Food Engineering Handbook, Two Volume Set: Food Engineering Handbook: Food Process Engineering [1 ed.] 1482261669, 9781482261660

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FOOD ENGINEERING HANDBOOK FOOD PROCESS ENGINEERING

EDITED BY

Theodoros Varzakas Constantina Tzia

FOOD ENGINEERING HANDBOOK

Contemporary Food Engineering Series Editor

Professor Da-Wen Sun, Director Food Refrigeration & Computerized Food Technology National University of Ireland, Dublin (University College Dublin) Dublin, Ireland http://www.ucd.ie/sun/

Handbook of Food Processing and Engineering, Volume II: Food Process Engineering, edited by Theodoros Varzakas and Constantina Tzia (2014) Handbook of Food Processing and Engineering, Volume I: Food Engineering Fundamentals, edited by Theodoros Varzakas and Constantina Tzia (2014) Juice Processing: Quality, Safety and Value-Added Opportunities, edited by Víctor Falguera and Albert Ibarz (2014) Engineering Aspects of Food Biotechnology, edited by José A. Teixeira and António A. Vicente (2013) Engineering Aspects of Cereal and Cereal-Based Products, edited by Raquel de Pinho Ferreira Guiné and Paula Maria dos Reis Correia (2013) Fermentation Processes Engineering in the Food Industry, edited by Carlos Ricardo Soccol, Ashok Pandey, and Christian Larroche (2013) Modiied Atmosphere and Active Packaging Technologies, edited by Ioannis Arvanitoyannis (2012) Advances in Fruit Processing Technologies, edited by Sueli Rodrigues and Fabiano Andre Narciso Fernandes (2012) Biopolymer Engineering in Food Processing, edited by Vânia Regina Nicoletti Telis (2012) Operations in Food Refrigeration, edited by Rodolfo H. Mascheroni (2012) Thermal Food Processing: New Technologies and Quality Issues, Second Edition, edited by Da-Wen Sun (2012) Physical Properties of Foods: Novel Measurement Techniques and Applications, edited by Ignacio Arana (2012) Handbook of Frozen Food Processing and Packaging, Second Edition, edited by Da-Wen Sun (2011) Advances in Food Extrusion Technology, edited by Medeni Maskan and Aylin Altan (2011) Enhancing Extraction Processes in the Food Industry, edited by Nikolai Lebovka, Eugene Vorobiev, and Farid Chemat (2011) Emerging Technologies for Food Quality and Food Safety Evaluation, edited by Yong-Jin Cho and Sukwon Kang (2011) Food Process Engineering Operations, edited by George D. Saravacos and Zacharias B. Maroulis (2011) Biosensors in Food Processing, Safety, and Quality Control, edited by Mehmet Mutlu (2011)

Physicochemical Aspects of Food Engineering and Processing, edited by Sakamon Devahastin (2010) Infrared Heating for Food and Agricultural Processing, edited by Zhongli Pan and Grifiths Gregory Atungulu (2010) Mathematical Modeling of Food Processing, edited by Mohammed M. Farid (2009) Engineering Aspects of Milk and Dairy Products, edited by Jane Sélia dos Reis Coimbra and José A. Teixeira (2009) Innovation in Food Engineering: New Techniques and Products, edited by Maria Laura Passos and Claudio P. Ribeiro (2009) Processing Effects on Safety and Quality of Foods, edited by Enrique OrtegaRivas (2009) Engineering Aspects of Thermal Food Processing, edited by Ricardo Simpson (2009) Ultraviolet Light in Food Technology: Principles and Applications, Tatiana N. Koutchma, Larry J. Forney, and Carmen I. Moraru (2009) Advances in Deep-Fat Frying of Foods, edited by Serpil Sahin and Servet Gülüm Sumnu (2009) Extracting Bioactive Compounds for Food Products: Theory and Applications, edited by M. Angela A. Meireles (2009) Advances in Food Dehydration, edited by Cristina Ratti (2009) Optimization in Food Engineering, edited by Ferruh Erdoˇgdu (2009) Optical Monitoring of Fresh and Processed Agricultural Crops, edited by Manuela Zude (2009) Food Engineering Aspects of Baking Sweet Goods, edited by Servet Gülüm Sumnu and Serpil Sahin (2008) Computational Fluid Dynamics in Food Processing, edited by Da-Wen Sun (2007)

FOOD ENGINEERING HANDBOOK FOOD PROCESS ENGINEERING

EDITED BY

Theodoros Varzakas Constantina Tzia

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2015 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20141015 International Standard Book Number-13: 978-1-4822-6168-4 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Dedicated to my wife Elia and my daughter Fotini for their endless support and love. To my mother for her love and understanding and to the memory of my father. Theodoros Varzakas

Dedicated to the memory of my parents. Constantina Tzia

Contents Series Preface ............................................................................................................xi Preface.................................................................................................................... xiii Acknowledgments .................................................................................................... xv Series Editor...........................................................................................................xvii Editors .....................................................................................................................xix Contributors ............................................................................................................xxi Chapter 1

Membrane Separation ..........................................................................1 Alfredo Cassano, Renè Ruby Figueroa, and Enrico Drioli

Chapter 2

Size Reduction .................................................................................... 31 Constantina Tzia and Virginia Giannou

Chapter 3

Centrifugation–Filtration ................................................................... 61 Theodoros Varzakas

Chapter 4

Crystallization .................................................................................. 131 Theodoros Varzakas

Chapter 5

Mixing-Emulsions ............................................................................ 181 Theodoros Varzakas, V. Polychniatou, and Constantina Tzia

Chapter 6

Solid–Liquid Extraction ................................................................... 253 Soia Chanioti, George Liadakis, and Constantina Tzia

Chapter 7

Supercritical Fluid Extraction .......................................................... 287 Epaminondas Voutsas

Chapter 8

Chilling and Freezing....................................................................... 319 M. Giannakourou and Virginia Giannou

Chapter 9

Drying of Foods ............................................................................... 375 Panagiotis A. Michailidis and Magdalini K. Krokida

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Chapter 10 Fluidized Bed, Spouted Bed, and In-Store Drying of Grain ........... 437 Robert H. Driscoll and George Srzednicki Chapter 11 Fermentation and Enzymes .............................................................. 489 Constantinos Katsimpouras, Paul Christakopoulos, and Evangelos Topakas Chapter 12 Fluid and Species Transfer in Food Biopolymers ............................ 519 Pawan S. Takhar Chapter 13 Encapsulation of Food Ingredients: Agents and Techniques ........... 527 Charikleia Chranioti and Constantina Tzia Chapter 14 Multiphysics Modeling of Innovative and Traditional Food Processing Technologies .................................................................. 571 Kai Knoerzer and Henry Sabarez Chapter 15 New/Innovative Technologies .......................................................... 595 George I. Katsaros and Petros S. Taoukis

Series Preface CONTEMPORARY FOOD ENGINEERING Food engineering is the multidisciplinary ield of applied physical sciences combined with the knowledge of product properties. Food engineers provide the technological knowledge transfer essential to the cost-effective production and commercialization of food products and services. In particular, food engineers develop and design processes and equipment to convert raw agricultural materials and ingredients into safe, convenient, and nutritious consumer food products. However, food engineering topics are continuously undergoing changes to meet diverse consumer demands, and the subject is being rapidly developed to relect market needs. In the development of food engineering, one of the many challenges is to employ modern tools and knowledge, such as computational materials science and nanotechnology, to develop new products and processes. Simultaneously, improving food quality, safety, and security continues to be a critical issue in food engineering studies. New packaging materials and techniques are being developed to provide more protection to foods, and novel preservation technologies are emerging to enhance food security and defense. Additionally, process control and automation regularly appear among the top priorities identiied in food engineering. Advanced monitoring and control systems are developed to facilitate automation and lexible food manufacturing. Furthermore, energy saving and minimization of environmental problems continue to be important food engineering issues, and signiicant progress is being made in waste management, eficient utilization of energy, and reduction of efluents and emissions in food production. The Contemporary Food Engineering Series, consisting of edited books, attempts to address some of the recent developments in food engineering. The series covers advances in classical unit operations in engineering applied to food manufacturing as well as topics such as progress in the transport and storage of liquid and solid foods; heating, chilling, and freezing of foods; mass transfer in foods; chemical and biochemical aspects of food engineering and the use of kinetic analysis; dehydration, thermal processing, nonthermal processing, extrusion, liquid food concentration, membrane processes, and applications of membranes in food processing; shelf-life and electronic indicators in inventory management; sustainable technologies in food processing; and packaging, cleaning, and sanitation. These books are aimed at professional food scientists, academics researching food engineering problems, and graduate-level students. The editors of these books are leading engineers and scientists from different parts of the world. All the editors were asked to present their books to address the market’s needs and pinpoint cutting-edge technologies in food engineering. All contributions are written by internationally renowned experts who have both academic and professional credentials. All authors have attempted to provide critical, comprehensive, and readily accessible information on the art and science of a

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Series Preface

relevant topic in each chapter, with reference lists for further information. Therefore, each book can serve as an essential reference source to students and researchers in universities and research institutions. Da-Wen Sun Series Editor

Preface This book provides a stimulating and up-to-date review of food process engineering phenomena. It addresses the basic and applied principles of food process engineering methods used in food-processing operations around the world. While it does cover the theory, it combines this with a practical hands-on approach. The book explores the basic and applied aspects of food process engineering phenomena from chilling/freezing, dehydration, and mixing-emulsions to new emerging foodengineering technologies, encapsulation, and modeling of innovative and traditional food-processing technologies.

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Acknowledgments The contributions by well-known, reputable, and distinguished researchers from around the world are much appreciated. We would like to acknowledge their valuable support and professionalism.

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Series Editor Born in Southern China, Professor Da-Wen Sun is a world authority in food engineering research and education; he is a member of the Royal Irish Academy (RIA), which is the highest academic honor in Ireland; he is also a member of Academia Europaea (The Academy of Europe) and a fellow of the International Academy of Food Science and Technology. His main research activities include cooling, drying, and refrigeration processes and systems, quality and safety of food products, bioprocess simulation and optimization, and computer vision technology. Especially, his many scholarly works have become standard reference materials for researchers in the areas of computer vision, computational luid dynamics modeling, vacuum cooling, and so on. Results of his work have been published in over 600 papers including about 300 peer-reviewed journal papers (Web of Science h-index = 45; Google Scholar h-index = 52). He has also edited 13 authoritative books. According to Thomson Scientiic’s Essential Science IndicatorsSM, based on data derived over a period of 10 years from the ISI Web of Science, there are about 2500 scientists who are among the top 1% of the most cited scientists in the category of agriculture sciences. For many years, Professor Sun has consistently been ranked among the top 100 scientists in the world (he was at 31st position in 2010). He received a irst class BSc Honors and MSc in mechanical engineering, and a PhD in chemical engineering in China before working in various universities in Europe. He became the irst Chinese national to be permanently employed in an Irish university when he was appointed college lecturer at the National University of Ireland, Dublin (University College Dublin [UCD]), in 1995, and was then continuously promoted in the shortest possible time to senior lecturer, associate professor, and full professor. Dr. Sun is now a professor of Food and Biosystems Engineering and the director of the Food Refrigeration and Computerised Food Technology Research Group at the UCD. As a leading educator in food engineering, Professor Sun has signiicantly contributed to the ield of food engineering. He has trained many PhD students, who have made their own contributions to the industry and academia. He has also delivered lectures on advances in food engineering on a regular basis in academic institutions internationally and delivered keynote speeches at international conferences. As a recognized authority in food engineering, he has been conferred adjunct/ visiting/consulting professorships from 10 top universities in China, including Zhejiang University, Shanghai Jiaotong University, Harbin Institute of Technology, China Agricultural University, South China University of Technology, and Jiangnan University. In recognition of his signiicant contribution to food engineering worldwide and for his outstanding leadership in the ield, the International Commission xvii

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of Agricultural and Biosystems Engineering (CIGR) awarded him the “CIGR Merit Award” in 2000, and again in 2006, the Institution of Mechanical Engineers based in the United Kingdom named him “Food Engineer of the Year 2004.” In 2008, he was awarded the “CIGR Recognition Award” in honor of his distinguished achievements as the top 1% of agricultural engineering scientists in the world. In 2007, he was presented with the only “AFST(I) Fellow Award” in that year by the Association of Food Scientists and Technologists (India), and in 2010, he was presented with the “CIGR Fellow Award”; the title of Fellow is the highest honor in CIGR and is conferred to individuals who have made sustained, outstanding contributions worldwide. In March 2013, he was presented with the “You Bring Charm to the World” Award by Hong Kong-based Phoenix Satellite Television. In July 2013, he received the “Frozen Food Foundation Freezing Research Award” from the International Association for Food Protection (IAFP) for his signiicant contributions to enhancing the ield of food freezing technologies. This is the irst time that this prestigious award was presented to a scientist outside the United States. He is a fellow of the Institution of Agricultural Engineers and a fellow of Engineers Ireland (the Institution of Engineers of Ireland). He has also received numerous awards for teaching and research excellence, including the President’s Research Fellowship, and has twice received the President’s Research Award of the UCD. He is the editor-in-chief of Food and Bioprocess Technology—An International Journal (2012 Impact Factor = 4.115), former editor of Journal of Food Engineering (Elsevier), and editorial board member for a number of international journals, including the Journal of Food Process Engineering, Journal of Food Measurement and Characterization, and Polish Journal of Food and Nutritional Sciences. He is also a chartered engineer. On May 28, 2010, he was awarded membership in the RIA, which is the highest honor that can be attained by scholars and scientists working in Ireland; at the 51st CIGR General Assembly held during the CIGR World Congress in Quebec City, Canada, on June 13–17, 2010, he was elected incoming president of CIGR and became CIGR president in 2013–2014—the term of his CIGR presidency is six years, two years each for serving as incoming president, president, and past president. On September 20, 2011, he was elected to Academia Europaea (The Academy of Europe), which is functioning as the European Academy of Humanities, Letters and Sciences, and is one of the most prestigious academies in the world; election to the Academia Europaea represents the highest academic distinction.

Editors Theodoros Varzakas earned a bachelor’s (honors) in microbiology and biochemistry (1992), a PhD in food biotechnology, and an MBA in food from Reading University, United Kingdom (1998). Dr. Varzakas was a postdoctoral research staff member at the same university. He has worked in large pharmaceutical and multinational food companies in Greece for 5 years and has at least 14 years experience in the public sector. Since 2005, he has served as an assistant and associate professor in the Department of Food Technology, Technological Educational Institute of Peloponnese (ex Kalamata), Greece, specializing in issues of food technology, food processing, food quality, and safety. Dr. Varzakas has been a reviewer in many international journals such as the International Journal of Food Science and Technology, Journal of Food Engineering, Waste Management, Critical Reviews in Food Science and Nutrition, Italian Journal of Food Science, Journal of Food Processing and Preservation, Journal of Culinary Science and Technology, Journal of Agricultural and Food Chemistry, Journal of Food Quality, Food Chemistry, and Journal of Food Science. He has written more than 90 research papers and reviews and has presented more than 90 papers and posters at national and international conferences. He has written two books in Greek, one on genetically modiied food and the other on quality control in food. He has edited a book on sweeteners, published in 2012 by CRC Press and another book on biosensors published by CRC Press in 2013. Dr. Varzakas has participated in many European and national research programs as a coordinator or scientiic member. He is a fellow of the Institute of Food Science & Technology (2007). Constantina Tzia earned a diploma (1977) and PhD (1987) in chemical engineering from the National Technical University of Athens (NTUA), Greece, and is a professor in the School of Chemical Engineering, NTUA, Greece. Professor Tzia’s main research ields are food science, food engineering, food quality, sensory evaluation of foods, food hygiene, food safety and HACCP (hazard analysis and critical control points), food processing (freezing, edible ilms/coatings, extraction, encapsulation), food technology (fats and oils, olives and olive oil, bakery products, dairy products), and utilization of food by-products (protein isolates). Dr. Tzia has more than 70 articles in international scientiic (SCI) journals, 2 books in the Greek language, 1 book (editor), and 6 chapters in international scientiic books. She has more than 120 presentations at international conferences and more than 100 at Greek conferences. She has participated in European research projects and has coordinated many national research projects and projects in cooperation with Greek food industries. She has been a reviewer in many international journals.

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Contributors Alfredo Cassano Institute on Membrane Technology, ITM-CNR University of Calabria Rende, Italy

M. Giannakourou Department of Food Technology Technological Educational Institute of Athens Athens, Greece

Soia Chanioti School of Chemical Engineering National Technical University of Athens Athens, Greece

Virginia Giannou School of Chemical Engineering National Technical University of Athens Athens, Greece

Charikleia Chranioti School of Chemical Engineering National Technical University of Athens Athens, Greece Paul Christakopoulos School of Chemical Engineering National Technical University of Athens Athens, Greece Enrico Drioli Institute on Membrane Technology, ITM-CNR University of Calabria Rende, Italy Robert H. Driscoll School of Chemical Engineering UNSW Australia Sydney, Australia Renè Ruby Figueroa Institute on Membrane Technology, ITM-CNR Rende, Italy

George I. Katsaros School of Chemical Engineering National Technical University of Athens Athens, Greece Constantinos Katsimpouras School of Chemical Engineering National Technical University of Athens Athens, Greece Kai Knoerzer CSIRO Animal Food and Health Sciences Melbourne, Australia Magdalini K. Krokida School of Chemical Engineering National Technical University of Athens Athens, Greece George Liadakis Hellenic Army Chemical Laboratory Keratsini, Greece

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Panagiotis A. Michailidis School of Chemical Engineering National Technical University of Athens Athens, Greece V. Polychniatou School of Chemical Engineering National Technical University of Athens Athens, Greece Henry Sabarez CSIRO Animal, Food and Health Sciences Melbourne, Australia George Srzednicki School of Chemical Engineering University of New South Wales Australia Sydney, Australia Pawan S. Takhar Food Science and Human Nutrition University of Illinois Urbana-Champaign, Illinois Petros S. Taoukis School of Chemical Engineering National Technical University of Athens Athens, Greece

Contributors

Evangelos Topakas School of Chemical Engineering National Technical University of Athens Athens, Greece Constantina Tzia School of Chemical Engineering National Technical University of Athens Athens, Greece Theodoros Varzakas Department of Food Technology Technological Educational Institute of Peloponnese School of Agricultural Technology, Food Technology and Nutrition Kalamata, Greece Epaminondas Voutsas School of Chemical Engineering National Technical University of Athens Athens, Greece

1

Membrane Separation Alfredo Cassano, Renè Ruby Figueroa, and Enrico Drioli

CONTENTS 1.1 1.2 1.3 1.4

Introduction ......................................................................................................1 Membrane Materials .........................................................................................2 Membrane Structure .........................................................................................3 Process Design and Operation .......................................................................... 5 1.4.1 Membrane Modules ..............................................................................6 1.4.2 Filtration Methods ................................................................................9 1.4.3 Process Coniguration......................................................................... 10 1.5 Membrane Performance ................................................................................. 11 1.5.1 Membrane Rejection and Volume Reduction Factor .......................... 11 1.5.2 Transport Mechanisms ....................................................................... 12 1.5.3 Concentration Polarization and Membrane Fouling .......................... 14 1.6 Selected Applications ..................................................................................... 17 1.6.1 Milk and Dairy Industry..................................................................... 18 1.6.2 Fruit and Vegetable Juices .................................................................. 19 1.6.3 Sugar Industry .................................................................................... 21 1.6.4 Brewing Industry ................................................................................ 23 1.7 Concluding Outlook ........................................................................................26 References ................................................................................................................26

1.1

INTRODUCTION

The irst commercial production of microporous membranes on a small scale started in 1930 together with the irst practical application of ion-exchange membranes and the development of the theory on ionic transport through charged membranes (Nunes and Peinemann 2001). However, until the late 1960s, membranes were used in a few laboratory and analytical applications, but not for industrial applications because they were too slow, too expensive, and too unselective. The seminal discovery that transformed membrane separation from a laboratory to an industrial process was the development of defect-free ultrathin cellulose acetate membranes by Loeb–Sourirajan process in the 1960s (Loeb and Sourirajan 1962; Mota et al. 2002). The situation today is different because membranes are more robust, modules and equipment are designed better, and costs have come down signiicantly, partly because of the maturing technology and partly because of competition from an increasing number of membrane suppliers and the original equipment manufacturers 1

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Food Engineering Handbook

(Cheryan 1998). Membrane technology is currently an established part of several industrial processes such as producing drinking water from the sea, cleaning industrial efluents and recovering valuable constituents, separating gases and vapors, and to concentrate, purify, or fractionate macromolecular mixtures in the food and drug industries (Strathmann et al. 2006). Membrane separation technologies have attracted much attention in the food industries over recent decades as low-energy processes, providing a gentle treatment of the product at low–moderate temperatures and covering steps such as separation, fractionation, concentration, puriication, and clariication of various streams. Even though membrane processes are guided by four major driving forces— temperature, activity, electrical potential, and hydrostatic pressure gradients—this chapter will mainly focus on the use of pressure-driven membrane processes, such as microiltration (MF), ultrailtration (UF), nanoiltration (NF), and reverse osmosis (RO) in the food industry by referring to both well-established and potential applications. These processes are based on the use of a permselective barrier through which luids and solutes are selectively transported when a hydrostatic pressure is applied across it. As a result, the feed solution is converted into a permeate containing all the components that have permeated the membrane and a retentate containing all the compounds rejected by the membrane. Section 1.1 of this chapter provides an overview on materials and structures of synthetic membranes. Section 1.2 is then focused on membrane design and evaluation of membrane performance. In Section 1.7, a summary of established and potential applications of this technology in the food industry will be provided.

1.2

MEMBRANE MATERIALS

A large variety of synthetic membranes have been reported in scientiic and patent literature. The differences may be caused by material partitioning during membrane formation or by some selected surface postformation treatments. Membrane chemistry determines the important properties such as hydrophilicity or hydrophobicity, presence or absence of ionic charges, chemical and thermal resistance, binding afinity for solutes or particles, biocompatibility, and so on (Cheryan 1998; Strathmann et al. 2006). Membrane materials must be chemically resistant to both feed and cleaning solutions, mechanically and thermally stable, and characterized by high selectivity and permeability. The materials used for the preparation of membranes can be synthetic polymers, cellulose derivatives, ceramics, inorganics, and metals that may be neutral or carry electrical charges. Although more than 130 materials have been used to manufacture membranes, only a few have achieved commercial status, and fewer materials still have to obtain regulatory approval for use in food. A brief summary of the typical materials suitable for pressure-driven membrane process is shown in Table 1.1.

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TABLE 1.1 Materials Used for the Manufacture of Membranes Material Alumina Carbon–carbon composites Cellulose esters (mixed) Cellulose nitrate Polyamide, aliphatic (e.g., nylon) Polycarbonate (track etch) Polyester (track etch) Polypropylene Polytetraluoroethylene (PTFE) PCV Polyvinylidene luoride (PVDF) Sintered stainless steel Cellulose (regenerated) Ceramic composites (zirconia on alumina) Polyacrylonitrile (PAN) Polyvinyl alcohol (PVA) Polysulfone (PS) Polyethersulfone (PES) Cellulose acetate (CA) Cellulose triacetate (CTA) Polyamide, aromatic (PA) Polyamide (PI) CA/CTA blends Composites (e.g., polyacrylic acid on zirconia or stainless steel) Composites, polymeric thin ilm (e.g., PA or polyetherurea on polysulfone) Polybenzimidazole (PBI) Polyetherimide (PEI)

1.3

Processes MF MF MF MF MF MF MF MF MF MF MF MF MF, UF MF, UF MF, UF MF, UF MF, UF MF, UF, and NF MF, UF, and RO MF, UF, and RO MF, UF, NF, and RO UF, RO RO RO RO RO RO

MEMBRANE STRUCTURE

Synthetic membranes can be classiied on the basis of their structure as porous membranes, homogeneous membranes, solid membranes carrying electrical charges, and liquid or solid ilms containing selective carriers (Strathmann et al. 2006). Porous membranes consist of a solid matrix with deined pores with diameters ranging from 300 Da are separated. The hydrostatic pressures applied as a driving force in RO are in the order of 10–100 bar.

1.4 PROCESS DESIGN AND OPERATION The selection of the most effective membrane for a speciic application plays an important role in determining the desired level of separation to be obtained. However, for an eficient utilization of membranes, the process design is equally important. MF, UF, NF, and RO are iltration processes in which a hydrostatic pressure gradient is utilized to transport speciic solutes through a membrane characterized by different permeability for different compounds. In these processes, the feed solution is converted into a permeate stream containing all the components that have permeated the membrane and a retentate containing all the compounds rejected by the membrane.

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Food Engineering Handbook

The performance of a membrane in a pressure-driven separation process depends on the iltration rate (the permeate lux) and on the membrane separation properties. These properties are a function of the membrane permeability of different compounds in the treated solution, the applied pressure, and the process design. The process design is deined by different aspects concerning the membrane coniguration, iltration methods (dead-end and cross-low coniguration), and the process coniguration. It is also of importance for the control of concentration polarization and fouling phenomena, determining to a large extent the useful membrane life for a speciic separation.

1.4.1 MEMBRANE MODULES The membrane module concept denotes the device where the membrane must be installed to perform the separation process. On a large industrial scale, membrane modules are available in six basic designs: cartridge, hollow iber, spiral wound, tubular, plate and frame, and capillary. They are quite different in their design, mode of operation, production costs, and energy requirement for pumping the feed solution through the module. Pleated cartridge modules are mainly used in dead-end MF; they consist of a pleated membrane cartridge installed in a pressurized housing. These systems are operated at relatively low pressures of 1–2 bars. The main applications are related with the sterile iltration of water and beverages such as wine, beer, and fruit juices, as well as pharmaceutical solutions. At an industrial scale, they are used as preilters in RO water desalination plants (Strathmann et al. 2006). Membrane modules for cross-low applications are illustrated in the following. The plate-and-frame coniguration (Figure 1.3a) is mainly used for smallscale applications (production of pharmaceuticals, bioproducts, or ine chemicals). Membranes, feed low spacers, and porous permeate support plates are layered together between two end plates and placed in a housing. The sheets are in the form of circular disks, elliptical sheets, or rectangular plates. The feed mixture is pressurized in the housing and forced across the membrane surface. A portion passes through the membrane, enters the permeate channel, and makes its way to a central permeate collection manifold. Plate-and-frame modules are quite expensive and the membrane replacement is labor intensive. They are used in a limited number of UF applications with highly fouling feeds. The feed channels are often