing conditions on the physicochemical quality of albacore (Thunnus alalunga) pretreated by high pressure processing. LWT Food Science and Technology, 145, 111538. Chen, X., Liu, H., Li, X., Wei, Y., & Li, J. (2022). Effect of ultrasonic-assisted immersion freezing and quick-freezing on quality of sea bass during frozen storage. LWT Food Science and Technology, 154, 112737. Cheng, L., Sun, D.-W., Zhu, Z., & Zhang, Z. (2017). Emerging techniques for assisting and accelerating food freezing processes: A review of recent research progresses. Critical Reviews in Food Science and Nutrition, 57(4), 769e781. Cheng, L., Zhu, Z., & Sun, D.-W. (2021). Impacts of high pressure assisted freezing on the denaturation of polyphenol oxidase. Food Chemistry, 335, 127485. Cheng, S., Wang, X., Li, R., Yang, H., Wang, H., Wang, H., & Tan, M. (2019). Influence of multiple freeze-thaw cycles on quality characteristics of beef semimembranous muscle: With emphasis on water status and distribution by LF-NMR and MRI. Meat Science, 147, 44e52. https://doi.org/10.1016/j.meatsci.2018.08.020 Creed, P. (2006). Quality and Safety of frozen ready meals. In D. W. Sun (Ed.), Handbook of frozen food processing and packaging (pp. 459e476). Boca Raton, FL: CRC/Taylor and Francis Group. Dempsey, P., & Bansal, P. (2012). The art of air blast freezing: Design and efficiency considerations. Applied Thermal Engineering, 41, 71e83. Diao, Y., Cheng, X., Wang, L., & Xia, W. (2021). Effects of immersion freezing methods on water holding capacity, ice crystals and water migration in grass carp during frozen storage. International Journal of Refrigeration, 131, 581e591. Ede, A. J. (1949). The calculation of the freezing and thawing of foodstuffs. Modern Refrigeration, 52, 52.

48

Low-Temperature Processing of Food Products

Evans, J. (2016a). Emerging refrigeration and freezing technologies for food preservation. In C. E. Leadley (Ed.), Innovation and future trends in food manufacturing and supply chain technologies (pp. 175e201). Cambridge, UK: Woodhead Publisher. Evans, J. (2016b). Emerging refrigeration and freezing technologies for food preservation. In Innovation and future trends in food manufacturing and supply chain technologies (pp. 175e201). Elsevier. Falsafi, S. R., Rostamabadi, H., & Jafari, S. M. (2020b). Chapter ninedX-ray diffraction (XRD) of nanoencapsulated food ingredients. In S. M. Jafari (Ed.), Characterization of nanoencapsulated food ingredients (Vol. 4, pp. 271e293). Academic Press. https://doi.org/ 10.1016/B978-0-12-815667-4.00009-2 Falsafi, S. R., Rostamabadi, H., & Jafari, S. M. (2020a). X-ray diffraction (XRD) of nanoencapsulated food ingredients. In Characterization of nanoencapsulated food ingredients (pp. 271e293). Elsevier. Fan, K., Zhang, M., Wang, W., & Bhandari, B. (2020). A novel method of osmoticdehydrofreezing with ultrasound enhancement to improve water status and physicochemical properties of kiwifruit. International Journal of Refrigeration, 113, 49e57. Fellows, P. J. (2000). Food processing technology: Principles and practice (2nd ed., p. 928). Boca Raton, FL: CRC Press. Fennema, O. R. (1975). Effect of freeze-preservation on nutrients. In R. S. Harris, & E. Karmas (Eds.), Nutritional evaluation of food processing (pp. 244e288). Connecticut: AVI, Westport. Fernandez-Seara, J., Dopazo, J. A., Uhía, F. J., & Diz, R. (2012). Experimental analysis of the freezing process in a horizontal plate freezer with CO2 as refrigerant in a cascade refrigeration system. Heat Transfer Engineering, 33(14), 1170e1176. Ferrero, C., & Zaritzky, N. E. (2000). Effect of freezing rate and frozen storage on starchsucrose-hydrocolloid systems. Journal of the Science of Food and Agriculture, 80, 2149e2158. Galetto, C. D., Verdini, R. A., Zorrilla, S. E., & Rubiolo, A. C. (2010). Freezing of strawberries by immersion in CaCl2 solutions. Food Chemistry, 123(2), 243e248. George, R. (1993). Freezing proceseses used in the food industry. Trends in Food Science and Technology, 4(5), 134e138. Hamzeh-Atani, S., Hamdami, N., & Fallah-Joshaqani, S. (2022). Effects of microwave-assisted freezing on the quality attributes of lamb meat. International Journal of Refrigeration, 143, 192e198. https://doi.org/10.1016/j.ijrefrig.2022.03.019 Hernandez, E., Raventos, M., Auleda, J., & Ibarz, A. (2009). Concentration of apple and pear juices in a multi-plate freeze concentrator. Innovative Food Science and Emerging Technologies, 10(3), 348e355. Hessami, M.-A. (2004). A study of the efficiency of plate freezing vs. blast freezing of boxed boneless meat in an abattoir. In Paper presented at the heat transfer summer conference. Hsu, C.-L., & Heldman, D. R. (2005). Influence of glass transition temperature on the rate of rice starch retrogradation during low-temperature storage. Journal of Food Process Engineering, 28, 506e525. Hu, R., Zhang, M., & Mujumdar, A. S. (2022). Application of infrared and microwave heating prior to freezing of pork: Effect on frozen meat quality. Meat Science, 189, 108811. Hung, Y. (1996). Fundamental aspects of freeze-cracking. Food Technology, 50, 59e61. James, C., Purnell, G., & James, S. J. (2015). A review of novel and innovative food freezing technologies. Food and Bioprocess Technology, 8, 1616e1634.

Fundamentals of freezing processes

49

Jiang, Q., Zhang, M., Mujumdar, A. S., & Hu, R. (2022). Combination strategy of CO2 pressurization and ultrasound: To improve the freezing quality of fresh-cut honeydew melon. Food Chemistry, 383, 132327. Kaale, L. D., Eikevik, T. M., Bardal, T., Kjorsvik, E., & Nordtvedt, T. S. (2013). The effect of cooling rates on the ice crystal growth in air-packed salmon fillets during superchilling and superchilled storage. International Journal of Refrigeration, 36(1), 110e119. Kaale, L. D., Eikevik, T. M., Rustad, T., & Kolsaker, K. (2011). Superchilling of food: A review. Journal of Food Engineering, 107(2), 141e146. Kiani, H., & Sun, D.-W. (2011). Water crystallization and its importance to freezing of foods: A review. Trends in Food Science and Technology, 22(8), 407e426. Lan, W., Zhao, Y., Gong, T., Mei, J., & Xie, J. (2021). Effects of different thawing methods on the physicochemical changes, water migration and protein characteristic of frozen pompano (Trachinotus ovatus). Journal of Food Biochemistry, 45(8), e13826. https://doi.org/10.11 11/jfbc.13826 LeBail, A., & Goff, H. (2008). 9 freezing of bakery and dessert products (p. 184). Frozen food science and technology. Levy, F. L. (1958). Calculating freezing time of fish in air blast freezers. Journal of Refrigeration, 1, 55e58. Lu, N., Ma, J., & Sun, D.-W. (2022). Enhancing physical and chemical quality attributes of frozen meat and meat products: Mechanisms, techniques and applications. Trends in Food Science and Technology, 124, 63e85. https://doi.org/10.1016/j.tifs.2022.04.004 Lucas, T., & Raoult-Wack, A. (1998). Immersion chilling and freezing in aqueous refrigerating media: Review and future trends: Réfrigération et congélation par immersion dans des milieux réfrigérants: Revue et tendances futures. International Journal of Refrigeration, 21(6), 419e429. Lv, Y., Chu, Y., Zhou, P., Mei, J., & Xie, J. (2021). Effects of different freezing methods on water distribution, microstructure and protein properties of cuttlefish during the frozen storage. Applied Sciences, 11(15), 6866. Magnussen, O. M., Hemmingsen, A. K. T., Hardarsson, V., Nordtvedt, T. S., & Eikevik, T. M. (2008). Freezing of fish. In J. A. Evans (Ed.), Frozen food science, and technology (p. 365). Oxford OX4 2DQ: Blackwell Publishing Ltd. Mahato, S., Zhu, Z., & Sun, D.-W. (2019). Glass transitions as affected by food compositions and by conventional and novel freezing technologies: A review. Trends in Food Science and Technology, 94, 1e11. Marazani, T., Madyira, D. M., & Akinlabi, E. T. (2017). Investigation of the parameters governing the performance of jet impingement quick food freezing and cooling systemsdA review. Procedia Manufacturing, 8, 754e760. Meziani, S., Kaci, M., Jacquot, M., Jasniewski, J., Ribotta, P., Muller, J.-M., … Desobry, S. (2012). Effect of freezing treatments and yeast amount on sensory and physical properties of sweet bakery products. Journal of Food Engineering, 111(2), 336e342. Miles, M. J., Morris, V. J., Orford, P. D., & Ring, S. G. (1985). The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydrate Research, 135, 271e281. Miyawaki, O. (2018). Water and freezing in food. Food Science and Technology Research, 24(1), 1e21. https://doi.org/10.3136/fstr.24.1 Mohammed, H. H. H., He, L., Nawaz, A., Jin, G., Huang, X., Ma, M., Abdegadir, W. S., Elgasim, E. A., & Khalifa, I. (2021). Effect of frozen and refrozen storage of beef and chicken meats on inoculated microorganisms and meat quality. Meat Science, 175, 108453. https://doi.org/10.1016/j.meatsci.2021.108453

50

Low-Temperature Processing of Food Products

Mok, J. H., Choi, W., Park, S. H., Lee, S. H., & Jun, S. (2015). Emerging pulsed electric field (PEF) and static magnetic field (SMF) combination technology for food freezing. International Journal of Refrigeration, 50, 137e145. Moreno, F., Raventos, M., Hernandez, E., & Ruiz, Y. (2014). Behaviour of falling-film freeze concentration of coffee extract. Journal of Food Engineering, 141, 20e26. Mulot, V., Benkhelifa, H., Pathier, D., Ndoye, F.-T., & Flick, D. (2019). Measurement of food dehydration during freezing in mechanical and cryogenic freezing conditions. International Journal of Refrigeration, 103, 329e338. https://doi.org/10.1016/j.ijrefrig.2019.02.032 Nagaoka, J., Takagi, S., & Hotani, S. (1956). Experiments on the freezing of fish by air blast freezer. Journal of the Tokyo University of Fisheries, 42(1), 65e73. Naing, A. H., & Kim, C. K. (2019). A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering. 3 Biotech, 9, 1e9. Norwig, J. F., & Thompson, D. R. (1984). Review of dehydration during freezing. Transactions of the American Society of Agricultural Engineers, 1619e1624. Otero, L., Pérez-Mateos, M., Rodríguez, A. C., & Sanz, P. D. (2017). Electromagnetic freezing: Effects of weak oscillating magnetic fields on crab sticks. Journal of Food Engineering, 200, 87e94. Palacz, M., Adamczyk, W., Piechnik, E., Stebel, M., & Smolka, J. (2019). Experimental investigation of the fluid flow inside a hydrofluidisation freezing chamber. International Journal of Refrigeration, 107, 52e62. Palacz, M., Piechnik, E., Halski, M., Stebel, M., Adamczyk, W., Eikevik, T. M., & Smolka, J. (2021). Experimental analysis of freezing process of stationary food samples inside a hydrofluidisation freezing chamber. International Journal of Refrigeration, 131, 68e77. Parreno, W., & Torres, M. (2006). Quality and safety of frozen vegetables (Vol 155, p. 377). Food Science and Technology-New York-Marcel Dekker. Pham, Q. T. (1986). Simplified equation for predicting the freezing time of foodstuffs. International Journal of Food Science and Technology, 21(2), 209e219. Phimolsiripol, Y., Siripatrawan, U., & Cleland, D. J. (2011). Weight loss of frozen bread dough under isothermal and fluctuating temperature storage conditions. Journal of Food Engineering, 106(2), 134e143. https://doi.org/10.1016/j.jfoodeng.2011.04.020 Powell-Palm, M. J., Preciado, J., Lyu, C., & Rubinsky, B. (2018). Escherichia coli viability in an isochoric system at subfreezing temperatures. Cryobiology, 85, 17e24. Qian, P., Zhang, Y., Shen, Q., Ren, L., Jin, R., Xue, J., … Dai, Z. (2018). Effect of cryogenic immersion freezing on quality changes of vacuum-packed bighead carp (Aristichthys nobilis) during frozen storage. Journal of Food Processing and Preservation, 42(6), e13640. Qui, S., Cui, F., Wang, J., Zhu, W., Xu, Y., Yi, S., Li, X., & Li, J. (2022). Effects of ultrasoundassisted immersion freezing on the muscle quality and myofibrillar protein oxidation and denaturation in Sciaenops ocellatus. Food Chemistry, 377, 131949. Rahman, M. S., & Velez-Ruiz, J. F. (2007a). Food preservation by freezing. In M. S. Rahman (Ed.), Handbook of food preservation (p. 1088). Boca Raton: CRC Press. Rahman, M. S., & Velez-Ruiz, J. F. (2007b). Food preservation by freezing Handbook of food preservation (pp. 653e684). CRC Press. Ramallo, L. A., & Mascheroni, R. H. (2010). Dehydrofreezing of pineapple. Journal of Food Engineering, 99, 269e275. Rostamabadi, H., Falsafi, S. R., & Jafari, S. M. (2019). 15dNanostructures of starch for encapsulation of food ingredients. In S. M. Jafari (Ed.), Biopolymer nanostructures for food encapsulation purposes (pp. 419e462). Academic Press. https://doi.org/10.1016/B978-012-815663-6.00015-X

Fundamentals of freezing processes

51

Ribotta, P. D., Leon, A. E., & A~non, M. C. (2003). Effect of freezing and frozen storage on the gelatinization and retrogradation of amylopectin in dough baked in a differential scanning calorimeter. Food Research International, 36, 357e363. Sadot, M., Curet, S., Chevallier, S., Le-Bail, A., Rouaud, O., & Havet, M. (2020). Microwave assisted freezing part 2: Impact of microwave energy and duty cycle on ice crystal size distribution. Innovative Food Science and Emerging Technologies, 62, 102359. Sadot, M., Curet, S., Le-Bail, A., Rouaud, O., & Havet, M. (2020). Microwave assisted freezing part 1: Experimental investigation and numerical modeling. Innovative Food Science and Emerging Technologies, 62, 102360. Santarelli, V., Neri, L., Sacchetti, G., Di Mattia, C. D., Mastrocola, D., & Pittia, P. (2020). Response of organic and conventional apples to freezing and freezing pre-treatments: Focus on polyphenols content and antioxidant activity. Food Chemistry, 308, 125570. https://doi.org/10.1016/j.foodchem.2019.125570 Schudel, S., Prawiranto, K., & Defraeye, T. (2021). Comparison of freezing and convective dehydrofreezing of vegetables for reducing cell damage. Journal of Food Engineering, 293, 110376. Sebranek, J. G. (1996). In L. E. Jeremiah (Ed.), Poultry and poultry products, freezing effects on food quality (p. 85). Marcel Dekker. Sanchez-Alonso, I., Martinez, I., Sanchez-Valencia, J., & Careche, M. (2012). Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR. Food Chemistry, 135(3), 1626e1634. https://doi.org/10.1016/j.foodchem.2012. 06.038 Stebel, M., Smolka, J., Palacz, M., Halski, M., Widuch, A., Tolstorebrov, I., & Eikevik, T. M. (2022). Numerical analysis of hydrofluidisation food freezing with moving products in different aqueous solutions by using CFD and MPM approaches. International Journal of Refrigeration, 135, 261e275. Sukumaran, L., & Radhakrishnan, M. (2021). Effect of frozen storage on the inhibition of microbial population, chemical and sensory characteristics of coconut neera. Journal of Applied Microbiology, 131(4), 1830e1839. https://doi.org/10.1111/jam.15068 Svendsen, E. S., Widell, K. N., Tveit, G. M., Nordtvedt, T. S., Uglem, S., Standal, I., & Greiff, K. (2022). Industrial methods of freezing, thawing and subsequent chilled storage of whitefish. Journal of Food Engineering, 315, 110803. Szymczak, M., Kaminski, P., Felisiak, K., Szymczak, B., Dmytr ow, I., & Sawicki, T. (2020). Effect of constant and fluctuating temperatures during frozen storage on quality of marinated fillets from Atlantic and Baltic herrings (Clupea harengus). LWT, 133, 109961. https://doi.org/10.1016/j.lwt.2020.109961 Tan, M., Lin, Z., Zu, Y., Zhu, B., & Cheng, S. (2018). Effect of multiple freeze-thaw cycles on the quality of instant sea cucumber: Emphatically on water status of by LF-NMR and MRI. Food Research International, 109, 65e71. https://doi.org/10.1016/j.foodres.2018.04.029 Tan, M., Mei, J., & Xie, J. (2021). The formation and control of ice crystal and its impact on the quality of frozen aquatic products: A review. Crystals, 11(1), 68. Tejada, L., Buendía-Moreno, L., Villegas, A., Cayuela, J. M., Bueno-Gavila, E., G omez, P., & Abellan, A. (2020). Nutritional and sensorial characteristics of zucchini (Cucurbita pepo L.) as affected by freezing and the culinary treatment. International Journal of Food Properties, 23(1), 1825e1833. https://doi.org/10.1080/10942912.2020.1826512 Tejada, L., Sanchez, E., Gomez, R., Vioque, M., & Fernandez-Salguero, J. (2002). Effect of freezing and frozen storage on chemical and microbiological characteristics in sheep milk cheese. Journal of Food Science, 67(1), 126e129. https://doi.org/10.1111/j.1365-2621. 2002.tb11371.x

52

Low-Temperature Processing of Food Products

Truonghuynh, H. T., Li, B., Zhu, H., Guo, Q., & Li, S. (2020). Freezing methods affect the characteristics of large yellow croaker (Pseudosciaena crocea): Use of cryogenic freezing for long-term storage. Food Science and Technology, 40, 429e435. Visser, K. (1986). Automatic plate freezer development. International Journal of Refrigeration, 9(6), 367. Wu, L., Orikasa, T., Tokuyasu, K., Shiina, T., & Tagawa, A. (2009). Applicability of vacuumdehydrofreezing technique for the long-term preservation of fresh-cut eggplant: Effects of process conditions on the quality attributes of the samples. Journal of Food Engineering, 91, 560e565. Wu, X.-F., Zhang, M., Adhikari, B., & Sun, J. (2017). Recent developments in novel freezing and thawing technologies applied to foods. Critical Reviews in Food Science and Nutrition, 57(17), 3620e3631. Xu, J.-C., Zhang, M., Mujumdar, A. S., & Adhikari, B. (2017). Recent developments in smart freezing technology applied to fresh foods. Critical Reviews in Food Science and Nutrition, 57(13), 2835e2843. Yang, F., Jing, D., Diao, Y., Yu, D., Gao, P., Xia, W., … Zhan, X. (2020). Effect of immersion freezing with edible solution on freezing efficiency and physical properties of obscure pufferfish (Takifugu Obscurus) fillets. LWT, 118, 108762. Yu, S., Ma, Y., & Sun, D.-W. (2010). Effects of freezing rates on starch retrogradation and textural properties of cooked rice during storage. LWT Food Science and Technology, 43, 1138e1143. Zaritzky, N. E. (2010). Chemical and physical deterioration of frozen foods Chemical deterioration and physical instability of food and beverages (pp. 561e607). Elsevier. Zaritzky, N. E. (2008). Frozen storage. In J. A. Evans (Ed.), Frozen food science, and technology (p. 365). Oxford OX4 2DQ: Blackwell Publishing Ltd. Zhan, X., Zhu, Z., & Sun, D.-W. (2019). Effects of extremely low frequency electromagnetic field on the freezing processes of two liquid systems. LWT Food Science and Technology, 103, 212e221. Zhang, B., Mao, J., Yao, H., & Aubourg, S. P. (2020). Label-free based proteomics analysis of protein changes in frozen whiteleg shrimp (Litopenaeus vannamei) pre-soaked with sodium trimetaphosphate. Food Research International, 137, 109455. https://doi.org/10.1016/ j.foodres.2020.109455 Zhang, F., Zhang, J., Di, H., Xia, P., Zhang, C., Wang, Z., Li, Z., Huang, S., Li, M., Tang, Y., Luo, Y., Li, H., & Sun, B. (2021). Effect of long-term frozen storage on health-promoting compounds and antioxidant capacity in baby mustard. Frontiers in Nutrition, 8. https:// www.frontiersin.org/article/10.3389/fnut.2021.665482. Zhang, Y., Li, Y., Wang, H., Oladejo, A. O., Zhang, H., & Liu, X. (2020). Effects of ultrasoundassisted freezing on the water migration of dough and the structural characteristics of gluten components. Journal of Cereal Science, 94, 102893. Zhao, Y., Ji, W., Chen, L., Jia, G., & Junjie, W. (2019). Effect of cryogenic freezing combined with precooling on freezing rates and the quality of golden pomfret (Trachinotus ovatus). Journal of Food Process Engineering, 42(8), e13296. https://doi.org/10.1111/jfpe.13296 Zhu, S., Ramaswamy, H. S., & Le Bail, A. (2005). Ice-crystal formation in gelatin gel during pressure shift versus conventional freezing. Journal of Food Engineering, 66(1), 69e76. Zhu, Z., Zhou, Q., & Sun, D.-W. (2019). Measuring and controlling ice crystallization in frozen foods: A review of recent developments. Trends in Food Science and Technology, 90, 13e25.

Elements of a low-temperature processing system

3

Busra Gultekin Subasi and Esra Capanoglu Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey

3.1

Introduction

Low-temperature processing is one of the critical unit operations in food science and industry in terms of preservation, which dates back to 1700s as the first milestone of mechanical refrigeration (Berk, 2009a). During storage, foods might undergo some undesirable but inevitable changes for their microbiological, physiological, biochemical, and/or physical properties. In order to prolong the storage period, decreasing the molecular mobility of free water in the structure by application of low-temperature processing would retard the microbial growth besides physiological, biochemical, and physical reactions. It should be noted that undesirable reactions and microbial growth only slow down and are limited temporarily under refrigeration conditions, unless an additional process is applied (like hurdle technologies). However, properties of the products are protected with low-temperature applications for a certain storage lifespan if the cold chain is maintained. Optimum storage periods are defined according to the nature and conditions of the applied method of low-temperature processing, chilling or freezing (James & James, 2014). Low-temperature processing, which is also known as refrigeration, is basically a kind of artificial/forced cooling by manipulation of ambient temperature. Removing the heat of sample and transferring toward a higher energy level are operated by refrigeration process (Singh & Heldman, 2014). Chilling and freezing are two different applications of low-temperature processing. Decreasing the temperature precisely above the freezing point of sample, into a range of 0e8
C, is the chilling process, while freezing is lowering the temperature down to 18
C or lower (Berk, 2009a). Furthermore, cooling the sample until a temperature point where the first ice crystal formation occurs at around 1e2
C is called as super chilling (Kaale et al., 2011). Depending on the ability of free water immobilization, the longest and the most effective protective period might be obtained by freezing followed by superchilling and chilling, respectively. In addition to protective properties, low temperature is applied on food products as a pretreatment of further processing such as hardening, concentrating, freeze drying, humidification/dehumidification, and size reduction (cryomilling, grinding) (Berk, 2009a). In this chapter, basics of low-temperature processing are provided including definitions, principles of heat and mass transfer phenomena with equations behind the

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00001-1 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

54

Low-Temperature Processing of Food Products

refrigeration applications, main elements of mechanical refrigeration, and their commonly used equipment. Conventional and innovative refrigerants, which are being used in low-temperature processing equipment, are also presented together with recent developments. The most widely used chilling and freezing systems for both industrial and household usages are also briefly discussed.

3.2

Basics of heat and mass transfer for refrigeration technology

Low-temperature processing of food materials is a complex thermophysical phenomena, mainly based on heat energy transfer as conduction, convection, and radiation besides mass transfer in the form of evaporation (James & James, 2014). Refrigeration of organic materials might include phase transition, removal of sensible, and/or latent heat as well as alterations of thermodynamic properties such as thermal conductivity and specific heat, depending on the process as either chilling of freezing. On the other hand, mass transfer has an influence on heat energy to be transferred by the motions of fluids (Zhao & Takhar, 2017). All these complex thermodynamic reactions are effective on refrigeration time, efficiency, and final product quality for both chilling and freezing. A deeper insight to the basics of heat and mass transfer phenomena is required to design and utilize any refrigeration process on foods to have desired product properties.

3.2.1

Thermal conductivity, diffusivity, and molecular diffusivity

Thermal conductivity and diffusivity are important and useful physical parameters of materials correlated with heat transfer analysis. Thermal conductivity “k” represents the ability of a material to conduct/transfer the heat energy across a temperature gradient. Since being highly dependent on temperature and pressure, “k” is a variable term, but it is considered as constant within a limited temperature range without any particular phase change in the structure. According to SI systems, the unit of “k” is defined as w mK1 -watts per meter kelvin (Becker & Fricke, 2003). Another significant term that is derivatized from thermal conductivity is thermal diffusivity (a), which is provided in Eq. (3.1). Basically, thermal diffusivity is the ratio of thermal conductivity to volumetric heat capacity of a material, which indicates the capability to transfer the stored heat of a material. a¼

k rCp

(3.1)

In the SI system, the unit of “a” is obtained as m2 s1 from the simplification of constitutive terms where “k” is the thermal conductivity, “r” is the density (kg m3) and “Cp” is the specific heat capacity (J K1 kg1) (Earle & Earle, 2004a).

Elements of a low-temperature processing system

55

As a similar term with thermal diffusivity, molecular/mass diffusivity, or in another word, diffusion coefficient, represents the diffusing molecular species into the media at a specified temperature. In Fick’s Law of Diffusion, diffusion coefficient is defined as “D” and for liquid systems, Brownian diffusion model is widely used and “D” is given in StokeseEinstein equation as it is in Eq. (3.2). In this system, the diffusing molecule is assumed as a sphere, and its dimension is represented with radius. D¼

kT 6p r m

(3.2)

In molecular diffusion equation, “k” is the Boltzmann’s constant (1.38 1023 J K1), and “m” is the viscosity of the solution. Based on SI system, the unit of “D” is defined as m2 s1. The diffusivities of molecules in water vary in a range of 10e9 to 10e11 m2 s1 for small to large molecules (Berk, 2009c; Zhao & Takhar, 2017).

3.2.2

Basics of mass transfer

During refrigeration process, mass transfer might be observed mainly in two different mechanisms; evaporation of water from the surface of chilled/frozen material and/or diffusion of water molecules toward recently formed ice crystals for propagation throughout the food matrix. Mobilize watery phase might include some dissolved substances, and this should be noted that presence of impurities in the watery phase, homogeneity and/or heterogeneity of food system are expected to influence the freezing time and final product quality (Murray et al., 2010). Evaporation is a simultaneous heat and mass transfer phenomena, which takes place on the surface of refrigerated material in case of ambient temperature and pressure difference (Kerr, 2019). The evaporated quantity as well as heat to be transferred could be obtained using Eq. (3.3). qv ¼

dQ ¼ ml CpðTo  TsÞ þ mi li dt

(3.3)

where, subscript “i” refers ice, “l” refers liquid and “v” refers vapor besides “q” is required total heat for evaporation, “Q” is time (t) dependent total heat, “m” is mass, “Cp” is the specific heat of water, “To” and “Ts” are the temperatures of outer environment and refrigerated surface, and “l” is the latent heat. The energy terms could change according to whether the system is chilling or freezing. On the other hand, mass transfer is an important step for refrigeration process in the heat exchanger unit where the vapor refrigerant releases the liquid it carries and complete the refrigeration cycle. Total heat transfer could be obtained using Eq. (3.3) neglecting the latent heat terms. Mass transfer of water phase during freezing with convection is hypothesized as the diffusion when one component (the rest of food matrix except water and dissolved compounds in it) is stagnant (Eq. 3.4) (Jain et al., 2019).

56

Low-Temperature Processing of Food Products

NA ¼ kðCA1  CA2 Þ; k ¼

DAB z

(3.4)

where, “NA” is the mass flux, “k” is mass transfer coefficient, “CA” is the concentration gradient (mol m3 or mole fraction), and “z” is the diffusion distance. Depending on the scope of problem, dimensionless numbers such as Schmidt number (Sc), Sherwood number (Sh), Reynolds number (Re), and Grashof number (Gr) associated with mass and simultaneous heat and momentum transfers might be used for calculations and to assess the transport phenomena from a wider perspective (Berk, 2009c).

3.2.3

Basics of heat transfer

Refrigeration process mostly consists of heat energy transfer in a time dependent manner of conduction, convection, and radiation (Earle & Earle, 2004a). When compared to convection and conduction, radiation is generally be neglected for refrigeration; nevertheless, it was briefly mentioned in this section. In conduction, heat energy is directly transferred to a closest (in contact) molecule from the molecule that had a higher energy level. Conductive heat transfer particularly matters for solid materials; hence, from the first nucleus formation (ice) to a fulfilled freezing conduction is of importance (Eq. 3.5). dQ dT ¼  kA dt dx

(3.5)

In conductive heat transfer equation (Eq. 3.5), the rate of heat transfer (dQ/dt) is a function of temperature gradient (dT/dx), the thermal conductivity of medium (k) and area (A) which heat is transferred from. This equation is known as the equation of Fourier heat conduction (Zhu et al., 2020). It should be noted that heat conduction is a time, temperature, and area/surface geometry-dependent energy transfer system for refrigeration technology. Rearranging and integrating Eq. (3.5) required time for a complete freezing of a liquid mass having a thickness “z” could be calculated using Eq. (3.6), which is also known as the Plank equation. t¼

  rl z z2 þ Tf  To h 2k

(3.6)

where, “r” is the density of liquid, “l” is the latent heat of freezing liquid, “h” is the convective heat transfer at the surface, “k” is thermal conductivity, and “Tf” and “To” are the freezing and outer medium temperatures. Heat transfer from the surface of a solid material when immersed in a cooling medium is explained with Newton’s law of cooling (Eq. 3.7), which is also another important way of energy transfer during refrigeration process and represents the convection. q ¼ hs A ðTo  Ts Þ

(3.7)

Elements of a low-temperature processing system

57

The Newton’s law of cooling is also analogous to Fourier heat conduction equation, where “hs” is surface heat-transfer coefficient through a hypothetical surface film having a thickness of “xf” hence is defined as “hs ¼ kf /xf,” while “kf” is the thermal conductivity of outer cooling medium (Berk, 2009c; Blikra et al., 2019). In the systems of simultaneous heat convection and conduction, one of them could be neglected in order to solve transport problems based on a dimensionless number, Biot number (Bi), which is basically the ratio of heat transfer coefficient at the surface to the conducted heat. On the other hand, Nusselt (Nu), Reynolds (Re), and Prandtl (Pr) numbers are other useful dimensionless numbers to be used for the calculations of heat transfer during refrigeration process (Earle & Earle, 2004a). As previously mentioned, radiation heat transfer might generally be neglected for refrigeration systems; however, occasionally might be considered as significant for the processes like freeze drying and cold storage (Sukumar & Kar, 2019). Transferred heat by electromagnetic radiation, which is also known as the radiant heat could be observed from StefaneBoltzmann law; q ¼ ε A sT 4

(3.8)

In Eq. (3.8), “ε” is the emissivity of the body, “s” is the StefaneBoltzmann constant, which is 5.73  108 J m2 s1 K4. The presence of roughened surface and/ or total surface area is important factors that have a direct effect on radiative heat transfer.

3.3

Main elements of mechanical refrigeration

Refrigeration of a material is applicable with three different methods which are natural conditions (cooling down at room temperature, ice immersion, wind energy, etc.), using cryogenic agents with the purpose of heat loss and applying mechanical refrigeration systems (Berk, 2009b). Within the scope of this chapter, mainly the last method is elaborated. As expressed in the second law of thermodynamics, high level of energy naturally flows toward a lower energy region. However, the principle of mechanical refrigeration is quite opposite of this natural energy flow (Fig. 3.1). To run a refrigeration operation, the heat engine receives energy from the cold zone where the materials were placed in to cool down and then delivers the heat energy to a region where the ambient temperature is higher than that of inside the refrigeration chamber. Briefly, the heat is delivered from a low energy level to high in a closed circuit by a heat pump, which is also known as the refrigeration machine that works as cycles (Dosset & Horan, 2001). Correlated with the explained principle of heat engine, refrigeration might be produced based on three different thermodynamic procedures; the vapor compression system, the absorption system, and the Peltier effect (Berk, 2009b).

58

Low-Temperature Processing of Food Products

Figure 3.1 Scheme of work, done by heat pump.

3.3.1

Vapor compression system

The vapor compression is the most widely used mechanical refrigeration method, which has a cyclic thermodynamic procedure following the vapor compression; a cyclic plot of entropy as a function of temperature. This closed circuit of entropy is represented by four interconnected components, which were declared and enumerated on Fig. 3.2 as compression, condensation, expansion, and evaporation of a refrigerant fluid. •

Compression (zone 1e2): As the initiation step, pressure of saturated vapor is increased by compression to P2 level from P1. The work is assumed to be done adiabatic and reversible by compressor. For this purpose, varying types of compressors might be used such as air-cooled piston, screw, or centrifugal compressors. Among them, air-cooled reciprocating piston compressors are commonly used in industrial scale; however, the compressors having hermetic units with permanent lubrication are designed for domestic fridges. Multiple compression units might be adapted to the system if very low operating temperatures are desired.

Figure 3.2 Theoretical thermodynamic cycle for vapor compression refrigeration (Berk, 2009b).

Elements of a low-temperature processing system

•

•

•

59

Condensation (zone 2e3): Compressed vapor is transferred to the condenser for cooling until a fully saturated liquid form was observed. The work is assumed to be done under constant pressure. The removed heat is discarded with a cooling medium, and either air or water might be used for this purpose. Air cooling is enabled by finned-tube radiators assisted with forced air flow by fans. On the other hand, shell-and-tube type heat exchangers are commonly utilized for water cooling condensers. Expansion (zone 3e4): The pressure of compressed refrigerant fluid is released (back to P1) throughout an expansion valve ending up with a mixture of liquid and vapor phases of the refrigerant fluid. Expansion valves are the main control units of refrigeration circuit. The system energy is assumed to be isenthalpic. Evaporation (zone 4e1): The heat energy to be removed is transferred into the vaporeliquid refrigerant mixture in order to evaporate the liquid to gain back all-vapor form with a heat exchanger. Types of the evaporator change according to the purpose of cooling or nature of the product to be refrigerated such as jacket type, finned-tube radiator type, and/or immersing type helical tube.

Considering energy efficiency and environmental factors like global warming and economic issues, which are of crucial and emerging issues for every branches of industry, novel approaches are required to develop the most energy efficient and low costed vapor compression cooling systems. One of these approaches is settling various hybrid systems into vapor compression units in order to achieve these purposes. Liquid desiccant dehumidification subsystem was incorporated to conventional vapor compression refrigeration unit to split the heat load (Mansuriya et al., 2020). In another perspective, humidification and dehumidification assisted the conventional system to improve the operation performance and reduced the energy consumption using augmented desalination (Anand & Murugavelh, 2020). Another approach for cost-effective and energyefficient cooling systems is the hybridization of conventional vapor compression elements with spray-assisted desalination process (Chen et al., 2019). With another perspective, settling a heat pipe system containing holder and plate fins into a conventional air conditioner with vapor compression unit enhanced the energy efficiency of the cooling system (Nakkaew et al., 2019). Similarly, a single vapor compression cooling chamber was aided with a Ranque-Hilsch vortex tube, and the hybrid system was analyzed in terms of performance, with energy, exergy, and economic analysis. The hybrid system had significantly higher energy efficiency than conventional chamber with reasonable costs (Senturk et al., 2019). Optimization of mixtures and proposing novel alternatives for refrigerants, which are being used conventionally in vapor compression systems, are other useful approaches for a better energy efficiency with lower cost (de Paula et al., 2020; Mota-Babiloni et al., 2019). Instead of electric power, alternative sources might be used as driving forces for refrigeration systems. The cascaded vapor compression/absorption units with a novel organic Rankine cycle is integrated in order to ensure the direct conversion of heat into refrigerating process (Patel et al., 2017). On the other hand, the solar energy is another remarkable and renewable alternative for hybrid vapor compression refrigeration systems (Jani et al., 2018; Salilih & Birhane, 2019). Briefly, hybridization, substitution, and modification of system elements for better engineered refrigerating circuits with lower costs and higher efficiencies are competing and demanding research areas, which probably will be the case for upcoming years as well.

60

Low-Temperature Processing of Food Products

3.3.2

Absorption cycle system

Even though the most extensively used mechanical refrigeration is the vapor compression system, absorption cycle is also of importance for special refrigeration purposes. It should be emphasized that the most outstanding advantage of absorption cycle refrigeration is enabling refrigeration without electric power for vapor compression and alternative energy sources such as solar or geothermal energy might be used as the driving force for power supply (Berk, 2009b). This system has a significant potential to be used widely in case of alternative energy sources (particularly solar energy) that was engineered to be used efficiently for both industrial and household usage. Schematic working principle of absorption cycle system is presented in Fig. 3.4. The system requires two different fluids running distinctive parts of the refrigerator, which are a refrigerant and an absorbent. Generally, this fluid couple is preferred as ammonia being the refrigerant and water as the absorbent. However, in some recent studies, lithium bromide is also being used in order to improve energetic and exergetic efficiencies of the refrigeration process (Sharifi et al., 2020). The absorption cycle also follows the same thermodynamic pattern provided for vapor compression system as shown in Fig. 3.2; however, the step of “compression” is naturally replaced by some customized operations of absorption refrigeration. The key points of absorption cycle can be briefly summarized as the following. •

Considering the thermodynamic circuit in Fig. 3.3, the refrigerant flows toward the absorber under low pressure to cool down with an absorbent (Fig. 3.4). The process here is exothermic.

Figure 3.3 Vapor compression system as mechanical refrigeration circuit (a) (re-drawn from Earle & Earle, 2004). The colored figure on the right corner (b) represents the heat of circulating refrigerant from hot (dark red [gray in print version]) to cold (turquoise [light gray in print version]) as temperature gradient (James & James, 2014).

Elements of a low-temperature processing system

61

Figure 3.4 Absorption refrigeration circuit with an example of watereammonia fluid couple system (Berk, 2009b).

• • •

The refrigerant that has low pressure and temperature is pumped into a heat exchanger where the pressure will increase. In generator, vaporized refrigerant at high pressure is desorbed with the presence of an outer heat input (from solar, geothermal sources). The process here is endothermic. Absorbent solution at low temperature returns back to the absorber.

After completing the sub-circuit unit of absorption refrigeration, the vaporized refrigerant at high temperature follows the same cycle as it was in vapor compression system step-by-step as condensation, expansion, and evaporation. Recent studies aiming to develop more efficient, environmental friendly, and costeffective methods for absorption refrigeration system have been conducted in a growing number. Designing and developing hybrid absorption systems are one of the most frequently studied area. In a recent study, a booster compressor was settled in between the generator and condenser of the absorption chamber, aiming to obtain absolute heat transfer by modulating pressure ratio with this hybridized refrigeration system (Razmi et al., 2018). In another study, researchers investigated and observed a higher system performance, better cooling capacity, and less energy consumption when a novel adsorption and absorption unit was integrated to the conventional refrigerating chamber (Nikbakhti et al., 2020). Organic Rankine cycle was combined with absorption refrigeration system, and the energy efficiency was evaluated at a building scale; hence, power production of hybridized system and electricity demand were significantly increased (Souza et al., 2020). Another hybridization study was conducted for the combination of absorption refrigeration system with recompression process. Hybrid system was stated to be more environmental friendly besides significantly higher coefficient of performance and exergy efficiency (Razmi et al., 2020). Combination of the absorption system with solar energy units such as solar absorption/dual compression hybridization to control temperature and humidity (Song et al., 2020); integration of concentrated solar power system into absorption refrigeration coupled

62

Low-Temperature Processing of Food Products

with desalination cycles (Mehrpooya et al., 2018); and using solar water heating system to optimize the absorption refrigeration circuit (Christopher et al., 2021) increased exergy efficiency and improved cooling coefficient of performance, significantly. On the other hand, integrating humidificationedehumidification desalination system (Qasem et al., 2020) or CO2 refrigeration units (Bellos & Tzivanidis, 2019) into absorption refrigeration cycles is another recent example concerning the performance development of the cooling chambers.

3.3.3

Peltier effect

Refrigeration with Peltier effect is the system, which is useful only in small-scale operations with limited capacities such as vending machines or simple household dehumidification purposes (Berk, 2009b). The refrigeration principle of Peltier effect is based on to create temperature differences between the junction points of two different metal probes when varying voltages are applied. In order to obtain thermoelectric based clean and sustainable cooling energy via Peltier effect, solar energy is also of interest mainly for small scale (portable) cooling units (Arjun et al., 2017). Despite the capacity limitation of this method, using electric energy as the driving force is considered as the most significant advantage of Peltier effect refrigeration system (Mardini-Bovea et al., 2019).

3.4 3.4.1

Mechanical equipment Compressors

Compressors are a kind of main fluid pumps of refrigerators, which enables the refrigerant to flow and complete the process cycle. Pressure and temperature increment of running refrigerant fluid are the driving forces for compressor unit. Varying types of compressors are being used throughout the history until the present day and commonly five types of compressors are in use depending on the purpose, which are reciprocating, rotary-vane, rotary-screw, scroll, and centrifugal compressors (Gu_zda & Szmolke, 2015). In Fig. 3.5, a brief summary of compressor type and their relevant use is provided (Rubik, 2006). Despite their differences for both mechanical and power supply points of view, the compressors that run with refrigerants have some common features in working principals; capability to achieve high compression with a single-stage unit, no operation restriction within the range of suction pressure and batch transfer of refrigerant (Gazinski, 2014). •

Reciprocating compressor: With another name, the piston compressor works with positive displacement principle, basically back and forward piston motions. Compression cycle follows the route as suction, compression with discharge, and extrusion of vaporized refrigerant (Fig. 3.6a) with processing elements of motor, some pistons and the most important one, the crankshaft that enables the piston to have reciprocating movement from the rotary motion of drive shaft. They also have some subtypes that vary according to their systems; number of

Elements of a low-temperature processing system

63

Figure 3.5 Compressors and their common utilization areas.

•

•

•

•

valves and cylinders, body design of compressor, number of steps, and type of refrigerant (Gu_zda & Szmolke, 2015; Rubik, 2006). The common types of reciprocating compressors are open type, serviceable semi-hermetic, bolted serviceable semi-hermetic, and welded hermetic compressors. Rotary-vane compressor: In this type, the work (the compression) is done by the rotating piston in the cylinder. The vane (Fig. 3.6b) splits the cylinder into suction (inlet) and discharge (outlet) elements. Operation steps due to continuous rotation of crankshaft are start, suction, compression, discharge, and termination (Gu_zda & Szmolke, 2015). Scroll compressor: Two coplanar scrolls (Fig. 3.6c), one of which is stationary, while the other in motion create compression with the planetary motion of movable scroll. Vapor refrigerant is sucked with planetary orbiting movement and started to compress by lowering the gap in between the scrolls. It has many advantages over reciprocating compressors such as having less moving units, smaller scale, resistant to extreme water pressure, stable motor shaft against varying loads, less vibration, and longer lifespan (Butrymowicz et al., 2014; Rubik, 2006). Rotary-screw compressor: Helical screw rotors are designed to compress very high amounts of refrigerants. Rotors having teeth and notches (Fig. 3.6d) rotate likewise the gearwheels, and these movements push the refrigerant toward the suction unit of compressor. Sucked fluid moves, extruded and compressed form at high pressure, and leaves the rotor from discharge port. This type is as abundant as reciprocating and centrifugal compressors with many advantages such as having no pulses, valves, or vibrations, resistant to extreme water pressure and prone to work more continuously to supply maximum power (Gu_zda & Szmolke, 2015; Rubik, 2006). Centrifugal (impeller blade) compressor: This type, also known as turbo or radial compressor, uses kinetic energy to rotate the impellers, hence compresses the refrigerant (Fig. 3.6e). The rotating impeller forces the fluid to flow toward the inlet vane. Pressure level is directly proportional to the impeller speed. In the following diffuser unit, fluid expands; hence, speed decreases at the same high-pressure level. Briefly, kinetic energy is converted into static energy such as conversion of high-speed low-pressure fluid into low-speed highpressure refrigerant. The centrifugal compressor is used for large-scale refrigerating systems such as commercial and industrial purposes (Gu_zda & Szmolke, 2015).

64

Low-Temperature Processing of Food Products

Figure 3.6 Diagrams of commonly used compressors in refrigeration systems; (a) reciprocating compressor (1-suction area, 2-working area, 3-pressure area, 4-piston); (b) rotary-vane compressor; (c) scroll compressor; (d) rotary-screw compressor (1-suction area, 2-rotors, 3pressure area) (Gu_zda & Szmolke, 2015), and (e) centrifugal (impeller) blade compressor (Shi & Xie, 2020).

3.4.2

Condensers

As explained in Section 3.1, the main function of the condenser is transferring the heat energy that refrigerator carries to a cooling medium such as air or water. When the heat energy is released, vaporized refrigerator condenses into the liquid form in the condenser chamber (Singh & Heldman, 2014). According to their working principal, condensers can be classified as water-cooled, air-cooled, and evaporative condensers

Elements of a low-temperature processing system

65

Figure 3.7 Diagrams of commonly used condensers in refrigeration systems; (a) and (b) are water cooled open shell and tube and double pipe condensers, respectively; (c) and (d) are air cooled plate and tube and fin condensers, respectively; (e) is the evaporative condenser (Singh & Heldman, 2014).

where both air and water are operated (Fig. 3.7). Water-cooled condensers are designed as open shell and tube form (Fig. 3.7a) or as double pipe (Fig. 3.7b); aircooled condensers are designed as plate (Fig. 3.7c) and tube and fin (Fig. 3.7d) condensers. •

•

•

•

Open shell and tube condenser: This type (Fig. 3.7a) is one of the simplest and low-cost condensers in which cooling water flows throughout the pipes, while the refrigerant is flowing counter-currently within the shell. Efficiency of heat transfer might be increased with assembling extra fins or pipes. Double-pipe condenser: Similar to shell and tube design, in the double-pipe condenser (Fig. 3.7b), cooling water and refrigerant flow counter-currently; however, both fluids are in different inner/outer concentric double pipes. Despite its higher energy efficiency and better cooling capacity than the shell and tube, it might induce some maintenance issues. Plate condenser: As an air cooling condenser, plate type (Fig. 3.7c) consists of a heat conductive plate and tube system merged into that plate. Refrigerant flows throughout the tube and dissipates its heat energy to the plate with conduction and afterward to the air with convection. Cooling efficiency is low, but using fans in order to create forced air convection might increase the heat transfer and efficiency. Tube and fin condenser: Similar to the plate condenser, this type also includes tube system but coupled with fins, which increase the surface area to induce higher heat energy transfer throughout the condenser surface. Tube and fin type (Fig. 3.7d) requires less surface area to dissipate heat rather than the plate condenser. Similar to the plate form, forced air convection by additional fans might be useful to increase heat transfer efficiency.

66

•

Low-Temperature Processing of Food Products

Evaporative condenser: Simultaneous works are done by both air and cooling system in evaporative condenser (Fig. 3.7e). Water is pumped and sprayed onto the coils, while air is sucked toward the same coils. Requiring latent heat energy to vaporize the sprayed water is supplied by the warm refrigerant (Berk, 2009b; Singh & Heldman, 2014).

3.4.3

Expansion valves

Expansion valves, and/or with their other name, throttles are a kind of regulators to control the flow rate of refrigerant at specific zones of cooling circuit and deliver the fluid to the evaporator. Diagrams of the most frequently used automatic types of valves in refrigerating systems are presented in Fig. 3.8, which are low-pressure float, high-pressure float, expansion, and thermostatic expansion valves. Except these variants, some other types such as pressostatic or electronic valves are also being used. •

•

Low-pressure float valve: The valve has a floating ball in the low-pressure side and is being used in flooded evaporators (Fig. 3.8a). Working principle is a simple mechanistic work; dropping of the ball in case of liquid boiling, letting the orifice to open, thus allowing more liquid with high pressure to flow inside the valve. High-pressure float valve: Contrary to low-pressure version, in this type, the float ball is immerged into the high-pressure zone (Fig. 3.8b). Refrigerant fluid (gas phase) is cooled and condensed into liquid phase and increases the liquid level and pushes the floating ball to rise and to open the orifice enables the high-pressure liquid for flowing into the evaporator.

Figure 3.8 Diagrams of commonly used expansion valves in refrigeration systems; (a) lowpressure float valve, (b) high-pressure float valve, (c) expansion valve, and (d) thermostatic expansion valve (Singh & Heldman, 2014).

Elements of a low-temperature processing system

•

•

67

Expansion valve: The automatic expansion valve keeps the pressure inside constant, hence enables to obtain constant fluid load and temperature. Inletting refrigerant induces the diaphragm to rise and increase the spring pressure which ends up with the closure of valve (Fig. 3.8c). The valve re-opens whenever the inner pressure decreases. Expansion valves are the most frequently used ones in household refrigerators. Thermostatic expansion valve: A thermostatic bulb (a sensor which detects the outlet superheated gas temperature also has a fluid core inside) is the main element of this expansion valve (Fig. 3.8d). When the core fluid has relatively high temperature than the refrigerant, pressure inside the bulb increases. This pressure is transmitted throughout the tube to the diaphragm and let the orifice to rise to allow fluid flow inside. Thermostatic expansion valve is the most widely used one for the large (industrial)-scale refrigerators (Berk, 2009b; Singh & Heldman, 2014).

3.4.4

Evaporator

Evaporators are the elements of refrigeration cycles where the cooling effect finally encounters with the system (Berk, 2009b). Basically, heat is eliminated from the targeted system to the outer environment directly passing over the evaporators either using a transferring medium (air/liquid) as it is in chilling process or with direct contact of a cooler surface as it is in freezing (Earle & Earle, 2004b). The design and geometry of an evaporator are dependent on the nature of the heat delivery. It might only be a jacket of a heat exchanger, finned-tube radiator with fans or just cold plates, varying from process to process (Berk, 2009b). However, all distinctive types of evaporators are mainly classified as air cooling, liquid cooling or plate evaporators. •

Air cooling evaporators: Finned pipe coils that are filled with refrigerants exposed to air aiming to lose heat with natural convection or forced convection, with additional installation of fan units to blow air over the coil and accelerates convectional heat transfer (Fig. 3.9). However, fan installation is only applicable for small cooling units not appropriate for large-scale air coolers. Aluminum fins/copper tubes/halocarbons or aluminum fins/stainless steelaluminum tubes/ammonia are the most favorable material pairs for fins/tubes/refrigerants (Earle & Earle, 2004b; Hundy et al., 2008a).

Figure 3.9 Diagram of air cooling evaporator in refrigeration systems (Deshmukh et al., 2017).

68

•

Low-Temperature Processing of Food Products

Liquid cooling evaporators: The tubes and coils are immersed into the liquid media in order to control and increase the efficiency of heat transfer rather than air cooling evaporators. Liquid cooling might be applied with either flooded systems or direct expansion (Fig. 3.10). As seen in Fig. 3.10a, flooded evaporators simply consist of a “shell-andtube” or “jacketed” designs, respectively. In shell-and-tube refrigerator, mainly the sample-to-be-cooled flows inside the tubes (pipes) and tubes are surrounded by the refrigerant fluid in the shell. Similar but simpler, in jacked evaporator, product flows through only in one tube, while an outer concentric tube filled with cooling refrigerant surrounds

Figure 3.10 Diagrams of commonly used liquid cooling evaporator designs in refrigeration systems; (a) flooded shell and tube cross-sectional, (b) flooded jacketed evaporators crosssectional, (c) entire shell and tube evaporator, (d) shell and coil evaporator with cross-sectional sketch, and (e) plate heat exchanger (Alfa Laval) (Hundy et al., 2008a).

Elements of a low-temperature processing system

69

Figure 3.11 Diagram and image of plate evaporator for freezing ((Singh & Heldman, 2014), Pacific West Ref.).

•

the inner tube and targets to cool the sample down. Fig. 3.10b represents an arrangement of simple flooded evaporator diagram, as an actual scaled evaporation system. With a slight modification, installation of an open tank for refrigerant circuit enables expansion and suction activities for refrigerant, which increases the cooling rate and efficiency (Fig. 3.10c). In order to maintain a continuous and constant velocity for fluid flow within the evaporator, a direct expansion unit addition is added to the system and estimated design is presented in Fig. 3.10d. As an example for the most frequent evaporator recently in the industry, a plate heat exchanger evaporator is presented in Fig. 3.10e. Designing the evaporation in assistance with heat exchanger, multiple-plate, countercurrent flow directions of fluids in the herringbone corrugated directions on the plates are all the elements to increase heat transfer efficiency (Berk, 2009b; Earle & Earle, 2004b; Hundy et al., 2008a). Plate evaporators: Plate-type evaporators are mostly used for freezing due to their allowance for direct surface contact of sample and freezing plate. This evaporator is useful particularly for freezing the packaged foods (organic materials) in planar geometries. Plate evaporators consist of welding tubular coils with plate metal or extruded aluminum together (Fig. 3.11). Refrigerant fluid circulates throughout the welded tubes, and heat is easily transferred with conduction due to the high heat transfer capability of used surface materials. Plates might be arranged either horizontal or vertical (Hundy et al., 2008a; Singh & Heldman, 2014).

3.4.5

Other assistive elements

In addition to the four main elements of refrigeration systems explained so far, many other assistive and control elements are extensively being used in chilling/freezing equipments. The assistive elements might be installed with different purposes such as controlling the process, increasing the cooling efficiency, decreasing the process time, improving the final product quality, and avoiding errors and/or automatization. Some of the most crucial and widely used low processing assistive elements might be listed as pumps, thermostats, humidifiers, pressure switches, pressure regulatory valves, filter/driers, suction accumulators, strainers, and charging connections (Hundy et al., 2008b). Most of the assistive elements are not permanent for many types of refrigerators since their requirements change together with the technological

70

Low-Temperature Processing of Food Products

improvements. The list of assistive elements is variable and low energy consumption and energy efficiency improvement are some of the main factors for them to be used in most of the systems.

3.5

Refrigerants

Theoretically, a vast amount of fluids was considered to be used as a refrigerant with the purpose of low-temperature processing in the past. However, the number of refrigerants that might be actually used is limited in the light of recently realized scientific facts and environmental conditions. For instance, ammonia was one of the first refrigerant that was commonly used for its spectacular mechanical properties but is no longer being used due to its high potential for toxicity, irritability, and flammability despite having the highest coefficient of performance compared to many other commercial refrigerant (Baakeem et al., 2018). The properties for an ideal refrigerant might be specified as having high latent heat and vapor density, operable at moderate positive pressure, being environmental friendly and cost-effective besides no toxicity, irritability, flammability, and corrosivity (Ciconkov, 2018). Choosing the most convenient refrigerant for all kinds of low-temperature processing equipment such as air conditioners, dehumidifiers, and/or refrigerators is of great importance since their vaporized forms are highly detrimental for both global warming and ozone layer in a case of uncontrolled leakage. Furthermore, engineering, design, production quality, and periodic maintenance of low-temperature processing equipment are other crucial points. Refrigerants are symbolized with codes starting with “R” and followed by the number of fluorine atoms, then the number of hydrogen atoms (þ1), and number of carbon atoms (1). For instance, difluorochloromethane (CHClF2) is coded as R-22 while tetrafluoroethane (C2H2F4) is represented as R-134 (Berk, 2009b). Instead of ammonia, chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) are being used but revealing of the ozone layer depleting potential due to high chemical stability of halogenated hydrocarbons CFSs and HCFCs, their production and usage as refrigerants were limited even so they (particularly their pure forms) will be banned gradually to be used for manufacturing refrigerating equipment by the UN authorities by 2020 (Abas et al., 2018). Usage of more environmental friendly refrigerants such as HFCs is being promoted, and scientific studies are being conducted to develop relatively better refrigerant alternatives. On the other hand, specified mixtures of pentafluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, difluoromethane, ammonia, and propane are also being used, which have commercial codes as R404A and R407c (James & James, 2014). Recently developed alternative refrigerants such as hydrofluoroolefin and their mixtures with HFC or R744 are of interest aiming to propose a better alternative for R134a, R404A, and R410A (HerediaAricapa et al., 2020; Nair, 2021). As another outstanding development, addition of nanomaterials in the form of nano-refrigerants and nano-lubricants into the cooling/ heating fluids aims to improve the thermodynamic and mechanical properties of the fluid efficiently, avoiding many undesirable concerns, particularly, ozone layer depleting potential (Yang et al., 2020).

Elements of a low-temperature processing system

3.6

71

Chilling and freezing systems

Depending on some deterministic issues such as product properties, desired degree of freezing or cooling, capital investment for cooling units, process requirements, scale/ capacity of processing, and/or other financial issues, various methods and processing chambers are being used for chilling or freezing. Widely used chilling and freezing systems might be classified as air systems, contact systems, immersion/spraying systems, scraped surface, and high-pressure freezing systems (James & James, 2014). Due to food safety concerns, chilling and freezing processes are applied as in-packed or incontainer, to avoid any possible contamination, but it should be noted that the presence of these packaging materials acts as a natural barrier, decreases the rate of heat transfer, and retards the completion of the process. While designing any packaging or container for foods, which are planned to be refrigerated, heat transfer coefficient and dimensions of chosen material should be considered in detail. •

•

•

•

Air systems: Air refrigerating is the most widely used cooling/freezing system for both household and industrial scales due to their flexible designs, ease of use, and being an economical operation. The diversity of air systems according to usage area changes in a range from simple cooling with a fan to more complex designs of tubes, tunnels, plates, and heat exchangers. The capacity of air systems also varies from a small cooling cabin (like mini-bar fridges) to large cooling units with continuous conveyor systems in the industry. Speed of cooling air is the most critical parameter to control, which should be in a specific range. Low air flow retards cooling, which is quite risky in terms of product quality, microbial safety, and process feasibility. Fast air flow might dry out the product surface and avoids heat transfer besides leading excessive energy consumption. Despite being the most economic and easy to use system, energy efficiency and rate of heat transfer are significantly lower when compared with other methods (Berk, 2009b; Jessen et al., 2013). Contact systems: Refrigerating the products via direct contact with a cooling surface is run by conductive heat transfer. Contact metal surfaces with high heat conduction capacities are widely used in plate coolers, jacketed heat exchangers, or falling film systems mainly by meat industry (Jessen et al., 2013). The critical points requiring to be considered are thickness and heat conductivity of the product besides contamination risks due to direct surface contact. A shield layer or packaging material applications are serious precautions to avoid cross-contamination; otherwise, residual accumulation on the surface of cooling plate might cause fouling, hence loss of energy. Immersion/spraying systems: Basically, immersing the desired product into a cooling liquid/ media or spraying a cooling fluid toward the product surface is some of the simple but fast cooling systems. Ice or cryogenic fluids having low boiling point temperatures like liquid nitrogen, carbon dioxide, and Freon 12 are being used as immersion or spraying materials (Manay & Shadaksharaswamy, 2007). This method has advantages for irregular-shaped products to be frozen or chilled immediately. Similar to the contact systems, contamination of food material is a serious risk; hence, precautions are required. Vacuum (evaporative) cooling: In order to chill the products that have a high surface to volume ratio, vacuum cooling is one of the most feasible technique to be used. During the vacuuming process, a simultaneous evaporation occurs, and approximately, 1% water is evaporated for every 5
C temperature reduction. Leafy vegetables are particularly appropriate to be cooled with evaporative approach, but it is also suitable to cool down the hot baked or cooked foods (Jessen et al., 2013).

72

•

•

Low-Temperature Processing of Food Products

Scraped surface freezers: Cylindrical surfaces are designed to freeze liquid samples whether contacting the food with their outer or inner surfaces. When the first layer of liquid contacts with the freezing cylindrical surface, it freezes rapidly and then scraped from the surface immediately for another layer of (mass) unfrozen liquid sample. It is a fast and continuous freezing system and mostly used for ice-cream production in the industry (Ciobanu, 1976). High-pressure freezers: Pressure shifting freezing is a relatively recent approach for refrigerating of foods. It aims a very fast freezing under high pressure to decrease the temperature below zero and maintains until complete freezing without pressure releasing. Fast nucleation of ice crystals all over the product and homogenous freezing of the sample are considered to protect sample’s initial quality (Otero & Sanz, 2012). This method is not as convenient as to be used widely like other techniques.

3.7

Conclusion

Low-temperature processing as a crucial unit operation is widely used by the food industry as well as by individuals in household purposes for vast amount of food products. Refrigerating is not only an essential step for microbial safety but also might be an important processing tool during food production. Despite distinctive designs of refrigeration chambers that are specific for various food samples/raw materials and processing method, the main mechanical elements and their working principles are in common. Depending on the technological developments, designing more efficient and environmental friendly low-temperature processing units with high efficiencies is in continuous progress with the support of scientists and refrigerator manufacturers. Brand-new designs with novel materials are used, and energy efficient and feasible low-temperature processing units are being developed. The lowest possible energy consumption and carbon footprint, use of unhazardous chemicals as refrigerants, safe and easy system designs, and prevention of the quality of the processed product are the common key points for all types of low-temperature processing systems that might diversify in a broad range of areas.

References Abas, N., et al. (2018). Natural and synthetic refrigerants, global warming: A review. Renewable and Sustainable Energy Reviews, 90, 557e569. https://www.sciencedirect.com/science/ article/pii/S1364032118301977. Anand, B., & Murugavelh, S. (2020). Performance analysis of a novel augmented desalination and cooling system using modified vapor compression refrigeration integrated with humidification-dehumidification desalination. Journal of Cleaner Production, 255, 120224. https://www.sciencedirect.com/science/article/pii/S0959652620302717. Arjun, K. G. B., Pruthviraj, B. G., Chethan, K. Y. K., & Rashmi, P. (2017). Design and implementation of peltier based solar powered portable refrigeration unit. In 2017 2nd IEEE international conference on Recent Trends in Electronics, Information & Communication Technology (RTEICT) (pp. 1971e1974).

Elements of a low-temperature processing system

73

Baakeem, S. S., Orfi, J., & Alabdulkarem, A. (2018). Optimization of a multistage vaporcompression refrigeration system for various refrigerants. Applied Thermal Engineering, 136, 84e96. https://www.sciencedirect.com/science/article/pii/S1359431117367947. Becker, B. R., & Fricke, B. A. (2003). Freezing | principles. In B. Caballero (Ed.), Encyclopedia of food sciences and nutrition (2nd ed., pp. 2706e2711). Oxford: Academic Press https:// www.sciencedirect.com/science/article/pii/B012227055X005216. Bellos, E., & Tzivanidis, C. (2019). Enhancing the performance of a CO2 refrigeration system with the use of an absorption chiller. International Journal of Refrigeration, 108, 37e52. https://www.sciencedirect.com/science/article/pii/S0140700719303949. Berk, Z. (2009a). Chapter 19: Refrigeration, chilling and freezing. In Z. Berk (Ed.), Food process engineering and technologyFood science and technology (pp. 391e411). San Diego: Academic Press. https://www.sciencedirect.com/science/article/pii/B9780123736 604000193. Berk, Z. (2009b). Chapter 20: Refrigeration, equipment and methods. In Z. Berk (Ed.), Food process engineering and technologyFood science and technology (pp. 413e428). San Diego: Academic Press. https://www.sciencedirect.com/science/article/pii/B978012373 660400020X. Berk, Z. (2009c). Chapter 3: Heat and mass transfer, basic principles. In Z. Berk (Ed.), Food process engineering and technologyFood science and technology (pp. 69e113). San Diego: Academic Press. https://www.sciencedirect.com/science/article/pii/B9780123736 60400003X. Blikra, M. J., Skipnes, D., & Feyissa, A. H. (2019). Model for heat and mass transport during cooking of cod loin in a convection oven. Food Control, 102, 29e37. https://www. sciencedirect.com/science/article/pii/S0956713519301008.  Butrymowicz, D., Baj, P., & Smierciew, K. (2014). Cooling technique. Warszawa: PWN. Chen, Q., Ja, M. K., Li, Y., & Chua, K. J. (2019). Energy, exergy and economic analysis of a hybrid spray-assisted low-temperature desalination/thermal vapor compression system. Energy, 166, 871e885. https://www.sciencedirect.com/science/article/pii/S0360544218 321510. Christopher, S. S., et al. (2021). Optimization of a solar water heating system for vaporabsorption refrigeration system. Environmental Progress and Sustainable Energy, 40, Article e13498. Ciconkov, R. (2018). Refrigerants: There is still no vision for sustainable solutions. International Journal of Refrigeration, 86, 441e448. https://www.sciencedirect.com/science/ article/pii/S0140700717305066. Ciobanu, A. (1976). Freezing. In A. Ciobanu, G. Lascu, V. Bercescu, & L. Niculescu (Eds.), Cooling technology in the food industry (pp. 139e222). Tunbridge Wells: Abacus Press. Deshmukh, S. B. M., et al. (2017). An overview of the applications and performance characteristics of the thermoelectric devices. ARPN Journal of Engineering and Applied Sciences, 12(7), 2063e2071. Dosset, R. J., & Horan, T. J. (2001). Principles of refrigeration (5th ed.). New Jersey: Pretince Hall. Earle, R. L., & Earle, M. D. (2004a). Heat transfer theory. In Unit operations in food processing. New Zealand: The New Zealand Institute of Food Science & Technology (Inc.). Earle, R. L., & Earle, M. D. (2004b). Refrigeration, chilling and freezing. In Unit operations in food processing. New Zealand: The New Zealand Institute of Food Science & Technology (Inc.). Gazinski, B. (2014). Refrigernat compressors. In B. Gazinski (Ed.), Construction an application. Poznan: Systherm.

74

Low-Temperature Processing of Food Products

Gu_zda, A., & Szmolke, N. (2015). Compressors in heat pumps. Machine Dynamics Research, 39(2), 71e83. Heredia-Aricapa, Y., et al. (2020). Overview of low GWP mixtures for the replacement of HFC refrigerants: R134a, R404A and R410A. International Journal of Refrigeration, 111, 113e123. https://www.sciencedirect.com/science/article/pii/S0140700719304773. Hundy, G. F., Trott, A. R., & Welch, T. C. (2008a). Chapter 7: Evaporators. In G. F. Hundy, A. R. Trott, & T. C. Welch (Eds.), Refrigeration and air-conditioning (4th ed., pp. 91e102). Oxford: Butterworth-Heinemann https://www.sciencedirect.com/science/article/ pii/B9780750685191000074. Hundy, G. F., Trott, A. R., & Welch, T. C. (2008b). Chapter 9: Controls and other circuit components. In G. F. Hundy, A. R. Trott, & T. C. Welch (Eds.), Refrigeration and airconditioning (4th ed., pp. 115e130). Oxford: Butterworth-Heinemann https://www. sciencedirect.com/science/article/pii/B9780750685191000098. Jain, A., et al. (2019). Ice formation modes during flow freezing in a small cylindrical channel. International Journal of Heat and Mass Transfer, 128, 836e848. https://www. sciencedirect.com/science/article/pii/S0017931018320222. James, S. J., & James, C. (2014). Chilling and freezing of foods. In S. Clark, S. Jung, & B. Lamsal (Eds.), Food processing: Principles and applications, Wiley Online Books (pp. 79e105). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781118846315.ch5 Jani, D. B., Mishra, M., & Sahoo, P. K. (2018). A critical review on application of solar energy as renewable regeneration heat source in solid desiccant e vapor compression hybrid cooling system. Journal of Building Engineering, 18, 107e124. https://www.sciencedirect. com/science/article/pii/S2352710218301050. Jessen, F., Nielsen, J., & Larsen, E. (2013). Chilling and freezing of fish. In Seafood processing (pp. 33e59). Chichester, UK: John Wiley & Sons, Ltd. https://onlinelibrary.wiley.com/doi/ 10.1002/9781118346174.ch3. Kaale, L. D., Eikevik, T. M., Rustad, T., & Kolsaker, K. (2011). Superchilling of food: A review. Journal of Food Engineering, 107(2), 141e146. https://www.sciencedirect.com/science/ article/pii/S0260877411003050. Kerr, W. L. (2019). Chapter 14: Food drying and evaporation processing operations. In B. T. Myer (Ed.), Handbook of farm Kutz Dairy and food machinery engineering (3rd ed., pp. 353e387). Academic Press https://www.sciencedirect.com/science/article/pii/ B9780128148037000142. Manay, N. S., & Shadaksharaswamy, M. (2007). Foods: Facts and principles. New Delhi: New Age International. Mansuriya, K., Patel, V. K., Raja, B. D., & Mudgal, A. (2020). Assessment of liquid desiccant dehumidification aided vapor-compression refrigeration system based on thermo-economic approach. Applied Thermal Engineering, 164, 114542. https://www.sciencedirect.com/ science/article/pii/S1359431119324871. Mardini-Bovea, J., et al. (2019). A review to refrigeration with thermoelectric energy based on the Peltier effect. Dyna, 86, 9e18. http://www.scielo.org.co/scielo.php?script¼sci_ arttext&pid¼S0012-73532019000100009&nrm¼iso. Mehrpooya, M., Ghorbani, B., & Hosseini, S. S. (2018). Thermodynamic and economic evaluation of a novel concentrated solar power system integrated with absorption refrigeration and desalination cycles. Energy Conversion and Management, 175, 337e356. https:// www.sciencedirect.com/science/article/pii/S0196890418309749. Mota-Babiloni, A., et al. (2019). Experimental influence of an internal heat exchanger (IHX) using R513A and R134a in a vapor compression system. Applied Thermal Engineering, 147, 482e491. https://www.sciencedirect.com/science/article/pii/S1359431118328382.

Elements of a low-temperature processing system

75

Murray, B. J., et al. (2010). Kinetics of the homogeneous freezing of water. Physical Chemistry Chemical Physics, 12(35), 10380e10387. https://doi.org/10.1039/C003297B Nair, V. (2021). HFO refrigerants: A review of present status and future prospects. International Journal of Refrigeration, 122, 156e170. https://www.sciencedirect.com/science/article/ pii/S014070072030459X. Nakkaew, S., et al. (2019). Application of the heat pipe to enhance the performance of the vapor compression refrigeration system. Case Studies in Thermal Engineering, 15, 100531. https://www.sciencedirect.com/science/article/pii/S2214157X19302540. Nikbakhti, R., Wang, X., & Chan, A. (2020). Performance analysis of an integrated adsorption and absorption refrigeration system. International Journal of Refrigeration, 117, 269e283. https://www.sciencedirect.com/science/article/pii/S0140700720301663. Otero, L., & Sanz, P. D. (2012). High-pressure shift freezing. In D. W. Sun (Ed.), Handbook of frozen food processing and packaging (pp. 667e683). Boca Raton, FL: CRC Press, Taylor & Francis Group. Patel, B., et al. (2017). Thermo-economic analysis of a novel organic Rankine cycle integrated cascaded vapor compressioneabsorption system. Journal of Cleaner Production, 154, 26e40. https://www.sciencedirect.com/science/article/pii/S0959652617306911. de Paula, C. H., et al. (2020). Optimal design and environmental, energy and exergy analysis of a vapor compression refrigeration system using R290, R1234yf, and R744 as alternatives to replace R134a. International Journal of Refrigeration, 113, 10e20. https://www. sciencedirect.com/science/article/pii/S0140700720300268. Qasem, N. A. A., et al. (2020). Novel and efficient integration of a humidificationdehumidification desalination system with an absorption refrigeration system. Applied Energy, 263, 114659. https://www.sciencedirect.com/science/article/pii/S0306261920 301719. Razmi, A. R., Arabkoohsar, A., & Nami, H. (2020). Thermoeconomic analysis and multiobjective optimization of a novel hybrid absorption/recompression refrigeration system. Energy, 210, 118559. https://www.sciencedirect.com/science/article/pii/S036054422 0316674. Razmi, A., Soltani, M., Kashkooli, F. M., & Farshi, L. G. (2018). Energy and exergy analysis of an environmentally-friendly hybrid absorption/recompression refrigeration system. Energy Conversion and Management, 164, 59e69. https://www.sciencedirect.com/science/article/ pii/S0196890418302012. Rubik, M. (2006). Heat pumps. In Guide, Osrodek Informacji. Warszawa, Poland: Technika instalacyjna w budownictwie. Salilih, E. M., & Birhane, Y. T. (2019). Modelling and performance analysis of directly coupled vapor compression solar refrigeration system. Solar Energy, 190, 228e238. https://www. sciencedirect.com/science/article/pii/S0038092X1930787X. Senturk, A. M., Erbas, O., & Arslan, O. (2019). The performance of vapor compression cooling system aided Ranque-Hilsch vortex tube. Thermal Science, 23(2 Part B), 1189e1201. Sharifi, S., et al. (2020). Comprehensive thermodynamic and operational optimization of a solarassisted LiBr/water absorption refrigeration system. Energy Reports, 6, 2309e2323. https://www.sciencedirect.com/science/article/pii/S2352484720312634. Shi, D., & Xie, Y. (2020). Aerodynamic optimization design of a 150 KW high performance supercritical carbon dioxide centrifugal compressor without a high speed requirement. Applied Sciences, 10(6), 2093. https://www.mdpi.com/2076-3417/10/6/2093.

76

Low-Temperature Processing of Food Products

Singh, R. P., & Heldman, D. R. (2014). Chapter 6: Refrigeration. In R. P. Singh, & D. R. Heldman (Eds.) (5th ed.,Introduction to food engineeringFood science and technology (pp. 475e520). San Diego: Academic Press https://www.sciencedirect.com/ science/article/pii/B9780123985309000061. Song, M., et al. (2020). Proposal and parametric study of solar absorption/dual compression hybrid refrigeration system for temperature and humidity Independent control application. Energy Conversion and Management, 220, 113107. https://www.sciencedirect.com/ science/article/pii/S0196890420306518. Souza, R. J., et al. (2020). Proposal and 3E (energy, exergy, and exergoeconomic) assessment of a cogeneration system using an organic Rankine cycle and an Absorption Refrigeration System in the Northeast Brazil: Thermodynamic investigation of a facility case study. Energy Conversion and Management, 217, 113002. https://www.sciencedirect.com/ science/article/pii/S019689042030546X. Sukumar, S., & Kar, S. P. (2019). A combined conductioneradiation model for analyzing the role of radiation on freezing of a biological tissue. Journal of Thermal Science and Engineering Applications, 12(1). https://doi.org/10.1115/1.4044428 Yang, L., et al. (2020). A review of heating/cooling processes using nanomaterials suspended in refrigerants and lubricants. International Journal of Heat and Mass Transfer, 153, 119611. https://www.sciencedirect.com/science/article/pii/S0017931019356959. Zhao, Y., & Takhar, P. S. (2017). Freezing of foods: Mathematical and experimental aspects. Food Engineering Reviews, 9(1), 1e12. Zhu, Z., Tian, L., & Sun, D.-W. (2020). Pressure-related cooling and freezing techniques for the food industry: Fundamentals and applications. Critical Reviews in Food Science and Nutrition, 1e16. https://doi.org/10.1080/10408398.2020.1841729

Section Two Different types of cooling and freezing systems

This page intentionally left blank

Refrigerated rooms and industrial systems for quick chilling and freezing

4

Chinglen Leishangthem 1 , Charis K. Ripnar 2 , Ribhahun Khonglah 2 , Macdonald Ropmay 2 , Tanya Luva Swer 3 and P. Mariadon Shanlang Pathaw 4 1 National Institute of Technology, Rourkela, Odisha, India; 2Food Processing, Govt. of Meghalaya, Shillong, Meghalaya, India; 3National Institute of Food Technology Entrepreneurship and Management (NIFTEM), Sonipat, Haryana, India; 4North East Centre for Technology Application and Reach, Shillong, Meghalaya, India

4.1

Introduction

Refrigeration is the process of removing heat from an area or a substance, which impedes the biological/chemical processes, degradation, and quality loss of food products (Love & Klee, 2015). A refrigerated room, also known as cold storage, is an insulated enclosed room maintained at the desired temperature for storing food products. Generally, the temperature inside the cold storage is held in the range of
40 to 20 C based on the types of food products. Cold storage where the temperature inside is above 1 C is called a chiller, and a temperature below 0 C is called a freezer. The components of the cold storage unit are an evaporator, condenser, expansion valve, pressure transmitter, and temperature sensor. There is an energy gap between energy production and energy utilized. Cold storage is worked on 24-h, weekly, and seasonal cycles. The cold storage unit has three main parts: chiller, load, and storage tank (Fig. 4.1).

Figure 4.1 Schematic of cold storage systems. Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00014-X Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

80

4.2

Low-Temperature Processing of Food Products

Present scenario of cold storage in India and global

India is a fast-growing economy and one of the largest producers of agricultural produce. As reported by the United Nations Food and Agriculture Organization (FAO), India is the second-largest producer of fruits and vegetables after China in the year 2019 (Food and Agriculture Organization of the United Nations and Nations, 2019). Based on the National Horticulture Database of 2019e20, it was found that the fruit and vegetable production of India amounts to 99.07 million MT and 191.77 million MT, respectively. However, the main issue is not the production but rather it is storing of fresh agricultural produce in cold storage. One of the most essential functions of cold storage is to keep the freshness and quality of perishable food intact (Bhat et al., 2020). There are different types of cold storage like bulk storage, multipurpose storage, frozen storage, and mini-storage, etc., which will be discussed later in the chapter. As per the Global Cold Chain Allowance Report, the capacity of the cold storage warehouse globally is about 719 million cubic meters. The cold storage capacity of India is about 150 million cubic meters, as per the All India Cold-chain Infrastructure Capacity (Vijjapu et al., 2019). But even with the cold storage system, perishable food product wastage is increasing yearly. About 40% is wasted due to improper management or nonavailability of the cold storage system in certain areas. The functioning of the cold storage system is affected due to improper handling of the perishable products, lacking standards and protocols, recordkeeping, traceability of the products in-store, unskilled workers and documentation work, etc.

4.3

Certain measures for the proper functioning of cold storage

Due to the ever demand for food supplies, the production of perishable commodities such as fruit and vegetables continues to rise (Gru
zauskas et al., 2019). To preserve these types of products, they need to be placed in cold storage facilities to ensure they do not rot. Cold rooms are of utmost importance because they not only help in extending the shelf life of fresh foods but also reduce food wastage as well as help the growers in selling their produce in the market at the most suitable time. There are many advantages of using cold storage; this includes prolonged product life, cost savings, customizable temperature settings, more storage space, etc. However, in order to derive such benefits, there are certain measures that need to be considered for the proper functioning of the cold storage system. Extreme cold damage is a significant cause for concern in any cold storage system. However, a cold storage system requires constant low temperatures to keep the other temperature-sensitive materials safe for human consumption. Therefore, it is crucial to manage cold storage in order to maintain low temperatures, food products’ viability for consumption, equipment’s efficacy, and workers’ health. Following are some of the practices that can be employed for the proper functioning of cold storage units.

Refrigerated rooms and industrial systems for quick chilling and freezing

81

⁃ Maintain temperature ranges: In a warehouse, multiple products are kept in storage at once, often at vastly different temperatures. Therefore, the cold storage unit’s temperature must be kept consistent throughout its various sections. Creating a partition between the temperature zones is one solution to the problem of storing items that require different temperatures in the same cold storage unit. A modular insulated curtain wall system that can be installed and relocated as needed is one risk-free and adaptable choice (Fig. 4.1). ⁃ Minimize heat loss: This is essential not just for reducing energy consumption but also for preventing the perishability of the items stored in the cold storage facility. The shift of heat from high-temperature areas to low-temperature areas must be kept to a minimal. This can be a little bit challenging because new commodities are regularly entering the cold storage; hence, the cold storage needs to be routinely reconfigured. Utilizing high-speed or quick doors and strip doors, which aid in the effective containment of cold air, is one approach that can be taken to alleviate some of the difficulties brought on by this issue. ⁃ Using suitable equipment: In a cold storage warehouse, several pieces of equipment and gear, such as computers, forklifts, barcode scanners, sensors, pallet jacks, and so on, are utilized for performing various functions, such equipment should be designed or modified according to the low temperatures that they are supposed to operate in. Electrical equipment like scanners can have their lifespan shortened by condensation that occurs when the instrument is moved from one temperature zone into another. Additionally, prolonged exposure to low temperatures has a negative impact on the lifespan of batteries, reducing the battery lifespan by between 40% and 50%. As a result, the usage of batteries with a greater voltage is required in order to lengthen their life cycle. ⁃ Ensure employees’ safety: A necessary step for the smooth functioning of cold storage is to ensure the safety of employees. They need to be provided with insulated coats, pants, gloves, and other safety gear. Employees in a cold storage warehouse should also receive training to familiarize themselves with the cold working conditions; this can help reduce the potential for health concerns and also guarantee that the employees do not impair the effectiveness of the cold storage system’s operation. ⁃ Manage energy demand: Due to the high cost of cooling air compared to heating it, energy efficiency is of paramount importance in cold storage facilities. In a cold storage facility, energy consumption can be reduced by both building design and the selection of automation systems that can minimize energy consumption in a cold storage unit and through the management of demand. ⁃ Maintain proper records: Products kept in cold storage are vulnerable to fluctuations in ambient temperature. Therefore, maintaining a precise and up-to-date record of the specifics of the products’ temperatures is an essential cold storage practice. One of the finest practices in cold storage management is to keep precise temperature records for all items stored there.

4.4

Refrigerated rooms

A refrigerated room or cold storage is a warehouse with an artificially generated specific temperature. Foods that are highly perishable are usually stored in bulk in a cold storage system prior to production, marketing, and processing. By maintaining a consistent temperature and level of humidity within the storage system, it ensures that perishable goods will remain in a clean and wholesome state for a greater amount of time. The temperature should be maintained sufficiently low to avoid any chilling

82

Low-Temperature Processing of Food Products

injury to the commodities. For most of the fresh commodities, the relative humidity in a cold store is required to be kept in the range of 80%e90% because a relative humidity below (or) above this range can affect the quality of the commodity (Krishnakumar & Dayanandhakumar, 2002). Most perishable foods (fruits and vegetables) have a short window of viability when stored at room temperature. Effective cooling of the produce post harvest helps in removing field heat rapidly, and this leads to longer storage periods. Carrying post harvest cooling in the appropriate manner can. ⁃ ⁃ ⁃ ⁃

Bring down the respiratory activity caused by enzymes; Reduce shriveling caused by water loss; Inhibit microbial growth; Reduce the release of ethylene.

Apart from maintaining the keeping quality, postharvest cooling provides flexibility to the grower by giving him/her the option to market his/her produce at any time most profitable time to him/her. Cold storage can be modified with the addition of carbon dioxide, sulfur dioxide, etc., according to the nature of commodity to be preserved. There is a noticeable advancement in the cold storage of perishable products in recent years, which has led to better maintenance of organoleptic qualities, longer shelf lives, and reduced spoilage (Krishnakumar & Dayanandhakumar, 2002).

4.4.1

Types of cold storage

Every fresh commodity has unique requirements and cold storage techniques in order to stay fresh for longer duration of time and at minimum cost consumption with negligible product loss (Ishann, 2021). Cold storage can be classified into the following categories. B Bulk cold storage: This is used for seasonal single fresh products. Potatoes, chilies, apples, and other foods are some of the things that can be stored in it. In this kind of storage system, the cold energy is stored in an insulated tank in the form of ice, which is extracted as chilled water for cooling the produce during the summer months. This helps in reducing the chiller running time, which in turn lowers the electricity consumption to a minimum and also reduces greenhouse gas emissions significantly. B Multipurpose cold storage: This is used for storing different commodities, which are required throughout the year, which include varied meat like chicken or lamb. Multipurpose cold storage is usually located near consumption centers. B Small cold storage: These have precooling facilities and food products such as fresh fruits like grapes, apple, etc. are stored. Small-scale producers can choose from various options ranging from mechanical refrigeration electric-based and passive evaporative cooling. The selection should be based on the cost, efficacy, and safety of the precooling system for the product to be cooled. B Frozen food cold storage: This type of cold storage is designed with processing and freezing facilities. The advantages of freeze preservation are convenience and protection, and it has negligible impact on food quality compared to other techniques, such as drying. The storage

Refrigerated rooms and industrial systems for quick chilling and freezing

83

temperature of every product has its unique temperature; however, a temperature range of 0 to
40 C is used for storing frozen foods. B Walk-in cold storage: Cold storage of these types is usually located at distribution centers and has a temperature range of
18 to
22 C. Walk-in cold storage is designed for storing consumables for months. B Controlled atmosphere (CA) cold storage: In this cold storage system, highly perishable fruit and vegetables are stored under controlled environmental conditions that will increase their shelf life. This cold storage process is a nonchemical technology in which oxygen levels are reduced and increased carbon dioxide levels in the storage atmosphere and refrigeration. This storage system sometimes also involves the addition of carbon monoxide and ethylene removal. The capital to operate and maintain is more. Therefore, it is more appropriate for long-term storage of fresh food like kiwis, apples, and pears. It also has an excellent potential to preserve fruits and vegetables with a high respiration rate.

4.4.2

Types of load and product load

The total amount of heat produced from various products and equipment in the cold storage space, which is required to be removed by cooling either by means of air conditioning or refrigeration in order to attain the desired temperature in the cold store, is called the cooling load. It is necessary to make an estimate of the cooling load in order to calculate the size of the equipment. The summation of heat from different sources in the cold storage will give us the cooling load. Some of the heat sources in the cold storage are mentioned below. ⁃ Heat leaks (from outside into cold storage) occur through the process of conduction. ⁃ Heat that leaks into the cold storage through any transparent material such as glass. ⁃ Heat that leaks into the cold storage when the doors or windows of the cold store are open or through any cracks. ⁃ Heat that leaks into the cold storage when the doors or windows of the cold store are open or through any cracks. ⁃ Heat that is produced by the products stored in the cold store. ⁃ Heat released by the employees or people working in the cold store. ⁃ Heat released by any equipment fixed or used inside the cold store. These can be any electronic equipment or material handling machines.

There are four types of cooling loads, which are described below. ⁃ ⁃ ⁃ ⁃

Wall gain load Product load Air change load Miscellaneous load

Wall gain load: Also known as wall leakage load, it measures the rate of heat flow conducted from the outside to the inside through the wall of the cold storage. The amount of heat conducted through the floor, ceiling, and walls of the cold store depends on variables such as insulation material, insulation thickness, the difference between storage space temperature, and ambient temperature. The quantity of heat that must be extracted from the products stored in a cold storage in order to bring the products

84

Low-Temperature Processing of Food Products

down to the desired temperature is referred to as the product load. Latent heat is removed when a product is frozen, becomes a part of the product load, and has to be calculated (Kumpavat & Sutar, 2019). Fresh fruits and vegetables have high moisture content; this water changes to the ice below the freezing point and remains in liquid form above the freezing point. The specific heat of a product is defined as the British thermal units (BTUs) needed to raise the temperature of one pound of the substance by 1 F. The heat to be removed from a product to reduce its temperature above freezing may be calculated as follow (Eq. 4.1): Q ¼ W  c  (T1
T2)

(4.1)

where, Q is the number of BTUs to be removed, W is the weight of the product in pounds, c is the specific heat above freezing, T1 is the initial temperature ( C), and T2 is the final temperature ( C) (freezing or above). Air change load (Eq. 4.2): When the warm external air leaks inside the refrigerated space owing to the opening of the storage door, it replaces the colder and denser air, which is lost through the opening. The quantity of heat that must be removed from the warm air that is present outside in order for the cold store to achieve the necessary temperature and humidity levels is referred to as the air change load. This heat removal process is considered to be part of the cooling load. Air change load, Qair ¼ m (hout
hin)

(4.2)

where, m is mass of air entering, kg/h, hout is enthalpy of outside air, kJ/kg dry air, and hin is enthalpy of inside air, kJ/kg dry air. Even when kept in a cold storage system, fruits and vegetables will continue to release heat through a process called respiration. This heat must be accounted for and taken into consideration when making storage decisions. This heat generated can be calculated as Eq. (4.3): Respiration load (Qr) ¼ (mass) mp (kg/h)  respiration rate (kJ/kg)

4.4.3

(4.3)

Structure and material

Refrigerated rooms are designed by five main components. I. A compressor compressing the refrigerant gas II. A condenser, in which the hot gas is cooled to a liquid III. An expansion valve, controlling the flow of the liquefied gas (where liquid gas expands to vapor) IV. Evaporator coils, where the liquid gas expands and boils (this process absorbs energy, cooling the coils) V. Fan(s), circulating the air over the cold evaporator coils, and thus cooling the cool room.

Air might also be circulate over pipes comprising some type of liquid antifreeze, which have themselves been cooled via the evaporator. Moreover, fan(s) circulate

Refrigerated rooms and industrial systems for quick chilling and freezing

85

air around the cool room to guarantee even distribution of the cold air and lower the temperature differences in the room. Freon and ammonia are the two most common and widely used refrigerants that can be found on the market today. The ammonia refrigerant is more cost-effective, readily available, and has a high latent heat of evaporation; nevertheless, it does have a few drawbacks due to the significant toxicity it exhibits in its natural state. It also has the ability to create an explosive mixture when mixed with oil, which has a high percentage of carbon. The different temperature chambers in a cold store must be separated by a type of insulation and should be moisture-proof. Whenever possible, the outside wall should be coated with a layer of foam glass that is vapor-proof. While coating the cold store with insulation, the following points are to be remembered. B The surface to be coated with the insulating material must be moisture-proof and smooth. B Enough care should be taken to make sure that the walls, ceiling, and floor are all moistureproof. B Also, the partition used for separating the different chambers in a cold store has to be coated with insulating material on both sides.

Prior to storage in the cold room, the fruits and vegetables are to be sorted in order to separate the good from the bad ones. The good product, which has been sorted out, is then arranged in separate wooden or plastic crates and then stacked in the cold store. Depending upon the type of product to be stored, the temperature and humidity must be calibrated accordingly.

4.4.4

Location and layout

Generally, the good practices in a cold storage facility usually include monitoring of temperature effectively, air circulation, control of relative humidity, and appropriate space between containers for sufficient ventilation and in order to prevent any incompatible commodity mixes. Care should be taken that only the products that can withstand the same temperature, ethylene level, and relative humidity should be kept together. Products that generate a significant quantity of ethylene, such as bananas and apples, have a tendency to set off a cascade of physiological responses in other ethylene-sensitive foods, such as lettuce, cucumbers, carrots, and other vegetables (Mahesh & Mahajan, 2018). This results in unpleasant color, flavor, and texture of the products. Some broad features of cold storage can be stated below. O O O O O

capacity, storage chambers number, cooling system, handling equipment, and accessibility.

Generally, only after deciding on the size of the cold store to be constructed, the site is chosen, but as a general rule of thumb, the chosen site should be away from direct sunlight contact. The land selected for the cold store must be massive enough to

86

Low-Temperature Processing of Food Products

include not just the cold store but all its adjoining extensions such as parking areas and any future enlargement (Mahesh & Mahajan, 2018). The overall area needs to be between six and 10 times that of the surface being covered. Despite the high surface: volume ratio, which affects heat loss, most cold storage facilities are built with only one story. However, there are many advantages of a singlestorey cold store, and these include lighter overall construction, pillar height can be increased, building on passive soils is possible, and transport inside the cold storage is easier. The use of forklifts inside the cold storage requires the building to have a high height, and this reduces the costs for construction for a particular total volume. Cold storage with towering height is vastly superior, with the only limitations being the stacking method and the resistance received from either the packaging material or the unpackaged products. The length and width of the cold rooms are determined by the quantity and method of merchandise handling (rails, forklifts), the number of chambers, and the dimensions of the most fundamental handling elements. A cold storage design that includes chambers of larger size though lesser in number is more economical because in such a design, certain unnecessary divisional walls and doors could be eliminated. Designing cold storage with large chambers makes it easier to control the temperature as well as relative humidity with better use of storage space. There are several parameters that need to be understood while designing cold storage. B Total volume is the entire space occupied in the cold storage. B Gross volume is the total volume where the commodities can be stored; this excludes the space not meant for storage. B Net volume refers to the space where the products are stacked; this excludes the space occupied by pillars, ducts, traffic passages, and coolers within the chambers which are part of the gross volume. B Storage density, which is the net volume and expressed in kg/m3, is also referred to as the gross volume.

In order to find out how economically the cold store has been designed, one has to divide the gross volume by the total volume; the result must be in the range of 0.50e0.80. Also, one should note that the gross volume should be about 50% greater than the net volume, and the gross area should be about 25% greater than the net area (Krishnakumar & Dayanandhakumar, 2002). The ratio of the quantity of produce that is stored in the cold storage at any given point of time to the quantity that can actually be stored will give us the extent up to which the cold storage system can be occupied. For better temperature management, the shape of the cold store should be a square over a rectangle. The reason is that a rectangular building tends to have a larger wall surface area but smaller storage space; this greater wall area allows for more heat to be conducted, hence the cost of operation. For better temperature control and costeffective operations, it is more advisable to construct a cold store under a shaded area; additionally, building walls must be painted white or sliver to reflect back excessive sun rays, and a sprinkler system can also be kept in place on the building roof for the purpose of evaporative cooling. Ventilation systems, as well as the use of gas absorbers like activated charcoal and potassium permanganate, can effectively change the air composition in the cold store.

Refrigerated rooms and industrial systems for quick chilling and freezing

4.5

87

Thermal bridges

Thermal bridging is the movement of heat across an object that is more conductive than the materials around it. The conductive material creates a path of least resistance to heat. It is also known as a cold bridge as it leads to the reduction of thermal resistance of objects. Therefore, it is crucial to consider the thermal bridges for energy consumption. Thermal bridges are the main concern and challenging thing. They reduce the thermal resistance of the storage building, leading to a rise in transmission load, which puts thermal insulation at risk (Al-Sanea & Zedan, 2012). The factor that affects cold storage due to thermal bridges is listed below. • • •

•

Conductive materialdThermally conductive material seeps through the insulating material by making it less resistant to heat transfer. Structural elementdStructural elements most often cause thermal bridges. They transfer the heat load from the building envelope to the building superstructure. Indoor air temperature, thermal fluxes, and surface temperature: According to Zedan et al. (2016), the thermal bridge incidence factor has been determined using the average indoor air temperature, the surface temperature, and the thermal variations of the entire building envelope. Indoor air temperature rises during the active hours of the ceiling. Consequently, the air becomes lighter and ascends to the top of the domes escaping from the small openings at the top. Land surface temperature is usually controlled by the surface energy balance, atmospheric state, and thermal properties of the surface, influencing the thermal bridge (Awuh et al., 2018). Mortar joints: Mortar joints cause thermal bridges in the outer wall of the building. Thermal bridges facilitate heat transmission across the building envelope and typically lead to increased heating and cooling loads in structures (Zedan et al., 2016).

4.6

Conclusion

Refrigeration has contributed so much help to the industries and the people utilizing the equipment in the household area, industries, etc. It makes it convenient for a person to receive the amount of ice products desired by them. However, it has been observed that when there are advantages, there also exist disadvantages. The cost of operating and initial investment in cold storage is high. Proper design of cold storage with excellent layout is a must for efficient use of cold storage. In designing cold storage, there is also a strong need for proper insulation with proper selection based on the surrounding environment. The ultimate aim of cold storage is to extend the shelf life of the food and store it for a longer time.

References Al-Sanea, S. A., & Zedan, M. (2012). Effect of thermal bridges on transmission loads and thermal resistance of building walls under dynamic conditions. Applied Energy, 98, 584e593. https://doi.org/10.1016/j.apenergy.2012.04.038

88

Low-Temperature Processing of Food Products

Awuh, M. E., Officha, M. C., Okolie, A. O., & Enete, I. C. (2018). A remote sensing analysis of the temporal and spatial changes of land surface temperature in Calabar Metropolis, Nigeria. Journal of Geographic Information System, 10(05), 562e572. https://doi.org/ 10.4236/jgis.2018.105030 Bhat, M. A., Wani, I. A., & Ashraf, S. (2020). Applications of nanomaterials in agriculture, food science, and medicine (1st ed.). IGI Global. Food and Agriculture Organization of the United Nations. (2019). Moving forward on food loss and waste reduction. The state of food and agriculture 2019. Rome: FAO. Gru
zauskas, V., Gim
zauskien_e, E., & Navickas, V. (2019). Forecasting accuracy influence on logistics clusters activities: The case of the food industry. Journal of Cleaner Production, 240, 118225. https://doi.org/10.1016/j.jclepro.2019.118225 Ishann. (August 18, 2021). 6 major types of cold storage. Logistics Brew. https://stockarea.io/ blogs/6-major-types-of-cold-storage/. Krishnakumar, T., & Dayanandakumar. (October, 2002). Design of cold storage for fruits and vegetables. Research Gate. https://www.researchgate.net/publication/316472114. Kumpavat, M. T., & Sutar, P. P. (2019). Drying and storage engineering. https://agrimoon.com/ drying-and-storage-engineering-icar-ecourse-pdf-book-free-download/. Love, A., & Klee, C. (April 13, 2015). Thermal bridging: Observed impacts and proposed improvement for common conditions | building research information knowledgebase. https://www.brikbase.org/content/thermal-bridging-observed-impacts-and-proposedimprovement-common-conditions. Mahesh, K., & Mahajan, B. V. C. (December 7, 2018). Design of cold storage for fruits and vegetables. Cooling India. https://www.coolingindia.in/design-of-cold-storage-for-fruitsvegetables/. Vijjapu, P., Kimothi, M. M., Roy, S., Mamatha, S., & Ray, S. S. (2019). Geospatial perspective for post-harvest infrastructure management: Positioning of new cold storage. ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XLII-3/W6, 339e344. https://doi.org/10.5194/isprs-archives-xlii-3-w6-339-2019 Zedan, M., Al-Sanea, S., Al-Mujahid, A., & Al-Suhaibani, Z. (2016). Effect of thermal bridges in insulated walls on air-conditioning loads using whole building energy analysis. Sustainability, 8(6), 560. https://doi.org/10.3390/su8060560

Still cooling in air and surface top icing

5

Mohammad Alipour Shotlou, Nader Pourmahmoud and Paria Sarvaree Mechanical Engineering Department, Urmia University, Urmia, Iran

5.1

Introduction of still cooling in air and surface top icing

Nowadays, food freezing has become one of the most important unit operations in food processing and preservation. Almost all food productsdraw, partially processed, and prepared foodsdcan be preserved by freezing. In the processed foods sector, the consumer preference for frozen food is even higher than that for dried and canned products. This is mainly visible in the meat, fruit, and vegetable sectors. Freezing gives added value to the product and gives a feeling of freshness to the products. In this chapter, we provide some general information about the proper cooling methods for food products, the danger zone while cooling food, and the factors that influence the cooling rate of food. Still air cooling and surface top icing are two of the most commonly used methods of preserving food in the food industry. These methods are widely used to maintain the quality and freshness of certain types of foods, especially perishable items such as fruits, vegetables, and seafood. Top icing and room cooling (with limited air movement) are slower and require longer cooling times. For a specific cooling system, the rate of cooling is determined by product temperature, cooling medium temperature, and the product to be cooled (Barbosa-Canovas et al., 2005).

5.2

Definition

In this part, we introduce exactly what is still air cooling and surface top icing and also their mechanisms. Then, we will compare these methods with others.

5.2.1

Still air cooling

Still air freezing is a common method used in the food industry to preserve food products. The process involves freezing food products in a freezer or cold storage room where there is no air movement. The mechanism of still air freezing is similar to that of natural freezing, where the heat from the food product is transferred to the surrounding environment, causing it to freeze. During the freezing process, the water molecules in the food product start to form ice crystals, which can cause damage to the

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00009-6 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

90

Low-Temperature Processing of Food Products

structure of the food. To minimize this damage, it is important to freeze the food product as quickly as possible. In still air freezing, the lack of air movement slows down the freezing process, which can lead to larger ice crystals and damage to the food structure (Dempsey & Bansal, 2012). To address this issue, some food manufacturers use blast freezing, which involves using forced air to circulate the food product, speeding up the freezing process and reducing the size of ice crystals. This method is commonly used for delicate food products such as fruits and vegetables, seafood, and meat. Overall, still air freezing is a simple and cost-effective method of preserving food products, but it may not be suitable for all types of food. Blast freezing or other methods may be necessary to ensure that the quality and structure of the food product are maintained during the freezing process. Still air cooling is a common method of cooling in many countries, particularly in developing countries where refrigeration is not widely available. However, it is important to note that the use of still air cooling may vary depending on the specific food product and local regulations. Compared to other cooling processes such as forced air cooling and vacuum cooling, still air cooling is a slower and less-efficient method of cooling. In a study (Lee et al., 1946), the researchers found that still air cooling was effective in maintaining the quality of the vegetables, but the cooling rate was slower compared to forced air cooling. Forced air cooling uses fans to circulate cool air around the food products, resulting in faster and more even cooling. Still air cooling results in slower cooling rates and higher bacterial growth compared to forced air cooling, but researchers showed that the quality of the beef was not significantly affected (Feng et al., 2012). Still air cooling is effective at reducing the temperature of the pineapple to safe levels, but the cooling rate is slower than forced air cooling. However, the results showed that the quality of the pineapple was not significantly affected by the cooling method (Mohd Ali et al., 2022). Vacuum cooling is a rapid evaporative cooling technique that can cool food products in a very short time. However, vacuum cooling requires specialized equipment and can be expensive. Slow freezers (e.g., still air freezers and cold stores) are generally used for the storage of frozen foods. The low heat transfer coefficient of naturally circulating air necessitates long holding times to achieve product freezing, resulting in significant quality loss. A major criterion for their use as storage facilities is their temperature stability. Constant temperatures help to minimize recrystallization, a major cause of quality loss during the storage of frozen foods (Brown & Dave, 2021).

5.2.2

Top-icing

Top-icing, or placing ice on top of packed containers, is a technique commonly used in the shipping and storage of perishable goods. This technique involves placing bags or blocks of ice on top of the packed containers, which helps to maintain a consistent temperature and prevent spoilage. The process of top-icing works by using a blast chiller or freezer to rapidly cool the surface of the food product. This causes a layer of ice to form on top of the product, which helps to transfer heat away from the product more quickly. The ice layer also

Still cooling in air and surface top icing

91

helps to prevent moisture loss, which can be a problem when cooling or freezing baked goods. Top-icing needs waterproof packaging to maintain durability during cooling. The use of top-icing is particularly important for products that are sensitive to temperature changes, such as fruits, vegetables, and seafood. By keeping the product cool and fresh, top-icing can help to extend its shelf life and reduce the risk of spoilage or waste (National Institute of Food and Agriculture, 2016). In addition to its use in shipping and storage, top-icing can also be used in other contexts where temperature control is important. For example, it may be used in the catering industry to keep food products cool during transport or at outdoor events. Overall, top-icing is a useful technique for preserving the quality and freshness of perishable goods during transport and storage. By helping to maintain a consistent temperature and prevent spoilage, top-icing can help to ensure that products reach their destination in the best possible condition. By using top-icing, producers, distributors can help to extend the shelf life of their products and reduce the risk of spoilage or waste. This can be especially important for products that are shipped long distances or stored for extended periods. Top-icing, or placing ice on top of packed containers, this is only used occasionally to supplement another cooling method. Because corrugated containers have largely replaced wooden crates, the use of top-icing has decreased. Wax-impregnated corrugated containers have allowed the use of icing products after packaging to continue; however, it is being replaced by hydro cooling and vacuum cooling (Senthilkumar et al., 2015). Packing finely crushed or flaked ice with produce is one of the oldest and simplest technical forms of cooling. This method is particularly valuable for products shipped in nonrefrigerated vehicles. Ice has a latent heat of 334 kJ kg
1 and absorbs heat well. Ice also maintains a high humidity in the box and minimizes moisture loss once the product has cooled to 0 C (Vigneault et al., 2009). This method involves filling packed containers or pallets with ice or covering pallets with ice. Individual package top icing is the oldest method. Ice is shoveled, raked, or blown on top of the produce in the container. Fast cooling with ice requires that ice is in close contact with most of the produce. Produce cools slowly if ice is just placed on the top of the produce. This method is not efficient in large operations because opening the containers, adding the ice, closing the containers, and re-palletizing them is labor-intensive. Further, the coating of ice may block vent openings, restrict air movement, and lead to center-load warming. Individual package top icing should be used only after precooling and before shipping, to assist in maintaining low temperature and high relative humidity (Prussia & Shewfelt, 1984). An improvement to top icing is icing by layer. Crushed ice and produce are alternately layered in the pallet box. It is recommended that all points in a bulk load of green leafy vegetables be within 150 mm from ice. As a general rule of thumb, the mass of ice should equal one-third of the produced mass. This method of icing is more labor-intensive than top-icing, but the cooling is faster and more uniform. Although relatively inexpensive, the cooling rate can be fairly slow since the ice only directly contacts the product on the top layer. For this reason, it is

92

Low-Temperature Processing of Food Products

recommended that top-icing be applied after precooling to crops with lower respiration rates such as leafy vegetables and celery but not for fruit of warm-season crops. Before shipping, ice is blown on top of loaded containers to aid in cooling and maintenance of higher relative humidity. However, care should be taken to avoid blockage of vent spaces in the load; this restricts airflow, which results in the warming of the product in the center of the load during shipment. Ice should also be “tempered” with water to bring the temperature to 32 F (0 C) to avoid freezing the product (Boyette & Estes, 1992). Top-icing is commonly used in cooling and freezing seafood. Studies show that top-icing is effective in maintaining the quality of oysters and mussels and salmon, reducing bacterial growth, and extending their shelf life (Alizadeh et al., 2007; Hsin-Shan et al., 2022; Mueda et al., 2019). Also, Kasmiati et al. found that topicing was effective in maintaining the quality of the squid, slowing down spoilage, and extending the shelf life (Kasmiati et al., 2022). Top-icing, or placing ice on top of packed containers, is one of several methods that can be used to cool or freeze food products.

5.3

Comparison of different types of cooling

Here is a comparison of top-icing with other types of cooling: Air cooling: Air cooling is a method that involves blowing cool air over the surface of the food product. This method is often used in the production of baked goods, such as bread and pastries. While air cooling can be effective, it is generally slower than topicing and may not be suitable for all types of products. Water cooling: Water cooling is a method that involves immersing the food product in cold water. This method is often used in the production of seafood and other perishable goods. While water cooling can be effective, it can be more timeconsuming and may require specialized equipment. Schmidt et al. found that still air cooling is effective at reducing the temperature of the chicken breasts to safe levels, but that the cooling rate is slower than other cooling methods such as forced air cooling or water immersion cooling (Schmidt et al., 2018). In the same way, the results showed that still air cooling is effective at reducing the temperature of the rice to safe levels, but that the cooling rate is slower than other cooling methods such as water immersion cooling. However, the quality of the rice was not significantly affected by the cooling method (Zhihang & Da-Wen, 2006). In terms of specific products, still air cooling is commonly used in the dairy industry for cooling milk and other dairy products and in the seafood industry for cooling fish and shellfish. Still air cooling is effective at reducing the temperature of the milk to safe levels, according to research by Sterup Moore et al. In the same way, Boonsumrej et al. found that still air cooling is effective at reducing the temperature of the shrimp to safe levels; in both studies, the cooling rate was slower than other cooling methods such as plate cooling or immersion cooling. However, the quality of the milk and shrimp was not significantly affected by the cooling method (Boonsumrej et al., 2007; Sterup Moore et al. 2023).

Still cooling in air and surface top icing

93

Blast chilling: Blast chilling is a method that involves using a specialized machine to rapidly cool the food product. This method is often used in the production of frozen desserts and other perishable goods. While blast chilling can be very effective, it can be expensive and may require specialized equipment (Narender Raju, 2018). Compared to these other methods, top-icing has several advantages. For example, top-icing is a relatively simple and cost-effective method that can be used for a wide range of products. It can also be very effective at rapidly cooling or freezing the product, which can help to preserve its quality and freshness.

5.4

History of using still cooling in air and surface top icing

In this section, we mention the history of still cooling in air and surface top icing.

5.4.1

Still air cooling

While air cooling has been around for thousands of years, the concept of still air cooling is a relatively modern one. Still air cooling refers to the process of cooling an object or space by allowing it to sit in a still cool environment without the use of fans or other mechanical devices. One of the earliest examples of still air cooling can be found in the design of traditional adobe homes in hot, dry climates. These homes were built with thick walls and small windows to keep the interior cool and often featured a central courtyard or other open space to promote airflow. By allowing the hot air to rise and escape through vents in the roof while drawing in cooler air from the shaded courtyard, these homes were able to maintain a comfortable temperature without the use of fans or air conditioning. In more recent times, still air cooling has been used in a variety of applications, from cooling electronic equipment to aging certain types of food products. The history of still air freezing can be traced back to the early 20th century when it was first used to freeze fruits and vegetables. This method of freezing is different from other methods, such as blast freezing, which involves rapidly freezing food products using cold air blown at high speeds. Over the years, still air freezing has been used to freeze a wide range of food products, including meats, poultry, fish, fruits, and vegetables. It has also been used in the production of frozen meals and other convenience foods (Food safety and inspection service, 2013). Today, still air freezing remains a popular method of freezing food products, although it has been largely replaced by blast freezing in many commercial applications. However, it is still used by some small-scale producers and home cooks who value its gentle freezing process and ability to preserve the quality of the food product.

5.4.2

Top-icing

The use of top-icing, or placing ice on top of packed containers, has a long history dating back to ancient times. In ancient Rome, for example, ice was harvested from

94

Low-Temperature Processing of Food Products

the mountains and transported to the city to preserve food and drinks. However, it was not until the 19th century that top-icing became a more widespread technique for preserving perishable goods during transport. With the advent of railroads and steamships, it became possible to transport goods over long distances and across different climates. In the early days of top-icing, ice was typically harvested from natural sources, such as lakes and rivers, and transported to the packing facilities. The ice was then broken into blocks and placed on top of the packed containers, which were typically made of wood or metal. As the transportation industry evolved, so did the technology used for top-icing. In the early 20th century, mechanical refrigeration systems were developed, which allowed for more precise temperature control and reduced reliance on natural ice. During World War II, top-icing became an important technique for preserving food and medical supplies during transport. The military developed specialized containers and refrigeration systems that could be used to transport perishable goods over long distances and in extreme conditions. In the post-war era, top-icing continued to be an important technique for the transportation and storage of perishable goods. With the growth of the global economy and the expansion of international trade, top-icing became an essential tool for ensuring that products could be transported safely and efficiently across different regions and climates (A brief history of ice). Today, top-icing remains a common technique for preserving the quality and freshness of perishable goods during transport and storage. While the technology has evolved, the basic principle of using ice to maintain a consistent temperature has remained the same.

5.5

Governing equations in cooling systems

5.5.1

Still air cooling equations

The process of still air cooling can be described using several equations and concepts from heat transfer and thermodynamics. Here are some key equations and concepts involved in still air cooling: Fourier’s Law of heat conduction: This law describes the heat transfer through a solid medium due to a temperature gradient. The equation is: q ¼
kAðdT=dxÞ

(5.1)

where, q is the heat transfer rate, k is the thermal conductivity of the material, A is the cross-sectional area through which heat is being transferred, and ðdT=dxÞ is the temperature gradient in the direction of heat transfer. Newton’s law of cooling: This law describes the rate of heat loss from an object to its surroundings. The equation is: q ¼ hA Tobject
Tambient




(5.2)

Still cooling in air and surface top icing

95

where, q is the heat transfer rate, h is the convective heat transfer coefficient, A is the surface area of the object, Tobject is the temperature of the object, and Tambient is the temperature of the surroundings. Specific heat capacity: The specific heat capacity (c) of a substance is the amount of heat required to raise the temperature of a unit mass of the substance by one degree Celsius. The heat transfer equation involving specific heat capacity is: Q ¼ mcDT

(5.3)

where, Q is the heat transferred, m is the mass of the substance, c is the specific heat capacity, and DT is the change in temperature. Latent heat of fusion: When a substance changes its phase from solid to liquid or vice versa, it absorbs or releases a certain amount of heat without changing its temperature. This heat is called the latent heat of fusion (Lf ). The equation for heat transfer during phase change is: Q ¼ mLf

(5.4)

where, Q is the heat transferred, m is the mass of the substance, and Lf is the latent heat of fusion. To analyze still air freezing, you would typically use a combination of these equations and concepts. You would first determine the heat transfer rate using Fourier’s law and Newton’s law of cooling. Then, you would calculate the amount of heat required to lower the temperature of the substance to its freezing point using the specific heat capacity equation. Finally, you would calculate the amount of heat required for the phase change using the latent heat of the fusion equation. By combining these calculations, you can estimate the time required for still air freezing (Jiji, 2006).

5.5.2

Top-icing equations

Top-icing is a method of cooling food products, particularly fish and seafood, by applying a layer of crushed ice on top of the products. This method helps to maintain the freshness and quality of the products during transportation and storage. The process of top-icing can be described using several equations and concepts from heat transfer and thermodynamics. Here are some key equations and concepts involved in top-icing: Sensible cooling: Sensible cooling refers to the process of cooling a substance without a change in its phase. The equation for sensible cooling is: Q ¼ mcDT

(5.5)

where, Q is the heat transferred, m is the mass of the substance, c is the specific heat capacity, and DT is the change in temperature.

96

Low-Temperature Processing of Food Products

Latent cooling: Latent cooling refers to the process of cooling a substance by absorbing heat during a phase change, such as the melting of ice. The equation for latent cooling is: Q ¼ mLm

(5.6)

where, Q is the heat transferred, m is the mass of the substance, and Lm is the latent heat of melting. Newton’s law of cooling: This law describes the rate of heat loss from an object to its surroundings. The equation is: q ¼ hA Tobject
Tambient




(5.7)

where, q is the heat transfer rate, h is the convective heat transfer coefficient, A is the surface area of the object, Tobject is the temperature of the object, and Tambient is the temperature of the surroundings. Heat balance: In top-icing, the heat absorbed by the melting ice must be equal to the heat removed from the food product. The heat balance equation is: Qice ¼ Qfood

(5.8)

where, Qice is the heat absorbed by the melting ice, and Qfood is the heat removed from the food product. To analyze top-icing, you would typically use a combination of these equations and concepts. You would first calculate the amount of heat required to cool the food product to the desired temperature using the sensible cooling equation. Then, you would calculate the amount of heat absorbed by the melting ice using the latent cooling equation. By equating these two values, you can determine the mass of ice required for topicing. Additionally, you can use Newton’s law of cooling to estimate the rate of heat transfer between the food product and the surrounding environment. This can help you determine the rate at which the ice melts and the effectiveness of the top-icing method in maintaining the desired temperature of the food product (Jiji, 2006).

5.6

Advantages and disadvantages of cooling methods

Advantages and disadvantages of cooling methods are listed as follows.

5.6.1

Advantages of still air cooling

Using still air cooling to freeze food goods, especially seafood, has several advantages. Beaudry et al. investigated the effect of still air cooling on the quality of fresh fruits, including apples, peaches, and strawberries, and results showed still air cooling was

Still cooling in air and surface top icing

97

effective in maintaining the quality of the fruits, but the cooling rate was slower compared to forced air cooling (Beaudry et al., 1997). We can classify the advantages of still air cooling as follows: ◦ Simplicity: Still air freezing is a straightforward method that does not require any specialized equipment or complex procedures. It can be easily done using a household freezer. ◦ Cost-effective: Since it does not require any additional equipment, still air freezing is a costeffective method for preserving food at home. ◦ Retains nutritional value: Freezing food helps to retain its nutritional value, as it slows down the enzymatic and chemical reactions that cause food to spoil. ◦ Long-term storage: Freezing food in a still air freezer allows for long-term storage, extending the shelf life of the food.

5.6.2 • • • •

Disadvantages of still air cooling

Slow cooling rate: Still air freezers have a slower freezing rate compared to other methods like air blast freezing or cryogenic freezing. This can result in the formation of larger ice crystals, which can damage the cell structure of the food and affect its texture upon thawing. Limited capacity: Household freezers have limited capacity, which may not be sufficient for freezing large quantities of food at once. Temperature fluctuations: The temperature in a still air freezer can fluctuate, especially when the door is opened frequently. These fluctuations can cause more rapid deterioration of the food and may lead to freezer burn. Energy consumption: Still air freezers can consume a significant amount of energy, especially if they are not energy-efficient models.

5.6.3

Advantages of top-icing

There are several benefits to using top-icing in the cooling and freezing of food products especially seafood. In a study (Haby & Coale, 1990, pp. 227e254), researchers found that top-icing is effective in maintaining the quality of the fish, slowing down spoilage, and extending the shelf life. In another study, Jeyakumari et al. showed that top-icing is effective in maintaining the quality of the shrimp, reducing bacterial growth, and extending the shelf life (Jeyakumari et al., 2015). Here are some of the main advantages of top-icing. ▫ Faster and more even cooling: Top-icing allows for faster and more even cooling of food products. This is because the layer of ice on top of the product helps to transfer heat away from the product more quickly, which can reduce cooling times and improve product quality. ▫ Reduced moisture loss: When food products are cooled or frozen without top-icing, they can lose moisture and become dry or stale. Top-icing helps to prevent this by creating a barrier that traps moisture inside the product, which can help to improve product quality and shelf life. ▫ Improved product quality: Top-icing can help to improve the quality of food products by reducing the risk of spoilage and preserving the texture, flavor, and appearance of the product. ▫ Increased efficiency: Top-icing can help to increase the efficiency of food production by reducing cooling times and allowing for faster processing times.

98

Low-Temperature Processing of Food Products

▫ Versatility: Top-icing can be used in the production of a wide range of food products, including baked goods, frozen desserts, meats, and seafood. This makes it a versatile technique that can be used in many different applications.

5.6.4

Disadvantages of top-icing

While top-icing is a useful technique in the cooling and freezing of food products, there are also some potential disadvantages to consider. Here are some of the main disadvantages of top-icing: n

n

n

n

n

Increased energy consumption: Top-icing requires the use of a blast chiller or freezer, which can consume a significant amount of energy. This can increase the cost of production and hurt the environment. Increased equipment costs: To implement top-icing, food manufacturers may need to invest in specialized equipment, such as blast chillers or freezers. This can be expensive and may not be feasible for smaller businesses. Risk of freezer burn: If the top-icing process is not done correctly, there is a risk of freezer burn. Freezer burn occurs when moisture is lost from the product, which can cause it to become dry and unappetizing. Limited application: While top-icing can be used in the production of a wide range of food products, it may not be suitable for all applications. For example, some delicate or highly perishable products may not be able to withstand the rapid cooling process required for top-icing. Quality concerns: While top-icing can help to improve the quality of food products, there is also a risk that it could hurt quality if not done correctly. For example, if the product is not cooled or frozen quickly enough, it could become dry or stale. Overall, while top-icing is a useful technique in the food industry, it is important to consider the potential disadvantages as well as the advantages. By carefully weighing the pros and cons of top-icing, food manufacturers can determine whether it is the right technique for their specific application.

5.7

Different cooling devices

For many food processors, choosing the right freezing equipment is the greatest challenge at the start, as the choices seem wide and many times confusing. This guide will try to give a better understanding of the differences between the many types of freezers out on the market. As a start, it is important to mention that freezing time is one of the most important parameters in the freezing process. The freezing time represents the time needed to decrease the temperature of the product’s thermal center to a specific temperature below zero, and the reason why it is so important is because it determines the quality of the final product and the operation costs. The International Institute of Refrigeration has defined several factors, which influence the freezing time and those include the shape and dimensions of the product, the

Still cooling in air and surface top icing

99

in-feed and out-feed temperatures, the temperature of the refrigerating medium, the surface heat transfer coefficient of the product, the change in the total heat content in the system, and the thermal conductivity of the product. Therefore, to get the optimal freezing time and by extension, the optimal freezing results, the right equipment should be chosen for specific products.

5.7.1

Still air cooling

Here air at very low temperatures is used for freezing the food products. Still air freezers, air blast tunnels, belt freezers, spray freezers, fluidized bed freezers, and impingement freezers fall into this category.

5.7.1.1

Still air freezers

Probably the oldest type of freezers, these are using still or forced air as a medium, and the product is kept static in freezing storage rooms. Still air freezers are like cold stores. They are relatively large and serve the purpose of freezing as well as the storage of the product. Refrigerant coils are generally located on one side of the room. Air flows in the room at very low velocities. The convective heat transfer coefficients are very low and the freezing requires a longer time. The slow freezing may lead to quality damage to the product because of the formation of large ice crystals. Weight loss of the product, especially unwrapped products, will be more as the product is in contact with the air for a long time. Still air freezer or cold storage is the simplest method with the lowest investment costs. It is most suitable for large or unprocessed products; however, it is the slowest freezing method. Forced air freezer is the improved version of cold storage, and it is using convection to circulate cold air in the freezing room. However, with this technology, the freezing time is still long as the airflow is not sufficiently controlled in the freezer leading to low surface heat transfer. As it is the cheapest freezing method, air blast freezers are used on a wide range of products. In some alternative versions of this method, the product is placed on rack trays and is frozen inside the cold storage with the help of cold air circulation. The trolleys or racks can be moved and replaced manually or by specialized trucks; however, the high manpower needed for operation is one of the main disadvantages of this method. The advantage though is that it can be suitable for many types of products.

5.7.1.2

Types of air freezers

Air is the most widely used method of freezing food as it is economical, hygienic, and relatively noncorrosive to equipment. Various forms of air blast freezers are used in industry. Sharp freezer or blast room freezer is a cold storage room that relies on natural convection and low air movement from evaporator fans to circulate the cooling air resulting in slow freezing times. This arrangement is sometimes used for bulk products like butter, beef quarters, and fish but not for processed food products.

100

Low-Temperature Processing of Food Products

Tunnel freezers: The refrigerated air is circulated by large fans over the product confined in an insulated closed room. Meat carcasses are supported by hooks suspended from a conveyor or specially designed racks. The trays or spacers are arranged to provide an air space between each layer of trays. The air can either be cross-flow or counter-flow, depending on the type of tunnel freezer. Various forms of tunnel freezers exist including: Batch freezers: The product is stacked on pallets, or hung from hooks on slide rails in the case of carcasses, and loaded into the freezer using fork hoists. This is an on/off process where the freezer is loaded, run until the meat is frozen to its desired temperature, then pumped down and switched off for unloading. Batch blast freezers are suitable for small quantities of varied products. Typically, the heat transfer coefficient is less than 50 W/m2 K (Fig. 5.1) (Dempsey & Bansal, 2012). Mechanized freezers: The pallet racks are fitted with casters or wheels. The racks or trolleys are usually moved on rails by a pushing mechanism, usually hydraulically powered. Such mechanized tunnel freezers are known as push-through tunnels or carrier freezers, which have two tiers, one on top of the other. These freezers are designed primarily for packaged goods, as well as carcasses. Advantages of mechanized freezers over batch freezers include improved air circulation over the product as it moves at a steady rate through the tunnel; labor costs are considerably decreased as pallets are not manually placed in the freezer; and there is added flexibility of the facility by varying the freezing time with the speed of the ram. Heat transfer coefficients in mechanized freezers are similar to batch freezers being less than 50 W/m2 K (Dempsey & Bansal, 2012). Belt freezers: The product is loaded on a continuous conveyor belt. Modern belt freezers usually employ vertical airflow to force air between the product items creating good contact with the product. Typically, the heat transfer coefficient of belt freezers

Figure 5.1 Schematic of a typical batch air blast freezer (Dempsey & Bansal, 2012).

Still cooling in air and surface top icing

101

varies between 25 and 80 W/m2 K. Multibelt freezers offer the advantage of smaller floor space compared to single-belt freezers. There are several forms of belt freezers, including: (i) Multitier belt freezers consist of several conveyor systems positioned one above the other with fans and coils positioned above the top belt. The air flow in belt freezers can either be vertical or horizontal over the product. The most efficient flow is determined by the product characteristics, dimensions, packed or unpacked, as well as degree of processing and composition. (ii) Spiral belt freezers: In this, the belt is coiled in numerous revolutions around one vertical central axis to optimize the use of floor space. The belt can stack 30 tiers or more, one above the other thus reducing floor space to a minimum. Spiral freezing is one of the most currently used methods in the freezing industry for large production needs due to its convenience, reduced floor space, flexibility, and efficiency (Fig. 5.2) (Dempsey & Bansal, 2012).

Fluidized bed freezers: These types of freezers are used to freeze particulate foods of uniform size and shape such as peas, cut corn, diced carrots, and strawberries. The foods are placed on a mesh conveyor belt and moved through a freezing zone in which cold air is directed upward through the mesh belt and the food particulates begin to tumble and float. This tumbling exposes all sides of the food to the cold air; thus, the product is individually quickly frozen (IQF). Typically, heat transfer coefficients range from 110 to 160 W/m2 K (Fig. 5.3). Impingement jet freezers: These freezers are straight-belt freezers involving only one step where the top, or more generally, both faces of the product receive very highvelocity air at low temperatures via uniformly distributed nozzles. The jets break the stagnant boundary layer surrounding the product, leading to a considerable increase in the heat-transfer coefficient, up to 300 W/m2 K. The performance is comparable to cryogenic freezers to freezing time and weight but at a much lower cost (typically half the price). Table 5.1 summarizes the characteristics and operating parameters of the freezers described above. The cooling air temperature for each freezer ranges between 30 and 45 C. With similar cooling air temperatures, it is the air velocity over the product that is the main factor affecting the heat transfer coefficient (Dempsey & Bansal, 2012).

Figure 5.2 Schematic of a typical spiral belt freezer (Dempsey & Bansal, 2012).

102

Low-Temperature Processing of Food Products

Figure 5.3 Schematic of a fluidized bed freezer (Dempsey & Bansal, 2012).

Other devices are as follows: Coolers and ice chests: These portable containers use still air cooling to keep food and beverages cold, making them ideal for outdoor activities such as camping, picnics, and tailgating. Coolers and ice chests also use still air cooling to maintain a consistent temperature inside the container. The cooling process in coolers and ice chests is similar to that of refrigerators, but instead of a compressor, they use insulation to keep the cool air inside. The insulation in coolers and ice chests helps to slow down the transfer of heat from the outside environment to the inside of the container. This allows the still air cooling system to work more efficiently, keeping the contents of the cooler or ice chest at a consistent temperature for longer periods. To further enhance the cooling process, many coolers and ice chests also include a layer of reflective material on the outside, which helps to reflect sunlight and heat away from the container. This reduces the amount of heat that enters the container, allowing the still air cooling system to work more effectively. Cold rooms and walk-in refrigerators: These commercial-grade refrigeration units use still air cooling to maintain a consistent temperature and humidity level, which is essential for preserving large quantities of food. Cold rooms and walk-in refrigerators also use still air cooling to maintain a consistent temperature inside the unit. The still air cooling system in these units works by circulating cool, dry air over the stored items, which helps to maintain a consistent temperature and humidity level. The cold room or walk-in refrigerator has a refrigeration system that cools the air inside the unit, creating a cool, dry environment. The still air cooling system then circulates this cool, dry air over the stored items, helping to maintain a consistent temperature throughout the unit. To ensure even cooling, many cold rooms and walk-in refrigerators have multiple shelves or compartments that allow for even distribution of the stored items. The still air cooling system ensures that each shelf or compartment receives the same amount of cool, dry air, which helps to prevent uneven cooling. A walk in cold room can be a benefit for many industries. Whether you work in the catering, dairy, meat and fish, or retail industry, investing in cold storage can assist in increasing efficiency within your business.

H.T.Ca W/m28C

Capacity

Advantages

Disadvantages

Freezer type

Product

Air velocity

Batch tunnel

Useful for all foods but better for bulk items, particularly carcasses Useful for all foods but better for bulk items. Mainly suited to packaged product due to hygiene issues Suitable for most foods, packaged or unpackaged, e.g., poultry, red meat, sea, bakery product.

1.5e6 m/s typically ¼ 4 m/s

h < 50

1e80 tones

(i) Low capital cost (ii) Versatile, can accommodate various product geometries

(i) Long freezing times (ii) Relatively low H.T.C

1.5e6 m/s typically z 4 m/s

h < 50

1000e20,000 kg/h

(i) Reduction in down time as the freezer is not stopped for loading/unloading (ii) Flexible with freezing times

(i) Requires additional space (ii) Reduced freezing capacity due to frost on evap. coils

3e8 m/s

h ¼ 25e80

500e6000 kg/h

(i) Compact (ii) Capable of IQF (iii) Higher efficiency than tunnel

(i) More expensive than tunnel freezers (ii) Hygiene issues

Continuous tunnel

Spiral

Still cooling in air and surface top icing

Table 5.1 Summary of forced convection freezing methods (Dempsey & Bansal, 2012).

Continued

103

104

Table 5.1 Continued

Product

Air velocity

Fluidized bed

IQF small products, .5e5 cm diameter, e.g., peas, French fries, shrimp, scallops, diced meat, meat balls IQF. Meat patties, fish fillets, shrimp, French fries. Product thickness typically 0e25 mm1

¼ 30 /s

10e100 m/s typically ¼ 40 m/s

Impingement

Capacity

Advantages

Disadvantages

h ¼ 110e160

100e20,000 kg/ h

(i) Very fast freezing times, comparable to cryogenic only cheaper (ii) High efficiency

(i) Only suitable for small products of fairly uniform shape and size

h ¼ 250e350

Depends on application, can be up to 1200 kg/h

(i) Reduced moisture loss (ii) Very fast freezing times, similar to cryogenic

(i) Only suitable for products of small thickness Low-Temperature Processing of Food Products

Freezer type

H.T.Ca W/m28C

Still cooling in air and surface top icing

105

Walk-in freezers provide fantastic access and ample storage space. They are ideal for large turnover businesses that have a heavy focus on stock rotation and preserving the integrity of their product. Walk-in freezers are commonly used to store consumable products for months or even years. Our walk-in freezers are specifically designed to boost stock longevity, preserving stock through even temperature control. A key focus is to minimize temperature fluctuations that can occur in other stores, even minimal changes can damage or make stock unsuitable (The experts in temperature controlled). Overall, still air cooling is an important component of these devices, allowing them to maintain a consistent temperature and humidity level, which is essential for preserving the freshness and quality of stored items.

5.7.2 5.7.2.1

Top-icing Flake ice machines

Flake ice is a soft, moldable form of ice similar to crushed ice. However, flake ice has more of a snow-like texture than crushed ice, which makes it easier to work with when creating food displays (Fig. 5.4). Crushed ice is made by crushing fully formed cubes. What results is a handful of crushed bits from a hard, solid cube. Flake ice, on the other hand, has a light, airy feel that allows it to mold together to form shapes easily. Flake ice is used in several applications. Flake ice was designed with food displays in mind. That includes seafood and produce displays, where food needs to stay on ice to keep fresh. Flake ice is also great for vegetables, beverage displays or drink tubs, where

Figure 5.4 Flake ice used for display foods (https://carnitec.com/maja-flake-ice-technologywell-proven-since-more-than-60-years/).

106

Low-Temperature Processing of Food Products

Figure 5.5 Flake ice produced by flake ice machine and used for cooling food products (https:// www.ziegra.com/en/applications/vegetables-fruits/asparagus-broccoli-fresh-long-lasting-with-ice; https://myicemachine.com/flake-ice-machine-for-fish/).

customers can grab their drinks (Fig. 5.5) Flake ice holds bottles and cans in place and provides even cooling throughout. Flake ice machines (Fig. 5.6) produce ice that is light and airy, so ice sticks to itself. The texture of the ice allows you to create mounds of ice to present food or drinks in any way you would like. Flake ice enables business owners to get creative with their products. Show food or drinks off in dazzling displays that entice customers but feel safe knowing they will stay fresh on display.

Figure 5.6 Flake ice machine (https://www.emsphysio.co.uk/product/scotsman-af80-flake-icemachine/).

Still cooling in air and surface top icing

107

Flake ice machines for fish can preserve fresh or frozen fish. Most ice machines produce sphere-shaped ice that is easily thrown into the water. Despite their large size, they are easy to use and do not require any special training to operate. Flake icing machines are also easy to maintain and require very little maintenance. You should weigh the ice you produce to avoid losing it and to make sure that it is as fresh as possible before you sell it (How can a flake ice).

5.8

Costs of still air cooling and top-icing

Here is an analysis of the costs associated with still air cooling and top-icing in food products.

5.8.1

Costs of still air cooling

Still air cooling is a relatively simple and passive method of cooling food products. It does not require any additional equipment or energy-intensive systems, which can make it a cost-effective cooling option. However, there are still some costs to consider. U Time: One of the main costs associated with still air cooling is the time it takes to cool the food products. Still air cooling generally has a slower cooling rate compared to other methods, which means that it may take longer to reach the desired temperature. This can impact production schedules and potentially increase labor costs if additional time is required for cooling. U Storage space: Still air cooling often requires adequate storage space to allow for proper air circulation around the food products. This can be a consideration for food manufacturers and retailers, as it may require additional storage facilities or space within existing facilities. The cost of acquiring or renting storage space should be taken into account. U Quality control: While still air cooling can effectively cool food products, it is important to monitor and control the cooling process to ensure food safety and quality. This may involve implementing temperature monitoring systems, training staff on proper cooling procedures, and conducting regular quality checks. These quality control measures can add to the overall cost of still air cooling. U Potential losses: Slower cooling rates with still air cooling can increase the risk of bacterial growth and spoilage in food products. If proper cooling protocols are not followed, there is a higher chance of product losses due to spoilage or foodborne illnesses. These losses can impact the overall cost of still air cooling.

5.8.2

Costs of top-icing

Top-icing, which involves placing ice or chilled water on top of food products, is another cooling method used in the food industry. Here are some costs associated with top-icing. ✗ Ice/water costs: The primary cost of top-icing is the ice or chilled water used to cool the food products. The cost of ice or water will depend on factors such as the quantity required, local

108

✗

✗

✗

✗ ✗

Low-Temperature Processing of Food Products

availability, and pricing. It is important to consider the ongoing cost of ice or water replenishment for effective top-icing. Packaging and insulation: Top-icing often requires appropriate packaging and insulation materials to maintain the desired temperature. This can include insulated containers, plastic wraps, or other packaging materials. The cost of these materials should be factored into the overall cost of top-icing. Handling and labor: Top-icing may require additional labor and handling to properly apply the ice or chilled water to the food products. This can include tasks such as arranging the products, applying the ice, and ensuring proper coverage. The cost of labor and handling should be considered when evaluating the cost-effectiveness of top-icing. Storage and transportation: Top-icing may require specific storage and transportation conditions to maintain the desired temperature. This can involve additional costs for refrigerated storage facilities, specialized vehicles, or temperature-controlled logistics. These costs should be taken into account when assessing the overall cost of top-icing. Waste and disposal: After the cooling process, there may be waste generated from melted ice or water. Proper disposal of this waste should be considered, including any associated costs for waste management or recycling. It is important to note that the costs of still air cooling and top-icing can vary depending on factors such as the scale of production, specific food products, and regional factors. Additionally, the costs mentioned above are general considerations and may not capture all the nuances of individual situations. Therefore, it is recommended to conduct a thorough cost analysis based on specific circumstances and consult with industry experts or professionals for accurate cost estimations.

5.9

Factors affecting the effectiveness of still air cooling and top icing in food products

Here are the factors that can affect the effectiveness of still air cooling and top-icing in food products: Temperature: Temperature is a critical factor that affects the effectiveness of both still air cooling and top-icing. The temperature of the surrounding environment and the initial temperature of the food product play a significant role in determining the cooling rate. Higher temperature differences between the food product and the surrounding air or ice/water can result in faster cooling. It is important to ensure that the cooling process brings the food product to safe temperatures within a reasonable time frame to prevent bacterial growth and maintain food quality. Humidity: Humidity levels in the environment can impact the cooling process. High humidity can reduce the evaporation rate of moisture from the food product’s surface, which can slow down the cooling process. On the other hand, low humidity can lead to faster evaporation, potentially causing dehydration and quality deterioration in certain food products. It is crucial to consider the optimal humidity range for specific food products during still air cooling or top-icing to maintain their quality and prevent moisture loss.

Still cooling in air and surface top icing

109

Airflow: Airflow, or the movement of air around the food product, is a critical factor in still air cooling. Adequate airflow is necessary to facilitate heat transfer from the food product to the surrounding air. Insufficient airflow can create stagnant pockets of air, leading to slower cooling rates. Factors that affect airflow include the design of the cooling area, the arrangement of food products, and the presence of obstacles that may impede air movement. Optimizing airflow through proper spacing and positioning of food products can enhance the effectiveness of still air cooling. Insulation: Insulation plays a crucial role in both still air cooling and top-icing. Insulation materials help to minimize heat transfer between the food product and the surrounding environment. In still air cooling, proper insulation of storage areas or containers can prevent heat gain from the surroundings, allowing the food product to cool more efficiently. In top-icing, insulation materials help to maintain the low temperature of the ice or chilled water, ensuring effective cooling of the food product. Choosing appropriate insulation materials and techniques is essential to maximize the effectiveness of both cooling methods. Surface area and shape: The surface area and shape of the food product can influence the cooling rate. Food products with larger surface areas have more contact with the surrounding air or ice/water, facilitating heat transfer and resulting in faster cooling. Irregularly shaped or unevenly sized food products may experience variations in cooling rates, as different parts of the product may have different levels of exposure to the cooling medium. It is important to consider the surface area and shape of the food product when designing cooling processes to ensure uniform and efficient cooling. Thermal conductivity: The thermal conductivity of the food product material affects how quickly heat is transferred from the product to the surrounding air or ice/water. Food products with higher thermal conductivity, such as metals, conduct heat more efficiently and cool faster compared to products with lower thermal conductivity, such as certain fruits or vegetables. Understanding the thermal properties of different food products is crucial for optimizing cooling processes and achieving desired cooling rates. Product packaging: The type and quality of packaging used for food products can impact the effectiveness of both still air cooling and top-icing. Packaging materials with good thermal insulation properties can help maintain the desired temperature and prevent heat transfer from the surroundings. Additionally, packaging that allows for proper airflow around the food product can enhance the cooling process. It is important to select appropriate packaging materials and designs that are compatible with the cooling method being employed. Product size and density: The size and density of the food product can affect the cooling rate. Larger and denser food products generally take longer to cool compared to smaller and less dense products. This is because larger and denser products have a higher thermal mass, requiring more time for heat to dissipate. It is essential to consider the size and density of the food product. Cooling medium: The choice of cooling medium, whether still air or ice/water in top-icing, can impact the cooling effectiveness. Still air cooling relies on the natural

110

Low-Temperature Processing of Food Products

convection of air to dissipate heat, while top-icing utilizes the cooling effect of ice or chilled water in direct contact with the food product. The specific heat capacity and thermal conductivity of the cooling medium can influence the cooling rate. Ice or chilled water can provide more rapid cooling due to its higher heat absorption capacity compared to still air. However, the choice of cooling medium should be based on the specific requirements of the food product and the cooling process. Cooling time: The duration of the cooling process is an important factor to consider. Longer cooling times can increase the risk of bacterial growth and quality deterioration in food products. It is crucial to determine the appropriate cooling time required to reach safe temperatures while considering factors such as the initial temperature, desired final temperature, and cooling method being employed. Monitoring and controlling the cooling time is essential to ensure food safety and maintain product quality. Pradhan et al. found that still air cooling results in slower cooling rates and higher bacterial growth compared to forced air cooling, but that the risk of Listeria contamination is still low as long as the chicken was cooled to safe temperatures within a reasonable time frame (Pradhan et al., 2012). Environmental factors: Environmental conditions, such as the ambient temperature and humidity in the cooling area, can impact the effectiveness of both still air cooling and top-icing. Higher ambient temperatures can reduce the temperature differential between the food product and the surrounding air or ice/water, resulting in slower cooling rates. Similarly, high humidity levels can affect the evaporation rate and potentially impact the cooling process. It is important to consider and control the environmental factors to optimize the cooling effectiveness. Food product characteristics: The specific characteristics of the food product, such as its composition, moisture content, and thermal properties, can influence the cooling process. Foods with higher moisture content may cool more slowly due to the latent heat of evaporation. Foods with high-fat content or low thermal conductivity may also exhibit slower cooling rates. Understanding the unique characteristics of different food products is crucial for designing effective cooling processes and achieving desired cooling rates. Regulatory requirements: Regulatory requirements and guidelines for food safety and quality may also impact the cooling process. Different food products may have specific temperature requirements that need to be met within certain time frames to ensure safety and prevent bacterial growth. Compliance with these regulations is essential and may influence the design and implementation of cooling methods. Equipment and facility design: The design and layout of the cooling equipment and facility can affect the effectiveness of still air cooling and top-icing. For still air cooling, the design of storage areas or containers should allow for proper air circulation around the food products. This may involve the use of shelving or racks that promote airflow and prevent the formation of stagnant air pockets. In the case of top-icing, the design of the equipment used for applying ice or chilled water should ensure even distribution and contact with the food products. Proper equipment and facility design can enhance the efficiency and effectiveness of the cooling process.

Still cooling in air and surface top icing

111

Production volume and scale: The production volume and scale of operations can impact the effectiveness of still air cooling and top-icing. Larger production volumes may require more extensive cooling systems or equipment to ensure efficient cooling of a larger quantity of food products. Scaling up the cooling process may involve considerations such as increased storage capacity, enhanced airflow management, and optimized workflow to maintain consistent cooling rates. It is important to assess the production volume and scale when designing cooling processes to meet the demands of the operation. Product handling and placement: The way food products are handled and placed during the cooling process can affect the cooling effectiveness. Proper handling techniques, such as avoiding excessive stacking or overcrowding, can ensure adequate airflow and promote uniform cooling. Placing food products in a way that allows for maximum exposure to the cooling medium, whether still air or ice/water, can enhance the cooling efficiency. Training staff on proper handling and placement techniques is essential to optimize the cooling process. Maintenance and calibration: Regular maintenance and calibration of cooling equipment and monitoring devices are crucial to ensure the effectiveness of still air cooling and top-icing. Malfunctioning equipment or inaccurate temperature monitoring can compromise the cooling process and lead to food safety risks or quality issues. Implementing a maintenance schedule and conducting routine checks and calibrations can help identify and address any issues promptly, ensuring the reliability and effectiveness of the cooling methods. Product-specific considerations: Different food products may have specific requirements or considerations that can impact the cooling process. For example, delicate fruits or vegetables may require gentle handling and controlled cooling to prevent damage or bruising. Certain products may have specific temperature requirements or cooling time limits to maintain their quality attributes. It is important to understand the unique characteristics and requirements of each food product and tailor the cooling process accordingly. Energy efficiency: Energy consumption and efficiency are important considerations in the effectiveness of still air cooling and top-icing. While still air cooling is generally considered energy-efficient as it does not require additional equipment, optimizing energy usage through proper insulation, airflow management, and equipment selection can further enhance efficiency. In the case of top-icing, energy-efficient refrigeration systems and insulation materials can help minimize energy consumption. Considering energy efficiency can contribute to cost savings and environmental sustainability. Regulatory compliance: Compliance with food safety and quality regulations is essential in the cooling process. Regulatory requirements may include specific temperature ranges, cooling time limits, or hygiene practices that need to be followed. Ensuring compliance with these regulations is crucial to prevent foodborne illnesses, maintain product quality, and meet legal obligations. Staying updated with relevant regulations and implementing appropriate control measures is vital for the effectiveness of still air cooling and top-icing.

112

Low-Temperature Processing of Food Products

It is important to note that the relative importance and impact of these factors may vary depending on the specific food product, cooling method, and operational conditions. Therefore, it is recommended to conduct thorough assessments and consider these factors in the context of the specific application to optimize the effectiveness of still air cooling and top-icing in food products.

5.10 5.10.1

Comparison A comparative analysis in food preservation

Food preservation is a critical aspect of the food industry, ensuring that food products remain fresh, safe, and of high quality for extended periods. Cooling is one of the primary methods employed in food preservation to slow down microbial growth, enzymatic reactions, and chemical deterioration. Two commonly used cooling methods are still air cooling and top-icing. In this comparative analysis, we will explore the similarities and differences between these two methods, their effectiveness in preserving food, and their applications in various food industries.

5.10.2

Similarities

U Cooling mechanism: Both still air cooling and top-icing rely on the principle of heat transfer through convection. In still air cooling, heat is transferred from the food products to the surrounding air through natural convection currents. U Cost-effectiveness: Both methods are relatively cost-effective compared to more advanced cooling techniques. They do not require complex equipment or energy-intensive processes, making them accessible to small-scale food operations.

5.10.3

Differences

✗ Air circulation: The key difference between still air cooling and top-icing lies in the presence or absence of air circulation. Still air cooling does not involve any forced air movement, relying solely on natural convection currents. In contrast, top-icing involves the use of forced air circulation to enhance cooling efficiency. ✗ Cooling rate: Top-icing is generally more effective in rapidly cooling food products compared to still air cooling. The forced air circulation in top-icing facilitates faster heat transfer, resulting in quicker cooling times. Still air cooling, on the other hand, is a slower cooling method and may not be suitable for highly perishable food products. ✗ Uniformity of cooling: Top-icing provides more uniform cooling throughout the food product compared to still air cooling. The forced air circulation in top-icing ensures that all parts of the product are exposed to the cooling effect, reducing the risk of temperature variations within the food. ✗ Application: Still air cooling is commonly used for certain types of food products that are not highly perishable, such as fruits, vegetables, and some bakery items. It is also suitable for small-scale operations or home refrigeration. Top-icing, on the other hand, is often employed in large-scale food processing facilities, where rapid and uniform cooling is essential for preserving the quality and safety of perishable food products.

Still cooling in air and surface top icing

5.11

113

Effectiveness in food preservation

Both still air cooling and top-icing play crucial roles in food preservation, albeit with varying effectiveness depending on the specific requirements of the food product. Still air cooling is effective in preserving less perishable food items that do not require rapid cooling. It is suitable for products with longer shelf lives, such as whole fruits and vegetables, where the primary goal is to maintain freshness rather than extend the product’s storage life significantly. Top-icing, on the other hand, is highly effective in preserving perishable food products that require rapid cooling to maintain their quality and safety. It is commonly used in the seafood industry, where the freshness and quality of fish and shellfish are critical. Top-icing ensures that the products are rapidly cooled to low temperatures, inhibiting microbial growth and enzymatic reactions that can lead to spoilage. In conclusion, while both methods rely on convection for heat transfer, they differ in terms of air circulation, cooling rate, uniformity of cooling, and application. Still air cooling is suitable for less perishable food items and small-scale operations, while topicing is more effective for rapidly cooling perishable food products in large-scale food processing facilities. Understanding the similarities and differences between these methods is crucial for selecting the appropriate cooling technique based on the specific requirements of the food product and the scale of the operation.

5.12

Challenges and limitations

One of the primary challenges associated with still air cooling is its relatively slow cooling rate compared to other methods. Still air cooling relies on the natural convection of air around the food product, which can be a slow process. This can be problematic when rapid cooling is required to maintain the quality and safety of perishable food items. Slow cooling can lead to an increased risk of bacterial growth, as the food remains in the temperature danger zone (between 40 and 140 F) for an extended period. To overcome the slow cooling rate, specialized equipment such as blast chillers or cold rooms can be used. Blast chillers are designed to rapidly cool food products by circulating chilled air around them. Cold rooms provide a controlled environment with low temperatures to facilitate faster cooling. However, the use of such equipment adds to the cost and infrastructure requirements for food processing facilities. Another limitation of still air cooling is the potential for uneven cooling. In still air environments, the air circulation may not be uniform, leading to temperature variations within the cooling space. This can result in inconsistent cooling of food products, with some areas cooling faster than others. Uneven cooling can compromise the quality and safety of the food, as it may lead to variations in texture, flavor, and microbial growth (Zhu et al., 2019). Top-icing, which involves applying a layer of ice on top of the food product, is often used in conjunction with still air cooling to enhance the cooling process. While top-icing can help improve the cooling rate, it also presents its challenges. One of the

114

Low-Temperature Processing of Food Products

main concerns with top-icing is the risk of bacterial growth. As the ice melts, it can create a moist environment that promotes the growth of bacteria. This is particularly true if the ice used for top-icing is not properly handled or stored, as it may contain contaminants. To mitigate the risk of bacterial growth, it is crucial to use clean and safe ice for topicing. Food processing facilities should follow strict hygiene practices and ensure that the ice used is made from potable water. Additionally, proper handling and storage of the food product after top-icing are essential to prevent cross-contamination and maintain food safety. Furthermore, the use of top-icing requires careful consideration of packaging and product design. The packaging should be able to withstand the weight and moisture of the ice without compromising its integrity. Additionally, the food product itself should be suitable for top-icing, as certain products may not be compatible with this method due to their texture or sensitivity to moisture. Overall, understanding these challenges and limitations is crucial for ensuring the quality and safety of food products during the cooling process.

5.13

Conclusion

In conclusion, the chapter on still air cooling and top-icing in food products highlights the research conducted in the food industry regarding these cooling methods. Still air cooling is effective in reducing the temperature of various food products, including cooked chicken breasts, vacuum-packed beef, fresh-cut pineapple, cooked rice, and seafood such as shrimp. However, it is important to note that the cooling rate with still air cooling is generally slower compared to other cooling methods like forced air cooling or water immersion cooling. The studies indicate that while still air cooling can achieve safe temperature reduction, it may not be the most efficient method in terms of cooling rate. This slower cooling rate can potentially impact the growth of bacteria, such as Listeria monocytogenes, in certain food products. Therefore, it is crucial to ensure that food products are cooled to safe temperatures within a reasonable time frame to minimize the risk of bacterial contamination. Top-icing, which involves placing ice or chilled water on top of food products, has not been extensively studied in the context of still air cooling. Further research is needed to evaluate its effectiveness and potential impact on food quality and safety. Overall, the choice of cooling method, whether still air cooling or other methods, should be based on the specific food product, cooling requirements, and desired cooling rate. Factors such as product characteristics, bacterial growth potential, and quality considerations should be taken into account when selecting the appropriate cooling method in the food industry. Further research and development in this area can contribute to optimizing cooling processes, ensuring food safety, and maintaining product quality in the food industry.

Still cooling in air and surface top icing

115

References A brief history of ice. Available from: https://www.howecorp.com/blog/a-brief-history-of-ice. Alizadeh, E., Chapleau, N., de Lamballerie, M., & Le-Bail, A. (2007). Effect of different freezing processes on the microstructure of Atlantic salmon (Salmo salar) fillets. Innovative Food Science & Emerging Technologies, 8, 493e499. Barbosa-Canovas, G. V., Altunakar, B., & Mejía-Lorío, D. J. (2005). Freezing of fruits and vegetables: An agribusiness alternative for rural and semi-rural areas. Food & Agriculture Organization. Beaudry, A., Hernandez, R., & Saltveit, E. (1997). Effect of still air cooling on the quality of fresh fruits. Postharvest Biology and Technology, 11, 93e106. Boonsumrej, S., Chaiwanichsiri, S., Tantratian, S., Suzuki, T., & Takai, R. (2007). Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing. Journal of Food Engineering, 80, 292e299. Boyette, M. D., & Estes, E. A. (1992). Postharvest technology series: Crushed and liquid ice cooling. North Carolina Cooperative Extension Service, North Carolina State University. AG-414-5. Brown, P., & Dave, D. (2021). Current freezing and thawing scenarios employed by North Atlantic fisheries: Their potential role in Newfoundland and Labrador’s northern cod (Gadus morhua) fishery. PeerJ. https://doi.org/10.7717/peerj.12526 Dempsey, P., & Bansal, P. (2012). The art of air blast freezing: Design and efficiency considerations. Applied Thermal Engineering, 41, 71e83. Feng, C., Drummond, L., Zhang, Z., Sun, D. W., & Wang, Q. (2012). Vacuum cooling of meat products: Current state-of-the-art research advances. Critical Reviews in Food Science and Nutrition, 11, 1024e1038. https://doi.org/10.1080/10408398.2011.594186 Food safety and inspection service. Freezing and Food Safety, (2013). Available from: https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safetybasics/freezing-and-food-safety. Haby, M., & Coale, C. (1990). Merchandising and managing a fresh seafood department. The Seafood Industry. How can a flake ice machine benefit my business?. Available from: https://www.easyice.com/ how-can-a-flake-ice-machine-benefit-my-business/. Hsin-Shan, T., Hsiao, Y., & Weng, Y. (2022). Effects of individual and block freezing on the quality of Pacific oyster (Crassostrea gigas) during storage under different pretreatment conditions. Sustainability (Volume14). https://doi.org/10.3390/su14159404 Jeyakumari, A., Remya, S., Jesmi, D., et al. (2015). Effect of delayed icing on the quality of white shrimp (Litopenaeus vannamei) during chilled storage. Journal of Food Processing and Preservation, 39. https://doi.org/10.1111/jfpp.12539 Jiji, L. M. (2006). Heat convection. Springer. Kasmiati, K., et al. (2022). Quality and safety of fresh squid (Loligo forbesii) sold in Daya Traditional Market, Makassar, Indonesia. IOP Conference, 1119. https://doi.org/10.1088/ 1755-1315/1119/1/012050 Lee, F. A., Gortner, W. A., & Whitcombe, J. (1946). Effect of freezing rate on vegetables. Industrial & Engineering Chemistry, 3, 341e346. https://doi.org/10.1021/ie50435a027 Mohd Ali, M., Hashim, N., Abd Aziz, S., & Lasekan, O. (2022). Quality prediction of different pineapple (Ananas comosus) varieties during storage using infrared thermal imaging technique. Food Control, 138.

116

Low-Temperature Processing of Food Products

Mueda, C., Nunal, S., & Mueda, R. (2019). Effect of storage temperature on the physicochemical and sensory properties of green mussel, Perna viridis (Linnaeus, 1758). Asian Fisheries Society, 32, 172e181. Narender Raju, P. (2018). Technology of processed foods: Fruits, vegetables, bakery and confectionery. INFLIBNET Centre. National Institute of Food and Agriculture. (2016). Cooling methods for broccoli. Available from: https://extension.tennessee.edu/publications/Documents/PB1904.pdf. Pradhan, A. K., Li, M., Li, Y., Kelso, L. C., Costello, T. A., & Johnson, M. G. (2012). A modified Weibull model for growth and survival of Listeria innocua and Salmonella Typhimurium in chicken breasts during refrigerated and frozen storage. Poultry Science, 91, 1482e1488. Prussia, S. E., & Shewfelt, R. L. (1984). Ice distribution for improved quality of leafy greens. ASAE, St-Joseph. MI. No. 84-6014. Schmidt, F. C., Silva, A. C. C., Zanoelo, E., & Laurindo, J. B. (2018). Kinetics of vacuum and air cooling of chicken breasts arranged in stacks. Journal of Food Sciences Technology, 6, 2288e2297. https://doi.org/10.1007/s13197-018-3146-6 Senthilkumar, S., Vijayakumar, R. M., & Kumar, S. (2015). Advances in precooling techniques and their implications in horticulture sector: A review. International Journal of Environmental & Agriculture Research (IJOEAR), 1, 24e30. Sterup Moore, S., Costa, A., Penasa, M., Callegaro, S., & De Marchi, M. (2023). How heat stress conditions affect milk yield, composition, and price in Italian Holstein herds. Journal of Dairy Science, 106, 4042e4058. The experts in temperature controlled storage. Benefits of a Walk in Freezer. Available from: https://www.crscoldstorage.co.uk/news/walk-in-freezer.html. Vigneault, C., Thompson, J., & Wu, S. (2009). Designing container for handling fresh horticultural produce. Postharvest Technologies for Horticultural Crops, 2, 25e47. Zhihang, Z., & Da-Wen, S. (2006). Effects of cooling methods on the cooling efficiency and quality of cooked rice. Journal of Food Engineering (volume77,, 269e274. Zhu, Zhiwei, Geng, Yi, & Sun, Da-Wen (2019). Effects of operation processes and conditions on enhancing performances of vacuum cooling of foods: A review. Trends in Food Science & Technology, 85, 67e77.

Air blast freezing in the food industry

6

Duy K. Hoang and James K. Carson School of Engineering, University of Waikato, Hamilton, New Zealand

6.1

Introduction

According to the Food and Agriculture Organization (FAO), the size of the global frozen food market in 2018 was worth between $225 billion and $228 billion (ResearchMarkets, 2020). For a food exporting country such as New Zealand, a significant quantity of its products is exported in the frozen state, meaning food freezing is a significant contributor to the country’s economy (Carson & East, 2018). Food freezing has been targeted as a key technology in reducing global food wastage, currently estimated to be one-third of total food production. It continues to be an attractive means of food preservation as it has the potential to circumvent the use of preservativesdsomething that is becoming increasingly important to consumers. Food refrigeration has been used for many years in various forms. Ice has been used to preserve food for many centuries and with the development of mechanical refrigeration in the 1800s, active food freezing has become an essential technology for providing food security for the world (Carson, 2013; Pearson, 2003). Clarence Birdseye was perhaps the first to recognize that the rate of freezing had an important effect on food quality, and subsequently others have designed mechanical devices to allow for enhanced freezing rates. In markets in developed countries, it is estimated that 10% of all food consumed has been frozen for at least part of its processing (Bogh-Sorensen, 2006), and it is likely that the freezing process was the most energy intensive operation in the food’s production (Werner et al., 2005). Air blast freezing is the most commonly employed foodfreezing method worldwide due to its versatility, relative simplicity, and reliability. A wide variety of foods can be frozen, but meat, seafood, dairy products, and horticultural produce make up the majority. As a cooling medium, air is cheap, hygienic, and comparatively noncorrosive to equipment. However, it is by no means an ideal heat transfer fluid due to its low volumetric heat capacity and thermal conductivity, which means that heat transfer rates are not as high as for other freezing systems, and careful consideration needs to be taken in equipment design to ensure sufficient cooling throughout the freezer without requiring excessive energy consumption. In this chapter, the different types of blast freezing apparatus are described, basic design principles are discussed, modeling for optimization of blast freezing processes is overviewed, and steps for improving energy efficiency are identified. “Blast freezing” in this chapter refers to processes that cool to below the initial freezing temperature of the food product using air that is propelled by fans. This definition Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00004-7 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

118

Low-Temperature Processing of Food Products

specifically excludes cooling without forced air movement (passive cooling), cooling by direct contact (e.g., plate-freezing) or cooling by a medium other than air (e.g., immersion cooling, spray cooling).

6.2

Types of air blast freezers

A wide variety of air blast freezers are used in industry, as outlined below.

6.2.1

Blast cell (batch) freezers

Blast-cell freezers (Fig. 6.1) are single-load units that have the simplest design of all blast freezers. A blast cell is essentially an insulated room or space that has refrigeration evaporator(s) and fans that blow cold air over the food items in a controlled manner (Becker & Fricke, 1999, 2003). Products are placed on trays or packed in cartons that are then placed in racks or on carts/trolleys. Blast cell freezers typically operate in batch mode in which product is loaded manually into the blast freezing cell before the doors are closed for the freezing process to begin. The product remains in the freezer until the food is frozen to the required temperature. The trays or cartons on each rack, and all racks in the freezer should be arranged to allow air to move at the highest velocity that can be achieved by the fans throughout the product zone. Uniformity of cooling rate (requiring minimal variation in spatial distribution of air velocities and temperatures) is also preferred. A blast cell can be used to freeze a wide variety of food products whether individually or in bulk, packaged or unpackaged, fresh/raw, or processed into preparations. By using different internal designs (e.g., trays, racks, rails), large packages and whole meat carcases can be frozen. It is also possible to freeze products with different sizes and shapes in the same batch. Depending on the form of packaging, product composition, airflow and temperature, the freezing time can range from a few hours to several days.

Figure 6.1 Schematic of a blast cell freezer.

Air blast freezing in the food industry

119

However, although blast cell freezers offer great versatility, they are comparatively labor-intensive due to the need for manual loading and unloading, unlike continuous freezers that may form part of a continuous production line. In addition, significant weight loss can occur if the blast cell is not properly used (Boast & Caballero, 2003), as discussed further in Section 6.5 of this Chapter. It is not uncommon for a blast cell freezer to be attached to a “cold-store room” (Fig. 6.2), which is a room that is designed to maintain product at its storage temperature as opposed to a blast cell freezer that is designed to lower the food product’s temperature from above its initial freezing point to its storage temperature (Carson, 2013). The advantage of this arrangement is that any cold air escaping the blast freezer (e.g., when the doors are opened during loading/unloading) will serve to reduce the load on the cold store refrigeration.

6.2.2

Continuous freezers

Continuous freezers differ from blast cell (batch) freezers in that product is conveyed through the freezer continuously, usually forming part of a production line. Examples of continuous freezers include straight belt tunnel freezers and spiral belt freezers.

Figure 6.2 Diagram of a cold store with blast cell freezers incorporated.

120

6.2.2.1

Low-Temperature Processing of Food Products

Straight belt tunnel freezers

Straight belt tunnel freezers may either by horizontal or inclined and may have a single level or a cascade of levels. The belt tunnel freezer is commonly used for small, individual, quick-frozen (IQF) products that range from 0.5 to 5 cm in diameter. Some examples of suitable products are vegetables (e.g., peas, beans, cut corn, mushrooms, diced carrots, Brussels sprouts), fruits (e.g., berries, diced pineapple, and sliced apple), and seafoods (e.g., shrimp, scallops). The freezing times typically range from 3 to 50 min. IQF straight belt tunnel freezers (Fig. 6.3) are typically designed with cascading, inclined conveyancing. The product may first be conveyed on to a dewatering and splitting shaker where any excess surface water is removed before the product is spread over the full width of the freezer loading belt section. As the product moves into the freezer, the cooling fan circulates the cold air from the refrigerated coils through a wire mesh belt and then through the product layer and back to the coils. Ideally, each item of food is exposed to the cold air on all sides to maximize cooling rates. The freezer is divided into zones: the precooled crust zone and the core freezing zone. In the precooled crust zone, the product is agitated and surface-frozen to sealin the moisture and ensure product agglomerations do not form. Next is the core freezing zone where the surface-frozen food is fluidized, and each individual particle is completely frozen to the required temperature (typically
18 C or below). The fluidized agitation of the product is designed to ensure sufficient freezing quality and reduced shrinkage. The floor space occupied by the freezer can be reduced by stacking belts above each other in a multilayered arrangement. This system utilizes horizontal air flow to enable heat to be continuously removed from all sides of product. Products may be conveyed directly onto a loading belt, which transports the product into the low-temperature zone. The product proceeds through multiple passes before it is discharged, either at the same end (but at a different level) or the opposite end of the freezer. The applications of the multipass system include poultry (e.g., chicken portions, chicken nuggets), red meat (e.g., meat cuts, hamburger patties, meatballs), and seafood (e.g., crab sticks,

Figure 6.3 Schematic of a straight belt individual, quick-frozen (IQF) tunnel freezer.

Air blast freezing in the food industry

121

raw shrimp, fish fillets). Poor design of this type of freezing system can cause product to be jammed at belt transfers with consequent damage to the product.

6.2.2.2

Spiral belt freezers

The spiral belt freezer (Fig. 6.4) consists of a continuous conveyor belt coiled in several revolutions around a rotating drum and is often used for products that require gentle handling or long freezing times. By stacking one belt layer on another, the belt surface area can be maximized while keeping the occupied floor space to a minimum. Depending on the production capacity, the number of layers in the spiral can be altered, and two spiral towers can be used in combination to form a twin double drum spiral freezer for very long freezing times. The food products are conveyed from the production line directly onto the freezer belt before being transported into the freezing zone. Modern spiral freezers are designed to eliminate any type of structure that may cause product jams. Each tier can be designed to be supported directly by the tier below and the food spirals upward or downward as it freezes on a continuous conveyor. As the food enters the freezing chamber, horizontal air flow provided by fans on one side of the spiral freezes the food on both the top and bottom sides of the product surface. The temperature of the refrigerated air is generally between
30 and
40 C, with velocity ranging from 3 to 8 m/s. In some designs, a single pass of turbulent air flows through each individual tier and returns to the evaporation coil in a horizontal loop pattern. By supplying the coolest air temperature to each tier of product independently, freezing rates may be maximized. Baffles, high-pressure fans, vanes, and flow dividers can be used to optimize air distribution and help balance the heat transfer rates on both the top and bottom sides of the food, achieving optimized freezing times and weight loss. According to one manufacturer, spiral freezers can be bought as a whole package or may be assembled on site, with the latter option being more common for larger units. The capacities available range from 45 kg/h to 4500 kg/h with belt widths ranging between 0.2 and 1.22 m, and air flow patterns may be in either the horizontal or vertical direction. Figure 6.4 Schematic of a spiral belt freezer.

122

Low-Temperature Processing of Food Products

Examples of food products that have been successfully frozen in spiral freezers include: chicken portions, patties, nuggets; meat patties, meatballs, raw hamburger, and crumbed, fried red meat cuts; crumbed fish sticks, fillets or patties, shrimp, scallops, some whole fish; pizza base, pies, cookies, pasta, bread dough; ice cream cups, and other processed foods requiring a long retention time.

6.2.3

Single and multiple retention time freezers

Some modern freezers are designed to handle different types of product on a single production line. For example, the Milmeq Single Retention Time (SRT) is a first in/ first out system for products requiring a single (retention) time, while their multiple retention time (MRT) freezers are capable of processing products having different required freezing times, thereby combining the versatility of batch freezers with the efficiency of continuous freezers. SRT (Fig. 6.5) and MRT (Fig. 6.6) freezers are typically large units that have their own building structure and tend to be integrated into a production line. SRT and MRT freezers can be designed to handle a wide range of packaging and/or product containers such as cartons/boxes, cases, molds, crates, or other arrangements that can be transported on a conveyor and transferred by a mechanized pusher (Fig. 6.7). According to one manufacturer, retention times could vary between 2 and 48 h, capacities could range from 600 to 20,000 cartons, carton mass could range from 4.5 to 27 kg, and the freezing air temperature can be as low as
50 C. Food products are packaged and, in some cases, placed in trays before being conveyed to the freezing tunnel inlet. Shelves within an MRT are allocated different retention times, and the loading conveyor automatically sorts and accumulates product types, allowing transfer onto the appropriate designated shelf according to the required product retention time. A second belt directly beneath the loading conveyor belt receives frozen product being unloaded from the tunnel. The conveyor loading and unloading processes occur essentially concurrently. The freezing tunnel is comprised of a two-tier structure, which

Figure 6.5 A milmeq Single Retention Time (SRT) freezer. Courtesy of MHM Automation.

Air blast freezing in the food industry

123

Figure 6.6 Milmeq Multiple Retention Time (MRT) blast freezer, capable of freezing a range of products with different residence times. Photo courtesy of MHM Automation.

provides for suspension and transfer of trays or pallets. Product in the tunnel is frozen by constant air flow forced through refrigeration coils at one end of the tunnel and then through the filled pallets suspended in the upper and lower tiers. The clearance between the food packages ensures each is exposed to a similar airflow profile and perforations in the shelves allow for airflow to pass over the underside of the packages. As each shelf of the pallet is indexed into position, frozen product is pushed off the shelf on to the unload belt. A system of encoder and position sensors provides for indexing of food

Figure 6.7 Infeed conveyors for a milmeq Single Retention Time (SRT). Photo courtesy of MHM Automation.

124

Low-Temperature Processing of Food Products

packages during loading and unloading and controls movement of product through the two-tier structure. All movements are protected by safety interlocks. In order to reduce the operational costs of loading and unloading in blast freezers with forklift trucks and to reduce high labor costs, automated storage and retrieval systems (ASRS) have been introduced into some high volume food processing industries (Bowater, 2001). Clearly all conveying systems and their auxiliaries (e.g., barcode readers, sensors, controls, and mechanics) must be designed to be suited to operation in low-temperature environments. These automated systems can accelerate the pace of transport and ensure integrated devices function seamlessly.

6.2.4

Impingement freezers

Impingement freezers (Fig. 6.8) incorporate multiple, high-velocity air-jets that are blasted directly (head on) at the surface of the product (impingement). The highvelocity airflow disrupts the boundary layer surrounding the product, maximizing the rate of heat transfer between product surface and refrigerated air. They may be designed with single or multiple passes of straight belt in which air flows perpendicular to both sides of product via air nozzles mounted above and below the conveyor. The speed of freezing in impingement freezers rivals cryogenic freezers but at a much lower cost (Dempsey & Bansal, 2012). They are most suitable for thin food products, for example, hamburger patties, fish fillets, shrimp and shellfish, and some bakery products and breads.

6.3 6.3.1

Air blast freezer design and operation Freezer capacity and temperature

The first considerations in the design of a freezer are the quantity per batch or processing rate of product that is expected to be frozen and the temperatures that the product is

Figure 6.8 Schematic diagram of the impingement freezers.

Air blast freezing in the food industry

125

required to be cooled from and to (Carson, 2013). The quantity per batch or per hour (in the case of the continuous process) will determine the size of the freezer (e.g., volume of a batch-cell freezer or the belt length and width of a continuous freezer), while both the production quantity and temperature will determine the required capacity of the refrigeration (in terms of kW). In addition to heat being released by the cooling food product, other heat sources in the freezer include (ASHRAE, 2014; Carson, 2013). • • • • • • •

Heat ingress through walls, floor, ceiling, supporting members such as pillars and beams, etc. (should be minimized by good insulation) Heat from air coming in through doors, openings or other access ways which may be warm and humid Heat from evaporator fans circulating the air in the freezer Heat from lights Heat of respiration (not only from humans present, but also from some products, fruit and vegetables in particular) Heat from vehicles (such as forklift trucks) used to load and unload product (particularly in the case of blast cell freezers) Heat from the defrost cycle

The relative quantities of each component of the total heat load will vary significantly, depending on freezer design. Methods for estimating these heat loads are provided in (ASHRAE, 2014). Methods for calculating the time required for a food product to reach a certain temperature, which may be used to calculate the product heat load are the topic of Section 6.4 of this Chapter. The refrigerated air circulating within the freezer must have a temperature low enough to freeze the product in the desired time and to the desired temperature. In many cases, particularly for meat and poultry, cooling times are regulated to fall within certain ranges for hygiene reasons (Carson & East, 2018). To provide some examples, in the poultry industry in New Zealand,
25 C freezing temperature is used to freeze chicken products to
18 C; in the UK, a freezing temperature of
35 C is recommended for fish before long-term frozen storage temperature at
29 C. The lower the air temperature in a freezer, the shorter the freezing time and, in general, the higher the product quality (see also Section 6.5 of this Chapter); however, the unit cost of the heat removal increases as the air temperature decreases. For example, a refrigeration system using a
46 C evaporator temperature instead of
40 C increases the electrical utility cost by about 15% (ASHRAE, 2014). Therefore, the freezing temperature should be selected to achieve the lowest capital and operating cost, while achieving the minimum required rate of cooling in terms of throughput and product quality. Selecting the optimal air temperature may be accomplished with the aid of modeling techniques discussed in Section 6.4 of this Chapter. Once the total heat load has been determined and the applicable design safety factor has been applied, the most suitable (in terms of both energy efficiency and cost) compressor and refrigerant pairing may be selected. Incorrect freezer loading can overload the refrigeration compressor resulting in high discharge pressures, extended freezing times and, potentially, failure to reach the required temperature.

126

Low-Temperature Processing of Food Products

When sizing evaporators for tunnel blast freezers, (Bowater, 2001) recommended that the size of the evaporators should be at least 50% larger than the average heat load for 1 day turnaround units, although this is not so critical for the 48 h freezing system. The reason behind the oversizing of the evaporator is that at the beginning of the process heat released from the product is many times higher than that in the last few hours. Therefore, the evaporators must be sized at a higher value than the average heat rejection rate to ensure the designed refrigerated air temperature is maintained during the freezing period; however, oversized evaporators can lead to excessive energy use, as discussed in Section 6.6 of this Chapter. If there is significant air leakage into the freezer, a factor to account for frost build-up should be applied with fin spacing of no more than four fins per inch recommended to avoid excessive reduction in performance due to frosting (Bowater, 2001). Condensers are typically selected with reference to the ambient conditions. If cooling water is available, water-cooled condensers can be used, or if the air humidity is low, evaporative condensers can be used since they can cool the refrigerant to close to the wet-bulb temperature of the air. Air cooled condensers are typically employed for smaller units because of their simplicity and ease of installation. Some condensers incorporate mechanisms for preventing overloading, since an overloaded condenser can damage the compressor. Condenser selection is often performed by the supplier of the refrigeration equipment.

6.3.2

Air movement

Once the size of the freezer has been determined, achieving optimal airflow distribution is perhaps the most critical challenge for air blast freezer designers (see also Section 6.5 of this Chapter). The evaporators of the refrigeration system are normally located in one part of the freezer with fans being used to circulate the cold air (Fig. 6.9). Air must be moved around the products as consistently and evenly as possible. If airflow is not uniform there is the risk that some of the product will not freeze during the product’s residence time, particularly product at the center of a package, or packages in the center of a stack. At the same time, the design needs to prevent the air from “short-circuiting” (i.e., air leaving the evaporator being returned to the inlet, without passing over much, if any, of the product). Short-circuiting leads to comparatively warm regions (“hotspots”) where cooling rates may be significantly reduced, or, particularly at locations far from the evaporator, product not being cooled to the specified temperature. Air movement and mixing within freezers may also be promoted by the installation of static devices such as diffusers, vanes, and ducting; however, such devices add to the pressure drop that must be overcome by the evaporator fans. In batch freezers, it is important not only for air to flow in the head-space above the product but also for sufficient flow through the product stacks so that required rates of cooling are achieved and also to reduce the variation in cooling rates between product stacks in different parts of the freezer. Generally, product farthest from the evaporator fans is at greatest risk of receiving inadequate cooling, but product close to heat sources (such as lighting) or products surrounded by stagnant air due to poor freezer design may also suffer. Many operational problems may be encountered due to poor

Air blast freezing in the food industry

127

Figure 6.9 Milmeq cheese chilling tunnel with evaporator fans on the left. Photo courtesy of MHM Automation.

positioning of the pallet/tray/rack/cart in the freezer even if the freezer itself was properly designed (Briley, 2002). It is vital that the products and pallets are arranged in such a way that the air is free to move over the entire product surface with the cold air circulating around and between the trays or cartons unhindered. For a carton freezing tunnel, it is recommended that a clearance of up to 50 mm is implemented to ensure each carton receives the same airflow profile and cooling air temperature. In addition, perforated or meshed shelving should ideally be used to allow air to flow past the underside of the packages. In some designs, products are placed within the freezer on open-top trays. In such cases, the tray should be designed to enhance rates of heat transfer in addition to having sufficient mechanical strength to hold the product without collapsing and should be practical to load and unload. (Sahin, 2004) recommended a freezing tray made from aluminum in which the upstream side of the tray should be lower than the height of product contained within, while the remaining edges should be kept higher than the product level. In this way, air will pass directly over product while minimizing the risk of spilling any loose product during unloading after freezing. Another recommended tray feature is the incorporation of vent holes in the two tray sides in the air flow direction to allow refrigerated air to pass through the tray in addition to the air flowing over it. The spacing between the trays is also an important consideration; it is recommended that the distance between the top product surface to the tray above it should be 2/3 of the product thickness but not greater than 50 mm (Sahin, 2004). Trays should be distributed evenly to allow for close to uniform air flow over the cross section of the freezer, and in the event that pallets or carts are partially loaded, they should be distributed evenly with fully loaded pallets/carts to minimize spatial variation of heat load in the freezer. It may sometimes be beneficial for empty packages to be placed beside full packages to ensure even air flow and prevent “short circuiting.” The heat transfer coefficient is a number derived from Newton’s Law of Cooling (Carson et al., 2006) that is commonly used to quantify the rate of heat transferred

128

Low-Temperature Processing of Food Products

between a solid surface and a fluid stream for a given temperature difference (ASHRAE, 2014; Harris et al., 2004; Willix et al., 2006). The heat transfer coefficient depends on the velocity of the fluid as well the density, viscosity, specific heat capacity, and thermal conductivity of the fluid (Cengel & Ghajar, 2011). Since air has low thermal conductivity, density, and heat capacity (Carson et al., 2016), it is important that air velocity is maximized to compensate; however, high air flow velocity requires high-pressure fans, which, in turn, increases cost (since the power consumption of a fan is proportional to the cube of air velocity). In addition to energy cost, increasing the fan speed will add to the heating load in the freezer. While increasing the air velocity will increase the heat transfer coefficient, the extent to which it affects the rate of freezing depends on the size and moisture content of the product being frozen. The Biot Number (Bi) relates the resistance to heat transfer within a cooling object to resistance at the surface of the object (Eq. 6.1): Bi ¼

hR k

(6.1)

Where h is the heat transfer coefficient over the surface, k is the thermal conductivity of the food product, and R is the characteristic length, normally taken to be the distance between the center and the surface of the product. When consistent units are used for h, k and R, Bi is dimensionless and may be used to characterize a cooling process (Cengel & Ghajar, 2011). When Bi is low (e.g., 10), and then the dominant resistance is the heat transfer between the center and the surface of the object, in which case further increases in fluid velocity will have minimal influence on the cooling time. Hence, the Biot number may be used to identify the “point of diminishing returns” for air velocity in a freezing process. While it will vary depending on the product being cooled, industry experience suggests that the most suitable and economical air speed is about 4 m/s. (Dempsey & Bansal, 2012) and (Kolbe et al., 2004) suggested that increasing the air velocity over 5 m/s only results in marginal improvements to the freezing rate as the Biot number becomes large. Enclosing individual or bulk food items in a bag or covering a pallet in polyethylene wrap (as is done sometimes with horticultural produce) has the effect of increasing the Biot number, thereby reducing the maximum economic air velocity and increasing the required cooling time. According to (Sahin, 2004), it is possible to reduce fan power while providing the desired air velocity by arranging the product such that air flows along the length of the product or product stack, rather than along the width so that the cross-section of airflow may be reduced. This was illustrated by considering a tunnel for freezing 1 ton of fish loaded on four pallets with the pallets stacked in two different arrangements (Fig. 6.10). Both arrangements delivered an air velocity of 5.08 m/s; however, the wider tunnel required 13 kW fan power, while the narrow tunnel only required 8.5 kW meaning a reduction in fan heating load and associated energy cost. However,

Air blast freezing in the food industry

129

Figure 6.10 Comparison of fan power of (a) narrow and (b) wide freezing tunnel.

the two tunnels may have a significantly different footprint, so there may be a trade-off between energy and space efficiencies. Current developments in freezer design tend to be focused on impingement freezers, dual air systems and improving the air flow distribution throughout air blast freezers with the aid of computational fluid dynamics (CFD) (Dempsey & Bansal, 2012). Due to the importance of air flow to the effectiveness of a freezing process, it has been the topic of numerous research efforts. In the 21st century, CFD is frequently employed to study air movement blast freezer applications (Hoang et al., 2020a,b; Hu et al., 1998; Jie & Jing, 2009; Kramer & Kristofersson, 2018; Nicolai et al., 2001; Xia & Sun, 2002). CFD models develop understanding of how air velocities and temperatures vary both in time and space and have facilitated the investigation of innovative new freezer designs, without the need for costly and time-consuming experimental trials. In addition, computer visualization gives direct insight into the process allowing for fast analysis of a range of problems. An example of such a study is outlined in Section 6.4 of this Chapter.

6.3.3

Insulation and management of moisture

Key considerations in the design of a blast freezer include the minimization of the infiltration of heat and moisture into the freezer space. It is very difficult to stop moisture entering refrigerated spaces where it not only adds to the cooling load (due its enthalpies of evaporation and fusion) but also causes frost and/or mold to build-up on the heat exchange surface of the evaporator, reducing its effectiveness. In blast freezers and cold stores, excessive moisture ingress can lead to the build-up of ice on the floor, which has the potential to cause injuries to staff working in the freezer/cold store. Moisture typically enters a refrigerated space, while the doors are open during product loading and unloading. Heat and moisture also come from the respiration of staff performing the loading/unloading (and in some cases food) and may also come from moisture evaporating from unwrapped product as it cools. As a consequence, most

130

Low-Temperature Processing of Food Products

evaporators have mechanisms for defrosting the heat exchange surface, typically by applying heat to melt any ice that has built-up. This may either be achieved externally (e.g., electrically) or by allowing some of the refrigerant exiting the compressor to bypass the condenser and expansion, and enter the evaporator as a hot vapor. Ideally, the thawed ice should be drained out of the refrigeration system to prevent it from returning to the evaporator coils once the defrost cycle has ended. Defrosting the evaporator adds to the heat load, but as it improves the performance of the evaporator, its use should result in greater efficiency overall. For batch-type freezers, measures may be taken to limit the amount of humid air entering the refrigerated space by using strip curtains and/or air curtains in the entryways (ASHRAE, 2014). Thermal insulation plays an essential role in restricting both heat and moisture ingress into the refrigerated space (Carson, 2013). Preferably, the structural elements of the building that houses the freezer or cold store will have in-built insulation, since this tends to provide greatest durability. Thermal insulation needs to have suitable moisture barriers incorporated not only to prevent moisture infiltration into the refrigerated space but also to prevent moisture from permeating the insulating material, thereby reducing its effectiveness. For freezers and cold stores, floor insulation is often necessary to prevent ice from forming in the soil under the floor, which may then cause the concrete floor to crack as it expands (often referred to as “frost heave”). Ceilings of refrigerated spaces should also be insulated.

6.4 6.4.1

Mathematical modeling of refrigeration processes Freezing time prediction

In practice, there are often large variations in the sizes and shapes of product items and so, coupled with wide ranges in air velocities between different regions of air blast freezers, predicting industrial freezing times with high levels of accuracy is very challenging (Cleland & Valentas, 1997). Accurate estimation of thermal properties and heat transfer coefficients, which are key model inputs, can also be difficult (Carson et al., 2016); Hoang et al., 2021). Hence, because of data uncertainties alone, freezing time estimates should be treated as being accurate to within about 15%e20% at best. Methods to predict freezing time in an air blast freezer (which can in turn be used to calculate time-variable heat loads) include analytical, empirical/semi-empirical, and numerical categories of solution (Carson & Larsen, 2011; Cleland, 1990; Pham & Evans, 2008). Analytical methods simplify the physical problem (e.g., by assuming regular geometry, constant thermophysical properties, and constant heat transfer coefficients) to obtain an exact solution. However, these simplifying assumptions are often not valid in practical settings, limiting the extent to which these analytical solutions can be applied, and as a result, they are mainly used for validating other modeling methods. Empirical formulas may be obtained by fitting curves to experimental data; however, these formulas tend to be highly inaccurate when applied outside the test conditions. Semi-empirical models are based on analytical models but incorporate parameters to account for nonideality, the values of which must be determined

Air blast freezing in the food industry

131

empirically. These can have wider ranges of applicability than purely empirical formulas, but the need, in many cases, to determine the value of the empirical parameters by experimentation is a drawback. Numerical modeling approaches are based on the discretization of space and time to convert the partial differential equations describing the physical mechanisms of heat transfer and fluid flow into a set of algebraic equations. In principle, they can produce very accurate results; in fact with recent advances in modeling techniques and computing power, modeling accuracy is often restricted more by the uncertainty in the model inputs than by the model itself (Datta, 2007; Pham & Evans, 2008). However, they have by far the greatest requirements of computational time and resources.

6.4.1.1

Analytical solutions

The most well-known analytical solution for predicting food freezing time is Plank’s method (Cleland, 1990; Pham & Evans, 2008). For one-dimensional geometries, Plank’s formula for calculating freezing time is:   Lf V R R2
þ tf ¼ AR Tf
Ta h 2k

(6.2)

The following simplifications were made in the derivation of Plank’s equation: phase change takes place at a single unique temperature, constant thermal properties are assumed, the freezing object has a regular shape (infinite slabs, infinite cylinders and spheres), there is zero sensible heat, and heat transfer coefficients are constant. As a result, predicted freezing times generated by Plank’s equation are frequently out by 50% (Wang et al., 2010).

6.4.1.2

Semi-empirical solutions

Most semi-empirical freezing time prediction methods were developed by modifying Plank’s equation (Eq. 6.2) in particular by taking into account the sensible heat effects and the nonuniform phase change temperature (Pham, 2014). The equivalent heat transfer dimensionality (E) is used to account for the effect of arbitrary shapes on freezing time as per Eq. (6.3): tir ¼

tslap E

(6.3)

where tir and tslab are the freezing time of multidimensional object and freezing time of an infinite slabs, respectively. Correlation equations used to calculate the freezing time of a one-dimensional object have been derived for three basic shapes (infinite slab, infinite cylinder, and sphere) with consideration for the variations in thermophysical properties and freezing conditions. A modified Plank’s equation presented by Pham (1986) is one of the most commonly used models:

132

Low-Temperature Processing of Food Products

tf ¼

   V DH1 DH2 R R2 þ þ As R DT1 DT2 h 2k

(6.4)

where DH1 and D T 1 are the specific enthalpy change and temperature driving force for precooling; DH2 and DT2 are the specific enthalpy change and temperature driving force for freezing and subcooling, determined from: DH1 ¼ rcu Tin
Tfm




DH2 ¼ rLf þ rcff Tfm
Tc DT1 ¼

(6.5)


Tin þ Tfm
Ta 2

DT2 ¼ Tfm
Ta

(6.6) (6.7) (6.8)

Tfm represents time-averaged product temperature during freezing and calculated from Eq. (6.9): Tfm
273:15 ¼ 1:8 þ 0:263ðTc
273:15Þ þ 0:105ðTa
273:15Þ

(6.9)

For a wide variety of operating conditions and materials, freezing time predictions by the method of Pham (1986) have been shown to be accurate to within 15% (Wang et al., 2010), and a large portion of the uncertainty was due to experimental error. A number of models have been presented to evaluate the equivalent heat transfer dimensionality of an object (Cleland et al., 1987a,b; Hossain et al., 1992a,b,c; Ilicali et al., 1999; Pham, 1991; Salvadori et al., 1996). For a three-dimensional irregular object, the most general equation is (Hossain et al., 1992b): E¼1 þ

1 þ 2=Bi 1 þ 2=Bi þ 2 þ 2b1 =Bi b2 þ 2b2 =Bi

b21

(6.10)

b1 ¼

Axs pR2

(6.11)

b2 ¼

3V 4pb1 R3

(6.12)

where AXS is the smallest cross-sectional containing the thermal center. If the volume of the object cannot be measured directly, then it can be estimated using the weight of the object divided by the effective density of the product.

6.4.1.3

Numerical solutions

Numerical methods can be classified as finite difference methods, finite element methods or finite volume methods. If formulated and implemented appropriately,

Air blast freezing in the food industry

133

they can be used for a variety of time-dependent boundary conditions, sophisticated object geometries, and more than one surface heat transfer mode. They also provide full temperatureetime histories rather than simply determining the freezing time, as is the case with Plank’s and Pham’s models. However, numerical approaches have several drawbacks, including their much greater complexity and implementation costs when compared to analytical and semi-empirical methods (particularly for computerprogram development, testing and data preparation, but to a lesser extent for computation time). The use of numerical methods to model food freezing processes began in the latter part of the 20th century as digital computing became more accessible to researchers (Cleland, 1990; Pham, 2006). Pham (1986) used numerical modeling to assess his modification of Plank’s equation for predicting freezing times for foods in general. Food Product Modeler, FPM, (MIRINZ) is a software tool developed in the 1990s by Pham and Lovatt based on a three-dimensional finite difference numerical method (Carson & Larsen, 2011). It has been employed by a variety of food processing engineers to improve the chillers and freezers design, as well as by researchers (e.g, Hoke et al., 2002). FPM is a modeling platform that can provide precise predictions of heat transfer within food products and comes complete with a library of thermophysical properties and heat transfer coefficient correlations. However, it is limited to applications involving a single product item or package and is not able to predict the air flow field in a tunnel. A common approach to deal with the nonlinearity effects of phase change during freezing is to employ the Enthalpy Kirchhoff approach that may be applied to food products in general (Fikiin, 1996; Scheerlinck et al., 2001). (Hoang et al., 2018) presented a simple numerical heat transfer model based on a one-dimensional finite difference solution for food chilling and freezing that accounts for variations in thermophysical properties and makes use of a shape factor to account for the heat transfer “dimensionality” of the object. Hoang’s method can be employed as a quick solution predicting with reasonable accuracy the temperature profile along the shortest axis of a three-dimensional object, which is typically of the greatest interest for food engineering investigations (Fikiin, 1996). Customized numerical methods have also been used to model the freezing process for specific foods, such as meat (Huan et al., 2003) bread (Hamdami et al., 2004; Santos et al., 2010), seafood (Dima et al., 2014; Nguyen et al., 2020), fruit and vegetables (Cevoli et al., 2018); Kiani & Sun, 2018), rice products (Lertamondeeraek & Jittanit, 2019), and others, as reviewed by (Fadiji et al., 2021).

6.4.2

Freezing process modeling example

To illustrate how freezing process simulations may be used to assist the design process, the following case study is overviewed. Hoang et al. (2020a,b) developed a CFD model for the forced air freezing of a tray of bulk-packed whole chickens and a tray of drumsticks enclosed in a polyliner within a carton in order to improve on predictions obtainable from FPM by accounting for air flow variations. The freezer considered was a Milmeq MRT where refrigerated air flows in parallel to the longest dimension of the

134

Low-Temperature Processing of Food Products

tray of chicken. The trays are on moving shelves, with two trays arranged one after the other on the shelf. The space between the trays ensures that all the trays are subjected to the same airflow pattern. Perforations in the shelves allow the cooling air to sweep across the tray’s bottom surface. The simulation was validated against experimental data and was subsequently used to estimate the effects of freezing conditions (e.g., initial product temperature, freezing air velocity, and temperature) on freezing time, as shown in Fig. 6.11 (for a tray of drumsticks) and Fig. 6.12 (for a tray of whole chickens). Predicted freezing times at different operating conditions were regressed to obtain correlation equations (Eq. 6.13 and Eq. 6.14) for drumsticks and whole chickens, respectively (Hoang, 2020):  
18
Ta
0:702 Tin
Ta

(6.13)

 
18
Ta
0:732 Tin
Ta

(6.14)

td ¼ 8:077u
0:189

tc ¼ 8:307u
0:233

where u is the freezing air velocity, (u varied from 1.0 to 4.5 m/s for whole chickens and from 1.0 to 4.3 m/s for drumsticks), Ta and Tin are the freezing air temperature and the initial temperature of chicken, respectively (Ta varied from
35 to
25 C, Tin varied from 0 to 10 C). Eqs. (6.13) and (6.14) can be employed to optimize a freezing tunnel design (e.g., product on shelves with cross-flowing air) for polylined chicken products by allowing the designers to assess the implications of varying air velocity and/or temperature on cooling time. This modeling approach may also be applied to other products and freezer designs. Figure 6.11 Freezing time of a tray of drumsticks at different freezing conditions (Hoang et al., 2020a).

Air blast freezing in the food industry

135

Figure 6.12 Freezing time of a tray of whole chickens at different freezing conditions (Hoang et al., 2020b).

6.4.3

Effect of packaging and packing arrangement on freezing rate

It is common practice to freeze meat, poultry or fish products in a liner bag within their packaging or wrapping (see also Section 6.5 of this Chapter). The packaging is used to minimize moisture loss in order to maintain the quality and appearance of food products. However, the packaging increases resistance to heat transfer since it prevents the refrigerated air from directly contacting the surface of the food products and hence extends the freezing time. This freezing time extension not only results from the insulating effect of the packaging material itself but also from air voids within the packaging. Hoang et al. (2020a) experimentally compared freezing times of a tray of chicken drumsticks packed in a regular arrangements both with and without a polyliner bag during air blast freezing. For the three air velocities tested, the drumsticks without the liner bag cooled substantially faster than those contained within the liner bag (Fig. 6.13). The seven-eighths cooling time, defined as the time required to reach seven eighths of the initial difference in temperature between the product and cooling air (SECT), in both cases were calculated for quantitative analysis of the effect of the polyliner bag, and results are summarized in Table 6.1. As the air velocity increased, the influence of the polyliner bag on freezing time also increased. At the highest air velocity (4.3 m/s), the SECT of polylined drumsticks was more than three times that of the unlined case. The slower cooling of polylined drumsticks is due to the insulating effect of the mostly stagnant air within the liner bag. Similarly, the effect of different packing methods on the freezing time of herring is shown in Table 6.2 (Sahin, 2004). Removing the lid of the box and allowing the air to sweep over the unwrapped product reduced the freezing time noticeably. The results in

136

Low-Temperature Processing of Food Products

Figure 6.13 Experimental temperatureetime histories of regularly packed drumsticks with and without the polyliner bag (Hoang et al., 2020a).

Table 6.1 Experimental SECT of bulk-packed drumsticks (Hoang et al., 2020a). With polyliner

Without polyliner

Air velocity, m/s

SECT, h

Experimental uncertainty, h

SECT, h

Experimental uncertainty, h

1.0 2.5 4.3

25.9 20.8 19.3

0.5 1.2 0.8

9.9 7.0 5.9

0.8 0.3 0.6

Table 6.2 The effect of packaging method on the freezing time of herring (Sahin, 2004). Packaging method

Freezing time, hours

Wood Wood Wood Wood Wood Wood

17.9 17.2 16.3 16.2 14.7 8.0

box, wrapped in paper, lid closed box, wrapped in folio, lid closed box, wrapped in paper, no lid box, wrapped in folio, no lid box, unwrapped, lid closed box, unwrapped, no lid

Table 6.2 also indicate that the major effect on freezing time was not the thermal properties of the packing material, but rather the fact that the polyliner prevents direct contact between freezing air and the product surfaces. Hoang et al. (2020a) examined how the packing structure of chicken drumsticks influenced freezing rates by comparing the temperatureetime histories of a tray of

Air blast freezing in the food industry

137

Figure 6.14 Photos of: (a) regularly arranged drumsticks, (b) randomly arranged drumsticks (Hoang et al., 2020a).

drumsticks packed regularly with a tray packed randomly (Fig. 6.14). Although the randomly arranged drumsticks tended to cool slightly faster on average than the regularly arranged drumsticks, the difference between the two packing arrangements was less than the measurement uncertainly for both low and high air velocities (Fig. 6.15). This suggests that when drumsticks are contained within the polyliner bag, the packing arrangement and alignment of the leg-bone had no significant impact on freezing time (Hoang et al., 2020a). Because the orientation of the drumsticks did not appear to effect freezing time, it was concluded that it is only the total fraction of air voids within the package rather than the size or shape of the air voids that is required as an input to a freezing process model.

6.5

Blast freezing and food quality

The quality of frozen food is affected significantly by the manner in which it is frozen and subsequently thawed (Bogh-Sorensen, 2006). Using air as a cooling medium means Figure 6.15 Experimental temperature-time histories of regularly packed and randomly packed drumsticks at different freezing air velocities (Hoang et al., 2020a).

138

Low-Temperature Processing of Food Products

that some moisture will inevitably evaporate during the freezing process, and for unpackaged foods, this can amount to more than 2% of the prefrozen weight. Even in packaged food evaporation may occur within air voids that may be present. The loss of moisture not only causes weight loss (which is undesirable for products sold by weight) but can cause significant shrinkage, wrinkling, and/or discoloration as well. As a general rule, retention of product quality is favored by higher rates of freezing as this tends to minimize the amount of evaporation loss. The freezing rate also affects the average size of ice crystals within the fooddthe faster the rate of freezing (or more specifically the degree of supercooling that is favored by fast freezing rates (Fadiji et al., 2021), the smaller the size of the crystals that form and the less likely the crystals are to rupture the tissue cells in the food, and the less water will be lost with consequent loss of quality upon thawing (Ngapo et al., 1999). Freezing rate may be defined in different ways, but the most common are in terms of (a) the rate of change of temperature in  C/hour, (b) the speed of progression of the freezing front in cm/hour (Table 6.3), or (c) rate of change of ice fraction within the product. Rapid or ultra-rapid freezing is generally desirable for maximizing food quality (Akbarian et al., 2016; De Kock et al., 1995; Gruji et al., 1993; Mowafy et al., 2020; Petrovi et al., 1993) and minimizing the effects dehydration such as freezer burn (Ashby et al., 1973), although the ideal rate does vary depending on the type of food involved, and in fact, some studies have suggested that ultra-rapid freezing does not necessarily improve significantly on normal freezing (Ban et al., 2016; Farouk et al., 2004). Increasing the freezing rate may be achieved by increasing the air velocity (bearing in mind the point of diminishing return discussed in Section 6.3) or by lowering the air temperature. Impingement freezing (Section 6.2) is an example of increasing the air velocity to increase freezing rate and is attractive for food products such as hamburger patties that are particularly susceptible to dehydration during freezing. The lower the air temperature, the less moisture it can absorb before saturation, and since a product cools the fastest at its surface, the slower the rate of evaporation from the surface. Fast freezing is also attractive from the point of view of maximizing processing volumes through a given blast freezer; however, increasing the air velocity and lowering the freezing temperature both come with increased energy cost. Reducing the air temperature too far may also have detrimental effects on quality for some food products, for example (Ban et al., 2016) observed that freezing temperatures belowd20 C reduced the quality of par-baked croissants. Table 6.3 Classification of freezing rates (Bogh-Sorensen, 2006). Characterization of the freezing process

Freezing rate (cm/h)

Very slow freezing Slow freezing Normal freezing Rapid freezing Ultra-rapid freezing

10

Air blast freezing in the food industry

6.6

139

Energy usage in air blast freezing

Air blast freezing is an energy-intensive process. For example, it was estimated that 8.1 GWh of electricity was consumed by air blast freezing in New Zealand in 2005 (Werner et al., 2005), which translates to 133 kWh/ton, making it the most energy intensive operation in the production of many frozen foods. In Denmark, the amount of product frozen in tunnels is approximately 1,500,000 tons annually with about 220 GWh of electrical energy consumption (Kramer & Kristofersson, 2018). According to a New Zealand Cold Storage Association survey, energy savings of up to 15% could be achieved for many air blast freezer sites, in particular by reducing the fan power if improved air flow designs are exploited (Werner et al., 2005). In a survey on energy efficiency of food refrigeration operations funded by the UK Government Department for Environment, Food and Rural Affairs, it was identified that blast freezing is an area where there was potential for 20%e30% energy saving to be achieved (James et al., 2009; James & James, 2014). This Section will discuss options for energy saving in air blast freezers including refrigeration system design, maintenance, and optimization of freezing tunnel operation.

6.6.1

System design

Sustainability Victoria (2009) produced a best practice guide to industrial refrigeration that highlighted the fact that since the design of each component in a refrigeration system affects other components of the system and therefore the efficiency of the overall system, a whole system approach to refrigeration system is likely to be needed to optimize energy efficiency throughout the refrigeration process. It is common for industrial refrigeration systems to be designed for the peak heat load conditions, which may only exist for less than 5% of the year (Carbon Trust, 2007). As a result, the systems commonly run at part load for considerable periods, which will be inefficient if the system was designed for optimized operation at peak loading. Therefore, a refrigeration system should be designed for maximum efficiency at the long-term average heat loading (i.e., over the entire year) while ensuring that peak demand may still be met. The increased use of variable speed drives on compressors and blast freezer fans in recent years has resulted in energy savings since they allow for effective load management.

6.6.2

Maintenance

In addition to energy optimization in system design, proper maintenance is also essential for energy efficiency. It has been recommended that refrigeration systems more than 10 years’ old should be considered for updating or replacement, since the incorporation of modern refrigeration technology may improve efficiencies by up to 30%e40% (Sustainability Victoria, 2009). For existing refrigeration systems, the operator should monitor and test overall performance on a regular basis to identify when efficiency has started to decline. Regular servicing of all components is recommended by most refrigeration equipment manufacturers.

140

Low-Temperature Processing of Food Products

Evaporators normally need to be defrosted regularly to ensure evaporator coils are free of ice and operate with maximum efficiency. Defrost should be initiated when a significant reduction in performance is detected and should stop once the evaporator fins are clear of ice. Condenser faults include blockages and fouling. Air or other noncondensable gases inside the refrigerant system will accumulate in the condenser and increase the condensing pressure (Welch & Wright, 2008). Not only will this result in greater energy consumption, but it will also cause more wear on mechanical parts if the system is required to operate at higher temperatures than it may have been designed for. Maintenance measures for condensers include keeping the coils clean and ensuring the fans and control systems are working correctly. For water-cooled condensers, maintenance of the water pump is also necessary, and fill membranes need to be cleaned regularly to ensure even distribution of water (Sustainability Victoria, 2009). Compressor faults are not always straightforward to identify but are often caused by internal blockages or some mechanical problem. Maintaining adequate oil levels, as well as regularly checking for leaks or worn bearings well help to keep the compressor operating efficiently (Sustainability Victoria, 2009).

6.6.3

Optimizing freezing tunnel operation

Energy efficiency in an air blast freezer can be improved by optimizing the operating conditions of the freezing tunnel. (Kramer & Kristofersson, 2018) investigated the potential energy saving opportunities in a batch freezing tunnel for meat, using laboratory tests and CFD simulations. In an industrial batch freezing process, the products may remain in the freezer until the next loading/unloading takes place, often with the fan at full speed the entire time. Two approaches to lower energy usage were presented: the first approach was to make full use of the available freezing time and allow the air velocity in the tunnel to vary over time (most likely being reduced); the second approach was to optimize the air distribution throughout the freezer. The results of the study showed that a reduction in air velocity from the reference value of 6.5 to 2.3 m/s, caused reduction in energy consumption of 86%, while the total freezing time remained within the 36 h allowed. The air distribution in the last pallet in line from the evaporator fans, which takes longest to freeze and determines the residence time of product in the tunnel, was improved by moving the pallets closer to the fan to allow more space behind the last pallet for airflow. Introducing baffles to both the top and bottom channels resulted in the best airflow and temperature distribution. By using baffles and reducing the flow to maintain the same freezing time as in the reference case (6.5 m/s air velocity and 30 h freezing time), a saving in energy of 68% was achieved. By further reducing the air flow and utilizing the total allowed freezing time, a saving of 93% was achieved. The study also suggested that a new fan concept (“EC fans”) is less expensive and more energy efficient than traditional fans and is also easier to control for speed (Kramer & Kristofersson, 2018). Alonso et al. (2011) simulated different airflow design arrangements and concluded that a thick ceiling with a vertical guide plate was better than the more common (thinner) false ceiling. This design reduced backflow through the evaporator and

Air blast freezing in the food industry

141

increased velocities over the products. Kolbe et al. (2004) used plywood and plastic sheeting to prevent air from by-passing the product in a freezing tunnel. Their baffling resulted in 15% reduction in freezing time and reduced fan energy use by 6%. The uniformity of the freezing times of the products was also improved significantly. Energy saving can also be achieved by improving the package design. Kemp and Chadderton (1992) surveyed different types of cardboard packaging used in batch blast freezers for beef cartons and found that changing the cardboard packaging could increase the freezing time by 8 h. Defraeye et al. (2014) investigated cooling rates and the system energy consumption of a standard shipping container and two new container designs (“Supervent” and “Ecopack”) in forced-convective cooling of citrus fruit by means of CFD. The new designs both showed improved cooling rates and cooling uniformity. The energy required to maintain airflow through the containers during the precooling process was also less for the new containers due to their lower aerodynamic resistance and lower cooling time, particularly in the case of the Ecopack.

6.7

Conclusion

Air blast freezing is a safe, versatile method of food preservation for which a variety of designs are commercially available. The design process for freezers is largely an exercise in ensuring that sufficient air velocity and temperature are distributed throughout the product space in the freezer, while keeping energy consumption at a minimum. Modeling can help with the design process particularly for the purposes of optimization. Food quality is generally enhanced by faster rates of freezing that may be achieved by high velocities and low air temperatures; however, faster freezing generally comes with increased energy costs and there may be practical temperature limits imposed by food quality constraints. To ensure energy efficient operation of blast freezers, it is necessary to have properly working defrost systems in place as well as regular maintenance program.

Nomenclature A c E H h k Lf R T t tc

heat transfer area (m2) specific heat capacity, J/kg/K equivalent heat transfer dimensionality enthalpy (J/kg) heat transfer coefficient (W/m2/K) thermal conductivity (W/m/K) latent heat of water solidification/fusion, (J/kg) characteristic dimension, (m) temperature, (K or  C) time (s) freezing time of a tray of whole chickens (hour)

142

td u V r

Low-Temperature Processing of Food Products

freezing time of a tray of drumsticks (hour) velocity (m/s) object volume (m3) density (kg/m3)

Subscripts a c f fm

air, ambient center initial freezing point mean freezing

References Akbarian, M., Koocheki, A., Mohebbi, M., & Milani, E. (2016). Rheological properties and bread quality of frozen sweet dough with added xanthan and different freezing rate. Journal of Food Science and Technology, 53(10), 3761e3769. Alonso, M. J., Andresen, T., Frydenlund, F., & Widell, K. N. (2011). Improvements of air flow distribution in a freezing tunnel using Airpak. Procedia Food Science, 1, 1231e1238. Ashby, B., James, G., & Kramer, A. (1973). Effects of freezing and packaging methods on freezer burn of hams in frozen storage. Journal of Food Science, 38(2), 258e260. ASHRAE. (2014). ASHRAE handbook refrigeration. Ban, C., Yoon, S., Han, J., Kim, S. O., Han, J. S., Lim, S., & Choi, Y. J. (2016). Effects of freezing rate and terminal freezing temperature on frozen croissant dough quality. LWT, 73, 219e225. Becker, B., & Fricke, B. (1999). Evaluation of semi-analytical/empirical freezing time estimation methods part II: Irregularly shaped food items. HVAC and Research, 5(2), 171e187. Becker, B., & Fricke, B. (2003). FREEZING operations. In B. Caballero (Ed.), Encyclopaedia of food sciences and nutrition (pp. 2712e2718). Academic Press. Boast, M. F. G. (2003). Blast and plate freezing. In B. Caballero (Ed.), Encyclopaedia of food sciences and nutrition (pp. 2718e2725). Academic Press. Bogh-Sorensen, L. (2006). Recommendations for the processing and handling of frozen foods. International Institute of Refrigeration. Bowater, F. (2001). Design of carton air blast freezing systems. Proceedings of the International Institute of RefrigerationeRapid Cooling of Food, Section, 2, 203e207. Briley, G. C. (2002). Blast freezing. ASHRAE Journal, 44(7), 99. Carbon Trust. (2007). Carbon trust networks project: Food and drink industry refrigeration efficiency initiative.guide 5: Site guidance topics. Reducing heat loads, reducing head pressure, improving part load performance, reducing power consumed by pumps and fans. https://iifiir.org/en/fridoc/guide-5-site-guidance-topics-reducing-heat-loads-reducing-head3889. Carson, J. K., & East, A. R. (2018). The cold chain in New ZealandeA review. International Journal of Refrigeration, 87, 185e192. Carson, J. K. (2011). Modelling chilling and freezing processe. In M. E. Larsen (Ed.), Refrigeration: Theory, technology and applications (pp. 239e266). Nova Science Publishers. Carson, J. K., Willix, J., & North, M. F. (2006). Measurements of heat transfer coefficients within convection ovens. Journal of Food Engineering, 72(3), 293e301.

Air blast freezing in the food industry

143

Carson, J. K., Wang, J., North, M. F., & Cleland, D. J. (2016). Effective thermal conductivity prediction of foods using composition and temperature data. Journal of Food Engineering, 175, 65e73. Carson, J. K. (2013). Refrigeration: Theory and applications. Bookboon (Ventus Publishing ApS). https://bookboon.com/en/refrigeration-theory-and-applications-ebook. Cengel, Y. A., & Ghajar, A. J. (2011). Heat and mass transfer: Fundamentals and applications. Cevoli, C., Fabbri, A., Tylewicz, U., & Rocculi, P. (2018). Finite element model to study the thawing of packed frozen vegetables as influenced by working environment temperature. Biosystems Engineering, 170, 1e11. Cleland, D. J., & Valentas, K. J. (1997). Prediction of freezing time and design of food freezers. Handbook of food engineering practice. Cleland, D. J., Cleland, A. C., & Earle, R. L. (1987a). Prediction of freezing and thawing times for multi-dimensional shapes by simple formulae Part 1: Regular shapes. International Journal of Refrigeration, 10(3), 156e164. Cleland, D. J., Cleland, A. C., & Earle, R. L. (1987b). Prediction of freezing and thawing times for multi-dimensional shapes by simple formulae part 2: Irregular shapes. International Journal of Refrigeration, 10(4), 234e240. Cleland, A. C. (1990). Food refrigeration processes: Analysis, design and simulation. Elsevier Applied Science. Datta, A. K. (2007). Porous media approaches to studying simultaneous heat and mass transfer in food processes. II: Property data and representative results. Journal of Food Engineering, 80(1), 96e110. De Kock, S., Minnaar, A., Berry, D., & Taylor, J. (1995). The effect of freezing rate on the quality of cellular and non-cellular par-cooked starchy convenience foods. LWT-Food Science and Technology, 28(1), 87e95. Defraeye, T., Lambrecht, R., Delele, M. A., Tsige, A. A., Opara, U. L., Cronjé, P., Verboven, P., & Nicolai, B. (2014). Forced-convective cooling of citrus fruit: Cooling conditions and energy consumption in relation to package design. Journal of Food Engineering, 121, 118e127. https://doi.org/10.1016/j.jfoodeng.2013.08.021 Dempsey, P., & Bansal, P. (2012). The art of air blast freezing: Design and efficiency considerations. Applied Thermal Engineering, 41, 71e83. Dima, J. B., Santos, M. V., Baron, P. J., Califano, A., & Zaritzky, N. E. (2014). Experimental study and numerical modeling of the freezing process of marine products. Food and Bioproducts Processing, 92(1), 54e66. Fadiji, T., Ashtiani, S.-H. M., Onwude, D. I., Li, Z., & Opara, U. L. (2021). Finite element method for freezing and thawing industrial food processes. Foods, 10(4), 869. Farouk, M., Wieliczko, K., & Merts, I. (2004). Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Science, 66(1), 171e179. Fikiin, K. A. (1996). Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation. International Journal of Refrigeration, 19(2), 132e140. Grujic, R., Petrovic, L., Pikula, B., & Amidzic, L. (1993). Definition of the optimum freezing rated1. Investigation of structure and ultrastructure of beef M. longissimus dorsi frozen at different freezing rates. Meat Science, 33(3), 301e318. Hamdami, N., Monteau, J.-Y., & Le Bail, A. (2004). Simulation of coupled heat and mass transfer during freezing of a porous humid matrix. International Journal of Refrigeration, 27(6), 595e603.

144

Low-Temperature Processing of Food Products

Harris, M. B., Carson, J. K., Willix, J., & Lovatt, S. J. (2004). Local surface heat transfer coefficients on a model lamb carcass. Journal of Food Engineering, 61(3), 421e429. Hoang, D. K., Lovatt, S. J., & Carson, J. K. (2018). A quick, reliable solution for modelling cheese chilling process. Hoang, D. K., Lovatt, S. J., Olatunji, J. R., & Carson, J. K. (2020a). Experimental measurement and numerical modelling of cooling rates of bulk-packed chicken drumsticks during forcedair freezing. International Journal of Refrigeration, 114, 165e174. Hoang, D. K., Lovatt, S. J., Olatunji, J. R., & Carson, J. K. (2020b). Validated numerical model of heat transfer in the forced air freezing of bulk packed whole chickens. International Journal of Refrigeration, 118, 93e103. Hoang, D. K. (2020). Modelling heat transfer during chilling and freezing of packaged foods in industrial refrigeration facilities. The University of Waikato. Hoang, D. K., Lovatt, S. J., Olatunji, J. R., & Carson, J. K. (2021). Improved prediction of thermal properties of refrigerated foods. Journal of Food Engineering, 297, 110485. Hoke, K., Houska, M., Kyhos, K., & Landfeld, A. (2002). Use of a computer program for parameter sensitivity studies during thawing of foods. Journal of Food Engineering, 52(3), 219e225. Hossain, M. M., Cleland, D. J., & Cleland, A. C. (1992a). Prediction of freezing and thawing times for foods of regular multi-dimensional shape by using an analytically derived geometric factor. International Journal of Refrigeration, 15(4), 227e234. Hossain, M. M., Cleland, D. J., & Cleland, A. C. (1992b). Prediction of freezing and thawing times for foods of three-dimensional irregular shape by using a semi-analytical geometric factor. International Journal of Refrigeration, 15(4), 241e246. Hossain, M. M., Cleland, D. J., & Cleland, A. C. (1992c). Prediction of freezing and thawing times for foods of two-dimensional irregular shape by using a semi-analytical geometric factor. International Journal of Refrigeration, 15(4), 235e240. Hu, Z.-h., Sun, D.-W., & Bryan, J. (1998). Modelling of an experimental air-blast freezer using CFD code. In Advance in refrigeration system, food technologies and cold chain (pp. 395e400). Paris, France: International Institute of Refrigeration. Huan, Z., He, S., & Ma, Y. (2003). Numerical simulation and analysis for quick-frozen food processing. Journal of Food Engineering, 60(3), 267e273. Ilicali, C., Teik, T. H., & Shian, L. P. (1999). Improved formulations of shape factors for the freezing and thawing time prediction of foods. LWT-Food Science and Technology, 32(5), 312e315. James, S., & James, C. (2014). Chilling and freezing of foods. Food Processing: Principles and Applications, 79e105. James, S., Swain, M., Brown, T., Evans, J., Tassou, S., Ge, Y., Eames, I., Missenden, J., Maidment, G., & Baglee, D. (2009). Improving the energy efficiency of food refrigeration operations. Proceedings of the Institute of Refrigeration. Jie, L., & Jing, X. (2009). Numerical simulation of freezing time of shelled shrimps in an air blast freezer and experimental verification. Transactions of the Chinese Society of Agricultural Engineering, 4. Kemp, R. M., & Chadderton, T. (1992). Blasting ahead with cartoned beef. Refrig- eration and Energy Section. MIRINZ Conference Proceedings. Kiani, H., & Sun, D.-W. (2018). Numerical simulation of heat transfer and phase change during freezing of potatoes with different shapes at the presence or absence of ultrasound irradiation. Heat and Mass Transfer, 54(3), 885e894. Kolbe, E., Ling, Q., & Wheeler, G. (2004). Conserving energy in blast freezers using variable frequency drives. In National industrial energy technology conference.

Air blast freezing in the food industry

145

Kramer, K. R., & Kristofersson, J. (2018). Energy optimization of batch freezing tunnel for meat. In 13th IIR gustav lorentzen conference, valencia. Lertamondeeraek, K., & Jittanit, W. (2019). The freezing of rice products in box containers: Temperature profile prediction, model validation and physical characteristics. International Journal of Food Engineering, 15(9). MIRINZ. Food product modeller. http://mirinz.org.nz/prod/foodprodmod.asp. Mowafy, S. G., Sabbah, M. A., Mostafa, Y. S., & Elansari, A. M. (2020). Effect of freezing rate on the quality properties of Medjool dates at the tamr stage. Journal of Food Processing and Preservation, 44(12), e14938. Ngapo, T., Babare, I., Reynolds, J., & Mawson, R. (1999). Freezing and thawing rate effects on drip loss from samples of pork. Meat Science, 53(3), 149e158. Nguyen, T., Do, Q., Vo, C., & Nguyen, T. (2020). A numerical approach for fish fillet modeling during freezing process _ case study from Vietnamese catfish fillets. Journal of Physics: Conference Series, 1457, Article 012018. Nicolai, B., Verboven, P., Scheerlinck, N., Hoang, M., & Haddish, N. (2001). Modelling of cooling and freezing operations. In International conference on rapid cooling of food, date: 2001/03/28-2001/03/30. Bristol, UK: Location. Pearson, S. F. (2003). Refrigerants past, present and future. In The international congress of refrigeration in Washington DC USA [cited July 22, 2008]. Petrovic, L., Grujic, R., & Petrovic, M. (1993). Definition of the optimal freezing rated2. Investigation of the physico-chemical properties of beef M. longissimus dorsi frozen at different freezing rates. Meat Science, 33(3), 319e331. Pham, Q. T. (2008). Modelling of freezing processes. In J. A. Evans (Ed.), Frozen food science and technology. Blackwell Publishing. Pham, Q. T. (1986). Simplified equation for predicting the freezing time of foodstuffs. International Journal of Food Science and Technology, 21(2), 209e219. Pham, Q. T. (1991). Shape factors for the freezing time of ellipses and ellipsoids. Journal of Food Engineering, 13(3), 159e170. Pham, Q. T. (2006). Modelling heat and mass transfer in frozen foods: A review. International Journal of Refrigeration, 29(6), 876e888. Pham, Q. T. (2014). Food freezing and thawing calculations. Springer. Research, & Markets. (2020). Frozen food market - forecast (2020 - 2025), research and markets report ID: 3501390. https://www.researchandmarkets.com/reports/3501390/frozen-foodmarket-forecast-2020-2025?utm_source¼GNOM&utm_medium¼PressRelease&utm_code ¼lgq2cv&utm_campaign¼1453152þ-þWorldwideþFrozenþFoodþIndustryþtoþ2025þ -þIncreasingþDemandþforþPreservativeþFreeþFood&utm_exec¼jamu273prd. Sahin, N. (2004). Blast freezing application in conventional room. https://www.friterm.com/ Uploads/Document/31c8dc82-1272-4abb-8668-eafc88cfa7c4.pdf?v-636865502600000000. Salvadori, V., Mascheroni, R., & De Michelis, A. (1996). Freezing of strawberry pulp in large containers: Experimental determination and prediction of freezing times. International Journal of Refrigeration, 19(2), 87e94. Santos, M. V., Vampa, V., Califano, A., & Zaritzky, N. (2010). Numerical simulations of chilling and freezing processes applied to bakery products in irregularly 3D geometries. Journal of Food Engineering, 100(1), 32e42. Scheerlinck, N., Verboven, P., Fikiin, K., De Baerdemaeker, J., & Nicolaï, B. (2001). Finite element computation of unsteady phase change heat transfer during freezing or thawing of food using a combined enthalpy and Kirchhoff transform method. Transactions of the ASAE, 44(2), 429.

146

Low-Temperature Processing of Food Products

Sustainability Victoria. (2009). Energy efficiency best practice guide industrial refrigeration. Melbourne, Australia: State Government, Sustainability Victoria. Wang, J., Pham, Q. T., & Cleland, D. J. (2010). Freezing, thawing, and chilling of foods. In mathematical modeling of food processing. In M. M. Farid (Ed.), Mathematical modeling of food processing. CRC Press. Welch, J., & Wright, J. (2008). Unique design considerations for large evaporative ammonia condenser installations IIR Gustav Lorentzen confer- ence on Natural Working Fluids. Werner, S., Vaino, F., & Cleland, D. (2005). Survey of energy use by the New Zealand cold storage industry. Palmerston North: Massey University. Willix, J., Harris, M. B., & Carson, J. K. (2006). Local surface heat transfer coefficients on a model beef side. Journal of Food Engineering, 74(4), 561e567. Xia, B., & Sun, D.-W. (2002). Applications of computational fluid dynamics (CFD) in the food industry: A review. Computers and Electronics in Agriculture, 34(1e3), 5e24.

Spray freezing and single/doublecontact freezing systems

7

€der-Taze 1 , Seid Reza Falsafi 2 and Hadis Rostamabadi 3 Bengi Hakgu 1 Department of Food Engineering, Faculty of Engineering, Usak University, Usak, Turkey; 2 Safiabad Agricultural Research and Education and Natural Resources Center, Agricultural Research, Education and Extension Organization (AREEO), Dezful, Iran; 3Department of Food Science and Technology, School of Nutrition and Food Science, Nutrition and Food Security Research Center, Isfahan University of Medical Sciences, Isfahan, Iran

7.1

Introduction

Foods are highly perishable products unless they are appropriately processed. Hence, the shelf life of food materials is mostly limited. Freezing is one of the best-known processing methods for extending the life span of a food product. Among freezing techniques, spray drying is the most widely applied one to obtain powder form of food materials. It includes the application of heat to atomized food material to convert the fluid food into a powdered form (Abdul Mudalip et al., 2021). Spray freezing is a proper technique for extending the shelf life of food substances, which are sensitive to thermal degradation. However, this technique has its own merits and demerits (MacLeod et al., 2006). Spray freeze drying (SFD) is a three-step process, which includes (i) pulverization of the liquid material, (ii) freezing of the small droplets, and (iii) lyophilization (Vishali et al., 2019). SFD can be further divided into subgroups depending on the process variables encountered; spray freezing and freeze-drying. Formation and solidification of micronized particles are considered in spray freezing stage of SFD (Al-Hakim et al., 2006). Therefore, spray freezing is also defined as production of solid droplets by spraying liquid into a cold fluid (Hindmarsh et al., 2007). The principles of spray freezing and different approaches are explained in the following sections.

7.2

Principles and mechanism of spray freezing

Stresses occur during freezing and drying steps of freeze drying process resulting in the instability of high-value components of the food materials (Yu et al., 2006). Instability originates from the formation of ice crystals, phase separation, and changes in concentration and pH value (Yu et al., 2002). Spray freezing offers a fast freezing immediately after atomization of the liquid, eliminating the degradation and loss of biologically active substances (Dutta et al., 2018).

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00011-4 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

148

Low-Temperature Processing of Food Products

Firstly, a feed solution is forced to pass through a fine-opening nozzle. This yields the formation of micron-sized liquid droplets, which then freeze when they come into contact with the cold fluid. New microstructures are formed during spray freezing. Hence, this process is also introduced as a “particle engineering process” (Hu et al., 2004). These microstructures enhance the heat and mass transfer rates by increasing the surface area (Gwie et al., 2006). Small droplets collide with the cold fluid, which is either a cold gas and/or liquid cryogenic, and are expose to fast freezing taking less than 2 s (Sebasti~ao et al., 2019b). The freezing process comprised some different stages: (i) supercooling step, (ii) ice nucleation, (iii) rapid crystal growth, (iv) maturation, and (v) cooling of the ice crystals to cold fluid temperature (Al-Hakim et al., 2006; Ishwarya et al., 2015; MacLeod et al., 2006; Wanning et al., 2015). It was reported that the freezing rate and degree of supercooling determine the surface properties of the obtained powder (Hindmarsh et al., 2007; Sebasti~ao et al., 2019a). As it was stated by Hindmarsh et al. (2007), some techno-functional properties of powders, such as stickiness, flow properties, and solubility characteristics, are affected by the repositioning of the food component on the surface of the powder. Therefore, atomization and spray freezing parameters are crucial to be taken into account to adjust the desired powder characteristics.

7.2.1

Spray parameters

There are various parameters affecting the spray freezing system (Fig. 7.1) including nozzle configuration, solution parameters, stirring, liquid cryogen, freezing rate, or temperature (Adali et al., 2020). Atomization step controls the particle size distribution in spray freezing (Ishwarya et al., 2015; Dutta et al., 2018; Vishali et al., 2019). Particle size obtained in spraying is highly correlated to the viscosity of the fluid, applied pressure (energy) in the nozzle, flow rate of the feed, and even surface tension (Vishali et al., 2019). As the viscosity increases, bigger droplets are obtained. Likewise, particles get bigger with the increase of flow rate. On the other hand, atomization pressure is inversely related to the particle size. Application of high energies results in smaller droplets. Furthermore, higher surface tension should be overcome to prevent the collision of small particles to build bigger ones. The use of emulsifiers and energy input helps obtain small-sized and uniform droplets by reducing the surface tension (Dutta et al., 2018). Surfactants, on the other hand, have been shown to have a negative impact on long-term stability of protein materials (Engstrom et al., 2007). Another aspect that affects particle size distribution is the spray conditions (Ishwarya et al., 2015). There are different types of atomizers used in spraying, namely, hydraulic (one-fluid), pneumatic (two-fluid, three-fluid, or four-fluid), and ultrasonic nozzles (Ishwarya et al., 2015; Vishali et al., 2019). Selection of the atomizer determines both the process economics and particle characteristics. Hydraulic nozzles use pressure to pass the feed solution through an orifice. Some process factors such as pressure, viscosity, and flow rate of the liquid change the size of atomized particles. The size of the droplets

Spray freezing and single/double-contact freezing systems

149

Figure 7.1 Critical parameters affecting the atomization, spray freezing, and freeze drying steps. Adapted from Adali et al. (2020).

shows variations in the range of 120e250 mm based on the processing factors. Conversion of pressure into kinetic energy fulfills the needed energy for this process (Adali et al., 2020). On the other hand, compressed gas flow supplies the energy for pneumatic nozzles. A shear field is created when the feed solution interacts with the gas flow, which ensures the formation of different-sized particles. The most common form of pneumatic nozzles is two-fluid atomizers, where both the liquid and the gas flow are fed into the system. These types of atomizers are indicated to be effective, especially for viscous fluids in food applications (Wanning et al., 2015). Other configurations involve two liquid feeds and one or two gas flows. These systems are known as three-liquid and four-liquid nozzles, respectively (Adali et al., 2020). Pneumatic nozzles allow the formation of fine droplets in the range of 5e100 mm, whereas they adversely affect the cooling rate due to the entry of warm gas into the freezing system. Similarly, particle size is also well-regulated by ultrasonic nozzles. They are able to create fine, homogeneous droplets with a diameter of less than 100 mm (Jafari et al., 2021). Droplet size can be controlled by feed flow rate and the frequency. Necessary energy is supplied from high-frequency electrical signals that turn into mechanical energy via piezoelectric transducers. Hence, ultrasonic vibrations are used for atomization purposes (Adali et al., 2020). Nevertheless, only fluids having low viscosity are suitable for spraying by ultrasonic-assisted atomizers (Jafari et al., 2021).

150

Low-Temperature Processing of Food Products

Atomization is the critical step in spray freezing process, since it decides on the particle size. Particle size in turn affects the freezing rate and also powder characteristics. Increasing the specific surface area enhances the freezing rate and consequently the removal of latent heat of fusion (Volkert et al., 2008). Thereby, careful selection of the spraying method as well as consideration of other process factors are the key factors for achieving food powders of desired quality.

7.3

Different spray freezing approaches

Spray freezing is sub-divided into three categories (Fig. 7.2): (i) spray freezing into vapor (SFV), (ii) spray freezing into vapor over liquid (SFV/L), and (iii) spray freezing into liquid (SFL) (Ishwarya et al., 2015; Dutta et al., 2018). This classification is done according to the physical state of the cryogen. Here, cryogen type, quantity, and the way the feed solution is exposed to cryogen have substantial importance concerning the freezing rate (Ishwarya et al., 2015). The cryogen might be liquid or gas N2, liquid argon, hydrofluoroether, pentane, propane, ethane, or carbon dioxide (Ishwarya et al., 2015; Adali, 2020). Among them, the most preferred one is N2 due to its inert nature, low boiling point (LBP), and viscosity changes depending on the pressure and the temperature (Vishali et al., 2019). Spray freezing approaches offer different modes of exposure to cryogen. It might occur as the direct contact of sprayed particles with the cold gas, cold vapor followed by the liquid cryogen, or the liquid cryogen. Different spray freezing approaches based on the mode of exposure to cryogen are explained in the following sections.

Figure 7.2 Illustration of different spray freezing techniques. Spray freezing into vapor over liquid (left), spray freezing into liquid (middle), and spray freezing into vapor (right). Adapted from Adali et al. (2020).

Spray freezing and single/double-contact freezing systems

7.3.1

151

Spray freezing into vapor

The equipment and a schematic representation of a spray freezing into vapor system are given in Fig. 7.3. As it is seen from the figure, the spray is encountered with the cold gas, which is mostly N2, immediately after atomization of the feed solution. Afterward, a heat transfer occurs between the droplets and the gas (Ishwarya et al., 2015). Hence, the temperature of small droplets is dramatically decreased to sub-freezing point (Volkert et al., 2008). This results in the formation of ice crystals and finally frozen droplets. A snow-like powder is obtained after the frozen spray, and the gas is separated from each other. This system enables better preservation of aroma constituents of foods and to obtain fine frozen particles and free-flowing powders as compared to the traditional freeze drying process (Adali et al., 2020). However, the separation and collection of the frozen particles are the key challenges in this line. Moreover, freezing and nucleation rates are the factors that specify the microstructure of the frozen particles (Volkert et al., 2008). Nevertheless, the lowest cooling rate occurs in the SFV system among the others. It was reported that the rate of supercooling influences the powder characteristics (Hindmarsh et al., 2007).

7.3.2

Spray freezing into vapor over liquid

The only difference between SFV and SFV/L is the distance between the nozzle and the cryogenic liquid (Vishali et al., 2019). The nozzle is placed at a small distance above the level of liquid refrigerant in this system (Ishwarya et al., 2015; Dutta et al., 2018).

Figure 7.3 Spray-freezing into vapor: photograph of the equipment (left) and schematic of chamber with spray and drying gas inlets (right) (ASFD: atmospheric spray freeze drying). Adapted from Sebasti~ao et al. (2017).

152

Low-Temperature Processing of Food Products

As can be seen in Fig. 7.2, the feed liquid is atomized into a cold gas atmosphere at temperatures greater than the freezing point of the solution. Sprayed particles are then precipitated onto the cryogenic liquid via passing through the vapor. Thereafter, supercooling of the droplets and complete freezing take place when the particles come into contact with the refrigerant (Wanning et al., 2015). At the end of the process, frozen droplets should be separated from the cryogen either by sieving or evaporation of the refrigerant. In the SFV/L system, spraying parameters have a vital importance concerning the quality of the end-products. For instance, protein aggregation may occur due to the large gaseliquid interface created by ambient gas during the atomization step (Engstrom et al., 2007; Ishwarya et al., 2015; Yu et al., 2006). Limiting the specific surface area by increasing the particle size may reduce the gaseliquid interface in spray freezing processes. However, reducing the surface area was shown to be related to undesired changes in the conformation of various proteins and their biological activity (Engstrom et al., 2007). Moreover, the main problem associated with this technique is the adsorption of proteins at the iceeliquid interface, which then gives rise to the instability of the biological materials (Ishwarya et al., 2015; Vishali et al., 2019). It is noteworthy that the large iceeliquid interface appears during rapid cooling stage of SFV/L.

7.3.3

Spray freezing into liquid

Spray freezing into liquid process has emerged to overcome the disadvantages of SFV and SFV/L (Engstrom et al., 2007). It has some superior characteristics over other spray freezing techniques, such as decreased exposure to gaseliquid interface, enhanced freezing rate and also specific surface area, low weight loss, better preservation of biological properties of the proteins, ease of operation and, simple and smallsized equipment (Engstrom et al., 2007; Zheng et al., 2022). As demonstrated in Fig. 7.2, in an SFL system, exposure to gaseliquid interface is minimized by submerging the nozzle into the cryogenic liquid. Hence, the feed solution is immediately sprayed into the liquid phase (Dutta et al., 2018; Engstrom et al., 2007; Rogers et al., 2002). A friction, which yields micronized particles, occurs during the travel of the droplets through the liquid (Ishwarya et al., 2015). Instant freezing starts right after the formation of small droplets. Agglomeration of the powdered particles can be prevented by agitating the cryogen using a stirrer during the SFL process (Ishwarya et al., 2015). The extended specific surface area achieved by very small droplets improves the heat transfer between atomized particles and the cryogen. Thereby, an ultrarapid freezing rate is obtained in this system. This contributes to the prevention of phase separation (Ishwarya et al., 2015). Moreover, it was noted that droplets are exposed to a gaseliquid interface for only 2 ms in SFL process. This gaseliquid interface builds up due to the evaporation of cryogenic liquid when the warm feed solution collides with the cold cryogen. This is known as “Leidenfrost Effect,” which also results in the loss of some cryogen (Engstrom et al., 2007). However, “Leidenfrost Effect” has an insignificant impact on the biological stability of the components.

Spray freezing and single/double-contact freezing systems

153

New microstructures generated by SFL provide an opportunity for the stabilization of biological materials (Gwie et al., 2006). Particles produced in the system were reported to have a narrow size distribution with a low bulk density and a nanoporous structure, which enhances the stability and dissolution ability of the product (Engstrom et al., 2007; Pascual-Pineda et al., 2019; Yu et al., 2004, 2006). Therefore, the technique has recently drawn attention of experts from the food sector. However, the cost and the type of the refrigerant used in the system might be a consideration for food industry. The refrigerant needs to be food-grade and noncontaminating in order to be utilized for food applications as stated by Gwie et al. (2006). Furthermore, the development of industrial-scale equipment and technology still urges (Zheng et al., 2022).

7.4

Single/double-contact freezing

Relying on the contact between the freezing medium and food material, the freezing units can be classified into two main groups that is, direct and indirect contact freezers. Regarding direct contact freezing systems, the food material to be frozen is entirely enclosed by the freezing environment (or refrigerant), maximizing the effectiveness of the heat transfer process. In these types of freezers, there is no barrier system between the food material and the environment used for the freezing process (Desrosier, 2012) (Fig. 7.4). Single/double-contact freezing process is considered as a mass production process with a comparatively high freezing rate (however, cryogenic refrigeration and individual quick freezing will yield yet higher freezing rates). Generally, contact freezers are extensively employed in the food industry to generate slabs of frozen foods, for example, mashed vegetables or fish filets (Fennema & Powrie, 1964; Toledo et al., 2007). Two groups of contact freezing systems can be defined; batch and continuous units. In the case of batch freezing systems, the food materials are typically frozen from both sides (Fig. 7.5) (double contact freezing), via plane heat exchangers applying a certain pressure against the food sample (Tian, Li, et al., 2020, Tian, Zhu, & Sun, 2020). On the other hand, the continuous units are generally operated using a thin food material on a refrigerated surface and via scraping it off following the freezing process. In this line, two main concepts have been developed, that is linear belt design and rotating drum design (Marizy et al., 1998). In batch contact freezing systems, the food material is typically installed in a cardboard box comprising a pouch or a plastic film. The product can ultimately be connected directly to the refrigerated surface layer, nevertheless, this can be problematic when separating the frozen food from this layer at the end of the freezing. The rotating drum freezing units (Fig. 7.6) have been designed in the food industry to freeze viscous/liquid products or even solid food materials (e.g., fish filets). In these freezers, the food materials are directly applied against a rotating metallic drum refrigerated from the inside using a brine, for instance. This mechanism has been modeled

154

Low-Temperature Processing of Food Products

Figure 7.4 Real image of a single-contact freezing system. Adapted from https://dsidantech.com/solutions/plate-freezing.

Refrigerated plates Circulating refrigerant

Food material

Figure 7.5 A batch system in a contact freezer.

by Marizy et al. (1998). The food sample with a thickness from 1 mm to a few cm is applied on one side and is separated following rotation. Machinery application of the linear belt units (Fig. 7.7) has been recently developed/proposed on the market, whereas the rotating units have been utilized for many years to freeze liquid/semi-liquid food products. A linear continuous contact freezing system comprises a refrigerated surface covered by a plastic film or a food product. In the former, the food materials are applied onto the film and frozen upon

Spray freezing and single/double-contact freezing systems

155

Scraper Rotating satellite

Frozen flakes

Layer of food material

Brine sprayer

Figure 7.6 A rotating drum design (up) and equipment (down) in contact freezers for liquid/ viscous food materials. Source: https://dohmeyer.com/products/equipment-4/cryoroll-for-iqf-foodstuffs-2/. Food material Plastic film

Refrigerated surface

Figure 7.7 A linear design in contact freezers equipped with a sliding plastic film.

translation onto the refrigerated surface. Following the freezing process, the frozen food sample is separated from the film that is discarded. These types of freezing processes are not very effective due to thermal contact resistance between the refrigerated surface and the food material. The plastic layer covering the refrigerated surface represents the first thermal resistance during the process. Furthermore, the uncontrollable deformation of the food materials can cause the apparition of an air film between the plastic film and the cold surface (Shiloh & Sideman, 1967). To improve the efficiency of the freezing mechanism, refrigerated air is typically applied on the top of the product to be frozen. The contact freezing process remains very handy in attaining superficial freezing of the food materials, averting the dehydration phenomenon upon conventional freezing.

156

Low-Temperature Processing of Food Products

The single-side contact freezers are less effective as compared to double-side designs. Nonetheless, a continuous freezing mechanism is extremely necessary in food industry applications for productivity and lowering contamination by handling. Vertical and horizontal contact freezers are also other types of freezers based on single- and/or double-contact freezing processes. The vertical systems are appropriate candidates for freezing a large volume of food materials in solid or liquid states, ensuring the food quality/safety and preserving the taste, texture, and nutritional value of the frozen product. Single-/double-contact freezers are ideal for products, for example, vegetables, fruits, fish, shellfish, meat, poultry, liquids, by-products, and even offal for pet food. In a vertical plate freezer, the freezing process is applied via a double contact system, and the approach is faster compared to the traditional blast freezers (Zaritzky, 2012). Horizontal plate freezing is among the proper methods for freezing food materials in boxes, trays, cartons, or frames. The approach involves a very fast freezing process, which sustains the quality of food samples and guarantees food safety. Horizontal plate freezers are operated using double and direct contact freezing systems, offering a fast freezing process of high product yield and quality. The horizontal plate freezers are particularly engineered to fit the capacity in terms of space on the production site and preferred batch weight/size (Goerlitz, 1994).

7.5 7.5.1

Different single/double-contact freezers Immersion freezers

Immersion freezers are one of the important freezing approaches, which utilize the direct contact system. An immersion freezer is contained in a stainless steel tunnel freezer with an immersion pan, in which a conveyor belt travels through the bath. Varying rate drive motors offer the freezing equipment proper flexibility in achieving various freezing times, capacities, temperatures, and even product freezing uniformity (Zarkadas & Mitrakas, 1999). Benefits of the direct immersion freezers includes: ⁃ Decreasing the resistance to heat transfer due to the intimate contact between the food/package and refrigerant. ⁃ Rapid freezing of irregularly shaped food products, for example, loose shrimp, mushrooms, etc. ⁃ Appropriate for foods sensitive to oxidation because of minimizing their contact with air upon the freezing process (George, 1993).

As the refrigerant comes in contact with unpackaged food material in this method, it must be nontoxic, tasteless, odorless, and colorless. Generally, the refrigerants employed in immersion freezing systems are categorized into two main groups (Chourot et al., 2003; Islam et al., 2014). Liquids of low freezing point (LFP), which are chilled by indirect contact with another refrigerant. The LFP liquids, which have been utilized for nonpackaged food, comprise solutions of sugars, NaCl, and even

Spray freezing and single/double-contact freezing systems

157

glycerol. The LFP solutions must be used at adequate concentrations to be effective at 18 C or lower. NaCl, for example, can be applicable at a concentration of 21% w/v. However, NaCl cannot be employed for unpackaged food, which should not become salty (particularly fish or fish products). Cryogenic liquids are liquefied gases with LBP (e.g., compressed liquefied N2 of the boiling point 196 C or CO2 of the boiling point 79 C) that give their cooling influence to their own evaporation. Nowadays, liquid N2 is the most commonly utilized cryogenic liquid in immersion freezing of food products (e.g., vegetables, pasta, and other foods). Food materials are fed by a shuttle/vibratory conveyor into the freezing tunnel. Then, they fall by gravity into the liquid N2 bath (boiling temperature at atmospheric pressure of 320 F ( 195 C), and, within a few seconds, their superficial parts are hard frozen. The food sample’s surface is instantly frozen, and by action of an open mesh conveyor belt, the frozen product is transferred from the cryogenic bath to a mechanical freezer, (in the form of a belt, spiral, tunnel, or even spray freezer), for product freezing temperature equilibrium (for attaining the frozen temperatures inside the food, an equilibrium time is required typically at the last step of the freezing process) (Levin et al., 1983; Qian et al., 2018). The application of multiple fans and/or spray systems in these freezers can improve the heat transfer mechanism and equipment efficiency. It is noteworthy that the liquid N2 level is automatically adjusted based on the food sample ingredients, water content, thickness, and so on (Resch et al., 2011). Freezing of food products via liquid N2 will create cold N2 gas due to the heat exchanges that occur between the food sample and the boiling liquid N2. In the equilibrium chamber, the generated cold N2 gas is then blasted on the food material, allowing the sample to continue to be frozen entirely. Convection and conduction are two heat transfer methods utilized in these freezing systems (Diao et al., 2021). The space needed for this single and integrated freezing unit is very small compared to other freezing systems. A continuous cryogenic liquid feeding system and storage tanks are key parts to supply the liquid N2 to the freezing processing line. To improve the efficiency of the freezing system, the sensible heat of the liquid N2 transformed into gas can be recycled back to the freezer and blown at high speed on the food sample. A sub-cooled closed loop system or an ammonia cooling system can be applied as the refrigeration media in secondary freezer units. The application of liquid N2 in an immersion freezing system offers manifold advantages (Cheng et al., 2017; Li et al., 2018; Rahman & Velez-Ruiz, 2007), including: , No need for a primary refrigerant, as the cold temperature originates from the evaporation of liquid N2 , Slow boiling at 196 C that offers a great driving force for heat transfer , Potential of encompassing all portion of irregularly shaped foods, thus decreasing resistance to heat transfer , Potential of developing frozen food products of superior quality as compared to noncryogenic freezing approaches , Atoxicity and potential of lowering oxidative damages during the freezing process and storage time

158

Low-Temperature Processing of Food Products

Notwithstanding the aforementioned beneficial properties of the liquid N2-based immersion freezing system, the high cost of the process still limits its wide application in the food industry. Besides the liquid N2, the utilization of CFC could be another strategy to be applied in immersion freezing systems. The CFC immersion approach is not considered a cryogenic technique. The heat transfer mechanisms applied in CFC immersion freezers are conduction heat transfer (during the immersion) and convection heat transfer (in the equilibrium chamber). To promote the efficiency and the rate of freezing process, the liquid CFC is sprayed on the top of food products in the equilibrium freezing chamber with any excess liquid returning to the bath (Heldman, 2006). Notwithstanding the simplicity of the CFC freezing system, the destruction of the ozone layer and the residual CFC in the food material are reckoned as the main concerns, which have forced the frozen industry to diminish the application of this technique.

7.5.2

Indirect contact freezers

The frozen food products are mostly the result of employing indirect contact freezing processes, where the food material is separated from the refrigerant via a barrier. In the case of indirect contact freezers, the product is separated from the heat transfer fluid via a conducting barrier/interface (typically a steel belt/plate or a product packaging material). Therefore, the food material is indirectly exposed to the freezing system. These systems are engineered to be continuous, via continuous product movement in a direction of concurrent airflow (Archer, 2004; George, 1993).

7.5.2.1

Plate freezers

Plate freezers are among the widely used indirect contact freezing systems, in which the freezing process of the food sample is applied without any direct contact with the medium employed for the product temperature. These types of the freezers are basically comprised of flat hollow plates (made up of mild steel/aluminum, which are designed by various extruded/hollow parts, butt-welded together along their length) and a refrigeration coil to cool the surface in contact with the food material. The plates are connected at each end to a header, facilitating ammonia to flow from each section of the plate. The food products are placed between stacked parallel plates, and then pressure is applied to the overall stacks to minimize the thermal contact resistance between the plates and the product. Using plate freezing units, the food sample should be in a planar geometry; therefore, unpackaged fish/meat products are suitable materials for freezing by these systems. Other irregularly shaped foods, that is, shrimp or vegetables (like cauliflower, spinach, broccoli, etc.) can be also frozen utilizing plate freezers by packaging the food material in a brick-shaped container before the freezing process. The applied temperature in this system is approximately 30 C to freeze packages of food products to below 10 C. In general, the plate freezing systems can be grouped into two main classes, including:

Spray freezing and single/double-contact freezing systems

159

⁃ Horizontal systems comprise a set of refrigerated, parallel plates in an insulated chamber. The freezer can operate in continuous or batch modes. Regarding the batch freezing mode, the spacing between the plates can be expanded to facilitate the loading of packaged food materials on the large trays. ⁃ Vertical units that are primarily utilized for freezing unpacked food, for example, fish. In this system, the food material is located directly between the freezing plates, and then pressure is applied to assure appropriate thermal contact. At the end of the freezing process, the plates are opened to remove the frozen food materials.

Overall, the main advantages of plate freezing approaches, include: ⁃ ⁃ ⁃ ⁃

high quality of the frozen food, high speed of the freezing process, proper stowage density in container, fast freezing time and fast temperature reduction, suitable for materials like hot offal or hot boned meat, ⁃ noteworthy reduction in energy, packaging, and even resource consumption, and ⁃ simplicity of the required requirements because of no need to high capacity fans in this freezing system.

Notwithstanding their manifold beneficial properties, the disadvantages of plate freezing systems are: • • •

high cost of the process, deed of a larger charge of refrigerant, and need of the same size packages to simplify loading.

7.5.2.2

Air blast freezers

Air blast freezers (ABFs) (Fig. 7.8 and Table 7.1) are applicable in direct/indirect freezing processes. In these systems, the food material is exposed to a high-velocity

Figure 7.8 A multilevel box air blast freezer (ABF) system. Adapted from https://www.koma.com/products/blast-freezing.

160

Low-Temperature Processing of Food Products

Table 7.1 Different types of air blast freezers (ABFs). Type

Characteristics

Batch ABF

⁃ Manually loading food materials stored on multi-pass conveyor belts, trays, shelves of racks, trolleys, or products (e.g., carcasses) hung from hooks on slide rails into batch ABF. ⁃ Application of guide rails in the freezing chamber for the facilitation of cabinet loading when using trolleys. ⁃ Application of a fan-driven circulating low-temperature air in direct contact with the product. ⁃ High dependency of the freezing time to the properties of the air (temperature or velocity), food material (size, shape, or thermal features), and the exposure time between the refrigerating air and food material. ⁃ Short freezing process and high-quality product for samples with small dimension and proper geometry. ⁃ An insulated enclosure with significant length and height, which is equipped with powerful fans (providing the needed velocity) and appropriate for freezing packages (i.e., plastic containers, cartons, shrink-wrapped. etc.) located on shelves/carriers. ⁃ Continuous loading/unloading via an automated system with in- and out-feed conveyors. ⁃ Transfer elevators insert/discharge the food products into/ from the rack structure. ⁃ The existence of enough spaces/channels in the freezer is important and facilitates the high-velocity air circulation between the food materials. ⁃ An insulated chamber of limited width and considerable length, where loading/unloading take place at the same/ opposite ends. ⁃ Vigorous circulation of refrigerating air via fans from the evaporator(s) over the food material (air flow is parallel (cocurrent or counter-current) or perpendicular (cross-flow) to the direction of movement. ⁃ Food material is located on trays that pass through the tunnel. ⁃ Semi-continuous freezing via loading/unloading of food material at the same end. ⁃ Continuous freezing via charging/discharging of food material at opposite ends.

Multilevel box ABF

Tunnel ABF

Spray freezing and single/double-contact freezing systems

161

Table 7.1 Continued Type

Characteristics

Tunnel ABF equipped by conveyor belt

⁃ Uniform distribution of food materials onto a long singlemesh conveyor belt (usually automatically) at proper time intervals to take the product throughout the tunnel freezer. ⁃ The continuous motion of the food product by using a conveyor belt facilitates the freezing of the sample and simultaneously averts sticking. ⁃ Different types of tunnel ABF are flighted freezers, straight belt tunnel freezers, and the multi-pass belt freezers. ⁃ Freezers with a meshed spiral belt, conveying the products from bottom-to-top along a helical path ⁃ The conveyor belt is helical self-stacking, or helically wound around a drum. ⁃ Suitability of horizontal flows for freezing of heavily packaged and flat food materials, while vertical flows through the spiral conveyor belt for the freezing of bare products of low dehydration losses. ⁃ Appropriate for freezing of food particles (or small food materials) ⁃ Separation of each particle from the others followed by surrounding by low-temperature air, evoking a high convective heat transfer coefficient on the surface of food material and rapid freezing process ⁃ Quick formation of a solid crust on the surface of food material, preventing the labile foods from sticking together in large lumps ⁃ Various air nozzles of corresponding return ducts are mounted above/below the conveyor. ⁃ The food materials are led past a large number of highvelocity jets of refrigerated air (on a proper conveyor belt), which are directed onto the top/bottom of the product. ⁃ Perpendicular to the surfaces of products, the airflow continuously tubulates the boundary layer, which surrounds the food materials and enhances the surface heat extraction rate, providing quick freezing time and crust freezing of the product. ⁃ Application of single-/multi-pass straight belts in these freezers

Spiral belt ABF

Fluidized-bed tunnel freezers

Impingement freezer

air steam at a low temperature. ABFs usually are operated under air velocities of 10e15 m/s at temperatures 30 to 45 C (Dempsey & Bansal, 2012). ABFs possess a package, which performs as the barricade for irregular-shaped food materials. Short freezing processes can be achieved via applying low air temperatures, high air velocities, and even proper contact between the food’s surface and the

162

Low-Temperature Processing of Food Products

packaging material. The ABF-based freezing process can be applied via both batch and continuous modes, while most freezers are operated continuously (Dempsey & Bansal, 2010). In ABFs, the refrigerator first decreases the temperature of an air stream to around 40 C. The air flows using an enclosed system, in which the food materials are moved via a movable belt (the structure of the conveyor system depends on the type and size of the food sample). In a simple design of conveyor systems, the food materials are conveyed along a straight belt via a tunnel freezer. Some other designs also include spiral and multitiered conveyor belts, which are applicable to lower the required space of the freezing system. It is noteworthy that ensuring the uniform airflow over the food material counts as a critical factor in designing ABFs (Bowater, 2001; Nagaoka et al., 1956). The direction of the airflow (i.e., parallel, counter, or cross flow) is another important parameter affecting the freezing process in such systems. The parallel approach is the most proper approach, in which the air flows parallel to the food material in the same direction. The other methods are counter- and crossflows, where the air flows in the opposite and perpendicular directions to the food materials, respectively (Briley, 2002; Chourot, 2003). A batch ABF usually comprises of a well-insulated (Luo et al., 2020) container equipped with an air cooler and fans. The food material is laden on a conveyor belt system of stacked trays. Preserving even airflow is highly crucial for a proper freezing process; thus, appropriate facilities are needed to guarantee uniform airflow over all the trays (Luo et al., 2020).

7.5.3

Contact belt freezers

The CBF is defined as a modified tunnel/blast freezer, which comprises a long stainless steel running a movable belt. The belt (a stainless-steel mesh) conveys the food material into an air-blast room with a temperature of around 40 C. Notwithstanding the simplicity of single belt arrangements, the multi-tiered belt can be applied to save floor space. For increasing the efficiency and capacity of the freezing system, a cryogenic gas or cold air can be utilized to improve the refrigeration mechanism. The applied gas or cold air moves over the food materials at a high velocity and opposite direction (Makroo et al., 2020). The solid or liquid forms of the food products are placed on top of the belt and are frozen via conductioneconvection heat transfer mechanism. The liquid-state food materials are frozen from the top and bottom. In the frozen state, the product is separated from the belt surface mechanically or spontaneously. The CBFs are cost-efficient and versatile relying on their specific application. These systems are also applicable for solid/semisolid and soft/high moisture food materials, for example, seafood, beef, pork, poultry, vegetables, etc (Muthukumarappan et al., 2019; Persson & Londahl, 1993). The CBFs are usually ideal for high-throughput freezing of delicate, sticky, and shape-sensitive food materials. The sticky food products, for example, pluck, proofed dough, and even marinated chicken parts can be frozen quickly via CBFs. When prefrozen on a closed belt, the soft food materials can be frozen on a small-meshed belt without sticking to the steel layer. These types of freezers are also proper for freezing very delicate materials, for example, minced products or cod roe (Follette, 2004; Rémy, 1987) (Fig. 7.9).

Spray freezing and single/double-contact freezing systems

163

Figure 7.9 Real image of a contact belt freezer. Source: https://www.afellc.com/equipment-solutions/contact-belt-freezers/.

7.6

Conclusion

Although freezing technology brings benefits and convenience to human life, improper freezing could induce quality loss of frozen foods due to growth of large ice crystals and ice accumulation. The theory and mechanism of spray freezing systems and their potential applications in the food freezing industry are reviewed. In the current chapter, principles, and processing conditions of single/double freezing systems are also offered. Although the research up-to-date shows that the commercial development of spray freezing and single-/double-contact freezing techniques is available, the concomitant application of these approaches with other novel methods like ultrasound can aid food freezing process and promote the quality of the frozen products.

References Abdul Mudalip, S. K., Khatiman, M. N., Hashim, N. A., Che Man, R., & Arshad, Z. I. M. (2021). A short review on encapsulation of bioactive compounds using different drying techniques. Materials Today: Proceedings, 42, 288e296. Adali, M. B., Barresi, A. A., Boccardo, G., & Pisano, R. (2020). Spray freeze-drying as a solution to continuous manufacturing of pharmaceutical products in bulk. Processes, 8(709), 1e27. Al-Hakim, K., Wigley, G., & Stapley, A. G. F. (2006). Phase Doppler anemometry studies of spray freezing. Chemical Engineering Research and Design, 84(A12), 1142e1151. Archer, D. L. (2004). Freezing: An underutilized food safety technology? International Journal of Food Microbiology, 90(2), 127e138. Bowater, F. J. (2001). Design of carton air blast freezing systems. In Rapid cooling of food, proceeding of bristol meeting. Bristol, UK: The International Institute of Refrigeration. Briley, G. C. (2002). Blast freezing. ASHRAE Journal, 44(7), 99.

164

Low-Temperature Processing of Food Products

Cheng, L., Sun, D. W., Zhu, Z., & Zhang, Z. (2017). Emerging techniques for assisting and accelerating food freezing processes: A review of recent research progresses. Critical Reviews in Food Science and Nutrition, 57(4), 769e781. Chourot, J. M., Macchi, H., Fournaison, L., & Guilpart, J. (2003). Technical and economical model for the freezing cost comparison of immersion, cryomechanical and air blast freezing processes. Energy Conversion and Management, 44(4), 559e571. Dempsey, P., & Bansal, P. (2010). Air blast freezers and their significance to food freezing: A review. In Proceedings of ENCIT 2010, 13th Brazilian congress of thermal sciences and engineering (pp. 05e10). Brazil: Uberlandia, MG. Dempsey, P., & Bansal, P. (2012). The art of air blast freezing: Design and efficiency considerations. Applied Thermal Engineering, 41, 71e83. Desrosier, N. W. (2012). Fundamentals of food freezing. Springer Science and Business Media. Diao, Y., Cheng, X., Wang, L., & Xia, W. (2021). Effects of immersion freezing methods on water holding capacity, ice crystals and water migration in grass carp during frozen storage. International Journal of Refrigeration, 131, 581e591. Dutta, S., Moses, J. A., & Anandharamakrishnan, C. (2018). Modern frontiers and applications of spray-freeze-drying in design of food and biological supplements. Journal of Food Process Engineering, 12881, 1e8. Engstrom, J. D., Simpson, D. T., Cloonan, C., Lai, E. S., Williams, R. O., III, Kitto, G. B., & Johnston, K. P. (2007). European Journal of Pharmaceutics and Biopharmaceutics, 65, 163e174. Fennema, O., & Powrie, W. D. (1964). Fundamentals of low-temperature food preservation. Advances in Food Research, 13, 219e347. Follette, G. (2004). The formative years: Frozen foods. ASHRAE Journal, 46(11), S35. George, R. M. (1993). Freezing proceseses used in the food industry. Trends in Food Science and Technology, 4(5), 134e138. Goerlitz, A. (1994). Mechanised freezing line with horizontal plate freezers. Mechanisierte Gefrierstrasse mit Horizontal-Plattengefrierapparaten. Gwie, C. G., Griffiths, R. J., Cooney, D. T., Johns, M. L., & Wilson, D. I. (2006). Microstructures formed by spray freezing of food fats. Journal of the American Oil Chemists’ Society, 83(12), 1053e1062. Heldman, D. R. (2006). Food freezing. In Handbook of food engineering (pp. 439e482). CRC Press. Hindmarsh, J. P., Russell, A. B., & Chen, X. D. (2007). Fundamentals of the spray freezing of foodsdmicrostructure of frozen droplets. Journal of Food Engineering, 78, 136e150. Hu, J., Johnston, K. P., & Williams, R. O., III (2004). Rapid dissolving high potency danazol powders produced by spray freezing into liquid process. International Journal of Pharmaceutics, 271, 145e154. Ishwarya, S. P., Anandharamakrishnan, C., & Stapley, A. G. F. (2015). Spray-freezedrying: A novel process for the drying of foods and bioproducts. Trends in Food Science and Technology, 41, 161e181. Islam, M. N., Zhang, M., Adhikari, B., Xinfeng, C., & Xu, B. G. (2014). The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms. International Journal of Refrigeration, 42, 121e133. Jafari, S. M., Arpagaus, C., Cerqueira, M. A., & Samborska, K. (2021). Nano spray drying of food ingredients; materials, processing and applications. Trends in Food Science and Technology, 109, 632e646. Levin, Z., & Yankofsky, S. A. (1983). Contact versus immersion freezing of freely suspended droplets by bacterial ice nuclei. Journal of Climate and Applied Meteorology, 1964e1966.

Spray freezing and single/double-contact freezing systems

165

Li, D., Zhu, Z., & Sun, D. W. (2018). Effects of freezing on cell structure of fresh cellular food materials: A review. Trends in Food Science and Technology, 75, 46e55. Luo, X., Li, J., Yan, W., Liu, R., Yin, T., You, J., Du, H., Xiong, S., & Hu, Y. (2020). Physicochemical changes of MTGase cross-linked surimi gels subjected to liquid nitrogen spray freezing. International Journal of Biological Macromolecules, 160, 642e651. MacLeod, C. S., McKittrick, J. A., Hindmarsh, J. P., Johns, M. L., & Wilson, D. I. (2006). Fundamentals of spray freezing of instant coffee. Journal of Food Engineering, 74, 451e461. Makroo, H. A., Talukdar, P., Hmar, B. Z., & Das, P. P. (2020). Frozen foods: Science, shelf life, and quality. In Shelf life and food safety (pp. 155e164). CRC Press. Marizy, C., Le Bail, A., Duprat, J. C., & Reverdy, Y. (1998). Modelling of a drum freezer. Application to the freezing of mashed broccoli. Journal of Food Engineering, 37(3), 305e322. Muthukumarappan, K., Marella, C., & Sunkesula, V. (2019). Food freezing technology. In Handbook of farm, dairy and food machinery engineering (pp. 389e415). Academic Press. Nagaoka, J., Takagi, S., & Hotani, S. (1956). Experiments on the freezing of fish by the air-blast freezer. Pascual-Pineda, L. A., Rascon, M. P., Quintanilla-Carvajal, M. X., Castillo-Morales, M., Marín, U. R., & Flores-Andrade, E. (2019). Effect of porous structure and spreading pressure on the storage stability of red onion microcapsules produced by spray freezing into liquid cryogenic and spray drying. Journal of Food Engineering, 245, 65e72. Persson, P. O., & Londahl, G. (1993). Freezing technology (pp. 20e58). Frozen food technology. Qian, P., Zhang, Y., Shen, Q., Ren, L., Jin, R., Xue, J., … Dai, Z. (2018). Effect of cryogenic immersion freezing on quality changes of vacuum-packed bighead carp (Aristichthys nobilis) during frozen storage. Journal of Food Processing and Preservation, 42(6), e13640. Rahman, M. S., & Velez-Ruiz, J. F. (2007). Food preservation by freezing. In Handbook of food preservation (pp. 653e684). CRC press. Resch, G. P., Brandstetter, M., Pickl-Herk, A. M., Königsmaier, L., Wonesch, V. I., & Urban, E. (2011). Immersion freezing of biological specimens: Rationale, principles, and instrumentation. Cold Spring Harbour Protocols, 2011(7), pdbetop118. Rémy, J. (1987). Modern freezing facilities. International Journal of Refrigeration, 10(3), 165e174. Rogers, T. L., Hu, J., Yu, Z., Johnston, K. P., & Williams, R. O., III (2002). A novel particle engineering technology: Spray-freezing into liquid. International Journal of Pharmaceutics, 242, 93e100. Sebasti~ao, I. B., Bhatnagar, B., Tchessalov, S., Ohtake, S., Plitzko, M., Luy, B., & Alexeenko, A. (2019a). Bulk dynamic spray freeze-drying part 1: Modeling of droplet cooling and phase change. Journal of Pharmaceutical Sciences, 108, 2063e2074. Sebasti~ao, I. B., Bhatnagar, B., Tchessalov, S., Ohtake, S., Plitzko, M., Luy, B., & Alexeenko, A. (2019b). Bulk dynamic spray freeze-drying part 2: Model-based parametric study for spray-freezing process characterization. Journal of Pharmaceutical Sciences, 108, 2075e2085. Sebasti~ao, I. B., Robinson, T. D., & Alexeenko, A. (2017). Atmospheric spray freeze-drying: Numerical modeling and comparison with experimental measurements. Journal of Pharmaceutical Sciences, 106(1), 183e192.

166

Low-Temperature Processing of Food Products

Shiloh, K., & Sideman, S. (1967). Direct contact heat: Transfer with change of phase: Evaporation rates in vacuum freezers. Canadian Journal of Chemical Engineering, 45(5), 300e305. Tian, Y., Li, D., Luo, W., Zhu, Z., Li, W., Qian, Z., Li, G., & Sun, D.-W. (2020). Rapid freezing using atomized liquid nitrogen spray followed by frozen storage below glass transition temperature for Cordyceps sinensis preservation: Quality attributes and storage stability. LWT - Food Science and Technology, 123, 109066. Tian, Y., Zhu, Z., & Sun, D. W. (2020). Naturally sourced biosubstances for regulating freezing points in food researches: Fundamentals, current applications and future trends. Trends in Food Science and Technology, 95, 131e140. Toledo, R. T., Singh, R. K., & Kong, F. (2007). Fundamentals of food process engineering (Vol. 297). New York: Springer. Vishali, D. A., Monisha, J., Sivakamasundari, S. K., Moses, J. A., & Anandharamakrishnan, C. (2019). Spray freeze drying: Emerging applications in drug delivery. Journal of Controlled Release, 300, 93e101. Volkert, M., Ananta, E., Luscher, C., & Knorr, D. (2008). Effect of air freezing, spray freezing, and pressure shift freezing on membrane integrity and viability of Lactobacillus rhamnosus GG. Journal of Food Engineering, 87, 532e540. Wanning, S., S€uverkr€up, R., & Lamprecht, A. (2015). Pharmaceutical spray freeze drying. International Journal of Pharmaceutics, 488, 136e153. Yu, Z., Garcia, A. S., Johnston, K. P., & Williams, R. O., III (2004). Spray freezing into liquid nitrogen for highly stable protein nanostructured microparticles. European Journal of Pharmaceutical Sciences, 58, 529e537. Yu, Z., Johnston, K. P., & Williams, R. O., III (2006). Spray freezing into liquid versus sprayfreeze drying: Influence of atomization on protein aggregation and biological activity. European Journal of Pharmaceutical Sciences, 27, 9e18. Yu, Z., Rogers, T. L., Hu, J., Johnston, K. P., & Williams, R. O., III (2002). Preparation and characterization of microparticles containing peptide produced by a novel process: Spray freezing into liquid. European Journal of Pharmaceutics and Biopharmaceutics, 54, 221e228. Zaritzky, N. E. (2012). Physical-chemical principles in freezing. Zarkadas, D. M., & Mitrakas, M. (1999). On the applicability of a plug flow immersion freezer: Theoretical considerations. LWT–Food Science and Technology, 32(8), 548e552. Zheng, S., Yang, Y., Li, Z., Pan, Z., Huang, Z., & Ai, Z. (2022). A comparative study of different freezing methods on water distribution, retrogradation, and digestion properties of liangpi (starch gel food). Starch e St€arke, 74, 2100205.

Direct or indirect immersion freezing systems

8


-Aguayo 2 and Rogelio S
anchez-Vega 1 , Ingrid Aguilo 3 María Janeth Rodríguez-Roque 1 Autonomous University of Chihuahua, Faculty of Zootechnics and Ecology, Chihuahua, Mexico; 2Institut de Recerca i Tecnologia Agroalimentaries (IRTA), Postharvest Programme, Processed Fruits and Vegetable, Parc Agrobiotech, Lleida, Spain; 3Autonomous University of Chihuahua, Faculty of Agrotechnological Science, Chihuahua, Mexico

8.1 8.1.1

Introduction to immersion freezing systems Overview of freezing systems

Freezing is one of the most worldwide used preservation technologies for its efficiency in the maintenance of food quality, microbiological stability, safety, and also long storage shelf-life. The low temperature applied during freezing delays the deteriorative reactions (physiological and physicochemical) of plant cells, as well as the growth of microorganisms (Zhu et al., 2019). Therefore, freezing allows the maintenance of organoleptic properties of food such as texture, taste, color, and odor and at the same time their nutritional value in comparison with other methods (Sadot et al., 2017). For this, freezing is among the most crucial, critical, and influential unit operation, which includes three stages (Kiani & Sun, 2011): (a) precooling or chilling stage, where the sensible heat is removed; (b) phase change stage, where the latent heat is removed and the ice crystals (crystallization) are formed, subsequently the crystals are grown (Zhu et al., 2019); and (c) tempering stage, where food products are cooled until reaching storage temperature and lastly ice crystal growth ends.

Diverse factors influence each stage of freezing. However, crystallization is one of the most critical stages of freezing. Because depending on the size of crystal formed, the quality and structure of food will be maintained. In this context, the large ice crystals formed, the greatest weakness of the physical food structure (Zhang et al., 2019). On the other hand, when small and homogeneously distributed ice crystals within the intracellular structure of plant cells are formed, less damage in the structure and highquality of foods are observed (Fu et al., 2020). Freezing systems can be divided into two groups, traditional freezing methods and novel freezing methods. The first group, traditional or slow freezing methods include air blast freezing, immersion freezing, cryogenic freezing, and direct-contact freezing (Cheng et al., 2017a, 2017b; Islam et al., 2017). The second group, novel freezing

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00007-2 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

168

Low-Temperature Processing of Food Products

methods also called rapid freezing methods include the following: antifreeze glycoproteins, antifreeze proteins, electrically disturbed freezing, high-pressure freezing, ice nucleating proteins, magnetically disturbed freezing, microwave-assisted freezing, osmo-dehydro-freezing, radiofrequency freezing, and ultrasound-assisted freezing (Astr
ain-Redín et al., 2021; Eickhoff et al., 2019; Fan et al., 2020; HafezparastMoadab et al., 2018; Jha et al., 2020; Pita-Calvo et al., 2018; Tang et al., 2020; Usman et al., 2020; Xanthakis et al., 2013). Each group of freezing and also each freezing system has advantages and disadvantages. Overall, it is well known that the ice crystals formed when applying traditional freezing systems are heterogeneous in terms of distribution, morphology, and size (Parandi et al., 2022). This effect can lead to drip loss in plant tissues and squeezing effect in animal tissues (meat). On the other hand, it has been reported that food processed by novel freezing systems retain higher flavor, taste, texture, and nutritional value as compared with those processed with traditional methods in apple and potatoes (Jha et al., 2020), cherry (Tang et al., 2020), strawberries (Cheng, Zhang, Adhikari, Islam, Xu, 2014), and porcine longissimus muscles (Zhang et al., 2019), among others. Similarly, inactivate deteriorative food enzymes reduce the browning index and the drip loss of apple and potatoes (Jha et al., 2020), lamb meat (Dalvi-Isfahan et al., 2016), white mushrooms (Lagnika et al., 2013), and wrapped red radish (Xu et al., 2015). For this reason, it is really important to select the best freezing system, taking into account the features of food, such as composition, structure, and the final use of products, as well as the infrastructure needed for applying freezing systems properly. In this chapter, direct or indirect immersion freezing systems are summarized taking into consideration the principles, advantages, drawbacks, applications, and future trends.

8.1.2

Freezing types focused on direct, indirect, and immersion

To meet both the consumer’s and the food industry’s demands for speed freezing, sustainable, and high-quality food, there are a great amount of commercially available freezing methods and equipment. The freezing method has been traditionally classified within three types: air freezing, indirect contact freezing, and immersion freezing. Their examples, advantages, and disadvantages are shown in Table 8.1. Another classification that is based on the mode of operation, on the contact with food and freezing medium or on the heat transfer systems are shown in Fig. 8.1. In this chapter, the attention is focused on direct and indirect immersion systems. A brief description of each one is the following: Direct contact freezing is when the product, packaged or unpackaged, is entirely surrounded by the freezing medium. In this case, the heat transfer is warranted making the method efficient, quick, and economical (Liang et al., 2015). On the contrary, indirect contact freezing is when the product and the freezing medium are not in direct contact. In this case, the freezing is reached because the product, packaged or unpackaged, is in contact with a surface that was cooled by the refrigerant (Zhao et al., 2020).

Direct or indirect immersion freezing systems

169

Table 8.1 Traditional classification of freezing methods. Freezing methods

Examples

Benefits

Drawbacks

Air freezing

- Still-air “sharp” freezer - Blast freezer - Fluidizedbed freezer

U The least expensive freezing method. U Efficiency did not depend on the size and shape of food. U High freezing rate, mainly in fluidized-bed freezer where the heat transfer is efficient.

Indirect contact freezing

- Single plate - Double plate - Pressure plate - Slush freezer

U Economical U Reduced dehydration U Package bulging is reduced.

Immersion freezing/ cryogenic freezing

- Heat exchange fluid - Compressed gas - Refrigerant spray

U The freezing process is fast; thus the freezing damage is reduced in the products. U The food quality is maintained. U The dehydration is reduced. U The oxidative spoilage reduces by the elimination of oxygen during this freezing type.

✗ Freezer burn, dehydration, and expansion of the products. ✗ The package may bulge because of the product’s expansion. ✗ The fluidization is difficult in irregular products. ✗ The freezing process is slow. ✗ The efficiency of freezing depends on thickness of products, being desirable for uniformity. ✗ The operation cost is high. ✗ The coolant suitable for this type of freezing is difficult to obtain.

Adapted from Potter and Hotchkiss (1995).

On the other hand, immersion freezing is when the product is submerged in a lowtemperature liquid refrigerant to directly exchange heat and quickly low the temperature (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020). The liquid refrigerants used in this method must avoid the flavor and odor transfer between the refrigerant and the food, as well as they must be pure, nontoxic, and have a low boiling point. The most widely used are solutions of alcohol, glycol, glycerol, salt (i.e., sodium chloride), or sugar (Galetto et al., 2010). In order to prevent a direct contact between food and the liquid refrigerant, the food can be covered with flexible films and coatings that allow a quick heat transfer. Additionally, the traditional solutions have been replaced by liquefied gases to get efficient continuous freezing processes (Fikiin, 2003).

170

Low-Temperature Processing of Food Products

Figure 8.1 Types of freezing systems and their examples.

8.1.3

Importance of immersion freezing

Immersion freezing can be defined as the process where a food is completely under a liquid freezing medium until reaching a freeze product. It is one of the quick and best methods for preserving food to deleterious reactions, microbial contamination, and loss of nutrient quality. Therefore, the food remains available and suitable for human consumption by a long period of time (Xu, Azam, et al., 2019; Xu, Song, et al, 2019). The main importance of immersion freezing is that it has been successfully applied in the food industry, because in addition to being a fast and efficient freezing method, it can be applied in a wide variety of products: fresh, cooked or processed; whole or cutproduct; animal or vegetable origin; among others. Moreover, it allows a massive production of a wide range of frozen food over other alternatives (i.e., canned products) and finally, it lets the availability of seasonal food all the year. In this sense, it has been reported that fruit and vegetable properties, such as color, texture, and the nutritional composition, were preserved as similar as the fresh food for a long period of time using immersion freezing (Galetto et al., 2010; Sun & Li, 2003; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al. 2015; Xu et al., 2014). Additionally, food retains their quality once cooked, highlighting the efficiency of immersion freezing. Meat (fish, pork, and snake) freezing by immersion with liquid nitrogen during 6e10 s maintain their nutritional composition and avoid the outflow of steam once cooked (Bodin et al., 2014; Hou et al., 2020; Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020).

8.2

Principles of immersion freezing

It is well known that a “principle” is described as the base, origin, and fundamental reason on which something proceeds. The principles of freezing process are based

Direct or indirect immersion freezing systems

171

on three points: first, the low temperature; second, the low water activity of the product as a result of the ice formation; and third, the pretreatments of product (i.e., blanching or with the enzyme pectin methylesterase) (Galetto et al., 2010; Zhao, 2007). The principles of immersion freezing are discussed in this section. The main one, unquestionably, is the crystallization of both water and some solutes contained in food into ice due to the reduction of temperature to
18 C or less. To reach the freezing of the products, their temperature must be reduced below their freezing point temperature. For this, other principles such as the sensible heat and latent heat must be taken into consideration during the freezing process (Zhu et al., 2019). Overall, the sensible heat has been described as the amount of heat energy applied to food in order to change its temperature into a desirable value. On the other hand, latent heat is the amount of energy removed from food for reaching the change of the water phase. Taking into consideration that at the beginning of the freezing process, the product possesses a temperature above its freezing point, the following sequence must be carried out: 1. The sensible heat must be removed from the food until reaching its freezing point temperature. 2. Remotion of latent heat generated during the crystallization process. 3. Remotion of more sensible heat until reaching the freezing point of the product.

The maintenance of food quality, the preservation of food by reducing deleterious reactions, as well as the microbial contamination are reached in immersion freezing by: •

•

The rate of biochemical, physicochemical, biological, and microbiological reactions is reduced by decreasing the water availability in freezing food. The availability of water changes when the phase “liquid water” from food is converted to “ice,” avoiding the participation of water in any of the previously mentioned reactions. The food quality, either physicochemical or microbiological, of freezing food is maintained by the reduction in the interaction between food and oxygen in direct immersion systems.

8.3 8.3.1

Direct immersion freezing Definition and working mechanism

The direct immersion freezing refers to the process where both the product and the freezing medium are in contact, exchanging heat and thus, quickly lowering temperature and freezing food. Immersion freezing uses a liquid coolant (freezing medium) with a high heattransfer coefficient that is up to 20 times higher in the liquid medium than in the air (Galetto et al., 2010; Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020). Food must be directly in contact with the coolant that absorbs the food heat and provides refrigeration. As a result, food is rapidly cooled and frozen, that is around 10e15 min to freeze many food types, depending on the agitation type and the thermo-physical properties of the refrigerating medium (Lucas & Raoult-Wack, 1998). For this, immersion

172

Low-Temperature Processing of Food Products

freezing is the fastest method for either crust chilling or deep freezing (Parandi et al., 2022). Thermal conductivity greatly influences three steps of freezing: the rate, the nucleation, and the crystal size. The range of thermal conductivity of liquids is between 0.116 and 0.628 W/m/ K. On the contrary, the thermal conductivity of air is 0.024 W/m/ K (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020). As the thermal conductivity of liquids is higher than the air, immersion freezing using liquids leads to high freezing rate, a uniform nucleation, and small ice crystals formation. In terms of microstructural features of food, immersion freezing causes less cell damage and maintains the structural stability of proteins due to the small crystal size formed during freezing (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020). All these, highlight the importance of immersion freezing technology. In fact, there are reported some studies in the literature evaluating the kinetics of immersion freezing, the ice crystal formation, and their influence on products such as apple (Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al. 2015), carrots (Xu et al., 2014), fish (Bodin et al., 2014), pork (Hou et al., 2020), potato (Sun & Li, 2003), snakehead (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020), and strawberries (Galetto et al., 2010). On the other hand, the liquid solutions used as freezing medium in this method are: calcium chloride, glycerol, propylene glycol, sodium chloride, salt, and/or sugar solutions, mixtures of sugar-water-ethanol (Barbosa-C
anovas, 2005; Galetto et al., 2010). Overall, the freezing medium must allow low temperatures from
10 to
40 C (Galetto et al., 2010). In this sense, a 23% of sodium chloride solution can reach
20 C of operating temperature, while a 40% of ethanolic solution gets
30 C. Those liquid solutions, which overall are good heat conductors, have been replaced by liquefied gases in order to increase the process efficiency (Fikiin, 2003).

8.3.2

Advantages and limitations

Direct immersion freezing is one of the best methods for preserving food for a longtime with several advantages with respect to other systems, highlighting the following ones (Cheng et al., 2017a, 2017b; Galetto et al., 2010; Xu, Azam, et al., 2019; Xu, Song, et al, 2019): 1. A quick freezing derived from the direct contact between the food and the freezing medium, allowing that the heat transfer rate be really high. 2. It is the best process to preserve food for a long term without the addition of preservers. 3. Oxidative reactions are reduced because direct immersion freezing minimizes the contact between food and the air. 4. When individual pieces of food are frozen by direct immersion, they remain separated reducing the formation of blocks of product. 5. It can be applied to different conditions of food: unpackaged, uncoated, regular or irregular shaped, raw or cooked, whole or cut-product; and animal or vegetable origin; among others. 6. The food quality is maintained, in some cases as similar as the fresh product. In the case, nutritional quality (bioactive compounds, vitamins, and nutrients) and sensorial features (color, flavor, smell, and texture) are conserved. Similarly, the spoilage microorganisms are

Direct or indirect immersion freezing systems

173

avoided. Additionally, the direct immersion freezing causes less dehydration of products by reducing both the drip loss and the moisture migration from the fruit to the environment during freezing and thawing. When freezing is carried out with cryogenic liquids by direct immersion, the food quality surpasses that obtained by any other method. 7. A massive production and continuous operations in the process can be easily obtained by direct immersion freezing. 8. The operation cost and also, the investment cost of direct immersion freezing is lower as compared with other freezing methods.

On the other hand, direct freezing process has following limitations: (a) The freezing medium sometimes did not reach the suitable features to be applied for any type of food and to be unfrozen at low temperatures. For instance, the sodium chloride brine is unsuitable to be applied in freezing fresh fruits unless they are processed. The liquid solutions with sugar (syrup) are really viscous at temperatures used during this method, making their use difficult. (b) Uncontrolled solute uptake from the freezing medium to the food (Galetto et al., 2010; Lucas & Raoult-Wack, 1998). A primary and secondary solute transfer has been reported in this regard (Luca et al., 1999). The first one occurs before thermal equilibrium between the food and the liquid solution. In this sense, cylinders of apple immersed in agitated watereNaCl solution during 15 min showed a NaCl increase of 0.5% when the thermal equilibrium was reached (Lucas et al., 1998). The second occurs after thermal equilibrium. Despite the latest being slower than the first phase, the impregnation is higher. In this case, the concentration of NaCl in cylinders of apple increased between 2.7% and 6.8% when stored during 1 or 6 days, respectively, in nonagitated watereNaCl solution. (c) The freezing temperature must be meticulously controlled for avoiding the osmosis or the freezing of the freezing medium. In this case, high temperatures allow the diffusion of solutes from the freezing medium into the product, while low temperatures cause a solid freezing of the coolant. Both cases are undesirable, as they diminish the effectiveness of the process. (d) Operational problems with the freezing medium. It is difficult to maintain a suitable/constant concentration, avoid the contamination, and keep the cleaning of the freezing medium in this type of freezing. (e) In some cases, the efficiency of direct immersion freezing is not achieved because during the freezing process, some reactions (chemical and biological) and changes in the cell/tissue/ texture of food can take place, which are closely related with the chemical composition and maturity stage of the products. These facts affect the freezing rate and must be taken into consideration in order to select the best freezing method and even the packaging type and the storage conditions (Zhao, 2007). (f) The use of cryogenic liquids is still restricted due to the high cost of liquefied gases. (g) Slow industrial development because of the mass transfer of water and solutes between food and the freezing medium is difficult.

8.3.3

Examples of direct immersion freezing

Direct immersion freezing is applied to a wide range of food: raw or cooked, whole or cut-product; from animal or vegetable origin, with regular or irregular shape, mainly unpackaged, and uncoated food. In fact, it is considered as the fastest freezing

174

Low-Temperature Processing of Food Products

technique due to the significantly higher heat transfer coefficient in liquid media as compared to air. Commercially, it is mainly applied to fruits, mushrooms, poultry, fish, and shrimp. For research purpose, it has been applied to fruit and vegetables such as apple, carrots, broccoli, potato, and strawberry (Galetto et al., 2010; Sun & Li, 2003; Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al. 2015; Xu et al., 2014; Xin et al., 2014a, 2014b) but also in fish (Bodin et al., 2014), pork (Hou et al., 2020), snakehead (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020), and cheese (Ribero et al., 2009). •

The freezing medium used could comprise low-freezing-point liquids or cryogenic liquids. Solutions of sugars, sodium chloride, or glycerol are used as low-freezing-point liquids for preserving nonpackaged foods which could be used at concentrations that maintain temperature below
18 C. Cold aqueous fluids, such as solutions of NaCl, CaCl2, or sucrose, which are maintained at low temperatures ranging from
10 to
40 C are commonly used for freezing fruit. However, the solution must be conveniently chosen to avoid transfer to the product. For instance, freezing of strawberries by immersion in CaCl2 solutions has been reported to provide benefit in reducing drip loss of thawed product (Galetto et al., 2010) and preserve firmness (Suutarinen et al., 2002). Combination of vacuum-assisted infusion using commercial pectin methylesterase and calcium improved texture of frozen-thawed mangoes (Sirijariyawat et al., 2012). In the case of cryogenic liquids, liquid nitrogen can contact even irregularly shaped food and offers a remarkable advantage in producing frozen food of high quality. In addition, food products such as mushrooms that are prone to excessive tissue damage when frozen using conventional methods preserve their integrity better when using liquid nitrogen. Liang et al. (2015) reported that direct immersion freezing using ultralow-temperature quaternary refrigerant taking about 10 min to freeze litchi fruit samples, helped to preserve the fruit for 6 months preserving close to 80% the nutritional quality compared to the fresh product. Additional examples on this regard are shown in Section 8.5.3 in Table 8.3.

8.4 8.4.1

Indirect immersion freezing Definition and working mechanism

Indirect freezing refers to the methods where the food and the heat transfer fluid are not in direct contact with each other, being separated by an interface (i.e., metal plate) or barrier (i.e., the packaging of food). The refrigerant circulates through the interface/ barrier beside the food, reducing the temperature considerably. Thus, the freezing is reached because the products or the packaged products are in contact with the surface that was cooled by the freezing brine or refrigerant. Overall, the principle of freezing is the same as that previously described in terms of heat transfer. The wide range of industrial production uses indirect freezing systems despite their efficiency being slow and more expensive than the direct immersion freezing. However, indirect immersion freezing improves the safety of the product and does not need material exchange between the refrigerant and the frozen material.

Direct or indirect immersion freezing systems

8.4.2

175

Advantages and limitations

Indirect immersion freezing possesses some advantages and drawbacks when compared with other freezing methods. Among the main advantages stand up the next: 1. It is a quick freezing method despite the indirect contact with the freezing medium. It must be taken into consideration to select an appropriate food (type, size, chemical composition, and maturity stage), package, interface/barrier, and freezing medium (with good heat transfer properties) for reaching this goal (Zhao, 2007). 2. Produces high-quality food in terms of nutrition, sensorial, and safety features, allowing a long shelf-life. 3. It can be applied to packaged and unpackaged food; coated or uncoated products, raw or cooked, animal or vegetable origin as similar as direct immersion freezing. 4. Controlled solute uptake from the freezing medium to the food when using brine as freezing medium. 5. It allows massive production and continuous freezing processes.

On the other hand, the drawbacks of this method are listed below: (a) A lower efficiency and a more expensive cost than the direct immersion freezing. (b) The rate of cooling depends on the thermal conductivity and size of food. There are many foods with low thermal conductivity that limit the rate of cooling in large objects (with low surface to mass ratios) (James et al., 2015). (c) Despite the high efficiency of cryogenic liquids, their use increases the operation cost.

8.4.3

Examples of indirect immersion freezing

Indirect immersion freezing has been commercially applied to packaged or canned food, such as fruit juices and concentrates, vegetables, meat, fish, and shrimp. This freezing type has shown an improvement on the freezing effect on meat quality. For instance, Ren et al. (2021) observed a higher freezing rate than traditional air freezing in beef longissimus muscle vacuum packaged at
35 C as well as better microstructure and better color quality during the first 75 days of frozen storage. Hou et al. (2020) obtained similar results when comparing quality changes of pork using immersion solution freezing and air blast freezing showing not only improvement in water-holding capacity but also inhibition in lipid oxidation during frozen storage of the product. Application of vacuum packaging coupled with cryogenic immersion freezing has been evaluated in carp fillet, especially considering safety aspects since in general fish products spoil faster than other muscle foods (Chen, Qu, et al., 2014). In this sense, Qian et al. (2018) reported better integrity of physical structure of cryogenically frozen carp fillets when using cryogenic immersion compared to air-blast freezing. Additional information on this regard is shown in Section 8.5.3 in Table 8.3.

176

8.5

Low-Temperature Processing of Food Products

Immersion freezing systems

Typically, a conveyor belt carrying solid goods through a liquid nitrogen bath is used in immersion freezers. After leaving the immersion freezer, the product is often transferred to another freezer, a combination of a liquid nitrogen bath and a mechanical system freezer, where it is totally frozen. Although both tunnel freezers and immersion freezers have been successfully employed for individual quick freezing (IQF) applications, each has pros and cons. Immersion freezers can produce more than tunnel freezers because they employ liquid nitrogen as the freezing agent rather than recirculated gaseous nitrogen. In contrast to tunnel freezers, which operate at temperatures between 35 and 50 W/m2  C, immersion freezers can remove heat at a range of 500e800 W/m2  C. The main drawback of immersion freezers is their lower nitrogen efficiency; they require 3e4 kg of nitrogen for every kg of product, compared to 1e2 kg for conventional tunnel freezers (Cachon et al., 2019). In addition, during immersion, the intense turbulence of the boiling liquid nitrogen creates IQF conditions that are suited for foods with irregular shapes and prevents food from adhering together. However, the residence time must be carefully managed to avoid over freezing or internal tensions brought on by the strong thermal shock that would cause the food to split or break. A 1.5 m long bath can freeze 1000 kg of microscopic food particles per hour due to the quick freezing, allowing for large production rates with minimal equipment (Fig. 8.2) (Annon, 2000). Cryogenic freezers, which can be batch cabinets, straight-belt freezers, spiral conveyors, or liquid immersion freezers, use liquid nitrogen or liquid carbon dioxide as the refrigerant. Cryogenic freezers have a high operational cost despite having a modest initial investment. Cryogenic freezing is so frequently used for low-volume production, novel products, overflow circumstances, or seasonal products. Straightthrough, single-belt tunnel cryogenic freezers are the most popular kind. At the freezer’s outfeed end, liquid nitrogen or carbon dioxide is injected directly onto the product at
196 or
79 C, respectively. The cold vapors that are produced as the liquid nitrogen or carbon dioxide vaporizes are pumped in the direction of the infeed

Figure 8.2 Immersion freezing system using liquid nitrogen. Adapted from Annon (2000).

Direct or indirect immersion freezing systems

177

end, where they are employed to precool and first freeze the product. The warmed vapors are then released into the environment at a temperature of typically 45 C. Rapid freezing is made possible by the liquid and vaporous nitrogen or carbon dioxide’s low temperature, which can enhance some products’ quality and lessen dehydration. However, the cost of freezing is significant, and if safety measures are not performed, the surface of items with a high-water content may shatter (Becker & Fricke, 2003).

8.5.1

Efficiency and energy consumption

The freezing rate of immersion freezing systems is high. This can be related to the heat transfer coefficient of the medium, being 5e26 times higher than air; the thermal conductivity of liquid freezing medium is around 0.116e0.628 W/m/ K, while air shows 0.024 W/m/ K (Qian et al., 2018). Important differences in the freezing rate between immersion chilling and freezing (ICF) and traditional air freezing (TAF) were reported: the freezing time was reduced 26.38 times in ICF beef than in TAF (0.683 h in ICF vs. 18.017 h in TAF); the freezing rate increased several times (5.124 cm/h in ICF vs. 0.194 cm/h in TAF); while the time to pass maximum ice crystal formation zone were 22 versus 734 min in ICF and TAF, respectively (Ren et al., 2021). Additionally, it possesses a high efficiency in the freezing process. The increase in the formation of small ice crystals is directly associated with the high freezing rate. This is because the speed for reaching the maximum ice crystal formation influences the features of that crystals (distribution within food cells, number, and size) (Ren et al., 2021).

8.5.2

Cost considerations

The frozen food market was valued at $397.3 billion in 2022 worldwide, being forecasted to reach $607.2 billion in 2032 (Snehal & Roshan, 2023). However, a number of expenses must be taken into consideration for analyzing the cost of immersion freezing food (Fig. 8.3). It is clear that the cost of operational and production expenses must be calculated case by case. Those directly concerning the immersion freezing process, as well as the purpose of this chapter are shown below. The energy cost depends on energy efficiency/consumption of the immersion system per hour, the cost, and number of operation hours (Table 8.2). The average price of electricity was about 12.49 ¢ kWh in 2022, in the United States (U.S.), being the cost 8.45 and 12.55 ¢ kWh the price of industrial and commercial electricity, respectively (EIA, 2023). When immersion freezing processes were compared with other freezing types, it showed an important energy saving. The cost reduction is mainly attributed to three facts (Lucas & Raoult-Wack, 1998): (a) Low power requirement: the freezing process required a short time and the liquids did not require a high flow/velocity.

178

Low-Temperature Processing of Food Products

Figure 8.3 Main expenses from immersion freezing.

Table 8.2 Items to calculate the immersion freezing cost per month. Feature

Description

Production rate Immersion freezer capacity Working capacity (WC) Electricity cost (EC) Power

kg of frozen product/month kg of frozen product/h h of operation/month U.S.$/kW kW  WC ¼ kWh/month kWh/month  EC ¼ U.S.$/month

(b) Overall, the immersion freezing equipment is small thus increasing the heat transfer efficiency of freezing medium (liquids). (c) The fast heat transfers of liquids, as well as the small number of devices for freezing processing reduce the cost.

A reduction of 25% energy consumption was observed in ICF freezing vegetables (2 min in liquid freezing medium at
18 C and velocity 0.07 m/s) as compared with air-blast freezing (7 min freezing time, air temperature
35 C, air velocity 3.81 m/s) (Robertson et al., 1976). In this sense, the final cost of sardines was reduced by a half when freezing with ICF instead of air-blast freezing (Crepey, 1972). Similarly, a 30% reduction in the cost of ICF minced beef and hacked spinach was obtained when compared with air-blast

Direct or indirect immersion freezing systems

179

freezing (Cornier, 1983). The fixed, operational, and worker costs were reduced when processing fish and poultry at industrial scale with ICF (Anon, 1971). On the other hand, the cost of water and fuel required for pretreatments of immersion freezing, such as washing, blanching, or chilling is variable and depends on the region, country, and type of practices (Barbosa-C
anovas et al., 2005).

8.5.3

Suitability for different applications

Immersion freezing is a technology widely applied in different types of food (fruits, vegetables, meat, milk, fish, and also processed foods), fresh or processed, packaged or unpackaged, as shown in Table 8.3. All they have been preserved using immersion freezing by traditional methods or in combination with another technology. As a result, food as similar as the fresh product or at least with reduced tissue damage, as well as with improved features (quality, taste, nutrition, safety) can be achieved by using immersion freezing.

8.6

Innovations in immersion freezing technologies

Freezing is being considered as one of the most energy consuming processes applied in the food industry. Precooling, phase transition, and sub-cooling are the main stages in the freezing process (Kami
nska & Lewicki, 2006). Innovations are focused in improving the quality of frozen food but also in saving energy cost of the process. The application of ultrasound has shown several benefits including improvement of the freezing efficiency and promoting the formation of small ice crystals and shorter freezing times leading to higher product quality (Wu et al., 2022). For instance, the use of ultrasound technology before or after the specific treatment has shown to be effective in optimizing crystallization of frozen meat. Li et al. (2022) improved the quality of pork muscle by inhibiting juice loss, enhancing tenderness and improving the stabilization of the color of the product when using ultrasound-assisted immersing freezing technology at 30 W/L. The product was packed in polyethylene bags and placed in a cooling tank as refrigeration medium. An ultrasound power was set to 300 W and the product frozen at
20 C until the central temperature decreased to
18 C. Ultrasound-assisted treatment with indirect immersion freezing has been also explored in fish products to improve muscle integrity and reduced thawing loss (Ma et al., 2021; Sun, Zhao, et al., 2019). Hu et al. (2022) observed less tissue damage during frozen storage and better freshness maintenance in packed shrimps and subjected to ultrasound-assisted immersion freezing using 50% ethanol solution in ultrasonic groove, temperature of
20 C, and ultrasonic frequency of 45 kHz. Ultrasoundassisted freezing has been exerted many benefits in different fruits and vegetables including reduction of drip loss, retention of color, maintenance of firmness, preservation of bioactive compounds such as ascorbic acid, total phenolic or anthocyanin, as well as the preservation of product integrity (Wu et al., 2022). Ultrasound technology has been also explored to overcome problems of immersion freezing in aqueous

Food product Fruit

Apple (Granny Smith, cylinders 1.8 cm diameter  2.5 cm high)

Litchi (whole)

Immersion freezing conditions

Main results B B

B B

B

B

Reference

The freezing rates were improved. The freezing efficiency increased by 10%e11% when ultrasound was applied at
1 and 0 C during 120 s.

Delgado et al. (2009)

The freezing rate was 10 times higher than AF. The average size of ice crystals was AF > 200 mm > IF, maintaining the integrity of the microstructure. A scarce drip loss, high texture retention (80%), high quality (red color, texture and taste) and nutrient content in IF samples were also observed. IF extended the shelf-life by 6 months.

Liang et al. (2015) Low-Temperature Processing of Food Products

- 50% Ethylene glycol solution at
25 C assisted with ultrasound in a bath, using refrigerated circulator. - The ultrasound conditions were: 40 kHz frequency, power level of 131.3 W (0.23 W/cm2), at different exposure times (80e120 s, intervals of 5 s) and different initial temperatures (0 to
2 C). - Freezing storage not determined. - Quaternary refrigerant (17.2 mol/L alcohol, 13.5 mol/L propylene glycol, 0.7 mol/L sodium chloride and pure water) at
35 C during 10 min. - Immersion instant freezer (Type: BN500, Guangzhou, China) equipped with a jet agitation regulator device. - Pre-cooled until the interior temperature of samples reached 0 C.

180

Table 8.3 Application of immersion freezing in different food products.a

- 30% Calcium chloride solution at
25 C assisted with US (30 kHz, 0.28 W/cm2, 30 s with intervals of 5 s). - US intensities at 0.09, 0.17, 0.28, 0.42 and 0.51 W/cm2 were used during the freezing process. - Freezing storage not determined.

B

B

B

Strawberry (whole)

- Liquid nitrogen at
18 C by immersion during 25 s. - Pretreatment with cryoprotectants (12 g/100 g trehalose solution; 0.2 g/ 100 g cold-acclimated wheatgrass solution containing antifreeze protein or combination of 12 g/100 g trehalose with 0.2 g/100 g cold-acclimated wheatgrass solution under vacuum for 14 min). Cryoprotectans were vacuum infused at 20 C/14 min/
86 kPa. - Freezing storage at
18 C/10 min, thawed at 20 C/2 h and let to drip overnight at 4 C.

B

B B

The combination of US irradiation temperature and intensity improved the nucleation and freezing processes. The US irradiation induced nucleation at a lower degree of supercooling compared to non-irradiated fruit. The degree of supercooling was linearly correlated to the US irradiation temperature. The CFT of irradiated products at
1.6 C was reduced. The higher US intensity the shorter CFT. The cryoprotectants trehalose and antifreeze protein improved the freezing tolerance of strawberries. The cryoprotection effect depended on the heterogeneity of fruit tissues. Tissues near the fruit surface were not protected from thawing; cortical and vascular tissues, as well as pith were protected from freezing and thawing.

Cheng, Zhang, Adhikari, Islam, Xu (2014)

Velickova et al. (2013)

Direct or indirect immersion freezing systems

Strawberry (whole)

Continued

181

182

Table 8.3 Continued Food product Strawberry (whole)

Vegetables

Broccoli (florets of 5  0.5 cm diameter)

Immersion freezing conditions - 30% Calcium chloride at
20 C in a basket. - Pretreatment with 0.05% PME at 38 C/ 30 min. - Freezing storage at
22 C for 55 days, thawed at 5 C/15 h.

B

B B B

B

Drip loss was reduced during freezing and thawing but not after freezing in comparison to slow freezing. Firmness decreased by 74% in thawed fruit. The pretreatment with PME did not provide additional benefits. The UAF at 0.250e0.412 W/cm2 decreased the freezing time and the loss of cell-wall bound calcium content. The texture, color and Lascorbic acid content were better preserved, while the drip loss was significantly minimized by the application of UAF in comparison to traditional freezing. Overall, the quality of broccoli frozen with UAF in a different range from the above mentioned (0.250e0.412 W/ cm2) was inferior as compared to traditional freezing.

Reference Galetto et al. (2010)

Xin et al. (2014a)

Low-Temperature Processing of Food Products

- 30% Calcium chloride solution at
25 C with a UAF (Hechuang Co., China) and a refrigeration system. - The US conditions were: 20 or 30 kHz frequency, 60 s on/60 s off duty cycle, and 0, 125, 150, 175, or 190 W power levels. - Pretreatment: blanching at 95  1 C for 3 min. - Freezing storage not determined.

Main results

- 40% Calcium chloride solution at
25 C, circulated through an immersion cooling bath. - The UAF (Hechuang Co., China) operates at 20 and 30 kHz frequency and dissipated powers from 125 to 190 W. - Pretreatment: Pretreatment: blanching at 95  1 C for 3 min. - Freezing storage not determined.

B

B B

Mushrooms (cubic pieces 17 mm sides; 3 varieties)

- 50% Ethylene glycol solution at
25 C. - The UAIF (Ningbo Scientz Biotechnology Co. Ltd.) operates at 20 kHz and nominal power levels of 33.33%, 66.66%, and 93.33% at intervals of 10 s. - Mushroom varieties: L. edodes, A. bisporus and P. eryngii).

B

B

B

B

The total freezing time and times required for precooling, phase change and subcooling stages were reduced when applying UAF at 150 W (30 kHz) or 175 W (20 kHz) power level, taking into consideration other parameters such as exposure time, US irradiation temperature and pulse mode. The drip loss was significantly reduced in UAF treated samples. The microstructure and the firmness were maintained in UAF as compared to traditional immersion freezing. The nucleation time decreased between 24% and 53% when applying UAIF at 0.39 W/cm2 (20 kHz). The drip losses were reduced by 10% in UAIF in comparison to control samples, improving the microstructure. High hardness and chewiness; low cohesiveness and springiness were achieved in postthawing UAIF samples. The activity of PPO and POD enzymes decreased in UAIF mushrooms.

Xin et al. (2014b)

Direct or indirect immersion freezing systems

Broccoli (florets of 5  0.5 cm diameter)

Islam et al. (2014)

Continued 183

184

Table 8.3 Continued Food product Potatoes (cubes 1.5 cm3 size, about 8 g)

Potatoes (stick shapes 76 mm length  17 mm width  17 mm height)

Immersion freezing conditions - 50% Glycerol at
6 C. - The US processor at 300 W, frequency 35 kHz, treatment time 8 s, pulse duration 1 s was applied when the temperature in the center of the potato sample was in the range of
0.1 to
3.0 C. - 50% Ethylene glycol solution at
18 or
20 C. - US bath system at 25 kHz, 7.34, 15.85 and 25.89 W, intervals of 30 s. - Freezing storage not determined.

Main results B B B

B

B

B

B

Comandini et al. (2013)

Li and Sun (2002) and Sun and Li (2003)

Low-Temperature Processing of Food Products

B

The US anticipated the nucleation. Supercooling degree was linearly related to US irradiation temperature. The freezing time was reduced when the US treated potato center was
2.0 C. The freezing rate increased when US (15.85 W for 2 min) was applied to the phase change period during the freezing process. The freezing rate was influenced by US power, exposure time and freezing phase. The higher US power and the longer the exposure time, the stronger the sonication. The US allowed controlling the crystallization processes by enhancing the nucleation rate and crystal growth. An improved structure of frozen and thawed tissue was improved by the US.

Reference

Beef (longissimus muscle, vacuum packed) Chicken breast

- Immersion chilling and freezing (ICF) system (Beijing Xuteng Xiangyuan Science and Technology Development Co. LTD) at
35 C. - Freezing storage
18 C for 150 days. - RL-1 Quaternary refrigerant liquid, the freezing point was
49.48 C and low viscosity. - Dynamic simulations and experimental investigations were performed.

B B

B

B

B

High freezing rate. Improved structural properties of tissue.

Ren et al. (2021)

The total freezing time was reduced by 12.85 times and the quality was high in IF in comparison to AF. The total freezing time was reduced by 36.9%. When the flow rate increased from 0.11 to 0.63 kg/s. However, a high flow rate of refrigerant increased the flow resistance and lead to unnecessary energy consumption. The total freezing time decreased by 35.5% when the temperature reduced from
25 to
40 C. However, the lowest temperature of the liquid refrigerant, the highest viscosity and power consumption.

Li et al. (2022)

Direct or indirect immersion freezing systems

Meat

Continued

185

186

Table 8.3 Continued Food product Fish

Milk

Carp (5 cm long chops)

- 95% Ethanol, 5% fluoride at
25 C. - Traditional IF and UAIF (Nanjing Xianou Co., Ltd., China). The output power was set at 0 (IF) and 175 W (UAIF), frequency 30 kHz, 30 s on/30 s off cycle/9 min. - Freezing storage at
18 C for 180 days.

- 50% Ethylene glycol solution at
15 C/90 min using a thermostatically controlled circulating cooling bath. - Generation of CO2 nano-bubble by sonication (indirect US vibration) at 20 kHz/20 s during immersion freezing of carbonated (0, 1000, and 2000 ppm) food. - Freezing storage not determined.

Main results B

B

B

B

In UAIF carps, the growth of ice crystals was inhibited; the mobility, loss of immobilized and free water decreased; the thawing and cooking loss was reduced; a good muscle tissue state was kept; the thermal stability was improved. The increase in TBARS and TVB-N were retarded during carp storage frozen with UAIF as compared to air freezing and IF. The presence of casein, fat, and other nanoparticles did not influence the water crystallization behavior in the carbonated and sonicated samples. The nucleation time in samples with or without nano-bubbles at 2000 ppm of CO2 was 7.9  0.1 and 2.8  0.8 min, respectively.

Reference Sun, Sun, et al. (2019) and Sun, Zhao, et al. (2019)

Adhikari et al. (2020) Low-Temperature Processing of Food Products

Milk (carbonated and noncarbonated)

Immersion freezing conditions

Apple juice (10, 30, and 50  Brix; carbonated and noncarbonated)

Vanilla soft-serve ice-cream (30  Brix; carbonated and noncarbonated)

- 50% Ethylene glycol solution at
15 C/90 min using a thermostatically controlled circulating cooling bath - Generation of CO2 nano-bubble by sonication (indirect US vibration) at 20 kHz/20 s during immersion freezing of carbonated (0, 1000, and 2000 ppm) food. - Freezing storage not determined.

B

- 50% Ethylene glycol solution at
15 C/90 min using a thermostatically controlled circulating cooling bath. - Generation of CO2 nano-bubble by sonication (indirect US vibration) at 20 kHz/20 s during immersion freezing of carbonated (0, 1000, and 2000 ppm) food. - Freezing storage not determined.

B

B

B

The effect of the US irradiation wave was only perceived in the low concentrate juice with dissolved CO2. The viscosity of concentrated juice restricted the water crystallization during freezing. The nucleation temperature in the juice with nano-bubbles (2000 ppm CO2) and 10  Brix was
9.3  0.3 C versus
11.7  0.9 C from the control juice. Fast nucleation, reduction of supercooling degree, and nucleation time during freezing by the assistance of the bubbles generated from the dissolved gas (without conventional cavitation bubbles) in the sample. The nucleation temperature was plunged to fivefold using US irradiation with 2000 ppm CO2, and thus, the time for onset of nucleation was halved due to the presence of nanobubbles.

Adhikari et al. (2020)

Adhikari et al. (2020)

Direct or indirect immersion freezing systems

Processed food

Continued

187

188

Table 8.3 Continued Food product Strawberry (fresh and jam)

Immersion freezing conditions - Liquid nitrogen freezer tunnel at
80 C/7 min (AGA Freeze Mini, model 30-06, Oy AGA Fricoscandia Ab, Espoo, Finland). - Pretreatments with 1% CaCl2, PME (2 mL enzyme dosage/kg of fruit) and sucrose (59.7% in the final solution). Carried out at 37 C, normal air pressure (101.3 kPa) for 15 min or in a vacuum of 16.7 kPa for 10 min. - Freezing storage
20 C for 2 months.

Main results B

B

B

Vitamin C of pretreated fruit was maintained during 2 months but after jam processing was reduced. Pretreatments with CaCl2 and PME pretreatments stabilized the original structure of the strawberries during freezing, jam cooking and storage. Higher jam quality in IF as compared to slow freezing.

Reference Suutarinen et al. (2002)

a

AF, air-blast freezing; CFT, characteristic freezing time; IF, immersion freezing; PME, pectin methylesterase; PPO, polyphenol oxidase; POD, peroxidase; TBARS, thiobarbituric acid reactive substance; TVB-N, total volatile base nitrogen; US, ultrasound; UAF, ultrasound-assisted freezer; UAIF, ultrasound-assisted immersion freezing.

Low-Temperature Processing of Food Products

Direct or indirect immersion freezing systems

189

refrigeration media due to uncontrolled penetration of solutes in the food product, reporting benefits of this combination technology in different food matrices including potato, apple, mushroom, broccoli, or strawberry (Comandini et al., 2013; Delgado et al., 2009; Islam et al., 2014; Xin et al., 2014a, 2014b; Cheng, Zhang, Adhikari, Islam, 2014). Nevertheless, studies on ultrasound application remain at the laboratory stage since need further efforts for large-scale production. The integration of nonthermal technologies as assisted immersion freezing process using high hydrostatic pressure or pulsed electric fields has also showed to enhance the freezing rate and modify the preserved the quality of food (Cheng et al., 2017a, 2017b, 2021; Li, 2022; Lu et al., 2022; Wiktor, Schulz, Voigt, Knorr, et al., 2015). Choi et al. (2016) reported that pork treated at pressure-shift freezing conditions of 100 Mpa did not differ from unfrozen control after thawing. Applying pulsed electric field treatments to apple tissue before direct immersion freezing has been reported to reduce the freezing time as well the total thawing time (Wiktor, Schulz, Voigt, WitrowaRajchert, et al. 2015). However, firmness and color were altered indicating that an optimal parameter of PEF treatment for each material need to be explored. Other innovations related to immersion freezing technologies include the use of edible liquid soaking as freezing liquid to preserve integrity of some food products, specially reported in fish (Liu, Zeng, et al., 2020; Liu, Zhang, et al., 2020; Lopkulkiaert et al., 2009; Wang et al., 2021; Xu, Azam, et al., 2019; Xu, Song, et al, 2019; Yang et al., 2020). Wang et al. (2021) reported the use of quick-freezing liquid composed by food-grade propylene glycol, oligosaccharides, and salts in indirect immersion freezing system observing a better preservation of the quality compared to air freezing. In order to improve the efficiency of current immersion freezing equipment, a mathematical model of the prefreezing process using computational fluid dynamics (CFD) software to simulate the three-dimensional unsteady state of the pork was applied (Chang et al., 2023). In this case, the sample (pork) was placed in a rotating hopper device in a flowing refrigerant carrier. The rotating device reduced the freezing time of the immersion and freezing equipment by 2830 s, improving by 55% the efficiency. The freezing time was shortened by 1290 s when the rotation speed r increased from 2 to 4 rad/s, increasing the freezing efficiency by 53%.

8.7

Conclusion

Freezing food, either directly or indirectly, is a technology that has been used for many years. However, it possesses a great variety of features and challenges that allow it to arouse the interest of researchers in this area. To improve the freezing process, it has been applied to different conditions, as pretreatments, freezing medium, innovative coolants/devices/processes, software, etc. With the increase in the consumer’s demand, and thus the market size of freezing products, a great variety of products are nowadays available, covering almost all the categories: fruits, vegetables, meat, fish, milk, processed or cooked food, etc.). The expansion of the global frozen food industry is warrantied for the next generations.

190

Low-Temperature Processing of Food Products

Therefore, it is essential to continue carrying out research in the opportunity areas within this process. It is necessary to expand the knowledge on new and sustainable immersion freezing systems, as well as to look for efficient coolants. It is important to find answers to questions such as: How can be achieved an efficient reduction in the freezing time and energy consumption without compromising the quality of frozen food? What kind of pretreatments/natural additives/cryoprotectants reduce the loss of quality/textural/sensorial/drip/thawing of food during the storage? How can be expanded to the food considered as nonsuitable for freezing without compromising their quality features? among a wide range of other challenges.

References Adhikari, B. M., Tung, V. P., Truong, T., Bansal, N., & Bhandari, B. (2020). Impact of In-situ co2 nano-bubbles generation on freezing parameters of selected liquid foods. Food Biophysics, 15(1), 97e112. https://doi.org/10.1007/s11483-019-09604-z Annon. (2000). Cryo-Quick® immersion tunnel freezer, company information from air products. Available at: www.airproducts.com/Products/equipment/FoodFreezers/PDF_Solution Finder/Cryo-Quick%20Immersion%20Tunnel%20Freezer.pdf. Anon. (1971). They took the ‘blast’ out of freezing. Food in Canada, 6, 40e41.
Astr
ain-Redín, L., Abad, J., Rieder, A., Kirkhus, B., Raso, J., Cebri
an, G., & Alvarez, I. (2021). Direct contact ultrasound assisted freezing of chicken breast samples. Ultrasonics Sonochemistry, 70, 105319. https://doi.org/10.1016/j.ultsonch.2020.105319 Barbosa-C
anovas, G. V., Altunakar, B., & Mejía-Lorio, D. (2005). Freezing of fruits and vegetables. An agri-business alternative for rural and semi-rural areas. FAO Agricultural Services Bulletin 158. https://www.fao.org/3/y5979e/y5979e00.htm#Contents. Becker, B. R., & Fricke, B. A. (2003). Freezing operations. In B. Caballero (Ed.), Encyclopedia of food sciences and nutrition (2nd ed., pp. 2712e2718). Academic Press. https://doi.org/ 10.1016/b0-12-227055-x/00522-8 Bodin, N., Lucas, V., Dewals, P., Adeline, M., Esparon, J., & Chassot, E. (2014). Effect of brine immersion freezing on the determination of ecological tracers in fish. European Food Research and Technology, 238(6), 1057e1062. https://doi.org/10.1007/s00217014-2210-3 Cachon, R., Girardon, P., & Voilley, A. (2019). Refrigeration (Chapter 7.1). In Gases in agrofood processes (pp. 223e318). Academic Press. https://doi.org/10.1016/B978-0-12812465-9.00014-1 Chang, J., Sun, P., Gong, X., Sun, Z., Wang, J., & Li, X. (2023). Simulation based analysis of the effect of new immersion freezing equipment on the freezing speed. Applied Sciences, 13, 2392. https://doi.org/10.3390/app13042392 Cheng, J.-H., Qu, J.-H., Sun, D.-W., & Zeng, X.-A. (2014). Visible/near-infrared hyperspectral imaging prediction of textural firmness of grass carp (Ctenopharyngodon idella) as affected by frozen storage. Food Research International, 56, 190e198. https://doi.org/10.1016/ j.foodres.2013.12.009 Cheng, L., Sun, D.-W., Zhu, Z., & Zhang, Z. (2017a). Emerging techniques for assisting and accelerating food freezing processes: A review of recent research progresses. Critical Reviews in Food Science and Nutrition, 57(4), 769e781. https://doi.org/10.1080/ 10408398.2015.1004569

Direct or indirect immersion freezing systems

191

Cheng, L., Sun, D.-W., Zhu, Z., & Zhang, Z. (2017b). Effects of high pressure freezing (HPF) on denaturation of natural actomyosin extracted from prawn (Metapenaeus ensis). Food Chemistry, 229, 252e259. https://doi.org/10.1016/j.foodchem.2017.02.048 Cheng, L., Zhu, Z., & Sun, D.-W. (2021). Impacts of high pressure assisted freezing on the denaturation of polyphenol oxidase. Food Chemistry, 335, 127485. https://doi.org/ 10.1016/j.foodchem.2020.127485 Cheng, X., Zhang, M., Adhikari, B., Islam, M. N., & Xu, B. (2014). Effect of ultrasound irradiation on some freezing parameters of ultrasound-assisted immersion freezing of strawberries. International Journal of Refrigeration, 44, 49e55. https://doi.org/10.1016/ j.ijrefrig.2014.04.017 Cheng, X.-F., Zhang, M., Adhikari, B., & Islam, M. N. (2014). Effect of power ultrasound and pulsed vacuum treatments on the dehydration kinetics, distribution, and status of water in osmotically dehydrated strawberry: A combined NMR and DSC study. Food and Bioprocess Technology, 7(10), 2782e2792. https://doi.org/10.1007/s11947-014-1355-1 Choi, M.-J., Min, S.-G., & Hong, Geun-Pyo (2016). Effects of pressure-shift freezing conditions on the quality characteristics and histological changes of pork. LWT e Food Science and Technology, 67, 194e199. Comandini, P., Blanda, G., Soto-Caballero, M. C., Sala, V., Tylewicz, U., Mujica-Paz, H., Valdez Fragoso, A., & Gallina Toschi, T. (2013). Effects of power ultrasound on immersion freezing parameters of potatoes. Innovative Food Science & Emerging Technologies, 18, 120e125. https://doi.org/10.1016/j.ifset.2013.01.009 Cornier, G. (1983). Comparaison technico-economique de systemes de congelation. In Vol. 4. Proceedings of the XVIth international congress of refrigeration, Paris (pp. 129e135). Crepey, J. R. (1972). Congelation continue de sardines en vrac par immersion dans la saumure. In IIR proceedings series ‘refrigeration science and technology’ (pp. 155e161). Varsovie. Dalvi-Isfahan, M., Hamdami, N., & Le-Bail, A. (2016). Effect of freezing under electrostatic field on the quality of lamb meat. Innovative Food Science and Emerging Technologies, 37, 68e73. https://doi.org/10.1016/j.ifset.2016.07.028 Delgado, A. E., Zheng, L., & Sun, D. W. (2009). Influence of ultrasound on freezing rate of immersion-frozen apples. Food and Bioprocess Technology, 2(3), 263e270. https:// doi.org/10.1007/s11947-008-0111-9 EIA. (2023). U.S. Energy Information Administration, independent statistics and analysis, electricity explained. Factors affecting electricity prices. Retrieved from www.eia.gov on August 10th, 2023. https://www.eia.gov/energyexplained/electricity/prices-and-factorsaffecting-prices.php. Eickhoff, L., Dreischmeier, K., Zipori, A., Sirotinskaya, V., Adar, C., Reicher, N., Braslavsky, I., Rudich, Y., & Koop, T. (2019). Contrasting behavior of antifreeze proteins: Ice growth inhibitors and ice nucleation promoters. Journal of Physical Chemistry Letters, 10(5), 966e972. https://doi.org/10.1021/acs.jpclett.8b03719 Fan, K., Zhang, M., Wang, W., & Bhandari, B. (2020). A novel method of osmoticdehydrofreezing with ultrasound enhancement to improve water status and physicochemical properties of kiwifruit. International Journal of Refrigeration, 113, 49e57. https:// doi.org/10.1016/j.ijrefrig.2020.02.013 Fikiin, K. (2003). Novelties of food freezing research in Europe and beyond. SMEs No.10. Retrieved on August 6th, 2023 from: http://www.cold.org.gr/library/downloads/Docs/ Novelties%20of%20food%20freezing%20research%20in%20Eur.

192

Low-Temperature Processing of Food Products

Fu, X., Belwal, T., Cravotto, G., & Luo, Z. (2020). Sono-physical and sono-chemical effects of ultrasound: Primary applications in extraction and freezing operations and influence on food components. Ultrasonics Sonochemistry, 60, 104726. https://doi.org/10.1016/ j.ultsonch.2019.104726 Galetto, C. D., Verdini, R. A., Zorrilla, S. E., & Rubiolo, A. C. (2010). Freezing of strawberries by immersion in CaCl2 solutions. Food Chemistry, 123(2), 243e248. https://doi.org/ 10.1016/j.foodchem.2010.04.018 Hafezparast-Moadab, N., Hamdami, N., Dalvi-Isfahan, M., & Farahnaky, A. (2018). Effects of radiofrequency-assisted freezing on microstructure and quality of rainbow trout (Oncorhynchus mykiss) fillet. Innovative Food Science & Emerging Technologies, 47, 81e87. https://doi.org/10.1016/j.ifset.2017.12.012 Hou, Q., Cheng, Y. P., Kang, D. C., Zhang, W. G., & Zhou, G.-H. (2020). Quality changes of pork during frozen storage: Comparison of immersion solution freezing and air blast freezing. International Journal of Food Science and Technology, 55(1), 109e118. https:// doi.org/10.1111/ijfs.14257 Hu, Z., Chin, Y., Huang, J., Zhou, J., Li, G., Pei, Z., Shang, W., Hu, Y., Yuan, C., & Chen, J. (2022). Fresh keeping mechanism of Fenneropenaeus chinensis by ultrasound-assisted immersion freezing: Effects on microstructure and quality changes. Journal of Food Processing and Preservation, 46(10), e16816. https://doi.org/10.1111/jfpp.16816 Islam, M. N., Zhang, M., & Adhikari, B. (2017). Ultrasound-assisted freezing of fruits and vegetables: Design, development, and applications. In Global food security and wellness (pp. 457e487). Springer. https://doi.org/10.1007/978-1-4939-6496-3_22 Islam, M. N., Zhang, M., Adhikari, B., Xinfeng, C., & Xu, B.-G. (2014). The effect of ultrasound-assisted immersion freezing on selected physicochemical properties of mushrooms. International Journal of Refrigeration, 42, 121e133. https://doi.org/10.1016/ j.ijrefrig.2014.02.012 James, C., Purnell, G., & James, S. J. (2015). A Review of novel and innovative food freezing technologies. Food and Bioprocess Technology, 8, 1616e1634. https://doi.org/10.1007/ s11947-015-1542-8 Jha, P. K., Chevallier, S., Xanthakis, E., Jury, V., & Le-Bail, A. (2020). Effect of innovative microwave assisted freezing (MAF) on the quality attributes of apples and potatoes. Food Chemistry, 309, 125594. https://doi.org/10.1016/j.foodchem.2019.125594 Kami
nska, A., & Lewicki, P. P. (2006). Effect of osmotic pre-treatment on the process of apple _ freezing and thawing. Zywno
s
c Nauka Technologia Jako
s
c, 47, 101e107. Kiani, H., & Sun, D.-W. (2011). Water crystallization and its importance to freezing of foods: A review. Trends in Food Science and Technology, 22(8), 407e426. https://doi.org/10.1016/ j.tifs.2011.04.011 Lagnika, C., Zhang, M., & Mothibe, K. J. (2013). Effects of ultrasound and high pressure argon on physico-chemical properties of white mushrooms (Agaricus bisporus) during postharvest storage. Postharvest Biology and Technology, 82, 87e94. https://doi.org/10.1016/ j.postharvbio.2013.03.006 Li, B., & Sun, D. W. (2002). Effect of power ultrasound on freezing rate during immersion freezing of potatoes. Journal of Food Engineering, 55(3), 277e282. https://doi.org/ 10.1016/S0260-8774(02)00102-4 Li, J. G., Ma, X. Y., Zhang, J., Wang, Y., Du, M., Xiang, Q., Wang, Y., Du, J., Li, K., & Bai, Y. (2022). Insight into the mechanism of the quality improvement of porcine after ultrasoundassisted immersion freezing. International Journal of Food Science and Technology, 57(8), 5068e5077. https://doi.org/10.1111/ijfs.15815

Direct or indirect immersion freezing systems

193

Li, L. (2022). Effects of high pressure versus conventional thawing on the quality changes and myofibrillar protein denaturation of slow/fast freezing beef rump muscle. Food Science and Technology (Brazil), 42, e91421. https://doi.org/10.1590/fst.91421 Liang, D., Lin, F., Yang, G., Yue, X., Zhang, Q., Zhang, Z., & Chen, H. (2015). Advantages of immersion freezing for quality preservation of litchi fruit during frozen storage. LWT, 60(2), 948e956. https://doi.org/10.1016/j.lwt.2014.10.034 Liu, S., Zeng, X., Zhang, Z., Long, G., Lyu, F., Cai, Y., Liu, J., & Ding, Y. (2020). Effects of immersion freezing on ice crystal formation and the protein properties of snakehead (Channa argus). Foods, 9(4), 411. https://doi.org/10.3390/foods9040411 Liu, S. L., Zhang, Z. Y., Tang, W. Y., Zhao, D. D., Chen, S. P., Sui, C., & Ding, Y. T. (2020). Effect of immersion freezing on quality changes of snakehead blocks during frozen storage. Food Science, 40, 256e262. Lopkulkiaert, W., Prapatsornwattana, K., & Rungsardthong, V. (2009). Effects of sodium bicarbonate containing traces of citric acid in combination with sodium chloride on yield and some properties of white shrimp (Penaeus vannamei) frozen by shelf freezing, air-blast and cryogenic freezing. LWT, 42(3), 768e776. https://doi.org/10.1016/j.lwt.2008.09.019 Lu, N., Ma, J., & Sun, D.-W. (2022). Enhancing physical and chemical quality attributes of frozen meat and meat products: Mechanisms, techniques and applications. Trends in Food Science and Technology, 124, 63e85. https://doi.org/10.1016/j.tifs.2022.04.004 Lucas, T., Flick, D., & Raoult-Wack, A. L. (1999). Mass and thermal behaviour of the food surface during immersion freezing. Journal of Food Engineering, 41(1), 23e32. https:// doi.org/10.1016/S0260-8774(99)00068-0 Lucas, T., François, J., & Raoult-Wack, A. L. (1998). Transport phenomena in immersioncooled apples. International Journal of Food Science and Technology, 33(5), 489e499. https://doi.org/10.1046/j.1365-2621.1998.00214.x Lucas, T., & Raoult-Wack, A. L. (1998). Immersion chilling and freezing in aqueous refrigerating media: Review and future trends. International Journal of Refrigeration, 21(6), 419e429. https://doi.org/10.1016/S0140-7007(98)00014-0 Ma, X., Mei, J., & Xie, J. (2021). Effects of multi-frequency ultrasound on the freezing rates, quality properties and structural characteristics of cultured large yellow croaker (Larimichthys crocea). Ultrasonics Sonochemistry, 76, 105657. https://doi.org/10.1016/ j.ultsonch.2021.105657 Parandi, E., Pero, M., & Kiani, H. (2022). Phase change and crystallization behavior of water in biological systems and innovative freezing processes and methods for evaluating crystallization. Discover Food, 2(1), 6. https://doi.org/10.1007/s44187-021-00004-2 Pita-Calvo, C., Guerra-Rodríguez, E., Saraiva, J. A., Aubourg, S. P., & V
azquez, M. (2018). High-pressure processing before freezing and frozen storage of European hake (Merluccius merluccius): Effect on mechanical properties and visual appearance. European Food Research and Technology, 244(3), 423e431. https://doi.org/10.1007/s00217-017-2969-0 Potter, N. N., & Hotchkiss, J. H. (1995). Cold preservation and processing (Chapter 9). In Food science. Food science text series. Boston, MA: Springer. https://doi.org/10.1007/978-14615-4985-7_9 Qian, P., Zhang, Y., Shen, Q., Ren, L., Jin, R., Xue, J., Yao, H., & Dai, Z. (2018). Effect of cryogenic immersion freezing on quality changes of vacuum-packed bighead carp (Aristichthys nobilis) during frozen storage. Journal of Food Processing and Preservation, 42(6), e13640. https://doi.org/10.1111/jfpp.13640 Ren, W., Yuan, G., Lin, X., Guo, X., & Want, Z. (2021). Comparison of the immersion chilling and freezing and traditional air freezing on the quality of beef during storage. Food Science and Nutrition, 9(12), 6653e6661. https://doi.org/10.1002/fsn3.2613

194

Low-Temperature Processing of Food Products

Ribero, G. G., Rubiolo, A. C., & Zorrilla, S. E. (2009). Influence of immersion freezing in NaCl solutions and of frozen storage on the viscoelastic behavior of mozzarella cheese. Journal of Food Science, 72(5), E301eC307. https://doi.org/10.1111/j.1750-3841.2007.00373.x Robertson, G. H., Cipoletti, J. C., Farkas, D. F., & Secor, G. E. (1976). Methodology for direct contact freezing of vegetables in aqueous freezing media. Journal of Food Science, 41(4), 845e851. https://doi.org/10.1111/j.1365-2621.1976.tb00736_41_4.x Sadot, M., Curet, S., Rouaud, O., Le-Bail, A., & Havet, M. (2017). Numerical modelling of an innovative microwave assisted freezing process. International Journal of Refrigeration, 80, 66e76. https://doi.org/10.1016/j.ijrefrig.2017.04.017 Sirijariyawat, A., Charoenrein, S., & Barrett, D. M. (2012). Texture improvement of fresh and frozen mangoes with pectin methylesterase and calcium infusion. Journal of the Science of Food and Agriculture, 92(13), 2581e2586. https://doi.org/10.1002/jsfa.5791 Snehal, & Roshan. (2023). Frozen food market by product type (frozen ready meals, frozen seafood, frozen meat and poultry, frozen fruit and vegetables, frozen potatoes, frozen soups), by end user (food service industry, retail users): Global opportunity analysis and industry forecast, 2023e2032. Report Code: A00581. Retrieved from www. alliedmarketresearch.com in August 01st, 2023. https://www.alliedmarketresearch.com/ frozen-food-market#:w:text¼The%20global%20frozen%20food%20market,referred%20 to%20as%20frozen%20food. Sun, D. W., & Li, B. (2003). Microstructural change of potato tissues frozen by ultrasoundassisted immersion freezing. Journal of Food Engineering, 57(4), 337e345. https:// doi.org/10.1016/S0260-8774(02)00354-0 Sun, Q., Sun, F., Xia, X., Xu, H., & Kong, B. (2019). The comparison of ultrasound-assisted immersion freezing, air freezing and immersion freezing on the muscle quality and physicochemical properties of common carp (Cyprinus carpio) during freezing storage. Ultrasonics Sonochemistry, 51, 281e291. https://doi.org/10.1016/j.ultsonch.2018.10.006 Sun, Q., Zhao, X., Zhang, C., Xia, X., Sun, F., & Kong, B. (2019). Ultrasound-assisted immersion freezing accelerates the freezing process and improves the quality of common carp (Cyprinus carpio) at different power levels. LWT, 108, 106e112. https://doi.org/10.1016/ j.lwt.2019.03.042 Suutarinen, J., Honkap€a€a, K., Heiniö, R.-L., Autio, K., Mustranta, A., Karppinen, S., Klutamo, T., Liukkonen-Lilja, H., & Mokkila, M. (2002). Effects of calcium chloridebased prefreezing treatments on the quality factors of strawberry jams. Journal of Food Science, 67(2), 884e894. https://doi.org/10.1111/j.1365-2621.2002.tb10694.x Tang, J., Zhang, H., Tian, C., & Shao, S. (2020). Effects of different magnetic fields on the freezing parameters of cherry. Journal of Food Engineering, 278, 109949. https://doi.org/ 10.1016/j.jfoodeng.2020.109949 Usman, M., Khan, S., & Lee, J.-A. (2020). AFP-LSE: Antifreeze proteins prediction using latent space encoding of composition of k-spaced amino acid pairs. Scientific Reports, 10(1), 7197. https://doi.org/10.1038/s41598-020-63259-2 Velickova, E., Tylewicz, U., Dalla-Rosa, M., Winkelhausen, E., Kuzmanova, S., & G
omezGalindo, F. (2013). Effect of vacuum infused cryoprotectants on the freezing tolerance of strawberry tissues. LWT, 52, 146e150. https://doi.org/10.1016/j.lwt.2011.09.013 Wang, Y., Zhang, T., Chen, Q., Wu, Y., Cai, Q., Zhao, Y., Cen, J., & Wei, Y. (2021). Effects of immersion freezing with coolant on the quality of grouper (\Epinephelus fuscoguttatus _ Epinephelus lanceolatus) during frozen storage. CyTA e Journal of Food, 19(1), 634e644. https://doi.org/10.1080/19476337.2021.1946159

Direct or indirect immersion freezing systems

195

Wiktor, A., Schulz, M., Voigt, E., Knorr, D., & Witrowa-Rajchert, D. (2015). Impact of pulsed electric field on kinetics of immersion freezing, thawing, and on mechanical properties of carrot [Wpływ pulsacyjnego pola elektrycznego na kinetykę zamra_zania immersyjnego, rozmra_zania oraz wła
sciwo
sci mechaniczne marchwi]. Zywnosc Nauka Technologia Jakosc/Food Science Technology Quality, 22(2), 124e137. https://doi.org/10.15193/zntj/ 2015/99/027 Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 8e16. https://doi.org/10.1016/ j.jfoodeng.2014.08.013 Wu, J., Jia, X., & Fan, K. (2022). Recent advances in the improvement of freezing time and physicochemical quality of frozen fruits and vegetables by ultrasound application. International Journal of Food Science and Technology, 57(6), 3352e3360. https://doi.org/ 10.1111/ijfs.15744 Xanthakis, E., Havet, M., Chevallier, S., Abadie, J., & Le-Bail, A. (2013). Effect of static electric field on ice crystal size reduction during freezing of pork meat. Innovative Food Science and Emerging Technologies, 20, 115e120. https://doi.org/10.1016/j.ifset.2013.06.011 Xin, Y., Zhang, M., & Adhikari, B. (2014a). Ultrasound assisted immersion freezing of broccoli (Brassica oleracea L. var. botrytis L.). Ultrasonics Sonochemistry, 21(5), 1728e1735. https://doi.org/10.1016/j.ultsonch.2014.03.017 Xin, Y., Zhang, M., & Adhikari, B. (2014b). The effects of ultrasound assisted freezing on the freezing time and quality of broccoli (Brassica oleracea L. var. botrytis L.) during immersion freezing. International Journal of Refrigeration, 41, 82e91. https://doi.org/ 10.1016/j.ijrefrig.2013.12.016 Xu, B., Azam, R. S. M., Wang, B., Zhang, M., & Bhandari, B. (2019). Effect of infused CO2 in a model solid food on the ice nucleation during ultrasound-assisted immersion freezing. International Journal of Refrigeration, 108, 53e59. https://doi.org/10.1016/ j.ijrefrig.2019.09.005 Xu, B.,-G., Zhang, M., Bhandari, B., Cheng, X.-F., & Sun, J. (2015). Effect of ultrasound immersion freezing on the quality attributes and water distributions of wrapped red radish. Food and Bioprocess Technology, 8(6), 1366e1376. https://doi.org/10.1007/s11947-0151496-x Xu, Y. S., Song, M., Xia, W. S., & Jiang, Q. X. (2019). Effects of freezing method on water distribution, microstructure, and taste active compounds of frozen channel catfish (Ictalurus punctatus). Journal of Food Process Engineering, 42(1), e12937. https://doi.org/10.1111/ jfpe.12937 Xu, Z. Q., Guo, Y. H., Ding, S. H., An, K. J., & Wang, Z. F. (2014). Freezing by immersion in liquid CO2 at variable pressure: Response surface analysis of the application to carrot slices freezing. Innovative Food Science and Emerging Technologies, 22, 167e174. https:// doi.org/10.1016/j.ifset.2013.06.005 Yang, F., Jing, D., Diao, Y.,D., Yu, D., Gao, P., Xia, W., Jiang, Q., Xu, Y., Yu, P., & Zhan, X. (2020). Effect of immersion freezing with edible solution on freezing efficiency and physical properties of obscure pufferfish (Takifugu Obscurus) fillets. LWT, 118, 108762. https://doi.org/10.1016/j.lwt.2019.108762 Zhang, M., Xia, X., Liu, Q., Chen, Q., & Kong, B. (2019). Changes in microstructure, quality and water distribution of porcine longissimus muscles subjected to ultrasound-assisted immersion freezing during frozen storage. Meat Science, 151, 24e32. https://doi.org/ 10.1016/j.meatsci.2019.01.002

196

Low-Temperature Processing of Food Products

Zhao, Y. (2007). Freezing process of berries (Chapter 10). In Berry fruit: Value-added products for health promotion (pp. 291e310). Boca Raton, FL: CRC Press, Taylor & Francis Group. Zhao, Y., Ning, J., & Sun, Z. (2020). Study on liquid nitrogen and carbon dioxide combined jet
quick-frozen strawberry [Etude sur le jet combiné d’azote liquide et de dioxyde de carbone pour la surgélation rapide de fraises]. International Journal of Refrigeration, 136, 1e7. https://doi.org/10.1016/j.ijrefrig.2022.01.008 Zhu, Z., Zhou, Q., & Sun, D.-W. (2019). Measuring and controlling ice crystallization in frozen foods: A review of recent developments. Trends in Food Science and Technology, 90, 13e25. https://doi.org/10.1016/j.tifs.2019.05.012

Section Three Application of freezing in the food industry

This page intentionally left blank

Freezing of fruits and vegetables 1

1

1

9

2

Marcello Alinovi , Maria Paciulli , Massimiliano Rinaldi , Seid Reza Falsafi and Emma Chiavaro 1 1 Department of Food and Drug, University of Parma, Parma, Italy; 2Safiabad Agricultural Research and Education and Natural Resources Center, Agricultural Research, Education and Extension Organization (AREEO), Dezful, Iran

9.1

Introduction

Fruits/vegetables are reported to have numerous health-promoting properties (Jideani et al., 2021). A minimum consumption of 400e500 g/day is suggested for the hindrance of high blood pressure, stroke, cardiovascular diseases, and other micronutrient-related deficiencies (WHO, 2004, pp. 7e9). Recommended consumption primarily referred to fresh and in-season fruits/vegetables, but, unfortunately, postharvest physiological modifications and the potential bacterial contaminations could cause rapid deterioration and loss of important compounds. In addition, fruits/ vegetables typically display a short shelf life in temperate zones and/or are not able to grow all over the world, so they must be imported from countries of origin. Thus, the application of food preservation methods is pivotal for hindering the propagation of microorganisms and preserving the quality of fruits/vegetables (Giannakourou & Tsironi, 2021). Freezing is one of the most diffused preservation techniques for fruits/vegetables, thanks to the well-reported ability in retaining a high qualitative level of final products. Freezing is reported to have been successfully used on a commercial scale to extend the shelf life of several foodstuffs including fruits/vegetables since more than 140 years ago (Hu et al., 2022). The freezing process has undergone to a long evolution course starting from the utilization of snow up to very advanced technologies. In general, the following categories are reported for freezing equipments (Bogh-Sorensen, 2006): (a) (b) (c) (d)

very slow freezers (10 cm h
1).

The freezing process can be used for preserving more or less all kinds of fruits/vegetables and increasing their off-season availability. It is very important to consider that during freezing and through ice formation, the volume of cellular water increases in plant cells, and the quality of final product could be negatively affected due to consequent cellular damages (Jha et al., 2019). A very common and fundamental recommendation is to choose, if possible, technologies for freezing as fast as possible; however, super-fast freezing at very low temperatures could result in freeze fracturing or cell Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00010-2 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

200

Low-Temperature Processing of Food Products

wall piercing by the quick water expansion (Schudel et al., 2021). For this reason, the freezing and thawing process on fruits/vegetables must be properly designed and controlled by considering the specific product and its particular properties. Since the estimation of the freezing rate of a food is complicated, most large-scale operations work with overdimensioned processes to assure the quality of the final product, leading to higher energy consumption (Goncalves & Silveira Junior, 2017). This fact represents a very relevant concern about the freezing process as energy consumption and relative operational costs must be considered also from the perspective of the probable increase of them in the future. A direct outcome of freezing cost is that prices of frozen fruits/vegetables are commonly higher than fresh and canned ones (Miller & Knudson, 2014). Despite these complexities, freezing is expected to be a staple technological solution for fruits/vegetables and maybe to gain more and more attention from consumers. In the present chapter, the fundamental principles of fruit/vegetable freezing will be explained starting from the physics behind the phase transition up to different technologies and machines, as a consequence, available on the market. Moreover, quality changes in frozen fruits/vegetables based on several qualitative parameters (microstructure, water status, texture, color, and pigments content as well as aroma and nutrients) will be addressed for different vegetables/fruits. Finally, market trends and consumers demand for frozen fruits/vegetables will be discussed.

9.2

Market trends and consumers’ demand for frozen fruits/vegetables

High moisture content and rich nutrition make foods sensitive against microbial contamination and deteriorating chemical reactions (Zhang et al., 2021). It is been estimated that approximately 25%e30% of sensitive fresh foods are deteriorated each year, and proper storage techniques can hamper most of the waste (Coulomb, 2008). Hence, food preservation approaches like cooling, drying, and particularly freezing have been considerably developed to keep the quality of food products. In this context, freezing methods grant the longest storage ability to foods. The global frozen food market was about $174.4 billion in 2021 where, Asia Pacific and North America gained the largest market with 40% and 30% shares of the market, respectively, while Africa possessed the least share of the frozen food market. With particular reference to the Europe, the frozen food industry is expected to grow up to 5.15% up to 2027 (Renub Research, 2021). Moreover, the COVID-19 pandemic caused an impact also on the frozen foods market. Particularly, this industry has experienced a remarkable evolution as the current human lifestyle demands food products with greater shelf stability. Moreover, the marketability of frozen foods, particularly ready meals, is growing as people prefer to store up foods, and it also eases them from cooking affairs at times of lock-down of restaurants. In this context, British Frozen Food Federation (BFFF) reported a massive increase in vegetables (þ42.5%), savory food (þ36.7%), and potato products (þ30%).

Freezing of fruits and vegetables

201

The American Frozen Food Institute (AFFI) and The Food Industry Association (FMI) published “The Power of Frozen 2021” report described that more than 99% of shoppers purchase an item from the frozen food aisle at least once a year, and among all the categories, plain vegetables take third place confirming their great importance in the frozen food market. Plain vegetable sales accounted for $3.0 billion, while frozen fruits stayed at $1.5 billion. The success of frozen vegetables is easily explicated by the main reasons for buying frozen food presented in the report. The most important driver is the ease of preparation. Frozen vegetables are already cleaned, graded, sorted, and trimmed without any further waste. Moreover, as stated above, freezing is a preservation technique without preservatives as the low temperature is enough for preventing microbial growth in 2020, 100% natural, and the absence of preservatives were reported to be the top claims of frozen food consumers. Although the outdated attitudes about the frozen products have gently been fainting among people, still the most important challenge for companies is to alter this vision and provides consumers a better insight about the eminence and nutritional quality of the frozen foods. The company Heron Foods performed a consumer survey and less than 30% of respondents classed frozen foods as “fresh.” Only a few consumers knew that, generally, the freezing process is applied a few hours from harvesting, fishing, and slaughtering leading to a quality that could be higher compared to fresh products. From a technological point of view, industrialists could utilize novel approaches like individual quick freezing (IQF) to enhance the efficiency of the process and offer frozen products of higher quality. In the IQF approach, each piece of food is processed separately, which along with improvement in process efficiency, the nutritional loss of the food product is also hindered by the short time of freezing. Finally, frozen foods and particularly vegetables/fruits are perfect responses to today’s shoppers’ requirement for environmentally friendly options. On one hand, the manufacturers are moving toward the use of recyclable packaging instead of petroleum-based counterparts, and on the other hand, by consuming frozen products, the food waste/cost would be reduced, given the higher shelf life of frozen foods.

9.3 9.3.1

Freezing Phase transition

In physical terms, freezing can be described as a first-order phase transition of water into ice. It can be schematically described by the state diagram reported in Fig. 9.1, which displays the physical states of a system subjected to freezing as a function of temperature and mass fraction of solutes and solids. The diagram is useful for understanding the complex changes occurred in water content and temperature of the food material, identifying its stability during storage (Rahman, 2006; Roos, 2010). This physical phenomenon is of critical importance in the case of high-moisture food items, for example, fruits/vegetables, as the amount of latent heat that has to be subtracted from the food matrix is generally higher than 100 btu/lb, corresponding to w233 kJ/kg (American Society of Heating, Refrigerating and Air-Conditioning

202

Low-Temperature Processing of Food Products

Figure 9.1 Schematic demonstrating the state diagram of a fruit/vegetable product.

Engineers, 2006); the enthalpy of crystallization is greatly dependent of the water content and of factors such as the cultivar, the stage of development/maturity, and the growing conditions. Moreover, the high moisture content of fruits/vegetables is also an important factor impairing the quality characteristics of the frozen food matrix, as later discussed in this chapter. Freezing starts when the temperature is lowered below the freezing temperature (Tf) of the system (Fig. 9.1); below Tf, liquid water present in the matrix starts to nucleate and ice crystals are formed. Noteworthy, the freezing point of the system is related to the mass fraction of solutes present in the solution. As liquid water starts to transform into ice, the solutes present in the remaining liquid phase are concentrated, and the freezing point is lowered (i.e., freezing point depression) (Fig. 9.1). Also, the concentration of solutes before freezing determines the initial freezing temperature: the higher the concentration of solutes, the lower the initial freezing temperature. If the temperature of the system is further faster dropped under a certain critical temperature (Tg, i.e., the glass transition temperature, which is dependent on the concentration of the solute), it causes the transition from a liquid state of the matrix to a vitreous, glassy state (Zhao & Takhar, 2017). The intersection point of x0 s and T0 g coordinates represented in Fig. 9.1 is a characteristic transition (maximal-freeze-concentration condition) in the state diagram (Rahman, 2006, 2008); the water content in this intersection point is considered as the unfreezable water (1
X0 s). Under this temperature condition, the formation of a glassy state of the freeze-concentrated solute matrix surrounding the ice crystals is promoted (Levine & Slade, 1986). On the other side, temperature conditions between T0 g and T0 m promote the formation of an amorphous, metastable viscoelastic fluid (rubbery state) characterized by a higher molecular mobility of polymeric chains if compared to the glassy state.

Freezing of fruits and vegetables

203

The so-called glass transition is a second-order time-temperature dependent transition, characterized by a discontinuity in the properties (physical, thermal, mechanical, etc.) of the food material (Rahman, 2006, 2008). This second-order transition is related to the vitrification of the unfrozen solution of the system because of freezingconcentration phenomena of components, and for this reason, it influences mechanical, rheological, and structural transformations of biological materials, for example, crystallization, stickiness, collapse, elasticity, shrinkage, and molecular mobility (Rahman, 2006; Roos, 2010). A glass state is a metastable, amorphous state performing as a barrier to further development of ice (within the experimental time frame), and disturbing all other diffusion-controlled processes (Levine & Slade, 1986). According to the food polymer science approach (Slade & Levine, 1991, 1995), the presence of water in a polymeric matrix, like a plasticizer, increases the mobility of polymeric chains. In particular, the formation of a glass state in the matrix of fruits/ vegetables can greatly promote the physico-chemical stability of the food system, as below glass transition temperature compounds (e.g., enzymes, reactants) involved in deterioration reactions take a long time period (months, years) to diffuse and approach each other to react (Guizani et al., 2010; Slade & Levine, 1991). As aforementioned, the state diagram depicted in Fig. 9.1 is generally representative of a food material that undergoes freezing and glass transition; nonetheless, to accurately estimate the temperatures and solutes concentrations of a specific food product, experimental, calorimetric determinations have to be performed on the specific matrix. Most fruits comprise fructose, glucose, and sucrose as the major water soluble components; accordingly, the thermal/calorimetric properties of these matrices is largely influenced by the concentration and presence of these sugars (Roos, 2010). Several research studies have been conducted on different fruits/vegetables, in order to determine the characteristic freezing state diagrams of the matrices. For example, Roos carried out a study of glass transitions of strawberries by performing differential scanning calorimetry (DSC) analyses (Roos, 1987), and he observed that the ice melting in frozen samples happened at temperatures far lower the normal temperatures of frozen storage (around
42 C). Similar stability data (with T0 g ranging between
40 and
60 C) have been reported for several other fresh fruits/vegetables, for example in the case of dates (Guizani et al., 2010), grapefruit (Fabra et al., 2009; S
a & Sereno, 1994), raspberry (Syamaladevi et al., 2010), mango (Zhao et al., 2015), onion (S
a & Sereno, 1994), mushrooms (Shi et al., 2012), apple (Bai et al., 2001), banana (Rahman & Al-Saidi, 2017), orange and pineapple (Grajales-Lagunes et al., 2018), green cauliflower, and navy beans (Wang et al., 2008) (Table 9.1). Accordingly, the most commonly, industrially applied frozen storage temperature (
18/20 C) of these fruits/vegetables matrices allows ice melting and recrystallization as this temperature condition are not sufficient for the creation of the extremely freeze-concentrated phase needed for the thorough physical stability (Roos, 2010). On the other side, other studies showed that some specific fruits/vegetables, as a consequence of a lower moisture and higher solutes content, were characterized by a higher T0 g, similar to which is close to the commonly used freezing storage temperatures, such as in the case of fruits/vegetables such as peas (Lim et al., 2006) and broccoli (Xin et al., 2013) (Table 9.1); this can reduce the variations in quality attributes during frozen storage and after thawing.

204

Low-Temperature Processing of Food Products

Table 9.1 Typical glass transition temperature ( C) of different fruits/vegetables. Fruit/vegetable matrix

Botanical name

T0 g

References

Peas Raspberry

Pisum sativum Rubus idaeus


20/
26 C
63 C

Strawberry Strawberry Broccoli


42 C
50 C
25 C

Mango Onion Grape Grape Date Apple Banana

Fragaria ananassa Fragaria ananassa Brassica oleracea L. var. botrytis L. Mangifera indica L. Allium cepa Vitis vinifera Vitis vinifera Phoenix dactylifera Malus domestica Musa balbisiana

Lim et al. (2006) Syamaladevi et al. (2010) Roos (1987) S
a and Sereno (1994) Xin et al. (2013)

Orange

Citrus sinensis


52 C

Pineapple

Ananas comosus


54 C

Mushroom Green cauliflower

Agaricus bisporus Brassica oleracea var. botrytis Phaseolus vulgaris


78 C
50/
55 C

Zhao et al. (2015) S
a and Sereno (1994) S
a and Sereno (1994) Fabra et al. (2009) Guizani et al. (2010) Bai et al. (2001) Rahman and Al-Saidi (2017) Grajales-Lagunes et al. (2018) Grajales-Lagunes et al. (2018) Shi et al. (2012) Haiying et al. (2007)


53/
58 C

Haiying et al. (2007)

Navy beans

9.3.2


55 C
58 C
50 C
50 C
48 C
58 C
41 C

Thermo-physical attributes of fruits/vegetables during freezing

Other than the glass transition that has been previously discussed, other thermophysical properties and parameters are important in defining the thermophysical changes of fruits/vegetables that occur during freezing and the quality variations that occur during the frozen storage period. As said, during freezing, the water present in a food product is transformed into ice when the temperature is lowered to the freezing temperature Tf (Fig. 9.1). Tf is a colligative property that is dependent on the compositional characteristics of fruits/vegetables, and it is lowered by an enhancement in the concentration of solutes in the tissues (salts, sugars, etc.), which lowers the effective number of solvent molecules that can undergo the phase transition. Different studies tried to elaborate mathematical equations that could be useful to estimate the Tf of different food matrices, given some boundary conditions and constraints. The relationship between chemical composition of the product and its Tf could be described in terms of the freezing temperature depression of its solution. The beginning of the freezing temperature for a solution can be measured via

Freezing of fruits and vegetables

205

ClausiuseClapeyron equation, which is given by Eq. (9.1) in the presence of a single solute (Heldman, 1974):




1

0

mi=M L MA 1 1 C B A
¼ Ln@ A T0 Ti R mi=M þ mB=M A

(9.1)

B

where, L refers to latent heat of fusion, R refers to the gas constant, MA refers to the molecular weight of water, T0 refers to the freezing point of pure liquid, mB refers to the mass fraction of product solute in solution, and MB refers to the effective molecular weight of product solute. Eq. (9.1) can be used to describe a continuous function of mi versus Ti, which can be used to predict the relationship between percent unfrozen water between percent unfrozen water versus temperature during freezing of a food matrix. In the case of food systems, where different solutes are often present, empirical correlations based on the water content are often used to determine the freezing temperature depression (Wang & Weller, 2006). For example, Chang and Tao (1981) proposed an empirical equation valid for fruits/ vegetables: Tf ¼
14:46 þ 49:19XA
37:07XA2

(9.2)

Other than from theoretical calculations, the freezing point of a food system can also be more accurately determined by the utilization of experimental methodologies, such as with differential scanning calorimetry (DSC) (Tylewicz et al., 2011) or by fitting the plateau phase of a temperature/time freezing curve (Alinovi & Mucchetti, 2020; Fennema et al., 1973). Experimentally measured initial freezing temperatures of some different fruits/vegetables are reported in Table 9.2 (American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2006; Heldman, 1974; Heldman & Singh, 1981; Larkin et al., 1984; Rahman & Driscoll, 1991). Many thermo-physical parameters greatly depend on the compositional characteristics of the food matrix. This is the case of parameters such as density (r), specific heat (cp) and thermal conductivity (k) that are also important technological factors able to influence the freezing process. Accordingly, during the freezing/thawing process, the composition of the selected fruit/vegetable is changed consequently the gradual transformation of water into ice, or vice versa. Despite analytical methods (e.g., calorimetric) can be used to experimentally determine these parameters, they are effective only if the value of a particular parameter is needed at a fixed temperature (Wang & Weller, 2006). In literature, different equations have been proposed to estimate the dependence of r, cp, and k in relation to the volume fractions of macro components (water, ice, protein, fat, fiber, carbohydrates, and ash) and/or with the temperature. One of the most famous and utilized series of equations to predict the temperature-dependent thermophysical properties of food components is that proposed by Choi and Okos (1986). These equations can be used in predictive models that use the volume fractions of all components to predict the combined

206

Low-Temperature Processing of Food Products

Table 9.2 Initial freezing temperatures ( C) of different fruits/vegetables. Product

Initial freezing point (8C)

References

Spinach Green peas Tomato juice Grape juice Apple Orange juice Peach Pear Asparagus Tomato Onion Strawberry Raspberry Artichokes Lettuce Lemon Cherries


0.55
1.74
1.6
2.9
1.45
1.17
0.89
1.61
0.52
0.72
0.89
0.78
1.22
1.22
0.22
1.39
1.7

Fikiin and Fikiin (1999) Fikiin and Fikiin (1999) Fikiin and Fikiin (1999) Fikiin and Fikiin (1999) Rahman and Driscoll (1991) Heldman (1974) ASHRAE (2006) ASHRAE (2006) Larkin et al. (1984) Heldman and Singh (1981) ASHRAE (2006) ASHRAE (2006) Heldman (1974) ASHRAE (2006) ASHRAE (2006) ASHRAE (2006) ASHRAE (2006)

thermophysical property of the food matrix. An example of simple predictive model is the parallel coefficients’ model (Eq. 9.3): Y¼

n X

vi Y i

(9.3)

i¼1

where Y is the estimated thermo-physical parameter (r, cp, or k), vi and Yi are the volume fraction and the estimated thermo-physical, temperature dependent, parameter of the ith component. In the literature also, more complex theoretical models have been proposed, that consider particular structural arrangements of the food components (Carson et al., 2016) or even incorporate a distribution factor (Rahman et al., 2012). Important factors that may have an impact in the accuracy of these models in estimating the thermophysical properties of fruits/vegetables are the water content and the porosity of the matrix (Sweat, 1974). Rahman et al. (2012) proposed neural networkbased modeling technique to predict the thermal conductivity of selected fruits/vegetables based on their moisture content and apparent porosity.

9.3.2.1

Processing parameters and effective factors

The primary technological objective of a freezing process is to lower the temperature of the food item below its initial freezing temperature, at a final temperature indicated for storage (usually
18/
20 C) at the slowest cooling location in a reasonable amount of time. In particular, the freezing time of a fruit/vegetable is a consequence

Freezing of fruits and vegetables

207

of the freezing rate of the process. The International Institute of Refrigeration (1986) defined the freezing rate as the minimum distance between the surface of the sample to the thermal center of the food (d) divided by the time passed for the surface to reach 0 C and the center to become 5 C cooler than the beginning of the freezing temperature. The freezing rate is generally reported as  C/h or in terms of penetration depth as cm/h (Castell-Perez, 2020). Based on their freezing rate, the freezing processes can be grouped in slow processes (1 cm/h), semi-quick processes (1e5 cm/h), quick processes (5e10 cm/h), and very quick processes (10 cm/h) (de Ancos et al., 2006). The rate of the freezing process reckons as one of the main parameters, which influence the quality of food products as it governs the dimension of the ice crystals where the greater the freezing rate, the faster the nucleation speed, and the superior the extent of smaller crystals (Chaves & Zaritzky, 2018); this can be particularly critical in a cellular structure such as that present in a fruit/vegetable product, that can suffer chemical (e.g., loss of nutrients), structural, and textural changes as a consequence of slow freezing processes that promote the rupture of cellular tissues. The rate of freezing is mainly hinges upon characteristics of the product (e.g., size, shape, water content, thermophysical properties, density, thermal conductivity, porosity, etc.) and freezing system (i.e., the modality of heat transfer of the system). Concerning the factors related to the technology, in particular, the temperature difference (DT) and the heat transfer coefficient of the freezing process play a crucial role in defining the freezing rate. As that the conductive heat transfer coefficient inside the food matrix is an intrinsic property and cannot be controlled, the coefficient of heat transfer that can be controlled and/or optimized in freezing processing is the surface heat transfer coefficient. The surface heat transfer coefficient represents the state at the borderline between the sample and the exterior edge of the heat transfer medium (Evans, 2008). In convection-based freezing systems (e.g., air blast freezers, impingement freezers, etc.), the heat transfer is regulated by the convective coefficient h. In the modern industrial freezing systems, based on air impingement, fluidized bed or cryogenic technologies, the h coefficient is generally relatively high (50e200 W/m2K), because of the application of high air velocities and/or cryogenic fluids/sprays/vapors as cooling media (George, 1993; James et al., 2015). These modern freezing technologies are used to produce Individually Quick Frozen fruit and vegetables. Even, in freezing technologies based on the immersion of food products in cryogenic fluids, the h coefficient can be higher than 1000 W/ m2K (Fellows, 2009). Relatively lower h coefficients are reported in the case of more traditional (but still industrially utilized) freezing systems such as in the case of air blast freezing tunnels (van der Sman, 2020). Also plate freezers can be used in the case of fruits/vegetables having regular shapes or in the case of fruit/vegetable pulp and purees (Sehrawat et al., 2018). In this case, the heat transfer coefficient is mediated by a metallic surface and the heat transfer follows a conduction phenomenon; the conductive heat transfer coefficient is relatively high (w50 W/m2K) (George, 1993). As aforementioned, in order to control the freezing rate, another important technological factor is the temperature difference between the food and the freezing environment (DT). Industrial air-blast freezing technologies generally utilize cold air at
40 C as processing medium. Lower temperatures can be reached when unfreezable liquids

208

Low-Temperature Processing of Food Products

(e.g., concentrated brines, ethanol, glycol) or cryogenic fluids are adopted (e.g., liquefied gasses such as CO2 or N2), reaching temperatures even below
100 C. Despite achieving high freezing rates is generally desirable and positive for industrial freezing processes, it should be noted that some products (e.g., such as whole fruits/vegetables of large size) can be subjected to cracking and surface damage phenomena when exposed to extremely low temperatures (de Ancos et al., 2006). This is due to an abrupt density decrease of outer, frozen part of the fruit/vegetable that cause volume expansion, internal stress, and mechanical damages (Rahman, 1999).

9.3.3

Freezing equipment and technologies

As the freezing rate and the freezing time are crucial parameters that are in direct relation with the final quality of frozen fruits/vegetables, it is essential to adopt suitable freezing techniques that can be technologically effective. In particular, the technological effectiveness of a freezing process can be firstly related to parameters such as the heat transfer coefficient of the process or the temperature of the cooling medium, as discussed in the previous paragraph. Still, there are additional technological factors that have to be taken into account when designing/selecting an adequate freezing equipment: the types of products or number of types of products to be frozen, size, shape, presence of packaging material, operational mode (i.e., batch or continuous operation), daily or hourly productivity, capital investments, and actual costs. The result of these considerations should be the design or the selection of an industrially scalable, cost-efficient freezing apparatus. Freezing systems could be generally classified relying on the adopted cooling medium into freezing systems that utilize cold air (air blast systems), systems that utilize the direct contact with cold surfaces (plate freezing systems), systems based on the direct contact with unfreezable liquids (immersion freezing systems), or cryogenic fluids (cryogenic systems) (Chaves & Zaritzky, 2018; Fellows, 2009). Air blast systems. The most industrially applied freezing systems to process fruits/ vegetables are mechanical freezing systems that utilize cold air as a cooling medium. Air blast freezers utilize air at
20/40 C flowed over the product at velocities of 0.5e10 m/s (George, 1997; Swer et al., 2018). Air blast freezing systems can operate in continuous/batch mode. In batch mode, the fruits/vegetables are placed on trays in thermally insulated rooms or cabinets. Despite these systems offer a good flexibility in terms of processed products type and characteristics and other operational advantages in terms of easiness of use and low cost of investment, they cannot reach high productivity rates. Continuous air blast systems can be configured in belt or tunnel freezers depending on the design and can be optimized for diverse kind of fruits/vegetables, by modulating the dwell speed (George, 1997). Generally, in these systems, the products are placed on trays in trolleys or on a belt conveyor, which passed through an insulated tunnel or room. To reduce floor space requirements, belt freezers can also be configured into spiral freezers in which a flexible long continuous mesh belt is wrapped cylindrically forming a “helix.” To faster the freezing process, along or in substitution of cold air as cooling medium, cryogenic sprays or vapors can be utilized (Fellows, 2009). In the continuous systems, airflow can be arranged both in co-current

Freezing of fruits and vegetables

209

or counter-current mode; in the case of belt systems, usually a meshed plastic or stainless-steel belt are used, and the air can also be flowed throughout the meshes perpendicularly to the product’s flow. This design has been adopted in the case of a particular type of air-blast freezer and the fluidized bed freezer; this system consists of a bed with a perforated bottom through which cold air is blown vertically upward at high velocities. During this process, fruits/vegetables are subjected to fluidization due to the upward airflow. In order to be floated, the products should be of small dimensions; the thickness of the bed and air velocity required for fluidization greatly depend on the dimensional characteristics and on the density of the product to be frozen and have to be controlled and modulated during processing. The mechanical forces together with the high freezing rates make the fluidized bed technology a good choice if IQF fruits/vegetables have to be produced. A similar technique to fluidized bed freezing is impingement freezing. Also impingement freezing systems utilize high air velocities (around 50 m/s) at perpendicular angles to the product surface. The main difference is in position of air nozzles: in impingement freezing air is flowed on both sides of the belt with the aid of numerous jet nozzles. The very high air velocities are able to disrupt the boundary layer surrounding the product and increase the surface heat transfer coefficient (Chaves & Zaritzky, 2018). This technique as the advantage to be comparably fast as cryogenic freezing but a lower operational cost (James et al., 2015; Salvadori & Mascheroni, 2002). Plate freezing systems. These systems are constituted by a series of vertical/horizontal hollow plates though which a coolant is pumped at
40 C. The product to be frozen has to be loaded by applying a slight pressure provided by the plates, in order to guarantee contact and a good heat transfer; because of the loading and unloading operations, plate freezers typically operate in batch or semi-continuous mode. Despite the relatively high heat transfer efficiency, plate freezers have some limitations; in order to provide good contact and heat transfer during the process, they can be successfully adopted only in the block-shaped packaged products (packed products) or in the case of fruits/vegetables slurries and purees. Also the thickness of the product has to be considered; the application of this system should be limited only to thin products in order to limit the processing times (Barbosa-C
anovas et al., 2005). Immersion freezing and cryogenic systems. Because of the direct contact between the product to be frozen and the cooling medium and the high heat transfer efficiency (Barbosa-C
anovas et al., 2005), immersion freezing and cryogenic systems are the fastest freezing systems among those that have found industrial application. In immersion freezers, packed food is moved forward through a bath of liquid coolant (refrigerated propylene glycol, brines, glycerol, sugar or alcohol solutions) by the aid of a conveyor belt; in contrast with cryogenic freezing, the liquid remains fluid and a change of state does not occur (Fellows, 2009). In the case of processing of unpacked foods, the mass transfer phenomena between the food product and the cooling liquid have to be taken into account. In the case of cryogenic freezing, the product to be frozen enters in contact with a cryogenic fluid (CO2 or N2), that undergoes a phase change when it absorbs the heat released by the product. As the boiling points of liquid N2 and liquid CO2 are
196 and
79 C, respectively, the freezing rate in cryogenic systems is very fast and can be useful to obtain top quality results in frozen fruits/

210

Low-Temperature Processing of Food Products

vegetables (Muthukumarappan et al., 2010). In order to avoid freeze cracking phenomena on the surface of fruits/vegetables, a precooling stage is usually needed before the immersion, freezing stage. Compared to mechanical systems, the beneficial properties of cryogenic counterparts are the lower price of instruments and their ability in freezing various types of foods without some simple changes in the system, while a major disadvantage is the relatively high cost of cryogens (Fellows, 2009). Cryogenic techniques are particularly suited to fruits/vegetables, which possess a high surface area to volume ratio and in which the thermal diffusivity does not restrict the heat transfer from the product to the freezing environment (George, 1993). As already stated, cryogenic-based technology can also be implemented in hybrid cryo-mechanical systems that also utilize the air blast freezing technology: these systems initially crust freeze the outer part of the food with cryogens followed by finalizing the freezing process via a conventional mechanical air blast/belt freezer (James et al., 2015). This combined strategy can be useful to limit and reduce the moisture losses of the product during freezing and to avoid product clumping during IQF of fruits/vegetables, because of the formation of a frozen crust; at the same time, this strategy is useful to reduce the overall costs of processing due to the limited use of cryogenic fluid (American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2006).

9.3.3.1

Innovative freezing technologies

As vegetables and fruits products can be very susceptible to quality changes induced by the freezing process, in the recent years, there has been growing attention in developing new systems, which can promote the organoleptic properties of frozen products together with the economics of production. James et al. (2015) and Cheng et al. (2017) recently published comprehensive reviews of novel freezing technologies adopted to process frozen foods, while Xin et al. (2015) reviewed some novel quick freezing techniques that have been studied for fruits/vegetables freezing. Technologies such as ultrasounds and pressure processing have been evaluated and utilized in order to assist and aid the freezing processes. High-pressure-assisted freezing techniques can be generally grouped into three categories: high-pressure-assisted freezing, pressure shift-assisted freezing, and pressureinduced solidesolid phase transition (James et al., 2015). With the utilization of high pressures, the freezing point of water undergoes a depression below the specific initial freezing temperature of the food system, resulting in a high super-cooling phenomenon that can aid to the formation of small ice crystals once the pressure in the system is released. The result of the instantaneous and homogeneous formation of small-size ice crystals is a limited damage to the cellular structure and to a better retained physical and sensory quality for several fruits/vegetables, compared to conventional freezing methods (Xin et al., 2015). Ultrasound-assisted freezing is a novel freezing method that rely in the effect of ultrasound-generated cavitation bubbles that act as crystallization nuclei and favor the nucleation step. The movement of the ultrasound waves within an aqueous food matrix causes cavitation phenomena, with the growth and subsequent collapse of small bubbles. The high mechanical forces generated by cavitation bubbles also intensify the

Freezing of fruits and vegetables

211

formation of new crystals by degrading the pre-existing crystals and escalating the number of nucleation cores. As a result, the final dimension of the ice crystals can be small, and the impairment to cell structure is limited (Cheng et al., 2017). Ultrasound-assisted freezing process has been demonstrated in different studies to have outstanding applications in freezing of fruits/vegetables (Xin et al., 2015). Another promising novel freezing technique that has been applied to vegetables/ fruits is dehydrofreezing. Dehydrofreezing is based on the partial dehydration of processed vegetables/fruits and to an appropriate moisture level prior to freezing. Decrease in moisture content would lower the amount of water to be frozen, thus dropping refrigeration load during the freezing process (Muthukumarappan et al., 2010). From a quality point of view, dehydrofreezing also potentially reduces the potential mechanical damages caused by the ice crystal to the cellular tissues, by reducing the cell turgor pressure.

9.3.4

Packaging and storage of frozen fruits/vegetables

As the rate of oxidative phenomena is not completely inhibited by freezing temperatures, frozen fruits/vegetables exposed to O2 or other oxidative factors are susceptible to oxidative degradation of some components (e.g., phenolic compounds, pigments), resulting in browning reactions and a reduced shelf life. For this reason, a valuable strategy to improve storability of frozen fruits/vegetables products is to remove O2 from the packaging, in order to avoid the contact between the O2 and the tissues. The utilization of the right packaging material having adequate barrier properties protects the frozen fruit/vegetable from O2, light, and water vapor; each of these factors can cause deterioration of color, oxidation of lipids and unsaturated fats, denaturation of proteins, degradation of ascorbic acid, and a general loss of characteristic sensory and nutritional qualities (de Ancos et al., 2012). Some of the techniques utilized for the packaging of frozen fruits are the replacement of O2 by inert gas (e.g., N2) consuming the O2 by glucose-oxidase and/or the use of vacuum and O2-impermeable films (Chaves & Zaritzky, 2018). During frozen storage and distribution, lowering the storage temperature is vital to retain the sensory and physico-chemical quality of frozen vegetables/fruits, as deteriorative processes are mostly temperature-dependent (Barbosa-C
anovas et al., 2005).

9.4

Quality variations in frozen fruits/vegetables

In the past, the concept of food quality was strictly related to food safety, that is, deactivating/hindering the pathogenic microorganisms dangerous to the individuals’ health. Recently, apart from the above notion, an indispensable part of all food safety approaches is to fulfill consumer satisfaction. Consumers these days describe the quality of food according to its nutritional value, organoleptic attributes, and shelf stability. When it comes to vegetables, the main concept of quality is the freshness of the product, where fresh vegetables, apart from being delicious, are a better source of healthpromoting nutrients.

212

Low-Temperature Processing of Food Products

Upon food preservation, freezing, storage and defrosting should be properly performed to acheive appropriate result. Various phenomena, that is, the application of low temperatures, the limited available water, and the blanching treatment prior to freezing, all facilitate the food preservation during freezing. Freezing has demonstrated superior efficiency in preserving the nutritional value and organoleptic features of the food when compared with other methods like canning and dehydration (Barbosa Canovas et al., 2005).

9.4.1

Water status

Water constitutes more than 90% of fruits and vegetables. During freezing, water is crystallized and converted into ice crystals. Freezing point represents the temperature at that ice crystals start to emerge. At this point, the liquid and solid water are in an equilibrium state. Pure water freezes at 0 C, while freezing a food matrix is more complicated due to the presence of both bound and free water. The presence of soluble components within the water makes it unfreezable. The presence of this type of water in the food matrix declines the freezing point of the food to temperatures below 0 C. Upon proceeding the freezing process, the remaining liquid water becomes more concentrated, resulting in a further reduction of the freezing temperature. For starting the nucleation, a specific amount of energy (activation energy) needs to be exceeded. In order to supply the free energy that is required for the generation of a crystal nucleus, super-cooling (i.e., temperature lower than the equilibrium melting point) should be occurred. As nucleation is an exothermic reaction, the temperature of the system starts to rise up to 0 C upon beginning the nucleation phenomenon and keeps this temperature until the end of crystallization process (Zaritzky, 2000). The dimension of the formed crystals is inversely related to the extent of the generated nucleus, where at high-speed freezing, a large number of nuclei are formed, leading to the development of more crystals of lesser size, while at slow freezing, a reverse phenomenon is expected. The dimension, shape, and distribution of ice crystals generated upon freezing is strictly associated to water distribution (Alabi et al., 2020). Following the classification made by van der Sman (2020), water in plant-based food systems is held in three sections: (a) in the intracellular space, both the vacuole and the cytoplasm, (b) the extracellular cell wall material, and (c) the capillary space. The nucleation mostly begins within the extracellular sections. Nevertheless, during ultrafast freezing, supercooling could also occur inside the tissue cells, leading to the intracellular nucleation of water molecules. Thus, the emergence of ice crystals inside the cells is an indication of fast freezing processes. During the growth of ice crystals outside the cells, the concentration of the liquid enhances. This will induce an imbalance in the osmotic pressure around the cell membrane and provoke water migration from the cell to the outside environment. Thereby, the tissue cells dehydrate, and the dimension of ice crystals outside the cells enlarges at low speeds of the freezing process (Zaritzky, 2000). The watereice transition has the advantage of separating the water fraction in the form of ice crystals in such a way that it is not available either as solvent or reactive component (decrease of the free water). These phenomena, together with the

Freezing of fruits and vegetables

213

temperature reduction, help to diminish the reaction rates (Delgado & Sun, 2001). Though, the dimension and site of the ice crystals could destruct cell membranes and deteriorate the physical architecture, resulting in alterations in texture, color, flavor, and nutrients. Minimizing the time of the phase change period contributes to optimum product quality (Delgado & Sun, 2001).

9.4.2

Microstructure

Fresh foods from living tissues consist of well-organized cellular architectures. During freezing, cell structures undergo destruction of cell wall, disintegration of cell membrane, variations in osmotic pressure, etc. Knowing the behavior of cell structure during freezing is imperative to enhance and control the freezing processes (Li et al., 2018). Plant tissues are typically made up of rectangular or cubic cells with diameters or lengths ranging from 30 to 300 mm. These cells are closed together to form tissues with some small air gaps. Such gaps could affect the mass/heat transmission throughout the freezing and offer extra spaces for the formation/expansion of ice crystals (Li et al., 2018). Plant cells are characterized by the presence, in the outer layers, of cell walls. The mechanical and architectural features of the fresh plant products are mostly determined by the cell wall constituents: cellulose, hemicellulose, and pectin, also responsible for the adhesion between cells in a structure called middle lamella (Waldron et al., 2003). Almost 90% of the plant cell volume is occupied by the vacuole that acts as storage organelles to store water and some small molecular components. Most of the chemicals that define the color and flavors of fruits/vegetables are kept in this organelles. Besides, the large central vacuole could also retain the turgor pressure versus the cell wall in fluctuating environmental circumstances and hinder the plasmolysis phenomenon. Cell membrane is the most important structural component for all plant and animal cells. It retains the integrity of the cells and balances the osmotic pressure around them, thereby governing the presence of water inside the cellular structures (Tan et al., 2019). Any alteration in cell membrane, cell wall, etc. upon freezing could cause a series of changes in food quality, such as varying of the food texture, leakage of nutritional elements, and modification of the flavor/aroma, thereby affecting the physiological interaction during oral digestion (Li et al., 2018). One of the important factors for the interaction of ice and the plant tissue is the location of nucleation, which will determine the integrity of the cell membrane. It is critical to control or even prevent intracellular ice formation. If the size of the intracellular ice approaches that of the cell size, it will damage the endomembrane system, leading to the occurrence of a series of undesirable biochemical reactions. The rupture of cell membrane results in the loss of intercellular water, leakage of nutrients, with loss of cell viability, and formation of unpleasant flavor and aroma compounds. The drop of osmotic pressure, consequent to damages on the cell membrane, also affects cell structure, including collapsing of cell walls, separation of the middle lamella, enlargement of the intercellular spaces, and tissue shrinkage (Li et al., 2018).

214

Low-Temperature Processing of Food Products

In plant tissue, it is energetically favorable that ice nucleation happens in the extracellular space; the presence of cell membrane delays the heat transfer causing supercooling of the compartments inside the cell that nucleates at very lower temperatures than the adjacent spaces outside the cells (Silva et al., 2008). Extracellular nucleation will indeed happen at sufficiently slow freezing rates. At relatively fast freezing rates, both extracellular and intracellular ice formation will happen because the cell gets sufficiently supercooled to ice nucleation to happen (Zaritzky, 2000). The alteration of osmotic pressure makes the cell shrinkage and certain cell components denaturation, such as protein and pectin. Water drawn from the interior of the cells will freeze onto the existing extracellular ice crystals (Li et al., 2018). Confirming this assumption, some authors observed marked cell dehydration after both freezing and boiling, in comparison to mere boiling, in asparagus and green beans samples (Paciulli et al., 2015). Overall, ultrafast freezing processes are more efficacious as they result in the generation of ice crystals of less dimension and with little damage to the cell membranes. In this case, the general mass of the ice is divided into a great number of tiny crystals. On the contrary, when freezing is performed at low speeds, a number of large crystals with sharp edges would be formed (Zaritzky, 2000). In this context, Roy et al. (2001) investigated the alterations in the cell wall and middle lamella of a carrot when it was frozen at various speeds of freezing. They outlined that higher speeds of freezing resulted in lesser damage to the fruit structure. The effect of freezing and storage on carrots slices has been reported to cause the formation of fissures in the parenchyma tissues as a consequence of the crystal’s growth (Paciulli et al., 2016); the effect of cooking after freezing makes this phenomenon even more evident (Paciulli et al., 2015, 2016). In the past decades, novel freezing methods have been investigated, in order to minimize the cell damage and obtain frozen cellular foods with better quality (Li et al., 2018). These methods include high-pressure freezing (LeBail et al., 2002; Otero et al., 2000), ultrasound-assisted immersion freezing (Dalvi-Isfahan et al., 2017; Zhang et al., 2018), electric- or magnetic fieldeassisted freezing (Dalvi-Isfahan et al., 2017; Kaur & Kumar, 2020), vacuum impregnation with cryoprotectant solutions (Martínez-Monz
o et al., 1998), etc.

9.4.3

Texture

Upon freezing, the firm architecture of the fruit/vegetable cells could be disrupted. The extent of this disruption mainly governs by the size of the ice crystals, where the crystals with less dimension, created at higher speeds of freezing, cause little damage to the cell integrity, while large ice crystals with sharp edges, created upon slow freezing, cause cell disruption and tissue softening (Gonçalves et al., 2011; Mowafy et al., 2020). Moreover, upon thawing, these phenomena may cause extensive drip loss from the damaged cells (Alabi et al., 2020). Investigating the blueberries texture changes under different freezing rates, Cao et al. (2018) observed that the hardness of fresh samples, resulted better retained when frozen at
80 C and in the liquid nitrogen, than in the samples frozen at
20 and
40 C. It should be

Freezing of fruits and vegetables

215

noted that the treatment of samples with calcium chloride and/or sucrose prior to freezing can diminish the softening of food texture during freeze-thaw cycles (Li et al., 2021). Other procedures that are applied to maintain the texture of fruits/vegetables, besides the chemical treatment, include blanching and control of ice crystal size during nucleation and growth. The selection of specific cultivars that are less sensitive to the alternative freezeethaw cycles is another strategy to preserve the raw material texture (Maestrelli, 2000). Zhan et al. (2019) reviewed that in many cases, during long-term frozen storage of plant foods, as long as the frozen storage temperature is maintained constant, negligible effects are detected on firmness. On the other hand, Gonçalves et al. (2011) observed that the firmness of frozen pumpkins stored at
7,
15 and
25 C changed significantly at all storage conditions. In general, preservation by freezing is applicable to vegetables that are cooked for consumption only. Thermal treatment could provoke various structural changes in the sample tissues resulting in a reduction in the firmness of the texture and an enhancement in the separation of cells due to the swelling of the cell walls (Waldron et al., 2003). However, such alterations could be drastically intensified when thermal treatment is applied to a previously frozen sample. In general, after blanching, the textural quality of vegetables is partially retained (Paciulli et al., 2015). After cooking, the textural behavior is strictly related to the anatomical structure of the vegetable. Paciulli et al. (2015) found that raw/boiled and industrially frozen/boiled asparagus stems possessed greater stability versus penetration and cut forces. Whereas, zucchini, both raw and frozen, completely softened following boiling, it was not possible to perform texture measurements on these samples. Industrially frozen/boiled green beans possessed greater values of cut and penetration forces, in comparison to those raw/boiled, probably due to a higher presence of swollen cell walls. The same authors investigated the effect of freezing and of different cooking methods on the texture of carrots slices (Paciulli et al., 2016). After thawing, the samples resulted significantly softer than the raw ones; moreover, the frozen cooked carrots appeared softer than the raw cooked ones, especially after boiling and steaming than microwaving.

9.4.4

Color and pigments content

Chlorophylls (green), carotenoids (orange, yellow, and red), and anthocyanins (red to purplish) are the most important components contributing to the development of color in vegetables/fruits. Poor data are available on the effect of mere freezing on the color of vegetables. It seems that it does not have any effect on the instrumental color perception of the treated product. Some changes have been registered during frozen storage, especially at relatively high temperature, attributed to deterioration and fading of the original pigments (Zhan et al., 2019). Chloroplasts and chromoplasts (pigment containing organelles) are decomposing through freezing. Upon storage, the liberated chlorophyll is gradually disintegrated to brown pheophytin even in blanched vegetables. Alterations in pH caused by precipitation of salts in concentrated liquids change the color of anthocyanins. The remained lipoxygenases in vegetables that are not blanched properly cause the destruction of carotenoids. However, the browning

216

Low-Temperature Processing of Food Products

through storage is mostly governed by the high polyphenoloxidase activity (Barbosa Canovas et al., 2005). Pellegrini et al. (2010) outlined a better color retain in Brassica vegetables that were cooked following freezing than cooked from fresh vegetables. They linked these finding with the positive impact of the previous blanching treatment on the enzymes deactivation and on the oxygen replacement with water that avoided pigments oxidation. Mazzeo et al. (2015) studied the pigment and color changes in asparagus, green beans, and zucchini during blanching, frozen storage, and further boiling. They found that the color indexes (
a*: greenness; b*: yellowness; H : hue angle) remarkably altered upon blanching and frozen storage for all the vegetables, even if such changes were only slightly in accordance with the enhance of pheophytin and decline of chlorophyll a. The authors hypothesized that those changes were also possibly related to the cellular alteration that impacted light reflectance and with the formation of chlorophyll derivatives, which could result in an intensification of green color intensity. Paciulli et al. (2016) observed that the color of frozen carrots resulted better retained after cooking than that of raw cooked carrots, in view of the stabilizing effect of the blanching step. A further investigation revealed the correlation of carrots instrumental color with the carotenoids content, measured by HPLC and Raman spectroscopy (Camorani et al., 2015). In particular, high statistical correlation was found between a* and trans-b-carotene; moreover, the decrease in lightness (L*), redness (a*), and yellowness (b*) correlated negatively with the ratio cis/all-trans-b-carotene. The effect of low storage temperature and freezing methods on anthocyanin content and sensory color of strawberry was investigated by Sahari et al. (2004). They found a decrease of anthocyanin content over a storage period of 90 days, in a larger extent for samples stored at higher temperatures (
12 C >
18 C >
24 C); moreover, a higher anthocyanin retention was observed for slow freezing in comparison to quick freezing. The color acceptability of the frozen strawberries resulted positively related with the anthocyanins content in all the studied conditions.

9.4.5

Aroma and nutrients

Freezing, frozen storage and thawing can affect the flavor profile in fruits/vegetables. The flavor change has been associated with factors such as change in aroma profile, lipid oxidation, accumulation of ethanol, and other volatile compounds and decrease in the organic acids (Jha et al., 2019). Kaewtathip and Charoenrein (2012) studied the changes in the volatile aroma compounds of pineapple during freezing and thawing; the number of freezeethawed cycles reduced proportionally some volatile aroma compounds, particularly esters, which were found to be the main characteristic of fresh pineapples, because of structure breakdown and aroma oxidation. Studying the effects of freezing modes and frozen storage time on the aroma compounds of Hami melon, Ma et al. (2007) found that liquid nitrogen ultra-rapid freezing maintained most aromatic components of the melon as compared with slow freezing. They associated the aromatic change in frozen melon to enzymolysis or reactions catalyzed by lipoxidase (LOX), particularly affecting the esters profile both in variety and concentration. Moreover, with the prolongation of the frozen storage, unsaturated alcohols and

Freezing of fruits and vegetables

217

aldehydes were increasingly produced because of the biochemical reaction of LOX system on unsaturated fatty acids. Consequently, more intense green notes were registered on the frozen stored melons, while the ester fragrance became weaker. Begona de Ancos et al. (2000) studied the evolution of the volatile compounds of four raspberry cultivars after freezing and during long-term frozen storage at
20 C for a 1-year period. The volatile aroma composition changes were minimal, both immediately after freezing and during long-term frozen storage. The cultivar Heritage had the initial highest amount of volatile compounds. Moreover, freezing and storage allowed better extraction of R-ionone, one of the characteristic compounds of raspberry aroma. The most important nutrients for human health available in fruits/vegetables are the vitamins A (as precursor carotenoids), C, K, B9 (folate); soluble and insoluble dietary fibers; polyunsaturated fatty acids of the n-6 and n-3 family, and the minerals potassium and magnesium. In addition to these nutrients that are essential for life, fruits/vegetables comprise other phytochemicals, with confirmed nutraceutical activities (Yahia et al., 2019). The freezing process itself has no effect on nutrients, the effect of pretreatments and frozen storage, mainly affect the nutritional profile. To preserve the nutritional value of freshly harvested vegetables/fruits, it is desirable to minimize the blanching and freezing time and cause minimal mechanical damage. The adverse effects of damage are caused by the release of enzymes from intracellular compartments that gets in touch with potential substrates (Berry et al., 2008). Ascorbate is often used as an indicator of potential nutrient loss because of its high solubility, sensitivity to heat, oxidation, and ease of measurement. Typical losses of ascorbate from vegetables during blanching are of the order 5%e40% (Berry et al., 2008), and the main mechanism of loss is by leaching into water. Puupponen-Pimi€a et al. (2003) studied the effects of blanching/freezing and longterm freezer storage on various bioactive compounds of more than 20 commonly used vegetables. They found that the effects were strongly species-dependent. Dietary fibers and minerals in general resulted to be stable, except for some losses of soluble minerals by leaching. Phenolic antioxidants and vitamins were clearly more sensitive: up to one-third of vitamin C and more than half content of folic acid were lost during blanching; further slight losses were detected for Vit C during the frozen storage, being instead folic acid more stable. Carotenoids and sterols resulted to be not affected by both blanching and frozen storage. Pellegrini et al. (2010) found that, after cooking, fresh Brassica vegetables retained phytochemicals and total antioxidant activity better than frozen samples. They justified these results saying that the previous blanching and subsequent freezing softened the vegetable matrix causing more extended losses after cooking. Some studies have also reported an increase of bioactive compounds or antioxidant activities after blanching and freezing. Paciulli et al. (2015) observed increased antioxidant activities, measured by TEAC and FRAP assays, for asparagus and green beans after blanching, being instead zucchini affected negatively by this pretreatment. The authors justified the antioxidant improvement by the higher release of bioactive molecules from the matrix softened by blanching. Other theories are that the thermal treatment can produce stronger radical-scavenging antioxidants and/or novel products by

218

Low-Temperature Processing of Food Products

chemical reactions, in addition to the inactivation of oxidative enzymes that would oxidize the bioactive molecules (Yamaguchi et al., 2001). In a study conducted on the same vegetables with the same blanching conditions (Mazzeo et al., 2015), after the treatment, the authors registered losses of ascorbic acid, almost stable contents of lutein and increase of total phenols and total flavonoids, in comparison to the raw samples. The same authors observed that a frozen storage of up to 2 months did not negatively affected phytochemicals; lutein and flavonoids resulted even increased in almost all samples. The further boiling of those frozen vegetables caused losses of both bioactive molecules and antioxidant activities, in higher percentages than the boiled nonfrozen ones, being instead lutein well retained or even enhanced. In general, if vegetables/fruits are adequately blanched and stored at conventional freezer temperatures without undue temperature fluctuations, they will still possess nutritionally valuable levels of potentially labile nutrients for a period of at least 12e 18 months (Barbosa Canovas et al., 2005).

9.5

Conclusions

Freezing is one of the oldest and most widely used methods for food preservation. It allows the retention of the agricultural products quality over long storage periods, extending their usage during off-season other than the transportation to remote markets that could not be accessed with fresh products. As a method of long-term preservation, freezing is generally regarded as superior to canning and dehydration with respect to retention in sensory attributes and nutritive properties. Despite the structural, organoleptic and nutritional properties of fruit/vegetables may be affected the freezing treatment, the availability of different types of equipment for several different food products results in a flexible process in which degradation of initial food quality is minimal if proper procedures are applied.

References Alabi, K. P., Zhu, Z., & Sun, D. W. (2020). Transport phenomena and their effect on microstructure of frozen fruits and vegetables. Trends in Food Science & Technology, 101, 63e72. Alinovi, M., & Mucchetti, G. (2020). A coupled photogrammetric e finite element method approach to model irregular shape product freezing: Mozzarella cheese case. Food and Bioproducts Processing, 122, 98e110. American Society of Heating, Refrigerating and Air-Conditioning Engineers. (2006). 2006 ASHRAE handbook refrigeration. 30329(404). Bai, Y., Rahman, M. S., Perera, C. O., Smith, B., & Melton, L. D. (2001). State diagram of apple slices: Glass transition and freezing curves. Food Research International, 34(2e3), 89e95. Barbosa-C
anovas, G. V., Altunakar, B., & Mejía-Lorío, D. J. (2005). Freezing of fruits and vegetables: An agribusiness alternative for rural and semi-rural areas (Vol 158). Food & Agriculture Org.

Freezing of fruits and vegetables

219

Berry, M., Fletcher, J., McClure, P., & Wilkinson, J. (2008). Effects of freezing on nutritional and microbiological properties of foods. In Frozen food science and technology (p. 26). Blackwell. Bogh-Sorensen, L. (2006). Recommendations for the processing and handling of frozen foods. International Institute of Refrigeration. Camorani, P., Chiavaro, E., Cristofolini, L., Paciulli, M., Zaupa, M., Visconti, A., … Pellegrini, N. (2015). Raman spectroscopy application in frozen carrot cooked in different ways and the relationship with carotenoids. Journal of the Science of Food and Agriculture, 95(11), 2185e2191. Cao, X., Zhang, F., Zhao, D., Zhu, D., & Li, J. (2018). Effects of freezing conditions on quality changes in blueberries. Journal of the Science of Food and Agriculture, 98(12), 4673e4679. Carson, J. K., Wang, J., North, M. F., & Cleland, D. J. (2016). Effective thermal conductivity prediction of foods using composition and temperature data. Journal of Food Engineering, 175, 65e73. Castell-Perez, M. E. (2020). Freezing of food. In N. M. Holden, M. L. Wolfe, J. A. Ogejo, & E. J. Cummins (Eds.), Introduction to biosystems engineering. Virginia Tech Publishing. Chang, H. D., & Tao, L. C. (1981). Correlations of enthalpies of food systems. Journal of Food Science, 46(5), 1493e1497. Chaves, A., & Zaritzky, N. (2018). Cooling and freezing of fruits and fruit products. In A. Rosenthal, R. Deliza, J. Welti-Chanes, & G. V. Barbosa-C
anovas (Eds.), Fruit preservation: Novel and conventional technologies (pp. 127e180). Springer. Cheng, L., Sun, D. W., Zhu, Z., & Zhang, Z. (2017). Emerging techniques for assisting and accelerating food freezing processes: A review of recent research progresses. Critical Reviews in Food Science and Nutrition, 57(4), 769e781. Choi, Y., & Okos, M. R. (1986). Effect of temperature and composition on the thermal properties of food. In M. L. Maguer, & P. Jelen (Eds.), Food engineering and process applications (Vol 1, pp. 93e101). Elsevier. Coulomb, D. (2008). Refrigeration and cold chain serving the global food industry and creating a better future: Two key IIR challenges for improved health and environment. Trends in Food Science & Technology, 19(8), 413e417. Dalvi-Isfahan, M., Hamdami, N., Xanthakis, E., & Le-Bail, A. (2017). Review on the control of ice nucleation by ultrasound waves, electric and magnetic fields. Journal of Food Engineering, 195, 222e234. de Ancos, B., Ibanez, E., Reglero, G., & Cano, M. P. (2000). Frozen storage effects on anthocyanins and volatile compounds of raspberry fruit. Journal of Agricultural and Food Chemistry, 48(3), 873e879. de Ancos, B., Sanchez-Moreno, C., de Pascual-Teresa, S., & Cano, M. P. (2006). Fruit freezing principles. In Y. H. Hui, J. Barta, M. P. Cano, T. W. Gusek, J. S. Sidhu, & N. K. Sinha (Eds.), Handbook of fruits and fruit processing (pp. 59e80). Blackwell Publishing Ltd. de Ancos, B., S
anchez-Moreno, C., de Pascual-Teresa, S., & Cano, M. P. (2012). Freezing preservation of fruits. In Handbook of fruits and fruit processing (2nd ed.). John Wiley & Sons. Delgado, A. E., & Sun, D. W. (2001). Heat and mass transfer models for predicting freezing processesea review. Journal of Food Engineering, 47(3), 157e174. Evans, J. (2008). Frozen food science and technology. Blackwell. Fabra, M. J., Talens, P., Moraga, G., & Martínez-Navarrete, N. (2009). Sorption isotherm and state diagram of grapefruit as a tool to improve product processing and stability. Journal of Food Engineering, 93(1), 52e58.

220

Low-Temperature Processing of Food Products

Fellows, P. J. (2009). Food processing technology: Principles and practice (3rd ed., pp. 1e913). Woodhead Publishing. Fennema, O. R., Powrie, W. D., & Marth, E. H. (1973). Low-temperature preservation of foods and living matter. Marcel Dekker. Fikiin, K. A., & Fikiin, A. G. (1999). Predictive equations for thermophysical properties and enthalpy during cooling and freezing of food materials. Journal of Food Engineering, 40(12), 1e6. George, R. M. (1993). Freezing processes used in the food industry. Trends in Food Science and Technology, 4(5), 134e138. George, R. M. (1997). Freezing systems. In M. C. Erickson, & Y.-C. Hung (Eds.), Quality in frozen food (pp. 3e9). Springer. Giannakourou, M. C., & Tsironi, T. N. (2021). Application of processing and packaging hurdles for fresh-cut fruits and vegetables preservation. Foods, 10(4), 830. Gonçalves, E. M., Pinheiro, J., Abreu, M., Brand~ao, T. R., & Silva, C. L. M. (2011). Kinetics of quality changes of pumpkin (Curcurbita maxima L.) stored under isothermal and nonisothermal frozen conditions. Journal of Food Engineering, 106(1), 40e47. Goncalves, M. D. P., & Silveira Junior, V. (2017). Energy consumption reduction strategy for freezing of packaged food products. Food Science and Technology, 38, 341e347. Grajales-Lagunes, A., Rivera-Bautista, C., Loredo-García, I. O., Gonz
alez-García, R., Gonz
alezCh
avez, M. M., Schmidt, S. J., & Ruiz-Cabrera, M. A. (2018). Using model food systems to develop mathematical models for construction of state diagrams of fruit products. Journal of Food Engineering, 230, 72e81. Guizani, N., Al-Saidi, G. S., Rahman, M. S., Bornaz, S., & Al-Alawi, A. A. (2010). State diagram of dates: Glass transition, freezing curve and maximal-freeze-concentration condition. Journal of Food Engineering, 99(1), 92e97. Haiying, W., Shaozhi, Z., & Guangming, C. (2007). Experimental study on the freezing characteristics of four kinds of vegetables. LWT-Food Science and Technology, 40(6), 1112e1116. Heldman, D. R. (1974). Predicting the relationship between unfrozen water fraction and temperature during food freezing using freezing point depression. ASHRAE Transactions, 91, 63e66. Heldman, D. R., & Singh, R. P. (1981). Food process engineering. Westport, CT: The AVI Pub. Co. Inc. Hu, R., Zhang, M., Liu, W., Mujumdar, A. S., & Bai, B. (2022). Novel synergistic freezing methods and technologies for enhanced food product quality: A critical review. Comprehensive Reviews in Food Science and Food Safety, 21, 1979e2001. International Institute of Refrigeration. (1986). Recommendations of the processing and handling of frozen foods. International Institute of Refrigeration. James, C., Purnell, G., & James, S. J. (2015). A review of novel and innovative food freezing technologies. Food and Bioprocess Technology, 8(8), 1616e1634. Jha, P. K., Xanthakis, E., Chevallier, S., Jury, V., & Le-Bail, A. (2019). Assessment of freeze damage in fruits and vegetables. Food Research International, 121, 479e496. Jideani, A. I., Silungwe, H., Takalani, T., Omolola, A. O., Udeh, H. O., & Anyasi, T. A. (2021). Antioxidant-rich natural fruit and vegetable products and human health. International Journal of Food Properties, 24(1), 41e67. Kaewtathip, T., & Charoenrein, S. (2012). Changes in volatile aroma compounds of pineapple (Ananas comosus) during freezing and thawing. International Journal of Food Science & Technology, 47(5), 985e990.

Freezing of fruits and vegetables

221

Kaur, M., & Kumar, M. (2020). An innovation in magnetic field assisted freezing of perishable fruits and vegetables: A review. Food Reviews International, 36(8), 761e780. Larkin, J. L., Heldman, D. R., & Steffe, J. F. (1984). An analysis of factors influencing precision of thermal property values during freezing. International Journal of Refrigeration, 7(2), 86e92. LeBail, A., Chevalier, D., Mussa, D. M., & Ghoul, M. (2002). High pressure freezing and thawing of foods: A review. International Journal of Refrigeration, 25(5), 504e513. Levine, H., & Slade, L. (1986). A polymer physico-chemical approach to the study of commercial starch hydrolysis products (SHPs). Carbohydrate Polymers, 6(3), 213e244. Li, D., Zhu, Z., & Sun, D. W. (2018). Effects of freezing on cell structure of fresh cellular food materials: A review. Trends in Food Science & Technology, 75, 46e55. Li, X. M., Ren, L. K., Yang, Y., Bian, X., Fu, Y., Zhao, L. C., … Zhang, N. (2021). Application of calcium chloride-sodium alginate to improve the texture of quick-frozen Heracleum moellendorffii. Journal of Food Quality, 2021, 1e11. Lim, M., Wu, H., Breckell, M., & Birch, J. (2006). Influence of the glass transition and storage temperature of frozen peas on the loss of quality attributes. International Journal of Food Science and Technology, 41(5), 507e512. Ma, Y., Hu, X., Chen, J., Chen, F., Wu, J., Zhao, G., … Wang, Z. (2007). The effect of freezing modes and frozen storage on aroma, enzyme and micro-organism in Hami melon. Food Science and Technology International, 13(4), 259e267. Maestrelli, A. (2000). Fruit and vegetables: The quality of raw material in relation to freezing. In Managing frozen foods (pp. 27e55). CRC Press. Martínez-Monz
o, J., Martínez-Navarrete, N., Chiralt, A., & Fito, P. (1998). Mechanical and structural changes in apple (var. Granny Smith) due to vacuum impregnation with cryoprotectants. Journal of Food Science, 63(3), 499e503. Mazzeo, T., Paciulli, M., Chiavaro, E., Visconti, A., Fogliano, V., Ganino, T., & Pellegrini, N. (2015). Impact of the industrial freezing process on selected vegetables-Part II. Colour and bioactive compounds. Food Research International, 75, 89e97. Miller, S. R., & Knudson, W. A. (2014). Nutrition and cost comparisons of select canned, frozen, and fresh fruits and vegetables. American Journal of Lifestyle Medicine, 8(6), 430e437. Mowafy, S. G., Sabbah, M. A., Mostafa, Y. S., & Elansari, A. M. (2020). Effect of freezing rate on the quality properties of Medjool dates at the tamr stage. Journal of Food Processing and Preservation, 44(12), e14938. Muthukumarappan, K., Tiwari, B., & Swamy, G. J. (2010). Refrigeration and freezing preservation of vegetables. In Handbook of vegetables and vegetable processing (p. 259). John Wiley & Sons. Otero, L., Martino, M., Zaritzky, N., Solas, M., & Sanz, P. D. (2000). Preservation of microstructure in peach and mango during high-pressure-shift freezing. Journal of Food Science, 65(3), 466e470. Paciulli, M., Ganino, T., Carini, E., Pellegrini, N., Pugliese, A., & Chiavaro, E. (2016). Effect of different cooking methods on structure and quality of industrially frozen carrots. Journal of food Science and Technology, 53(5), 2443e2451. Paciulli, M., Ganino, T., Pellegrini, N., Rinaldi, M., Zaupa, M., Fabbri, A., & Chiavaro, E. (2015). Impact of the industrial freezing process on selected vegetablesdPart I. Structure, texture and antioxidant capacity. Food Research International, 74, 329e337. Pellegrini, N., Chiavaro, E., Gardana, C., Mazzeo, T., Contino, D., Gallo, M., … Porrini, M. (2010). Effect of different cooking methods on color, phytochemical concentration, and

222

Low-Temperature Processing of Food Products

antioxidant capacity of raw and frozen brassica vegetables. Journal of Agricultural and Food Chemistry, 58(7), 4310e4321. Puupponen-Pimi€a, R., H€akkinen, S. T., Aarni, M., Suortti, T., Lampi, A. M., Eurola, M., … Oksman-Caldentey, K. M. (2003). Blanching and long-term freezing affect various bioactive compounds of vegetables in different ways. Journal of the Science of Food and Agriculture, 83(14), 1389e1402. Rahman, M. S. (1999). Food preservation by freezing. In M. S. Rahman (Ed.), Handbook of food preservation (p. 259). Marcel Dekker. Rahman, M. S. (2006). State diagram of foods: Its potential use in food processing and product stability. Trends in Food Science and Technology, 17(3), 129e141. https://doi.org/ 10.1016/j.tifs.2005.09.009 Rahman, M. S. (2008). Food properties handbook. CRC Press. Rahman, M. S., & Al-Saidi, G. S. (2017). Exploring validity of the macro-micro region concept in the state diagram: Browning of raw and freeze-dried banana slices as a function of moisture content and storage temperature. Journal of Food Engineering, 203, 32e40. Rahman, M. S., & Driscoll, R. H. (1991). Thermal conductivity of seafoods: Calamari, octopus and king prawn. Food Australia-Official Journal of CAFTA and AIFST. Rahman, M. S., Rashid, M. M., & Hussain, M. A. (2012). Thermal conductivity prediction of foods by Neural Network and Fuzzy (ANFIS) modeling techniques. Food and Bioproducts Processing, 90(2), 333e340. Renub Research. (2021). Europe frozen food market, forecast, impact of COVID-19, industry trends, by product, category, growth, opportunity company analysis. Roos, Y. H. (1987). Effect of moisture on the thermal behavior of strawberries studied using differential scanning calorimetry. Journal of Food Science, 52(1), 146e149. Roos, Y. H. (2010). Glass transition temperature and its relevance in food processing. Annual Review of Food Science and Technology, 1(1), 469e496. Roy, S. S., Taylor, T. A., & Kramer, H. L. (2001). Textural and ultrastructural changes in carrot tissue as affected by blanching and freezing. Journal of Food Science, 66(1), 176e180. Sahari, M. A., Boostani, F. M., & Hamidi, E. Z. (2004). Effect of low temperature on the ascorbic acid content and quality characteristics of frozen strawberry. Food Chemistry, 86(3), 357e363. Salvadori, V. O., & Mascheroni, R. H. (2002). Analysis of impingement freezers performance. Journal of Food Engineering, 54(2). Schudel, S., Prawiranto, K., & Defraeye, T. (2021). Comparison of freezing and convective dehydrofreezing of vegetables for reducing cell damage. Journal of Food Engineering, 293, 110376. Sehrawat, R., Khan, K. A., Goyal, M. R., & Paul, P. K. (2018). Technological interventions in the processing of fruits and vegetables. Apple Academic Press Inc. Shi, Q., Wang, X., Zhao, Y., & Fang, Z. (2012). Glass transition and state diagram for freezedried Agaricus bisporus. Journal of Food Engineering, 111(4), 667e674. Silva, C. L., Gonçalves, E. M., & Brandao, T. R. (2008). Freezing of fruits and vegetables. In Frozen food science and technology (p. 165). Blackwell Publishing Ltd. Slade, L., & Levine, H. (1991). Beyond water activity: Recent advances based on an alternative approach to the assessment of food quality and safety. Critical Reviews in Food Science and Nutrition, 30(2e3), 115e360. Slade, L., & Levine, H. (1995). Glass transitions and water-food structure interactions. Advances in Food & Nutrition Research, 38(C), 103e269.

Freezing of fruits and vegetables

223

S
a, M. M., & Sereno, A. M. (1994). Glass transitions and state diagrams for typical natural fruits and vegetables. Thermochimica Acta, 246(2), 285e297. Sweat, V. E. (1974). Experimental values of thermal conductivity of selected fruits and vegetables. Journal of Food Science, 39(6), 1080e1083. Swer, T. L., Mukhim, C., Sehrawat, R., & Gaikwad, S. T. (2018). Applications of freezing technology in fruits and vegetables. In Technological interventions in the processing of fruits and vegetables (pp. 133e162). Apple Academic Press. Syamaladevi, R. M., Sablani, S. S., Tang, J., Powers, J., & Swanson, B. G. (2010). Water sorption and glass transition temperatures in red raspberry (Rubus idaeus). Thermochimica Acta, 503e504(1), 90e96. Tan, X., Li, K., Wang, Z., Zhu, K., Tan, X., & Cao, J. (2019). A review of plant vacuoles: Formation, located proteins, and functions. Plants, 8(9), 327. Tylewicz, U., Panarese, V., Laghi, L., Rocculi, P., Nowacka, M., Placucci, G., & Rosa, M. D. (2011). NMR and DSC water study during osmotic dehydration of Actinidia deliciosa and Actinidia chinensis Kiwifruit. Food Biophysics, 6(2), 327e333. van der Sman, R. G. M. (2020). Impact of processing factors on quality of frozen vegetables and fruits. Food Engineering Reviews, 12(4), 399e420. Waldron, K. W., Parker, M. L., & Smith, A. C. (2003). Plant cell walls and food quality. Comprehensive Reviews in Food Science and Food Safety, 2(4), 128e146. Wang, H., Zhang, S., & Chen, G. (2008). Glass transition and state diagram for fresh and freezedried Chinese gooseberry. Journal of Food Engineering, 84(2), 307e312. Wang, L., & Weller, C. (2006). Thermophysical properties of frozen foods. In D.-W. Sun (Ed.), Handbook of frozen food processing and packaging (pp. 101e128). CRC, Taylor & Francis Group. WHO. (2004). Fruit and vegetables for health; report of a Joint FAO/WHO workshop. Geneva, Switzerland: World Health Organization. Xin, Y., Zhang, M., & Adhikari, B. (2013). Effect of trehalose and ultrasound-assisted osmotic dehydration on the state of water and glass transition temperature of broccoli (Brassica oleracea L. var. botrytis L.). Journal of Food Engineering, 119(3), 640e647. Xin, Y., Zhang, M., Xu, B., Adhikari, B., & Sun, J. (2015). Research trends in selected blanching pretreatments and quick freezing technologies as applied in fruits and vegetables: A review. International Journal of Refrigeration, 57, 11e25. Yahia, E. M., García-Solís, P., & Celis, M. E. M. (2019). Contribution of fruits and vegetables to human nutrition and health. In Postharvest physiology and biochemistry of fruits and vegetables (pp. 19e45). Woodhead Publishing. Yamaguchi, T., Mizobuchi, T., Kajikawa, R., Kawashima, H., Miyabe, F., Terao, J., … Matoba, T. (2001). Radical-scavenging activity of vegetables and the effect of cooking on their activity. Food Science and Technology Research, 7(3), 250e257. Zaritzky, N. E. (2000). Factors affecting the stability of frozen foods. In Managing frozen foods (pp. 111e133). Cambridge, UK: Woodhead Publishing Limited. Zhan, X., Zhu, Z., & Sun, D. W. (2019). Effects of pretreatments on quality attributes of longterm deep frozen storage of vegetables: A review. Critical Reviews in Food Science and Nutrition, 59(5), 743e757. Zhang, P., Zhu, Z., & Sun, D. W. (2018). Using power ultrasound to accelerate food freezing processes: Effects on freezing efficiency and food microstructure. Critical Reviews in Food Science and Nutrition, 58(16), 2842e2853.

224

Low-Temperature Processing of Food Products

Zhang, W., Ma, J., & Sun, D. W. (2021). Raman spectroscopic techniques for detecting structure and quality of frozen foods: Principles and applications. Critical Reviews in Food Science and Nutrition, 61(16), 2623e2639. Zhao, J. H., Liu, F., Wen, X., Xiao, H. W., & Ni, Y. Y. (2015). State diagram for freeze-dried mango: Freezing curve, glass transition line and maximal-freeze-concentration condition. Journal of Food Engineering, 157, 49e56. Zhao, Y., & Takhar, P. S. (2017). Freezing of foods: Mathematical and experimental aspects. Food Engineering Reviews, 9(1), 1e12. https://affi.org/insights/power-of-frozen-resources/.

Freezing of meat, poultry, and seafoods

10

Gizem Sevval Tomar, Meryem Seri, Rukiye Gundogan, Humeyra Cavdar and Asli Can Karaca Department of Food Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul, Turkey

10.1

Introduction

10.1.1 Importance of the frozen meat, poultry, and seafood products in industry One of the most important issues in the food industry is to obtain products with optimum quality that can withstand long storage periods. Fresh food spoils very quickly for a variety of reasons (Zou et al., 2019). The freezing method is frequently preferred as it has been used for many years and can be applied to a wide variety of products. The fact that technologies such as chemicals and irradiation are not used in the freezing method makes this method more reliable. In addition, thanks to the low temperatures used, nutrient losses can be minimized (Campa~ none et al., 2002). The free water in the food is converted to ice by the low temperatures used, thus reducing the water activity. With the decrease of water activity, microbial growth is inhibited, chemical and enzymatic degradation reactions are slowed down (Jha et al., 2017). The original quality of food products can be almost completely preserved with freezing depending on the method and processing parameters applied. Freezing of foods began with the use of ice cellars in China around 1000 BCE. Later, the Greeks and Romans also used this method. In the 1500s, the French produced flavored ice for consumption. In the mid-1800s, fish were deliberately frozen using salt and ice. With the freezing of fish and the development of mechanical freezing tools used for this purpose, this method has become even more common. By the late 1800s, frozen meat and poultry were being transported extremely long distances. Since the 1930s, the number and variety of frozen foods have increased. Today, frozen ready-to-cook foods have become a large component of retail food sales (Archer, 2004).

10.1.2 Product composition, properties, and characteristics Meat consists of approximately 72%e75% water, 21% nitrogenous compounds of which 19% is protein, 2.5%e5% lipids, 1% nonnitrogen compounds, and 1% ash. Meat is a very important source of protein. Meat proteins can be divided into three classes. These are myofibrils, which are responsible for muscle contraction and relaxation and are soluble in concentrated salt solutions, sarcoplasmic, and insoluble Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00012-6 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

226

Low-Temperature Processing of Food Products

connective tissue proteins soluble in water or diluted salt solutions. Meat and meat products are also very important sources of water-soluble vitamins. These are vitamins B1, B2, B6, and B12. The concentration of vitamins in meat ranges from a few micrograms to several milligrams per 100 g. Poultry is the second most consumed meat type in the world after meat. The term poultry is used to refer to domesticated poultry, particularly meat such as chickens, turkeys, ducks, and geese. Like other meats, poultry also contains high protein (20%e22%). Although the composition of poultry meat largely depends on parameters such as bird species, diet, cuts, and skin presence, it is generally known to have good nutritional value and low energy content. Poultry meat contains a good amount of protein and many micronutrients. In addition, being consumed without skin and being relatively low in fat and cholesterol increases the preference for consumption. Moreover, the fact that poultry meat is rich in u-3 polyunsaturated fatty acids makes this product stand out in terms of nutrition (Bordoni & Danesi, 2017). Seafood consumption, on the other hand, has been increasing gradually, especially in recent years, as it is associated with health. Almost 98% of the total mass of seafood meats consists of water, protein, and fat. However, the proportions of these components vary considerably according to the type of fish and processing technology. Seafood is an important source of protein, vitamin D, and minerals. Fish from seafood has been called brain food for many years. Thanks to its u-3 fatty acids, it supports the development of the brain and retina (Aberoumand, 2013). Recent studies have confirmed the importance of nutritional components in fish in cardiovascular health, brain development, and reproduction (Aberoumand, 2013). Soyer et al. (2010) investigated the effects of freezing temperature and freezing storage time on lipid and protein oxidation in chicken leg and breast meat. Chicken legs and breast meat were frozen at three different temperatures,
7,
12, and
18 and stored at
18 C. A significant effect of storage time on lipid oxidation was found, but freezing time was reported to have no significant effect. In addition, lipid and protein oxidation occurred simultaneously in chicken meat during frozen storage and was more intense in thigh meat than breast meat (Soyer et al., 2010).

10.1.3

Quality aspects and microstructure

The most important function of the freezing process is the inhibition of microorganisms and its ability to control proteolytic, hydrolytic, and lipolytic activities. In very fast freezing conditions, small ice crystals are formed in the cells, which ensure that meat, poultry, and seafood are not structurally degraded, and their quality characteristics are minimally affected. However, at slow freezing rates, rather large extracellular ice crystals form in the structure. These large crystals disrupt the muscle fibers and cause the structure to be negatively affected (Desrosier, 2012). During frozen storage, many different reactions can occur in different meat components. For example, fish and poultry are particularly susceptible to oxidative reactions due to their high oxidation catalysts such as myoglobin and iron, and their high lipid concentrations. It is one of the main causes of spoilage of lipid cells, in frozen meat products. As a result of oxidative effects in meat, undesirable changes may occur in taste, texture, nutritional value, and color properties

Freezing of meat, poultry, and seafoods

227

(Soyer et al., 2010). Another important degradation process is microbial spoilage. Meat, poultry, and seafood are below a certain degree of microbial growth, and any bacteria, yeast, and molds that may be present are kept in a dormant state. In this case, the direct chemical activities of microorganisms are stopped and no toxin or enzyme production takes place (Desrosier, 2012). As a result of the freezing of water in the freezing process, microorganisms tend to condense in the unfrozen fraction of water containing solutes. As a result, water diffuses from the microbial cell into the surrounding concentrated solution. The development and various activities of microorganisms are stopped due to extracellular ice formation, intracellular ice formation, the concentration of extracellular solutes, the concentration of intracellular solutes, and finally low temperature (Archer, 2004). Despite many beneficial properties of freezing on storage and degradation, it can cause undesirable results in quality, one of which is the trickle loss problem. During the freezing process, the surface of the food loses moisture. This negatively affects the sensory quality of various meat products. In addition, color is a very important quality parameter in the choice and consumption of various meats. In this sense, undesirable changes may occur due to the denaturing of the myoglobin responsible for the color during the freezing process. One of the most important quality losses is protein denaturation. Softening occurs as a result of protein denaturation and may cause both quality and nutritional losses (Desrosier, 2012). Dominguez and Schaffner (2009) evaluated the survival of Salmonella, which is a great risk for chicken products, during
20 C storage of processed chicken products. For this purpose, four Salmonella strains isolated from poultry were inoculated into frozen chicken nuggets and frozen chicken strips in initial populations of 104e105 CFU/g. These products were then evaluated by storing them at
20 C for 16 weeks. As a result of the microbial analysis, it was reported that the number of microorganisms remained relatively constant for both products (Dominguez & Schaffner, 2009).

10.2

Methods used for freezing meat, poultry and seafoods

Freezing is a method that has been used since ancient times and became commercially viable in the food industry with the spread and development of mechanical cooling systems in the late 19th century (Muthukumarappan et al., 2019). It has emerged as one of the most favored food processing techniques. In addition to extending the shelf life of food products (Oyinloye & Yoon, 2020), it is an effective technique in the development of many innovative products, such as frozen yoghurt, which has gained popularity in recent years. Therefore, it is necessary to be aware of the existing freezing equipment and methods to increase the application area of the freezing process and get the highest performance level. Various factors influence the selection of equipment for a product. These factors include size, shape, sensitivity, production rate, required space, investment capacity, desired final product quality, and the cooling medium

228

Low-Temperature Processing of Food Products

used (Muthukumarappan et al., 2019). All these considerations collectively determine the type of equipment that is chosen. Fundamentally, freezer equipment can be divided into two groups as direct and indirect contact freezers.

10.2.1

Direct contact freezers

Plate freezers are the well-known types of direct contact freezers. In plate freezers, the cooling medium is separated from the food product by the metal wall of the plates, which are hallowed and placed inside an insulated cabinet with the cooling medium circulating through coils (Hall, 2010). There is a direct contact between the food and the plate, which enables energy transfer with conduction. Plates in plate freezers can be arranged horizontally for food products with a regular size and shape or vertically for sensitive food products such as fish, meat, and poultry products (Jessen et al., 2014). Plate freezers are space-efficient and provide a high freezing rate, resulting in higher throughput than air blast freezers (Muthukumarappan et al., 2019).

10.2.2

Indirect contact freezers

Cabinet freezers are one of the types of the indirect contact freezers with a slower freezing process. In the investigation of Li et al. (2022), the effect of freezing on collagen and textural characteristics of yak meat was measured during storage at 4 C. The findings indicated a significant decrease in collagen content and solubility in yak meat during storage. Additionally, the study found that the shear force, hardness, cohesiveness, springiness, gumminess, and chewiness of the yak meat significantly decreased (Li et al., 2022). Air-blast freezing (Fig. 10.1) is a commonly used direct contact freezing method in the industry. An air-blast freezer equipment incorporates a well-insulated tunnel with circulating cooling air through fans. At the same time, the food product that needs to be frozen is conveyed through the tunnel on trolleys (Dempsey & Bansal, 2012). In batch mode, products which are located on trolleys are loaded into the tunnel for a specific residence time before being replaced with a fresh batch. In contrast, in continuous systems, products exit the tunnel after completion of the required residence time (Muthukumarappan et al., 2019). Recent studies in the literature have been dedicated to examining the influence of this equipment on the quality and nutritional composition of food products. Choi et al. (2015) revealed the impact of air blast freezing on beef ultrastructure and sensory characteristics was examined to mitigate quality deterioration during extended storage periods. The study evaluated beef muscle’s ultrastructure, ice crystal size changes of frozen product during storage, and the quality properties after thawing for beef subjected to air blast freezing. The results showed that larger ice crystals appeared during the storage time, significantly lower thawing loss in beef frozen using air blast freezing, higher thawing loss in the round cut compared to the loin, and an obvious decrease in water holding capacity during an 8-month storage period (Choi et al., 2015). The sensory evaluation also revealed that frozen beef provided higher acceptability after 4 months, suggesting that freezing influences beef’s ultrastructure and quality characteristics.

Freezing of meat, poultry, and seafoods

229

Figure 10.1 Air-blast freezing. Adapted from Dempsey and Bansal (2012).

Another type of direct contact freezer is an immersion freezer. Immersion freezers, which employ coolants such as glycol, brine, sugar alcohol, and aqueous propylene glycol, are widely utilized to freeze packaged products and liquid foods (James & James, 2010). Immersion systems provide a rapid and effective freezing process by utilizing the shallow temperatures of the freezing media, which facilitates direct contact between all product surfaces and the coolant (Muthukumarappan et al., 2019). When choosing the freezing media, it is crucial to thoroughly consider the product’s safety, ensuring that the product is heavier than the freezing fluid to prevent any buoyancyrelated problems (Velez-Ruiz & Rahman, 2020). In a study of Hou et al. (2020), the impacts of air-blast freezing and immersion freezing on quality changes of pork were compared. The study demonstrated that immersion freezing led to small and regular ice crystals due to their higher freezing rate. Additionally, immersion freezing exhibited improved water holding capacity and slower lipid oxidation compared to air-blast freezing (Hou et al., 2020). Yang et al. (2020) also conducted a comparative analysis between air-blast freezing and immersion freezing using pufferfish fillets and discovered that immersion freezing was effective in preserving the physical properties of frozen fish (Yang et al., 2020). Yuduan et al. (2022) conducted a study to assess the impact of immersion freezing and air-blast freezing on the protein structure of frozen grass carp muscle, as the softening tissue of frozen fish is partly attributed to alterations in fish protein structure. After 24 weeks, it was found that the immersion freezing method resulted in a higher salt-soluble protein content (106.22  1.01 mg/g meat) compared to air-blast freezing (90.77  1.11 mg/g meat) (Yuduan et al., 2022).

230

Low-Temperature Processing of Food Products

Compared to air-blast freezing, immersion freezing showed higher alpha-helix content and lower beta-turn and random coil content. These findings indicate that immersion freezing effectively reduces protein denaturation and may be considered as an enhanced freezing technique instead of air-blast freezing. Nevertheless, conventional freezing methods such as air-blast freezing have generated significant and irregular ice crystals, leading to tissue damage and nutrient depletion in meat products (Mahato et al., 2019; Tian et al., 2020). Also, long freezing times and high energy consumption are other disadvantages of the vase manufacturer (Delgado et al., 2009; Zhu et al., 2006). Cryogenic freezing (Fig. 10.2), a quick and effective freezing technique, offers a viable solution to the aforementioned problems. This technique involves immersing the food in a refrigerant, allowing for energy transfer between the food and the liquid, thus facilitating rapid freezing (Liang et al., 2015). Numerous and small ice crystals are distributed within the tissue and cell, thereby decreasing tissue damage and enhancing the final product quality of products which are frozen (Cheng et al., 2017a, 2017b; Zhu et al., 2006). As a result, cryogenic technology has garnered significant attention in recent times, demonstrating considerable potential in the field of freezing process. Cryogenic liquid freezing also provides benefits such as high capacity, enhanced quality, minimal product weight loss, low initial capital investment, reduced floor space requirement, low maintenance cost, and ease of handling; nevertheless, it comes with drawbacks, including the expensive cryogenic liquid, relatively higher consumption, dependence on a limited number of suppliers, and the necessity for sophisticated storage installations (Saravacos et al., 2016). In a study by Qian et al. (2018) investigating the effects of cryogenic freezing on the

Figure 10.2 Cryogenic freezing. Adapted from Zhao et al. (2019).

Freezing of meat, poultry, and seafoods

231

product quality of big-head carp compared to air-blast freezing, it was found that cryogenic freezing achieved a freezing rate approximately 4.5 times faster than air-blast freezing. Furthermore, it demonstrated 60% more texture retention rate and enhanced preservation of the microstructure (Qian et al., 2018). Truonghuynh et al. (2020) investigated the quality changes of yellow croaker during preservation. Freshly collected fish were frozen using cryogenic freezing and stored for 6 months. The moisture loss, water holding capacity, color, and texture properties of frozen fish were assessed. Water holding capacity decreased significantly after the freezing process. The storage of samples subjected to cryogenic freezing at temperatures of
60 and
80 C led to increased yellowness values. In contrast, Truonghuynh et al. (2020) observed that samples frozen at
60 C exhibited the highest values for gumminess and shear force. Freezing as a crucial process plays a vital role in the food industry; it is valued for its capability to regulate multiple parameters and the wide range of equipment utilized. Different freezing equipment impact the quality, nutritional value, and sensory attributes of various food products in distinct manners. It is difficult to establish the superiority of one freezing technique over another, as each has its unique characteristics along with the specific properties of the food being processed. Furthermore, the basic freezing equipment can be improved by integrating various technologies.

10.3

Thawing

The thawing process is the process of making a frozen product free of ice residue. Thawing usually takes longer than freezing (Ansarifar et al., 2023). With the thawing, the activity of microorganisms and various biological reactions are also started. The thawing can have various effects on meat, poultry, and seafoods. The main effects are moisture loss, protein denaturation, lipid and protein oxidation, color loss, drip loss, sensitivity, and microbial degradation. Choosing the right thawing process is very important in terms of product quality. In order to ensure food quality and prevent food denaturation, it is preferred that the thawing process takes place at a low temperature and quickly (Li & Sun, 2002). The development of innovative technologies has an important role in ensuring that food quality is not adversely affected by this process (Cai et al., 2019). Thawing methods can be examined under two main groups as traditional and innovative methods (Fig. 10.3). In this section, traditional methods such as air thawing, water thawing, vacuum thawing, and microwave thawing will be examined. Among the innovative methods, high pressure thawing, ohmic thawing, and ultrasound-assisted thawing methods will be examined. The easiest method to thawing frozen products is in an area with stagnant air at 0e4 C conditions. Here, the frozen product is thawed naturally or forcibly due to heat transfer by convection. The efficiency of the actual heat transfer varies depending on the temperature difference between the air and the product, the velocity and relative humidity of the air, and the size and properties of the product to be dissolved. This thawing method increases the risk of lipid oxidation and unwanted surface drying.

232

Low-Temperature Processing of Food Products

Air Thawing

Water Thawing

Traditional Methods

Vacuum Thawing

Microwave Thawing

High Pressure Thawing

Innovative Methods Ohmic Thawing

Ultrasound Assisted Thawing

Figure 10.3 Traditional and innovative thawing methods.

At the same time, there may be significant drip loss and the thawing process may not always be homogeneous. The water thawing process is a commonly used process in which the product is thawing by immersion in water. This process is faster than air thawing. This is because the rate of heat transfer in water is faster than in air. Thanks to this thawing, drying of the surface of the product and lipid oxidation are prevented. However, this process requires a large area and water. In addition, the thawing medium must be changed frequently in order to maintain heat transfer and prevent microbial contamination. Vacuum thawing is based on lowering the boiling point of water, thanks to the decreasing pressure. The purpose of this method is to reduce the condensation temperature of the steam, to remove air molecules, and to increase the amount of heat transport. Vacuum thawing is widely used to thaw meat, poultry, and seafoods (Ansarifar et al., 2023). Microwave thawing, which is another traditional thawing method, has the feature of accelerating the dissolution by penetrating deep into food products. With microwave thawing, shorter and smaller areas can be processed. It also reduces drip loss, microbial, and chemical degradation. However, the problem of local overheating and inability to achieve homogeneous thawing limits the use of this method (Zou et al., 2019). One of the innovative methods, high pressure thawing is an application that has been more researched and used recently. In this method, since the pressure is evenly transmitted throughout the product, the rate of thawing depends only on heat conduction. Thanks to high-pressure thawing, large quantities of food products can be thawed. The main disadvantages of this method are the high cost and the possibility of protein denaturation due to high pressure in products with high protein content such as meat, poultry, and seafoods. This problem causes color change in the products mentioned and leads to loss of quality of these food products (Li & Sun, 2002). Ohmic thawing,

Freezing of meat, poultry, and seafoods

233

on the other hand, is the process of obtaining heat by passing an electric current through a conductive food with high electrical resistance and thus thawing it. This process is highly efficient because almost all of the energy is converted to heat, so there is no limit to the depth of penetration. It also has advantages such as high heating rate, high energy conversion efficiency, and volumetric heating. However, frozen products are less conductive than thawed foods. For this reason, during the thawing of frozen food, the current flows faster through the thawed parts, which may cause undesirable exposure to heat and cooking of the product. This is known as runaway heating or hotspot formation. This problem needs to be overcome for this application to be preferable due to its fast processing time. Ultrasound-assisted thawing is a method in which ultrasonic waves are used. Ultrasonic waves are similar to sound waves but have frequencies higher than 16 kHz and cannot be heard by a human. These waves, together with temperature and pressure, can cause bubble formation called cavitation. The resulting cavitation causes degradation of cell membranes, local warming and free radical formation. In this way, it contributes to the inhibition of microorganisms. As ultrasonic waves pass through a frozen food, some of their energy is also converted into heat. When the temperature exceeds the initial freezing point, the thawing process accelerates, and it can absorb more energy. During thawing, the physical effects of ultrasound can raise the water temperature and create extremely fast jets, causing the bubbles to collapse asymmetrically. This increases heat transfer. This method is one of the most remarkable innovative methods in recent times (Ansarifar et al., 2023). Guo et al. (2021) evaluated the effect of ultrasound-assisted thawing method on the longissimus dorsi muscles obtained from white beef. Ultrasound treatment at different power levels of 0, 200, 400, and 600 W at 20 kHz frequency was evaluated for the dissolution process. As a result of the analysis, it was observed that the processing time was reduced by 30.95%e64.28% compared to the control sample. As a result of the analyzes on meat quality, it was observed that the thawing loss, cooking loss, L* and b* values and pH values decreased significantly at 400 W power level, while the a* value and cutting force increased significantly. In addition, it was reported that the ultrasound-assisted dissolution process increased the content of free amino acids, minerals, and vitamins (Guo et al., 2021). Hong et al. (2014) evaluated the effect of ultrasound-assisted thawing treatment applied in water or salt water at 40 kHz and 150 W power on the quality characteristics of pork. Water was chosen as 4 C for the application process. As a result of the process, it was observed that the temperature of the water increased to 16 C. It was reported that less cooking loss occurred thanks to the applied process compared to the control. In addition, low shear force, that is, high sensitivity, was achieved with the ultrasound process applied in salt water. However, it was reported that the treatment in salt water had a negative effect on the color characteristics of the meat (Hong et al., 2014). In another study, high-pressure thawing and ohmic thawing were applied, and their synergistic effect was investigated. In this sense, 200 MPa pressure and 40 V/cm ohmic treatment were applied. Both processes and their individual applications were evaluated for thawing frozen beef. It was reported that the sample applied in both processes had the shortest dissolution time. It was reported that the quality characteristics

234

Low-Temperature Processing of Food Products

of the beef treated in both treatments were better when compared to the control (Min et al., 2016). Ersoy et al. (2008) evaluated different thawing processes to thaw frozen eel (Anguilla anguilla). Thawing in refrigerator, water, ambient temperature, and microwave was evaluated. The results obtained on the quality of the eel were compared with the fresh fish values. The pH, TBA, and a* values of the thawed samples were reported to be generally significantly reduced compared to the fresh control. It was reported that the total number of aerobic mesophilic bacteria of all thawed fish decreased, but the yeast count of the samples thawed in the refrigerator increased. Since the lowest total aerobic mesophilic bacteria and yeast counts were obtained in the samples dissolved in water, it was reported that the water dissolving process was suitable for eels (Ersoy et al., 2008).

10.4 10.4.1

Effect of freezing on the quality of meat, poultry and seafood products Effects on microbial quality

Freezing is a frequently used technique from past to present to inhibit spoilage and pathogenic microorganisms and to prevent spoilage of meat, poultry, and seafood products (Zhan et al., 2018). Key findings of selected studies on the effects of freezing in meat, poultry, and seafoods are compiled in Table 10.1. Choi et al. (2016) examined the effects of pressure freezing (0.1, 50, 100, 150, and 200 MPa) on the quality of pork. The authors reported that the total plate count decreased as the pressure increased compared to the control. Although it is known that chilling temperature is a critical factor in maintaining microbial stability in meat, Choe et al.’s study with lamb fillet showed that aging/freezing-thaw order did not make a difference on E. coli count. In another study examining the sous-vide cooking method with prefreezing made with beef, the counts of mesophilic and psychrotrophic bacteria and Pseudomonas, lactic acid bacteria, and Enterobacteriaceae were found to be acceptable (Botinestean et al., 2016). This finding was attributed to the vacuum packaging of the meats, the short waiting time in the frozen storage and the cooking immediately after thawing. Frozen meat products must be thawed before being processed or consumed. The thawing step is a longer process compared to freezing. In the meantime, different temperature zones occur in the meat. As the frozen water crystals begin to dissolve, the meat cannot hold this water and releases it out of the cell. As a result, both the temperature and the amount of free water in the environment come to a state desired by the microorganisms (Leygonie et al., 2012). Therefore, temperature fluctuations and multiple freeze/thaw cycles in meat are important factors on microbial quality. In a study by Lan et al. (2020) examining the effects of multiple freeze/thaw cycles in Pacific white shrimp, while the total viable count was 3.88  0.01 Ig CFU/g at the beginning, it increased to 5.14  0.09 Ig CFU/g after the fourth cycle and reached 6.54  0.05 Ig CFU/g after the seventh cycle. In another study with beef and chicken, the effects of

Table 10.1 Effects of freezing on meat, poultry, and seafoods. Freezing process

Process conditions

Key findings

Reference

Pork loins (M. longissimus thoracis et lumborum)

Pressure-shift freezing (PSF)

Pressure: 0.1 (atmospheric freezing), 50, 100, 150 and 200 MPa The coolant (ethanol) temperature:
50 C

Choi et al. (2016)

Beef muscles [M. semitendinosus (ST)]

Blast frozen and sousvide cooking

Freezing temperature:
20 C Freezing time: 48 h Sous-vide cooking: at 60 C for 270 min

Lamb loin (M. longissimus lumborum)

Four different aging/ freezing conditions


1.5ANF: aged at
1.5 C for 14 d, never frozen. 3AF: aged at 3 C for 8 d then frozen/thawed (
18 C) 7AF: aged at 7 C for 8 d then frozen/thawed (
18 C)
1.5AF: aged at
1.5 C for 14 d then frozen/thawed (
18 C)

Drip loss was the lowest in fresh meat, while it increased with the increase in pressure in frozen samples. An increase in tissue damage and deterioration was observed with the increase in pressure in PSF-treated samples. PSF-treated pork at 100 MPa (shifting at 9 C) showed fresh meat-like qualities when thawed. After prefreezing, the sous vide cooking technique increased the tenderness, stickiness, and gumminess of the steaks compared to the controls. The counts of mesophilic and psychrotrophic bacteria and Pseudomonas, lactic acid bacteria and Enterobacteriaceae were found to be acceptable. E. coli was not found in any of the samples. The increased aging temperature caused protein degradation, accelerating the development of sensitivity, while causing more drip loss and lower color stability. In the optimal conditions (freezing/ thawing after 8 days of aging at 3 C), the meat retained its color stability on display for 4 days at
1.5 C.

Freezing of meat, poultry, and seafoods

Food product

Botinestean et al. (2016)

Choe et al. (2016)

235 Continued

236

Table 10.1 Continued Freezing process

Process conditions

Key findings

Reference

Crab sticks

Oscillating magnetic field (OMF) freezing

OMF application in the freezing process failed to prevent quality losses, but also failed to reduce the damage to the sample after thawing.

Otero et al. (2017)

Chicken breast

Slow and fast freezing with probiotic diet

Cells Alive System (CAS) freezer conditions: 0%, 10%, 50%, and 100% CAS at
25 C Air-blast and static-air freezing temperature:
25 C OMF: 6e59 Hz Slow freezing: at
30 C with conventional air freezer Fast freezing: at
70 C in a liquid nitrogen chamber Core temperature:
20 C Probiotic diet: Bacillus subtilis

Probiotic supplementation inhibited lipid oxidation in frozen/thawed chicken. The fast freezing/thawing process, on the other hand, decreased the loss of clear and suppressed the formation of primary and secondary lipid oxidation products.

Kim et al. (2017)

Chicken breast

Freezing in a plate freezer

Fast freezing at
40 C Storage temperature:
18 C Storage time: 0, 1, 2, 3, 4, 5, 6, 7, or 8 months

As the storage time increased, discoloring, decrease in pH and a proportional decrease in water holding capacity were observed in chicken breast. The solubility of total protein, myofibrillar protein and sarcoplasmic protein decreased gradually with increasing freezing time.

Wei et al. (2017)

Low-Temperature Processing of Food Products

Food product

Slow freezing:
20 C with blast freezer Fast freezing:
80 C with a liquid nitrogen freezing cabinet

Tuna meat (Thunnus obesus)

Air-blast freezer

Common carp (Cyprinus carpio)

Ultrasound-assisted immersion freezing (UIF), air freezing (AF) and immersion freezing (IF)

First freeze:
60 C (walk in freezer) Sliced: 2 cm thickness Salting concentrations: 0.25e3 M of NaCl solution Second freeze:
20 C AF: frozen in a common refrigerator
25 C If: frozen in a freezing tank with 95% ethanol þ 5% fluoride as a coolant at
25 C UIF: same conditions as IF with 10 ultrasound transducers (power 175 W and frequency of 30 kHz) 30 s on/30 s off cycle for 9 min

Fast freezing resulted in less cryodamage to the muscle structure in AFT samples compared to slow freezing. Weight loss (2.3%) of FTA pork loins is lower than that of AFT pork loin (4.2%). Slow-frozen FT pork loins showed the highest shear force, while slow-frozen FTA pork loins showed the lowest shear force. AFT samples showed the highest lipid oxidation, followed by FTA and FT samples. Freezing and aging sequences were also found to have significant effects on color quality. An increase in the water holding capacity of meat after freezing and thawing was observed when optimum salting (approximately 1M) was provided. As the salt concentration increased, water-soluble proteins became insoluble. Ultrasound treatment prevented the growth of ice crystals during freezing, reduced tissue damage, reduced water loss in thawing, provided a higher thermal stability compared to other samples, and prevented the increase of lipid oxidation.

Kim et al. (2018)

Jiang et al. (2019)

Sun et al. (2019)

237

Slow and fast freezing

Freezing of meat, poultry, and seafoods

Pork loin

Continued

Table 10.1 Continued Freezing process

Key findings

Reference


18 C

Process conditions

Stored in a freezer

Freezing conditions: for 6 days, thawing conditions:
4 C for 24 h (one freeze-thaw cycle (F-T)) 0, 1, 2, 3, 4, 5, 6, 7 freezethaw cycles were studied

Ice crystal reformation after repeated F-T cycles caused endomysia to rupture, fiber spacing to widen, and holes to enlarge throughout muscle fibers. The color change in meat may be the result of many freeze-tempering cycles causing lipid oxidation.

Cheng et al. (2019)

Beef (Longissimus lumborum and Semitendinosus muscles)

Freezing

Freezing conditions:
20 C for 3 weeks

Setyabrata and Kim (2019)

Pork

Freezing with air blast freezer

Temperature:
18 C Storage time: 0, 3, 6, 9, 12, 15 and 18 weeks

Chicken liver

Mild heat and freezing

Heat treatment: at 60 C for 1 or 5 min Freezing: at
25 C for 48 h

Water loss was found to be higher in samples that were first frozen and then thawed, compared to other samples. The ice crystallization that occurred during the freezing process before aging caused structural deformation in the muscle tissue. A large desmin degradation was observed in both freezing processes. As the storage time increased, the thawing loss increased, while the pH value did not change until the 3rd week and then decreased in the 6th and 9th weeks. Mild heat treatment before freezing significantly reduced the total aerobic bacteria and Campylobacter counts. A 5-minute pasteurization process at 60 C led to a lightening of the color of the meat, although it had a reducing effect on the microbial load.

Zequan et al. (2019)

Berrang et al. (2020)

Low-Temperature Processing of Food Products

Beef (semimembranous muscles of cattle carcass)

238

Food product

Freezing thawing

Pacific white shrimp (Litopenaeus vannamei)

Freeze-thaw cycles

Beef (minced) and chicken meats

Freezing and refreezing

Constant temperature:
18 C Controlled temperature fluctuations:
18 to
17 C,
18 to
15 C, and
18 to
13 C Freezing: stored at
20 C for 12 h Thawing: with crushed ice at 4 C for 12 h 8 freeze-thaw cycles were studied

Freezing:
20 C for 2.0, 4.5, and 9.0 months and then thawed Refreezing: frozen at
20 C then thawed at 4 C for 1 day and then refreeze at
20 C for 2.0, 4.5, and 9.0 months

As the amplitude of temperature fluctuations increased, tissue damage and therefore a decrease in water holding capacity and color loss were observed.

Wang et al. (2020)

Especially after the 3rd freezing/thawing cycle, oxidative denaturation of the protein occurred with damage to the muscle tissue, and after the 6th cycle, the deterioration became unacceptable. The amount of immobilized water in the meat decreased. The brightness of the meat and the color quality of the meat decreased. Freezing/thawing cycles caused an increase in the total number of bacteria and a decrease in moisture and essential amino acids in both meat types. Except for Pseudomonas and E. coli in frozen meat, and Pseudomonas and S. aureus in chicken, the number of microorganisms decreased with the increase in storage time. Compared to chicken meat, beef relaxation was influenced by longer storage times and microorganisms.

Lan et al. (2020)

Freezing of meat, poultry, and seafoods

Beef

Mohammed et al. (2021)

Continued 239

240

Table 10.1 Continued Food product

Freezing process

Process conditions

Key findings

Reference

Turkey (Musculus pectoralis) meat and s ausage products

Frozen storage

Frozen storage: for 12 weeks (at
18 C or
80 C) and 24 weeks (at
18 C or
80 C)

Kluth et al. (2021)

Lamb meat

Microwave (MW)assisted freezing

The coolant temperature:
30 C The coolant flow rate: 3 L/ min The power level of microwave radiation: 0%, 40%, 50%, and 60% (based on the 30 s cycle)

Rainbow trout (Oncorhynchus mykiss)

Multiple freeze-thaw cycles

Freezing conditions:
20 C for 48 h Thawing conditions: 4 C for 12 h 9 freeze thaw cycles were studied.

Storage at
80 C in chicken meat resulted in higher water holding capacity than at
18 C. In both chicken and fermented sausage, Pseudomonas spp. and Enterobacteriaceae growth was successfully inhibited by freezing. MW irradiation during the freezing process reduced the size of the ice crystals, resulting in reduced drip loss and color change. Limited temperature fluctuation during the freezing process causes alternate ice crystal growth and melting, which inhibits crystal growth and results in the creation of many little ice crystals. As the number of freeze-thaw cycles increased, mechanical damage had a negative effect on the quality attributes of meat such as color, chewiness, firmness, and water holding capacity. With the increase of cycles, a significant increase in lipid oxidation and protein denaturation was also observed, and after the 7th cycle, the meat was now unacceptable due to the highest draining rate, loss of nutrition, and severe microstructural damage.

Atani et al. (2022)

Low-Temperature Processing of Food Products

Du et al. (2023)

Isochoric freezing

Isochoric freezing chamber Isochoric liquid: NaCl solutions with various concentrations of 0 (i.e., pure water), 1.5% and 2.5% at
4 and
8 C

Chicken breast

Low voltage electric field (LVEF) thawing

Fast freezing: at 36 C in 2 h (core temperature:
20 C) Thawing: stage I: 20e5 C, stage II: 5e1 C with low voltage electric field rapid thawing cabinet (voltage 2.5 kV)

Increasing solution concentrations increased the water holding capacity and reduced weight loss, but the sample treated with 2.5% NaCl solution gave similar results to the control, considering the damage to the microstructure. The lowest microbial count was obtained by thawing at 15e15 C with low electric field. Chicken meat closest to fresh, with the highest water holding capacity, least dissolution loss, lowest TVB-N content and highest quality, is meat thawed at 22.5e7.5 C by low voltage electric field.

Rinwi et al. (2023)

Zhang, Zhang, et al. (2023) and Zhang, Jin, et al. (2023)

Freezing of meat, poultry, and seafoods

Chicken breast

241

242

Low-Temperature Processing of Food Products

cryo-storage time and freeze-thaw cycle on nutritional changes and microbial load in meats were investigated. The study showed that while the freezeethaw cycle causes an increase in all microorganisms, the microbial load decreases as the storage time increases in the cryopreservation process without allowing temperature fluctuations (Mohammed et al., 2021). In a study with chicken liver, mild heat treatment before freezing significantly reduced the total aerobic bacteria and Campylobacter counts (Berrang et al., 2020). New techniques to minimize microbial growth in the dissolution stage are also an important subject of study. The total plate count of frozen chicken meat with two-stage (from
20 to
5 C and from
5 to
1 C) thawing in a low voltage electric field was found to be much lower (4.35 logCFU/g) than the air thawing (4.65 log CFU/g) (Zhang, Zhang, et al., 2023; Zhang, Jin, et al., 2023).

10.4.2

Effects on physical quality attributes

Irregular ice crystals formed between the tissues during the freezing of meat products disrupt the cellular integrity and cause the cells damaged during the thawing stage to be unable to retain water and release it, resulting in weight loss, drip loss, and cooking loss (Zhang, Zhang, et al., 2023; Zhang, Jin, et al., 2023). In addition, meat that loses water also loses its firmness and discoloration occurs with the effect of other physicochemical reactions such as oxidation of lipids and proteins. It has been observed that the optimal conditions in the production of aged/frozen/thawed meat are freezing/ thawing after aging at 3 C for 8 days (Choe et al., 2016). Thus, the meat retained its color stability on display for 4 days at
1.5 C. Kim et al. (2018) studied the effects of aging and slow/fast freezing on quality in pork. Three types of processes were applied in the study (FT, freeze/thaw only; AFT, aging before freezing/thawing; FTA, freeze/thaw after aging). The results of the study revealed that the fastfreezing process after aging can minimize the freezing/thawing quality defects in meat. The study by Cheng et al. (2019) reveals that repetitive freeze-annealing cycles that may occur during storage and transportation can cause adverse changes in quality criteria such as water state and distribution, microstructure, and physicochemical properties in cattle muscle. In another study, in comparison to other samples, samples that were first frozen and subsequently thawed showed a higher rate of water loss (Setyabrata & Kim, 2019). This result shows that the water holding capacity of meat is affected by the order of freezing/thawing and aging processes. As the amplitude of the temperature fluctuations increased, the structural changes also increased (Wang et al., 2020). The recrystallization of ice leads to the formation of pores in the meat. Tissue damage occurs proportional to the increase in diameter and volume of the recrystallized ice during freezing, resulting in quality losses such as decreased water binding capacity and darkening of color in meat. In a recent study examining the effects of multiple freeze/thaw cycles, a severe loss of quality occurred in fish fillets after the first cycle (Du et al., 2023). With the reformation of ice crystals, the muscle cells were deformed and the amount of free water between the tissues increased. Factors such as metmyoglobin accumulation, degradation reactions in pigments, and the interaction of free radicals produced by oxidation reactions of unsaturated fatty acids with proteins are responsible for the color changes. The firmness,

Freezing of meat, poultry, and seafoods

243

elasticity, chewiness, and water holding capacity of meat also decreased as the number of cycles increased. In the study of Wei et al. (2017), on investigation of the effects of freezing on the quality of chicken breast, metmyoglobin accumulation and lipid oxidation on the surface during storage were indicated as the factors causing color changes. In order to ensure freezing stability during the freezing process, tunas were sliced and salted at different concentrations just before freezing (Jiang et al., 2019). When the optimum salt concentration (approximately 1M) is used, an increase in water holding capacity is observed, while as this concentration increases, large ice crystals form and the pores expand, which leads to water retention. One of the key stages in the freezing process is the thawing process. A thawing process that is not performed with correct and effective techniques can increase existing textural damage, accelerate microbial growth, and increase thawing losses. Zhang, Zhang, et al. (2023) and Zhang, Jin, et al. (2023) used a two-step tempering process using a low-voltage electric field to thaw frozen chicken breast. The low-voltage electric field thawing process resulted in lower thawing time, reduced thawing loss, and improved product quality compared to air thawing. When two-stage thawing processes performed at different temperatures (from 0 to 30 C) are compared, the thawing process performed at 22.5 and 7.5 C resulted in a quality similar to fresh meat, allowing the meat to retain more moisture, and minimizing thawing and cooking loss.

10.4.3 Effects on nutritional quality In particular, mechanical damage of muscle proteins by ice crystals formed during freezing and denaturation by oxidative enzymes is one of the most important negative effects of freezing on meat products (Li et al., 2018). In a study with chicken breast, it was found that increased freezing time had a reducing effect on the solubility of total protein, myofibrillar protein, and sarcoplasmic protein (Wei et al., 2017). In the freezing process with beef and chicken, the amount of essential and nonessential amino acids in the refrozen samples was found to be lower than in the frozen and stocked samples alone. This study reveals the negative effects of freezeethaw cycle on nutritional components (Mohammed et al., 2021). Inhibition of lipid oxidation was observed in chickens fed diets containing three different species of Bacillus subtilis for 45 days (Kim et al., 2017). According to the findings, despite the high phospholipid content, probiotic supplementation inhibited the formation of both primary and secondary oxidation products. In addition, the fast-freezing process helped inhibit lipid oxidation in chicken meat, improved the water holding capacity of the meat, and minimized tissue damage and clear losses. Novel techniques are also studied to minimize the damage caused by the freezing process to the nutritional values of meat. With the ultrasound-assisted immersion freezing process applied to the carp, the growth of ice crystals was prevented and the increase in lipid oxidation during storage was prevented (Sun et al., 2019). Total volatile basic nitrogen (TVB-N) content is an indicator of meat freshness. In the study of Zhang, Zhang, et al. (2023) and Zhang, Jin, et al. (2023), while the TVB-N content in fresh chicken meat was 13.07 mg/100 g, it reached a maximum (20.53 mg/100 g) at temperatures above 15 C in the air thawing process. Microbiological growth, lipid

244

Low-Temperature Processing of Food Products

oxidation, enzymatic autolysis, and protein oxidation caused the change in TVB-N content. The lowest TVB-N content (13.17 mg/100 g) was obtained with a two-stage thawing process at 22.5e7.5 C with the application of a low-voltage electric field. In a study in which Abraha et al. (2018) compiled changes in fish processing, they mentioned the undesirable quality defects of freezing, such as membrane damage, oxidation of proteins and lipids, and the resulting off-flavor, off-odor, and off-color. Kim et al. (2018) examined the effects of fast and slow freezing in pork loin and the sequencing of aging/freeze/thaw cycle and found that aging prior to freezing resulted in the highest lipid oxidation in samples. The amount of carbonyl indicating protein oxidation was found at the highest scale on the eighth day in slow-frozen, first frozen/thawed, and then aged samples. The growth of ice crystals formed in slow freezing may have damaged the muscle tissue of the meat and thus the proteins, making them susceptible to oxidation. Studies have shown that an increase in the number of freezeethaw cycles leads to loss of nutritional content (Abraha et al., 2018). Lan et al. (2020) studied the effect of multiple freeze/thaw cycles on Pacific white shrimp. According to the findings, the amount of immobilized water decreased, and especially after the third cycle, the reformation of ice crystals, and the damage to the polyphenol oxidase enzyme, as well as the deterioration of tissue properties and color are in question. Oxidative denaturation of the protein has occurred. These deteriorations reached an unacceptable level after the sixth cycle. The fact that multiple freezeethaw cycles with trout fillet increase lipid oxidation is attributed to the fact that the process inactivates the antioxidative enzymes in the meat and the growth of the air-contacting surface by the formation of micropores with the growth of the ice crystals formed (Du et al., 2023). In addition, lipid oxidation products such as hydroperoxides, aldehydes, and free radicals can act as protein oxidation substrates and induce oxidative denaturation of proteins. Considering the nutritional values, it was observed that the amount of moisture decreased significantly, the amount of protein and lipid decreased with increasing cycles, while the mineral content was not significantly affected by these cycles.

10.5

Packaging and storage of frozen meat, poultry, and seafood products

Packaging is an important technique to protect food from environmental factors as well as microbial and biochemical factors (Rahimzade et al., 2019). The process of lipid oxidation is a significant biochemical issue that results in the reduction of nutritional value, the formation of unpleasant tastes, and a shortened shelf life for food. It can also lead to color loss in meat products and affect consumer satisfaction (KarpinskaTymoszczyk & Draszanowska, 2019). Oxidative products are commonly formed during the storage of food items, which is why it is preferable to use frozen storage packaging for perishable foods such as meat, poultry, and seafoods. This method effectively prevents microbial growth and biochemical reactions, thereby enhancing the quality and safety of the food.

Freezing of meat, poultry, and seafoods

245

Modified atmosphere packaging (MAP) with high oxygen content of 70%e80% is commonly used in the meat industry to preserve the red color and prevent microbial contamination. On the other hand, this packaging may lead to lipid or protein oxidation to occur owing to its high oxygen content (Li et al., 2023). The effect of frozen temperature and storage time on the beef rolls are investigated by Wang et al. (2021). They showed that the color of beef was brighter and had higher OxyMb% and pH values at
18 C storage compared to that of
12 C storage. When the storage time extended, color, OxyMb%, and pH values decreased, but MetMb% and lipid oxidation (thiobarbituric acid reactive substance, TBARS) values increased. Daszkiewicz et al. (2018) stated that besides storage at
26 C, vacuum packaging protects lamb meat against oxidation. However, they reported that long-term storage at low temperatures such as 12 months may cause a decrease in meat quality characteristics such as water holding capacity and flavor acceptability. Meat, poultry, and fish products are perishable products for which extending shelf life is a major problem (Karpi nska-Tymoszczyk & Draszanowska, 2019). Microbial growth in meat, poultry, and seafoods varies depending on packaging type, storage temperature, and duration. Vacuum packaging is widely used to prevent the growth of aerobic and spoilage-causing microorganisms such as psychrotrophic and facultative anaerobic bacteria (Sauvala et al., 2023). The effect of vacuum packaging on physicochemical properties of Tra catfish (Pangasius hypophthalmus) fillets during 12 months storage above
18 C, which is called industrial storage condition, was investigated by Dang et al. (2018). The storage method used resulted in higher drip loss and lipid oxidation, but vacuum packaging effectively protected the fish from these problems. The authors recommended using controlled constant temperatures during storage to prevent damage to the fish. Al-Hilphy et al. (2022) examined the modified atmosphere packaging stored frozen chicken thigh pieces for 1e90 days at
18 C. Vacuum and various compositions of gases (O2, CO2 and N2) in MAP were compared in view of the packaging of chicken thigh. As the frozen storage extended, the drip loss, thiobarbituric acid (TBA), peroxide number, and pH of samples increased. The lowest values of TBA and peroxide values were reached in 15% O2/15% N2/70% CO2, and 30% N2/70% CO2, respectively, and when applied these compositions of MAP, the drip loss was decreased during storage and cooking. Overall acceptability of samples improved after MAP applications. In another study, packaged chicken thighs and boneless chicken breasts stored at
18 C for 6 months were examined at the end of each month. The carbonyl content of proteins in chickens increased during storage. Denaturation of proteins occurred with increasing oxidation reaction, therefore, the solubility of the proteins decreased. Proteolytic activities were observed in samples after 3 months of storage (Demirok Soncu, 2020). Combination of various techniques during storage of frozen food products has recently been investigated. Rovira et al. (2023) compared the vacuum packaged beef striploins in terms of different temperature and packaging materials. Microbial changes were monitored during storage for 120 days at 0e1.5 C and 28 days at 0e1.5 C, then 92 days at
20 C in the presence of low O2 permeable vacuum package (LV), and high O2 permeable vacuum package containing antimicrobial agents (AHV). The numbers of Pseudomonas and Enterobacteriaceae in LV were found to

246

Low-Temperature Processing of Food Products

be lower than in AHV samples till the end of the storage time. Samples stored at frozen temperature indicated effective inhibition of microorganisms and provided a stable microbiome. Storage temperature is a vital parameter in the cold chain. However, during the shelf life and transportation of perishable foods, fluctuations in the temperature of the foods can be seen and may cause an increase in the proliferation of microorganisms. To solve this problem, time-temperature indicators (TTI) are used to attach to foods or their packaging. Thus, it is possible to monitor the temperature and chemical changes of foods during storage (Gao et al., 2020). Wang et al. (2018) created a TTI biosensor consisting of chitosan and gold nanoparticles (AuNPs) nanocomposite. This biosensor was capable of detecting thermal changes and the frozen state of food by producing visible color changes. Researchers investigated the use of nanocomposite of AuNPs as a detector that changes color from pink to gray after freezing. They suggested integrating this biosensor into food packaging to monitor the frozen storage of perishable foods such as meat, poultry, and fish, which would aid in maintaining the quality and safety of the products. It was discovered that the colors of the products appeared to be more vivid when they were subjected to elevated temperatures as opposed to being frozen. Jaiswal et al. (2020) conducted a study to explore the potential of a lipasebased time-temperature indicator (TTI) for monitoring frozen chicken during transportation. The TTI was designed to change color from green to red upon exposure to temperature fluctuations and a decrease in pH from 8.1 to 5.3. However, the study found that there was no significant correlation between kinetic parameters and temperature changes, and therefore, the use of the lipase-based TTI as a quality indicator for frozen chicken could not be concluded.

10.6

Recent advances in freezing of meat, poultry, and seafoods

Storing food in freezing temperatures can enhance its shelf life by preventing oxidation (Li et al., 2023). Conventional freezing techniques used in industry are air freezing and immersion freezing with freezing rate and temperature fluctuations being crucial factors. Slow freezing rates and temperature fluctuations lead to the formation of large and irregular ice crystals that harm cells and organelles, thereby resulting in significant drip loss after thawing and increased enzymatic reactions. Researchers are exploring innovative freezing methods to improve efficiency and maintain the nutritional, physical, and visual properties of foods (Daszkiewicz et al., 2018; Firouz et al., 2022; Lu et al., 2022). The freezing techniques for meat, poultry, and seafoods have made significant progress, as demonstrated in Table 10.2. Ultrasound-assisted freezing is a promising technique to use in freezing of foods. UAF increases the freezing rate, resulting in small air crystals and control over the size distribution of ice crystals during the process. Ultrasound causes cavitation, which is the main reason for the faster freezing rate. Additionally, ultrasound can regulate the size distribution of ice crystals by enhancing the nucleation capability in supercooled

Table 10.2 Recent advances in freezing of meat, poultry, and seafoods. Technique(s) applied

Experimental conditions

Main findings

References

Common carp (Cyprinus carpio)

Ultrasound-assisted immersion freezing (UIF), air freezing (AF), and immersion freezing (IF)

The frequency of the ultrasound equipment was set at 30 kHz, with output power ranging from 0 (IF) to 175W (UIF).

Sun et al. (2019)

White shrimp (Litopenaeus vannamei)

Magnetic fieldeassisted immersion freezing (MFIF)

MFIF at 20, 40, 60, and 80 mT

Largemouth bass (Micropterus salmoides)

Pressureeshift freezing (PSF) and conventional freezing methods including air freezing (AF) and liquid immersion (LI) High pressure freezing (HPF), pressureeshift freezing (PSF) and immersion freezing (IF)

150 MPa for PSF and
30 C for conventional freezing

The use of UIF resulted in smaller ice crystals and decreased thawing and cooking losses in frozen fish. Samples treated with UIF exhibited greater thermal stability and lower levels of thiobarbituric acid reactive substances compared to other samples. The use of MFIF (60 mT) resulted in the quickest freezing time, reduced thawing loss, maintained water holding capacity, and preserved the textural properties of the shrimp. PSF showed lower thawing and cooking loss, and TBARS values than those of AF and LI.

Prawn (Metapenaeus ensis)

100, 150, 300, 400, 500 MPa at
20 C, 25 min for HPF; 200 MPa at
20 C, 25 min for PSF, and 0.1 MPa at
20 C, 30 min for IF

PSF of 200 MPa decreased the denaturation of protein while 300 MPa showed critical role in denaturation of proteins.

Freezing of meat, poultry, and seafoods

Food samples

Sun et al. (2023)

Li et al. (2022)

Cheng et al. (2017a, 2017b)

247

Continued

248

Table 10.2 Continued Food samples

Technique(s) applied

Experimental conditions

Main findings

References

Pork meat

Radiofrequency-assisted cryogenic freezing (RFCF), cryogenic freezing (CF) and air freezing (AF)

2 kV or 7 kV voltage for RFCF and stored at
18 C; air flow rate of 2 m/s and at
40 C for AF; 20 s of cryogenic flow and stored at
18 C for CF

Anese et al. (2012)

Cultured large yellow croaker

Multiple-frequency effect of ultrasound

Triple ultrasound frequency of 20, 28, and 40 kHz (TUAF), dual ultrasound frequencies of 20 and 28 kHz (DUAF) and single ultrasound frequency of 20 kHz in the ultrasoundassisted freezing.

Shrimp

High voltage electric field (HEF) assisted freezing

Various electric field intensities (5, 10, 15, and 20 kV/m) in a
20 C

The RFCF method resulted in less thawing loss compared to CF and AF. Additionally, meat treated with RFCF exhibited a superior structure with minimal cell and cell void damage. The freezing rate of cultured large yellow croakers has been enhanced by UAF. Samples treated with TUAF demonstrated superior waterholding capacity, textural properties, and lower levels of thiobarbituric acid reactive substances. TUAF-treated samples displayed smaller and more uniformly distributed ice crystals. Ice crystals formed uniformly, enhancing the textural properties of the shrimp while preventing the effects of polyphenol oxidase. Additionally, antimicrobial activity was observed.

Ma et al. (2021)

Low-Temperature Processing of Food Products

Liu et al. (2022)

Raw chicken

Static magnetic field assisted freezing (SMF), electrostatic field assisted freezing (EF), combination of both (ESMF), and freezing without magnetic field and electric field (control) Crust freezing (CrF) (alone) and in conjunction with ultraviolet (UV) light

SMF at 10 mT; EF at 5 kV/cm; ESMF at 10 mT and 5 kV/cm

Air temperatures and freezing durations for CrF are 5, 15 and 20 C at 70, 15, and 6 min, respectively.

The freezing time control has been enhanced by ESMF. Samples treated with ESMF exhibited improvement in gel strength and protection in the protein’s secondary and tertiary structures. The combination of CrF and UV light showed better inhibition of C. jejuni than CrF alone without minimum skin color changes of chicken.

Jiang et al. (2023)

Haughton et al. (2012)

Freezing of meat, poultry, and seafoods

Gelatin model solution

249

250

Low-Temperature Processing of Food Products

water. UAF can enhance the quality of frozen foods by improving their color, texture, and chemical structure (Firouz et al., 2022; Zhang et al., 2019). The study conducted by Ma et al. (2021) focused on the impact of multiple-frequency of ultrasound on freezing cultured large yellow croaker. The authors used different ultrasound frequencies, including triple frequencies of 20, 28, and 40 kHz (TUAF), dual frequencies of 20 and 28 kHz (DUAF), and a single frequency of 20 kHz. The results showed that the use of UAF significantly improved the freezing rate of cultured large yellow croakers. Among the different ultrasound frequencies, TUAF was found to be the most effective in terms of water-holding capacity, texture, and low levels of thiobarbituric acid reactive substances, which were similar quality characteristics to fresh materials. The ice crystals in TUAF samples were also smaller and more uniformly distributed, leading to less damage during the freezing process. Based on these findings, the researchers recommended the use of multifrequency ultrasound for freezing large yellow croakers to enhance their quality characteristics. One of the quickest freezing methods is immersion freezing (IF), which involves using liquid refrigerants with high thermal coefficients as the heat transfer medium. This technique allows food to come into direct or indirect contact with the refrigerant. Compared to air, liquid coolants have 20 times more heat transfer capabilities. IF can result in the formation of small ice crystals due to its rapid freezing rate, resulting in improved frozen food quality. However, the use of IF in the food industry is restricted due to the possibility of food contamination by refrigerants (Liu et al., 2020; Qian et al., 2018). Researchers are exploring new methods to improve the effectiveness of traditional immersion freezing. Some specific techniques such as ultrasound and electrostatic field techniques are now being integrated to enhance the process. In a study conducted by Sun et al. (2019), the impact of different freezing methods including ultrasound-assisted immersion freezing (UIF), air freezing (AF), and immersion freezing (IF) on common carp (Cyprinus carpio) during storage was examined. The study found that UIF yielded smaller ice crystals compared to air freezing AF and IF, which helped prevent muscle damage. Frozen fish treated with UIF had the lowest thawing and cooking losses compared to other methods. Furthermore, UIF samples demonstrated higher thermal stability and lower thiobarbituric acid reactive substance values than the other methods. A recent research study examined the effects of using magnetic field-assisted immersion freezing (MFIF) to preserve white shrimp (Litopenaeus vannamei). The study tested various intensities, ranging from 20 to 80 mT. Results showed that using 60 mT of MFIF resulted in the fastest freezing time, reduced thawing loss, and maintained the water holding capacity and texture of the shrimp. Moreover, using 60 mT of MFIF helped preservation of both immobilized and free water in the shrimp and prevented quality losses in the shrimp’s muscles during freezing (Sun et al., 2023). A cutting-edge technique for enhancing the quality of frozen foods is high-pressure freezing. This technology falls into two categories: high-pressure-assisted freezing and pressure-shift freezing (PSF), which are influenced by pressure and temperature, leading to varied types of ice crystals and crystallization paths (Cheng et al., 2017a, 2017b). In a recent study by Li et al. (2022), the impact of PSF at 150 MPa was compared with conventional freezing methods such as air freezing (AF) and liquid

Freezing of meat, poultry, and seafoods

251

immersion (LI) on frozen largemouth bass (Micropterus salmoides) stored at
30 C. Throughout storage, PSF displayed lower thawing and cooking loss in comparison to AF and LI. Additionally, the TBARS values of the frozen fish treated with PSF of 0.25 were lower than AF and LI of 0.54 and 0.65, respectively. After 28 days of storage, the a-helix content of the protein declined in ultrasound-treated samples compared to the fresh ones. The use of electric and magnetic fields during the freezing process can impact the crystallization of water, resulting in the formation of small and evenly distributed ice crystals. This technique helps to maintain the quality characteristics of frozen samples, making them comparable to their fresh counterparts (Jiang et al., 2023). In a study by Liu et al. (2022), high-voltage electric fields (HEF) were used to freeze shrimp (Solenocera melantho). This method produced uniform ice crystals at 15 and 20 kV/m while also improving the texture of the shrimp and preventing oxidation through the inhibition of polyphenol oxidase. The antimicrobial effect of HEF varied depending on the intensity of the electric field used. Jiang et al. (2023) conducted a study using gelatin model solution, applying electrostatic field-assisted freezing (EF), static magnetic field-assisted freezing (SMF), and a combination of both (ESMF). The ESMF technique increased the freezing time and reduced the phase transition time compared to the control group, which received no magnetic or electric field application. Samples treated with ESMF showed better gel strength than those treated with EF or SMF while also preserving the secondary and tertiary structures of protein. Additionally, a 50% decrease in ice crystal area was observed in the ESMF-treated model solution.

10.7

Conclusion and future perspectives

The freezing process is a very useful technology that has been used for many years and ensures that the quality of food products remains unchanged during stages such as storage and transportation and that they are delivered to the consumer with the desired properties. Meat, poultry, and seafoods are rich in compounds such as high protein, vitamins, and minerals, making these food products very important in terms of nutrition. However, fresh meat, poultry, and seafoods deteriorate very quickly due to high water activity, protein, and lipid content. In order to overcome this problem, freezing process has been a preferred method for many years. The freezing process is generally conducted fast. This is due to the fact that smaller ice crystals are formed in the fast freezing process, and thus minimal changes in the structural properties of the product can be achieved. Since traditional freezing methods often cause long processing times and large ice masses, recent studies have focused on innovative freezing technologies that provide faster processing and do not adversely affect quality. Examples of innovative freezing methods can be listed as high-pressure freezing, magnetic assisted freezing, and UAF. Overcoming the high cost and various other disadvantages of innovative methods will allow these methods to be preferred much more in the future. As well as freezing of food products, thawing of these products is of great importance in terms of quality characteristics. Microbial and various biological and chemical

252

Low-Temperature Processing of Food Products

reactions, which are inhibited or slowed down during freezing, restart with the thawing process. This process takes place more slowly in the freezing process. However, it is of great importance that the processing times are not too long and that they are homogeneous so that the quality characteristics of the products are not adversely affected. As in the freezing process, it is divided into two groups: the traditional methods that have been used for years and the innovative methods preferred in recent years. Traditional methods can cause very long processing times and various quality losses. Innovative thawing methods can provide much faster and higher quality products. Examples of traditional thawing methods are air, water, vacuum, and microwave thawing methods. High-pressure thawing, ultrasound-assisted thawing, and ohmic thawing methods can be given as examples of innovative methods. With these methods, food products can be thawed much faster and higher quality products can be obtained. In this section, the freezing and thawing of meat, poultry and seafood products and the freezing process are examined in detail, with a special focus on the quality characteristics during these processes. In addition to these, a special emphasis is given to the recent innovations and techniques of freezing techniques used for meat, poultry, and seafoods.

References Aberoumand, Ali (2013). Nutritive profile of seafoods of different regions of Iran. Journal of Agricultural Technology, 9(2), 383e388. http://www.ijat-aatsea.com (May 25, 2023). Abraha, B., Tessema, H. A., Mahmud, A., Tsighe, K.,N., Shui, X., & Yang, F. (2018). Effect of processing methods on nutritional and physico-chemical composition of fish: A review. MOJ Food Processing & Technology, 6, 376e382. Al-Hilphy, A. R., Al-Asadi, M. H., Khalaf, J. H., Mousavi Khaneghah, A., & Faisal Manzoor, M. (2022). Modified atmosphere packaging of chicken thigh meat: Physicochemical and sensory characteristics during the frozen storage period. Journal of Food Quality, 2022, 1e10. https://doi.org/10.1155/2022/8876638 Anese, M., Manzocco, L., Panozzo, A., Beraldo, P., Foschia, M., & Nicoli, M. C. (2012). Effect of radiofrequency assisted freezing on meat microstructure and quality. Food Research International, 46(1), 50e54. https://doi.org/10.1016/j.foodres.2011.11.025 Ansarifar, E., Hedayati, S., & Jafari, S. M. (2023). Thawing equipment for the food industry. In High-Temperature processing of food products (pp. 175e224). Woodhead Publishing. Archer, D. L. (2004). Freezing: An underutilized food safety technology? International Journal of Food Microbiology, 90(2), 127e138. Atani, S. H., Hamdami, N., Dalvi-Isfahan, M., Soltanizadeh, N., & Fallah-Joshaqani, S. (2022). Effects of microwave-assisted freezing on the quality attributes of lamb meat. International Journal of Refrigeration, 143, 192e198. https://doi.org/10.1016/j.ijrefrig. 2022.03.019 Berrang, M. E., Cox, N. A., Meinersmann, R. J., Bowker, B. C., Zhuang, H., & Huff, H. C. (2020). Mild heat and freezing to lessen bacterial numbers on chicken liver. The Journal of Applied Poultry Research, 29(1), 251e257. https://doi.org/10.1016/j.japr.2019.10.012 Bordoni, A., & Danesi, F. (2017). Poultry meat nutritive value and human health. In Poultry Quality Evaluation: Quality Attributes and Consumer Values (pp. 279e290). Woodhead Publishing.

Freezing of meat, poultry, and seafoods

253

Botinestean, C., Keenan, D. F., Kerry, J. P., & Hamill, R. M. (2016). The effect of thermal treatments including sous-vide, blast freezing and their combinations on beef tenderness of M. semitendinosus steaks targeted at elderly consumers. LWT, 74, 154e159. https:// doi.org/10.1016/j.lwt.2016.07.026 Cai, L., Cao, M., Joe, R., & Cao, A. (2019). Recent advances in food thawing technologies. Comprehensive Reviews in Food Science and Food Safety, 18(4), 953e970. https:// onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12458 (May 25, 2023). Campa~none, L. A., Roche, L. A., Salvadori, V. O., & Mascheroni, R. H. (2002). Monitoring of weight losses in meat products during freezing and frozen storage. Food Science and Technology International, 8(4), 229e238. https://doi.org/10.1106/108201302028555. https://journals.sagepub.com/doi/pdf/10.1106/108201302028555 (May 25, 2023). Cheng, L., Sun, D.-W., Zhu, Z., & Zhang, Z. (2017a). Effects of high pressure freezing (HPF) on denaturation of natural actomyosin extracted from prawn (Metapenaeus ensis). Food Chemistry, 229, 252e259. https://doi.org/10.1016/j.foodchem.2017.02.048 Cheng, L., Sun, D. W., Zhu, Z., & Zhang, Z. (2017b). Emerging techniques for assisting and accelerating food freezing processes: A review of recent research progresses. Critical Reviews in Food Science and Nutrition, 57(4). https://www.tandfonline.com/doi/abs/10. 1080/10408398.2015.1004569. Cheng, S., Wang, X., Li, R., Yang, H., Wang, H., Wang, H., & Tan, M. (2019). Influence of multiple freeze-thaw cycles on quality characteristics of beef semimembranous muscle: With emphasis on water status and distribution by LF-NMR and MRI. Meat Science, 147, 44e52. https://doi.org/10.1016/j.meatsci.2018.08.020 Choe, J.-H., Stuart, A., & Kim, Y. H. B. (2016). Effect of different aging temperatures prior to freezing on meat quality attributes of frozen/thawed lamb loins. Meat Science, 116, 158e164. https://doi.org/10.1016/j.meatsci.2016.02.014 Choi, M.-J., Min, S.-G., & Hong, G.-P. (2016). Effects of pressure-shift freezing conditions on the quality characteristics and histological changes of pork. LWT e Food Science and Technology, 67, 194e199. https://doi.org/10.1016/j.lwt.2015.11.054 Choi, Y.-S., Ku, S.-K., Jeong, J.-Y., Jeon, K.-H., & Kim, Y.-B. (2015). Changes in ultrastructure and sensory characteristics on electro-magnetic and air blast freezing of beef during frozen storage. Korean Journal for Food Science of Animal Resources, 35(1), 27e34. https:// doi.org/10.5851/kosfa.2015.35.1.27 Dang, H. T. T., Gudjonsdottir, M., Tomasson, T., Nguyen, M. V., Karlsd ottir, M. G., & Arason, S. (2018). Influence of processing additives, packaging and storage conditions on the physicochemical stability of frozen Tra catfish (Pangasius hypophthalmus) fillets. Journal of Food Engineering, 238, 148e155. https://doi.org/10.1016/j.jfoodeng.2018. 06.021 Daszkiewicz, T., Kubiak, D., & Panfil, A. (2018). The effect of long-term frozen storage on the quality of meat (Longissimus thoracis et Lumborum ) from Female Roe Deer (Capreolus capreolus L.). Journal of Food Quality, 2018, 1e7. https://doi.org/10.1155/2018/4691542 Delgado, A. E., Zheng, L., & Sun, D. W. (2009). Influence of ultrasound on freezing rate of immersion-frozen apples. SpringerLink. https://link.springer.com/article/10.1007/s11947008-0111-9. Demirok Soncu, E. (2020). Protein oxidation and subsequent changes in chicken breast and thigh meats during long-term frozen storage. Agricultural and Food Science, 29(5). https:// doi.org/10.23986/afsci.97338 Dempsey, P., & Bansal, P. (2012). The art of air blast freezing: Design and efficiency considerations. Applied Thermal Engineering, 41, 71e83. https://doi.org/10.1016/j.applthermaleng. 2011.12.013

254

Low-Temperature Processing of Food Products

Desrosier, N. W. (2012). Fundamentals of food freezing. Springer Science & Business Media. Dominguez, S. A., & Schaffner, D. W. (2009). Survival of Salmonella in processed chicken products during frozen storage. Journal of Food Protection, 72(10), 2088e2092. Du, N., Sun, Y., Chen, Z., Huang, X., Li, C., Gao, L., Bai, S., Wang, P., & Hao, Q. (2023). Effects of multiple freeze-thaw cycles on protein and lipid oxidation, microstructure and quality characteristics of rainbow trout (Oncorhynchus mykiss). Fishes, 8(2), Article 2. https://doi.org/10.3390/fishes8020108 € Ersoy, B., Aksan, E., & Ozeren, A. (2008). The effect of thawing methods on the quality of eels (Anguilla anguilla). Food Chemistry, 111(2), 377e380. Firouz, M. S., Sardari, H., Alikhani Chamgordani, P., & Behjati, M. (2022). Power ultrasound in the meat industry (freezing, cooking and fermentation): Mechanisms, advances and challenges. Ultrasonics Sonochemistry, 86, 106027. https://doi.org/10.1016/j.ultsonch.2022. 106027 Gao, T., Tian, Y., Zhu, Z., & Sun, D.-W. (2020). Modelling, responses and applications of timetemperature indicators (TTIs) in monitoring fresh food quality. Trends in Food Science & Technology, 99, 311e322. https://doi.org/10.1016/j.tifs.2020.02.019 Guo, Z., et al. (2021). Ultrasound-assisted thawing of frozen white yak meat: Effects on thawing rate, meat quality, nutrients, and microstructure. Ultrasonics Sonochemistry, 70, 105345. Hall, G. M. (2010). Fish processing. Wiley Online Books. https://onlinelibrary.wiley.com/doi/ book/10.1002/9781444328585#page¼88. Haughton, P. N., Lyng, J., Cronin, D., Fanning, S., & Whyte, P. (2012). Effect of crust freezing applied alone and in combination with ultraviolet light on the survival of Campylobacter on raw chicken. Food Microbiology, 32(1), 147e151. https://doi.org/10.1016/j.fm.2012. 05.004 Hong, G. P., Chun, J. Y., Jo, Y. J., & Choi, M. J. (2014). Effects of water or brine immersion thawing combined with ultrasound on quality attributes of frozen pork loin. Korean Journal for Food Science of Animal Resources, 34(1), 115. https://www.ncbi.nlm.nih.gov/ pmc/articles/PMC4597821/ (May 25, 2023). Hou, Q., Cheng, Y. P., Kang, D. C., Zhang, W. G., & Zhou, G. H. (2020). Quality changes of pork during frozen storage: Comparison of immersion solution freezing and air blast freezing. International Journal of Food Science & TechnologydWiley Online Library. https://ifst.onlinelibrary.wiley.com/doi/full/10.1111/ijfs.14257?casa_token¼t8MHoM0X YrkAAAAA%3AgsHEIsHmv-jk97nqC7aMuP6IONAvh4myNRp-Fezy80_HNSX0C720_ pDw9C3gbd3syDJ9wBAsIr-bw07N. Jaiswal, R. K., Mendiratta, S. K., Talukder, S., Soni, A., Chand, S., & Saini, B. L. (2020). Application of lipase based enzymatic time temperature indicator (TTI) as quality marker for frozen chicken meat. Food Science and Technology Research, 26(1), 9e16. https:// doi.org/10.3136/fstr.26.9 James, C., & James, S. J. (2010). Handbook of meat processing. Google Kitaplar. https:// books.google.com.tr/books?hl¼tr&lr¼&id¼VYXRl4LTHqwC&oi¼fnd&pg¼PA105& dq¼James,þC.,þ%26þJames,þS.þJ.þ(2010).þFreezing/thawing.þHandbookþofþ meatþprocessing,þ105-124.&ots¼B2QSBaaI-O&sig¼9aHgBl9PAQzhtwbNgcl1_se66 TE&redir_esc¼y#v¼onepage&q&f¼false. Jessen, F., Nielsen, J., & Larsen, E. (2014). Chilling and freezing of fish. In I. Boziaris (Ed.), Seafood pocessing: Technology, quality and safety. John Wiley & Sons, Ltd. Jha, P. K., Xanthakis, E., Jury, V., & Le-Bail, A. (2017). An overview on magnetic field and electric field interactions with ice crystallisation; application in the case of frozen food. Crystals, 7(10), 299. https://www.mdpi.com/2073-4352/7/10/299/htm (May 25, 2023).

Freezing of meat, poultry, and seafoods

255

Jiang, Q., Nakazawa, N., Hu, Y., Osako, K., & Okazaki, E. (2019). Changes in quality properties and tissue histology of lightly salted tuna meat subjected to multiple freeze-thaw cycles. Food Chemistry, 293, 178e186. https://doi.org/10.1016/j.foodchem.2019.04.091 Jiang, Q., Zhang, M., Mujumdar, A. S., & Chen, B. (2023). Effects of electric and magnetic field on freezing characteristics of gel model food. Food Research International, 166, 112566. https://doi.org/10.1016/j.foodres.2023.112566 Karpinska-Tymoszczyk, M., & Draszanowska, A. (2019). The effect of natural and synthetic antioxidants and packaging type on the quality of cooked poultry products during frozen storage. Food Science and Technology International, 1e11. https://doi.org/10.1177/ 1082013219830196 Kim, H.-W., Kim, J.-H., Seo, J.-K., Setyabrata, D., & Kim, Y. H. B. (2018). Effects of aging/ freezing sequence and freezing rate on meat quality and oxidative stability of pork loins. Meat Science, 139, 162e170. https://doi.org/10.1016/j.meatsci.2018.01.024 Kim, H.-W., Miller, D. K., Yan, F., Wang, W., Cheng, H., & Kim, Y. H. B. (2017). Probiotic supplementation and fast freezing to improve quality attributes and oxidation stability of frozen chicken breast muscle. LWT, 75, 34e41. https://doi.org/10.1016/j.lwt.2016.08.035 Kluth, I.-K., Teuteberg, V., Ploetz, M., & Krischek, C. (2021). Effects of freezing temperatures and storage times on the quality and safety of raw Turkey meat and sausage products. Poultry Science, 100(9), 101305. https://doi.org/10.1016/j.psj.2021.101305 Lan, W., Hu, X., Sun, X., Zhang, X., & Xie, J. (2020). Effect of the number of freeze-thaw cycles number on the quality of Pacific white shrimp (Litopenaeus vannamei): An emphasis on moisture migration and microstructure by LF-NMR and SEM. Aquaculture and Fisheries, 5(4), 193e200. https://doi.org/10.1016/j.aaf.2019.05.007 Leygonie, C., Britz, T. J., & Hoffman, L. C. (2012). Impact of freezing and thawing on the quality of meat: Review. Meat Science, 91(2), 93e98. https://doi.org/10.1016/j.meatsci. 2012.01.013 Li, Bing, & Sun, Da Wen (2002). Novel methods for rapid freezing and thawing of foods e A review. Journal of Food Engineering, 54(3), 175e182. Li, D., Zhu, Z., & Sun, D.-W. (2018). Effects of freezing on cell structure of fresh cellular food materials: A review. Trends in Food Science & Technology, 75, 46e55. https://doi.org/ 10.1016/j.tifs.2018.02.019 Li, S., Zhang, Y., & Liu, S. (2022). Effect of refrigeration on the collagen and texture characteristics of yak meat. Canadian Journal of Animal Science, 102(1), 175e183. https:// doi.org/10.1139/cjas-2021-0059 Li, Z., Warner, R. D., & Ha, M. (2023). Rinse and chill®, frozen storage and retail packaging influence the quality of lamb loins. Meat Science, 195, 109000. https://doi.org/10.1016/j. meatsci.2022.109000 Liang, D., Lin, F., Yang, G., Yue, X., Zhang, Q., Zhang, Z., & Chen, H. (2015). Advantages of immersion freezing for quality preservation of litchi fruit during frozen storage. LWT e Food Science and Technology, 60(2, Part 1), 948e956. https://doi.org/10.1016/j.lwt. 2014.10.034 Liu, J., Wang, Y., Zhu, F., Yang, J., Ma, X., Lou, Y., & Li, Y. (2022). The effects of freezing under a high-voltage electrostatic field on ice crystals formation, physicochemical indices, and bacterial communities of shrimp (Solenocera melantho). Food Control, 142, 109238. https://doi.org/10.1016/j.foodcont.2022.109238 Lu, N., Ma, J., & Sun, D.-W. (2022). Enhancing physical and chemical quality attributes of frozen meat and meat products: Mechanisms, techniques and applications. Trends in Food Science & Technology, 124, 63e85. https://doi.org/10.1016/j.tifs.2022.04.004

256

Low-Temperature Processing of Food Products

Liu, S., Zeng, X., Zhang, Z., Long, G., Lyu, F., Cai, Y., Liu, J., & Ding, Y. (2020). Effects of immersion freezing on ice crystal formation and the protein properties of snakehead (Channa argus). Foods, 9(4), 411. https://doi.org/10.3390/foods9040411 Ma, X., Mei, J., & Xie, J. (2021). Effects of multi-frequency ultrasound on the freezing rates, quality properties and structural characteristics of cultured large yellow croaker (Larimichthys crocea). Ultrasonics Sonochemistry, 76, 105657. https://doi.org/10.1016/ j.ultsonch.2021.105657 Mahato, S., Zhu, Z., & Sun, D.-W. (2019). Glass transitions are affected by food compositions and conventional and novel freezing technologies: A review. Trends in Food Science & Technology, 94, 1e11. https://doi.org/10.1016/j.tifs.2019.09.010 Min, Sang Gi, Hong, Geun Pyo, Chun, Ji Yeon, & Park, Sung Hee (2016). Pressure ohmic thawing: A feasible approach for the rapid thawing of frozen meat and its effects on quality attributes. Food and Bioprocess Technology, 9(4), 564e575. https://link.springer.com/ article/10.1007/s11947-015-1652-3 (May 25, 2023). Mohammed, H. H. H., He, L., Nawaz, A., Jin, G., Huang, X., Ma, M., Abdegadir, W. S., Elgasim, E. A., & Khalifa, I. (2021). Effect of frozen and refrozen storage of beef and chicken meats on inoculated microorganisms and meat quality. Meat Science, 175, 108453. https://doi.org/10.1016/j.meatsci.2021.108453 Muthukumarappan, K., Marella, C., & Sunkesula, V. (2019). Chapter 15dFood freezing technology. In M. Kutz (Ed.), Handbook of farm, dairy and food machinery engineering (3rd ed., pp. 389e415). Academic Press. https://doi.org/10.1016/B978-0-12-8148037.00015-4 Otero, L., Pérez-Mateos, M., Rodríguez, A. C., & Sanz, P. D. (2017). Electromagnetic freezing: Effects of weak oscillating magnetic fields on crab sticks. Journal of Food Engineering, 200, 87e94. https://doi.org/10.1016/j.jfoodeng.2016.12.018 Oyinloye, T. M., & Yoon, W. B. (2020). Effect of freeze-drying on quality and grinding process of food produce: A review. Processes, 8(3), Article 3. https://doi.org/10.3390/pr8030354 Qian, P., Zhang, Y., Shen, Q., Liping, R., Renyoa, J., Xue, X., Hongzheng, Y., & Zhiyuan, D. (2018). Effect of cryogenic immersion freezing on quality changes of vacuum-packed bighead carp (Aristichthys nobilis) during frozen storage. Journal of Food Processing and Preservation. https://doi.org/10.1111/jfpp.13640 Rahimzade, E., Bahri, A. H., Moini, S., & Nokhbe Zare, D. (2019). Influence of vacuum packaging and frozen storage time on fatty acids, amino acids and u-3/u-6 ratio of rainbow trout (Oncorhynchus mykiss). Iranian Journal of Fisheries Sciences. https://doi.org/ 10.22092/ijfs.2019.118283 Rinwi, T. G., Sun, D.-W., Ma, J., & Wang, Q.-J. (2023). Effects of isochoric freezing on freezing process and quality attributes of chicken breast meat. Food Chemistry, 405, Article 134732. https://doi.org/10.1016/j.foodchem.2022.134732 Rovira, P., Brugnini, G., Rodriguez, J., Cabrera, M. C., Saadoun, A., De Souza, G., Luzardo, S., & Rufo, C. (2023). Microbiological changes during long-storage of beef meat under different temperature and vacuum-packaging conditions. Foods, 12(4), 694. https://doi.org/ 10.3390/foods12040694 Saravacos, G., Kostaropoulos, A. E., Saravacos, G., & Kostaropoulos, A. E. (2016). Refrigeration and freezing equipment. SpringerLink. https://link.springer.com/chapter/10.1007/ 978-3-319-25020-5_9. Sauvala, M., Johansson, P., Björkroth, J., & Fredriksson-Ahomaa, M. (2023). Microbiological quality and safety of vacuum-packaged white-tailed deer meat stored at 4 C. International Journal of Food Microbiology, 390, 110110. https://doi.org/10.1016/j.ijfoodmicro.2023. 110110

Freezing of meat, poultry, and seafoods

257

Setyabrata, D., & Kim, Y. H. B. (2019). Impacts of aging/freezing sequence on microstructure, protein degradation and physico-chemical properties of beef muscles. Meat Science, 151, 64e74. https://doi.org/10.1016/j.meatsci.2019.01.007 € Dalmis¸, U., € & Bilgin, V. (2010). Effects of freezing temperature and Soyer, A., Berna, O., duration of frozen storage on lipid and protein oxidation in chicken meat. Food Chemistry, 120(4), 1025e1030. Sun, Q., Sun, F., Xia, X., Xu, H., & Kong, B. (2019). The comparison of ultrasound-assisted immersion freezing, air freezing and immersion freezing on the muscle quality and physicochemical properties of common carp (Cyprinus carpio) during freezing storage. Ultrasonics Sonochemistry, 51, 281e291. https://doi.org/10.1016/j.ultsonch.2018.10.006 Sun, Q., Zhang, H., Yang, X., Hou, Q., Zhang, Y., Su, J., Liu, X., Wei, Q., Dong, X., Ji, H., & Liu, S. (2023). Insight into muscle quality of white shrimp (Litopenaeus vannamei) frozen with static magnetic-assisted freezing at different intensities. Food Chemistry X, 17, 100518. https://doi.org/10.1016/j.fochx.2022.100518 Tian, Y., Li, D., Luo, W., Zhu, Z., Li, W., Qian, Z., Li, G., & Sun, D.-W. (2020). Rapid freezing using atomized liquid nitrogen spray followed by frozen storage below glass transition temperature for Cordyceps sinensis preservation: Quality attributes and storage stability. LWT, 123, 109066. https://doi.org/10.1016/j.lwt.2020.109066 Truonghuynh, H. T., Li, B., Zhu, H., Guo, Q., & Li, S. (2020). SciELO e BrazildFreezing methods affect the characteristics of large yellow croaker (Pseudosciaena crocea): Use of cryogenic freezing for long-term storage freezing methods affect the characteristics of large yellow croaker (Pseudosciaena crocea): Use of cryogenic freezing for long-term storage. https://www.scielo.br/j/cta/a/FCNMHBm9SNfNPctSJZ3TThF/?format¼html&lang¼en. Velez-Ruiz, J. F., & Rahman, M. S. (2020). Freezing methods of foods e45. In Handbook of food preservation. Vol 3. https://www.taylorfrancis.com/chapters/edit/10.1201/978042909148345/freezing-methods-foods-jorge-fernando-velez-ruiz-mohammad-shafiur-rahman. Wang, F., Liang, R., Zhang, Y., Gao, S., Zhu, L., Niu, L., Luo, X., Mao, Y., & Hopkins, D. L. (2021). Effects of packaging methods combined with frozen temperature on the color of frozen beef rolls. Meat Science, 171, 108292. https://doi.org/10.1016/j.meatsci. 2020.108292 Wang, Y.-C., Mohan, C. O., Guan, J., Ravishankar, C. N., & Gunasekaran, S. (2018). Chitosan and gold nanoparticles-based thermal history indicators and frozen indicators for perishable and temperature-sensitive products. Food Control, 85, 186e193. https://doi.org/10.1016/ j.foodcont.2017.09.031 Wang, Y., Liang, H., Xu, R., Lu, B., Song, X., & Liu, B. (2020). Effects of temperature fluctuations on the meat quality and muscle microstructure of frozen beef. International Journal of Refrigeration, 116, 1e8. https://doi.org/10.1016/j.ijrefrig.2019.12.025 Wei, R., Wang, P., Han, M., Chen, T., Xu, X., & Zhou, G. (2017). Effect of freezing on electrical properties and quality of thawed chicken breast meat. Asian-Australasian Journal of Animal Sciences, 30(4), 569e575. https://doi.org/10.5713/ajas.16.0435 Yang, F., Jing, D., Diao, Y., Yu, D., Gao, P., Xia, W., Jiang, Q., Xu, Y., Yu, P., & Zhan, X. (2020). Effect of immersion freezing with edible solution on freezing efficiency and physical properties of obscure pufferfish (Takifugu Obscurus) fillets. LWT, 118, 108762. https://doi.org/10.1016/j.lwt.2019.108762 Yuduan, D., Gao, P., Jiang, Q., Xia, W., & Yang, F. (2022). Effect of immersion freezing with the edible medium on protein structure, chemical bonding and particle size in grass carp (Ctenopharyngodon idellus) during frozen storage. International Journal of Food Science & TechnologydWiley Online Library. https://ifst.onlinelibrary.wiley.com/doi/full/10. 1111/ijfs.15957.

258

Low-Temperature Processing of Food Products

Zequan, X., Zirong, W., Jiankun, L., Xin, M., Hopkins, D. L., Holman, B. W. B., & Bekhit, A. E.-D. A. (2019). The effect of freezing time on the quality of normal and pale, soft and exudative (PSE)-like pork. Meat Science, 152, 1e7. https://doi.org/10.1016/ j.meatsci.2019.02.003 Zhan, X., Sun, D.-W., Zhu, Z., & Wang, Q.-J. (2018). Improving the quality and safety of frozen muscle foods by emerging freezing technologies: A review. Critical Reviews in Food Science and Nutrition, 58(17), 2925e2938. https://doi.org/10.1080/10408398.2017. 1345854 Zhang, L., Zhang, M., & Mujumdar, A. S. (2023). Technological innovations or advancement in detecting frozen and thawed meat quality: A review. Critical Reviews in Food Science and Nutrition, 63(11), 1483e1499. https://doi.org/10.1080/10408398.2021.1964434 Zhang, M., Jin, Z., Guo, R., & Liu, D. (2023). The two-stage air thawing based on low voltage electric field (LVEF) can make the quality of thawed chicken breast close to that before freezing. LWT, 173, 114344. https://doi.org/10.1016/j.lwt.2022.114344 Zhang, M., Xia, X., Liu, Q., Chen, Q., & Kong, B. (2019). Changes in microstructure, quality and water distribution of porcine longissimus muscles subjected to ultrasound-assisted immersion freezing during frozen storage. Meat Science, 151, 24e32. https://doi.org/ 10.1016/j.meatsci.2019.01.002 Zhao, Y., Ji, W., Chen, L., Guo, J., & Wang, J. (2019). Effect of cryogenic freezing combined with precooling on freezing rates and the quality of golden pomfret. Journal of Food Process Engineering, 42(8), e13296. Zhu, S., le Bail, A., Ramaswamy, H. S., & Chapleau, N. (2006). Characterization of ice crystals in pork muscle formed by pressure-shift freezing as compared with classical freezing methods. Journal of Food SciencedWiley Online Library. https://ift.onlinelibrary.wiley. com/doi/abs/10.1111/j.1365-2621.2004.tb06346.x. Zou, L., Xie, A., Zhu, Y., & McClements, D. J. (2019). Cereal proteins in nanotechnology: Formulation of encapsulation and delivery systems. Current Opinion in Food Science, 25, 28e34.

Freezing of baked goods and prepared foods

11

Perla G. Armenta-Aispuro 1,2 , Ofelia Rouzaud-Sa
ndez 1 ,
pez-Franco 2 , Jaime Lizardi-Mendoza 2 , José L. C
ardenas-Lo
pez 1 and Yolanda L. Lo 3,4 Cristina M. Rosell 1 Departamento de Investigaci
on y Posgrado en Alimentos, Universidad de Sonora, Hermosillo, Sonora, México; 2Grupo de Investigaci
on en Biopolímeros, Centro de Investigaci
on en Alimentaci
on y Desarrollo, Hermosillo, Sonora, México; 3Food and Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada; 4Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC), Valencia, Espa~na

11.1

Introduction

Frozen baked goods and prepared foods are a constantly growing segment of the food industry, driven by consumers that demand innovative, healthy, and convenient food products. The global market for frozen baked goods and prepared food products is projected to grow at a CAGR of 8% and 4.3%, respectively, from 2021 to 2026 (Markets & Markets, 2020; Mordor Intelligence, 2021). Studies on the acceptance of frozen and prepackaged prepared foods have been started since the 1960s. The manager of Hotel du Pont (Wilmington, Delaware, USA) published a report in 1962 to illustrate the problems as well as the advantages of frozen prepared foods in a hotel or restaurant (Weber, 1962). Nowadays, consumers are looking for a wide range of goods, ethnic or health-promoting, which are nonallergenic and fresh and possess good organoleptic properties. Freezing is widely used to produce “ready-to-bake” or “ready-to-eat” foods such as bread, cakes, pastries, morning goods, pizza crust, and other bakery goods. Currently, on the market, there is a wide variety of bread products that are classified according to the type of ingredients incorporated (whole flour, other sources of flour, omega-3 fatty acids, protein isolates, and others), type of leavening (chemical or biological), and the cooking process (baked, steamed, fried, and other emerging heating technologies). Most of them are frozen at the point of sale. A possible classification of frozen baked goods based on the frequency of consumption is presented in Fig. 11.1. Due to their increased consumption, fiber-enriched and fortified multigrain bakery products are in the “basic consumption” group (Weegels, 2019). The discretionary consumption group includes products whose consumption is not essential, such as some special bread or pastries, ethnic products, and bread for special needs like gluten-free products. Market research, in its global forecast until 2026, mentions that the world market for the frozen bakery in 2021 was 22,287.2 million dollars and is forecast to be 29,490.9 million dollars in 2026, growing at an annual compound rate of 5.8% during

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00003-5 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

260

Low-Temperature Processing of Food Products

Figure 11.1 Classification by frequency of consumption of frozen bakery goods, in any of the presentations: “ready-to-bake” or “ready-to-eat”. Information collected from: Frozen Bakery Report (2019); Markets and Markets (2021); Market Research Future (2020).

the forecast period. The exponential growth of this market can be attributed to an increase in the number of convenient retail channels and online retail, disposable income, health awareness, the busy lifestyle of consumers, and the growing need to have products available in the shortest possible time (Markets & Markets, 2020). Freezing is one of the main unitary operations in food preservation, as it prolongs the shelf life of the food product, prevents the growth of microorganisms responsible for its decomposition, and slows the chemical and physical reactions during storage time. In addition, the loss of nutrients is minimal. In addition, the loss of nutrients is minimal. Freezing slows down biological and chemical processes at low temperatures via the restriction of molecular mobility (Berk, 2013; Muthukumarappan et al., 2019, pp. 389e415). The technology of freezing bakery products is not a recent one; in fact, there are records dating back to 1950 (Omedi et al., 2019). Despite the improvements made to the process over the years (modifications to the freezing process, addition of additives to the formulation), the frozen bakery industry still presents serious technological challenges to address. The main challenges are in the quality of frozen products that have been baked, such as premature hardening, low volume on bread loaves, and crust flaking (Giannou et al., 2003). Such problems and possible solutions have been discussed in great detail in the literature. For this reason, progress in understanding the interactions between water and ingredient components and their relationship to bread dough structure, texture, and stability during freezing and frozen storage is notable. Freezing technology allows ready-to-eat meals and ready-to-bake frozen goods to be available at any time of the day in their original form, which can be stored for long periods without the skill required to deliver a finished product of uniform quality to the end customer. The main representatives of freezing technology in prepared foods are frozen baked

Freezing of baked goods and prepared foods

261

goods, namely ready-to-bake, ready-to-proof, and ready-to-eat. Information on the two or three most common products in each category of frozen baked goods will be included in this chapter. The steps of the freezing process will be described, and new additives and upcoming technologies will also be covered.

11.2

Frozen bakery goods

Frozen baked goods have been incorporated into daily diet of many people around the world, as with the increase of an accelerated lifestyle, having products available “ready-to-bake or ready-to-serve” simplifies and saves time when cooking. Frozen baked goods are advantageous not only for consumers but also for the food industry since their manufacturing and distribution processes are centralized, in addition to standardization in the quality of the products they offer. Likewise, for the restaurant, hotel, and catering sectors, the use of frozen baked goods reduces operating costs by not needing specialized personnel, reduces losses, and allows consumers to offer products with constant quality (Akbarian et al., 2015).

11.2.1 Classification Prefermented, unfermented, and par-baked frozen dough products are often cited as categories in many publications. It is easy to distinguish that one of the differences is the process step at which the freezing stage is introduced: before fermentation, after prefermentation, and after prebaking (Omedi et al., 2019). In this chapter, we mention three categories of frozen bakery goods present at the point of sale: “ready-to-proof” “ready-to-bake” and “ready-to-eat” (Fig. 11.2).

11.2.1.1 Ready-to-proof products To prevent the development of yeast, the dough pieces are quickly frozen after being molded. They are thawed at cooling temperatures of around 4e5
C. Then, the

Figure 11.2 Classification of frozen bakery goods at the point of sale.

262

Low-Temperature Processing of Food Products

fermentation process begins and the fermented pieces are baked. The most traditional product is dough for bread loaves and sweet rolls. Due to decreased yeast fermentation activity and decreased gas retention, this product typically exhibits volume-related problems (Omedi et al., 2019).

11.2.1.2 Ready-to-bake products Following molding and fermentation, the dough pieces are often immediately frozen before being stored. They do not need to be thawed before baking; thus, the baking procedure takes less time. Making fresh baked goods is possible with the ready-tobake. Two groups make up this category, including (Omedi et al., 2019). (1) Dough that has been fermented and frozen. Dough is produced for conventional direct bread making; the dough pieces are fermented until before their full development and then frozen. Generally, freezing quickly is advised. It is successfully used in puff pastry dough or in “layers” for crunchy products such as Danish bread. These products may be thawed and baked in the oven all at once (Le-Bail et al., 2010). (2) Partially baked bread. The pieces of dough are made with the conventional process and baked twice (Almeida et al., 2016). In the initial stage of baking, which is often a bit shorter than what is needed for the complete cooking, the structure of the crumb is formed without the crust being crispy or developing color, that is, before the Maillard reaction occurs (Rosell & Gomez, 2007). Subsequently, the prebaked piece of bread is cooled and frozen. At the point of consumption, the second bake is complete; water from the top layers evaporates, the crust forms, and the Maillard reaction takes place (Rosell, 2015). Partially baked technology is mainly used in baguette loaves, pizza crusts, pizza, and cakes (Karao glu, 2015). According to Hamdami et al. (2007), the main objectives of the partially baked bread freezing process are to minimize weight loss and ice accumulation under the crust while minimizing the freezing duration.

11.2.1.3 Ready-to-eat products This classification includes all bakery and pastry goods that have been baked in their entirety and then frozen to just thaw and consume. They include cake (Díaz-Ramirez et al., 2016; Byun & Koh, 2017), donuts, pizza (Karao glu, 2015), pasta (Olivera & Salvadori, 2011), bagel (Lasekan et al., 2021), waffles (Tiefenbacher, 2017), as well as some special gluten-free bread (Ronda & Roos, 2011).

11.2.2

Effect of freezing on the quality of frozen bakery goods

Studies on the impact of freezing treatment, before or after fermentation, or baking, have been focused mainly on quality attributes and shelf life of traditional bread (like loaf, pan bread, and baguette types). However, given less attention is placed on the characteristics of other bread types, such as flatbread, muffins, pita bread, pizza, buns, pretzels, and products other than bread (puff pastry, biscuits, cakes, wafers, donuts, and so on). Table 11.1 summarizes frequent quality attribute defects associated with the type of frozen bakery goods. In general, the characteristics of frozen bakery goods are determined mainly by the stage of the bread production process in which the freezing

Freezing of baked goods and prepared foods

263

Table 11.1 Common defects in quality attributes of frozen bakery goods.

Type

Product

Common defects in product quality

References

Ready-to-bake - Frozen fermented dough

- Partially baked bread

- Puff pastry

- Loss of volume

- Croissants

- Loss of cell viability

- Danish bread - Bread

- Baguette - Pizza crust

- Fast hardening

Le-Bail et al. (2010)

Almeida et al. (2016)

- Loss of aroma - Loss of volume - Separation of the crust from the crumb - Crust peeling

Ready-toproof

- Bread - Sweet rolls

- Cakes - Donuts - Pays

- Loss of volume - Loss of cell viability - Loss of the integrity of the gluten network - Fast hardening - Loss of elasticity and firmness

Omedi et al. (2019)

Asghar et al. (2007); Olivera and Salvadori (2011); Ronda and Ross (2011)

- Pizza - Pasta - Gluten free bread - Tortillas

technology is applied but also by other factors such as ingredients or additives in the formulation (Omedi et al., 2019).

11.2.2.1 Ready-to-proof Nonfermented dough freezing is a common practice in the frozen bakery industry. It is mainly used to produce products such as bread loaves and sweet bread (Phimolsiripol

264

Low-Temperature Processing of Food Products

et al., 2008). Studies on the rheological changes that occur in the frozen unfermented dough, the rate of freezing and thawing, the length of time and temperature of frozen storage, and temperature swings date back to the 2000s. Angioloni et al. (2008) examined the impact of sub-zero storage time on the viscoelastic performance of the nonfermented dough and reported significant changes in hardness, elasticity, adhesiveness, and viscoelasticity during the first 15 days of frozen storage. These authors hypothesized that the mechanical activity of ice crystals disrupts the gluten network causing favorable viscoelastic characteristics to decrease. Recent research has focused on the impact of freezing rate and storage time on this type of dough since traditional Chinese bread is made using nonfermented dough. The quality of frozen, nonfermented dough often lags behind that of fresh dough and becomes even more distinct with extended freezing storage. According to Yang, Zhang, et al. (2021), the texture and stability of the unfermented dough were most adversely affected by a slower freezing rate paired with extended storage. The quality of dough degrades after freezing and frozen storage, depending on the amount of gluten, glutenin, and gliadin it naturally contains. Smaller volume, a less even and heterogeneous crumb, and premature hardening are all potential flaws in bread made from nonfermented frozen dough, in addition to bark flaking (Selomulyo & Zhou, 2007). These phenomena are primarily caused by the dough’s exposure to low temperatures during freezing and storage.

11.2.2.2 Ready-to-bake In general, ready-to-bake good are classified as follows. (1) Frozen fermented dough. The most frequently mentioned deficiencies are poor strength, time-consuming process, restricted volume of loaf, coarse/irregular crumb, and darkness of crust. For example, the bottom crust of rolls from frozen dough usually has a dark grain. The side crust of a pan loaf from dough retarding often has dark streaks where the crust had contact with the pan during freezing. In particular, the crust at the edges of the loaf is darker. The darker crust color of crusty rolls is often accompanied by blisters on the top crust (Sluimer, 2005).

There are many factors affecting such defects. Some are related to the dough formulation and processing conditions before freezing, while others are a direct consequence of the freezing conditions, thawing, or proving conditions. Fermented frozen dough is a challenge for the frozen food industry due to its fragile structure. During freezing, the internal pressure of the gas cells is reduced, which leads to the reduction in the volume of the dough and the rupture of the gas cells by the formation of ice crystals (Fig. 11.3a) (Le-Bail et al., 2010). A few studies have concentrated on maintaining the yeast gas productivity and the gluten networks’ ability to retain gas protecting both the viability of the yeast and the gluten networks from freezing damage (Ban et al., 2016). According to a study by Ban et al. (2016), the size of the ice crystals in frozen croissant dough is determined by the freezing rate. Since yeast viability is influenced by ice crystal size, the freezing rate influences croissant quality characteristics, including specific volume and stiffness. They also demonstrated that maintaining a consistent freezing rate, and final

Freezing of baked goods and prepared foods

265

Figure 11.3 Effect of freezing on (a) rupture of gas cells in fermented dough, as explained by Le-Bail et al. (2010), and on (b) development of the flaking crust of frozen prebaked bread, based on the hypothesis of Le-Bail and Goff (2008).

temperature ensures the quality of croissants made from frozen dough. Additionally, the temperature of the dough must be kept above the point at which yeast cytoplasmic water crystallizes. The irresistibly soft, fluffy texture of a warm, freshly baked, sweet croissant keeps demand for this culinary item at an all-time high. The croissant made from frozen dough, however, rapidly goes stale. The main problem is retrogradation, which shortens the already limited shelf life caused by physiochemical reactions and results in humidity loss that alters the texture and turns sweet bread stale (Luo et al., 2018). Some studies recommend using hydrocolloids and cryoprotectants, which are discussed later in this chapter, to solve these issues. Le-Bail et al. (2010) looked at how prefermentation prior to freezing affected baguette dough and discovered that a low prefermentation level paired with a high freezing rate minimizes the loss of bread volume brought on by processing conditions (freezing rate and temperature). The entire process must be carefully examined to determine the reasons for quality losses (Cauvain, 2015). (2) Partially baked. An effective approach to stopping baked foods from aging is the technology of partially cooked bread and its frozen storage (B
arcenas et al., 2003). However, the separation of the crust from the crumb and the formation of a white tint similar to snow immediately below the crust are the primary issues with partly cooked bread (Cauvain, 2015). According to Le-Bail et al. (2005), the proving and chilling conditions following partial baking are the two process variables that have the greatest influence on how easily French baguettes’ crusts flake. To reduce crust flaking, these stages of the process should be completed in extremely humid air. They advised a precooling step since the product’s core temperature should not be too high when freezing first begins.

In the other study, Le-Bail and Goff (2008) proposed two hypotheses to explain crust flaking. The first is influenced by the fact that while freezing, the bread’s middle remains warm for a time as the freezing front moves away from the bread’s surface (Fig. 11.3b). Due to the significant vapor pressure differential caused by this circumstance, moisture diffuses from the warmer areas, resulting in a concentration of ice under the crust. The fact that bread compresses during chilling and freezing, creating thermomechanical tension between the crust and the crumb, supported the second hypothesis.

266

Low-Temperature Processing of Food Products

Another common problem of baked bakery goods that have been precooked is their premature aging, which is reflected in a hard and dry bread. According to B
arcenas and Rosell (2006), this phenomenon is connected to a decline in the ability of bread components to retain water as storage days pass at low temperatures, as well as an increase in the hardness of the partially frozen and stored bread’s crumb. According to some authors’ theories (Schiraldi & Fessas, 2001), water works as a plasticizer, and a drop in moisture content encourages the creation of hydrogen bonds between starch polymers or between starch and proteins, which results in increased hardness. Cakes may be produced effectively using the freezing par-baked process. Cakes are bakery goods that are both chemically and mechanically leavened. High-quality cakes feature a variety of characteristics, including a homogeneous crumb structure, a low cake crumb stiffness, and a high volume. These characteristics are dependent on the balanced formulae, the aeration of cake batters, the fluid batters’ stability during the first stages of baking, and the thermal-setting stage. According to Karaoglu (2015), cakes with greater specific volumes typically have lower firmness. Karaoglu et al. (2008) looked into the quality characteristics of frozen storage and the initial baking time of cupcakes acquired after thawing and rebaking. Those authors observed that the best specific volume and textural properties are obtained with 20 min initial baking and 3 months storage at 18
C. In a subsequent study, Karaoglu (2015) explains the effects of very short and very long initial baking time with respect to the firmness of the cake crumb. Moisture content is the most important factor affecting the crumb softness of cakes. Therefore, further research is recommended to increase the moisture-holding capacity of the cake produced by the two-step baking process, for example, by adding moisture-retaining additives, such as polysaccharides or gums. Freezing partially baked bread is most successful with products that have a large surface area in relation to the area of the crumb, such as pizza crust, tortilla, and pita bread, where the transfer of heat can be quick. The major disadvantage of frozen par-baked products is the high storage cost of the large product volume, while the main advantage is that they have a long shelf life. For example, frozen precooked bread can be stored in a freezer for up to 12 months without microbial spoilage (Karaoglu, 2015).

11.2.2.3 Ready-to-eat The cake (like sponge cakes or Garaetteok, a classic Korean rice cake) (Díaz-Ramírez et al., 2016; Byun & Koh, 2017) is an important ready-to-eat frozen baked product for the food industry, although there is not much research on it in the most recent scientific literature. Byun and Koh (2017) investigated how the addition of agar and casein affected the texture of frozen and thawed Garaetteoks. Regardless of the length of frozen storage, they discovered that casein is a useful ingredient with just a little impact on the textural qualities of cooked Garaetteok. One of the problems observed in frozen stored sponge cake is crumb fracture, which could be caused by decreased humidity, increased starch crystallinity and sugar recrystallization (Díaz-Ramírez et al., 2016). Cakes are often frozen at around 1 dt


Ao

1
n

(12.3)

¼
ð1
nÞkt

There are two alternative methods, the graphical or a least square linear fit (a trialand-error process), to mathematically estimate the apparent reaction order n. The procedure is detailed in Labuza (1984) and Taoukis et al. (1997). In the case of frozen foods, most of the reactions which are kinetically studied have been shown to be adequately described by a pseudo-zero or pseudo-first order reaction, obeying at the mathematical equations shown in Table 12.2.

12.3.2 Secondary models Secondary models are appropriate equations, used to mathematically depict the effect of external factors, (e.g., temperature, water activity, gas composition, pH, etc) on k, which is the main kinetic parameter of the primary model (Eq. 12.2). Among other factors, the crucial impact of temperature has been systematically studied for frozen foods quality degradation, since not only the average temperatures but also the detrimental fluctuations during distribution have been found to significantly affect product’s shelf life. The most common equations used as secondary models are briefly presented, with an overview being shown in Table 12.3.

12.3.2.1 Arrhenius law The most widely applied secondary equation is based on the Arrhenius equation, derived from thermodynamics as well as statistical laws (Arrhenius, 1889). The Arrhenius equation was initially proposed for reversible molecular chemical reactions, before being widely applied to describe the effect of temperature on the rate of most reactions that lead to quality deterioration of frozen foods (Eq. 12.4):  
EA k ¼ kA exp RT

(12.4)

Zero-order (n ¼ 0)

Example of index measured

Relevant frozen food matrix

References

A ¼ Ao
kt

Color change

Broccoli (hue angle change)

Gonçalves, Abreu, et al. (2011) Giannakourou and Taoukis (2003a, 2003b) Dermesonlouoglou et al. (2007a, 2007b) Gonçalves, Abreu, et al. (2011) Dermesonluoglu et al. (2015) Dermesonlouoglou et al. (2018) Xu et al. (2016) Xu et al. (2016) S
anchez-Valencia et al. (2014) Tsironi et al. (2009)

Green peas (DCa change) Watermelon (DCa change) Drip loss

Broccoli

Overall sensory assessment

Spinach Kiwi

TVB-N Salt Extractable Protein (SEP) Kramer shear resistance Color (b-value), sensory score of color Sensory acceptability (overall)

Shrimp Shrimp Hake fillets Shrimps

Color change (L-value) Sensory scoring (taste and overall acceptability) Relaxation times of hake muscle TBARs

Shrimps Blue shark Gilthead seabream, seabass, yellowfin tuna Gilthead seabream, seabass, yellowfin tuna Hake Blue shark

Tsironi et al. (2009) Giannoglou et al. (2014) Tsironi et al. (2020) Tsironi et al. (2020) S
anchez-Valencia et al. (2015) Giannoglou et al. (2014)

Low-Temperature Processing of Food Products

Mathematical equation

298

Table 12.2 Most frequently applied primary models and representative examples of plant and animal tissue (frozen foods).

A ¼ Ao e
kt

Vitamin C degradation

Spinach Green beans Green beans Broccoli Green peas Watercress Strawberry Kiwi

Color change

Broccoli Mushroom

Chlorophyll degradation Lycopene Sensory assessment TVB-N

Shrimp Shrimps Gilthead seabream, seabass, yellowfin tuna Blue shark Shrimps Scallop meat

Giannoglou et al. (2014) Tsironi et al. (2009) Chung and Merritt (1991) Continued

299

TMA-N (trimethylamine-nitrogen) Texture, cook drip and free fatty acid

Green beans Spinach Watermelon

Dermesonluoglu et al. (2015) Martins and Silva (2004) Giannakourou and Taoukis (2003b) Gonçalves, Abreu, et al. (2011) Giannakourou and Taoukis (2003b) Gonçalves et al. (2009) Dermesonlouoglou et al. (2016) Dermesonlouoglou et al. (2018) Gonçalves, Abreu, et al. (2011) Giannakourou and Taoukis (2002) Martins and Silva (2004) Dermesonluoglu et al. (2015) Dermesonlouoglou et al. (2007a, 2007b) Xu et al. (2016) Tsironi et al. (2009) Tsironi et al. (2020)

Quality kinetics and shelf life prediction and management in the frozen foods chain

First order (n ¼ 1)

300

Table 12.2 Continued Mathematical equation Fractional model

 ln

A0
AN At
AN



¼ kt

Example of index measured

Relevant frozen food matrix

References

Vitamin C degradation

Pumpkin

Color change

Green beans (total color difference) Pumpkin (total color difference) Strawberry (DCa change)

Gonçalves, Pinheiro, et al. (2011) Martins and Silva (2004)

Kiwi (total color difference)

  C C0

¼ ekt

n

n is r termed as “form factor.” (Corradini & Peleg, 2004, 2006)

Where DC ¼

a

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2ffi a
ao  þ b
bo  , based on L*, a*, b* measurements (LAB scale).

Green beans Pumpkin Hake fillets Rose Hip Pulp Rose Hip Pulp Rose Hip Pulp Beef burgers Beef burgers Beef burgers Atlantic salmon Atlantic salmon Atlantic salmon Phosphate-Buffered Saline

Low-Temperature Processing of Food Products

Weibull model

Starch hydrolysis Texture change (firmness and energy) Water Holding Capacity Vitamin C Total phenols degradation Antioxidant capacity TBA Peroxide value (PV) Redness (a*) TVB-N Soluble protein Texture Profile Analysis (TPA) Inactivation of V. vulnificus

Gonçalves, Pinheiro, et al. (2011) Dermesonlouoglou et al. (2016) Dermesonlouoglou et al. (2018) Martins et al. (2005) Gonçalves, Pinheiro, et al. (2011) Sanchez-Valencia et al. (2014) Quevedo et al. (2020) Quevedo et al. (2020) Quevedo et al. (2020) Quevedo et al. (2018) Quevedo et al. (2018) Quevedo et al. (2018) Aguilera Barraza et al. (2015) Aguilera Barraza et al. (2015) Aguilera Barraza et al. (2015) Seminario et al. (2011)

Quality kinetics and shelf life prediction and management in the frozen foods chain

301

Table 12.3 Most frequently applied secondary models and representative examples (frozen foods).

Mathematical equation Arrhenius (Arrhenius, 1889) equation  


Ea 1 1 k ¼ kref R T
Tref kref stands for the rate constant at Tref (in K), R: the universal gas constant and Ea: the activation energy (in J/mol or cal/mol) Exponential model (Peleg et al., 2012, 2017)
 
 kðTÞ ¼ k Tref exp c $ T
Tref T and Tref are in  C and c is a constant having  C
1 units Ea cw 2 or RðTref þ 273:16Þ
2 Ea w cR Tref þ 273:16 WLF model

C1 $ ðT
Tref Þ 2 þ ðT
Tref Þ

log kkref ¼ C

kref: rate constant at the reference temperature Tref (Tref > Tg) C1, C2 are system dependent coefficients (Williams et al., 1955)

Q10 model

 

ln Q10 $T kðTÞ ¼ ko exp 10 Q10: ratio of the respective rate constants k at temperatures that differ by 10 C, where T and Tref in  C

Example of corresponding reaction studied

References

See information of Table 12.2. In all cases reported, the Arrhenius law was applied as the secondary model to show the temperature effect (where such analysis was presented).

Ascorbic acid oxidation in commercial starch hydrolyzate Polyphenoloxidase activity in sucrose, glycerol and fructose solutions and (POD) activity in fructose and glycerol solutions De-esterification of Pectin, catalyzed by PME, in model systems Hydrolysis of di-sodium-pnitrophenyl phosphate, catalyzed by alkaline phosphatase (model systems) Ascorbic acid loss in frozen green peas

Biliaderis et al. (1999) Manzocco et al. (1998) Terefe and Hendrickx (2002) Terefe et al. (2014) Giannakourou and Taoukis (2003a, 2003b)

Taoukis et al. (1997)

302

Low-Temperature Processing of Food Products

with kA being the constant of the Arrhenius equation, EA (in Joules or calories per mole) the activation energy, that is, the excess energy barrier that the particular factor A must overcome to derive degradation products, and R, the universal gas constant. However, in most cases, a reference temperature, Tref, is included in Eq. (12.4), that corresponds to a frequently used value in the range of the actual storage or processing conditions under investigation. Eq. (12.4) can then be mathematically transformed to the following formula (Eq. 12.5): k ¼ kref




EA 1 1
exp T Tref R

(12.5)

with kref being the rate constant at Tref, (frequently set at 255 K for frozen foods). The above transformed Arrhenius relation allows for better performance during parameter calculation, providing also a practical and comprehensive physical meaning to the constant. When studying the quality degradation of frozen foods, there are numerous studies that use the Arrhenius as the secondary model (Table 12.3, in combination with the quality loss parameters reported in Table 12.2). Most of reactions reported in Table 12.2, described mathematically with either apparent zero or first, or even a fractional primary model, are shown to obey to the Arrhenius law, as far as their temperature dependence is concerned. A detailed list of published activation energies for frozen foods (based on the Arrhenius equation) is also available in Giannakourou and Taoukis (2019) and Lai and Heldman (1982). Nonetheless, despite the wide application of the Arrhenius law, deviations have been reported (Labuza & Riboh, 1982; Taoukis et al., 1997), with many factors being responsible, such as possible phase changes. In frozen foods, noncrystalline, freeze-concentrated structures are usually formed, exhibiting crystallization and recrystallization phenomena, as well as significant change of the molecular mobility (Roos, 2021). In this context, the effect of such a change is very pronounced in the stability of frozen tissues, in the immediate subfreezing temperature zone. The Arrhenius plot is then expected to show a discontinuity, with an abrupt slope change in this range. Another phenomenon affecting the uniform use of the Arrhenius equation is related to glass transition, a reversible shift between solid-like and liquid-like forms of an amorphous matrix. Since frozen foods include ice crystals dispersed in an amorphous, unfrozen medium, they are subjected to such a transition, and a slope change in the Arrhenius plot at or in the proximity of the glass transition temperature of the system may be observed (Giannakourou & Taoukis, 2003a, 2003b). However, there are cases where that behavior was not exhibited and a linear trend was rather shown for the Arrhenius plot in all the relevant temperature zone studied (Lim & Reid, 1991, p. 103). One may conclude that a kinetic study including a broader temperature range is required to verify this behavior that does not conform with the Arrhenius linearity.

Quality kinetics and shelf life prediction and management in the frozen foods chain

303

Alternatively, Peleg et al., (2012) have proposed the use of a different form of Arrhenius equation (exponential model), namely:
 
 kðTÞ ¼ k Tref exp c $ T
Tref

(12.6)

with T and Tref being in  C and c a constant (in  C
1 units), as follows:
2 Ea cw
2 or Ea w cR Tref þ 273:16 R Tref þ 273:16 The main scope, as demonstrated by the authors, is to reliably describe temperature dependency of a chemical reaction without assuming that the activation energy in question is temperature-independent, as frequently implied in the traditional Arrhenius law.

12.3.2.2 WLF equation As previously described, glass transition is related to severe modifications of molecular mobility, and thus food mechanical properties are dramatically changed. This is frequently observed in carbohydrate-rich foods, when conditions are abruptly altered, for example, during rapid cooling or dehydration. In literature, there are numerous examples of glass transition phenomena leading to a kinetic pattern that do not conform to the Arrhenius law, such as frozen carbohydrate-containing model systems/foods (Biliaderis et al., 1999; Blond & Simatos, 1991; Carrington et al., 1996; Champion et al., 2000), osmotically dehydrated frozen fruits and vegetables (Chiralt et al., 2001; Torregianni et al., 1999), etc. In matrices that undergo a glass transition, a dramatic rate increase of the diffusioncontrolled reactions occurs at temperatures above Tg, and an overall Arrhenius equation cannot adequately describe the temperature effect. This behavior was shown to be adequately described by the so-called WLF equation (Williams-Landel-Ferry) (Eq. 12.7) that depicts the effect of temperature on dielectric and mechanical phenomena in the zone of Tg < T < Tg þ 100:
 C1 T
Tref kref 
log ¼ k C2 þ T
Tref

(12.7)

with kref being the rate constant at Tref (Tref > Tg) and C1, C2 the coefficients that are strongly dependent on the system in question. Average values of the coefficients C1 ¼
17.44 and C2 ¼ 51.6, where estimated by Williams et al. (1955), assuming Tref ¼ Tg and applying Eq. (12.7) for a number of different polymers. However, one should be cautious in uniformly applying these constants (Buera & Karel, 1995; Peleg,

304

Low-Temperature Processing of Food Products

1992; Terefe & Hendrickx, 2002) and the system-specific calculation if feasible, is strongly recommended. Based on the aforementioned assumption (Tref ¼ Tg), the typical formula of WLF equation (Eq. 12.7) can be rearranged to provide a linearized function: log

kg k


1

¼


C 1
2 
C1 C1 $ T
Tg

(12.8)

So that a linear plot of

kg log k


1 vs

1 T
Tg

(12.9)

is described by a straight line with a slope equal to eC2/C1 and an intercept of
1/C1, in case the WLF model is the most appropriate one. Nonetheless, as stressed out by Le Meste et al. (2002), there are specific processes such as caking, crystallization, and operational procedures such as freeze-drying, extrusion, etc where WLF approach, based on Tg data, is a reliable predictive tool. On the other hand, chemical/biochemical reactions may not be always restrained at temperatures below Tg, since glass transition phenomenon is not the unique criterion for molecular mobility, and WLF kinetics may be also affected by multiple factors. After an extended literature review concerning WLF kinetics implementation, it was observed that they are mostly used in an empirical way, without describing the real underlying mechanism that causes frozen food degradation (Giannakourou & Taoukis, 2019). This can be explained by two main reasons, the one referring to the experimental temperature conditions that are frequently deviating from the actual glass transition zon, and most importantly, the real phenomena that include other complicated mechanisms besides glass transition, such as freeze-concentration, are too complicated to be integrated into a single mathematical equation.

12.3.2.3 Q10 approach The Q10 value of a reaction is an alternative and practical way to describe the effect of temperature on biological reactions in foods. Defined as “the number of times a reaction rate changes with a 10 C change in temperature,” it actually demonstrates directly how storage at a temperature differing at a fact of 10 C can reduce product’s shelf life q s: Q10 ¼

kðTþ10Þ qs ðTÞ ¼ qs ðTþ10Þ kðTÞ

(12.10)

Quality kinetics and shelf life prediction and management in the frozen foods chain

305

In combination with Q10 approach, an alternative temperature dependence is introduced, as follows: kðTÞ ¼ ko ebT 0ln k ¼ ln ko þbT

(12.11)

When the two last equations are combined, Eq. (12.12) is generated, which introduces the so-called shelf-life plots, by plotting lnk versus temperature, and a straight line is fitted to experimental data. qs ðTÞ ¼ qsoe
bT 0ln qs ¼ ln qso
bT

(12.12)

One should note that these plots can be strictly considered as straight lines only for narrow temperature ranges of approximately 10e20 C. Under this prerequisite, the Arrhenius and the Q10 concept are related using the following equation: ln Q10 ¼ 10b ¼

EA 10 R TðT þ 10Þ

(12.13)

12.3.3 Effect of other parameters on the quality of frozen foods Besides temperature, moisture content and water activity (aw) have been recognized as the most important factors affecting the rate of quality deterioration at a wide range of storage temperatures (Taoukis & Giannakourou, 2007). Water activity is actually a measure of the degree of boundness of the water contained in a food and provides information on its availability to participate in chemical reactions. Specifically, in Schneeberger et al. (1978), fundamental thermodynamic aspects of water activity in frozen foods are briefly reviewed. Assuming that water assumes the form of a crystal as pure ice in frozen matrices and the participation of other substances is neglected, then the water activity of a frozen food is a function of temperature, being independent of the presence of other solutes. Nonetheless, examples of diffusion-controlled phenomena, enzymatic reactions and growth of microorganisms are presented, showing that the study of water activity, as a sole controlling factor, cannot describe sufficiently those reactions, as it does not take into consideration the influence of the dissolved solutes. With the molecular mobility and the physical state of the frozen matrix being an important parameter for frozen food stability, it is crucial to investigate the impact of moisture content and aw on the glass transition temperature of the system (Roos, 1995). When more water is available in a system, aw is increased and Tg found to decrease. As was already discussed when commenting on the WLF secondary model, passing into the rubbery state through Tg temperature, has a detrimental effect on viscosity depended phenomena but also in reaction rates and their temperature dependence. Nonenzymatic browning (Bell, 1996; Karmas et al., 1992; Miao & Roos, 2005; Roos & Himberg, 1994), aspartame degradation (Bell & Hageman, 1994),

306

Low-Temperature Processing of Food Products

enzymatic activities in frozen model systems (Champion et al., 2000; Terefe & Hendrickx, 2002) are case studies of reactions significantly influenced by the glass transition temperature.

12.4

12.4.1

Shelf-life determinationdCase studies applying conventional and stochastic mathematical/ statistical tools ASLT methodology

When designing a new product and making decisions about its introduction to the competitive food market, detailed information on the effect of temperature conditions on quality decay is necessary, in order to predict its shelf life (Fu & Labuza, 1993). Depending on the special characteristics of each food, its preservation method, and the expected storage (ambient/chill or frozen), the decision on the main cause of spoilage is crucial, with the shelf life of most foods being mostly limited by sensory and/or microbiological criteria. For frozen foods, the main deterioration mechanisms are occurring through slow chemical reactions that can be hardly recognizable by consumers. Taking into account that experiments with frozen foods may last more than a year, an accelerated shelf-life test (ASLT) can be applied in the appropriate temperature zone, so as to come up with a quick, but reliable assessment of the rate of degradation of the product. ASLT principles is based on the application of the Arrhenius equation at temperatures higher than the ideal ones, through a systematic shelf-life study, aiming at extrapolating the results to expected, normal storage conditions. The basic steps of the ASLT approach, detailed in Taoukis et al. (1997), are briefly outlined as follows, focusing on the case of frozen foods: 1. Select the main quality factors for the product in question, based on which are the predominant reactions that affect shelf life. This requires a thorough study of the food matrix in question, based on previous observations and a systematic literature research. 2. The appropriate package should be then selected for the shelf-life testing. For frozen foods, the actual product packaging, used in the actual food market, can be selected. 3. One of the most crucial steps involves the definition of the test’s storage temperatures, depending on the type of shelf-life testing. As far as frozen foods are concerned, a set of abusive temperatures of
5,
10, and
15 C are suggested (Taoukis et al., 1997), with control samples being kept and studied at a temperature lower than
40 C, where the experiment may last more than 18 months. 4. Another important step involves the investigation in literature of a reliable and realistic value of Q10, which will allow for the calculation of the testing duration at each experimental condition chosen, as long as the desired shelf life at the expected storage is selected. 5. The frequency of sampling at each temperature is also a matter to be decided and a practical formula is frequently used, according to the testing design at the highest temperature DT=10

f2 ¼ f1 $Q10

(12.14)

Quality kinetics and shelf life prediction and management in the frozen foods chain

307

with f1 being the time between successive measurements at the highest abusive temperature T1; f2 the time between successive measurements at T2; and DT the respective temperature difference ( C). This step needs a careful study, since scarce data may not allow for a correct calculation of the order of the reaction, whereas too frequent sampling may exhaust too soon available samples and invalidate the experiment. A useful rule is that at least six measurements are necessary to minimize statistical errors, at each condition investigated. The issue of confidence limits/uncertainty of kinetic parameters will be separately discussed in a latter section. 6. The next step is focused on estimating the order of the reaction and the corresponding rate by a graphical plot of the data. The Arrhenius plot should then be designed, and the equation parameters are estimated through linear regression, to predict the shelf life at the actual storage condition. To validate the procedure, it is suggested to perform an additional, independent experiment at a preset dynamic temperature profile.

With a well-designed and effective implementation of ASLT, the duration of an experiment can be substantially reduced, especially when kinetically studying frozen foods. Nonetheless, the expected duration of the shelf-life experimental protocol, based on ASLT principles depends on the EA of the quality loss (Taoukis et al., 2006), as illustrated in Table 12.4. As it will be discussed in detail, there are numerous kinetic studies that apply ASLT principles to assess the shelf life of frozen foods, and some representative examples are reported in Table 12.2 (order of popular quality degradation reactions for frozen foods of plant and animal origin); in the majority of these cases, the Arrhenius relation is reliably used to depict the temperature effect on the reaction rate of the deterioration pathway studied. Nevertheless, only few among these researches report a validation experiment under nonisothermal conditions, and even fewer test the model obtained under realistic dynamic conditions, that aim at mimicking the actual cold chain of frozen food distribution (Giannakourou & Taoukis, 2020).

12.4.2 Alternative approaches for kinetic parameter estimation: Frequentist versus stochastic approach As already discussed, despite acknowledging the role of ice crystallization, freeze concentration, and glass transition the two-step “apparent kinetics” approach is widely Table 12.4 Duration of ASLT protocol for a frozen food with a 18 months targeted shelf life at an ideal temperature of
20 C, as affected by the activation energy (EA) of the main quality degradation reactions.

EA (kJ/mol)

Storage time at L158C (d)

Storage time at L108C (d)

Storage time at L58C (d)

45 85 125

355 250 171

240 115 57

163 56 20

308

Low-Temperature Processing of Food Products

applied to mathematically account for quality loss of frozen foods. This includes the selection of an appropriate primary model to describe the change of the quality factor chosen as a function of postprocessing storage/distribution; then, an equation describing the impact of external conditions (especially temperature) on primary model’s parameters (e.g., secondary model) is used. To do so in practical terms, proper isothermal experiments are designed, based on ASLT principles, and the values of the kinetic parameters of Eq. (12.1) (k and n) are estimated by fitting the change over time of the experimentally determined values of (A). As already described, by integrating Eq. (12.1) the so called “quality function” (Eq. 12.2) is generated, providing the overall quality change, as a function of all influencing parameters and time. Going a step further, there are few published works where those models were validated under nonisothermal conditions, so that they could be reliably applied to predict quality decay of frozen matrices at any stage of food postprocessing chain (including distribution, storage, etc) (Cruz et al., 2009; Dermesonluoglu et al., 2015; Giannakourou & Taoukis 2003a, 2003b; Giannoglou et al., 2014; Gonçalves, Abreu, et al., 2011; Gonçalves, Pinheiro, et al., 2011; Martins et al., 2005; Tsironi et al., 2009). In this case, the quality value, Q(At) at any time t, defined by Eq. (12.2) for isothermal experiments, is revisited and re-estimated by introducing an appropriate integral: Z

ttot

QðAt Þ ¼

k½TðtÞ$dt ¼ keff $ttot

(12.15)

0

where T(t) denotes the overall temperature change over time, and keff represents the rate of the quality loss reaction at a temperature, termed as Teff (i.e., the temperature resulting in the same value of the selected quality index, as the dynamic temperature profile, estimated at the same overall time period, ttot). To numerically solve the problem, the T(t) function can be discretized in small ti (time increments) of isothermal conditions, Ti (note that Sti ¼ ttot), so that Eq. (12.15) derives Eq. (12.16), assuming that the Arrhenius relation is used as the secondary model: kref $

X i

  



Ea 1 1 Ea 1 1

exp
$ $ ti ¼ keff $ ttot ¼ kref $ exp
$ $ttot R R Ti Tref Teff Tref (12.16)

From the left part of this last equation, keff can be mathematically calculated, and as a next step, from the Arrhenius equation, the value of Teff can be estimated. Alternatively, the kinetic parameters of the secondary model (Ea and kref, if the Arrhenius law is used) can be calculated in a unique, “global” step, where all data at isothermal conditions are considered simultaneously. Mathematically, this can be obtained through a nonlinear regression analysis, where an integrated, overall equation is used, by introducing the secondary model within the primary model. As discussed in (Giannakourou & Taoukis, 2019, 2020, 2021), the main outcome of those two “frequentist” methodologies is the average values (estimates) of the kinetic parameters,

Quality kinetics and shelf life prediction and management in the frozen foods chain

309

frequently characterized by an inherent error. This error represents a different statistical value and should be appropriately calculated, presented, and thoroughly discussed. As a result, when applying a 2-step approach, the uncertainty estimated by a regression analysis, is usually much wider than the one found with the global methodology of a single step algorithm (Giannakourou & Taoukis, 2020; Martino & Marks, 2007) and mainly represents the error of the repeated measurements. Recently, a stochastic approach, frequently implemented in other research sectors, has been successfully implemented to better describe parameter uncertainty in food kinetics. The basis of this methodology lies on the observation that deterministic techniques do not exploit the whole information obtained from the experimental measurements at isothermal conditions, and kinetic parameters are not adequately described by a single value. In this context, Monte Carlo simulation schemes are implemented, under the assumption that the parameters of the Arrhenius relation (Ea and kref) are statistically described by an appropriate distribution, and the outcome of this analysis, the predicted shelf life of the food matrix in question, is a frequency line instead of a single value, allowing for much more realistic and reliable results. Going a step deeper in analysis, the variability of experimental data, obtained by a systematic experimental design with adequate repetitions, can also be taken into account within the calculations, according to the Bayesian approach, that also use Monte Carlo iterative procedure. The outcome of this more complex analysis, accounting for all types of error included in the calculations, is that the shelf life of a certain food at a selected temperature (the principal practical prediction expected from kinetics) is described by a distribution instead of being assigned a single value, predicting, in a more realistic way, the actual uncertainty involved in shelf-life estimations. A general scheme, depicting the evolution and/or the alternative approaches in food kinetics, is shown in Fig. 12.1, and based on these proposed methodologies, a case study on frozen food spoilage will be presented, as a step-by-step analysis (Giannakourou & Taoukis, 2021). Van Boekel (2021) proposed a similar algorithm applying Bayesian statistics, using published data of L-carnitine, to derive the probability of inactivation parameters, and not solely their mean values (Goula et al., 2018).

12.4.3 Frequentist approaches (two versus one step analysis)dIsothermal data As a characteristic case study to apply the different approaches, the shelf life of frozen spinach will be investigated, using raw data of L-ascorbic degradation (Giannakourou & Taoukis, 2003a, 2003b). Isothermal experimental measurements were mathematically described by a first-order reaction order and the Arrhenius relation was applied to describe the effect of temperature: C ¼ C0 e
kvitC t k ¼ kref

   Ea 1 1
exp
R T Tref

(12.17) (12.18)

310

Low-Temperature Processing of Food Products

Figure 12.1 Workflow of the two-step approach versus one step, nonlinear analysis (frequentist approach), based on an example of a first order reaction rate (primary model) and the Arrhenius relation (secondary model), resulting in a prediction of the shelf life, expressed as mean value 95% confidence intervals.

with C0 being the initial concentration of vitamin C (in mg/100 g of raw material), kref the rate of vitamin C degradation at Tref (assumed equal to
18 C), Ea the activation energy of the specific degradation mode and R the universal gas constant. Results are presented in Fig. 12.2, where linear regression is applied (ln(C/C0) versus t) at all constant temperatures studied to estimate each reaction rate (Fig. 12.2a) and the corresponding Arrhenius plot was then built, aiming at estimating the kinetic parameters, Ea and kref (Fig. 12.2b). Based on the two-step analysis, results for the Arrhenius parameters were as follows: Ea ¼ (120.0  9.1) kJ/mol and kref ¼ (0.00365  0.0012) d
1 with Tref ¼
20 C. It should be noted that the error presented (95% confidence intervals)

Figure 12.2 (a) Vitamin C loss of frozen spinach, in a linearized form and (b) Arrhenius plot for reaction rate constants (with Tref ¼
20 C)dtwo-step analysis.

Quality kinetics and shelf life prediction and management in the frozen foods chain

311

is calculated through regression analysis and depends only on the linear regression statistics. Using those kinetic parameters (mean estimates) and applying the criterion of 50% vitamin C loss (as the rejection nutritional limit), one can predict spinach shelf life at any arbitrary constant temperature, for example, 99 d at
18 C (and 150 d at
20 C). Alternatively, if the global approach is applied, using an overall mathematical equation (Eq. 12.19) that incorporates both primary and secondary models (Eqs. 12.17 and 12.18), based on nonlinear regression (SYSTAT 8.0): C ¼ exp C0

    
Ea 1 1
$
kref $ exp $t T Tref R

(12.19)

then, results are slightly different, that is, Ea ¼ 113.6  7.0 (in kJ/mol) and kref ¼ 0.00459  0.00073 (at
20 C, in d
1), and the 95% C.I. are narrower when compared to those estimated using the conventional 2-step approach. Data are presented in Fig. 12.3a. In this case, joint confidence intervals can also be constructed (Fig. 12.3b), to investigate the correlation that can exist between the kinetic parameters, that has an impact on model’s performance (Giannakourou et al., 2021; Giannakourou & Taoukis, 2020). Up to now, kinetic analysis was based on isothermal data; however, conditions at the real cold chain of frozen foods distribution deviates from constant and ideal temperatures, as verified by the FRISBEE database, a tool that provides data for all distinct stages of storage/transport/distribution of frozen foods (www.frisbee-project.eu/coldchaindb, Gogou et al., 2015). Based on more than 2500 records of time-temperature profiles, more realistic distribution scenarios can be built, that take into consideration actual temperature conditions at any stage of stock rotation when predicting food shelf life. In this context, the purpose of the current approach is to incorporate temperature

Figure 12.3 (a) Vitamin C degradation at five storage temperatures of frozen spinach and (b) joint confidence intervals for the kinetic parameters of the Arrhenius relation based on a global single-step approach (Tref ¼
20 C).

312

Low-Temperature Processing of Food Products

variability in the cold chain, aiming at more realistic shelf-life predictions. This is implemented using kinetic parameters of one-step analysis, and retrieving randomly temperature of each stage of a 70-days distribution of frozen spinach, using temperature data of three important stages of frozen food marketing route (FRISBEE database), as shown in Fig. 12.4. In order to account for temperature variability, Monte Carlo technique, implemented through an appropriately developed FORTRAN code, where a 70 days scenario is assumed and temperature conditions at each stage are randomly retrieved out of the distribution curves of Fig. 12.4. Values of Ea and kref of the single step analysis are used, aiming at calculating Vitamin C retention, using Eq. (12.18), and the shelf life can be then estimated applying the 50% vitamin C loss criterion). The case study analyzed involves a 30-day storage at the distribution center/production warehouse (Fig. 12.4a), 30 days at the retail stage (Fig. 12.4b) and 10 days at the household appliance (Fig. 12.4c). In Fig. 12.5, vitamin C loss over time is shown, for three representative distribution examples, throughout the frozen spinach rotation, including ideal and abusive handling procedures. To expand the approach, a Monte Carlo iterative scheme was applied, and 3000 different scenarios were run. For each scenario, the reaction rate constant at the

Figure 12.4 Data on temperature for storage at (a) distribution center/production warehouse, (b) retail stage, and (c) consumer storage (based on statistical analysis of FRISBEE database records) for frozen food life cycle.

Quality kinetics and shelf life prediction and management in the frozen foods chain

313

Figure 12.5 Vitamin C decrease for three alternative temperature scenarios of frozen spinach stock rotation (black dotted arrow line represents the 50% vitamin C loss nutritional criterion). Temperature profiles are depicted in the interior of the plot and kinetic parameters Eaekref in Eq. (12.7) are the mean estimates from the one-step analysis.

effective temperature is mathematically determined using Eq. (12.16), and then the value of the effective temperature is estimated as follows:  

Ea 1 1
keff ¼ k ref exp
$ Teff Tref R

(12.20)

The range of the effective temperatures is depicted in Fig. 12.6a, deviating from the mean value of
18 C, frequently assumed for the frozen food distribution. Similarly, the shelf life remaining (SLR) after 70 days of commercial rotation is depicted as a frequency plot in Fig. 12.6b, providing a much more realistic prediction of product quality, than the one assessed based on an isothermal handling at
18 C (nominal SLR at
18 C ¼ 30 d). From Fig. 12.6a and b, one can observe that more than 35% of frozen spinach items already expired before being consumed at the 70th day of rotation, products that have been exposed to an effective temperature >
16 C. Based on these

Figure 12.6 (a) Effective temperatures of the integrated profile and (b) shelf life remaining of the 3000 scenarios of frozen spinach distribution, after 70 days in the cold chain.

314

Low-Temperature Processing of Food Products

findings, real temperatures throughout the cold chain of frozen vegetables, especially abusive ones, have a crucial impact on overall variability, when predicting the quality level, and the shelf life remaining, at any time point of stock rotation. As discussed in Giannakourou and Taoukis (2020, 2021), a stochastic approach may be applied as an alternative to the so-called deterministic analysis; the basic reasoning underlined by this procedure is that kinetic parameters (appearing in both primaryesecondary models) should be preferably described by an appropriate distribution, instead of a single estimate, so as to assess the impact of parameter uncertainty on the prediction of product shelf life. Therefore, the kinetic analysis presented in this chapter may be expanded so as to exploit the whole information obtained from both the raw data obtained under isothermal experiments (measurements’ variability) and models’ statistical analysis (parameter uncertainty).

12.5

Application of TimeeTemperature Integrators for postprocessing cold chain monitoring and optimization

Since the real cold chain temperature conditions differ from the recommended conditions, the monitoring and recording the actual cold chain temperatures by intelligent packages or devices would be essential for cold chain management and optimization (Giannakourou & Taoukis, 2002; Giannoglou et al., 2014; Taoukis & Labuza, 1989a, 1989b; Tsironi et al., 2008). Time-temperature integrators (short: TTIs) are intelligent labels on the food package that can show an easily measurable, time-temperaturedependent change reflecting the temperature history of the food (Taoukis & Labuza, 2003). This change can be a reaction (physical, chemical, enzymatic reaction, or microbiological) that is expressed by a not reversible color change or a color movement along a scale. The extent of this change is related to the increase of time and temperature. Several TTIs are commercially available patented prototypes that are based on enzymatic activity, molecular diffusion, microbial growth, photochemical, and polymerization reactions (Table 12.5). The application of TTIs is still limited because of a number of problems such as the safety of TTIs (e.g., migration of toxic substances), and the accuracy of TTIs (e.g., high cost, inaccuracy of measurement) (Wang et al., 2015). The prerequisite is the food kinetic modeling and their temperature dependence (Pandian et al., 2021). TTIs monitor and record the cold chain temperatures’ history of the attached product, by a temperature-dependent change that is measured easily (Taoukis et al., 1989). TTI response’s kinetic study must match with the food quality loss’s the kinetic study taking into consideration the storage temperature effect on the quality loss indicating factor of the food target (Taoukis & Labuza, 2003). More specifically, the storage temperature effect of TTI response and food quality loss is described by activation energy value (Ea); these 2 Ea values must be similar. The end of TTI response must be near to the food product’s shelf-life end. TTI-based approach has been effectively used to optimize the chill chain management of food products, plant origin as well as meat-based (Giannakourou et al., 2001; Koutsoumanis et al., 2005, 2016; Lorentzen et al., 2022;

TTI typea, manufacturing company

TTI function

Storage

Activation

Drawbacks

Diacetylene crystals polymerize via 1,4 addition polymerization to a colored polymer, and the reflectance change is measured by scanning with a laser optic wand. The pigmentary water ink turns from noncolor to blue color at UV light irradiation. The organic photochromic pigment exists in two states A and B: A is thermodynamically stable and noncolored, B is metastable and blue; in dark, B changes to A.

Low temperature

Room temperature

Toxicity, Cost

Room temperature

Light

Inaccuracy

Oxygen free

Oxygen

Inaccuracy

Low temperature

Mixture

Inaccuracy, Cost

Low temperature

Mixture

Toxicity, Cost

Chemical TTIs Polymer, Fresh-check, lifelines Freshness Monitor (Lifelines Technology Inc.)/HEATmarker (Zebra) Photochromic, Freshpoint (Patent WO/2006/048412) OnVu (Ciba Specialty Chemicals)

Redox reaction

Physical TTIs Diffusion-based TTIs, 3M Monitor Mark & Freshness Check (3M Company)/Tempix (TEMPIX COLD CHAIN TECHNOLOGY AB) Electronic TTIs

Nanoparticle-based TTIs

A colored fatty acid ester is diffused along a porous wick made of high-quality blotting paper; the distance of the advancing diffusion front is measured. Thermal sensor that converts temperature signals to electrical signals and then converts electrical signals to a final visual output. Use of nano-materials with thermochromic property.

315

Continued

Quality kinetics and shelf life prediction and management in the frozen foods chain

Table 12.5 Time temperature indicators (TTIs): Types, manufacturing company and modes of function, and evaluation (including storage temperature, activation temperature, and potential drawbacks).

TTI typea, manufacturing company

316

Table 12.5 Continued

TTI function

Storage

Activation

Drawbacks

Hydrolysis of the substrate causes a drop in pH and color change in the pH indicator from dark green to bright yellow by a five-point scale. The activation is made by mechanical breakage of a seal separating two compartments (manually or on-line automation).

Low temperature

Mixture

Inaccuracy

It contains microorganisms and a gel, and changes color to opaque when the product is no for consumption. It is based on the anaerobic respiration of yeast to generate acid that causes color change of pH indicator. It includes two states A and B: A contains the reactants, including microorganisms and color indicator made of aqueous ink with appropriate carrier separating them, both of which are attached to a transparent plastic film; B has an activator with an aqueous adhesive layer. TTI is activated when the reactant contacts the activator on the surface.

Room temperature

Mixture

Inaccuracy

Enzymatic TTIs Acidebase reaction-based TTIs, CheckPoint TTI (VITSAB A.B.)

Microbiological or Biological TTIs

a

Other new systems of TTIs include: TTIs based on photonic lattice change, TTIs based on thermochromic polymer/dye blends (Wang et al., 2015).

Low-Temperature Processing of Food Products

Lactic acid bacteria-based TTIs, TRACEO & eO (CRYOLOG S.A.) Yeast-based TTIs

Quality kinetics and shelf life prediction and management in the frozen foods chain

317

Tsironi et al., 2008). The most applied approach is based on the equation of Arrhenius that correlates the temperature dependent rate of food quality loss (spoilage) with TTI color change rate (Taoukis & Labuza, 1989a, 1989b; Tsironi et al., 2008). TTI response was defined as a kinetic function of time characterized by the response rate constant (Shimoni et al., 2001; Taoukis & Labuza, 1989a, 1989b). Wells et al. (1987) applied the approach with the indicator action diagram simplifying the mathematical modeling. Smolander et al. (2004) reported the correlation of TTI color change rates with the microbiological growth rates. Despite the potential use and the benefits of using TTI to improve, their applications have not stand up to expectations (Koutsoumanis et al., 2005; Kreyenschmidt et al., 2009). More scientific research is necessary to improve the existing technologies. At the same time, there is need to communicate TTI technologies to stakeholders (Newsome et al., 2014). The most important requirement is the systematic knowledge of the food quality loss during storage to be monitored and the respective kinetic models. Safety Monitoring and Assurance System (SMAS) and Shelf-Life Decision System (SLDS) are proposed as TTI-based cold chain management systems, instead of First In First Out (FIFO system, taking into account food product characteristics, microbial growth models, and temperature time history of the studied food product (Koutsoumanis et al., 2005; Tsironi et al., 2008). In IQ-Freshlabel project, an enzymatic and photochromic TTIs’-based cold (frozen) chain management system has been proposed. In the same project, >276 European food industry, packaging industry, as well as consumers trained regarding the use of TTIs (Tsironi et al., 2015). TTI applicability for predicting shelf-life of foods plant and animal origin frozen foods from production to consumption has been studied, and the relative references are reported in Table 12.6. Table 12.6 Representative research papers on timeetemperature indicators (TTIs) applicability for frozen chain management: Frozen food (plant or animal origin) product, food quality index, timeetemperature (TTI) type, and main research outcome. Frozen food product Seafood (blue shark and arrow squid) Seafood (blue shark and arrow squid) Vegetables (green peas, white mushrooms) Vegetables (green peas, white mushrooms) Fruits (strawberries)

Food quality index

TTI type

References

Lipid oxidation index (TBARs), sensory evaluation Lipid oxidation index (TBARs), sensory evaluation Color change, vitamin C, water holding capacity, texture

Photochromic, enzymatic TTIs Photochromic and enzymatic TTIs Enzymatic TTIs

Tsironi et al. (2016)

Color change, vitamin C, water holding capacity, texture

Enzymatic TTIs

Giannakourou and Taoukis (2003a, 2003b)

Color change, vitamin C

Enzymatic TTIs

Dermesonlouoglou et al. (2004)

Giannoglou et al. (2014) Giannakourou and Taoukis (2002)

318

12.6

Low-Temperature Processing of Food Products

Concluding remarks

A detailed critical review of current literature on frozen food kinetics revealed that only few works provide a thorough kinetic study of food quality loss. Choosing the representative indices, measuring their change over storage time with an accurate method, implementing a successful experimental design and selecting the appropriate (primary and secondary) models are crucial steps for a reliable kinetic modeling. Additionally, little consideration has been focused on the quality and uncertainty of the data provided. As shown with some examples, the use of techniques/simulations (e.g., Monte Carlo) should be preferably used, to have more realistic shelf life predictive models. Finally, a critical evaluation of TTI applicability for frozen chain management was presented. The most important observation is the successful application of TTIs systematic mathematical modeling of the characteristic index of the target food. TTI effectiveness as monitoring and optimizing tools for the actual cold chain should be validated at the existing conditions, including temperature abuse conditions. Further studies on the actual assessment of TTI applicability (e.g., field tests) are essential, in order to develop a TTI based cold chain management system that could result in a significant decrease of frozen food erroneously wasted or mishandled.

References
Aguilera Barraza, F. A., Le
on, R. A. Q., & Alvarez, P. X. L. (2015). Kinetics of protein and textural changes in Atlantic salmon under frozen storage. Food Chemistry, 182, 120e127. https://doi.org/10.1016/j.foodchem.2015.02.055 € Arrhenius, S. A. (1889). Uber die Dissociationsw€arme und den Einfluß der Temperatur auf den Dissociationsgrad der Elektrolyte. Zeitschrift f€ur Physikalische Chemie, 4, 96e116. https:// doi.org/10.1515/zpch-1889-0408 Bedane, T. F., Altin, O., Erol, B., Marra, F., & Erdogdu, F. (2018). Thawing of frozen food products in a staggered throughfield electrode radio frequency system: A case study for frozen chicken breast meat with effects on drip loss and texture. Innovative Food Science Emerging Technologies, 50, 139e147. https://doi.org/10.1016/j.ifset.2018.09.00 Bell, L. N. (1996). Kinetics of non-enzymatic browning in amorphous solid systems: Distinguishing the effects of water activity and the glass transition. Food Research International, 28(6), 591e597. https://doi.org/10.1016/0963-9969(95)00052-6 Bell, L. N., & Hageman, M. J. (1994). Differentiating between the effects of water activity and glass transition dependent mobility on a solid state chemical reaction: Aspartame degradation. Journal of Agricultural and Food Chemistry, 42, 2398e2401. https://doi.org/ 10.1021/jf00047a007 Biliaderis, C. G., Swan, R. S., & Arvanitoyannis, I. (1999). Physicochemical properties of commercial starch hydrolyzates in the frozen state. Food Chemistry, 64(4), 537e546. https://doi.org/10.1016/S0308-8146(98)00165-4 Blond, G., & Simatos, D. (1991). Glass transition of the amorphous phase in frozen aqueous systems. Thermochimica Acta, 175, 239e247. https://doi.org/10.1016/0040-6031(91)80070-Y

Quality kinetics and shelf life prediction and management in the frozen foods chain

319

Buera, M. P., & Karel, M. (1995). Effect of physical changes on the rates of nonenzymatic browning and related reaction. Food Chemistry, 52, 167e173. https://doi.org/10.1016/ 0308-8146(94)P4199Carrington, A. K., Goff, H. D., & Stanley, D. W. (1996). Structure and stability of the glassy state in rapidly and slowly cooled carbohydrate solutions. Food Research International, 29(2), 207e213. https://doi.org/10.1016/0963-9969(95)00064-X Champion, D., Blond, G., Le Meste, M., & Simatos, D. (2000). Reaction rate modeling in cryoconcentrated solutions: Alkaline phosphatase catalyzed DNPP hydrolysis. Journal of Agricultural and Food Chemistry, 48, 4942e4947. https://doi.org/10.1021/jf000457s Cheng, L., Zhu, Z., & Sun, D.-W. (2021). Impacts of high pressure assisted freezing on the denaturation of polyphenol oxidase. Food Chemistry, 335, 127485. https://doi.org/ 10.1016/j.foodchem.2020.127485 Chiralt, A., Martínez-Navarrete, N., Martínez-Monz
o, J., Talens, P., Moraga, G., Ayala, A., & Fito, P. (2001). Changes in mechanical properties throughout osmotic processes: Cryoprotectant effect. Journal of Food Engineering, 49, 129e135. https://doi.org/10.1016/ S0260-8774(00)00203-X Chung, S. L., & Merritt, J. H. (1991). Kinetic study of quality losses in frozen scallop meats. Journal of Food Process Engineering, 14, 209e220. https://doi.org/10.1111/j.1745-4530. 1991.tb00092.x Corradini, M., & Peleg, M. (2004). Demonstration of the applicability of the WeibulleLogLogistic Survival Model to the isothermal and nonisothermal inactivation of Escherichia coli K-12 MG1655. Journal of Food Protection, 67(11), 2617e2621. Corradini, M. G., & Peleg, M. (2006). On modeling and simulating transitions between microbial growth and inactivation or vice versa. International Journal of Food Microbiology, 108(1), 22e35. https://doi.org/10.1016/j.ijfoodmicro.2005.10.011 Cruz, R. M. S., Vieira, M. C., & Silva, C. L. M. (2009). Effect of cold chain temperature abuses on the quality of frozen watercress (Nasturtium officinale R. Br.). Journal of Food Engineering, 94(1), 90e97. https://doi.org/10.1016/j.jfoodeng.2009.03.006 Dermesonlouoglou, E., Giannakourou, M., & Taoukis, P. (2004). Shelf-life prediction and management of frozen strawberries with time temperature integrators. In C.-T. Ho, C. J. Mussinan, & Tratras Contis (Eds.), Food flavor and chemistry: Exploration into the 21st century (pp. 459e472). Royal Society of Chemistry (RSC. Dermesonlouoglou, E., Giannakourou, M., & Taoukis, P. (2007a). Kinetic modelling of the quality degradation of frozen watermelon tissue: Effect of the osmotic dehydration as a pretreatment. International Journal of Food Science and Technology, 42, 790e798. https:// doi.org/10.1111/j.1365-2621.2006.01280.x Dermesonluoglu, E., Katsaros, G., Tsevdou, M., Giannakourou, M., & Taoukis, P. (2015). Kinetic study of quality indices and shelf life modelling of frozen spinach under dynamic conditions of the cold chain. Journal of Food Engineering, 148, 13e23. https://doi.org/ 10.1016/j.jfoodeng.2014.07.007 Dermesonlouoglou, E. K., Pourgouri, S., & Taoukis, P. S. (2008). Kinetic study of the effect of the osmotic dehydration pre-treatment to the shelf life of frozen cucumber. Innovative Food Science & Emerging Technologies, 9, 542e549. https://doi.org/10.1016/j.ifset.2008. 01.002 Dermesonlouoglou, E., Zachariou, I., Andreou, V., & Taoukis, P. S. (2018). Quality assessment and shelf life modeling of pulsed electric field pretreated osmodehydrofrozen kiwifruit slices. International Journal of Food Studies, 7, 34e51. https://doi.org/10.7455/ijfs/7.1. 2018.a4

320

Low-Temperature Processing of Food Products

Dermesonlouoglou, E. K., Giannakourou, M. C., & Taoukis, P. S. (2007b). Stability of dehydrofrozen tomatoes pretreated with alternative osmotic solutes. Journal of Food Engineering, 78, 272e280. https://doi.org/10.1016/j.jfoodeng.2005.09.026 Dermesonlouoglou, E. K., Giannakourou, M. C., & Taoukis, P. S. (2016). Kinetic study of the effect of the osmotic dehydration pre-treatment with alternative osmotic solutes to the shelf life of frozen strawberry. Food and Bioproducts Processing, 99, 212e221. https://doi.org/ 10.1016/j.fbp.2016.05.006 Fu, B., & Labuza, T. P. (1993). Shelf life prediction: Theory and application. Food Control, 4, 125e133. https://doi.org/10.1016/0956-7135(93)90298-3 Fukuda, Y., Okazaki, E., & Wada, R. (2006). Effect of fluctuations of temperature during frozen storage on denaturation of fish myofibrillar protein. Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers, 23, 335e340. Giannakourou, M. C., Dermesonlouoglou, E. K., & Taoukis, P. S. (2020). Osmodehydrofreezing: An integrated process for food preservation during frozen storage (Review). Foods, 9(8), 1042. https://doi.org/10.3390/foods9081042 Giannakourou, M. C., Gogou, E., & Taoukis, P. S. (2020). Reaction kinetics in food processing and shelf life. In S. M. Jafari (Ed.), Unit operations and processing equipment in the food industry, engineering principles of unit operations in food processing (pp. 443e470). Cambridge, USA: Woodhead Publishing, Elsevier. Giannakourou, M. C., Koutsoumanis, K., Nychas, G. J. E., & Taoukis, P. S. (2001). Development and assessment of an intelligent shelf life decision system for quality optimisation of the food chill chain. Journal of Food Protection, 64, 1051e1057. Giannakourou, M. C., & Stoforos, N. G. (2018). Principles of kinetic modeling of safety and quality attributes of foods. In E. Carvajal-Millan, C. O. Mohan, & C. N. Ravishankar (Eds.), Food process engineering & quality assurance (pp. 377e438). NJ, USA: Apple Academic Press, Inc. Giannakourou, M., & Taoukis, P. (2020). Holistic approach to the uncertainty in shelf life prediction of frozen foods at dynamic cold chain conditions. Foods, 9(6). https://doi.org/ 10.3390/foods9060714 Giannakourou, M. C., & Taoukis, P. S. (2021). Effect of alternative preservation steps and storage on vitamin C stability in fruit and vegetable products: Critical review and kinetic modelling approaches. Foods, 10, 2630. https://doi.org/10.3390/foods10112630 Giannakourou, M. C., & Taoukis, P. S. (2002). Systematic application of time temperature integrators as tools for control of frozen vegetable quality. Journal of Food Science, 67(6), 2221e2228. https://doi.org/10.1111/j.1365-2621.2002.tb09531.x Giannakourou, M. C., & Taoukis, P. S. (2003a). Stability of dehydrofrozen green peas pretreated with nonconventional osmotic agents. Journal of Food Science, 68(6), 2002e2010. https:// doi.org/10.1111/j.1365-2621.2003.tb07009.x Giannakourou, M. C., & Taoukis, P. S. (2003b). Kinetic modelling of vitamin C loss in frozen green vegetables under variable storage conditions. Food Chemistry, 83, 33e41. https:// doi.org/10.1016/S0308-8146(03)00033-5 Giannakourou, M. C., & Taoukis, P. S. (2019). Meta-analysis of kinetic parameter uncertainty on shelf life prediction in the frozen fruits and vegetable chain. Food Engineering Reviews, 11(1), 14e28. https://doi.org/10.1007/s12393-018-9183-0 Giannoglou, M., Touli, A., Platakou, E., Tsironi, T., & Taoukis, P. S. (2014). Predictive modeling and selection of TTI smart labels for monitoring the quality and shelf-life of frozen seafood. Innovative Food Science & Emerging Technologies, 26, 294e301. https:// doi.org/10.1016/j.ifset.2014.10.008

Quality kinetics and shelf life prediction and management in the frozen foods chain

321


Gogou, E., Katsaros, G., Derens, E., Alvarez, G., & Taoukis, P. (2015). Cold chain database development and application as a tool for the cold chain management and food quality evaluation. International Journal of Refrigeration, 52, 109e121. https://doi.org/10.1016/ j.ijrefrig.2015.01.019 Gonçalves, E. M., Abreu, M., Brand~ao, T. R. S., & Silva, C. L. M. (2011). Degradation kinetics of colour, vitamin C and drip loss in frozen broccoli (Brassica oleracea L. ssp. Italica) during storage at isothermal and non-isothermal conditions. International Journal of Refrigeration, 34, 2136e2144. https://doi.org/10.1016/j.ijrefrig.2011.06.006 Gonçalves, E. M., Cruz, R. M. S., Abreu, M., Brand~ao, T. R. S., & Silva, C. L. M. (2009). Biochemical and colour changes of watercress (Nasturtium officinale R. Br.) during freezing and frozen storage. Journal of Food Engineering, 93, 32e39. https://doi.org/ 10.1016/j.jfoodeng.2008.12.027 Gonçalves, E. M., Pinheiro, J., Abreu, M., Brand~ao, T. R. S., & Silva, C. L. M. (2011). Kinetics of quality changes of pumpkin (Curcurbita maxima L.) stored under isothermal and nonisothermal frozen conditions. Journal of Food Engineering, 106, 40e47. https://doi.org/ 10.1016/j.jfoodeng.2011.04.004 Goula, A. M., Prokopiou, P., & Stoforos, N. G. (2018). Thermal degradation kinetics of Lcarnitine. Journal of Food Engineering, 231, 91e100. https://doi.org/10.1016/j.jfoodeng. 2018.03.011 Hashimoto, K., Kawashima, Y., Yoshino, N., Shirai, T., & Takiguchi, A. (2015). Effects of freshness on thawing drip and ice crystal formation in frozen spotted mackerel Scomber australasicus. Nippon Suisan Gakkaishi, 81(1), 124e129. Hien, T. T., Long, T. B., Muoi, N. V., & Truc, T. T. (2022). Effect of pretreatment on quality of frozen Cau Duc pineapple (Ananas comosus). Materials Today: Proceedings, 57(Part 2), 447e453. https://doi.org/10.1016/j.matpr.2022.01.070. Jia, F., Jing, Y., Dai, R., Li, X., & Xu, B. (2020). High-pressure thawing of pork: Water holding capacity, protein denaturation and ultrastructure. Food Bioscience, 38, 100688. https:// doi.org/10.1016/j.fbio.2020.100688 Kaale, L. D., Eikevik, T. M., Bardal, T., Kjorsvik, E., & Nordtvedt, T. S. (2013). The effect of cooling rates on the ice crystal growth in air-packed salmon fillets during superchilling and superchilled storage. International Journal of Refrigeration, 36(1), 110e119. https:// doi.org/10.1016/j.ijrefrig.2012.09.006 Kaewthong, P., Pomponio, L., Carrascal, J. R., Knøchel, S., Wattanachant, S., & Karlsson, A. H. (2019). Changes in the quality of chicken breast meat due to superchilling and temperature fluctuations during storage. The Journal of Poultry Science, 56(4), 308e317. https:// doi.org/10.2141/jpsa.0180106 Karel, M., & Lund, D. B. (2003). Reaction kinetics. In Physical principles of food preservation (pp. 28e49). New York: Marcel Dekker, Inc. Karmas, R., Buera, M. P., & Karel, M. (1992). Effect of glass transition on rates of nonenzymatic browning in food systems. Journal of Agricultural and Food Chemistry, 40, 873e879. https://doi.org/10.1021/jf000.7a035 Katsouli, M., Semenoglou, I., Kotsiri, M., Gogou, E., Tsironi, T., & Taoukis, P. (2022). Active and intelligent packaging for enhancing modified atmospheres and monitoring quality and shelf life of packed gilthead seabream fillets at isothermal and variable temperature conditions. Foods, 11(15), 2245. https://doi.org/10.3390/foods11152245. Kim, H.-W., Miller, D. K., Yan, F., Wang, W., Cheng, H., & Kim, Y. H. B. (2017). Probiotic supplementation and fast freezing to improve quality attributes and oxidation stability of frozen chicken breast muscle. LWT, 75, 34e41. https://doi.org/10.1016/j.lwt.2016.08.035

322

Low-Temperature Processing of Food Products

Kobayashi, P., Tamura, T., Watanabe, M., & Toru, S. (2015). Effect of muscle protein denaturation on drip loss in tuna meat during thawing process. Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers, 32(2), 155e161. Koutsoumanis, K., Taoukis, P. S., & Nychas, G. J. E. (2005). Development of a safety monitoring and assurance system (SMAS) for chilled food products International. Journal of Food Microbiology, 100, 253e260. https://doi.org/10.1016/j.ijfoodmicro.2004.10.024 Kreyenschmidt, J., Albrecht, A., Beierle, E., Chonsch, L., Scherer, A., & Petersen, B. (2009). Determination of the shelf life of sliced cooked ham based on the growth of lactic acid bacteria in different steps of the chain. Journal of Applied Microbiology, 108, 510e520. https://doi.org/10.1111/j.1365-2672.2009.04451.x Labuza, T. P. (1984). Application of chemical kinetics to deterioration of foods. Journal of Chemical Education, 61, 348e358. https://doi.org/10.1021/ed061p348 Labuza, T. P., & Riboh, D. (1982). Theory and applications of Arrhenius kinetics to the prediction of nutrient losses in food. Food Technology, 36, 66e74. Lai, D. J., & Heldman, D. R. (1982). Analysis of kinetics of quality change in frozen foods. Journal of Food Process Engineering, 6, 179e200. https://do.org/10.1111/j.1745-4530. 1982.tb00291.x. Le Meste, M., Champion, D., Roudaut, G., Blond, G., & Simatos, D. (2002). Glass transition and food technology: A critical appraisal. Journal of Food Science, 67(7), 2444e2458. https:// doi,.org/10.1111/j.1365-2621.2002.tb08758.x. Li, D., Zhu, Z., & Sun, D.-W. (2018). Effects of freezing on cell structure of fresh cellular food materials: A review. Trends in Food Science and Technology, 75, 46e55. https://doi.org/ 10.1016/j.tifs.2018.02.019 Liang, D., Lin, F., Yang, G., Yue, X., Zhang, Q., Zhang, Z., & Chen, H. (2015). Advantages of immersion freezing for quality preservation of litchi fruit during frozen storage. LWT Food Science and Technology, 60(2), 948e956. https://doi.org/10.1016/j.lwt.2014.10.034 Liave, Y., Kambayashi, D., Fukuoka, M., & Sakai, N. (2020). Power absorption analysis of twocomponent materials during microwave thawing and heating: Experimental and computer simulation. Innovative Food Sciences and Emerging Technologies, 66, 102479. https:// doi.org/10.1016/j.ifset.2020.102479 Licciardello, J. J., Rvesi, E. M., Lundstrom, R. C., Wilhelm, K. A., Correia, F. F., & Allsup, M. G. (1982). Time- temperature tolerance and physical chemical quality tests for frozen red hake. Journal of Food Quality, 5, 215e234. https://doi.org/10.1111/j.17454557.1982.tb00745.x Lim, M. H., & Reid, D. S. (1991). Studies of reaction kinetics in relation to the Tg’ of polymers in frozen food model systems. In H. Levine, & L. Slade (Eds.), Water relationships in foods (pp. pp103e122). New York: Plenum Press. Liu, C., Grimi, N., Bals, O., Lebovka, N., & Vorobiev, E. (2021). Effects of pulsed electric fields and preliminary vacuum drying on freezing assisted processes in potato tissue. Food and Bioproducts Processing, 125, 126e133. https://doi.org/10.1016/j.fbp.2020.11.002 Lorentzen, G., Rosnes, J. T., Rotabakk, B. T., Skuland, A. V., Hansen, J. S., & Ageeva, T. N. (2022). A simulated e-commerce cold chain for fresh cod (Gadus morhua L.) products: Applicability of selected TTIs and effects of pre-treatment and packaging. Food Packaging and Shelf Life, 31, 100794. https://doi.org/10.1016/j.fpsl.2021.100794 Manzocco, L., Nicoli, M. C., Anese, M., Pitotti, A., & Maltini, E. (1998). Polyphenoloxidase and peroxidase activity in partially frozen systems with different physical properties. Food Research International, 31(5), 363e370. https://doi.org/10.1016/S0963-9969(98)00095-7

Quality kinetics and shelf life prediction and management in the frozen foods chain

323

Martino, K. G., & Marks, B. P. (2007). Comparing uncertainty resulting from two-step and global regression procedures applied to microbial growth models. Journal of Food Protection, 70, 2811e2818. https://doi.org/10.4315/0362-028x-70.12.2811 Martins, R. C., Lopes, I. C., & Silva, C. L. M. (2005). Accelerated life testing of frozen green beans (Phaseolus vulgaris, L.) quality loss kinetics: Colour and starch. Journal of Food Engineering, 67, 339e346. https://doi.org/10.1016/j.jfoodeng.2004.04.037 Martins, R. C., & Silva, C. L. M. (2002). Modelling colour and chlorophyll losses of frozen green beans (Phaseolus vulgaris, L.). International Journal of Refrigeration, 25, 966e974. Martins, R. C., & Silva, C. L. M. (2003). Kinetics of frozen stored green beans (Phaseolus vulgaris, L.) quality changes: Texture, vitamin C, reduced sugars and starch. Journal of Food Science, 68(7), 2232e2237. Martins, R. C., & Silva, C. L. M. (2004). Frozen green beans (Phaseolus vulgaris, L.) quality profile evaluation during home storage. Journal of Food Engineering, 64, 481e488. https://doi.org/10.1016/j.jfoodeng.2003.11.015 Miao, S., & Roos, Y. H. (2005). Nonenzymatic browning kinetics in low-moisture food systems as affected by matrix composition and crystallization. Journal of Food Science, 70(2), E69eE77. https://doi.org/10.1111/j.1365-2621.2005.tb07093.x Nakazawa, N., & Okazaki, E. (2020). Recent research on factors influencing the quality of frozen seafood. Fisheries Science, 86(2), 231e244. https://doi.org/10.1007/s12562-02001402 Newsome, R., Balestrini, C., Baum, M., Corby, J., Fisher, W., Goodburn, K., Labuza, T., Prince, G., Thesmar, H., & Yiannas, F. (2014). Applications and perceptions of date labeling of food. Comprehensive Reviews in Food Science and Food Safety, 13. https:// doi.org/10.1111/1541-4337.12086 Olivera, D., Vi~na, S., Marani, C., Ferreyra, R., Mugridge, A., Chaves, A., & Mascheroni, R. (2008). Effect of blanching on the quality of Brussels sprouts (Brassica oleracea L. gemmifera DC) after frozen storage. Journal of Food Engineering, 84, 148e155. https:// doi.org/10.1016/j.jfoodeng.2007.05.005 Pandian, A. T., Chaturvedi, S., & Chakraborty, S. (2021). Applications of enzymatic timee temperature indicator (TTI) devices in quality monitoring and shelf-life estimation of food products during storage. Journal of Food Measurement and Characterization, 15, 1523e1540. https://doi.org/10.1007/s11694-020-00730-8 Peleg, M. (1992). On the use of WLF model in polymers and foods. Critical Reviews in Food Science, 32, 59e66. Peleg, M., Normand, M. D., & Corradini, M. G. (2012). The Arrhenius equation revisited. Critical Reviews in Food Science, 52(9), 830e851. https://doi.org/10.1080/10408398. 2012.667460 Peleg, M., Normand, M. D., & Corradini, M. G. (2017). A new look at kinetics in relation to food storage. Annual Review of Food Science and Technology, 8(1), 135e153. Peleg, M., Normand, M. D., Dixon, W. R., & Goulette, T. R. (2018). Modeling the degradation kinetics of ascorbic acid. Critical Reviews in Food Science, 58, 1478e1494. https://doi.org/ 10.1080/10408398.2016.1264360 Pukszta, T., & Palich, P. (2007). The effect of freezing conditions of strawberry storage on the level of thawing drip loss. Acta Agrophysica, 9. Quevedo, R., Pedreschi, F., Valencia, E., Díaz, O., Bastías, J., & Mu~ noz, O. (2018). Kinetic modeling of deterioration of frozen industrial burgers based on oxidative rancidity and color. Journal of Food Processing and Preservation, 42(7). https://doi.org/10.1111/ jfpp.13655

324

Low-Temperature Processing of Food Products

Quevedo, R., Valencia, E., Pedreschi, F., Diaz, O., Bastias-Montes, J., Siche, R., & Munoz, O. (2020). Kinetic deterioration and shelf life in Rose hip pulp during frozen storage. Journal of Berry Research, 10, 133e143. https://doi.org/10.3233/JBR-190382 Rafael, S. (1992). Effect of storage timeefood processing plants and marketing conditions on the quality of some frozen vegetables (Ph.D. thesis). Egypt: University of Alexandria. Roos, Y. H. (1995). Phase transitions in foods (p. 360p). New York: Academic Press. Inc. Roos, Y. H. (2021). Glass transition and re-crystallization phenomena of frozen materials and their effect on frozen food quality. Foods, 10, 447. https://doi.org/10.3390/foods10020447 Roos, Y. H., & Himberg, M. J. (1994). Nonenzymatic browning behavior, as related to glass transition of a food model at chilling temperatures. Journal of Agricultural and Food Chemistry, 42, 893e898. https://doi.org/10.1021/jf00040a011 Schnewberger, R., Voilley, A., & Weisser, H. (1978). Activity of water in frozen systems. International Journal of Refrigeration, 1(4), 201e206. https://doi.org/10.1016/01407007(78)90113-5 Seminario, D. M., Balaban, M. O., & Rodrick, G. (2011). Inactivation kinetics of Vibrio Vulnificus in phosphate-buffered saline at different freezing and storage temperatures and times. Journal of Food Science, 76(2), E232eE239. https://doi.org/10.1111/j.1750-3841. 2010.02036.x Serpen, A., Gökmen, V., Bahçeci, K. S., & Acar, J. (2007). Reversible degradation kinetics of vitamin C in peas during frozen storage. European Food Research and Technology, 224, 749e753. https://doi.org/10.1007/S00217-006-0369-Y S
anchez-Valencia, J., S
anchez-Alonso, I., Martinez, I., & Careche, M. (2014). Estimation of frozen storage time or temperature by kinetic modeling of the Kramer shear resistance and water holding capacity (WHC) of hake (Merluccius merluccius, L.) muscle. Journal of Food Engineering, 120, 37e43. https://doi.org/10.1016/j.jfoodeng.2013.07.012 S
anchez-Valencia, J., S
anchez-Alonso, I., Martinez, I., & Careche, M. (2015). Low-field nuclear magnetic resonance of proton (1H LF NMR) relaxometry for monitoring the time and temperature history of frozen hake (Merluccius merluccius L.) muscle. Food and Bioprocess Technology, 8, 2137e2145. https://doi.org/10.1007/s11947-015-1569-x Shimoni, E., Anderson, E. M., & Labuza, T. (2001). Reliability of time temperature indicators under temperature abuse. Journal of Food Science, 66, 1337e1340. https://doi.org/ 10.1111/j.1365-2621.2001.tb15211.x Smolander, M., Alakomi, H.-L., Ritvanen, T., Vainionp€a€a, J., & Ahvenainen, R. (2004). Monitoring of the quality of modified atmosphere packaged broiler chicken cuts stored in different temperature conditions. A. Timeetemperature indicators as quality-indicating tools. Food Control, 15, 217e229. https://doi.org/10.1016/S0956-7135(03)00061-6 Syamaladevi, R. M., Manahiloh, K. N., Muhunthan, B., & Sablani, S. S. (2012). Understanding the influence of state/phase transitions on ice recrystallization in Atlantic Salmon (Salmo salar) during frozen storage. Food Biophysics, 7, 57e71. Szymczak, M., Kaminski, P., Felisiak, K., Szymczak, B., Dmytr ow, I., & Sawicki, T. (2020). Effect of constant and fluctuating temperatures during frozen storage on quality of marinated fillets from Atlantic and Baltic herrings (Clupea harengus). LWT, 133(April), 1e9. https://doi.org/10.1016/j.lwt.2020.109961 Tang, J., Zhang, H., Tian, C., & Shao, S. (2020). Effects of different magnetic fields on the freezing parameters of cherry. Journal of Food Engineering, 278, 109949. https://doi.org/ 10.1016/j.jfoodeng.2020.109949 Taoukis, P. S., & Giannakourou, M. C. (2007). Reaction kinetics. In Shyan S. Sablani, M. S. Rahman, A. K. Datta, & A. S. Mujumdar (Eds.), Handbook of food and bioprocess modelling techniques (pp. 235e263). CRC Press, Taylor and Francis Group.

Quality kinetics and shelf life prediction and management in the frozen foods chain

325

Taoukis, P. S., Giannakourou, M. C., & Tsironi, T. N. (2006). Monitoring and control of the cold chain. In D. W. Sun (Ed.), Handbook of frozen food processing and packaging. CRC Press, Taylor and Francis. Taoukis, P. S., & Labuza, T. P. (1989a). Applicability of time temperature indicators as shelf life monitors of food products. Journal of Food Science, 54, 783e788. https://doi.org/10.1111/ j.1365-2621.1989.tb07882.x Taoukis, P. S., & Labuza, T. P. (1989b). Reliability of time-temperature indicators as food quality monitors under non isothermal conditions. Journal of Food Science, 54, 789e792. https://doi.org/10.1111/J.1365-2621.1989.TB07883.X Taoukis, P. S., & Labuza, T. P. (2003). Timeetemperature indicators (TTIs). In R. Ahvenainen (Ed.), Novel food packaging techniques (pp. 103e126). Cambridge, UK: Woodhead Publishing Ltd. Taoukis, P. S., Labuza, T. P., & Saguy, S. (1997). Kinetics of food deterioration and shelf-life prediction. In K. J. Valentas, E. Rotstein, & R. P. Singh (Eds.), Handbook of food engineering practice (pp. 361e403). New York: CRC Press. Terefe, N. S., Buckow, R., & Versteeg, C. (2014). Quality-related enzymes in fruit and vegetable products: Effects of novel food processing technologies, part 1: high-pressure processing. Critical Reviews in Food Science and Nutrition, 54(1), 24e63. https://doi.org/10.1080/ 10408398.2011.566946 Terefe, N. S., & Hendrickx, M. (2002). Kinetics of the pectin methylesterase catalyzed deesterification of pectin in frozen food model systems. Biotechnology Progress, 18(2), 221e228. https://doi.org/10.1021/bp010162e Torreggiani, D., Forni, E., Guercilena, I., Maestrelli, A., Bertolo, G., Archer, G. P., Kennedy, C. J., Bone, S., Blond, G., Contreras-Lopez, E., & Champion, D. (1999). Modification of glass transition temperature through carbohydrates additions: Effect upon colour and anthocyanin pigment stability in frozen strawberry juices. Food Research International, 32, 441e446. Tsironi, T., Dermesonlouoglou, E., Giannakourou, M., & Taoukis, P. (2009). Shelf life modelling of frozen shrimp at variable temperature conditions. LWT e Food Science and Technology, 42(2), 664e671. https://doi.org/10.1016/j.lwt.2008.07.010 Tsironi, T., Giannoglou, M., Platakou, E., & Taoukis, P. (2016). Evaluation of Time Temperature Integrators for shelf-life monitoring of frozen seafood under real cold chain conditions. Food Packaging and Shelf Life, 10, 46e53. https://doi.org/10.1016/j.fpsl.2016. 09.004 Tsironi, T., Gogou, E., Velliou, E., & Taoukis, P. S. (2008). Application and validation of the TTI based chill chain management system SMAS (Safety Monitoring and Assurance System) on shelf life optimization of vacuum packed chilled tuna. International Journal of Food Microbiology, 128, 108e115. Tsironi, T., Maltezou, I., Tsevdou, M., Katsaros, G., & Taoukis, P. (2015). High-pressure cold pasteurization of gilthead seabream fillets: Selection of process conditions and validation of shelf life extension. Food and Bioprocess Technology, 8, 681e690. https://doi.org/10.10 07/s11947-014-1441-4 Tsironi, T. N., Stoforos, N. G., & Taoukis, P. S. (2020). Quality and shelf-life modeling of frozen fish at constant and variable temperature conditions. Foods, 9(12), 1893. https:// doi.org/10.3390/foods9121893 Tu, J., Zhang, M., Xu, B., & Liu, H. (2015). Effect of physicochemical properties on freezing suitability of Lotus (Nelumbo nucifera) root. International Journal of Refrigeration, 50, 1e9. https://doi.org/10.1016/j.ijrefrig.2014.10.006

326

Low-Temperature Processing of Food Products

Ullah, J., Takhara, P. S., & Sablani, S. S. (2014). Effect of temperature fluctuations on ice-crystal growth in frozen potatoes during storage. LWT e Food Science and Technology, Part 1, 59(2), 1186e1190. https://doi.org/10.1016/j.lwt.2014.06.018 Van Boekel, M. A. J. S. (1996). Statistical aspects of kinetic modeling for food science problems. Journal of Food Science, 61(3), 477e486. https://doi.org/10.1111/j.1365-2621.1996. tb13138.x Van Boekel, M. A. J. S. (2021). Kinetics of heat-induced changes in foods: A workflow proposal. Journal of Food Engineering, 306, 110634. https://doi.org/10.1016/j.jfoodeng. 2021.110634 Van Buggenhout, S., Grauwet, T., Van Loey, A., & Hendrickx, M. (2008). Use of pectinmethylesterase and calcium in osmotic dehydration and osmodehydrofreezing of strawberries. European Food Research and Technology, 226, 1145e1154. https://doi.org/10.1007/ S00217-007-0643-7 Van Buggenhout, S., Lille, M., Messagie, I., Van Loey, A., Autio, K., & Hendrickx, M. (2006). Impact of pretreatment and freezing conditions on the microstructure of frozen carrots: Quantification and relation to texture loss. European Food Research and Technology, 222, 543e553. https://doi.org/10.1007/s00217-005-0135-6 Van Buggenhout, S., Messagie, I., Maes, V., Duvetter, T., Van Loey, A., & Hendrickx, M. (2006). Minimizing texture loss of frozen strawberries: Effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions. European Food Research and Technology, 223, 395e404. https://doi.org/10.1007/s00217-005-0218-4 Vicent, V., Ndoye, F.-T., Verboven, P., Nicolaï, B., & Alvarez, G. (2019). Effect of dynamic storage temperatures on the microstructure of frozen carrot imaged using X-ray micro-CT. Journal of Food Engineering, 246, 232e241. https://doi.org/10.1016/j.jfoodeng.2018. 11.015 Wang, S., Liu, X., Yang, M., Zhang, Y., Xiang, K., & Tang, R. (2015). Review of time temperature indicators as quality monitors in food packaging. Packaging Technology and Science, 28, 839e867. https://doi.org/10.1002/pts.2148 Wang, Y., Liang, H., Xu, R., Lu, B., Song, X., & Liu, B. (2020). Effects of temperature fluctuations on the meat quality and muscle microstructure of frozen beef. International Journal of Food Refrigeration, 116, 1e8. https://doi.org/10.1016/j.ijrefrig.2019.12.025 Wells, J. H., Singh, R. P., & Noble, A. C. (1987). A graphical interpretation of time-temperature related quality changes in frozen food. Journal of Food Science, 52(2), 436e444. Williams, M. L., Landel, R. F., & Ferry, J. D. (1955). The temperature dependence of relaxation mechanisms in amorphous polymers and other glass forming liquids. Journal of Chemical Engineering, 77, 3701e3707. Wu, B., Qiu, C., Guo, Y., Zhang, C., Guo, X., Bouhile, Y., & Ma, H. (2022). Ultrasonic-assisted flowing water thawing of frozen beef with different frequency modes: Effects on thawing efficiency, quality characteristics and microstructure. Food Research International, 157, 111484. https://doi.org/10.1016/j.foodres.2022.111484 Wu, J., Zhang, M., Bhandari, B., & Yang, C-h. (2021). Drip loss control technology of frozen fruit and vegetables during thawing: A review. International Agrophyics, 35, 235e250. https://10.31545/intagr/142289. Wu, X.-F., Zhang, M., Adhikari, B., & Sun, J. (2017). Recent developments in novel freezing and thawing technologies applied to foods. Critical Reviews in Food Science and Nutrition, 57, 3620e3631. https://doi.org/10.1080/10408398.2015.1132670 Xu, Z., Liu, X., Wang, H., Hong, H., & Luo, Y. (2016). Comparison between the Arrhenius model and the radial basis function neural network (RBFNN) model for predicting quality

Quality kinetics and shelf life prediction and management in the frozen foods chain

327

changes of frozen shrimp (Solenocera melantho). International Journal of Food Properties, 20(11), 2711e2723. https://doi.org/10.1080/10942912.2016.1248292 Yuan, J., Li, H., Tao, W., Han, Q., Dong, H., Zhang, J., Jing, Y., Wang, Y., Xiong, Q., & Xu, T. (2020). An effective method for extracting anthocyanins from blueberry based on freezeultrasonic thawing technology. Ultrasonics Sonochemistry, 68, 105192. https://doi.org/ 10.1016/j.ultsonch.2020.105192 Zhang, C., Li, Y., Xia, X., Liu, Q., Chen, Q., & Kong, B. (2022). Changes in muscle quality and physicochemical characteristics of chicken breast subjected to ultrasound-assisted immersion freezing during long-term frozen storage. International Journal of Refrigeration, 142, 10e18. https://doi.org/10.1016/j.ijrefrig.2022.06.020

Further reading Kreyenschmidt, J., Christiansen, H., H€ubner, A., Raab, V., & Petersen, B. (2010). A novel photochromic timeetemperature indicator to support cold chain management. International Journal of Food Science and Technology, 45(2), 208e215. https://doi.org/10.1111/ J.1365-2621.2009.02123.X Roos, Y. H., & Drusch, S. (2015). Phase transitions in foods. Academic press. Inc. Shiferaw Terefe, N., Van Loey, A., & Hendrickx, M. (2004). Modelling the kinetics of enzymecatalysed reactions in frozen systems: The alkaline phosphatase catalysed hydrolysis of disodium-p-nitrophenyl phosphate. Innovative Food Science & Emerging Technologies, 5(3), 335e344. https://doi.org/10.1016/j.ifset.2004.05.004 Wang, Y., Miyazaki, R., Saitou, S., Hirasaki, K., Takeshita, S., Tachibana, K., & Taniyama, S. (2018). The effect of ice crystals formations on the flesh quality of frozen horse mackerel (Trachurus japonicus). Journal of Texture Studies. https://doi.org/10.1111/jtxs.12310 Zhang, Z., Huber, D. J., Qu, H., Yun, Z., Wang, H., Huang, Z., Huang, H., & Jiang, Y. (2015). Enzymatic browning and antioxidant activities in harvested litchi fruit as influenced by apple polyphenols. Food Chemistry, 171, 191e199. https://doi.org/10.1016/j.foodchem. 2014.09.001

This page intentionally left blank

Section Four Design, control, and efficiency of freezers

This page intentionally left blank

Design and simulation of freezing processes

13

Narjes Malekjani 1 and Mina Homayoonfal 2, 3 1 Alexander von Humboldt Research Fellow, Otto von Guericke University Magdeburg, Magdeburg, Germany; 2Research Center for Biochemistry and Nutrition in Metabolic Diseases, Institute for Basic Sciences, Kashan University of Medical Sciences, Kashan, Iran; 3 Nutrition Department, School of Medicine, Kashan University of Medical Science, Kashan, Iran

13.1

Introduction

Theoretical food freezing is a complex phenomenon that involves multiple concurrent physical phenomena, including the transfer of heat and mass, the growth of crystals, mechanical strain and stress, nucleation, and volume change. Mathematically formulating the heat and mass transfer occurring while food undergoes freezing, thawing, and storage at sub-zero temperatures presents substantial challenges. Near the freezing point, thermal and physical features of food components, like thermal conductivity and specific heat, can undergo sudden and important changes, resulting in strongly nonlinear partial differential equations (PDEs) that can be challenging to solve. Analytical approaches can only handle idealized samples individually, making it challenging to model the freezing process in objects with intricate shapes. In such cases, numerical modeling becomes necessary. The freezing process is associated with various phenomena, including significant and abrupt volume alteration, cellular desiccation, mass flux, subcooling, mechanical strain and fracturing, ice nucleation, and expansion, all needing to be considered in freezing process modeling. One critical aspect of frozen storage is moisture migration at the microscale (recrystallization) and macroscale (weight loss). Therefore, in the following sections, this paper aims to introduce the different variables and phenomena that govern the freezing process and describe various modeling strategies for freezing.

13.2

An introduction to physical and transport phenomena involved in the freezing process

13.2.1 Heat transfer Heat transfer in food freezing predominantly occurs through three distinct approaches: convection, conduction, and irradiation. The dominant methods of heat transfer within refrigeration systems are conduction and convection. Conduction refers to transferring

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00005-9 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

332

Low-Temperature Processing of Food Products

heat through direct contact between continuous masses or bodies. It encompasses the conveyance of energy from molecules with higher energy to neighboring molecules with lower energy due to molecular interactions. Fourier’s principle of thermal conduction elucidates this phenomenon: Q¼ kA

dT dx

(13.1)

Here, T represents the temperature, A denotes the area that is perpendicular to the heat flow, and x stands for the position along the direction of the heat flow. According to Eq. (13.1), heat conduction occurs in the direction where the temperature decreases. Therefore, the heat transfer rate in a particular direction corresponds to the temperature gradient in that specific direction. The ability of a mass to conduct heat mainly depends on the properties of the object itself. This capability is referred to as the thermal conductivity of materials (k), expressed in kilowatt per meter Kelvin [kW/(m K)] (Holman, 1986; Mills, 1992). Heat convention typically is a combination of heat conduction and the movement of fluids. It involves transferring energy at the interface of a solid surface and the adjacent moving gas or liquid. Convection phenomena may be natural (free) or forced based on the flow velocity. In the free type, the fluid flow corresponds to buoyancy forces, stimulated by density difference as a result of the temperature variations in a fluid. However, the liquid is forced to move through exterior forces, including a pump or fan in the forced ones. Newton’s cooling law describes the measure of transferring heat via convection: 
Q ¼ ht A Tsur  Tf

(13.2)

where A (m2) represents the surface area of the material, Tf (K) signifies the fluid temperature, Tsur (K) denotes the surface temperature, and h is a parameter obtained through experimental measurements regarded as the coefficient for heat transfer through convection and expressed in kilowatt per square meter Kelvin [kW/(m2 K)]. Its value is chiefly associated with the properties of the fluid flow, attributes of fluid, and surface configuration (Welti-Chanes et al., 2005).

13.2.2

Diffusion-based mass transfer

While the system is steady-state, moisture diffusion within food materials during the freezing process can be characterized using Fick’s first law: ma ¼ DA

dCa dy

(13.3)

The mass flow (ma, kg/s) can be determined using the diffusion coefficient (D, m2/s) and the concentration of the diffusing components (Ca, kg.m3). Eq. (13.3) is the equivalent of Eq. (13.1) in mass transfer phenomena and explains the steady-state diffusion of gas or liquid (Treybal, 1980).

Design and simulation of freezing processes

333

13.2.3 Mass transfer through convection Based on Fick’s law, diffusion of all food species inside of the food structure is governed at the rate of ma. Subsequently, they are conveyed to or from the surface via convective mass transport, much like free convective heat transfer: ma ¼ hm AðCs  CN Þ

(13.4)

Cs and Cm represent the concentrations of components on the food’s surface and within the balk of the fluid, respectively, and hm denotes the coefficient of mass transfer measured through empirical relations presented in the literature (Dash et al., 2023).

13.2.4 Supercooling and nucleation Assume a small water droplet dispersed in a cold, subzero surrounding. Due to its minuscule size, the droplet maintains a uniform temperature throughout its entirety. The sole hindrance to the instant freezing process is the finite surface or external obstruction to transferring heat, governing the rate of heat transfer from the droplet surface to the surrounding air. The surface resistance is attributed to the limited thermal conductivity of the air surrounding the droplet. Cooling water to 0 C, it will remain in a liquid state; it is necessary to achieve temperatures (T) significantly below the freezing point (Tf) before ice formation begins. Defined as DTs ¼ Tf  T, supercooling or undercooling in pure water is a necessary condition for nucleation to take place. Accordingly, nucleation is the process of forming a minimum crystal owning a critical radius that may subsequently develop or increase. In the process of nucleation, the latent heat of solidification is liberated, and water molecules assemble to create organized particles of sufficient size to serve as sites for the significant growth of water crystals (Mason, 1958; Stonehouse & Evans, 2015; You et al., 2021).

13.2.5 Crystal growth Following the formation of the ice nucleus, further crystal growth occurs by inserting molecules into the boundary between the solid and liquid phases. Crystal growth is not an instantaneous process but is influenced by the rate of latent heat removal during the phase change as well as the mass transfer of solutions. Nonetheless, heat transfer does not singularly dictate the rate of crystal growth or ice development. When ice formation takes place within a solution, the rate of ice spread is influenced by mass transfer as well due to the diffusion of water molecules and their attachment to the expanding ice crystal. At the same time, the solutes are excluded from the region occupied by pure ice crystals by diffusing away from the interface of crystal and incorporation into the bulk liquid (Bevilacqua et al., 1979; Devireddy et al., 2002).

13.2.6 Volume changes Throughout the freezing process, there are alterations in the volume of food materials related to the water expansion (about 9%) following transformation into ice. However,

334

Low-Temperature Processing of Food Products

the expansion rate of most food components and living samples is lower than that of pure water. Because other food components contract as the temperature decreases, it becomes evident that volume change throughout the system is not consistent, which may result in mechanical damage (Desrosier, 2012).

13.2.7

Mechanical strain and stress

Subsequent freezing of food materials, the expansion and contraction related to phase changes, and following contraction owing to further cooling may lead to developing mechanical stress, which in turn causes microstructural damage, large-scale cracking, and deformation. The expansion of liquid water molecules during freezing produces remarkable stress in foods. Frozen food is fragile, and these stresses can result in food fractures, especially with rapid cooling rates. Stress analysis in frozen food materials illustrated that the total strain comprises both mechanical strain (because of mechanical stress) and thermal strain (because of temperature change). The thermal strains should account for variations in temperature and encompass both expansion due to phase change and contraction caused by ice formation when measured. In contrast, the mechanical strain contains the expansion part and a shear or deviatoic part (Pham et al., 2005).

13.3

Definitions of physical properties and coefficients involved in modeling the freezing process

During the freezing of food materials, phase changes occur over a range of temperatures. Accordingly, the initial freezing point is defined as the temperature at which ice crystals initially appear without the presence of supercooling. Prior to estimating the time of freezing and thermal load, it is imperative to possess the necessary physical parameters or inputs. These inputs are classified into two distinct categories: environmental variables and food properties. The environmental factors include ambient temperature and the coefficient of heat transfer, while the second one, that is, food properties, can be quite challenging and is a comprehensive topic. However, this work will provide only a concise overview of this calculation (Desrosier, 2012). The pertinent physical attributes of food include the freezing point, density, enthalpy, thermal conductivity, and specific heat. The latter four characteristics vary with temperature, often exhibiting significant changes near the freezing point. Even when data are accessible, it is essential to transform them into a practical format using curve-fitting (regression) equations. In cases where reliable property data are not accessible, estimation becomes necessary based on composition data. This chapter outlines various approaches to accomplish this task. It is important to mention that the methods of property prediction described here are not the exclusive or most cuttingedge options available. There may be methods better suited to specific food types. Nevertheless, these methods are conceptually straightforward and, in most instances, yield satisfactory results (Rahman et al., 2009; Sweat, 1986).

Design and simulation of freezing processes

335

13.3.1 Coefficient of heat transfer The coefficient of heat transfer, denoted as h, is defined as the quotient of the heat flux q (the rate of heat transfer per unit area) and the temperature difference between the temperature of surface Ts and the cooling medium temperature Ta. h¼

q Ts  Ta

(13.5)

The inverse of h, which is 1/h, is referred to as the resistance at the surface to heat transfer. For an unwrapped product exposed to air, the heat transfer coefficient h encompasses effects from convection, radiation, and evaporative cooling and is symbolized as hsurf (Davey & Pham, 1997). hsurf ¼ hconv þ hrad þ hevap

(13.6)

The reciprocal of hsurf characterizes the heat transfer resistance at the interface between the food and the encompassing fluid. The convective part of hsurf relies on factors such as the configuration of the product, the characteristics of the encompassing fluid, the flow behaviors, and the degree of turbulence. Empirical correlations can often be employed to estimate the convective heat transfer coefficient in numerous typical product configurations. Alternatively, it can be calculated through the application of computational fluid dynamics as long as a proper turbulence model is utilized (Hu & Sun, 2001; Pham et al., 2009).

13.3.2 Density In a composite material consisting of various components, each element i adds a mass to the system, denoted as Xi, and a volume equal to Xi/ri, with ri representing the density associated with component i. Consequently, the density of the overall material can be determined by dividing the total mass (1) by the total volume, yielding (Singh & Mannapperuma, 1990): 1 r¼P Xi i ri

(13.7)

13.3.3 Freezing point In the context of food freezing, the expression “initial freezing point” is applied to describe the temperature at which ice crystals initially emerge (assuming no supercooling occurs). This temperature is determined based on the solute concentration via the following thermodynamic correlation:  lnaw ¼

  Mw lf 1 1  Rg Tf T0

(13.8)

336

Low-Temperature Processing of Food Products

Here, aw represents the water activity, Mw stands for the molar mass of water (18.02 kg$kmol1), lf denotes the latent heat to freeze a unit mass of water (334 kJ$kg1), Rg is the universal gas constant (8.314 kJ$K1 kmol1), Tf is the freezing point of the solution, and T0 corresponds to the freezing point of pure water (273.15 K). In the case of dilute solutions, Raoult’s law is applicable, and water activity is determined using the following equation: aw ¼ 1ixsol

(13.9)

Here, xsol is the fraction of moles represented by the solute in the solution, and the parameter i indicates the van’t Hoff factor, which considers the extent of molar or ionic dissociation that occurs within the solution (Schwartzberg, 1976; Schwartzberg et al., 2007).

13.3.4

Bound water

The calculation for bound water content can be expressed as follows: Xb ¼ bXds

(13.20)

The term “bound water” demonstrates the quantity of water that is tightly associated with the solids, Xds represents the overall mass fraction of dry solids, and b is the ratio of bound water mass to solids mass (Pham, 1987a, 1987b).

13.3.5

Enthalpy

Enthalpy (H) is a measure of the amount of heat contained per unit mass of food at a specific temperature and is typically expressed in joules per kilogram (J$kg1). In all calculations involving enthalpy, changes in enthalpy are primarily interested. When conducting freezing calculations, the commonly employed reference temperature is Tref ¼ 40 C. Following the determination of ice content, the enthalpy of food is measured easily by merely adding together the enthalpies of its various constituents. This calculation is conducted as follows: H ¼ Xuw Huw þ Xice Hice þ Xprot Hprot þ Xfat Hfat þ Xcarb Hcarb þ Xfib Hfib þ Xash Hash

(13.21)

For every component i other than water, the enthalpy Hi is determined using the specific heat ci (measured in J$kg1K1) as follows: Z Hi ¼

T

ci dT Tref

(13.22)

Design and simulation of freezing processes

337

The calculation of Huw, unfrozen water enthalpy, differs from the enthalpy of the remaining components due to the presence of water in two phases, with ice being used as the reference state at Tref. To determine the enthalpy of liquid water at temperature T, a process is followed where the ice at the specified reference temperature is first heated to T0 (0 C), subsequently melted, and finally, the resulting liquid water is brought to the desired temperature T. The enthalpy of this liquid water can be expressed as follows (Pham, 1987a, 1987b; Pham and Pham, 2014a, 2014b, 2014c): Z Huw ¼

T0

Tref

Z Cice dT þ lf 0 þ

T

cuw dT

(13.23)

T0

13.3.6 Sensible specific heat Certain analytical and empirical techniques for determining the durations of freezing/ thawing processes and the associated heat requirements necessitate knowledge of the sensible or real specific heat capacity, denoted as cf (for frozen material) and cu (for unfrozen material), which excludes the phase change latent heat, at specific temperatures. These specific heats can be computed using the following relationships (Choi, 1986; Singh & Heldman, 2014): cf ¼ Xuw cuw þ Xice cice þ Xprot cprot þ Xfat cfat þ Xcarb ccarb þ Xfib cfib þ Xash cash cu ¼ Xuw cuw þ Xprot cprot þ Xfat cfat þ Xcarb ccarb þ Xfib cfib þ Xash cash

(13.24)

(13.25)

13.3.7 Apparent specific heat The derivative of enthalpy, denoted as capp h dH/dT, is referred to as the observable or practical specific heat of food materials. This term is used because it takes into account latent heat effects, such as phase changes. The most comprehensive approach for determining it entails numerically differentiating the relationship between enthalpy and temperature using the formula (Hoang et al., 2021): capp ¼

HðT þ dTÞ  HðT  dTÞ 2dT

(13.26)

here, dT represents a minor temperature range. It is crucial to emphasize that numerical differentiation can be challenging, especially when working with pure water or highly diluted solutions in close proximity to or at the freezing point. This difficulty arises due to the abrupt changes in enthalpy in this temperature range. To address this issue, a common approach is to introduce some degree of smoothing or averaging of around the latent heat peak, specifically the temperature range associated with freezing, in order to simplify the numerical differentiation

338

Low-Temperature Processing of Food Products

procedure. When determining the apparent specific heats dependent on the composition, at temperatures exceeding the freezing point, capp equal to cu as specified in Eq. (13.25). However, at temperatures lower than the freezing point, the situation becomes increasingly complex due to phase change effects. The impact of water/ice on the apparent specific heat is described by the following equation (Fikiin, 1996; Cogné et al., 2003): d dXuw ðXuw Huw þ Xice Hice Þ ¼ Xuw cuw þ Xice cice þ ðHuw  Hice Þ dT dT

13.3.8

(13.27)

Thermal conductivity

The thermal conductivity of food indicates its capacity to conduct heat, and several techniques are available for its measurement. These methods can be categorized into steady-state, quasi-steady-state, and transient techniques (Braun et al., 2019; Hammerschmidt, 2003). Two commonly used experimental instruments for determining thermal conductivity are the guarded hot plate and heated probe methods. However, food materials typically exhibit low thermal conductivities, leading to extended time periods (e.g., 12 h) required to attain a steady state. This prolonged exposure to high temperatures can result in moisture migration and changes in properties. Consequently, conventional standard techniques like the guarded hot plate, which are effective for nonbiological materials, are less appropriate for food materials due to these challenges, as well as the need for large sample sizes (Rao et al., 2014). Both transient and quasi-steady-state approaches are preferred for determining the thermal conductivity of food materials since they offer shorter computing times and require comparatively small sample sizes (Sweat & Haugh, 1974). A commonly suggested approach for a wide range of food-related uses involves utilizing a thermal conductivity probe with a linear heat source, particularly one based on transient techniques. Within this probe design, there is an insulated heating wire that extends from the handle to the tip, housed within the needle tubing. Incorporated within the tubing is an insulated thermocouple, where the junction is strategically positioned at the midpoint between the handle of the probe and the tip of the needle. The needle, thermocouple, and heater wire are electrically isolated from one another using plastic tubing. In the measurement process, the line heat source probe is introduced into a food sample that initially possesses a consistent temperature. Subsequently, the probe undergoes uniform heating at a steady rate, with continuous monitoring of the temperature in close proximity to the line heat source. After a brief transient phase, the graph depicting the natural logarithm of time versus the monitored temperature exhibits a linear relationship, where the slope corresponds to Q/4pk. Hence, thermal conductivity is determined as follows (Rao et al., 2014; Sweat & Haugh, 1974): k¼Q

ln½ðt2  t0 Þ=ðt1  t0 Þ 4p ðT2  T1 Þ

(13.28)

Here, k represents the sample thermal conductivity, Q stands for the power produced by the heater in the probe, t0 denotes a time-associated correction factor, and

Design and simulation of freezing processes

339

T1 and T2 signify the temperatures recorded by the probe thermocouple at times t1 and t2, respectively. The presence of ice in frozen materials significantly impacts the thermal conductivities of these materials. Ice has a much higher thermal conductivity (roughly 2.0 W m1 C1) compared to liquid water (about 0.5 W m1 C1), nearly four times higher. Therefore, the precision or reliability of a thermal conductivity model for frozen materials primarily hinges on how accurately the measure of ice is predicted. Murakami and Okos (1989), in their research, explored multiple models designed for diverse nonporous food items. At temperatures exceeding the freezing point, they recommended utilizing the straightforward parallel model as the most efficient approach, they recommended the use of the simple parallel model as the most effective. This model can be expressed as: k¼

n X

k j εj

(13.29)

j¼1

Below the freezing point, Murakami and Okos (1989) proposed a combined parallel-series model for thermal conductivity. In this model, the constituents other than water are arranged in parallel with each other and both the nonwater and water components are organized perpendicular to one another. This combined parallele series model can be expressed as: 1 1  εw εw ¼ þ k ks kw

(13.30)

where, ks ¼

ns X

kj εj

(13.31)

j¼1

13.3.9 Thermal diffusivity Thermal diffusivity has a pivotal function in calculating the rate at which heat is transferred within a solid food material, irrespective of its geometry. When physical attributes are considered, the mathematical representation of the transfer of energy within a food substance can be described using the well-known Laplace equation, which is provided as follows (Glavina et al., 2006): vT ¼ aV2 T vt

(13.32)

where V2T signifies the Laplacian operator applied to temperature, which quantifies the temperature’s spatial variation of temperature. a is the proportionality constant, known as thermal diffusivity, and it has SI units of square meters per second (m2/s),

340

Low-Temperature Processing of Food Products

and vT/vt donates the rate of temperature change over time. Physically, thermal diffusivity measures the capability of a material to conduct heat in relation to its capacity to retain heat. It provides important insights into how quickly temperature changes propagate within a material. Directly measuring thermal diffusivity in food materials is not a widespread practice. Additionally, there is no widely applicable model to make direct predictions of thermal diffusivity for temperatures under the freezing point. For a frozen food item, the apparent thermal diffusivity is typically measured using established values of density, thermal conductivity, and specific heat. The definition for apparent thermal diffusivity is as follows (Holdsworth et al., 2008): ae ¼

k rce

(13.33)

In this equation, ae, k, r, and ce denote the apparent thermal diffusivity of the frozen food, the thermal conductivity, the density, and the specific heat, respectively. The calculation of k, r, and ce can be performed utilizing the equations and methodologies outlined in the preceding sections.

13.4

Analytical methods

Mathematically modeling the freezing process in food and related phenomena presents unique challenges. Near the freezing point, significant and abrupt changes occur in thermophysical characteristics like specific heat and thermal conductivity. Consequently, this leads to a complex PDE characterized by high nonlinearity, making it a formidable challenge to solve. In the case of objects with intricate or irregular shapes, predicting the progression of the freezing boundary can be notably uncertain. Therefore, modeling freezing food is an intricate and multifaceted process because of the numerous intertwined factors and intricate mathematical relationships involved in the process. Researchers continue to explore and study these phenomena to improve our understanding and ability to predict freezing behavior in various food products (Alexiades, 2018; Delgado & Sun, 2001).

13.4.1

Governing equations

In the straightforward scenario of the transfer of heat within a solid food substance, the Fourier heat conduction equation is applicable. This equation describes the process of heat conduction in solid materials and is a fundamental tool for understanding how heat propagates through a material (Finlay, 2019). rc

vT ¼ VðkVTÞ þ q vt

(13.34)

Design and simulation of freezing processes

341

13.4.2 Analytical solution for the Stephane problems The circumstance that all phase transitions and the release of latent heat occur at a single temperature is referred to as the Stefan problem. For certain simplified scenarios, analytical solutions have been developed. While these solutions may have limited practical applicability, they are valuable for verifying the accuracy of numerical calculations. One such analytical solution is Plank’s pseudo-steady state solution (McNabb et al., 1990). This solution is applicable to a hypothetical scenario where specific heats are assumed to be zero and can be represented in the subsequent format: tplank ¼

  rLf R Bi
 1þ 2 EFreeze h Tf  Ta

(13.35)

where r denotes the material’s density (kg$m3), Lf stands for the latent heat of phase change per unit mass of the food material (J$kg1), Tf denotes the initial freezing temperature (K), Ta signifies the environmental temperature (K), R corresponds to half of the object’s dimension (m), h represents the heat transfer coefficient t (W m2 K1), EFreeze is the shape factor specific to freezing processes, and Bi denotes the Biot number, calculated as (hR/k) where k is the material’s thermal conductivity (Chourasia & Goswami, 2007). In the provided equation, the shape factor EFreeze assumes various values based on the specific geometry of the object being considered: For slabs, EFreeze is equal to 1; for infinite cylinders, EFreeze takes a value of 2; and for spheres, EFreeze is set to 3. Additionally, analytical equations are accessible for calculating the EFreeze shape factor when dealing with more intricate multidimensional regular shapes like finite cylinders, infinite rectangular rods, and rectangular bricks. These expressions account for the specific geometry of these objects and provide a means to calculate the proper value of EFreeze for these shapes in the context of the Stefan problem. Empirical solutions have been developed for cases where specific heat is non-zero, and these solutions have been derived using perturbation methods (Riley et al., 1974). Additionally, researchers have proposed several semi-empirical relations associated with the original solution of Plank’s equation to account for finite specific heat and the gradual latent heat release (Pham, 2001). One of the easiest and most precise adaptations entails substituting the term Lf (Tf  Ta) in Plank’s equation (Eq. 13.35) with the summation of the heat load-to-temperature difference ratios for both the precooling and freezing phases. This modification is represented as:


Qprecooling = DTprecooling Þ þ Qfreezing = DTfreezing



(13.36)

This adjustment allows for a more accurate representation of both finite specific heat and gradual latent heat release contributions during both the precooling and freezing phases of the process (Pham, 1986a, 1986b).

342

Low-Temperature Processing of Food Products

13.5

Empirical solutions

In the context of this solution approach, approximate methods are those that are derived from simplified models of reality. These methods often break down the process of freezing food materials into separate phases, encompassing cooling and phase transition steps, making certain assumptions to simplify the calculations. On the other hand, empirical methods encompass the utilization of empirical parameters, typically obtained through fitting the curve to the experimental results or numerical data. These methods may not rely on a comprehensive theoretical model but are based on observed trends and relationships. Novel approximate and empirical techniques strive to forecast freezing durations for a diverse array of food items, while considering fluctuations in thermal characteristics, geometrical configurations, and freezing environments. Most of such strategies build upon the analytical solution of Plank’s equation and strive to focus on the limitations of this model, particularly addressing issues such as sensible heats that are not zero both above and below the freezing point, along with the gradual progression of the phase transition (Pham & Pham, 2014a, 2014b, 2014c). In the present work, the focus will be on discussing some of the most widely applicable and rigorously validated methods within the realm of food freezing prediction. These methods have been developed to provide accurate estimates of freezing times while considering a range of factors that affect the process.

13.5.1

Cleland and Earle’s empirical method

Cleland and Earle were pioneers in developing an empirical method for predicting freezing times systematically. Their approach considered the influence of sensible heat effects and was supported by a comprehensive dataset that encompassed a broad spectrum of conditions pertinent to the food sector. They formulated prediction methods for the three fundamental geometries (infinite slabs, infinite cylinders, and spheres) in the following manner (Cleland & Earle, 1984a, 1984b): tf ¼

    rDH10 2P1 R 4P2 R2 1:65Ste T c  Ta
 þ ln 1 h kf kf Tref  Ta EFreeze Tf  Ta

(13.37)

where, P1 ¼ 0:5½1:026 þ 0:5808Pk þ Steð0:2296Pkþ0:1050Þ

(13.38)

P2 ¼ 0:125½1:202 þ Steð3:410Pkþ0:7336Þ

(13.39)


 Pk ¼ cu Ti  Tf =DH10

(13.40)


 Ste ¼ cf Tf  Ta =DH10

(13.41)

Tref ¼ 263:15Kð  10  CÞ

(13.42)

Design and simulation of freezing processes

343

In this equation, DH10 represents the alteration in enthalpy of the material in joules per kilogram (J$kg⁻1) in the temperature range from the freezing point (Tf) down to 10 C. Instead of using the freezing latent heat, DH10 is employed to compute the Stefan (St) and Plank (Pk) values. This substitution is made because measuring the latent heat separately from the sensible heat can be quite challenging. St and Pk numbers are dimensionless and quantify the extent of precooling and subcooling impacts, respectively. These influences are primarily factored into the empirical correction coefficients denoted by parameters P1 and P2.

13.5.2 Mascheroni and Calvelo’s approximate method Mascheroni and Calvelo’s approach, introduced in 1982, is one of the approximate techniques discussed within this study. This method divides the overall freezing duration into distinct periods, incorporating precooling (starting from the initial product temperature to reach the freezing point), the phase transition, and subcooling (from the freezing temperature to reach the final product center temperature) phases. The duration of the phase transition is determined using Plank’s equation (Eq. 13.35), which accounts for the latent heat release during freezing (Mascheroni & Calvelo, 1982). Meanwhile, the durations for precooling and subcooling are determined using analytical formulas derived from the research conducted by Carslaw et al. (1962). These analytical expressions make certain simplifying assumptions, presuming a consistent initial temperature and unchanging thermal characteristics throughout both the precooling and subcooling intervals. tf ¼ tprecool þ tPlank þ tsubcool

(13.43)

The precooling and subcooling expressions in Mascheroni and Calvelo’s method involve infinite series, making it necessary to use a computer program or graphical solution to calculate these periods. This complexity has limited the widespread adoption of this method. However, the approach of dividing the total freezing time into cooling and phase change periods, as used in Mascheroni and Calvelo’s method, serves as the foundation for simpler methods developed by researchers such as Pham (1984, 1986a, 1986b), Ilicali and Saglam (1987) and Lacroix and Castaigne (1988). These methods build upon the concept of separating cooling and phase change times, making them more accessible and practical for estimating freezing times. In the following sections, the details of Pham’s methods (Pham 1984, 1986a, 1986b) will be introduced.

13.5.3 Pham’s method 1 (1984) Pham (1984) introduced the subsequent mathematical equation: tf ¼

rR EFreeze

      Lf DH1 Bi1 Bi2 DH3 Bi3 1þ 1þ 1þ þ þ h DT1 3 DT2 2 DT3 3 

(13.44)

344

Low-Temperature Processing of Food Products

where
 DH1 ¼ cu Ti  Tfav

(13.45)


 DH3 ¼ cf Tfav  Te

(13.46)


ðTi  Ta Þ  Tfav  Ta DT1 ¼ Ti  Ta ln Tfav  Ta

(13.47)

DT2 ¼ Tfav  Ta

(13.48)




 Tfav  Ta  ðTe  Ta Þ DT3 ¼ Tfav  Ta ln Te  Ta Bi1 ¼

1 2



hR hR þ ku kf

Bi2 ¼ Bi3 ¼

hR kf

(13.49)

 (13.50)

(13.51)

Tfav represents the average freezing temperature or the centroid of the region beneath the latent heat peak. This parameter is particularly important for products abundant in water and is determined in standard freezing conditions encountered in commercial settings. For such foods, Tfav can be approximated as follows: Tfav ¼ Tf 15

(13.52)

Te stands for the mean temperature of the product upon completion of the freezing procedure. Its estimation can be achieved by assuming a linear temperature distribution, which is given by the following formula: Te ¼ Tc 

Tc  Ta 4 2þ Bi3

(13.53)

The expression for Te provided in Eq. (13.44) strictly applies to slabs, but for simplicity, it is also commonly used for other geometries. It is worth noting that all temperatures in these equations can be either in Kelvin (K) or degrees Celsius ( C). Eq. (13.44) essentially represents a variation of Eq. (13.43), wherein the durations of precooling and subcooling phases are approximated through analytical expressions. Like Mascheroni and Calvelo’s method (Mascheroni & Calvelo, 1982), Pham’s

Design and simulation of freezing processes

345

method (Pham, 1984) does not rely on parameters derived through the process of fitting freezing time data to a curve. Therefore, it may be categorized as an approximate approach rather than an empirical technique. The utilization of logarithmic mean temperature differences, the average freezing temperature, the average product temperature, and parameters like Bi1/3 and Bi3/3 for cooling all stem from analytical assessments, highlighting the method’s foundation in theoretical principles.

13.5.4 Pham’s method 2 (1986) Pham’s method from 1986 (Pham, 1986a, 1986b) can be expressed as follows: tf ¼

rR EFreeze



DH1 DH2 þ h DT1 DT2

 1þ

Bif 2

 (13.54)

In the provided equation, DH1 represents the specific enthalpy change during the precooling period, while DT1 denotes the temperature difference for this phase. Similarly, DH2 stands for the specific enthalpy change during the combined freezing and subcooling period, with DT2 representing the temperature difference for this phase. These values, DH1, DT1, DH2, and DT2, can be determined using the following expressions:
 DH1 ¼ rcu Ti  Tfm

(13.55)


  DH2 ¼ r Lf þ cf Tfm  Tc

(13.56)

Ti þ Tfm  Ta 2

(13.57)

DT1 ¼

DT2 ¼ Tfm  Ta

(13.58)

Tfm refers to an approximate average freezing temperature, and its definition differs from that of Tfav in Pham’s 1984 approach. In the case of most moisture-laden biological substances, the following equation has been proposed to calculate Tfm: Tfm  T0 ¼ qfm ¼ 1:8 þ 0:263qc þ0:105qa

(13.59)

Eq. (13.54) can be seen as a further development of Plank’s formula (Eq. 13.35), where DH1/DT1 accounts for the precooling time, DH2/DT2 represents the duration of phase transition and subcooling, while the expression 1 þ Bif/2 reflects the impact of internal heat transfer resistance. Tfm denotes the product temperature averaged over the duration, encompassing both the phase change and subcooling. Within the formula for Tfm, the segment associated with qc captures the influence of the subcooling duration on the average product temperature, whereas the portion including qa is construed as an adjustment for the temperature profile within the frozen materials throughout the phase change and subcooling periods. In Pham (1986a, 1986b) method, the only empirical parameters are the three constants found in Tfm.

346

Low-Temperature Processing of Food Products

13.6

Numerical solutions

Robust numerical methods have the capacity to yield accurate and reliable solutions for a wide array of physical challenges, provided that all pertinent physical phenomena are appropriately considered. These methods achieve this via subdividing both space and time, effectively converting the governing PDEs into a set of algebraic equations that can subsequently be resolved. These methods achieve this by subdividing both spatial and temporal domains, thereby transforming the controlling PDEs into a collection of algebraic expressions that can subsequently be resolved. In scenarios where the freezing of a material is primarily dictated via heat transfer, the key formula in play is the heat conduction relation. Eq. (13.34) numerically consists of a two-step process: First, the space domain is discretized, resulting in a collection of ordinary differential equations (ODEs) that relate the temperatures at nodes. Next, this system of ODEs is solved. The ODEs may be represented in matrix notation as: C

dT þ KT ¼ f dt

(13.60)

In this equation, T represents a vector containing the temperatures at various nodal points, C corresponds to the comprehensive capacitance matrix that encompasses the specific heat capacity denoted by c. K stands for the universal conductance matrix involving k, that is, the thermal conductivity. f denotes the overall forcing matrix, comprising predefined elements related to heat generation and boundary conditions. The specific structure of Eq. (13.60) relies on the choice of spatial discretization method employed, with the most prevalent approaches encompassing the finite difference method (FDM), finite element method (FEM), and finite volume method (FVM). The selection of one of these methods determines the particular form of the equation used for solving heat transfer problems in discrete spatial domains (Pham & Pham, 2014a, 2014b, 2014c).

13.6.1

Numerical solution: Space stepping

13.6.1.1 Finite difference method Out of the three methods of discretization, the FDM holds the distinction of being the oldest, even though FVM might have been employed in an informal manner previously. FDM is especially suitable and effective for addressing problems characterized by simple geometric shapes such as cylindrical structures, flat slabs, or entities resembling bricks. When dealing with shapes that closely approximate regular geometries, FDM can be further enhanced by employing a boundary-fitted orthogonal grid, which offers notable advantages over the unstructured meshes commonly associated with FEM or FVM. FDM entails the placement of a structured grid consisting of organized nodes distributed throughout the computational domain. Temperature derivatives across these nodes are then computed using central differences, enabling the calculation of spatial gradients (Califano & Zaritzky, 1997; Pham, 2006).

Design and simulation of freezing processes

347

As an example, when considering heat transfer in one dimension across the thickness of a solid slab, Eq. (13.34) can be expressed as follows: vT v rc ¼ vt vx



vT k vx

 þq

(13.61)

When utilizing a grid of nodes spaced uniformly at Dx on the slab, the temperature gradient between node i and node i þ 1 is formulated as follows:   vT Tiþ1  Ti ¼ vx þ Dx

(13.62)

Likewise, in the segment between nodes i  1 and i, the temperature gradient can be expressed as:   vT Ti  Ti1 ¼ vx  Dx

(13.63)

Under these conditions, Eq. (13.34) can be represented as: rc

vTi kþ ðTiþ1  Ti Þ  k ðTi  Ti1 Þ ¼ þq Dx2 vt

(13.64)

rc

vTi k Ti1  ðk þ kþ Þ Ti þ kþ Tiþ1 ¼ þq vt Dx2

(13.65)

When all of these equations are compiled for nodes 1, 2, and so forth, they lead to the matrix differential equation represented by (Eq. 13.60). In this equation, C takes the form of a diagonal matrix incorporating components such as rc, while K assumes the structure of a tridiagonal matrix, encompassing elements like k/Dx2, (k þ kþ)/Dx2, and kþ/Dx2. Additionally, f includes elements originating from heat generation or heat fluxes occurring at the boundaries. This matrix differential equation can be solved (integrated) using a time-stepping approach, allowing for addressing heat transfer issues within the specified domain (Pham, 2006; Sun, 2005). When employing the FDM, challenges arise when discretizing a boundary condition of the Neumann type. In such cases, the surface heat flux is directly assigned to the surface node, whereas the heat flux on the interior side of the surface node is imposed at a location Dx/2 apart, creating an asymmetric condition. Similarly, if grids with uneven spacing are employed, it becomes essential to guarantee that alterations in grid spacing occur gradually and a considerable number of nodes are employed to mitigate inaccuracies. Additionally, a practical issue arises when dealing with extremely elevated heat transfer coefficients, as this can lead to temperature instabilities at the surface nodes because of an exceptionally high surface heat flux. These considerations highlight the need for careful handling of boundary conditions and grid spacing in FDM simulations (Sun, 2005).

348

Low-Temperature Processing of Food Products

A more effective treatment of boundary conditions is achieved through a controlvolume approach within the finite difference framework, which rigorously enforces the conservation law at all nodes. In this modified version, the solid is initially divided into control volumes, each having a thickness of Dx (although equal volumes are used for simplicity, this is not mandatory). Nodes are situated in the middle of each control volume. As a result, the boundary node is not located directly at the surface boundary but rather at some distance within the solid. The thermal resistance between the environment and node one is given by 1/h þ [(Dx/2)/k]. The boundary condition is incorporated through the thermal balance of the first control volume (Pham, 2006; Pham and Pham, 2014a, 2014b, 2014c): rc

vT1 kþ ½ðT2  T1 Þ=Dx  ½ðT1  Ta Þ=ð1=h þ Dx=2k Þ þq ¼ Dx=2 vt

(13.66)

By setting the distance between the surface and the first node as Dx/2, this effectively places it midway from the surface. This adjustment reinstates second-order precision to the nodes that are close to the boundary. For a Dirichlet boundary condition, the reciprocal of the heat transfer coefficient (1/h) is established as zero. The temperature denoted as T1 indicates the temperature at a location beneath the surface. If necessary, the temperature of surface can be determined by interpolating between Ta and T1, considering the specific requirements of the problem (Sun, 2005).

13.6.1.2 Finite element method In the case of geometries that do not conform to a regular orthogonal grid, both the FEM and FVM offer greater flexibility compared to the FDM. Within the FEM, the object is divided into discrete elements, which have certain shared nodes. In each element, the temperature distribution at a given position, denoted as x, is estimated using interpolation techniques (Segerlind, 1991; Zienkiewicz et al. 2005, 2013): T ðx; tÞ ¼ N T ðxÞTN ðtÞ

(13.67)

In the equation provided, TN(t) represents vectors containing the temperatures of nodes, and N(x) represents a vector comprising shape functions. These shape functions are actually position-dependent coefficients that facilitate the estimation of the approximate temperature at any point inside the element by interpolating the temperatures at the nodes. For instance, in the case of a one-dimensional linear element that constitutes a segment defined by two nodes, the temperature T at any point P inside the segment is determined through linear interpolation between the endpoints A and B: T ¼ ð1  xÞTA þ xT B

(13.68)

Design and simulation of freezing processes

349

Therefore, 1x

N¼

! (13.69)

x

In the Galerkin FEM, it is essential that the weighted differences in the heat conduction equation, represented by Eq. (13.34), become zero when identical shape functions are employed as weighting functions:  vT N rc VðkVTÞ  q dU ¼ 0 vt 

Z U

(13.70)

By substituting Eq. (13.67) into Eq. (13.70) and solving for the relevant variable, a correlation between the temperatures at the nodes is derived: dT e þ K ðeÞ T ðeÞ ¼ f ðeÞ dt Z Ce ¼ rcNN T dU

Ce

(13.71)

(13.72)

U

and for cases involving a convective boundary condition:  B ¼ VT N ¼

vN vN vN vx vy vz

Z K ¼ e

 (13.73)

Z T

hNN T ds

kBB dUþ U

(13.74)

s

Z fe ¼

hTa Nds

(13.75)

s

In this context, T (e) represents the vector of temperatures at the nodes, C (e) is referred to as the capacitance matrix, K (e) is the conductance matrix, and f (e) is the forcing vector. The forcing vector encompasses all elements that do not rely on the temperatures at the nodes, containing factors related to boundary constraints and heat production. U signifies the domain of the elements, while S denotes its boundary. The superscript (e) signifies that this correlation pertains to the nodes inside a single item. Aggregating this correlation across all elements yields the conventional matrix as described in Eq. (13.60). In FEM, the interpretation of the nondiagonal components in the capacitance matrix, as shown in Eq. (13.60) might not be immediately intuitive

350

Low-Temperature Processing of Food Products

and stems from how heat capacity is allocated within the element. Nonetheless, a basic physical explanation can be provided to help understand the underlying principles of the approach. Within an element, the distribution of thermal energy (rcT) at each location is allocated to the individual nodes using the shape functions as a basis, greater energy is assigned to the closest node while diminishing amounts are allocated to the more distant nodes. Following the change of temperature at node i, the temperature profile within the element is affected, leading to an altered distribution of heat energy within the material. Consequently, the term Cij signifies the impact of a temperature shift, Ti, at node i on the distribution of thermal energy allocated to node j (Pham & Pham, 2014a, 2014b, 2014c). When employing the lumped capacitance approach FEM adaptation, all the thermal energy alterations caused by a temperature variation at node i are assigned solely to node i, resulting in a diagonal capacitance matrix (C). Essentially, this approach assumes that the mass of each element is concentrated entirely at its nodes. This formulation offers several advantages compared to the Galerkin formulation, including simplicity and improved stability (Banaszek, 1990). It proves especially valuable when addressing the peak of latent heat that occurs during the freezing process, as will be demonstrated subsequently. Like any numerical approximation method, it is essential to carefully plan the grid design in the FEM to achieve optimal precision. The grid should be more densely populated in regions with sharp thermal gradients and where the elements need to maintain a reasonably regular shape without excessive skewness or elongation. In contemporary commercial FEM software, automatic grid adaptation features are often available to address these considerations and ensure that the grid is appropriately designed (Sun, 2005).

13.6.1.3 Finite volume method The concept of FVM, although relatively new in terminology, has been employed in some rudimentary form by engineers in their work for a considerable period, even prior to the emergence of computing technology and the advent of computers, owing to the lucidity of its conceptual framework. In practice, every engineering PDE can be obtained by approaching the infinitesimal limit of a finite volume model (Bird et al., 2006). The fundamental element of FVM was similarly utilized in the control volume rendition of FDM. Nonetheless, in the current work, we will refer to this specific submethod will be referred to as “control volume FDM” rather than FVM due to the substantial distinctions in its applicability and computational efficiency. FDM relies on structured arrays that are orthogonal, resulting in tridiagonal matrices, whereas FVM does not necessitate such regularity and can, therefore, be applied to nonuniform or irregular spatial configurations (Sun, 2005). Within the framework of FVM, the region of interest is partitioned into control volumes, with each one linked to a central node. These control volumes and nodes need not follow a regular grid, allowing for significant flexibility in handling complex shapes, similar to the FEM. The heat conservation equation is considered valid across the entirety of each control volume (Pham, 2006):

Design and simulation of freezing processes

Z  U

 vT rc VðkVTÞ  q dU ¼ 0 vt

351

(13.76)

By applying the divergence theorem, the second term within the volume integral can be converted into an integrated surface flux along the volume’s boundaries:  Z  Z vT  q dU n•ðkVTÞdS ¼ 0 rc vt U

(13.77)

s

In the equations above, dS represents a surface element, and n denotes the outward normal vector associated with this surface element. The initial term corresponds to the rate of enthalpy increase within the control volume and is estimated as follows (Pham, 2006; Pham & Pham, 2014a, 2014b, 2014c): Z rc U

vT vTi dU z d Vrm cm vt vt

(13.78)

The subsequent term in Eq. (13.77) accounts for the cumulative sum of all heat fluxes entering the control volume across its boundaries. The heat flux of each surface can be computed using the average temperature gradient that is perpendicular to that particular surface. Several techniques have been suggested to approximate this average temperature gradient, all of which lead to linear expressions incorporating the nodal temperatures in the vicinity of the surface under consideration. Therefore, Eq. (13.77) can be replaced with the following equation: N vTi X ¼ kBij Tj þ qdV vt j¼1

(13.79)

vT vTi dU z d Vrm cm vt vt

(13.80)

d Vrc Z rc U

The coefficients Bij in the equation above depend on the specific arrangement of nodal points in the control volume. For each node i, a similar equation is available, and this process ultimately leads to Eq. (13.60). Unlike Galerkin FEM, but similar to FDM or lumped capacitance FEM, the matrix C in Eq. (13.60) is diagonal, which has its own set of advantages (Sun, 2005).

13.6.2 Numerical solution: Time stepping Once a set of ODEs relating to nodal temperatures has been derived through the discretization of the spatial domain (as shown in Eq. 13.60), the solution proceeds through a

352

Low-Temperature Processing of Food Products

sequence of time increments, commencing with established initial conditions. Various techniques exist for solving ODEs, including the RungeeKutta approach, backward differentiation formulas, and the CrankeNicolson method, which employs central differences. In heat conduction simulations, a common process involves using timeaveraged nodal temperature values to compute heat fluxes (Sun, 2005). C

T New  T ¼ KT þ f Dt

(13.81)

with T ¼ aT New þ ð1  aÞT

(13.82)

In the equation provided, the superscript New indicates temperatures at the conclusion of the time step that is yet to be determined. The parameter a can take values between 0 and 1. When a is equal to 0, it corresponds to the Euler method for timestepping. When a is equal to 1, it corresponds to the backward stepping or fully implicit strategy. When a is equal to 0.5, it corresponds to the CrankeNicolson approach, which is quite popular because it offers good accuracy while maintaining unconditional stability (Scheerlinck et al., 2001). The Euler approach can be expressed as follows:
 CT New ¼ TDt KT þ f

(13.83)

In FDM, FVM, and lumped mass FEM, the matrix C is diagonal, allowing the equation above to be solved independently for each node, yielding TNew: TiNew ¼ Ti Dt

X

! Kij Ti Tj þ fi

(13.84)

j

13.6.2.1 Time stepping in FDM When a is set to 0, the temperature field Ti, which has been computed beforehand and is known, is employed to determine the gradients. Therefore, the temperatures of nodes can be calculated sequentially. For instance, consider the interior nodes within a regularly spaced 1-D FDM grid: TiNew ¼ Ti þ

kþ ðTiþ1  Ti Þ  k ðTi  Ti1 Þ q Dt þ Dt rcDx2 rc

(13.85)

While the Euler method is straightforward to implement and is advisable for basic programs or small-scale problems, it has a first-order accuracy and can be unstable for kDt 1 > rcDx2 2

(13.86)

Design and simulation of freezing processes

353

In two and three dimensions, the stability restrictions become even more stringent: the upper limit for the time step decreases to 1/4 and 1/6, respectively. Additionally, even in cases where the Euler method is stable, within these limits, its accuracy deteriorates rapidly as the time step Dt increases. It is important to note that the critical time interval reduces quadratically with the spatial interval Dx, which means that finding a solution becomes excessively time-consuming for the highly finepartitioned domains. With a set to 1 (indicating a backward difference approach), the gradients are computed using the new temperatures, which remain to be determined. When a is equal to 0.5, signifying a central difference or CrankeNicolson method, the mean temperature, calculated as the average of both the old and new temperatures, is employed. The CrankeNicolson scheme is highly favored because it blends unconditional stability with accuracy at the second-order level. However, even when utilizing the CrankeNicolson approach, large, slow-decaying oscillations can occur when the ratio of thermal conductivity (k), time step (Dt), and space interval (Dx) is too large. For any a value other than 0, Eq. (13.81) includes unknown nodal temperatures on both sides, and these equations need to be rearranged to shift all the undetermined temperatures to the left-hand side of the equations (Crank & Nicolson, 1996). The appropriate efficiency of time-stepping in FDM is attributed to the structured orthogonal grid configuration. In the context of one-dimensional FDM, every equation encompasses solely three adjacent temperature values: Ti1, Ti, and Tiþ1. The matrix equation that emerges from this process possesses a tridiagonal structure and can be conveniently resolved using techniques such as the tridiagonal matrix algorithm (Teukolsky et al., 1992). In cases involving regular geometries with two or three dimensions (such as finite cylinders, rods, or brick shapes), FDM employs an orthogonal grid for implementation. However, when applying any time-stepping technique other than Euler’s, the resulting system of equations ceases to be tridiagonal due to the fact that the temperature of each node is influenced by the temperatures of its neighbors. In two dimensions, it is influenced by four neighboring nodes, and in three dimensions, it is influenced by six. To circumvent the resolution of extensive and intricate matrix equations, the alternating direction method is frequently employed. This approach encompasses performing calculations independently in the x, y, and z directions, essentially breaking down the problem into a sequence of pseudo-one-dimensional solutions (Peaceman & Rachford, 1955). In the first sweep along the x-direction, one row of nodes at a time is taken into consideration, and an array of intermediate temperature values denoted as T* is calculated. This calculation uses a time increment of Dt/2. The T* intermediate values are subsequently employed to represent the gradients of the temperature in the x-direction, while the currently known T values are utilized to represent temperature gradients in the y-direction (Sun, 2005). Tij ¼ Tij þ

Dt 2



vx T  þ vy T þ

q rc

 (13.87)

354

Low-Temperature Processing of Food Products

where,

 kþ Tiþ1;j  Ti;j  k Ti;j  Ti1;j vx T ¼ rcDx2

(13.88)



 kþ Ti;jþ1  Ti;j  k Ti;j  Ti;j1 vy T ¼ rcDy2

(13.89)



In the second sweep along the y-direction, a single column of nodes at each time iteration is taken into consideration. The discretized form of the Fourier equation is written down for the next Dt/2, utilizing the newly acquired, unidentified values to describe temperature gradients in the y-axis direction. Meanwhile, the temperature gradients in the x-direction are expressed using the already established intermediate values T*. This process results in a matrix equation with a tridiagonal structure for every column, which can be resolved to obtain the new temperature vector. The alternating direction method thus allows for the step-by-step calculation of temperature changes in different directions, reducing the size of the matrix equations and simplifying the solution process (Sun, 2005): TijNew ¼ Tij þ

 Dt
vx T  þ vy T New 2

(13.90)

Lee’s three-level scheme for FDM can also be seamlessly integrated with the alternating direction method (Lees, 1966). This method effectively addresses the calculation of temperature changes in different directions, employing tridiagonal matrix equations for each row and column to solve for the new temperature values, thereby simplifying the solution process (Pham, 1987a, 1987b).

13.6.2.2 Time stepping in FEM and FVM In FEM and FVM, the grid is frequently unstructured. Unless the Euler scheme is used, each time increment necessitates the solution of matrix equations featuring sparse matrices, as opposed to the tridiagonal matrices found in other cases. It is crucial to emphasize that there is no benefit in applying the Euler approach in conjunction with Galerkin FEM. This is because the capacitance matrix (C) lacks a diagonal structure, rendering it impossible to compute individual nodal temperatures. However, within the lumped capacitance FEM, C adopts a diagonal form, enabling the explicit and separate calculation of new temperatures, similar to the procedures in FDM and FVM. While the time-stepping techniques grounded on Eq. (13.81) have gained extensive usage, alternate generic ODE solving methods, encompassing both explicit and backward approaches, provide a different perspective for addressing highly nonlinear issues stemming from abrupt alterations in thermal properties near the freezing point (Shampine & Reichelt, 1997). In a study conducted by Scheerlinck et al. (2001), they undertook an examination comparing the effectiveness of explicit RungeeKutta

Design and simulation of freezing processes

355

methods, the implicit backward difference technique, and the CrankeNicolson scheme. This comparison was conducted in conjunction with the enthalpy formulation and Kirchhoff transformation. Their findings suggest that, when evaluating accuracy, stability, and speed collectively, both fifth-order backward difference and Cranke Nicolson schemes are more favorable than explicit ones.

13.6.3 Considering changes in physical properties The primary obstacle when numerically simulating the freezing process lies in effectively managing the abrupt alterations in material characteristics occurring in proximity to the freezing temperature. This includes effectively managing the progression of the release of latent heat e and, to a lesser extent, variations in thermal conductivity.

13.6.3.1 Addressing the release of latent heat The primary challenges when numerically addressing the heat transport equation arises from effectively managing the considerable latent heat fluctuations occurring within an exceedingly limited temperature range. The techniques for addressing phase change can be categorized into two main groups: stationary grid approaches and mobile grid approaches. In the mobile grid strategy, the object is partitioned into two distinct regions: one is the frozen zone, and the other is the unfrozen zone. Certain control volume boundaries, element boundaries, or nodes are positioned at the freezing interface and are allowed to move along with it (Sultana et al., 2018). Moving grid methods offer the advantage of providing precise and reliable solutions for temperature profiles and the position of the ice front. However, they have limitations in terms of flexibility, especially when dealing with foods that do not exhibit an abrupt transition temperature yet instead freeze progressively. Defining the freezing front in such cases can be challenging, particularly for complex-shaped foods where determining the location of the boundary and adjusting the grid accordingly becomes problematic. Consequently, the current work will focus on fixed grid techniques, which can still pinpoint the freezing front by employing interpolation techniques to identify the location at the freezing point is applicable (Pham, 1986a, 1986b; Udaykumar et al., 2002). Among the fixed grid strategies, certain approaches consider latent heat as a contributing factor, represented by the variable q in Eq. (13.34). However, this method is not well-suited in the majority of food products because latent heat is generated over during a broad temperature spectrum and is challenging to differentiate from sensible heat (Voller & Swaminathan, 1991). Therefore, we would not delve further into these approaches. The remaining methods fall into two categories: methods based on apparent specific heat and techniques employing enthalpy. These methods are more versatile as they can handle both abrupt and gradual phase changes, making them generally applicable.

13.6.3.2 Effective specific heat methods Methods based on effective or apparent specific heat involve incorporating latent heat alongside sensible heat to construct a specific heat curve that exhibits a notable peak in the vicinity of the freezing temperature. Due to the substantial variations in specific

356

Low-Temperature Processing of Food Products

heat, an iterative process is required at each time step: the specific heat value at each node is approximated, typically derived from the current temperatures. This value is then used to compute the C matrix, and subsequently, Eq. (13.81) is solved to determine the updated nodal temperatures. Following this, the average temperature during the recent time interval is determined, followed by a re-evaluation of the specific heat using the specific heat-temperature correlation. This iterative process is then repeated. Achieving convergence with this method can be challenging, and there is always a potential for underestimating latent heat, a situation known as “jumping the latent heat peak.” This situation arises when the temperature of a node surpasses the apex in the apparent specific heat curve. As a consequence, the average specific heat value, positioned between the initial and final temperatures, consistently falls below the peak value. Consequently, this leads to an overestimation of the temperature alteration. Because of these issues, it is advisable to refrain from employing the apparent specific heat method. Although various approximate techniques have been suggested for estimating effective specific heat in the proximity of the solidification temperature, none of them have demonstrated complete satisfaction. Consequently, the enthalpy formulation has gained popularity as an alternative approach (Pham, 2006).

13.6.3.3 Enthalpy method The fundamental heat conduction equation may be expressed as follows: r

vH ¼ VðkVTÞ þ q vt

(13.91)

where H represents the specific enthalpy: ZT H¼

Capp dq

(13.92)

Tref

Tref represents a reference temperature that can be chosen arbitrarily, while capp denotes the apparent specific heat. Following the standard transformations applied in FDM, FEM, and FVM, the obtained matrix equations are: M

dH þ KT ¼ f dt

(13.93)

Within FDM, FVM, and lumped capacitance FEM, it is customary to depict M as a diagonal matrix, which facilitates the calculation of individual nodal enthalpies, labeled as Hi: dt HiNew ¼ Hi þ Mii

"

N
X j¼1



#

Kij Tj þ fi ; i¼ 1to N

(13.94)

Design and simulation of freezing processes

357

In this equation, all the elements on the right side are already established and represent the current values. This approach was originally proposed for FDM by Eyres et al. (1946). For precise results in any implicit (a > 0) solution of Eq. (13.93), it is necessary to perform iteration at every time increment. The DH enthalpy change vector, defined as HNew  H, is incrementally modified until the residual of Eq. (13.93) reaches an acceptable level. While a progressive substitution technique such as Gauss-Seidel may be employed, it tends to converge quite slowly. Alternatively, a Newtone Raphson iteration method is a more effective approach (Voller et al., 1990). Conceptual challenges of notable magnitude are encountered when discretizing highly nonlinear problems, such as those related to phase change, using Galerkin FEM. The Galerkin method operates under the assumption that temperature is distributed within the element according to the shape function, expressed as T ¼ NTT, where T represents the nodal temperature vector. However, since H is a nonlinear function reliant on T, it is inaccurate to assume that H is distributed following the formulation H ¼ NTH. This inaccuracy is particularly pronounced in the vicinity of the freezing point; within a 1-D element, nodal temperatures are situated slightly above and below the freezing point. However, when transforming Eq. (13.91) into a Galerkin FEM equation within the enthalpy method, this assumption becomes essential. Users of the Galerkin FEM approach in the effective specific heat method encounter difficulties when estimating an effective specific heat across both time intervals (Dt) and the spatial extent of the element’s domain. When c(T) displays a highly pronounced peak, numerical averaging techniques that entail a sampling process across the domain of the element can pose challenges. Consequently, it is advisable to opt for FVM or lumped capacitance FEM instead of Galerkin FEM in such cases (Pham, 2014a, 2014b).

13.6.3.4 Quasi-enthalpy method Pham (1985) introduced a straightforward approach that is effective in managing the latent heat peak without necessitating iterative processes. Initially designed for FDM, this method was later adapted to lumped capacitance FEM as well as Galerkin FEM (Comini et al., 1990; Pham, 1986a, 1986b). The technique is grounded in the apparent specific heat method but introduces specific heat estimation and temperature correction procedures during each time increment. Subsequent research studies have indicated that the pivotal element is the temperature correction phase. Following the acquisition of a series of updated nodal temperatures (TNew i ) derived from Eq. (13.81), alterations in the enthalpy of nodes are determined by employing ci (TNew  Ti). The calculation i of the new nodal enthalpies (HNew ) relies on the previous nodal enthalpies (Hi): i
 HiNew ¼ Hi þ ci TiNew  Ti

(13.95)

and the updated nodal temperatures are fine-tuned to
 TiCorrected ¼ T HiNew

(13.96)

358

Low-Temperature Processing of Food Products

This Eq. (13.95) ensures the conservation of enthalpy, leading to the term “quasienthalpy method” for this approach.

13.6.3.5 Variable thermal conductivity The sudden shift in thermal conductivity around the freezing temperature poses a challenge in numerical phase change modeling. When calculating the heat flux (k(Tiþ1  Ti)) between nodes i þ 1 and i, there is uncertainty about which value of thermal conductivity (k) should be employed: the thermal conductivity can be determined by evaluating it at the average temperature ((Tiþ1 þ Ti)/2), considering the mean of thermal conductivities ((kiþ1 þ ki)/2), or employing an alternative combination method like the series model (1/kiþ1 þ 1/ki)1. A more meticulous method is attained by applying the Kirchhoff transformation (Fikiin, 1996; Ezekoye, 2016): ZT u¼

k dq

(13.97)

TRef

or du ¼ k dT

(13.98)

This expression, when inserted into the Fourier equation (Eq. 13.34), results in the following equation: rc vu ¼ V2 u þ q k vt

(13.99)

The ratio rc/k signifies a temperature-dependent material attribute, which is exclusively reliant on the variable u. By consolidating all the nonlinear elements into a singular factor, this approach enables the equation to be addressed utilizing the apparent specific heat technique, which was previously elucidated (with T substituted by e and c substituted by c/k) within the framework of FDM, FEM, or FVM. In an alternative approach, the left-hand side can be reformulated with reference to enthalpy (Voller & Swaminathan, 1993): rc vH ¼ V2 u þ q k vt

(13.100)

Applying the Kirchhoff transformation can result in a significant decrease in computational time, particularly when employing iterative techniques, as it renders the K matrix constant and eliminates the need for recomputation (Sun, 2005). However, with composite materials, this transformation can pose challenges in modeling boundaries between different materials, particularly in the context of FEM. For example, in cases where two neighboring elements consisting of dissimilar materials

Design and simulation of freezing processes

359

have common nodes, u values at these locations may exhibit discrepancies contingent upon whether they are examined from one standpoint of the element or the others. Consequently, the elemental equations (as represented in Eq. 13.71) may not be combined into a global matrix equation using the customary process. Instead, each node that is common to two different materials should be handled as two distinct nodes.

13.7

Modeling coupled heat and mass transfer phenomena

Up to this point, the analysis has primarily focused on heat conduction as the exclusive mechanism dictating the freezing process of foodstuffs, as described by Eq. (13.34). In practice, phase change rarely takes place independently, with various other phenomena occurring concurrently alongside heat transfer. Moisture migration occurs at both macro and micro levels, and supercooling is a common occurrence. The application of high pressure has the potential to impact nucleation and phase alteration, giving rise to intricate stress and strain patterns. This could practically lead to concerns like the formation of cracks and alterations in the texture and other quality attributes of the food item (Pham, 2014a, 2014b). Within the realm of the food freezing process, the heat transfer phenomenon is invariably associated with mass transfer, and this interplay can have substantial impacts on both product quality and weight loss. In this part, the primary focus will be on the movement of moisture, which is the most common situation, although it is worth noting that solute transfer can also take place during immersion freezing procedures. When mass transfer is involved, conduction alone does not account for all aspects of heat transfer. In cases where mass transfer plays a role, it is essential to recognize that heat conduction alone does not explain all aspects of heat transfer. Thermal energy is additionally carried by the diffusing material, necessitating the inclusion of a secondary transport component. This concept is most accurately conveyed when using the enthalpy-based formulation of the heat transport equation (Pham, 2006): vðrHÞ ¼ VðkVTÞþVðHw m_w Þ vt

(13.101)

This equation accounts for density changes caused by mass flux imbalances, where m_ symbolizes the mass flow rate, Hw represents the enthalpy of the diffusing material, and it is assumed that the mass flux adheres to Fick’s law. _ rds Dw VW m¼

(13.102)

In this context, rds signifies the mass concentration of solid components in their dry state, W stands for the dry basis mass proportion of the diffusing material (measured in kg per kg of dry solid), and Dw denotes its effective diffusivity. This equation describes

360

Low-Temperature Processing of Food Products

the diffusion of the diffusing substance in the material over time. Hence, the equation governing mass transfer can be expressed as follows: vW ¼ VðDw VWÞ vt

(13.103)

The modeling of freezing in foods needs to consider various factors beyond heat transfer. In particular, mass transfer, moisture movement, and other phenomena play important roles in the freezing process. The interaction of heat and mass transfer can significantly impact the quality and characteristics of frozen foods. For instance, in impermeable foods such as meat, the process involves surface water evaporation and its subsequent replenishment through deep water diffusion toward the surface until the onset of freezing. Subsequently, water undergoes sublimation from the ice front located near the surface, with limited water mobility within the food product. Mass transfer predominantly takes place within a narrow surface layer, differing from heat transfer, which is distributed throughout the food (Sun, 2005). On the contrary, in permeable foods like bread and dough, moisture migration continues throughout freezing, penetrating deeply into the food structure. Each of these scenarios necessitates a unique modeling strategy to accurately capture the intricacies of heat and mass transfer throughout the freezing process. It is important to highlight that other factors like mechanical effects, gravity, pressure gradients, Soret effect (mass diffusion driven by temperature gradients), and Dufour effect (heat diffusion driven by concentration gradients) may also come into play but have been neglected in this discussion (Pham, 2014a, 2014b).

13.7.1

Mass transfer during the freezing of dense foods

Moisture within food can coexist in several phases concurrently, encompassing vapor, unbound liquid, ice, and diverse bound moisture forms, each characterized by its distinct diffusion rate. Typically, it is assumed that these phases are in thermodynamic balance with one another, but this presumption may not be valid when supercooling and kinetic impacts come into play. Because of a lack of sufficient available information, it is often simplified by assuming that moisture migration within food items can be represented using a single-phase diffusion equation, as demonstrated in Eq. (13.103), where an effective diffusivity, Dw, is employed. The equation bears a resemblance to the heat conduction equation (Eq. 13.34) in its structure and can be addressed using analogous numerical techniques such as FDM, FEM, or FVM. Moisture diffusion within dense foods is typically sluggish, and its impact on heat transfer may often be disregarded, except at the actual evaporating surface (Pham, 2006). In the precooling stage, before the occurrence of freezing at the surface, there is a balance between water evaporating from the food surface and moisture migrating from the interior to the surface. This equilibrium is represented by the equation provided.

Design and simulation of freezing processes

361

However, it is essential to consider alterations in boundary conditions and the varying scales of heat and mass transfer occurring in these scenarios.   vW ¼ kg ðPs  Pa Þ rs D w vn s

(13.104)

where rs represents the density of the solid component, n stands for the unit normal vector, kg represents the mass transfer coefficient, Ps is the partial pressure of water at the surface of food, and Pa donates the partial pressure of water in the surrounding environment. Ps is associated with the surface moisture and can be expressed in relation to it (Pham, 2014a, 2014b): Ps ¼ aw ðTs ; Ws ÞPsat ðTs Þ

(13.105)

In this context, Psat (Ts) denotes the saturated water vapor pressure at the surface temperature Ts, and aw represents the surface water activity, a factor influenced by both the surface temperature Ts, and the surface moisture content Ws. Taking into account the latent heat of vapourization, denoted as Ly, is crucial when establishing the boundary condition in the heat conduction equation (Sun, 2005): k

  vT ¼ heff ðTs  Ta Þ þ Lv kg ðPs  Pa Þ vn s

(13.106)

Here, heff represents an effective heat transfer coefficient, which may encompass the influences of radiation. The boundary conditions for both heat and mass transfer take on a nonlinear character due to the inclusion of the term Ps. This expression exhibits nonlinearity as it depends on both temperature and moisture. When employing the Euler time-stepping approach, this does not present a specific challenge, as all variables are explicitly computed from established conditions. However, for other time-stepping methods, Ps may be approximated as linear with respect to the current temperature and moisture values (Davey & Pham, 1997): Ps ¼ a1 þ b1 Ts

(13.107)

Ps ¼ a2 þ b2 Ws

(13.108)

and the terms b1Ts and b2Ws should be incorporated into the vector KT or KW within the discretized Eq. (13.60) and its equivalent for mass transfer. Another approach is to perform an iteration at each time step. Because of the substantial contrast in diffusivity between moisture and heat in dense foods, at the end of the freezing process, alterations in moisture content are limited to an extremely thin layer near the surface. To accurately simulate moisture migration, a highly detailed grid and correspondingly minute time intervals would be necessary. To address this issue, a solution involving a two-grid method has

362

Low-Temperature Processing of Food Products

been proposed. In this approach, an additional, finely detailed one-dimensional finite volume grid is placed immediately beneath the surface to simulate mass transfer. In each time increment, the primary grid, which encompasses the entire product, is employed to solve the heat flow equation initially. Subsequently, the second grid is utilized to solve the mass transfer equation (Pham, 2006). After the surface has undergone freezing (started by an initial freezing point determined based on surface water activity), water is rendered immobile, and any further internal diffusion stops. At this point, moisture begins to sublime. At first, it undergoes sublimation from the surface, and subsequently, it infiltrates through a layer of dehydrated food. The thickness of this layer increases gradually as the ice front moves back, and the speed of this progression is established by Pham and Willix (1984) and Pham and Mawson (1997). m_ ¼

Psat ðTs Þ  Pa 1=kg þ d=Dd

(13.109)

Here, d represents the thickness of the desiccated layer, and Dd denotes the diffusivity of water through this layer. The problem was tackled by modeling it via employing a one-dimensional geometry through the utilization of a front-tracking FDM (Campa~ none et al., 2001). In this particular model, the desiccated region was represented using an adaptable grid, where the spacing between increments increased proportionally with the depth of the freezing zone. On the other hand, the zone that remains undehydrated, which includes both the frozen and unfrozen regions, was simulated using a fixed grid, except for the final node, which tracked the movement of the sublimating interface. Consequently, the final spatial increment in the undehydrated region diminished as time progressed. It appears that a method based on apparent heat capacity was employed to handle the freezing front in this model (Sun, 2005). Since the desiccated layer is typically extremely thin during the freezing of dense foods, achieving accurate numerical modeling necessitates an exceedingly fine grid. In certain situations, such as when freezing initiates and the desiccated layer is essentially nonexistent, the need for an infinitely fine grid can pose challenges (Campa~none et al., 2001). In such cases, when sublimation occurs very slowly, and the desiccated layer remains exceptionally thin (less than approximately half the thickness of a control volume), it is feasible to assume pseudo-steady state conditions. This implies that the moisture vapor distribution within the desiccated layer behaves as though the sublimation front were not moving, allowing for the use of an ODE approach, which provides an adequate level of accuracy (Pham, 2014a, 2014b). dd m_ ¼ dt rs W ðdÞ

(13.110)

where W(d) represents symbolizes the moisture content at a specific depth, denoted as d. The integration of this equation can be performed for each time interval, and subsequently, the obtained d value can be inserted into Eq. (13.110) to determine the

Design and simulation of freezing processes

363

surface mass flow rate. The derived mass flow rate can subsequently be employed as part of the boundary conditions in the governing PDEs for heat and mass transfer. In cases where the desiccated layer is significantly thicker, especially for porous foods, it becomes more appropriate and accurate to represent it through a grid-based approach, such as FDM, FEM, or FVM, rather than relying on the pseudo-steady state approach.

13.7.2 Mass transfer during the freezing of porous foods The process of mass diffusion in porous food items occurs more rapidly compared to dense foods. This diffusion can be attributed to a range of mechanisms, including the molecular movement of gases within the pores of food, Darcy flow, and capillary diffusion (Datta, 2007). When foods are frozen under atmospheric pressure, the primary mechanism at play involves the diffusion of vapor through the pores of food. In this process, moisture evaporates from the warmer interior portions of the food and migrates toward the outer regions. As the temperature drops to the freezing point, the water vapor undergoes condensation and transforms into ice. Researchers like Van der have developed various study models for bread freezing, particularly focusing on the potential influence of ice formation beneath the crust on the detachment of the crust as it freezes (Hamdami et al., 2004). The widely used approach for estimating heat transfer within porous foods involves employing the evaporation-condensation model. In this model, as moisture evaporates, it absorbs latent heat, and upon subsequent condensation, this heat is liberated. Research has demonstrated that this evaporationecondensation process results in an increase in effective thermal conductivity (Bouddour et al., 1998; Sun & Hu, 2003). The effective thermal conductivity arising from the evaporation-condensation model can be expressed as shown in Eq. (13.111). kevpcon ¼ 4

L v M w D v aw Patm dPsat Rg T Patm  aw Psat dT

(13.111)

In this equation, 4 represents a factor that considers both the void fraction and tortuosity of the diffusion path and Dv is the water vapor diffusivity in air. Theoretically, the evaporationecondensation model is well-founded, and it has been indicated to accurately account for the substantial alterations in effective thermal conductivity that is observed with temperature fluctuations in porous food materials. However, in practice, the parameter 4 typically needs empirical determination through a process of curve fitting (Hamdami et al., 2004).

13.7.3 Mass transfer during immersion freezing During immersion freezing, the food is brought into a liquid with a temperature lower than its freezing point. This liquid can be a refrigerant other than water or a solution containing water mixed with additives like alcohol, salt, sugar, or a combination thereof. The concentration of solutes in the liquid is typically high enough to prevent

364

Low-Temperature Processing of Food Products

it from transitioning into a solid phase, even at low temperatures. Incorporating ice slurry can significantly improve the efficiency of the freezing process by utilizing the latent heat of ice (Evans, 2008). When food is frozen through immersion and is not sealed in an impermeable package, solutes from the liquid can diffuse into the food, while water from the food can diffuse out into the surrounding liquid. These mass transfer processes occur concurrently with the transfer of heat. Depending on the specific objectives, one may seek to either minimize or optimize these mass diffusion effects. For instance, freezing fruit in aqueous solutions containing sugar and ethanol or in ice slurries may lead to the creation of new dessert products with desirable impacts on factors like color, flavor, and texture, which are attributed to the enzymeinhibiting properties of sugar (Sun, 2005). In the context of modeling in such cases, the goal is to forecast both the temperature and concentration patterns inside the food. As solutes infiltrate the food structure, the freezing point of the food can be lowered to varying degrees, and it is crucial to account for this effect in the modeling process. In a study, Lucas et al. (2001) developed a model to simulate the process of immersion freezing within a concentrated solution. This was achieved by using a one-dimensional inert porous material slab saturated with a dilute aqueous solution. This model simultaneously solved equations for solute diffusion and heat conduction. They treated the porous medium as a homogeneous phase, deriving average transport characteristics based on the proportions of ice, solid beads, water, and solute. Since diffusion only occurred within the liquid channels, they accounted for the void fraction and tortuosity when calculating effective mass diffusivities. In another study, the transport equations were solved using an FDM. To validate the model, the researchers conducted experiments involving the freezing of a bed of glass beads soaked in a dilute NaCl solution via brine immersion. According to the findings of the model, during the initial stages of the process, solute diffusion had the potential to inhibit surface freezing and promote the thawing of currently frozen layers. As a result, a nonfrozen surface layer coexisted with an interior layer or core that was frozen. Solute diffusion persisting within the nonfrozen layers caused the melting of neighboring ice crystals. If this progression persisted, the product would ultimately undergo complete thawing, and its solute concentration would approximate that of the surrounding solution (Lucas et al., 1999).

13.8

Supercooling and nucleation effects

Until now, it has mainly considered freezing as a process driven solely through heat transfer. Nevertheless, in numerous instances, the interplay between nucleation and mass transfer dynamics plays crucial roles. When water is cooled below its freezing point, it typically remains as a liquid until it reaches a low enough temperature for the formation and growth of stable ice crystals. It occurs at temperatures above the nucleation point, where ice crystals tend to lose molecules more rapidly due to surface energy effects (Kiani & Sun, 2011). There are two primary categories of nucleation: homogeneous and heterogeneous. Homogeneous nucleation occurs exclusively in

Design and simulation of freezing processes

365

pure water, typically at extremely low temperatures, around 40 C. Heterogeneous nucleation is the dominant mechanism in the freezing process of food materials. It occurs when foreign materials or impurities come into contact with the food, providing sites for the initiation and expansion of ice crystals (Sanz et al., 2013). Heterogeneous nucleation takes place at higher temperatures than homogeneous nucleation because foreign materials facilitate the clustering of water molecules on their surfaces, reducing surface energy. When water or a substance with a high water content is rapidly cooled, there might not be enough time for nucleation to take place (Geidobler & Winter, 2013). Instead, when reaching the glass transition temperature, the liquid within the food undergoes a transition into an amorphous solid state, a phenomenon referred to as vitrification. Vitrification necessitates exceptionally swift cooling rates, typically not achievable in conventional food freezing processes. Most food freezing processes involve some degree of supercooling, where the surface experiences a brief dip below the freezing point before quickly rebounding to it. After nucleation, ice crystals grow, and the freezing process becomes predominantly controlled by heat transfer (Pham, 2006). Some researchers used an FDM along with the quasi-enthalpy method to simulate this behavior, while others separately applied the apparent specific heat approach to address the identical issue. In their simulation of supercooling, they assumed that the specific heat (and thermal conductivity) remains consistent below the initial freezing point until the coldest node reaches the nucleation temperature. At that moment, the normal time-stepping process stops; nodes having enthalpy values below freezing freeze abruptly, liberating latent heat and warming up to the equilibrium temperature. Calculations then proceed as usual (Sun, 2005). Pham (1989) found that supercooling, as commonly observed in practice (a few degrees), has minimal effects on freezing time. However, it is important to note that this conclusion might not be applicable across all food varieties. For instance, in emulsions like ice cream or butter, where water is held in small droplets, every ice crystal needs to expand within its individual droplet, leading to a gradual and potentially complex freezing process. Modeling nucleation and crystal growth are essential for understanding their impacts on food quality, cellular harm, and moisture loss. In meat, maximum drip loss occurs when large intracellular ice crystals form in each cell, causing significant distortion and cell wall damage. This typically occurs during freezing at moderate rates; quick freezing leads to the production of numerous small intracellular crystals, whereas slow freezing results in extracellular freezing (Bevilacqua et al., 1979). Devireddy et al. (2002) developed a finite volume model for the prediction of intracellular ice formation in biological tissues, primarily within the domain of cryosurgery. They divided the material into two phases, extracellular and intracellular, with the assumption that extracellular liquid freezes without supercooling. As extracellular freezing occurs, there is an elevation in solute concentration, which triggers water to diffuse through cell membranes, resulting in a reduction in cell volumes. As ice grows within a liquid food, solutes are pushed away from it, leading to the formation of a concentration gradient in the liquid ahead of the freezing front. This gradient in concentration raises the freezing point of the nearby water, occurring near the freezing front, a phenomenon known as constitutional supercooling. If irregularities in the front cause its extension into the unfrozen region, this portion

366

Low-Temperature Processing of Food Products

encounters liquid with a reduced concentration and, consequently, a lower freezing point. As a result, it tends to freeze earlier than the liquid in other regions, giving rise to the growth of a protrusion that evolves into a dendrite. During extremely rapid freezing rates, the diffusion of solutes could have a substantial impact on regulating the advancement of the freezing boundary (Körber, 1988; Velegol et al., 2016). In processes like the freezing or freezing concentration of liquid fruit, such as fruit juice, the speed of freezing influences the rate of dendrite growth, subsequently impacting the separation of solute and ice. With slower rates of dendrite growth, solutes are afforded sufficient time to move away from the freezing boundary, resulting in effective separation. Conversely, at higher growth rates, solutes and particles might end up being trapped within the ice structure. In solid foods, the process of mass diffusion typically proceeds at a slow pace, causing local concentration to increase as ice forms. This concentration elevation lowers the freezing point and contributes to the distinctive gradual enthalpye temperature curve observed (Butler, 2002). So far, the influence of nucleation, crystal growth, and vitrification on the quality of frozen food products has not been adequately addressed by numerical modeling. The primary reason may be the limited availability of data concerning the relevant parameters. Some approximate analytical equations have been proposed for evaluating crystal size based on dendritic growth theory. These equations have been verified using data obtained from the freezing of agar gel. Additionally, there are finite volume techniques that calculate dendritic crystal growth from pure melts under the assumption of diffusion control. Another modeling method employs the use of cellular automata or hybrid automata, where the material is depicted as an assembly of microscopic elements that undergo stochastic phase changes based on the states of neighboring elements.

13.9

CFD modeling of freezing

Computational fluid dynamics (CFD) models are employed to compute fluid flow patterns and temperature distributions both in the vicinity of food products and within them. These models employ spatial discretization techniques, with FEM and FVM being the most common choices, although FDM is also occasionally utilized. When dealing with nonsolid regions, the CFD approach necessitates the resolution of fluid flow equations to determine fluid velocities (Xia & Sun, 2002). The significant advantage of CFD lies in its capability to calculate heat transfer coefficients, obviating the need for educated guesses or experimental measurements. In principle, this means that the cooling and freezing rates for a specific product under various conditions may be achieved without the need for experimentation, provided that the properties of the product are well-defined (Sun, 2007). However, CFD encounters two principal challenges. Firstly, fluid flow in many scenarios is turbulent, characterized by random, high-speed fluctuations that defy direct resolution from fundamental principles (Woo et al., 2009). These intricate and geometry-dependent fluctuations are typically approximated using turbulence models, such as the k-ε

Design and simulation of freezing processes

367

model. Such approaches establish and solve transport equations for parameters like turbulent kinetic energy (k) and turbulent dissipation rate (ε) (Defraeye et al., 2013). While these models provide valuable insights, they often rely on empirical parameters derived from experiments, making the accuracy of results less certain, particularly in scenarios with swirling flows or extensive recirculation (Kuriakose & Anandharamakrishnan, 2010). The second challenge is the considerable computational time required by CFD simulations. Because of the characteristics of the fluid flow equations, a precise computational grid with millions of nodes or elements is typically necessary. Additionally, a substantial number of equations must be solved iteratively at each time step (Xia & Sun, 2002). For instance, simulating the chilling of a beef side, which corresponds to approximately 20 h in real time, may take up to a week on a highperformance supercomputer. To mitigate these challenges, a common practice is to employ CFD to determine the surface heat transfer coefficient, which is subsequently utilized as an input parameter for FDM or FEM programs that focus exclusively on heat conduction within the product. This combination allows for efficient predictions while reducing computational demands (Raman et al., 2018; Zawawi et al., 2018). In summary, while CFD holds great potential for predicting cooling and freezing processes, its utility is often constrained by the complexities of turbulent flow and extensive computational requirements. As such, an integrated approach, where CFD informs subsequent modeling steps, often offers an optimal balance between accuracy and computational efficiency.

13.10

Conclusion

In summary, the modeling of the freezing process in food has made significant progress, primarily through the adoption of enthalpy or quasi-enthalpy methods in conjunction with control-volume finite difference methods (FDM), lumped capacitance FEM, or finite volume methods (FVM). However, it is evident that most freezing scenarios are not solely dictated by thermal considerations, prompting a shift in focus toward addressing the intricate interplay of various physical phenomena. These encompass mass transfer, nucleation, crystal growth, mass exchange across cell membranes, vitrification, thermal expansion, mechanical strain, stress, and the potential influence of internal pressure on the freezing point, a factor previously overlooked. Contemporary food engineers no longer restrict their interests to freezing times or heat loads alone; rather, they seek to comprehend intricate food quality aspects such as drip, color, texture, flavor, distortion, cracks, and microbial growth, especially during thawing. To make accurate predictions in these domains, comprehensive modeling is imperative, extending beyond the realm of heat transfer. Despite the remarkable computational capabilities of modern computers, the numerical modeling of threedimensional freezing processes continues to demand significant time and resources, even when secondary effects like crystal growth or mass transfer are omitted. Furthermore, the integration of freezing models into larger frameworks, such as models of entire food processing plants, presents a challenge worth addressing.

368

Low-Temperature Processing of Food Products

Ultimately, the pursuit of efficient, multiscale models that comprehensively account for all pertinent phenomena and accurately predict the impact of freezing processes on food quality remains a critical objective. The aim is not just modeling for its own sake but harnessing these models to optimize products and processes, a task that often entails running the model numerous times as part of optimization procedures, including stochastic methods like genetic algorithms. Thus, ongoing research endeavors are essential for the continued advancement of freezing process modeling in the realm of food engineering.

References Alexiades, V. (2018). Mathematical modeling of melting and freezing processes. Routledge. Banaszek, J. (1990). Comparison of control volume and Galerkin finite element methods for diffusion-type problems. Numerical Heat Transfer, Part B Fundamentals, 16(1), 59e78. Bevilacqua, A., Zaritzky, N., & Calvelo, A. (1979). Histological measurements of ice in frozen beef. International Journal of Food Science and Technology, 14(3), 237e251. Bird, R. B., Stewart, W. E., & Lightfoot, E. N. (2006). Transport phenomena. Wiley. Bouddour, A., Auriault, J.-L., Mhamdi-Alaoui, M., & Bloch, J.-F. (1998). Heat and mass transfer in wet porous media in presence of evaporationdCondensation. International Journal of Heat and Mass Transfer, 41(15), 2263e2277. Braun, J. L., Olson, D. H., Gaskins, J. T., & Hopkins, P. E. (2019). A steady-state thermoreflectance method to measure thermal conductivity. Review of Scientific Instruments, 90(2). Butler, M. F. (2002). Freeze concentration of solutes at the ice/solution interface studied by optical interferometry. Crystal Growth & Design, 2(6), 541e548. Califano, A., & Zaritzky, N. (1997). Simulation of freezing or thawing heat conduction in irregular two-dimensional domains by a boundary-fitted grid method. LWT-Food Science and Technology, 30(1), 70e76. Campa~none, L. A., Salvadori, V. O., & Mascheroni, R. H. (2001). Weight loss during freezing and storage of unpackaged foods. Journal of Food Engineering, 47(2), 69e79. Carslaw, H. S., Jaeger, J. C., & Feshbach, H. (1962). Conduction of heat in solids. Physics Today, 15(11), 74e76. Choi, Y. (1986). Effects of temperature and composition on the thermal properties of foods. Transport Phenomena, 99e101. Chourasia, M., & Goswami, T. (2007). Steady state CFD modeling of airflow, heat transfer and moisture loss in a commercial potato cold store. International Journal of Refrigeration, 30(4), 672e689. Cleland, A., & Earle, R. (1984a). Assessment of freezing time prediction methods. Journal of Food Science, 49(4), 1034e1042. Cleland, A., & Earle, R. (1984b). Freezing time predictions for different final product temperatures. Journal of Food Science, 49(4), 1230e1232. Cogné, C., Andrieu, J., Laurent, P., Besson, A., & Nocquet, J. (2003). Experimental data and modelling of thermal properties of ice creams. Journal of Food Engineering, 58(4), 331e341. Comini, G., Giudice, S. D., & Saro, O. (1990). A conservative algorithm for multidimensional conduction phase change. International Journal for Numerical Methods in Engineering, 30(4), 697e709.

Design and simulation of freezing processes

369

Crank, J., & Nicolson, P. (1996). A practical method for numerical evaluation of solutions of partial differential equations of the heat-conduction type. Advances in Computational Mathematics, 6(1), 207e226. Dash, S. K., Chandra, P., & Kar, A. (2023). Food engineering: Principles and practices. CRC Press. Datta, A. K. (2007). Porous media approaches to studying simultaneous heat and mass transfer in food processes. I: Problem formulations. Journal of Food Engineering, 80(1), 80e95. Davey, L., & Pham, Q. (1997). Predicting the dynamic product heat load and weight loss during beef chilling using a multi-region finite difference approach. International Journal of Refrigeration, 20(7), 470e482. Defraeye, T., Verboven, P., & Nicolai, B. (2013). CFD modelling of flow and scalar exchange of spherical food products: Turbulence and boundary-layer modelling. Journal of Food Engineering, 114(4), 495e504. Delgado, A., & Sun, D.-W. (2001). Heat and mass transfer models for predicting freezing processesea review. Journal of Food Engineering, 47(3), 157e174. Desrosier, N. W. (2012). Fundamentals of food freezing. Springer Science & Business Media. Devireddy, R. V., Smith, D. J., & Bischof, J. C. (2002). Effect of microscale mass transport and phase change on numerical prediction of freezing in biological tissues. Journal of Heat Transfer, 124(2), 365e374. Evans, J. A. (2008). Frozen food science and technology. Wiley Online Library. Eyres, N., Hartree, D. R., Ingham, J., Sarjant, R., & Wagstaff, J. (1946). The calculation of variable heat flow in solids. Philosophical Transactions of the Royal Society of London e Series A: Mathematical and Physical Sciences, 240(813), 1e57. Ezekoye, O. A. (2016). Conduction of heat in solids. SFPE Handbook of Fire Protection Engineering, 25e52. Fikiin, K. A. (1996). Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation. International Journal of Refrigeration, 19(2), 132e140. Finlay, W. H. (2019). Chapter 4: Particle size changes due to evaporation or condensation. In W. H. Finlay (Ed.), The mechanics of inhaled pharmaceutical aerosols (2nd ed., pp. 53e101). London: Academic Press. Geidobler, R., & Winter, G. (2013). Controlled ice nucleation in the field of freeze-drying: Fundamentals and technology review. European Journal of Pharmaceutics and Biopharmaceutics, 85(2), 214e222. Glavina, M. Y., Di Scala, K. C., Ansorena, R., & del Valle, C. E. (2006). Estimation of thermal diffusivity of foods using transfer functions. LWT-Food Science and Technology, 39(5), 455e459. Hamdami, N., Monteau, J.-Y., & Le Bail, A. (2004). Simulation of coupled heat and mass transfer during freezing of a porous humid matrix. International Journal of Refrigeration, 27(6), 595e603. Hammerschmidt, U. (2003). A quasi-steady state technique to measure the thermal conductivity. International Journal of Thermophysics, 24, 1291e1312. Hoang, D. K., Lovatt, S. J., Olatunji, J. R., & Carson, J. K. (2021). Improved prediction of thermal properties of refrigerated foods. Journal of Food Engineering, 297, 110485. Holdsworth, S. D., Simpson, R., & Barbosa-Canovas, G. V. (2008). Thermal processing of packaged foods. Springer. Holman, J. P. (1986). Heat transfer. McGraw Hill. Hu, Z., & Sun, D.-W. (2001). Predicting local surface heat transfer coefficients by different turbulent k-e models to simulate heat and moisture transfer during air-blast chilling. International Journal of Refrigeration, 24(7), 702e717.

370

Low-Temperature Processing of Food Products

Ilicali, C., & Saglam, N. (1987). A simplified analytical model for freezing time calculation in foods. Journal of Food Process Engineering, 9(4), 299e314. Kiani, H., & Sun, D.-W. (2011). Water crystallization and its importance to freezing of foods: A review. Trends in Food Science & Technology, 22(8), 407e426. Körber, C. (1988). Phenomena at the advancing iceeliquid interface: Solutes, particles and biological cells. Quarterly Reviews of Biophysics, 21(2), 229e298. Kuriakose, R., & Anandharamakrishnan, C. (2010). Computational fluid dynamics (CFD) applications in spray drying of food products. Trends in Food Science & Technology, 21(8), 383e398. Lacroix, C., & Castaigne, F. (1988). Freezing time calculation for products with simple geometrical shapes. Journal of Food Process Engineering, 10(2), 81e104. Lees, M. (1966). A linear three-level difference scheme for quasilinear parabolic equations. Mathematics of Computation, 20(96), 516e522. Lucas, T., Flick, D., & Raoult-Wack, A. (1999). Mass and thermal behaviour of the food surface during immersion freezing. Journal of Food Engineering, 41(1), 23e32. Lucas, T., Chourot, J.-M., Bohuon, P., & Flick, D. (2001). Freezing of a porous medium in contact with a concentrated aqueous freezant: Numerical modelling of coupled heat and mass transport. International Journal of Heat and Mass Transfer, 44(11), 2093e2106. Mascheroni, R., & Calvelo, A. (1982). A simplified model for freezing time calculations in foods. Journal of Food Science, 47(4), 1201e1207. Mason, B. (1958). The supercooling and nucleation of water. Advances in Physics, 7(26), 221e234. McNabb, A., Wake, G., Hossain, M. M., & Lambourne, R. (1990). Transition times between steady states for heat conduction: Part IdGeneral theory and some exact results. Occasional Publications in Mathematics and Statistics, 20. Mills, A. F. (1992). Heat transfer. CRC Press. Murakami, E., & Okos, M. (1989). Measurement and prediction of thermal properties of foods. In Food properties and computer-aided engineering of food processing systems (pp. 3e48). Springer. Peaceman, D. W., Rachford, J., & Henry, H. (1955). The numerical solution of parabolic and elliptic differential equations. Journal of the Society for Industrial and Applied Mathematics, 3(1), 28e41. Pham, Q. (1984). Extension to Planck’s equation for predicting freezing times of foodstuffs of simple shapes. International Journal of Refrigeration, 7(6), 377e383. Pham, Q. T. (1985). A fast, unconditionally stable finite-difference scheme for heat conduction with phase change. International Journal of Heat and Mass Transfer, 28(11), 2079e2084. Pham, Q. (1986a). Simplified equation for predicting the freezing time of foodstuffs. International Journal of Food Science & Technology, 21(2), 209e219. Pham, Q. (1986b). The use of lumped capacitance in the finite-element solution of heat conduction problems with phase change. International Journal of Heat and Mass Transfer, 29(2), 285e291. Pham, Q. (1987a). A note on some finite-difference methods for heat conduction with phase change. Numerical Heat Transfer, Part A Applications, 11(3), 353e359. Pham, Q. (1987b). Calculation of bound water in frozen food. Journal of Food Science, 52(1), 210e212. Pham, Q. (1989). Effect of supercooling on freezing time due to dendritic growth of ice crystals. International Journal of Refrigeration, 12(5), 295e300. Pham, Q. (2001). Prediction of cooling/freezing/thawing time and heat load. Advances in Food Refrigeration, 110e152.

Design and simulation of freezing processes

371

Pham, Q. T. (2006). Modelling heat and mass transfer in frozen foods: A review. International Journal of Refrigeration, 29(6), 876e888. Pham, Q. T. (2014a). In Q. T. Pham (Ed.), Modelling coupled phenomena. Food freezing and thawing calculations (pp. 95e131). New York, NY: Springer. Pham, Q. T. (2014b). Food freezing and thawing calculations. Springer. Pham, Q., & Mawson, R. (1997). Moisture migration and ice recrystallization in frozen foods. In Quality in frozen food (pp. 67e91). Springer. Pham, Q. T., & Pham, Q. T. (2014a). Approximate and empirical methods. Food Freezing and Thawing Calculations, 37e64. Pham, Q. T., & Pham, Q. T. (2014b). Heat transfer coefficient and physical properties. Food Freezing and Thawing Calculations, 5e24. Pham, Q. T., & Pham, Q. T. (2014c). Introduction to the freezing process. Food Freezing and Thawing Calculations, 1e4. Pham, Q., & Willix, J. (1984). A model for food desiccation in frozen storage. Journal of Food Science, 49(5), 1275e1281. Pham, Q. T., Le Bail, A., Hayert, M., & Tremeac, B. (2005). Stresses and cracking in freezing spherical foods: A numerical model. Journal of Food Engineering, 71(4), 408e418. Pham, Q., Trujillo, F., & McPhail, N. (2009). Finite element model for beef chilling using CFDgenerated heat transfer coefficients. International Journal of Refrigeration, 32(1), 102e113. Rahman, M. S., Machado-Velasco, K., Sosa-Morales, M., & Velez-Ruiz, J. F. (2009). Freezing point: Measurement, data, and prediction. Food Properties Handbook, 2, 153e192. Raman, R. K., Dewang, Y., & Raghuwanshi, J. (2018). A review on applications of computational fluid dynamics. International Journal of LNCT, 2(6), 137e143. Rao, M. A., Rizvi, S. S., Datta, A. K., & Ahmed, J. (2014). Engineering properties of foods. CRC Press. Riley, D., Smith, F., & Poots, G. (1974). The inward solidification of spheres and circular cylinders. International Journal of Heat and Mass Transfer, 17(12), 1507e1516. Sanz, E., Vega, C., Espinosa, J., Caballero-Bernal, R., Abascal, J., & Valeriani, C. (2013). Homogeneous ice nucleation at moderate supercooling from molecular simulation. Journal of the American Chemical Society, 135(40), 15008e15017. Scheerlinck, N., Verboven, P., Fikiin, K., De Baerdemaeker, J., & Nicolaï, B. (2001). Finite element computation of unsteady phase change heat transfer during freezing or thawing of food using a combined enthalpy and Kirchhoff transform method. Transactions of the ASAE, 44(2), 429. Schwartzberg, H. G. (1976). Effective heat capacities for the freezing and thawing of food. Journal of Food Science, 41(1), 152e156. Schwartzberg, H., Singh, R., & Sarkar, A. (2007). Freezing and thawing of foodsecomputation methods and thermal properties correlation. Heat Transfer in Food Processing: Recent Developments and Applications, 21, 61. Segerlind, L. J. (1991). Applied finite element analysis. John Wiley & Sons. Shampine, L. F., & Reichelt, M. W. (1997). The matlab ode suite. SIAM Journal on Scientific Computing, 18(1), 1e22. Singh, R. P., & Heldman, D. R. (2014). In R. P. Singh, & D. R. Heldman (Eds.), Chapter 4: Heat transfer in food processing. Introduction to food engineering (5th ed., pp. 265e419). San Diego: Academic Press. Singh, R. P., & Mannapperuma, J. D. (1990). Developments in food freezing. Biotechnology and Food Process Engineering, 309e358.

372

Low-Temperature Processing of Food Products

Stonehouse, G., & Evans, J. (2015). The use of supercooling for fresh foods: A review. Journal of Food Engineering, 148, 74e79. Sultana, K., Dehghani, S., Pope, K., & Muzychka, Y. (2018). Numerical techniques for solving solidification and melting phase change problems. Numerical Heat Transfer, Part B: Fundamentals, 73(3), 129e145. Sun, D.-W. (2005). Handbook of frozen food processing and packaging. CRC Press. Sun, D.-W. (2007). Computational fluid dynamics in food processing. CRC Press. Sun, D.-W., & Hu, Z. (2003). CFD simulation of coupled heat and mass transfer through porous foods during vacuum cooling process. International Journal of Refrigeration, 26(1), 19e27. Sweat, V. E. (1986). Thermal properties of foods. Engineering Properties of Foods, 49. Sweat, V., & Haugh, C. (1974). A thermal conductivity probe for small food samples. Transactions of the ASAE, 17(1), 56e0058. Teukolsky, S. A., Flannery, B. P., Press, W., & Vetterling, W. (1992). Numerical recipes in C. Somatosensory & Motor Research, 693(1), 59e70. Treybal, R. E. (1980). Mass transfer operations. New York, 466, 493e497. Udaykumar, H., Mao, L., & Mittal, R. (2002). A finite-volume sharp interface scheme for dendritic growth simulations: Comparison with microscopic solvability theory. Numerical Heat Transfer Part B: Fundamentals, 42(5), 389e409. Velegol, D., Garg, A., Guha, R., Kar, A., & Kumar, M. (2016). Origins of concentration gradients for diffusiophoresis. Soft Matter, 12(21), 4686e4703. Voller, V. R., & Swaminathan, C. (1991). ERAL Source-based method for solidification phase change. Numerical Heat Transfer, Part B Fundamentals, 19(2), 175e189. Voller, V., & Swaminathan, C. (1993). Treatment of discontinuous thermal conductivity in control-volume solutions of phase-change problems. Numerical Heat Transfer, Part B Fundamentals, 24(2), 161e180. Voller, V. R., Swaminathan, C., & Thomas, B. G. (1990). Fixed grid techniques for phase change problems: A review. International Journal for Numerical Methods in Engineering, 30(4), 875e898. Welti-Chanes, J., Vergara-Balderas, F., & Bermudez-Aguirre, D. (2005). Transport phenomena in food engineering: Basic concepts and advances. Journal of Food Engineering, 67(1e2), 113e128. Woo, M. W., Daud, W. R. W., Mujumdar, A. S., Wu, Z., Talib, M. Z. M., & Tasirin, S. M. (2009). Non-swirling steady and transient flow simulations in short-form spray dryers. Chemical Product and Process Modeling, 4(1). Xia, B., & Sun, D.-W. (2002). Applications of computational fluid dynamics (CFD) in the food industry: A review. Computers and Electronics in Agriculture, 34(1e3), 5e24. You, Y., Kang, T., & Jun, S. (2021). Control of ice nucleation for subzero food preservation. Food Engineering Reviews, 13, 15e35. Zawawi, M. H., Saleha, A., Salwa, A., Hassan, N., Zahari, N. M., Ramli, M. Z., & Muda, Z. C. (2018). A review: Fundamentals of computational fluid dynamics (CFD). In AIP conference proceedings. AIP Publishing. Zienkiewicz, O. C., Taylor, R. L., & Zhu, J. Z. (2005). The finite element method: Its basis and fundamentals. Elsevier. Zienkiewicz, O. C., Taylor, R. L., & Nithiarasu, P. (2013). The finite element method for fluid dynamics. Butterworth-Heinemann.

Different parameters affecting the efficiency of freezing systems

14


ska, Magdalena Trusin
ska and Małgorzata Nowacka, Agnieszka Ciurzyn Emilia Janiszewska-Turak Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences e SGGW, Warsaw, Poland

14.1

Introduction

Freezing is one of the oldest and most widely used food preservation process. The main goal of food freezing is the extension of shelf life by inhibiting the activity of microorganisms and reducing the chemical and enzymatic activity in food products (Berk, 2018; Dincer, 2017). It consists of lowering the product’s temperature below freezing point, resulting in water turning into ice. At the same time, significant amounts of heat must be removed, which is explained by the decrease in the kinetic energy of the molecules in the rigid crystal structure compared to the liquid phase. The transformation of water into ice changes its physical properties, that is, density, specific heat, thermal conductivity, and thermal diffusivity. This point is often between
0.5 C and
2 C but depends on the frozen product type (Chenchaiah & Kasiviswanathan, 2013; George, 1993). There is no pure water in food but solutions of salts and organic compounds. Part of the water is additionally “trapped” in the structures of proteins and polysaccharides; therefore, the process of freezing food products and pure water is slightly different. During freezing, three stages are distinguished: cooling the product from its initial temperature to cryoscopic temperature, proper freezing, during which the phase change of water into ice takes place, and further freezing to the temperature assumed in the technological process. During proper freezing, in the case of pure substances such as water, the temperature does not change noticeably. Whereas in food products, when the water freezes, the concentration of the cellular solution increases and the cryoscopic temperature constantly decreases. The process ends when the product reaches the temperature of the cooling medium (Dadan et al., 2021). The availability of various freezing techniques and devices allows to select the best method to preserve a specific raw material with minimal changes to its quality (Chenchaiah & Kasiviswanathan, 2013).

Low-Temperature Processing of Food Products. https://doi.org/10.1016/B978-0-12-818733-3.00002-3 Copyright © 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

374

14.2

Low-Temperature Processing of Food Products

Freezing processdgeneral factors affecting freezing

Freezing is an age-old and widely practiced preservation technique for food. Its primary objective is to extend the shelf life of food by restraining the activity of microorganisms and minimizing the chemical and enzymatic reactions in food products (Stebel et al., 2021). This process leads to the formation of ice crystals, which is why it is often compared to crystallization. However, there is a difference between these two processes. Freezing involves the crystallization of water, whereas crystallization process simply involves the formation of crystals (Silva et al., 2008). Freezing is considered a heat exchange process due to the significant heat transfer resistance observed during the phase transformation of water to ice. On the other hand, crystallization is classified as a mass exchange process (Bulut et al., 2018; Dadan et al., 2021; Silva et al., 2008). Freezing occurs when the heat is taken away from the water in the product, resulting in a drop in temperature. As a result, the Brownian motion between the water particles decreases, and they tend to get closer to each other due to mutual attraction. Under pure water conditions, when the energy of particle orientation exceeds the Brownian motion energy, water particles form a hexagonal crystal shape (Abdollahzadeh & Park, 2016). Generally, the factors affecting freezing process are related to the material and the freezing process (freezing time, tf, and freezing rate/speed uf ). The primary objective of the freezing process is to achieve complete freezing of the product. However, the freezing process differs between a solution and a solid. In a solid product, usually, free water is frozen, while trapped water inside the tissues and that which are bounded stay unfrozen. Independently of the type of food, if there are impurities or additional substances freezing temperature is lowered below the freezing temperature of pure water (below 0 C); that temperature is called cryoscopic temperature (Tf) (Fig. 14.1) (Dincer, 2017; Gruda & Postolski, 2000).

Figure 14.1 Freezing curves for water and food product: temperature history distribution. Own figure on the basis of Dadan et al. (2020).

Different parameters affecting the efficiency of freezing systems

375

In order to properly carry out the freezing process, the duration of the process and the speed (freezing rate) must be properly determined. The freezing time can be determined for the entire process; from the moment, the product is placed in the freezer (T0) until it is completely frozen, or there can be measured the specific time of freezing, in which, only the phase transformation of water into ice is taken into account. The freezing time includes the specific time of freezing (phase transition) as well as the remaining cooling time (the time calculated from the moment the product is placed in the freezer until it cools to the cryoscopic temperature) and the cooling of ice and solids time/subfreezing (calculated from the end of the phase transformation of free water until the product reaches the temperature of the cooling medium (Tm)) (Berk, 2018; Gruda & Postolski, 2000). The rate at which freezing take place is dependent on the rate at which ice is formed throughout the frozen material.This rate varies with the distance from the external surface in the cross-section of the material. In freezing practice, it is more common to determine the average rate of the frozen layer to the time of freezing (Bulut et al., 2018). The distance of the thermal center of the product from the frozen surface is taken as a measure of the thickness of the frozen material. The thermal center of the product is the point with the lowest freezing rate (Dadan et al., 2021; Dincer, 2017; Gaukel, 2016). When designing freezers or selecting a freezing method, it is essential to know the accurate knowledge of the freezing time of the process. However, determining the exact time can be challenging due to various factors influencing the process. As a result, only approximate formulas are available to estimate the duration of the process. Among the commonly used formulas, the Plank formula (Pham, 2014a,b; Plank, 1941) and its modified versions have become classic in freezing technology. It is important to note that these formulas introduced simplifying assumptions, which are (Pham, 2014a,b; Plank, 1941). 1. homogeneous heat containing water is cooled to a cryoscopic temperature before the onset of freezing; 2. the formation of ice in that body occurs without transition and is isothermal at the cryoscopic temperature; 3. the specific heat of the frozen body part is equal to zero; 4. the specific heat conductivity is constant and independent of temperature; 5. the temperature of the medium and the heat entry coefficient is constant.

These assumptions allow for the development of formulas that provide estimates for the freezing time. Additionally, the relationship between time and the shape of the material being frozen can be explored using specific patterns. However, it is important to note that these formulas and patterns are approximations and may not capture the exact dynamics of the freezing process in all scenarios. Plank equation for time prediction is given in Eq. (14.1) (Plank, 1941): tf ¼


  q$rf Y$a Z$a2  þ a kf Tf
Tm

(14.1)

376

Low-Temperature Processing of Food Products

where, tf, is freezing time (s), rf is density in a frozen state (kg/m3), q is latent heat in frozen food (kJ/kg), Tf is cryoscopic temperature of food ( C), Tm is temperature of freezing medium ( C), a is dimension (thickness or diameter) (mm), Y and Z are shape factor parameters determined by shape (values shown in Table 14.1), a is convective heat transfer coefficient (W/m2$K), and kf is thermal conductivity of frozen food (W/ m$K). In this equation, the different shape factor parameters (Table 14.1) can be used, and it is influenced the freezing process. By considering these shape factor parameters, engineers and scientists can analyze how the shape of an object affects heat transfer, freezing time, and overall freezing efficiency. This understanding can be used to optimize freezing processes, improve product quality, and design efficient freezing equipment (Lewicki et al., 2017). In addition, the freezing time is determined as the duration needed to freeze the geometric center of the product. On the other hand, the freezing rate is determined by the speed at which the ice formation front advances into the interior of the frozen material. This rate varies depending on the distance from the outer surface within the crosssection of the material being frozen. To calculate the freezing rate or speed (uf , measured in cm/h), the thickness of the food is divided by the time it takes for the geometric point (typically the center of the food) to freeze (Mittal, 2006): uf ¼

s tf

(14.2)

where, uf , freezing rate (cm/h); s, 1/2 sample size l (height) or d (diameter) (cm); tf, freezing time (h). It is worth mentioning, that temperature variations exist between the surface and the thermal center of a product during the freezing process, with the surface freezing at a faster rate compared to the center. Therefore, when determining the cryoscopic temperature of the product, temperature data collected at the thermal center are preferred. This is because the thermal center provides a more accurate representation of the overall freezing characteristics and behavior of the product (Pham, 2016). Fig. 14.2 illustrates the temperature disparity between the surface and thermal center of a product throughout the freezing process of the potato cylinder.

Table 14.1 Shape factors values used in Eq. (14.1) (L
opezLeiva & Hallström, 2003). Shape

Y

Z

Infinite plate Infinite cylinder Cylinder Sphere Cube

0.5 0.25 0.33 0.33 0.33

0.125 0.0625 0.0417 0.0417 0.0417

Different parameters affecting the efficiency of freezing systems

377

Figure 14.2 Freezing curves for potato: temperature history distribution on the surface and in the center (own not published data).

Scientific literature shows that freezing time and speed depend on (Chenchaiah & Kasiviswanathan, 2013; Silva et al., 2008; Xiaoyu et al., 2023): 1. the type of substance to be frozen - liquids (pure water or aqueous solutions or emulsions) - solid (homogeneous or tissue-like) 2. the size of the object to be frozen 3. the presence or absence of packaging 4. the type of freezer used - the temperature of the freezing agent - the method of contact between the refrigerant and the raw material 5. pretreatment (e.g., ultrasound, PEF, osmotic dehydration, vacuum impregnation with salt or sugar, addition of cryoprotectans, etc.).

14.3

Parameters influence the freezing time and freezing rate/speed

14.3.1 Type of frozen material On the basis of the time formula given by Plank (Eq. 14.1), it can be stated that the time values are strongly influenced by the type of raw material being frozen (raw material dimensions, density, the thermal conductivity of frozen food) and the heat transfer resistance associated with the freezer itself or the presence of packaging (Dincer, 2017). The phase transformation in food products initiates during heat removal when the subcooling state is disrupted. This is because the water in the food contains various mineral and organic substances that, lowering the temperature leads to corresponding changes in the concentration of the liquid solution. Also, food components such as

378

Low-Temperature Processing of Food Products

moisture, carbohydrate, protein, and lipids has and influence on the freezing process (Swati et al., 2019). The freezing point, also known as the cryoscopic/nucleation temperature, is affected by factors such as the concentration of the solution and degree of dissociation of dissolved substances, molecular weight. Generally, the higher degree of dissociation of dissolved substances the lower the cryoscopic temperature is, while the higher the molecular weight the higher the cryoscopic temperature is. For most natural foods, cryoscopic/nucleation temperature ranges from
0.5 to
2.0 C. It can be calculated from an equation based on Roul’s law (Dadan et al., 2021; Lewicki, 2000): DT f ¼ εf $n

(14.3)

where: εf, the solvent-specific coefficient, the so-called cryoscopic constant, for water equal to 1.86 K/mol, and n, refers to the molar concentration of the solution (in moles of substance per 1000 g of solvent). Another parameter describing thermal properties in food is the thermal conductivity of frozen food (kf (W/m$K)). This parameter is influenced by the food structure, composition, and its temperature (Duy et al., 2021). The time it takes to freeze the product can be reduced by making the frozen layer thinner, which may not always be feasible or recommended. Generally, it is best to avoid freezing small fruit and vegetable slices using the contact method (e.g., in cartons or trays) as the porous layer significantly decreases the effective thermal conductivity value. The effect of thermal conductivity on freezing time is more pronounced with increasing body thickness (l, height or d, diameter), and a lower value of has a greater effect. From an energy perspective, it is beneficial to increase the value of the convective heat transfer coefficient (a) and thermal conductivity (kf) to a certain limit to maintain the relationship a < 10 - kf (Tarnawski et al., 2014). While food products freeze due to the production of ice in a liquidesolid system, they are multicomponent systems that often include an inert component (cell membranes and solid parts of the suspension). As such, the freezing process is usually analyzed using temperature curves that show temperature changes over time. The shape of the graph for a food product changes depending on the freezing method used, the nature of the product to be frozen, its size, shape, and chemical composition (Duy et al., 2021; Gruda & Postolski, 2000; Lewicki et al., 2017). In addition, the important thing is the type of used packaging or lack thereof (Dincer, 2017). Depending on these factors, the freezing curve becomes steeper or less steep or shifted up or down. Three characteristic stages can be distinguished in the course of the curve: cooling, freezing (this is where the phase transition occurs), and subfreezing (Gruda & Postolski, 2000). The physical state of the raw material, whether it is in liquid or solid form, plays a significant role in determining the freezing time and freezing rate/speed of the process as well as the shape of the temperature graph of freezing (as shown in Fig. 14.1). Furthermore, the freezing process differs for tissue-structured solids and non-tissuestructured solids. The amount of water bound in the product is a crucial factor that affects the rate of freezing (Duy et al., 2021). The product with higher water content will

Different parameters affecting the efficiency of freezing systems

379

freeze more slowly. Regardless of the raw material type, free water will be frozen first, followed by bound water. Structural water, which is present in the intertissue spaces of solids, usually remains unfrozen (Nesvadba, 2008; Silva et al., 2008).

14.3.1.1 Water and liquid products The freezing of water is a well-known and extensively studied phenomenon due to its importance in daily life and scientific research (Powell-Palm et al., 2020). In the early stages of freezing, liquid subcooling occurs due to heat dissipation before the solid crystalline phase forms. The formation of an orderly pseudocrystalline structure in water and aqueous solutions is a result of subcooling. The duration and level of subcooling are determined by various factors. For example, the subcooling temperature of the water is reduced in capillaries, depending on the water’s purity. When a crystal embryo is introduced into overcooled water, the equilibrium is disrupted, leading to crystal growth and the release of freezing heat. Greater overcooling leads to a higher rate of crystal growth (Jia et al., 2022; Nesvadba, 2008). However, the liquid products refer to a wide range of substances that exist in a liquid state, other than water. Such products contain not only the water, but also carbohydrate, protein, and/or lipids. The freezing characteristics of different liquid products can vary significantly depending on their composition, additives, and intended use (Swati et al., 2019). For example, in the case of apple juice, pear juice, and peach juice there were noticed a correlation between the freezing point and the relative concentrations of sugars present, which were glucose, fructose, and sucrose. When plotting the freezing point versus concentration curves (in  Brix), it was observed that the curves for apple juice, pear juice, and peach juice fall between the curves for sucrose (a disaccharide) and glucose (a monosaccharide) (Auleda et al., 2011). Another issue is connected with the emulsions products such as ice-creams. The texture of ice cream is a critical quality attribute that is currently under study. When producing ice cream, the emulsion is frozen while foaming, resulting in the formation of dispersed bubbles and ice crystals ranging from 20 to 50 mm in size (Goff, 2006). These bubbles and crystals are surrounded by a continuous matrix of sugars, proteins, salts, polysaccharides, and temperature-dependent water. Ice cream is made up of fat globules, ice, air, protein-hydrocolloid structures, and unfrozen water with dissolved substances like sugars, proteins, or salts, all enclosed within a matrix that helps create permanent structures. Fat can occur in the form of individual beads or complex clusters, but homogenization is crucial in preventing the formation of large clusters within the ice structure, ensuring even taste sensations (Varela et al., 2014; Wr
obelJedrzejewska & Polak, 2023). During freezing, air microcells are formed, usually surrounded by a watereprotein layer, and water crystals are also formed, giving ice cream its structure (Kami
nska-Dw
orznicka et al., 2019).

14.3.1.2 Food products Freezing plant and animal tissues induces changes in the properties of the cell membrane. Cell membrane loses its semi-permeability and, after thawing, the tissue loses

380

Low-Temperature Processing of Food Products

its turgor, is flaccid, the sap leaks out, and the cells lose irreversibly their ability to contract or swell when exposed to hypertonic or hypotonic solutions. Also, quite often, the tissue is mechanically damaged by ice crystals (Nesvadba, 2008; Stebel et al., 2021). During freezing, the cells containing hypertonic solution lose their water to ice crystals that form in the intercellular spaces. This results in so-called cryo-osmosis or cryoconcentration. This phenomenon is related to the dehydration of a frozen cell solution, which is caused by the semipermeable properties of the cell membrane. What is more in food products, water is never present in a pure state, but in the form of solutions of salts and organic compounds; in addition, some water is bound permanently in the structures of proteins and polysaccharides. These factors strongly influence the physical properties of water and the freezing process. The presence of substances in water, forming a molecularly fragmented solution with it, changes its characteristic physical points and lowers its cryoscopic freezing point tf, raises its boiling point and lowers its vapor pressure over the solution (Bakhach, 2009; Li et al., 2018). In food products, the cryoscopic temperature of food products, similar to solutions, depends on the concentration of their cellular juice. Additionally, in food products, the structure of the tissues, the size, and shape of the product, as well as the heat exchange conditions and the temperature of the cooling agent have influenced the cryoscopic temperature of food products (Silva et al., 2008). Thus, the cryoscopic temperature of food products is not a strictly fixed value. For most natural food products, it is close to
1 C; for products containing higher amounts of solutes, the initial cryoscopic temperature is much lower, for example,
3.5 C, for grapes
5 C (Gruda & Postolski, 2000; Lewicki et al., 2017). More examples is given in Table 14.2. The physical properties of frozen and unfrozen products differ significantly due to the varying amount of frozen water present. This difference is determined by the final temperature of the product rather than the duration of the freezing process (Table 14.2). The physical coefficients of frozen food products show a significant change in value when the cryoscopic temperature is exceeded. To determine the amount of frozen water, simplified Raoul’s formula (Eq. 14.4) is considered the most accurate. During freezing, the cryoscopic temperature decreases due to an increase in mineral substances and sugar concentration, which also causes the product’s density to decrease by about 5%e8% (Gruda & Postolski, 2000; Yanat & Baysal, 2018). Water freezes at 100% (Powell-Palm et al., 2020), but different foods have varying percentages of free water, which easily freezing, and permanently bound water in protein and polysaccharide structures. This water does not freeze even at temperatures as low as
40 C. By knowing the initial freezing temperature and moisture content of the product, the unfrozen water present at a given freezing or frozen storage temperature can be estimated using Raoult’s law (Eq. 14.4) (Chenchaiah & Kasiviswanathan, 2013; Mulot et al., 2019; Tarnawski et al., 2014). u ¼ 1


Tf Tm

(14.4)

Product

Density [kg/m3]

Specific heat [kJ/(kg$K)]

Specific thermal conductivity [W/(m$K)]

Water content W [%]

Cryoscopic temperature Tf [oC]

Unit heat of freezing qz [kJ/kg]

T > Tf rO

T < Tf rf

T > Tf CO

T < TKr Cf

T > Tf lO

T < Tf lf

82.3


1.90

275.0

1000

950

3.60

1.89

0.53

1.76

84.1 82.0 84.7


2.00
1.05
1.00

282.0 283.8 279.6

990 998 1000

e e 950

3.60 3.56 3.69

1.89 1.88 1.89

0.54 0.53 0.53

1.79 1.82 1.86

85.7 90.0 83.0


2.20
1.15
3.30

286.1 289.6 279.6

1030 950 1040

980 840 990

3.68 3.88 3.64

1.88 2.01 1.89

0.54 0.56 0.53

1.80 1.95 1.67

87.6 88.9 88.2 94.1 77.8


0.50
1.30
1.35
0.85
1.70

293.6 298.2 293.6 312.2 258.6

1053 950 1035 1000 1055

e 890 e 940 e

3.77 3.81 3.77 3.98 3.44

1.92 1.97 1.92 2.01 1.80

0.55 0.55 0.57 0.57 0.52

1.96 1.92 1.90 2.06 1.69

Fruits Black berries Apples Raspberries Black currants Plums Strawberries Cherries

Different parameters affecting the efficiency of freezing systems

Table 14.2 Physical characteristics of certain foods (Gruda & Postolski, 2000; Lewicki et al., 2017).

Vegetables Beets Green beans Carrots Tomatoes Potatoes

Continued 381

Product

382

Table 14.2 Continued

Density [kg/m3]

Specific heat [kJ/(kg$K)]

Specific thermal conductivity [W/(m$K)]

Water content W [%]

Cryoscopic temperature Tf [oC]

Unit heat of freezing qz [kJ/kg]

T > Tf rO

T < Tf rf

T > Tf CO

T < TKr Cf

T > Tf lO

T < Tf lf

87.5 60e65


0.60 e

288.4 217.7

1000 e

e e

3.89 3.27

2.05 1.88

0.53 0.49

1.95 e

60.0 51.0


2.20
2.20

201.0 172.0

1000 950

e e

2.85 2.55

1.34 1.49

0.44 0.43

1.56 1.18

74.0 74.0


2.50
2.50

246.6 246.6

e e

e e

3.31 3.31

1.87 1.87

0.41 0.50

1.57 1.62

80.0 70.0


2.20
2.20

259.8 230.5

1000 e

e e

3.77 3.18

2.05 1.72

0.54 0.49

1.70 1.52

Dairy Milk Ice cream

Meat Lean pork Beef fatty

Poultry

Fish Cod Herring

Low-Temperature Processing of Food Products

Chickens Turkeys

Different parameters affecting the efficiency of freezing systems

383

where u is the proportion of frozen water in the product (kg/kg), Tf is cryoscopic temperature of the product ( C), and Tm is average final temperature of the product ( C). During the freezing process, products come into contact with refrigerant, causing a reduction in temperature. The first stage ends when the temperature falls below the freezing point, known as the cryoscopic temperature for food products (Jia et al., 2022; Tan et al., 2021). The second stage involves the formation of ice crystals. In liquid products and pure water, a homogeneous process occurs, resulting in hexagonal crystals. However, most tissue-structured food products experience heterogeneous nucleation, resulting in crystals forming around suspended particles or cell walls in the form of dendrites stage is complete when free and structured water is frozen. The final stage involves reducing the temperature of the product (frozen water, bound water, and total tissue and mineral particles) to the temperature of the refrigerant (Dincer, 2017; Gaukel, 2016; Gruda & Postolski, 2000; Jia et al., 2022). For food products, there is often a crystallization zone referred to as the second stage, occurring within a temperature range of 0e5 C. The time taken for food products to pass through this zone determines the number and size of ice crystals that form (Stebel et al., 2021). The freezing of food products differs from physical solutions due to their tissue structure, which is discontinuous, with the liquid phase trapped in the walls of solid cells. This structure is similar to living systems, causing the freezing process to destroy tissue structures and inhibit biological processes. The type of freezer used and the temperature of the cooling medium also influence ice crystallization (Silva et al., 2008; Zheng & Sun, 2006). The ice crystallization process in food products is usually divided into two stages. The first stage involves the formation of small individual areas of crystallization from crystal nuclei. The rapid growth of crystals during this stage is influenced by the rate of heat release, temperature, water content, and system properties. Crystallization can be delayed by proteins or cell walls in products with low water content. Further freezing of water in the tissue results in an advanced stage of crystallization called the crystal growth state, limited by free space in the cells. This process is not visible on the freezing curve. The final stage is evident on the curve as a drastic drop and the greatest change. In tissue products, crystals in the form of irregular dendrites predominate (Li & Sun, 2002; Stebel et al., 2021; Yanat & Baysal, 2018). In a study conducted by Wiktor, Fijalkowska, et al. (2015), various substrates such as apples, carrots, and potatoes were subjected to freezing in shock-air freezers at different temperatures (
20 C and
40 C). The researchers found that the freezing time was faster at lower temperatures, regardless of the substrate. The fastest freezing time was recorded for apples (510 s) and carrots (560 s) at
40 C, while potatoes froze faster (475 s) at
20 C. These differences in freezing time can be attributed to the unique tissue structures and biodiversity of the substrates. It was observed that carrots had the strongest vegetable tissue and took the least amount of time to freeze (Wiktor, Fijalkowska, et al., 2015).

384

Low-Temperature Processing of Food Products

14.3.2

Dimensions and shape of frozen material

The freezing time is mainly influenced by the thickness (l)/diameter (d) of the body to be frozen. From the calculation of freezing time point of view, other dimensions are less important. The shape of the body is also very important. If, under the same freezing conditions (cooling on all sides), there is a plate of thickness l and a cylinder or a sphere of diameter d, the ratio of the respective velocities and freezing times will be (Lewicki et al., 2017): Vplate ¼ Vcylinder ¼ Vsphere 0 splate : scylinder : ssphere ¼ 1: 2: 3

(14.5)

Analyzing these properties show that the freezing time of a plate is, under the same conditions, two times longer than that of a cylinder and three times longer than that of a sphere. Therefore, when dealing with small bodies (berries, currants, peas, etc.), it is more expedient to use individual-fluidization freezing (IQF), ensuring cooling over the entire surface of each grain, than, for example, the use of contact apparatus or classic wind tunnels, in which heat is removed only over a small area of the grains in contact with the plates or the surrounding air (Lewicki et al., 2017). Furthermore, Fig. 14.3 presents the effect of shape on freezing time. The cylinder required a longer time than the cube, which was especially seen in the subfreezing stage.

14.3.3

Packaging

Packaging can be treated as an intermediate element between the frozen product and the external environment. Especially multilayered packaging used in freezing significantly reduces the freezing rate. Therefore, in the previous Eq. (14.1), the thermal transmittance a should be replaced by the total permeability (kf), in which the

Figure 14.3 Freezing curves for different shapes of the same product on example of beetroot (own not published data).

Different parameters affecting the efficiency of freezing systems

385

additional thermal resistance of the packaging d/a shown in the table below is also taken into account: tf ¼
where:

P

    q$rf 1 X d Z$a2  Y $a þ þ a lpac kf Tf
Tm d lpac ,

(14.6)

thermal resistance of package ((m2K)/W) (values see Table 14.3).

Even a small layer of air enclosed in the packaging has a particularly high thermal resistance. An air layer 0.8 mm thick gives a thermal resistance 100 times greater than that of a paraffin-coated cardboard box 0.27 mm thick. Therefore, the walls of the packaging should, at all times, adhere tightly to the product (Gruda & Postolski, 2000). In addition to the aforementioned criteria, packaging materials should possess certain characteristics to facilitate efficient freezing of the contents while withstanding expansion during the process. These materials should exhibit impermeability to liquids, resistance to moisture, weak acids, and low temperatures. They should also have reflective properties and be as opaque as possible. In cases where reheating or cooking might be done in microwave ovens, the packaging materials should be both permeable to and resistant to microwave energy. These considerations ensure that the packaging effectively supports the freezing process and maintains the quality and safety of the product (Silva et al., 2008). For example, metal packaging is not a factor in retarding heat transfer, as its values are much greater than those of food products (Gruda & Postolski, 2000).

Table 14.3 Thermal resistance of packs of frozen products at pressure P ¼ 7 kPa. Thermal resistance Package

((m2K)/W)

Paraffined half-parchment Paraffined paperboard Cellophane film Parchment double-waxed Paperboard lined with aluminum foil Paraffin-embossed cardboard, wrapped in cellophane four layers Aluminum foil Waxed paper þ cardboard Air layer PVC foil PE foil Corrugated cardboard Packaging paper

0.00359 0.00826 0.00224 0.00300 0.00690 0.00940 0.0000005 0.01550 0.40400 0.00250 0.000138 0.02200 0.00143

Based on the Gruda and Postolski (2000).

386

Low-Temperature Processing of Food Products

The thicknesses of trapped air layers are not easy to measure or estimate but can be very important for the effect on the overall heat transfer coefficient (Cleland & Valentas, 1997). Pałacha and G
orski (2017) also confirmed that the presence of an air layer is unfavorable and significantly prolonged the freezing time, and the greater the thickness of the air layer, the longer the freezing time. They conducted the study of the impact of packaging on the freezing process of beef and lean pork, turkey, and cod fillets in the shape of a cuboid, freezing products without packaging and in eight types of packaging: aluminum foil, PE foil, cellophane foil, PVC foil, double waxed parchment paper, cardboard lined with aluminum foil, waxed cardboard, and waxed cardboard wrapped in cellophane four layers. Based on the analyses carried out, it was shown that the type of packaging had a varied effect on the increase in freezing time, and the decisive parameter was the value of the thermal resistance of the package. The aluminum foil did not extend the freezing time, and packaging made of paraffin cardboard wrapped in four-layer cellophane with the highest thermal resistance extended the freezing time by 24.2% in relation to unpackaged products.

14.3.4

Type of the freezer

Efforts have been ongoing in the freezing industry for many years to reduce the freezing time of food, increase the productivity of equipment, and achieve frozen products that are comparable in quality to fresh products. Significant reductions in freezing time are achieved primarily by the correct choice of the type of freezing apparatus, while not by aiming for a maximum value of convective heat transfer coefficient (a). Thus, modern freezing technology and techniques strive to have products frozen in apparatus adapted to their specific characteristics (Bulut et al., 2018; Lewicki et al., 2017; Yanat & Baysal, 2018; Zheng & Sun, 2006). Currently, rapid freezing methods fall into four categories. In Fig. 14.4 there are present different categories of freezers such as (Bulut et al., 2018; Lewicki et al., 2017; Yanat & Baysal, 2018; Zheng & Sun, 2006): L air freezing with intensive medium circulation, L contact freezing using multiplate, belt, and drum equipment,

Figure 14.4 Types of freezers category.

Different parameters affecting the efficiency of freezing systems

387

L immersion freezing in nonboiling liquids through immersion or spray, L immersion freezing in cryogenic boiling liquids like liquid nitrogen (LNF), liquid carbon dioxide (LCO2F), and liquid air (LAF), as well as freezing in liquid freon (LFF).

Freezing food by air is the most typical and well-known method of freezing. In this method, the refrigerant is usually cold air, which flows through the raw material, absorbs heat from it and cools it down by convection (Chenchaiah & Kasiviswanathan, 2013; Claudio et al., 2018). The air stream also removes a significant amount of moisture from the surface of the raw material, which results in a significant weight loss of the frozen raw material. This process is continuous with decreasing temperature. Cold air blowing over the raw material takes over its heat and mass, which is transferred to colder surfaces of the cooler evaporators, where heat and moisture are released in the form of frost deposited on the walls. Then, the air is returned to the inside of the freezing chamber to receive another portion of heat and moisture (Pham, 2006). This process is repeated until the raw material reaches cryoscopic temperature, at which water turns into ice. From this moment, the evaporation process is replaced by the sublimation process and the rate of freezing slows down. Freezing by air is carried out in simple devices such as chambers, freezing tunnels, and belt freezers with forced air circulation (Pham, 2016; Ren et al., 2021). In order to obtain the lowest weight loss of the frozen raw material, the lowest possible air temperature should be used, and the process should be carried out with intensive heat exchange. Another freezing method is using multiplate, belt, and drum equipment for contact freezing. Thus, this equipment utilizes direct contact between the freezing agent and the product to rapidly cool and freeze it. Multiplate freezers consist of multiple flat plates where the product is placed for freezing, belt freezers use a continuous conveyor belt to transport the product through the freezing zone, and drum freezers involve the product being placed on the surface of a rotating drum that is cooled to freeze the product. These contact freezing methods offer efficient heat transfer and can be particularly useful for freezing flat or thin products, ensuring rapid and uniform freezing (George, 1993; Hui et al., 2004). The direct contact between the freezing agent and the product ensures efficient heat transfer, minimizing the formation of large ice crystals and reducing the potential for cell damage. This results in the better texture of the frozen product due to due to minimize the loss of moisture during freezing, further contributing to the quality of the frozen product (North & Lovatt, 2016). The most preferred method of freezing is immersion freezing. There can be listed two types of this method. First, immersion freezing in nonboiling liquids is based on the immersion or spraying with a nonboiling liquid, to rapidly cool and freeze it. The liquid quickly absorbs heat from the product, resulting in fast freezing and minimal formation of ice crystals (North & Lovatt, 2016; Ren et al., 2021; Wiktor et al., 2016). The second is based on cryogenic boiling liquids, and due to direct contact between the very low temperature of the coolant and the product, the product is frozen very fast. The coolant in this freezing method can be liquid nitrogen (LNF) or liquid carbon dioxide (LCO2F) as well as liquid air (LAF), or liquid freon (LFF). The phase change of water into ice proceeds very quickly, and the heat transfer coefficient increases rapidly. As a result of the use of this method of freezing, after thawing,

388

Low-Temperature Processing of Food Products

products with a very well-preserved texture and a clearly smaller size of the dried on the surface of the product are obtained. This method clearly reduces the time of the freezing process and also enables the freezing of products, which are difficult to freeze (Mei et al., 2018; North & Lovatt, 2016; Xiaoyu et al., 2023). Other classifications based on the average freezing rate are given in Table 14.4. There are slow freezers, quick freezers, rapid freezers, and ultrarapid freezers (Bulut et al., 2018; Cleland & Valentas, 1997; Gururaj Pejavara et al., 2023). Moreover, the difference in temperature between the product and the cooling environment, also known as DTFr, is a crucial factor in classic air-vented freezers. These freezers have low permeability, which is dependent on air velocity. In order to reduce freezing time, air temperature is lowered significantly. Modern air-vented freezers, on the other hand, use a low boiling point medium with a required air temperature of
35 to
40 C, which leads to a high energy requirement and reduced compressor efficiency. Freezers with high permeability, such as contact, immersion, and fluidized bed freezers, do not experience significant reductions in freezing time with an increase in a temperature difference (Tan et al., 2021). With regard to the conditions for crystallization of water by freezing, it can be expected that slow cooling of the material to
2 to
5 C will result in the formation of large ice crystals, while rapid cooling will result in the formation of many very small ice crystals (Yanat & Baysal, 2018). Experimentally, it was shown that in the course of slow freezing, maintaining a slow drop in temperature resulted in the formation of large hexagonal ice crystals which destroyed cell walls and caused intercellular ice to form. From a technical point of view, this phenomenon is disadvantageous, as during thawing there is a significant loss of cellular juice and significant deterioration of the structure of the frozen material. In the case of rapid freezing, clusters of ice microcrystals of nondestructive dendrites of the cell walls are formed. In order to increase the intensity of heat dissipation, the small size of the frozen material is necessary (Li et al., 2018; Shi et al., 2018; Sun & Ng, 2011). Freezing of porous food using immersion freezing is much different from the contact freezing point. We can use here the mixture of salt, sugar, or alcohol with a concentration enough to maintain a liquid phase at a low-temperature freezing (Chang et al., 2023). The shortest total freezing time was recorded for the potato frozen by the air-shock method at
20 C, and the longest for the air-shock (
20 C) freezing of carrots.

Table 14.4 Types of freezers classification (Bulut et al., 2018; Cleland & Valentas, 1997). Freezer type

Freezing rate

Slow Fast Rapid Ultra-rapid

0e1 cm/h 1e3 cm/h 5e10 cm/h up to 100 cm/h

Different parameters affecting the efficiency of freezing systems

389

Analyzing the results obtained, it can also be concluded that, irrespective of the type of plant tissue, the air-shock method proved to be the fastest. For all tested types of freezers, authors show that for carrot the cooling time was the same in all processes, almost the same was observed for potato. It should be noted that carrot and potato samples frozen using the blast freezing method had the shortest phase transformation times for both freezing. In the case of apple, the shortest phase transformation time during freezing was recorded for the immersion method. The authors predicted that this could be related to the high porosity of this material, so that the liquid medium used in this technique could penetrate the intercellular spaces, and thus, heat transfer was more intense (Wiktor, Fijalkowska, et al., 2015). Also, reason for this behavior can be attributed to the size of the ice crystals that form as a result of rapid and slow freezing. When the shock method was used, the water contained in the cells is frozen in the form of small ice crystals. Slow freezing, on the other hand, involves slower crystallization of water and thus, the formation of larger ice crystals (Jia et al., 2022) (Fig. 14.5).

14.3.5 Pretreatment There are several innovative pretreatment techniques that are being explored for enhancing the freezing process. Some of these techniques include ultrasound, pulsed electric field (PEF), osmotic dehydration, vacuum impregnation with salt or sugar, and the addition of cryoprotectants. Generally, these methods aim to improve freezing efficiency, minimize quality degradation, and enhance the overall preservation of food products during freezing (Alabi et al., 2022; Sutariya & Sunkesula, 2021). Some of the examples of used different novel technologies for the freezing process are presented in Table 14.5. Osmotic dehydration as pretreatment before freezing is a technology to shorten the freezing process and prolong the preservation of fruits and vegetables. Osmotic dehydration has an impact on the freezing process by altering the composition and structure

Figure 14.5 Fast and slow freezing.

390

Table 14.5 Different novel technologies for the freezing process. Material

Pretreatment

Parameters

Effect

References

Tomato

OD

OD (time ¼ 0e1410 min) in 55% sucrose and 21DE maltodextrin

Concentrated fruit juices

OD

OD (time ¼ 0e1410 min) in 10, 15, 20, 25, 30, 35 and 40  Brix apple, pear and peach concentrated fruit juices

(Goula & Lazarides, 2012) (Auleda et al., 2011)

Mango

VI

VI (5 min at 21.33, 48, and 74.66 kPa) in mango juice-sugar mixtures (0, 5, 10, 15 and 20 Brix)

Potato

US

US treatment (25 kHz, power 0, 4.66, 7.34, 15.85, 25.89, 66.77, 90, 140.2, 170 W), coolant was mixture of ethylene glycol and water (50%:50% in volume).

The type of the osmotic dehydration solution effects the freezing time, and the use of sucrose resulted in shorter freezing process. As the concentration increases, the freezing point of the juices decreases. The variations observed among the juices can be attributed to several factors, including the relative concentrations of sugars (fructose, glucose, and sucrose), total solid concentrations, and other unaccounted characteristics of the juices. The juice/sugar-infused mangoes had high sensory scores and low drip loss, indicating improved tolerance to freezing damage compared to ripe mango. The flavor and color were enhanced. The freezing rate was found to be influenced by the ultrasound power, exposure time, and the phase of freezing during which ultrasound was applied. Stronger sonication was observed with higher ultrasound power and longer exposure time. A significant improvement in freezing rate was observed when using 15.85 W of US for 2 min. Applying ultrasound during the phase change period of the freezing process also resulted in a significant increase in freezing rate.

(Wanwisa & Waraporn, 2011) Low-Temperature Processing of Food Products

(Li & Sun, 2002)

US

US treatment (40 kHz, power 131.3 W, 0.23 W/cm2, exposure time 80, 90, 120 s, US application and intervals 30 s/30 s) PEF treatment (electric field strength of 0, 185, 300, 500 V/cm)

Apple

PEF

Apple

PEF þ OD

PEF treatment (electric field strength of 800 V/cm) OD (time ¼ 0e180 min) in 0%, 20%, 40%, and 60% glycerol concentrations

Spinach leaves

PEF þ VI þcryoprotectants

PEF treatment (25 pulses, 350 V) VI (5 min at 15 kPa) in glucose, sucrose, mannitol, trehalose

Spinach leaves

PEF þ VI

PEF treatment (electric field strength of 580 V/cm) VI (20 min at
86 kPa) in 40% trehalose

The ultrasound-assisted freezing significantly improved the freezing rate, and the freezing time was shortened by up to 8% compared to immersion freezing without ultrasound. The total freezing time was reduced by approximately 17%, and the total thawing time was reduced by around 23%. The phase transition time during thawing of samples pretreated with PEF was 52%e72% shorter compared to the reference material. It accelerates the freezing-thawing processes and improves the texture of the samples. The presence of glycerol inside the tissue contributes to a strong texture after defrosting, similar to fresh apples. However, rehydration in apple juice reduces the texture. PEF treatment alone increased freezing temperatures, except for leaves treated with trehalose, which showed a significant increase in ice propagation rate. The combination of VI and PEF showed comparable results to VI treatment alone. The application of PEF þ VI in trehalose significantly enhanced the freezing tolerance of spinach, resulting in maintained turgor similar to fresh leaves after thawing. In contrast, untreated samples and those treated without PEF þ VI exhibited a loss of turgor after freezing-thawing.

(Delgado et al., 2009) (Wiktor, Schulz, Voigt, Knorr, et al., 2015) (Parniakov et al., 2016)

(Dymek et al., 2015)

Different parameters affecting the efficiency of freezing systems

Apple

(Phoon et al., 2008)

391

392

Low-Temperature Processing of Food Products

of the food material and can accelerate the freezing process and enhance the quality of osmotically dehydrated frozen fruits and vegetables. The process parameters and nature of the product are important for product quality. The novel ultrasound and PEF techniques, which can provide cryoprotection from in situ interference, were proposed for the production of products with many-functional characteristics. These techniques can enhance the performance of osmotic dehydration to promote fast freezing, produce small ice crystals, and raise the glass transition temperature of cellular tissues (Alabi et al., 2022). Vacuum impregnation was initially developed to enhance osmotic dehydration and facilitate mass exchange. However, its application has extended to support various mass exchange processes, including freezing (Mierzwa et al., 2022; Wanwisa & Waraporn, 2011). Vacuum impregnation has shown remarkable effectiveness in interacting with freezing, as it offers protective benefits to the frozen tissue through microstructural phenomena. By mitigating the adverse effects associated with freezing, this treatment plays a significant role in preserving the quality and integrity of the food product. In particular, the application of vacuum impregnation with calcium ions has shown positive effects on enhancing tissue texture and controlling cell fluid leakage. Therefore, incorporating this pretreatment technique before freezing can be beneficial in improving the overall quality of processed fruits and vegetables (Assis et al., 2019). Ultrasonic waves used for pretreatment of plant tissue have a huge impact on its physical properties and microstructure. This is caused by the cavitation effect, that is, the formation of gas bubbles in the cells and sudden changes in pressure inside them and consequently tissue tearing (Awad, 2011). The phenomenon of cavitationinduced microstreaming plays a role in enhancing the heat and mass transfer during the freezing process (Awad, 2011). In addition, the change in the microstructure of the tissues of the raw material is also caused by the “sponge effect” which causes the formation of microchannels, through which the mass exchange between the raw material and the surrounding medium takes place (Azoubel et al., 2010). Furthermore, the use of ultrasound has a positive effect on the water crystallization process in the frozen tissue, shortening the time of formation of ice crystals and reducing their size (Zheng & Sun, 2006). The rapid formation of small ice crystals causes less tissue damage and, after thawing, better quality of the frozen raw material (Chemat et al., 2011). The use of ultrasonic waves also has a positive effect on the speed of the freezing process by increasing the mass transfer coefficient (Das et al., 2022; Li & Sun, 2002). Pulsed electric field (PEF) treatment is an application of high-intensity electric field pulses to food materials, resulting in the electroporation of cell membranes. Both reversible and irreversible electroporation can be utilized as a pretreatment step before freezing, improving freezing kinetics and product quality (Dadan et al., 2020). Irreversible electroporation enhances the freezing process by creating additional centers of crystallization and improving heat transfer, resulting in faster freezing. Studies have shown that PEF pre-treatment can reduce phase transition time during freezing by up to 40% (Jalte et al., 2009) and decrease thawing time by up to 72% (Wiktor, Schulz, Voigt, Witrowa-Rajchert, et al., 2015). The mechanical properties and drip

Different parameters affecting the efficiency of freezing systems

393

loss of frozen-thawed materials are also influenced by PEF treatment, with effects varying depending on the type of food material (Wiktor, Schulz, Voigt, Knorr, et al., 2015). While PEF treatment can lead to improved texture and reduced drip loss in some cases, results may vary due to the different properties of raw materials (Shayanfar et al., 2013, 2014). Combining different supportive methods is also being explored. One such combination involves the utilization of PEF and vacuum impregnation techniques. As mentioned earlier, PEF treatment disrupts cell membranes, promoting the development of a homogeneous structure within porous cells. This phenomenon can be harnessed by impregnating the food source with cryoprotectant solutions during vacuum impregnation prior to freezing. Studies conducted by Phoon et al. (2008) and Dymek et al. (2015) demonstrated the synergistic benefits of these techniques on spinach leaves. The combination allowed the cryoprotectant (trehalose) to be effective both outside and inside the cells, resulting in improved tolerance to freezing. Furthermore, vacuum impregnation of leafy vegetables with cryoprotectants revealed that viable elements were concentrated near the main veins, while the porous leaf edges suffered damage (Velickova et al., 2018). Similarly, Velickova et al. (2018) investigated the impact of using PEF and vacuum impregnation on strawberry freezing. Their findings indicated that both processes contributed to improved cell viability as well as better color retention in frozen or thawed strawberries. These combined approaches show promise in enhancing the freezing outcomes of various food products (Velickova et al., 2018). Also, PEF treatment was used by Parniakov et al. (2016) for osmotic dehydration process in apple juice-glycerol solutions. The use of PEF combined with OD resulted in faster freezing/thawing processes when compared to untreated samples. Particularly, when applying optimal osmotic treatment conditions such as a dehydration time of 180 min and a glycerol concentration of approximately 20%, the texture of the defrosted samples closely resembled that of fresh apples. Literature shows that also other novel technics, not yet so popular, can be used for freezing processing such us high hydrostatic pressure (Dadan et al., 2020; Sutariya & Sunkesula, 2021), radio-frequency (Choi et al., 2017), microwave (Sutariya & Sunkesula, 2021), magnetic field (Mohsen et al., 2017), etc.

14.4

Conclusion

This chapter describes the course of the food freezing process in terms of liquid and tissue products. Factors affecting the time and rate of freezing were analyzed. The most common types of freezers and packaging used during freezing are also described. Finally, the latest pretreatment techniques used before freezing and their impact on the freezing process and the quality of the final product are discussed. To summarize, the efficiency of freezing systems is related to the freezing time and freezing speed of a product. Furthermore, these parameters depend on several factors. The type of substance being frozen and its composition, whether it is a liquid or a solid, greatly influences the freezing process. Additionally, the size of the object, the

394

Low-Temperature Processing of Food Products

presence or absence of packaging, the type of freezer used, and any pretreatment techniques applied all play significant roles in determining the freezing time and speed. Moreover, the incorporation of novel pretreatment techniques, such as ultrasound, PEF, osmotic dehydration, vacuum impregnation with salt or sugar, or the addition of cryoprotectants, holds promise for improving freezing efficiency and preserving the quality of frozen products. Understanding these factors is crucial for designing efficient freezing processes. By considering the nature of the substance, optimizing the size and packaging, selecting an appropriate freezer, and implementing suitable pretreatment techniques, one can achieve desired freezing outcomes. This knowledge enables the production of highquality frozen products while maintaining their essential characteristics. Further research and exploration in this field can contribute to advancements in freezing technology and enhance the efficiency of freezing systems.

References Abdollahzadeh, J. M., & Park, J. H. (2016). Effects of Brownian motion on freezing of PCM containing nanoparticles. Thermal Science, 20(5), 1533e1541. Alabi, K. P., Olalusi, A. P., Olaniyan, A. M., Fadeyibi, A., & Gabriel, L. O. (2022). Effects of osmotic dehydration pretreatment on freezing characteristics and quality of frozen fruits and vegetables. Journal of Food Process Engineering, 45(8), e14037. Assis, F. R., Rodrigues, L. G. G., Tribuzi, G., de Souza, P. G., Carciofi, B. A. M., & Laurindo, J. B. (2019). Fortified apple (Malus spp., var. Fuji) snacks by vacuum impregnation of calcium lactate and convective drying. LWT, 113, 108298. https://doi.org/ 10.1016/j.lwt.2019.108298 Auleda, J., Ravent
os, M., S
anchez, J., & Hern
andez, E. (2011). Estimation of the freezing point of concentrated fruit juices for application in freeze concentration. Journal of Food Engineering, 105(2), 289e294. https://doi.org/10.1016/j.jfoodeng.2011.02.035 Awad, S. B. (2011). High-power ultrasound in surface cleaning and decontamination. In Ultrasound technologies for food and bioprocessing (pp. 545e558). Springer. Azoubel, P. M., Baima, M.d. A. M., da Rocha Amorim, M., & Oliveira, S. S. B. (2010). Effect of ultrasound on banana cv Pacovan drying kinetics. Journal of Food Engineering, 97(2), 194e198. Bakhach, J. (2009). The cryopreservation of composite tissues: Principles and recent advancement on cryopreservation of different type of tissues. Organogenesis, 5(3), 119e126. https://doi.org/10.4161/org.5.3.9583 Berk, Z. (2018). Food process engineering and technology. Academic press. € Kırtıl, E., & Bayındırlı, A. (2018). Effect of freezing rate and storage on the Bulut, M., Bayer, O., texture and quality parameters of strawberry and green bean frozen in home type freezer. International Journal of Refrigeration, 88, 360e369. Chang, J., Sun, P., Gong, X., Sun, Z., Wang, J., & Li, X. (2023). Simulation-based analysis of the effect of new immersion freezing equipment on the freezing speed. Applied Sciences, 13(4), 2392. https://www.mdpi.com/2076-3417/13/4/2392. Chemat, F., Zill e, H., & Khan, M. K. (2011). Applications of ultrasound in food technology: Processing, preservation and extraction. Ultrasonics Sonochemistry, 18(4), 813e835. https://doi.org/10.1016/j.ultsonch.2010.11.023

Different parameters affecting the efficiency of freezing systems

395

Chenchaiah, M., & Kasiviswanathan, M. (2013). Chapter 13 - food freezing technology. In M. Kutz (Ed.), Handbook of farm, dairy and food machinery engineering (2nd ed., pp. 355e378). Academic Press. https://doi.org/10.1016/B978-0-12-385881-8.00013-6 Choi, E. J., Park, H. W., Yang, H. S., Kim, J. S., & Chun, H. H. (2017). Effects of 27.12 MHz radio frequency on the rapid and uniform tempering of cylindrical frozen pork loin (Longissimus thoracis et lumborum). Korean Journal for Food Science of Animal Resources, 37(4), 518e528. https://doi.org/10.5851/kosfa.2017.37.4.518 Claudio, Z., Giulia, R., Giovanni, P., & Giovanni, A. L. (2018). Analysis of the freezing time of chicken breast finite cylinders. International Journal of Refrigeration, 95, 38e50. https:// doi.org/10.1016/j.ijrefrig.2018.08.013 Cleland, D. J., & Valentas, K. J. (1997). Prediction of freezing time and design of food freezers. In Handbook of food engineering practice. Dadan, M., Matys, A., Kaminska-Dworznicka, A., Lammerskitten, A., Toepfl, S., & Parniakov, O. (2021). Improvement of freezing processes assisted by ultrasound. In Design and optimization of innovative food processing techniques assisted by ultrasound (pp. 217e273). Elsevier. Dadan, M., Nowacka, M., Czyzewski, J., & Witrowa-Rajchert, D. (2020). Modification of food structure and improvement of freezing processes by pulsed electric field treatment. In Pulsed electric fields to obtain healthier and sustainable food for tomorrow (pp. 203e226). Academic Press. Das, K., Zhang, M., Bhandari, B., Chen, H., Bai, B., & Roy, M. C. (2022). Ultrasound generation and ultrasonic application on fresh food freezing: Effects on freezing parameters, physicochemical properties and final quality of frozen foods. Food Reviews International, 1e31. https://doi.org/10.1080/87559129.2022.2027436 Delgado, A. E., Zheng, L., & Sun, D.-W. (2009). Influence of ultrasound on freezing rate of immersion-frozen apples. Food and Bioprocess Technology, 2(3), 263e270. https:// doi.org/10.1007/s11947-008-0111-9 Dincer, I. (2017). Food freezing. In I. Dincer (Ed.), Refrigeration systems and applications (pp. 573e630). JohnWiley & Sons Ltd. https://doi.org/10.1002/9781119230793.ch9 Duy, K. H., Simon, J. L., Jamal, R. O., & James, K. C. (2021). Improved prediction of thermal properties of refrigerated foods. Journal of Food Engineering, 297, 110485. https://doi.org/ 10.1016/j.jfoodeng.2021.110485 Dymek, K., Dejmek, P., Galindo, F. G., & Wisniewski, M. (2015). Influence of vacuum impregnation and pulsed electric field on the freezing temperature and ice propagation rates of spinach leaves. LWT-Food Science and Technology, 64(1), 497e502. Gaukel, V. (2016). Cooling and freezing of foods. In G. Smithers (Ed.), Reference module in food science. Elsevier. https://doi.org/10.1016/B978-0-08-100596-5.03415-6 George, R. (1993). Freezing proceseses used in the food industry. Trends in Food Science & Technology, 4(5), 134e138. Goff, H. D. (2006). Ice cream. In P. L. H. McSweeney (Ed.), 2. Advanced dairy chemistry Volume 2 Lipids, Fox, P.F. Boston: Springer. https://doi.org/10.1007/0-387-28813-9_12 Goula, A. M., & Lazarides, H. N. (2012). Modeling of mass and heat transfer during combined processes of osmotic dehydration and freezing (Osmo-Dehydro-Freezing). Chemical Engineering Science, 82, 52e61. https://doi.org/10.1016/j.ces.2012.07.023 Gruda, Z., & Postolski, J. (2000). Food freezing. Warszawa: WNT. Gururaj Pejavara, N., Piyush Kumar, J. H. A., Ashish, R., & Alain, L.-B. (2023). Changes in the quality of apple tissue subjected to different freezing rates during long-term frozen storage at different temperatures. International Journal of Refrigeration. https://doi.org/10.1016/ j.ijrefrig.2023.03.022

396

Low-Temperature Processing of Food Products

Hui, Y. H., Legarretta, I. G., Lim, M. H., Murrell, K., & Nip, W.-K. (2004). Handbook of frozen foods (Vol. 133). CRC Press. Jalte, M., Lanoiselle, J.-L., Lebovka, N. I., & Vorobiev, E. (2009). Freezing of potato tissue pretreated by pulsed electric fields. LWT-Food Science and Technology, 42(2), 576e580. Jia, G., Chen, Y., Sun, A., & Orlien, V. (2022). Control of ice crystal nucleation and growth during the food freezing process. Comprehensive Reviews in Food Science and Food Safety, 21(3), 2433e2454. https://doi.org/10.1111/1541-4337.12950 Kami
nska-Dw
orznicka, A., Gondek, E., Łaba, S., Jakubczyk, E., & Samborska, K. (2019). Characteristics of instrumental methods to describe and assess the recrystallization process in ice cream systems. Foods, 8(4), 117. https://www.mdpi.com/2304-8158/8/4/117. Lewicki, P. P. (2000). Raoult’s law based food water sorption isotherm. Journal of Food Engineering, 43(1), 31e40. https://doi.org/10.1016/S0260-8774(99)00130-2 Lewicki, P. P., Lenart, A., Kowalczyk, R., & Pałacha, Z. (2017). In_zynieria procesowa i aparatura przemysłu spo_zywczego. Wydawnictwo Naukowe PWN. Li, B., & Sun, D.-W. (2002). Effect of power ultrasound on freezing rate during immersion freezing of potatoes. Journal of Food Engineering, 55(3), 277e282. Li, D., Zhu, Z., & Sun, D.-W. (2018). Effects of freezing on cell structure of fresh cellular food materials: A review. Trends in Food Science & Technology, 75, 46e55. https://doi.org/ 10.1016/j.tifs.2018.02.019 L
opez-Leiva, M., & Hallström, B. (2003). The original Plank equation and its use in the development of food freezing rate predictions. Journal of Food Engineering, 58(3), 267e275. https://doi.org/10.1016/S0260-8774(02)00385-0 Mei, Y., Jiang, H., Lin, Y., Wang, F., & Nie, Q. (2018). Design of refrigerating and quick freezing equipment based on liquid nitrogen technology. IOP Conference Series: Earth and Environmental Science, 199(3), 032021. https://doi.org/10.1088/1755-1315/199/3/032021 Mierzwa, D., Szadzi
nska, J., Gapi
nski, B., Radziejewska-Kubzdela, E., & Biega
nskaMarecik, R. (2022). Assessment of ultrasound-assisted vacuum impregnation as a method for modifying cranberries’ quality. Ultrasonics Sonochemistry, 89, 106117. https:// doi.org/10.1016/j.ultsonch.2022.106117 Mittal, G. (2006). Freezing loads and freezing time calculation. In Food science and technology (Vol. 155, p. 127). New York: Marcel Dekker. Mohsen, D.-I., Nasser, H., Epameinondas, X., & Alain, L.-B. (2017). Review on the control of ice nucleation by ultrasound waves, electric and magnetic fields. Journal of Food Engineering, 195, 222e234. https://doi.org/10.1016/j.jfoodeng.2016.10.001 Mulot, V., Benkhelifa, H., Pathier, D., Ndoye, F.-T., & Flick, D. (2019). Experimental and numerical characterization of food dehydration during freezing. Journal of Food Engineering, 263, 13e24. https://doi.org/10.1016/j.jfoodeng.2019.05.009 Nesvadba, P. (2008). Thermal properties and ice crystal development in frozen foods. In Frozen food science and technology (pp. 1e25). https://doi.org/10.1002/9781444302325.ch1 North, M. F., & Lovatt, S. J. (2016). Freezing methods and equipment. In D.-W. Sun (Ed.), Handbook of frozen food processing and packaging (2nd ed., pp. 187e200). CRC press. Parniakov, O., Bals, O., Lebovka, N., & Vorobiev, E. (2016). Effects of pulsed electric fields assisted osmotic dehydration on freezing-thawing and texture of apple tissue. Journal of Food Engineering, 183, 32e38. https://doi.org/10.1016/j.jfoodeng.2016.03.013 Pałacha, Z., & G
orski, A. (2017). WpłyW rodzaju opakoWania oraz grubo
sci WarstWy poWietrza na czas zamra_zania Wybranych produkt
oW pochodzenia zWierzecego®. Postepy techniki przetw
orstwa spo_zywczego, (1), 39e45. Pham, Q. (2014a). Analytical solution. In Food freezing and theory calculations. Springer, New York: Springer Briefs in Food Health and Nutrition.

Different parameters affecting the efficiency of freezing systems

397

Pham, Q. T. (2016). Freezing Theory. In B. Caballero, P. M. Finglas, & F. Toldr
a (Eds.), Encyclopedia of food and health (pp. 110e118). Cambridge, MA, USA: Academic Press. Pham, Q. T. (2014b). Freezing time formulas for foods with low moisture content, low freezing point and for cryogenic freezing. Journal of Food Engineering, 127, 85e92. https:// doi.org/10.1016/j.jfoodeng.2013.12.007 Pham, Q. T. (2006). Modelling heat and mass transfer in frozen foods: A review. International Journal of Refrigeration, 29(6), 876e888. https://doi.org/10.1016/j.ijrefrig.2006.01.013 Phoon, P. Y., Galindo, F. G., Vicente, A., & Dejmek, P. (2008). Pulsed electric field in combination with vacuum impregnation with trehalose improves the freezing tolerance of spinach leaves. Journal of Food Engineering, 88(1), 144e148. Plank, R. (1941). Beitrage zur Berechnung and Bewertung der Gefriergeschwindigkeit von Lebensmitteln. Beihefte Zeitsschrift Gesampte Kalte-Industrie, 3(10), 22. Powell-Palm, M. J., Rubinsky, B., & Sun, W. (2020). Freezing water at constant volume and under confinement. Communications Physics, 3(1), 39. https://doi.org/10.1038/s42005020-0303-9 Ren, W., Yuan, G., Lin, X., Guo, X., & Wang, Z. (2021). Comparison of the immersion chilling and freezing and traditional air freezing on the quality of beef during storage. Food Sciences and Nutrition, 9(12), 6653e6661. https://doi.org/10.1002/fsn3.2613 Shayanfar, S., Chauhan, O., Toepfl, S., & Heinz, V. (2014). Pulsed electric field treatment prior to freezing carrot discs significantly maintains their initial quality parameters after thawing. International Journal of Food Science and Technology, 49(4), 1224e1230. Shayanfar, S., Chauhan, O., Toepfl, S., & Heinz, V. (2013). The interaction of pulsed electric fields and texturizing-antifreezing agents in quality retention of defrosted potato strips. International Journal of Food Science and Technology, 48(6), 1289e1295. Shi, J., Zhang, L., Lei, Y., Shen, H., Yu, X., & Luo, Y. (2018). Differential proteomic analysis to identify proteins associated with quality traits of frozen mud shrimp (Solenocera melantho) using an iTRAQ-based strategy. Food Chemistry, 251, 25e32. Silva, C. L. M., Gonçalves, E. M., & Brand~ao, T. R. S. (2008). Freezing of fruits and vegetables. In Frozen food science and technology (pp. 165e183). https://doi.org/10.1002/9781444 302325.ch8 Stebel, M., Smolka, J., Palacz, M., Piechnik, E., Halski, M., Knap, M., Felis, E., Eikevik, T. M., Tolstorebrov, I., Peralta, J. M., & Zorrilla, S.,E. (2021). Numerical modelling of the food freezing process in a quasi-hydrofluidisation system. Innovative Food Science & Emerging Technologies, 74, 102834. https://doi.org/10.1016/j.ifset.2021.102834 Sun, Z., & Ng, K.-H. (2011). Coronary computed tomography angiography in coronary artery disease. World Journal of Cardiology, 3(9), 303. Sutariya, S. G., & Sunkesula, V. (2021). 3.03 - food freezing: Emerging techniques for improving quality and process efficiency a comprehensive review (pp. 36e63). https:// doi.org/10.1016/B978-0-08-100596-5.23035-7 Swati, M., Zhiwei, Z., & Da-Wen, S. (2019). Glass transitions as affected by food compositions and by conventional and novel freezing technologies: A review. Trends in Food Science & Technology, 94, 1e11. https://doi.org/10.1016/j.tifs.2019.09.010 Tan, M., Mei, J., & Xie, J. (2021). The formation and control of ice crystal and its impact on the quality of frozen aquatic products: A review. Crystals, 11(1), 68. Tarnawski, V., Leong, W., & Momose, T. (2014). Modeling the thermal conductivity of frozen foods. In J. Gli
nski, J. Horabik, & J. Lipiec (Eds.), Encyclopedia of agrophysics. Encyclopedia of earth sciences series (pp. 483e489). Springer. https://doi.org/10.1007/978-90481-3585-1_93

398

Low-Temperature Processing of Food Products

Varela, P., Pintor, A., & Fiszman, S. (2014). How hydrocolloids affect the temporal oral perception of ice cream. Food Hydrocolloids, 36, 220e228. https://doi.org/10.1016/j. foodhyd.2013.10.005 Velickova, E., Tylewicz, U., Dalla Rosa, M., Winkelhausen, E., Kuzmanova, S., & Romani, S. (2018). Effect of pulsed electric field coupled with vacuum infusion on quality parameters of frozen/thawed strawberries. Journal of Food Engineering, 233, 57e64. https://doi.org/ 10.1016/j.jfoodeng.2018.03.030 Wanwisa, S., & Waraporn, B. (2011). Utilization of partially ripe mangoes for freezing preservation by impregnation of mango juice and sugars. LWT - Food Science and Technology, 44(2), 375e383. https://doi.org/10.1016/j.lwt.2010.08.012 Wiktor, A., Fijalkowska, A., Kucko, I., Wojnowski, M., Kr
olikowski, K., Hankus, M., Chudoba, T., Lojkowski, W., & Witrowa-Rajchert, D. (2015). Zastosowanie przewodno
sci elektrycznej wła
sciwej do oceny przebiegu procesu zamra_zania i rozmra_zania tkanki ro
slinnej (p. 582). Zeszyty Problemowe Postep
ow Nauk Rolniczych. Wiktor, A., Schulz, M., Voigt, E., Knorr, D., & Witrowa-Rajchert, D. (2015). Impact of pulsed electric field on kinetics of immersion freezing, thawing, and on mechanical properties of carrot. Food Science Technology Quality, 22(2), 124e137. Wiktor, A., Schulz, M., Voigt, E., Witrowa-Rajchert, D., & Knorr, D. (2015). The effect of pulsed electric field treatment on immersion freezing, thawing and selected properties of apple tissue. Journal of Food Engineering, 146, 8e16. Wiktor, A., Sledz, M., Nowacka, M., Rybak, K., & Witrowa-Rajchert, D. (2016). The influence of immersion and contact ultrasound treatment on selected properties of the apple tissue. Applied Acoustics, 103, 136e142. Wr
obel-Jedrzejewska, M., & Polak, E. (2023). Carbon footprint analysis of ice cream production. Sustainability, 15(8), 6887. https://www.mdpi.com/2071-1050/15/8/6887. Xiaoyu, T., Yu, L., Lipin, C., Changhu, X., & Zhaojie, L. (2023). Effects of liquid nitrogen freezing at different temperatures on the quality and flavor of Pacific oyster (Crassostrea gigas). Food Chemistry, 422, 136162. https://doi.org/10.1016/j.foodchem.2023.136162 Yanat, M., & Baysal, T. (2018). Effect of freezing rate and storage time on quality parameters of strawberry frozen in modified and home type freezer. Hrvatski casopis za prehrambenu tehnologiju, biotehnologiju i nutricionizam, 13(3e4), 154e158. Zheng, L., & Sun, D.-W. (2006). Innovative applications of power ultrasound during food freezing processesda review. Trends in Food Science & Technology, 17(1), 16e23. https://doi.org/10.1016/j.tifs.2005.08.010

Index Note: ‘Page numbers followed by f indicate figures.’ A Absorption cycle system, 60e62 Accelerated shelf-life test (ASLT), 306e307 Air-blast freezing, 32e33, 159e162, 228 design and operation, 124e130 in food industry, 117e118 blast freezing and food quality, 137e138 energy usage in, 139e141 refrigeration processes, mathematical modeling of, 130e137 types of, 118e124 Air chilling, 13 Air cooling, 13, 92 evaporators, 67 Air freezers, types of, 99e105 American Frozen Food Institute (AFFI), 201 Animal origin foods, 293e294 Antifreeze proteins (AFP), 45, 279e280 Antimicrobial agents (AHV), 245e246 Arrhenius law, 297e303 Automated storage and retrieval systems (ASRS), 124 B Batch freezers, 100 Belt freezers, 100e101 Blast cell (batch) freezers, 118e119 Blast chilling, 93 Blast freezing, 117e118, 137e138 Bound water, 336 during freezing, 35e36 British Frozen Food Federation (BFFF), 200 Bulk cold storage, 82 C Cabinet freezers, 228 Campylobacter, 234e242 Chicken legs and breast meat, 225e226 Chilling and freezing systems, 71e72

Chilling/cooling processes, 3e4 capacity, 14e15 classification of, 8e10 curve or phases, 7e8 in food preservation, 4e5 mechanism of, 6e7 methods of, 11e14 modeling of, 18e19 rate, 15e18 stages, 11 super-chilling, 9e10 Cleland and Earle’s empirical method, 342e343 Cold rooms and walk-in refrigerators, 102 Cold storage functioning of, 80e81 in India and global, 80 types of, 82e83 Cold-store room, 119 Combined recrystallization, 39 Computational fluid dynamics (CFD), 129, 366 modeling of freezing, 366e367 software, 189 Contact belt freezers, 162 Continuous freezers, 119e122 Controlled atmosphere (CA) cold storage, 83 “Control volume finite difference method,” 350 Cooling systems, governing equations in, 94e96 Cooling time, 110 Crank-Nicolson method, 351e352 Crank-Nicolson schemes, 354e355 Cryogenic freezing, 34, 176e177 Cryogenic liquids, 157 Cryogenic techniques, 209e210 Cryo-protectant additives, 278e280

400

Cryoscopic/nucleation temperature, 377e378 Crystal growth, 333 D Differential scanning calorimetry (DSC) analyses, 203 Different single-/double-contact freezers, 156e162 Different spray freezing approaches, 150e153 Diffusion-based mass transfer, 332 Diffusivity, 54e55 Direct contact freezing, 168, 228 Direct immersion freezing, 171e174 Double-pipe condenser, 65 Dough freezing, 267e269 E Effective specific heat methods, 355e356 Efficiency and energy consumption, 177 Empirical solutions, 342e345 Energy consumption, 97e98 Energy efficiency, 111 Enthalpy method, 336e337, 356e357 Environmental factors, 110 Equipment and facility design, 110 Equipment costs, 98 Evaporative condenser, 66 Evaporative cooling, 13e14 Expansion valves, 66e67 Extracellular ice nucleators (ECINs), 280 F Finite difference method (FDM), 346e348 Finite element method (FEM), 348e350 Finite volume methods (FVM), 350e351, 367 Flake ice machines, 105e107 Fluidized bed freezers, 101 Food and Agriculture Organization (FAO), 80, 117 Food constituents, freezing on, 37 Food Industry Association (FMI), 201 Food preservation, 3e4 comparative analysis in, 112 effectiveness in, 113

Index

Food products, 379e383 characteristics, 110 Food quality, 137e138 Freezer burn, 40 capacity and temperature, 124e126 type of, 386e389 “Freeze-tolerant” yeasts, 277 Freezing processes, 25e26, 201e211, 334e340 approaches, 30e34 baked goods, constituents of, 274e278 equipment and technologies, 208e211 of fruits and vegetables. See Fruits and vegetables, freezing of microbial and physicochemical aspects of foods, 35e38 of meat, poultry and seafoods, 225, 227e231, 244e251 modeling example, 133e134 novel freezing system and future trends, 42e45 physical and transport phenomena involved in, 331e334 point, 335e336 postfreezing events, 38e42 process-general factors affecting freezing, 374e377 on quality of frozen bakery goods, 262e267 rate on characteristics of ice crystals, 269e270 rate/speed, 377e393 technologies, 271e274 thermochemistry of, 26e30 time, parameters influence, 377e393 types focused on direct, indirect, and immersion, 168e169 Freezing systems, 167e168 Freezing time determination of, 27e30 prediction, 130e133 Frequentist approaches (two versus one step analysis)-isothermal data, 309e314 Frequentist versus stochastic approach, 307e309 Frozen bakery goods, 261e267

Index

Frozen dough, 267e270 Frozen foods, 294te295t cold storage, 82e83 modes of deterioration of, 290e294 parameters on quality of, 305e306 Frozen fruits/vegetables, consumers’ demand for, 200e201 Frozen material dimensions and shape of, 384 type of, 377e383 Fruits and vegetables, freezing of, 199e200 equipment and technologies, 208e211 market trends and consumers’ demand for, 200e201 packaging and storage of, 211 phase transition, 201e203 quality variations in, 211e218 thermo-physical attributes of, 204e208 G Gel ice mat, 13 Global frozen food industry, 189e190 Gluten, 274e276 Gold nanoparticles (AuNPs) nanocomposite, 246 H Handling and labor, 108 Heat and mass transfer for refrigeration technology, 54e57 Heat balance, 96 Heat transfer, 56e57, 331e332 High-pressure-assisted freezing, 273 High-pressure float valve, 66 Horizontal plate freezers, 156 Hydro/water cooling, 14 I Ice chilling, 12e13 Ice nucleation agents, 280 Ice nucleation proteins (INPs), 280 Ice-water refrigerating system, 4 Immersion chilling and freezing (ICF), 177 Immersion freezing, 32, 156e158, 169e170 principles of, 170e171 systems, 167e170, 176e179 technologies, 179e189

401

Impingement freezers, 124 Impingement jet freezers, 101 Indirect contact freezing, 158e162, 168, 228e231 Indirect immersion freezing, 174e175 Individual-fluidization freezing (IQF), 384 Individual quick freezing (IQF), 120, 176, 201 Innovative freezing technologies, 210e211 Intelligent packaging systems, 290 Isomassic recrystallization, 39 K Kinetic parameter estimation, 307e309 Kinetics for frozen foods’ degradation, 296e306 L Latent cooling process, 8, 96 Latent heat, release of, 355 Leidenfrost Effect, 152 Levy equation, 29 Limited capacity, 97 Lipoxidase (LOX), 216e217 Liquid cooling evaporators, 68e69 Liquid immersion (LI), 250e251 Liquid nitrogen spray freezing, 273e274 Liquids of low freezing point (LFP), 156e157 Load and product load, 83e84 Long-term storage, 97 Low-pressure float valve, 66 Low-temperature processing system, 53e54 chilling and freezing systems, 71e72 heat and mass transfer for refrigeration technology, 54e57 main elements of mechanical refrigeration, 57e62 mechanical equipment, 62e70 refrigerants, 70 M Magnetic field-assisted immersion freezing (MFIF), 250 Magnetic resonance image (MRI) techniques, 36

402

Mascheroni and Calvelo’s approximate method, 343 Mass transfer basics of, 55e56 dense foods, during freezing of, 360e363 during immersion freezing, 363e364 phenomena, 359e364 porous foods, during freezing of, 363 through convection, 333 Mechanical refrigeration, 57e62 Mechanical strain and stress, 334 Mechanized freezers, 100 Microbial quality, effects on, 234e242 Migratory recrystallization, 39 Minor food constituents during freezing, 38 Modeling coupled heat, 359e364 Modified atmosphere packaging (MAP), 245 Modified Plank’s equations, 29 Molecular diffusivity, 54e55 Multiple retention time (MRT) freezers, 122 Multipurpose cold storage, 82 N Nagaoka equation, 29 Natural polysaccharides, 278e279 Newton’s law, 57, 94e96 Nucleation, 333, 364e366 Numerical solutions, 132e133, 346e359 Nutritional quality, effects on, 243e244 O Optimizing freezing tunnel operation, 140e141 Ordinary differential equations (ODEs), 346 Oxidative flavor deterioration, 40e41 P Packaging arrangement on freezing rate, 135e137 effect of, 135e137 and insulation, 108 and storage of frozen fruits/vegetables, 211 Partial differential equations (PDEs), 331 Particle engineering process, 148 Peltier effect, 62 Pham method, 29e30

Index

Pham’s method 1 (1984), 343e345 Pham’s method 2 (1986), 345 Phase transition, 201e203 Plank’s method, 28e29 Plant origin foods, 290e292 Plate condenser, 65 Plate evaporators, 69 Plate freezing, 31e32, 158e159, 228 Postfreezing events, 38e42 Post processing cold chain monitoring, 314e317 Primary models, 296e297 Processing parameters and effective factors, 206e208 Product handling and placement, 111 Production volume and scale, 111 Product packaging, 109 Product size and density, 109 Product-specific considerations, 111 Pulsed electric field (PEF) treatment, 392e393 Q Q10 approach, 304e305 Quality aspects and microstructure, 226e227 Quality variations in frozen fruits/ vegetables, 211e218 Quasi-enthalpy method, 357e358 R Rancidity, 40e41 Ready-to-bake, 262, 264e266 Ready-to-eat, 262, 266e267 Ready-to-proof, 261e264 Reciprocating compressor, 62e63 Recrystallization, 39 Reduced moisture loss, 97 Refrigerants, 70 Refrigerated rooms, 81e86 Refrigerated seawater, 13 Refrigeration processes, mathematical modeling of, 130e137 Regulatory compliance, 111 Retains nutritional value, 97 Retrogradation, 41e42 Rotary-screw compressor, 63

Index

S Safety Monitoring and Assurance System (SMAS), 317 Salmonella strains, 227 Scroll compressor, 63 Seafood, 225e226 Secondary models, 297e305 Semi-empirical solutions, 131e132 Sensible cooling process, 8, 95 Sensible specific heat, 337 Sharp freezer, 99 Shelf-Life Decision System (SLDS), 317 Shelf-life determination, 306e314 Single and multiple retention time freezers, 122e124 Single-/double-contact freezing process, 153e156 Single Retention Time (SRT), 122, 123f Slow cooling rate, 97 Slush ice, 12 Small cold storage, 82 Sodium trimetaphosphate (STMP), 37 Space stepping, 346e351 Specific cooling system, 89 Specific heat capacity, 95 Spiral belt freezers, 101, 121e122 “Sponge effect,” 392 Spray freeze drying (SFD), 147 Spray freezing, 147e150 into liquid, 152e153 into vapor, 151 into vapor over liquid, 151e152 Spray parameters, 148e150 Starch, 274 Stephane problems, analytical solution for, 341 Still air cooling, 89e90, 93, 96e97, 99e105 costs of, 107e108 disadvantages of, 97 equations, 94e95 and top icing in food products, 108e112 Still air freezers, 99 Stochastic mathematical/statistical tools, 306e314 Storage and transportation, 108 Straight belt tunnel freezers, 120e121

403

Sub-zero temperatures and temperature fluctuations, 270 Super-chilling phase, 9e10, 20 Supercooling, 333, 364e366 Surface area and shape, 109 Surface top icing, 89 System design, 139 T Texture, 214e215 Thawing, 231e234 Thermal bridges, 87 Thermal conductivity, 54e55, 109, 338e339 Thermal diffusivity, 339e340 Thermochemistry of freezing process, 26e30 Thermo-physical attributes of fruits/ vegetables during freezing, 204e208 Thermostatic expansion valve, 67 Thiobarbituric acid reactive substances (TBARS) value, 37 Time stepping, 351e355 in finite difference method (FDM), 352e354 in finite element method (FEM), 354e355 in finite volume method (FVM), 354e355 Time-temperature indicators (TTI), 246 Time-temperature integrators (TTI), 290, 314e317 Top-icing, 90e94, 105e107 advantages of, 97e98 costs of, 107e108 disadvantages of, 98 equations, 95e96 Total Volatile Basic Nitrogen (TVBN), 293 Traditional air freezing (TAF), 177 Transformations in free, 35e36 Tube and fin condenser, 65 Tunnel freezers, 100 U Ultrasonic-assisted freezing, 210e211, 271e272 Ultrasonic waves, 392

404

V Vapor compression system, 58e59 Variable thermal conductivity, 358e359 Versatility, 98 Vitamin C, 292, 310f W Walk-in cold storage, 83 Wall gain load, 83e84 Water and liquid products, 379

Index

Water cooling, 92 Water-ice transition, 212e213 Water immersion chilling, 13 Water status, 212e213 Williams-Landel-Ferry (WLF) equation, 303e304 Y Yeast, 276e278