Dietary Fiber, Fruit and Vegetable Consumption and Health (Nutrition and Diet Research Progress) [1 ed.] 1608760251, 9781608760251

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NUTRITION AND DIET RESEARCH PROGRESS SERIES

DIETARY FIBER, FRUIT AND VEGETABLE CONSUMPTION AND HEALTH

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NUTRITION AND DIET RESEARCH PROGRESS SERIES Diet Quality of Americans Nancy Cole and Mary Kay Fox 2009. ISBN: 978-1-60692-777-9 (Hardcover Book) Diet Quality of Americans Nancy Cole and Mary Kay Fox 2009. ISBN: 978-1-60876-499-0 (Online Book) School Nutrition and Children Thomas J. Baxter 2009. ISBN: 978-1-60692-891-2 Appetite and Nutritional Assessment Shane J. Ellsworth and Reece C. Schuster (Editors) 2009. ISBN: 978-1-60741-085-0 Flavonoids: Biosynthesis, Biological Effects and Dietary Sources Raymond B. Keller (Editor) 2009. ISBN: 978-1-60741-622-7 Beta Carotene: Dietary Sources, Cancer and Cognition Leiv Haugen and Terje Bjornson (Editors) 2009. ISBN: 978-1-60741-611-1 Handbook of Vitamin C Research: Daily Requirements, Dietary Sources and Adverse Effects Hubert Kucharski and Julek Zajac (Editors) 2009. ISBN: 978-1-60741-874-0 Dietary Supplements: Primer and FDA Oversight Timothy H. Riley (Editor) 2010. ISBN: 978-1-60741-891-7

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NUTRITION AND DIET RESEARCH PROGRESS SERIES

DIETARY FIBER, FRUIT AND VEGETABLE CONSUMPTION AND HEALTH

FRIEDRICH KLEIN AND

GEORG MÖLLER EDITORS

Nova Science Publishers, Inc. New York

Copyright © 2010 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Available upon request ISBN: 978-1-61761-666-2 (Ebook)

Published by Nova Science Publishers, Inc.

New York

CONTENTS Preface Chapter 1

ix Processing Techniques and Their Effect on Fruit Phytochemicals Adel A. A. Mohdaly, Abdelrahman R. Ahmed and Iryna Smetanska

Chapter 2

Dietary Fibers and Gut Motility Mauro Bortolotti and Andrea Lugli

Chapter 3

Dietary Fibers-Purification, Structure and Their Health Benefits with Particular Reference to Feruloyl Arabinoxylans R.Shyama, Prasad Rao and G.Muralikrishna

Chapter 4

Chapter 5

Chapter 6

1

51

83

Nutraceuticals in Rhinacanthus Nasutus (Hattkaku-Reishi-Soh) Noboru Motohashi

119

Use of in vitro Digestion and Fermentation Models to Study Health Effects of Dietary Fibres in Cultured Cells Daniel Scharlau, Anke Borowicki, Katrin Stein and M. Glei

157

Bamboo Shoots: A Rich Source of Dietary Fibres C. Nirmala, H. Sheena and E. David

173

viii Chapter 7

Chapter 8

Chapter 9

Chapter 10

Index

Contents Tropical and Temperate Fruits as a Source of Dietary Fiber and Bioactive Compounds Antonio Jiménez-Escrig Fruit and Vegetable Consumption, Physical Activity and Body Mass Index among Teenagers in Hong Kong Mimi M.Y. Tse and Iris F.F. Benzie Beneficial Effects of Soluble Fiber (Plantago Ovata Husk) on Plasma Triglycerides and Apolipoprotein B to Apolipoprotein A-I Ratio in Men in Cardiovascular Disease Secondary Prevention Rosa Solà, Adriana Alvaro,Rosa M. Valls, Joan-Carles Vallvé, Anna Anguera The Paradox of Dietary Fiber and Colorectal Cancer Da-Hong Wang, Michiko Kogashiwa and Keiki Ogino

189

199

211

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PREFACE Fruits are an excellent source of essential vitamins, minerals, and dietary fiber in the human diet. They are also a rich source of secondary metabolites that are proving to play an important role in the protection against numerous chronic diseases. These substances are almost ubiquitous in plant-derived foods and inherently have more subtle effects than nutrients. This book explores the different processing methods used in the food industry, which may modify their contents, structure, and biological activity in humans. In addition, the relationships between dietary fibers and gut motility are explored since dietary fibers carry out many physiological functions in the gastrointestinal tract aimed at health preservation. This book also summarizes recent progressions on the use of in vitro models to study health effects of dietary fibres and other nutrients using in vitro colon cell models. In addition, epidemiological studies evidence that plantbased food play a crucial role in the prevention of diseases. The authors highlight the potential of tropical and temperate fruits as sources of dietary fiber with associated antioxidant compounds. Other chapters in this book examine the fruit and vegetable consumption, physical activity levels and body mass index among teenagers, explore new dietary strategies to reduce cardiovascular disease (CVD) and discuss the potential of using alternative dietary assessment methods for researches of dietary fiber colorectal cancer. Chapter 1 - Fruits are an excellent source of essential vitamins, minerals, and dietary fiber in the human diet. They are also a rich source of secondary metabolites that proving to play an important role in protection against numerous chronic diseases. These substances are almost ubiquitous in plant-derived foods and inherently have more subtle effects than nutrients. Carotenoids and flavonoids, the mostly spread secondary metabolites in fruits, have received much attention over the past decade due to their putative health-protective effects. A

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significant portion of the fruits consumed are processed and many of the processed products are stored in a variety of packaging materials for extended periods of time prior to consumption. Bioactive compounds that are naturally present in fruits may undergo transformations during food processing that neither decrease their nutritional value nor bioactive value but may increase it by favoring their absorption and metabolism in the human body. Thus, in this chapter there is a significant need to understand how the different processing methods used in the food industry may modify their contents, structure, and biological activity in humans. Chapter 2 - The relationship between dietary fibers and motility of the digestive tract is essential for the accomplishment of their functions, but is somewhat complex, as there may be reciprocal influences. In fact, it is well known that fibers can modify gastrointestinal motility, but it is not as much known that gastrointestinal motility may modify the functions of fibers and reverse their beneficial effects. The effects of motility on fiber functions obviously is not irrelevant with respect to the fiber characteristics (e.g. viscosity, water holding capacity, fermentability etc.) and vice-versa. Consequently the kind of fibers and the kind of gut motility should be taken into account when considering their functional interactions. Fibers may influence both the motor activity of the stomach, by delaying in most cases gastric emptying, and that of the small intestine, where the most frequent fiber effect is an acceleration of transit, whereas in the colon the transit may be variously modified. However, when the motor activity is impaired, the presence of fibers in the gut lumen may became deleterious. In fact, if there is an inefficient gastric motility with gastric stasis, the accumulation of fibers in the gastric cavity induces a further worsening of gastric motility and in some cases may lead to an abnormal fermentation of fibers and formation of bezoars. A delayed intestinal transit may favour the small intestinal bacterial overgrowth, which is responsible of an out of place fiber fermentation in the small intestine with many patho-physiological problems, and, in addition, if there is a chronic pseudo-obstruction, may provoke an episode of functional obstruction. The altered transit in the colon due to constipation or diarrhoea may produce differences in fiber fermentation, that in its turn may modify the colonic transit with an abnormal production of gases. In addition, when there is a condition of severely altered colonic transit the addition of a large quantity of fibers to diet may further worsen the motor activity leading to an impaction.

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For these reasons the addition of fibers to a diet, that usually is beneficial for the gut transit, should be done with caution in patients with the above mentioned alterations of gut motility. Chapter 3 - The nature of carbohydrates present in the food is growing field of interest within the food industry due to the potential of some of them to help prevent diseases of lifestyle. Non-glycemic carbohydrates, i.e., those carbohydrates (or their components) that are not absorbed in the small intestine and, therefore, transit down to become fermented in the colon, have drawn lot of attention. In fact, food carbohydrates can be broadly classified on the basis of their in vivo digestibility into digestible and non-digestible carbohydrates. Nondigestible carbohydrates have been collectively referred to as ‘dietary fibre’. Some of these carbohydrates are of particular interest to the food industry for the purpose of developing ‘functional foods’, i.e., foods that are able to exert positive health effects. Non-digestible oligo/polysaccharides are considered as prebiotics, which stimulate the growth of bifidobacteria in the colon. Chapter 4 - Rhinacanthus nasutus (Hattkaku-Reishi-Soh, Thong-Pun-Chang) are widely cultivated in tropical and subtropical regions of South Asia just like Japanese tea trees and have been used in treatments and preventions of diverse diseases as a folklore medicines. The phytochemicals of Rhinacanthus nasutus have been noticed for their healthy effects. Recently, their phytochemicals have been isolated from various parts such as leaves, stems, roots and total plants and also their effects Rhinacanthus nasutus found by researchers. The purpose of this review is to represent their components and their actions known by now. Chapter 5 - To study health effects of different foodstuffs and nutrients, e.g. dietary fibres, on the large intestine, it is a prerequisite to obtain samples that resemble contents of the gut after digestion of the respective foodstuffs. Since the content of the human large bowel is inaccessible for routine investigations, several different in vitro systems have been established to simulate digestion and bacterial fermentation in the human gastrointestinal tract. The simplest form of these in vitro models is the batch style fermentation using defined populations of bacteria or faecal material to simulate digestive processes in the large intestine. More sophisticated models involve multistage systems simulating the whole gastrointestinal tract, including mouth, stomach as well as small and large intestine. In vitro fermentation models have been extensively used to analyse the metabolites generated by digestion and fermentation of different dietary fibres and other foodstuffs and how these metabolites influence the gut microbiota. Additionally these in vitro fermentation systems have been also used to produce samples resembling gut contents and to analyse possible health effects of these samples in in vitro cell culture studies.

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Since dietary fibres reach the colon undigested, simple batch fermentation models of the large intestine are sufficient to study possible health effects of dietary fibres on cultured cell lines. Dietary fibres are recognised for their potential to prevent cancer, e.g. colorectal cancers. Therefore a lot of research has been done to analyse effects of fermentation supernatants from dietary fibres on colon cancer prevention using different colon cell models. Chemical analyses of fermentation supernatants obtained by in vitro fermentation of dietary fibres, provided information on the respective concentrations of different components, e.g. short chain fatty acids (SCFA). Synthetic mixtures of the different components were then used to investigate which components are especially active. Dietary fibres are typically ingredients of foodstuffs that have numerous other ingredients. To analyse possible synergistic effects of dietary fibres and these ingredients, more complex in vitro systems, taking into account earlier stages of digestion, e.g. mouth, stomach or small intestine, have to be used. These multi-stage fermentation systems have therefore been modified to be used in cell culture studies. Such models will improve studies analysing the effects of foodstuffs on prevention of colon cancer and gut health in general. The following chapter summarises recent progressions on the use of in vitro models to study health effects of dietary fibres and other nutrients using in vitro colon cell models. Chapter 6 - Bamboo is a grass which belongs to the same family as our staple cereal crops and has multifarious uses in industry besides being used by rural people for food, housing and other domestic purposes. A little known fact is the edible characteristics of its juvenile shoots in the form of fresh, fermented and canned form. Use of juvenile, fresh and soft bamboo shoots as vegetable, and in the form of fermented food produced by traditional and industrial methods is well known, more particularly in bamboo growing Asian countries. Commercially, bamboo shoots are available in canned form, though fresh shoot is far superior in taste and texture. Bamboo shoots are considered as a health food as they are endowed with health enhancing properties being rich in nutrient components mainly proteins, carbohydrates, minerals, fibre, amino acids and vitamins, are low in fat and sugar and have no cholesterols. The shoots contain phytosterols and a high amount of fibre due to which they are labeled as nutraceuticals or natural medicines. Dietary fibre contents are cellulose, hemicelluloses and lignin. There are two broad types of dietary fibre described according to its solubility: insoluble and soluble. Nutrient detergent fibre (NDF) determines the indigestible component of the plant material. It consists of hemicellulose, cellulose and lignin. Acid detergent fibre (ADF) primarily represents cellulose and lignin. ADF is often used to calculate digestibility, while NDF is often used to predict intake potential. The major function of dietary fibre is to reduce the time of release of ingested

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food in colon. The roughage aids in the digestive process and elimination of waste It also functions for holding water and acts like sponge in alimentary canal. The content of dietary fibre and its components in bamboo shoots increases with age, but as the tissue grows old, the shoots become inedible. With fermentation and canning also, their content increases in the shoots. Whereas, the fermented shoots have a lesser amount of ADF, the canned as well as the fresh shoots have nearly equal amount of ADF. Lignin content in both the fresh and canned shoots was less than the fermented shoots. The canned shoots have a comparatively higher content of hemicelluloses than the fermented as well as the fresh shoots. The fermented shoots have higher amounts of cellulose than the fresh shoots while canned shoots have lower amount of cellulose than both the fresh and fermented shoot. The dietary fibre content in the fresh juvenile shoots ranges between 2.255-4.490 g/100g fresh weight and reaches upto 13.840/100 gm fresh weight in 10 days old emerged shoots of some bamboo species. The recommended level of fibre for adults is 25-30 g a day, in combination with at least 2 litres of fluid to ensure thorough digestion. Foods and food products that contain 6 g fibre per 100 g or 100 ml are labeled as a ‘high fibre’ food. Thus, bamboo shoots can be considered as ‘fibre rich’ foods and can meet the daily requirement of fibre in the diet. German and US companies Qualicel and Vitacel market fibre additives in white powder form with at least 95% fibre and bamboos, being the fastest growing plants can provide raw material for production of such fibre additives. Chapter 7 - Epidemiological studies provide evidence that plant-based foods play a crucial role in the prevention of chronic diseases. The association between dietary vegetable intake and chronic diseases is mainly attributed, along with the dietary fiber constituent, to a wide range of plant secondary compounds called phytochemicals. Fiber-rich foods are very good sources of these phytochemicals, which include polyphenolics, carotenoids, plant sterols and lignans. These socalled co-passengers, or co-travelers, of dietary fiber may contribute to the nutritional benefits of fiber-rich food and are an essential part of the healthful dietary fiber complex. Fruits are rich sources of various vitamins, minerals and dietary fiber required by the human body for optimal health. In addition, fruits are diverse in antioxidant composition and antioxidant activity. The objective of this chapter is to highlight the potential of tropical and temperate fruits as sources of dietary fiber with associated antioxidant compounds. Chapter 8 – Background: Increasing fruit and vegetable intake in the general population is one of the major concerns and aims of health promotion programs around the world. The teenage years are an important transition period from childhood to adulthood, when patterns of behavior and lifestyle choices are developing that will affect their current and future health. The heavy

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consumption of fast food and lack of adequate fruit and vegetable intake among adolescents in most developed countries are of increasing concern. Objective: The study aims to examine the fruit and vegetable consumption, physical activity levels and body mass index among teenagers. Methodology: A total of 203 adolescents (115 males and 88 females, mean age 13.5 years) from a secondary school in Hong Kong took part in the study, in which their body mass index, dietary habits and physical exercise pattern were recorded. Results: The prevalence of overweight and obesity, together with body fat content, were high among participants. Seventeen percent (n=35) were overweight or obese, while 26% (n=53) had body fat content that was higher than desirable. Participants’ intake of fruits and vegetables was inadequate, with half consuming ≤ 1 serving of fruit per day and the great majority (90%) consuming < 3 servings of vegetables per day. The reported reasons for the low consumption of fruits and vegetables included dislike of these foods, (47%), lack of availability of fruits and vegetables at home (25%), and habitually dining out (28%). Physical activity levels were far from optimal, with almost 50% of the participants not performing any form of exercise during the previous seven days, and only 28% having done some form of exercise during the week prior. Only 22% reported doing moderate amounts of exercise. Conclusion: In light of the inadequate consumption of fruits and vegetables, low physical activity level, and high prevalence of overweight and obesity found in this study, educational initiatives are urgently needed to encourage teenagers in Hong Kong to adopt a healthier diet and more active lifestyle. Chapter 9 - Background: New dietary strategies to reduce cardiovascular disease (CVD) risk include, as part of secondary prevention, the addition of fiber to the diet. Objective: To study the effect of treatment with soluble-fiber derived from Plantago ovata (Po) husk on lipids, in 28 men with CVD and plasma low density lipoprotein (LDL)-cholesterol concentration ≤3.35 mmol/L (≤130 mg/dL). A lowsaturated-fat diet supplemented with 10.5 g/d Po husk was consumed for 8 weeks, under controlled conditions. Results: Following Po husk treatment, plasma apolipoprotein (apo) A-I increased 4.3% (P capsaicinoids) influenced their diffusion and solubility into the brine during processing. The effects of three different methods of processing tomatoes into sauce and paste on flavonoid content were reported by Re et al. (2002). Only 9% of naringenin was retained

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after processing tomatoes into sauce regardless of the processing method used, whereas 71% and 75% of rutin were retained by super cold break (65°C under vacuum) and hot break (90°C) methods, respectively, compared to only 48% retained by the cold break (65°C) method. The effects of three different time–temperature process conditions (101°C for 40 min, 104°C for 10 min, and 110°C for 2.4 min) on the total phenolic and procyanidin contents in clingstone peaches were reported by Asami et al. (2003b). Peaches processed at 104°C for 10 min lost 21% of total phenolics, those processed at 110°C for 2.4 min lost 11% of total phenolics, while those processed at 101°C for 40 min retained comparable levels of total phenolics as the raw material. Peaches processed at 104°C for 10 min were analyzed for procyanidins with results compared to levels in frozen fruit. Marked reductions, 49% and 88% of procyanidin monomers and dimers, respectively, and a complete loss of procyanidin trimers through heptamers occurred in thermally processed peaches. In a follow-up study, the authors determined that loss of procyanidins in peaches during thermal processing was the result of leaching from the fruit into the syrup (Hong et al., 2004). Several studies have reported changes in anthocyanins and other polyphenolics during canning of highly pigmented fruit. The total anthocyanin and total phenolic contents of pitted Bing cherries canned in light syrup did not change appreciably during canning, but approximately 50% of the anthocyanins and phenolics were transferred from the fruit into the syrup (Chaovanalikit and Wrolstad, 2004a). In another study involving canned Bing cherries increased levels of anthocyanins, total phenolics, hydroxycinnamates, epicatechin, and flavonol glycosides were observed after canning, which was attributed to increased extraction efficiency of the softened fruit (Chaovanalikit and Wrolstad, 2004b). Consistent with results from the first study, approximately 50% of the polyphenolics were leached into the syrup during canning. The anthocyanin content of fresh and frozen plums decreased 17% and 37%, respectively, during canning (Weinert et al., 1990a). During canning decreased levels of anthocyanins in the skin were accompanied by increased levels in the flesh and syrup, with uniformly distributed levels obtained in the skin, flesh, and syrup after one week of storage. In a follow-up study Weinert et al. (1990b) reported that anthocyanins losses during canning of plums were not associated with changes in polymer concentration, and suggested the losses were due to thermal destruction, irreversible binding, or oxidation. The effects of processing unit operations on the total phenolic and total anthocyanin content of strawberry puree were studied by Klopotek et al. (2005). The mashing step resulted in a 15% loss in total phenolics, but an apparent 20%

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increase in total anthocyanins, which was thought to be the result of enhanced extractability. After pasteurization an additional 11% of total phenolics were lost, while total anthocyanin levels remained unchanged. Vacuum treated purees had similar levels of total phenolics and total anthocyanins than non-vacuum treated purees, indicating that the loss of phenolics was not related to oxidation. Strawberry processing to produce jams decreased the total ellagic acid content by 20% and the flavonoids by 15–20% (Hakkinnen et al., 2000). Aguilar-Rosas et al., (2007) who observed that, the high temperature sort time (HTST) treatment of apple juice caused a considerable lost of phenols (32.2%) when compared with the PEF treatment, which only caused a 14.49% reduction. Spanos and Wrolstad (1992) reported that total phenol concentration is reduced up to 50% in apple juice pasteurized thermally at 80°C for 15 min. Gardner et al., (2000) observed also considerable losses in phenolics in apple juice pasteurized by thermal means.

6.4 Effects of Drying Processing on Phytochemical Content of Fruit 6.4.1 Fruit Drying Fruit drying has a long tradition. Inhabitants living close to the Mediterranean Sea and in the Near East traded fruits that had been dried in the open sun. Dried fruit is a delicacy, because of the nutritive value (66– 90% carbohydrate) and shelf life. For example, inhabitants of hillside villages isolated from the outside world by snow ate diets consisting primarily of seeds and dried fruits. Today, the production of dried fruits is widespread. Nearly half of the dried fruits in the international market are raisins, followed by dates, prunes, figs, apricots, peaches, apples, pears, and other fruits. Significant amounts of sour cherries, cherries, pineapples, and bananas are also dried. Fruit may be dried as a whole (e.g., grapes, various berries, apricot, plum, etc.), in sliced form (e.g., banana, mango, papaya, kiwi, etc.), in puree form (e.g., mango, apricot, etc.), as leather, or as a powder by spray or drum drying. Depending on the physical form of the fruit (e.g., whole, paste, slices), different types of dryers must be used for drying. Figure 2 illustrates the wide assortment of dryers that may be found in practice for drying of fruits. The selection of fruit for drying depends on local circumstances and customs. For example, in the Middle East, lemons with thin peel are dried whole. The taste and aroma are preserved in the brownish inner fleshy part, which remains soft. In the United States, blackberries, cowberries (ligonberries), and grapes are dried, while in Spain, red grapes are dried. Apricots, dates, plums, and tropical fruits are dried in the sun in several countries, while apples, pears, prunes, and peaches are dried by artificial means. Dryers with natural air ventilation were

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Adel A. A. Mohdaly, Abdelrahman R. Ahmed and Iryna Smetanska

used in the 19th century in California for apple drying or to finish products that have previously been dried by the sun. Fruits dried in the sun or in dryers with natural air ventilation are referred to as “evaporated fruit,” while fruits dried in dryers with artificial ventilation are described as “dehydrated fruits.” The residual moisture content varies from small (3–8%) to large (16–18%) amounts, according to the type of fruit. Significant amounts are packaged in small portions (200–1000 g) in manufacturing plants. Often, countries importing dried fruit repackage it to meet the needs of consumers and large kitchens.

Figure 2. Various types of dryers for drying of fruit.

Fruit mixtures are widely consumed both in the United States and Europe. Fruit is packed as a mixture or each component is packed separately in a transparent, appealing packaging. Well-known components are round slices of apples, apricots and peaches, pear halves, prunes, sour cherries, and dates. Often, walnuts and almonds are also added to the mixture. Dried fruit is widely used by the confectionery, baking, and sweets industries. Soup manufacturing plants use dried fruits in the various sauces, garnishments, puddings, and ice powders, and food for infants and children. Dried fruits are used in various teas, e.g., rose hips, and by the distilling industry (dried prunes, apricots). Applications include fruit powders processed from juices or pulps that dissolve quickly. The development of the fruit powders was possible through processing, which preserves color and flavor (vacuum drying, lyophilization, and swelling). Artificial drying made it economically possible to use raw materials at competitive prices and of high quality; examples are apples, prunes, and rose hips. Various milling procedures make it possible to dry highly valuable berries with soft flesh (strawberries, raspberries) and mature stone-fruits (apricots, peaches) (Hui et al., 2006).

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6.4.2 Effects Of Dehydration On Flavonoids And Phenolic Compounds Dehydration is one of the oldest methods for preserving foods and is still widely used in commercial manufacturing of dried fruit products. It is well known that drying methods employing high temperatures and long drying times result in thermal degradation of heat sensitive nutrients, including carotenoids and flavonoids, which can adversely affect the color of dehydrated products. Several different dehydration techniques available for preserving fruits vary significantly in both drying temperature and duration. Solar drying (SD) and conventional hotair drying (HAD) methods require high temperatures and long durations, parameters that are detrimental to the texture, color, flavor, and nutritional quality of the product. Conversely, freeze drying (FD) of foods, although expensive compared to other dehydration methods, is a relatively benign method that minimizes thermal damage and generally results in excellent retention of color, flavor, texture, and nutritional quality. Vacuum microwave drying (VMD) has recently been promoted as an alternative method to improve the quality of dehydrated products. By combining the positive effects associated with vacuum (lower drying temperature and rapid mass transfer) with those of microwave heating (rapid energy transfer), products can be dried rapidly at lower temperatures. Additionally, VMD reduces the exposure of nutrients to oxygen, a critical step in minimizing oxidation of pigments responsible for acceptable product color. The effects of different dehydration methods on the retention of carotenoids and flavonoids in fruits have been studied. The studies indicate that phenolic compounds are much more susceptible to thermal degradation during dehydration than carotenoids, and that FD and VMD result in greater retention of the compounds than HAD. In a study of Saskatoon berries, the retention of total anthocyanins in FD, VMD, and HAD samples dried to similar water activity levels of 73%, 49%, and, 18%, respectively, as compared with levels found in fresh frozen berries (Kwok et al., 2004). Different classes of phenolic compounds show marked differences in their retention during dehydration, which appears to be related to their susceptibility to enzymatic oxidation. Changes in the phenolic composition of raisins subjected to three different dehydration treatments – sundried, dipped in hot water and dried (dipped), and dipped in hot water, treated with sulfur dioxide and dried (golden) – were compared with fresh and frozen Thompson seedless grapes (Karadeniz et al., 2000). Procyanidins and flavan-3-ols were completely degraded in all raisin samples, only 10% of the two major hydroxycinnamic acids (caftaric and coutaric acids) were retained, while approximately 38% of the major flavonols (quercetin and kaempferol glycosides) were retained. Golden raisins retained higher levels of caftaric and coutaric acids

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and had lower levels of oxidized cinnamic acids than the sun-dried and dipped samples, suggesting that the sulfur dioxide treatment ameliorated oxidation. The retention of flavonols among the three treatments varied, with golden raisins retaining higher levels of one quercetin glycoside but lower levels of rutin and two kaempferol glycosides than the sun-dried and dipped raisins. Ferreira et al. (2002) studied the effect of sun drying on the phenolic composition and content of a Portuguese pear (var. Bartolomeu). Compared to fresh fruit only 4%, 9%, and 32% of hydroxycinnamic acids, monomeric catechins, and procyanidins, respectively, were retained in the dried fruit. Arbutin was the only phenolic compound that was not degraded during sun drying presumably due to the low affinity of polyphenol oxidase (PPO) for the compound. Results from this study also indicated that the loss of large molecular weight procyanidins during sun drying was in part due to irreversible binding to cell wall polysaccharides, a phenomenon that may explain the sensorial loss of astringency in sun dried pears. Shi et al. (1999) measured lycopene degradation and isomerization in tomatoes subjected to osmotic-vacuum drying, vacuum drying, and HAD. Osmotic-vacuum drying resulted in greater retention and less isomerization of lycopene than the vacuum and air drying methods. This was explained by the protective role of sugar present on the tomato surface in preventing oxygen from penetrating and oxidizing lycopene. HAD tomatoes retained the least amount of lycopene and contained the highest level of cis-isomers due to the adverse effects of heat and oxygen.

6.5 Effects of Microwave Heating on Carotenoids, Phenolic Acids and Flavonoids Heating rate remains one of the major limitations for the optimization of conventional thermal processes in which the heat is transferred through both conduction and convection, although advanced equipment such as rotary retorts and scraped-surface exchangers, etc., have been developed. Microwave heating is one of the volumetric heating methods that has the potential to lead to a quantum change in the ability of the food processor to achieve the heating rates necessary to deliver profiles that could improve current UHT process routes (Mullin, 1995). Microwaves used in the food industry for heating are of ISM (industrial, scientific and medical) frequencies (2450 or 900 MHz, corresponding to 12 or 34 cm in wavelength). In this frequency range the dielectric heating mechanism dominates up to moderated temperatures. Polar molecules, the dominant water try to align themselves with the rapidly changing direction of the electric field. The energy to achieve this alignment

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is taken from the electric field. When the field changes direction, the molecule “relaxes” and the energy previously absorbed is dissipated into the surroundings, that is, directly inside the food. This means that the water content of the food is an important factor in the microwave heating performance of foods. Microwave heating has been widely applied in industrial food applications such as defrosting or thawing of frozen foods, drying, blanching, and pasteurization. Sterilization using microwaves has been investigated for many years but the commercial introduction of this technique has only come about in the last few years in Europe and Japan. Microwave pasteurization and sterilization promise to give very quick heat processing that should lead to small quality changes due to the thermal treatment according to the HTST principle. However, it has turned out that very high requirements of heating uniformity must be met in order to fulfill these quality advantages (Ohlsson, 1991). Microwave heating is reported to have varying effects on the retention of carotenoids and phenolics. De Ancos et al. (1999) studied the effects of microwave heating on carotenoid, chlorophyll, and anthocyanin contents of fruit purees. Generally, microwave heating produced minor modifications of the qualitative and quantitative composition of carotenoids in papaya and anthocyanins in strawberry purees, but resulted in extensive losses of chlorophyll a and b and xanthophylls in kiwi puree. In a study on apple mashes, juice from four heat treatments (40°C, 50°C, 60°C, and 70°C) in a 2450 MHz microwave oven at 1500 W of Fuji and McIntosh apple mashes were compared to juice from unheated mash. Microwave heat treatment of the mash increased extraction of phenolics and flavonoids from apple mash and resulted in juice with increased concentrations of total phenolics and flavonoids. Therefore, microwave heating of apple mash before juice extraction resulted in a high quality juice with increased phenolic and flavonoid content as well as increased juice yield (Gerard and Roberts 2004). Chlorogenic acid concentration increased 2–3 times after the microwave heating of Idared apple puree, in comparison with control samples. Microwave energy has the advantage of heating solids rapidly and uniformly, thus inactivating the enzymes more quickly; it minimizes phenolic oxidation. The addition of ascorbic acid and microwave heating significantly increased not only chlorogenic acid concentrations, but also polymeric procyanidin concentration from 145 mg/kg to 404 mg/kg and 620 mg/kg, respectively. (Jan Oszmianski et al., 2008)

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7. NON-THERMAL PROCESSING TECHNIQUES INFLUENCING PHYTOCHEMICAL CONTENT OF FRUIT Thermal processing is the most common method for extending the shelf life of fruit products, by inactivating microorganisms and enzymes. However, thermal processing can diminish the sensory and nutritional qualities of juices (Pedro Elez-Martinez, 2007; Braddock, 1999).Consumer requirements for foods are constantly changing. Today consumers demand foods that are both fresh and natural. Therefore the steps used to process foods should be designed to preserve their natural quality. Hence non-thermal processing techniques such as highpressure processing (HPP) and pulsed electric field (PEF) have been attracting more attention from food scientists and engineers in recent years not only because of their food preservation capabilities but also because of their potential to achieve some interesting functional effects.

7.1 Effects of High-Pressure Processing on Carotenoids and Flavonoids High-pressure processing (HPP) is an excellent alternative to thermal processing of fruits as pressures commonly used affect primarily covalent bonds allowing for inactivation of microorganisms and enzymes, without adverse effects on flavor and nutritional quality. Homogeneous foods are most amenable to HPP, thus most of the research has focused on juices, purees, and soups. Most studies consistently show that HPP does not significantly alter levels of bioactive compounds or antioxidant activity of fruits. In a study of tomato puree HPP (400 MPa/25°C/15 min) treated purees retained much higher levels of individual and total carotenoids than purees subjected to low (70°C/30 sec) and high (90°C/1 min) pasteurization treatments (Sanchez-Moreno et al., 2006). In this as well as other studies of tomato (Sanchez-Moreno et al., 2004) and persimmon (De Ancos et al., 2000) purees HPP treatment increased the amount of extractable carotenoids compared with raw purees. The enhanced extraction of carotenoids by HPP may be due to several factors including membrane alteration, disruption of carotene–protein complexes, and alteration of macromolecular structures such as proteins and cell wall carbohydrates. Likewise, the carotenoid contents of a mixed juice (orange, lemon, and carrot) and carrot juice (Butz et al., 2003), tomato homogenate (Butz et al., 2002), and orange juice (Bull et al., 2004) were unaffected by ultra high pressure treatments 600 MPa. The effects of HPP

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treatments on flavonoids have received little attention. Anthocyanins in strawberry jam are reported to be well retained after HPP processing compared with heat-processed jam, but anthocyanins in HPP-treated jam were more susceptible to degradation during storage (Gimenez et al., 2001). The greater instability of anthocyanins during storage of HPP-treated jams as opposed to heatprocessed jams is most likely the result of residual enzymatic activities (peroxidase, polyphenol oxidase, and ß-glucosidase) that are readily destroyed by heat during traditional jam processing.

7.2 Effects Of Pulsed Electric Field Processing on Ascorbic Acid, Carotenoids and Flavonoids The pulsed electric field (PEF) process is a new and innovative non-thermal minimal processing technology that is used as an alternative preservation process for fruit juices. The aim of this technology is to inactivate microorganisms and to decrease the activity of enzymes in order to increase the shelf life of food products without undesirable heat and chemical effects. The theoretical basis of PEF technology is the use of an external electric field to destabilize cell membranes and form one or more pores in them. PEF technology applies high voltage pulses (generally 20– 80 kV/cm) for very short time (µs to ms), producing PEFs between two electrodes. This technique is very similar to electroporation, used in cell biology and genetic manipulation of cells. But, in the case of foods, the applied pulses are shorter and much more intense. The aim of the application of high voltage pulses to foods is not only to disrupt temporarily the cell membranes of microorganisms. However, in this process, the microorganisms are also killed or their numbers are drastically decreased by irreversible disruption of cell membranes. PEF has been mainly applied to preserve the quality of foods, such as to improve the shelf-life of bread, milk, orange juice, apple juice and liquid eggs (Hui et al., 2006). A high retention of vitamin C content in orange juice was observed after PEFprocessing with maximum values of 98.2% for PEF-treated orange juice. Retention of this vitamin after PEF treatment was always above 87.5% for orange juice, working with 35 kV/cm during 1000 µs at 200 Hz with monopolar pulses of 4 µs. Min, et al. (2003a) reported no differences between fresh orange juice and PEF-treated orange juice when they processed orange juice at 40 kV/cm for 97 µs at 2000 Hz with bipolar pulses of 2.6 µs and a maximum temperature of 45 °C. On the other hand, after processing orange juice by PEF with bipolar pulses of 4 µs at 800 Hz and 35 kV/cm during 750 µs (maximum temperature of 50 °C), a

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vitamin C retention of 93% was observed (Sanchez-Moreno et al., 2005). Evrendilek et al. (2000) reported that PEF-processing of apple juice did not alter the natural vitamin C of the juice (35 kV/cm, 94 µs, 952 Hz, monopolar pulses of 1.92 µs, maximum temperature 38 °C). Min et al. (2003b) did not observed differences in vitamin C retention between fresh and PEF-processed tomato juice at 40 kV/cm for 57 µs with bipolar pulses of 2 µs and a maximum temperature of 45 °C. When a thermal pasteurization (90 °C, 1 min) was applied to orange juice, the retention levels of vitamin C were 82.4%. Min, et al. (2003a, 2003b), and Sanchez-Moreno et al. (2005) also reported higher levels of vitamin C retention in orange and tomato juices treated by PEF compared with those processed by thermal treatment. High temperatures led to a loss of vitamin C because heat is known to speed the oxidation process of ascorbic acid (Gahler et al., 2003). Moreover, the depletion of vitamin C in fresh juices is also attributed to oxidative enzyme reactions promoted by ascorbate oxidase and peroxidase (Davey et al., 2000). Gemma et al., (2009) who found that watermelon juices treated at 25 kV/cm for 50 µs at 50 Hz using mono- or bipolar 1-µs pulses exhibited the highest vitamin C retention (96.4–99.9%). On the other hand, vitamin C loss was higher than 50% when PEF treatment was set up at 35 kV/cm for 2050 µs at 250 Hz applying mono- or bipolar 7-µs pulses. Such severe conditions seem to greater affect vitamin C retention in watermelon juice than in other juices such as orange, orange–carrot or strawberry juices, which exhibited retention of vitamin C above 80% (Odriozola-Serrano et al., 2009). Applying the same PEF conditions, differences in vitamin C retention among PEF-treated juices could be due to their different pH, since more acidic conditions are known to stabilise vitamin C. Increased vitamin C retention of PEF-treated fruit juices in monopolar mode may be related to inactivation of enzymes that catalyse vitamin C oxidation. In PEFtreated orange juices, enzymes such as peroxidase were more inactivated with monopolar pulses than with bipolar pulses (Elez-Martinez et al., 2006). Loss of vitamin C in watermelon juice was accelerated when increasing severity of PEF treatments. In accordance, the lower the electric field strength, the treatment time, the pulse frequency or the pulse width, the higher the vitamin C retention in orange, tomato and strawberry juices. Lycopene retention in PEF-processed watermelon juice ranged from 87.6% to 121.2%. The content achieved with PEF treatments set up at 35 kV/cm with pulses of 250 Hz was slightly higher than that of untreated samples. The application of 35 kV/cm at low frequency led to a decrease in the lycopene content of treated watermelon juice of up to 10–12% compared to the fresh fruit juice. Maximal lycopene content of 114% in watermelon juice was achieved with 7-µs bipolar pulses for 1050 µs at 35 kV/cm

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and frequencies ranging from 200 to 250 Hz (Odriozola-Serrano et al., 2009). Cortés et al., (2006) observed that the carotenoid concentration in orange juice rose slightly after applying intense PEF treatments of 35 and 40 kV/ cm for 30– 240 µs.

8. EFFECT OF FREEZING PROCESSING, FROZEN STORAGE AND THAWING ON BIOCHEMICAL CHANGES Freezing is one of the best methods for long-term storage of fruits. Freezing preserves the original color, flavor, and nutritive value of most fruits. Fresh fruits, when harvested, continue to undergo chemical, biochemical, and physical changes, which can cause deterioration reactions such as senescence, enzymatic decay, chemical decay, and microbial growth. The freezing process reduces the rate of these degradation reactions and inhibits the microbiological activity. However, it should be recognized that a number of physical, chemical, and biochemical reactions can still occur and many will be accentuated when recommended conditions of handling, production, and storage are not maintained. Although few microorganisms grow below −10°C, it should be recognized that freezing and frozen storage is not a reliable biocide. The production of safe frozen fruits requires the same maximum attention to good manufacturing practices (GMP) and hazard analysis critical control points (HACCP) principles as those used in fresh products. The quality of the frozen fruits is very dependent on other factors such as the type of fruit, varietal characteristics, stage of maturity, pretreatments, type of pack, and the rate of freezing. The freezing process reduces the fruit temperature to a storage level (−18°C) and maintaining this temperature allows the preservation of the frozen product for 1 year or more. Fruits are frozen in different shapes and styles: whole, halves, slices, cubes, in sugar syrup, with dry sugar, with no sugar added, or as juices, purees, or concentrates, depending on the industrial end-use (Hui et al., 2006).

8.1 Freezing Principles The freezing process reduces food temperature until its thermal center (food location with the highest temperature at the end of freezing) reaches −18°C, with the consequent crystallization of water, the main component of plant tissues. Water in fruit and fruit products constitute 85–90% of their total composition.

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Crystallization of water during freezing reduces water activity (aw) in these tissues and consequently produces a decline in chemical and biochemical reactions and microbial growth. Freezing also involves the use of low temperatures and reactions take place at slower rates as temperature is reduced. The study of temperature changes during freezing is basic to an understanding of how products are processed. Figure 3 shows typical freezing curves at different freezing rates. When the product is cooling down to 0°C, ice begins to develop (see section A–S, Figure 3). The exact temperature for the formation of first ice crystal depends on the type of product and is a consequence of the constituents concentration independent of water content; for example, fruits with high water content (≈90%) have a freezing point below −2°C or −3°C, while meat with less water content (≈70%) has a freezing point of −1°C; the main difference being the high sugar and organic acid concentration in fruits. Ice formation takes place after the product reaches a temperature below its freezing point (−5°C to −9°C) for only a few seconds. This process is known as super-cooling (position S in Fig. 3). After that, due to heat release during the first ice formation, the temperature increases until the freezing point is reached (position B in Fig. 3). Section B–C in Fig. 3 corresponds to the freezing of most of the tissue water at a temperature that is practically constant, with a negative slope from a decline of the freezing point due to solute concentration. The increase of solute concentration as freezing progresses causes the unfrozen portion to undergo marked changes in such physical properties as ionic strength, pH, and viscosity. This increases the risk of enzymatic and chemical reactions, e.g., enzymatic browning or oxidation– reduction, with adverse effects on frozen fruit quality. A short B–C section increases the quality of frozen fruit. This means that a fast rate freezing produces a better quality frozen fruit (see curves b and c of Figure 3). Section C–D corresponds with the cooling of the product until the storage temperature, with an important increase of solute concentration in the unfrozen portion. Below −40°C, new ice formed is undetected. Up to 10% of the water can be unfrozen, mainly joined to protein or polysaccharide macromolecular structures that take part in the physical and biochemical reactions. In frozen foods the relationship between the frozen water and the residual solution is dependent on the temperature and the initial solute concentration. The presence of ice, and an increase in solute concentration, has a significant effect on the reactions and state of the fruit matrix. The concentration of the solute increases as freezing progresses; and thus, solute concentration of the unfrozen matrix can leach out of the cellular structures causing loss of turgor and internal damage. Solute-induced damage can occur whether freezing is fast or slow, and cryoprotectants, such as sugars, are usually

Processing Techniques and Their Effect on Fruit Phytochemicals added to aqueous (Rahman, 1999).

solution

to

reduce

the

cell

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damage

8.2 Plant Cell Structure Understanding the effect of freezing on fruit requires a short review of plant cell structure. Plant cells are surrounded by a membrane and interspersed with extensive membrane systems that structure the interior of the cell into numerous compartments. The plasmalemma or plasma membrane encloses the plasma of the cell and is the interface between the cell and the extracellular surroundings. Contrary to animal cells, plant cells are almost always surrounded by a cell wall and many of them contain a special group of organelles inside the plastids (chloroplasts, leucoplasts, amyloplasts, or chromoplasts). An important property of the plant cell is its extensive vacuole. It is located in the center of the cell and makes up the largest part of the cells volume and is responsible for the turgor. It helps to maintain the high osmotic pressure of the cell and the content of different compounds in the cell, among which are inorganic ions, organic acids, sugars, amino acids, lipids, oligosaccharides, tannins, anthocyanins, flavonoids, and more.

Figure 3. Typical freezing curves of foods at different rates: (a) very slow; (b) fast; and (c) very fast (Fennema, 1976).

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Vacuoles are surrounded by a special type of membrane, the tonoplast. The cell wall of plants consists of several stacked cellulose microfibrils embedded in a polysaccharide matrix able to store water thereby increasing the cell volume (hydration and absorption). According to their capacity to bind or store water, the polysaccharides involved in the matrix can be classified as follows: pectin>hemicellulose>cellulose>lignin. Pectins are mainly polygalacturonic acids with differing degrees of G-galactosyl, L-arabinosyl or L-rhanmosyl residue and are predominant in the middle lamella, the layer between cells. The deesterification process of pectin is related to the softness of fruit tissues during ripening and processing (Hui et al., 2006).

8.3 Color Changes Color is the most important quality characteristic of fruits because it is the first attribute perceived by the consumers and is the basis for judging the product acceptability. The most important color changes in fruits are related to chemical, biochemical, and physicochemical mechanisms: (a) breakdown of cellular chloroplasts and chromoplasts, (b) changes in natural pigments (chlorophylls, carotenoids, and anthocyanins), and (c) development of enzymatic browning. Mechanical damage (ice crystals and volume expansion) caused by the freezing process can disintegrate the fragile membrane of chloroplasts and chromoplasts, releasing chlorophylls and carotenoids, and facilitating their oxidative or enzymatic degradation. Also, volume expansion increases the loss of anthocyanins by lixiviation due to disruption of cell vacuoles.

(I) Chlorophylls Chlorophylls are the green pigment of vegetables and fruits, and their structures are composed of tetrapyrroles with a magnesium ion at their center. Freezing and frozen storage of fruits cause a green color loss due to degradation of chlorophylls (a and b) and transformation in pheophytins, which transfers a brownish color to the plant product (Cano, 1996). One example is kiwi-fruit slices that show a decrease in chlorophyll concentration between 40% and 60%, depending on cultivar, after freezing and frozen storage at −20°C for 300 days (Cano et al., 1993).

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Figure 4. Pathways of chlorophyll degradation. (adapted from Heaton et al., 1996)

Different mechanisms can cause chlorophyll degradation; loss of Mg due to heat and/or acid, which transforms chlorophylls into pheophytins; or loss of the phytol group through the action of the enzyme chlorophyllase, which transforms chlorophyll into pheophorbide. Loss of the carbomethoxy group may also occur and pyropheophytin and pyropheophorbide can be formed (Figure 4) (Heaton et al., 1996). Acids, temperature, light, oxygen, and enzymes easily destroy the chlorophylls. Thus, blanching (temperature/time), storage (temperature/time), and acidity are the important factors to be controlled during processing in order to preserve chlorophylls. Other chlorophyll degradation mechanism can cause degradation by the action of peroxides, formed in the fruit tissue due to the oxidation reaction of polyunsaturated fatty acids catalyzed by the enzyme LOX. An important quality parameter employed to determine the shelf life of frozen green fruits is the formation of pheophytins from chlorophylls. As different types of enzymes can be involved in chlorophyll degradation (LOX, POD, and chlorophyllase), blanching and addition of inorganic salts such as sodium or potassium chloride and sodium or potassium sulphate are efficient treatments to preserve green color (Cano et al., 1993).

(II) Carotenoids Carotenoids are among the most abundant pigment in plant products and are responsible for the yellow, orange, and red color of most of the fruits. All of them are tetraterpenes and contain 40 carbon atoms in eight isoprenes residues. ß-

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carotene and lutein are the carotenoids present in most of the fruits. Important sources of these pigments are as follows: • • • •

ß-cryptoxanthin: oranges lycopene: tomatoes, watermelon, papaya and persimmon α-carotene: banana and avocado zeaxanthin: orange and peach

Carotenoids are affected by pH, enzymatic activity, light, and oxidation associated with the conjugated double bond system. The chemical changes occurring in carotenoids during processing have been reviewed by several authors (Rodriguez-Amaya, 1997). The main degradation reaction that damages carotenoid compounds is isomerization. Most plants appear to produce mainly trans forms of carotenoids but with increased temperature, the presence of light, and catalysts such as acids, isomerization to the cis forms increases, and the biological activity is dramatically reduced. However, heat treatments of products rich in carotenoids reduce the degradation of carotenoids because of the inactivation of enzymes LOX and POD. Blanching fruits before freezing could be efficient in the preservation of carotenoids due to enzyme inactivation. Although most carotenoids are heat resistant, some carotenoids, such as epoxycarotenoids, could be affected. Carotenoids are fat-soluble pigments and breakdown of chromoplasts, by heat treatment or mechanical damage, improves their extraction with organic solvents and bioavailability but not their loss by lixiviation (Hof et al., 2000). Freezing without protector pretreatment slightly decreases total carotenoid concentration (20%) of some fruits rich in carotenoids, such as mango and papaya. But after 12 months of frozen storage at −18°C, an important decrease of total carotenoid concentration (between 40% and 65%) occurred, although the carotenoid profilewas unchanged (Cano et al., 1996). Similar results have been found with frozen tomato cubes. A pronounced stability of total carotenoids, ß-carotene, and lycopene was recorded up to the 3rd month of storage. But after 12 months of storage at −20°C, the losses of carotenoids reached 36%, of ß-carotene 51%, and of lycopene 48% (Lisiewska and Kmiecik, 2000). Freezing and frozen storage could affect the carotenoid structure and concentration depending on the type of fruit and cultivar (pH, fats, antioxidants, etc.) and the processing conditions (temperature, time, light, oxygen, etc.) (Rodriguez-Amaya, 1997).

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(III) Anthocyanins Anthocyanins are one class of flavonoid compounds, which are widely distributed plant polyphenols, and are responsible for the pink, red, purple, or blue hue of a great number of fruits (grape, plum, strawberry, raspberry, blackberry, cherry, and other types of berries). They are water-soluble flavonoid derivatives, which can be glycosylated and acylated. The effect of freezing, frozen storage, and thawing in different fruits rich in anthocyanins pigments have been reviewed by Skrede (1996). Anthocyanins in cherryfruit underwent pronounced degradation during storage at −23°C (87% after 6 months), but they are relatively stable at −70°C storage (Chaovanalikt and Wrolstad, 2004a). But in raspberry fruit, the stability of anthocyanins to freezing and frozen storage depends on the seasonal period of harvest. Spring cultivars were practically unaffected by freezing and frozen storage for 1 year at −20°C, but autumn cultivars showed a decreasing trend in total anthocyanin content (4–17%)(De Ancos et al., 2000b). In general, the freezing process does not affect the level of anthocyanins in raspberry fruit (Mullen et al., 2002). Authors explain degradation of anthocyanins during frozen storage by different chemical or biochemical mechanisms. Anthocyanins are water-soluble pigments located in the vacuoles of cell and are easily lost by lixiviation when the cell membranes break down. Also oxidation can play an important role in anthocyanin degradation catalyzed by light. PPO and POD enzymatic activities have been related to anthocyanin degradation. Thus, frozen– thawed cherry discoloration disappeared when the fruits were blanched before freezing. In slightly acidic aqueous solution at ambient temperatures, anthocyanins exist as essentially four species in equilibrium. These are the blue quinoidal base (A), the red flavylium cation (AH+), the colourless hemiacetal base (B), and the colourless chalcone form (C) (Figure 5). The changes in pH during processing can affect anthocyanin stability. Maintenance of red fruit requires an acid medium (pH < 3.5). The flavylium cation structure of anthocyanins transfers a red color to the fruit. But an increase in pH value produces a change from red to blue until the product is colorless, a consequence of transforming flavylium cation into a neutral structure (Figure 5). The loss of characteristic red color can also be produced by formation of the anthocyanin complex with different products present in the fruit matrix: ascorbic acid, acetaldehyde, proteins, leucoanthocyanins, phenols, quinones, metals (Fe3+ and Al3+), hydrogen peroxide, etc. (Escribano-Bailon et al., 1996).

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Figure 5. Structural transformations of anthocyanins (anthocyanidin-3-glucosides). R3 and R5 are normally H, OH or OCH3 moieties; GL represents a glycosyl moiety (adapted from Dangles and Brouillard, 1992)

(IV) Enzymatic Browning Browning usually occurs in certain fruits during handling, processing, and storage. Browning in fruit is caused by enzymatic oxidation of phenolic compounds by PPO (Martinez and Whitaker, 1995). PPO catalyzes either one or two reactions involving molecular oxygen. The first type of reaction is hydroxylation of monophenols, leading to formation of o-hydroxy compounds. The second type of reaction is oxidation of o-hydroxy compounds to quinones that are transformed into polymeric brown pigment. Freezing, frozen storage, and thawing of fruits, like mangoes, peaches, bananas, apples, apricots, etc., quickly develop color changes that result in nonreversible browning or darkening of the tissues. Freezing does not inactivate enzymes; however, some enzyme activity is slowed during frozen storage. Browning by PPO can be prevented by the addition of sulfites, ascorbic acid, citric acid, cysteine, and others. Selection of varieties with low PPO activity could help to control browning in frozen–thawed fruits (Cano et al., 1998).

8.4 Effect of Freezing Processing on Vitamin C, Carotenoids and Phenolic Compounds (I) Vitamin C Freezing processes have only a slight effect on the initial vitamin C content of fruit (Cano and Marin, 1992). The destruction of vitamin C (ascorbic acid) occurs

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during freezing and frozen storage, and this parameter has been employed to limit the frozen storage period of frozen fruit. The main cause of loss of vitamin C is the action of the enzyme ascorbate oxidase. If pretreatments or freezing processes do not destroy this enzyme, it is continuously active during the frozen storage. Vitamin C degradation depends on different factors, such as time–temperature conditions, type of fruit, variety, pretreatments, type of package, freezing process, etc. (Skrede, 1996). Thus as the frozen storage temperature decreases, higher vitamin C retention is achieved for different fruits like berries, citrus, tomato, etc. (Skrede, 1996; Lisiewska and Kmiecik, 2000). Also, significantly different vitamin C retention values have been achieved between varieties of fruits such as raspberry (De Ancos et al., 2000c), mango, and kiwi (Cano and Marin, 1992), which were frozen and stored under the same conditions. Vitamin C stability in freezing and frozen storage of strawberries seems to be more dependent on storage temperature than on the type of freezing process. Nonstatistical differences were observed between strawberries processed by fast rate freezing (at −20°C) and quick rate freezing (at −50°C to –100°C), but great loss was shown between strawberries stored at −18°C and −24°C (Sahari et al., 2004).

(II) Provitamin A and Antioxidant Carotenoids Some carotenoids, like ß-carotene, α-carotene, and ß-cryptoxanthin, are recognized as precursors of vitamin A. This provitamin A carotenoids, in addition to lycopene and lutein, constitute the group of antioxidant carotenoids. The prevailing opinion is that freezing and frozen storage do not prevent degradation of carotenoids. The content of ß-carotene, and consequently the provitamin A value, was decreased during frozen storage of mango, kiwi (Cano and Marin, 1992), papaya (Cano, 1996), and tomato (Lisiewska and Kmiecik, 2000). The losses were mainly due to the activity of enzymes (POD, LOX, and CAT), particularly during frozen storage in an oxygen environment. Lycopene, a characteristic carotenoid in tomato fruit, has been recognized as a powerful antioxidant (Lavelli et al., 2000). After 3 months of frozen storage (−20°C and−30°C), great stability of lycopene was recorded. After this period, slow losses occurred, the rate being faster at the higher storage temperature. After 12 months at −20°C and −30°C, the lycopene content was 48% and 26%, respectively, lower than that in the raw material (Lisiewska and Kmiecik, 2000). Other authors have reported an increase in the extraction of lycopene after 1 month of frozen storage, although after 3 and 6 months the loss of lycopene concentration was significantly higher than 40% (Urbanyi and Horti, 1989). Papaya fruit could be an important source of lycopene, but freezing and frozen storage at −20°C during 12 months

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produced a significant loss of lycopene concentration (34%) in frozen papaya slices (Cano, 1996).

(III) Phenolic Compounds The freezing process does not modify either total phenolic content or ellagic acid concentration in raspberry fruit. There is an increasing interest in ellagic acid, a dimeric derivative of gallic acid, due to its anticarcinogenic and antioxidant effects. Although frozen storage produces a slight decrease in ellagic acid content because of PPO enzyme activity, frozen storage is a good methodology to preserve phenolic compounds during long term periods (De Ancos et al., 2000c). Asami et al. (2003b) evaluated the effects of storage at refrigeration and frozen temperatures on the concentration of total phenolics in clingstone peaches. Maturity stage III peaches of the Ross variety were peeled, pitted, sliced, and frozen at –12°C for a period of 3 months. There appeared to be a statistically significant increase (P < 0.05) in total phenolic content following freezing, and this higher content was retained after 2 and 3 months of frozen storage. It was postulated that the freezing process may have resulted in cellular disruption and more facilitated extraction of phenolics. The effect of freezing and frozen storage on raspberry phytochemicals and volatiles was the subject of two manuscripts by De Ancos and colleagues (De Ancos et al., 2000a, 2000b). These authors compared two early-season and two late-season raspberry cultivars and found differential effects of freezing. In the early-season cultivars, freezing resulted in increased anthocyanin content, while in the late-season cultivars, which initially had higher concentrations of anthocyanins, freezing caused an overall reduction. The authors suggested that the preservation of anthocyanins during freezing depends on the pH of the fruit, organic acid content, sugar concentration, initial anthocyanin concentration, and initial cyaniding-3-glucoside content. They did not find a relationship between polyphenol oxidase activity and anthocyanin content. De Ancos et al., (2000b) also found that freezing had a slight effect on ellagic acid, vitamin C, and total phenolics, depending on the raspberry cultivar. Free radical scavenging capacity was decreased as a result of the freezing process, anywhere from 4 to 26%, again related to cultivar. Frozen storage of raspberries at –20°C for a 1-year period did not appear to affect total phenolics or free radical scavenging capacity, but did cause a decline in ellagic acid vitamin C. In another study of the effects of freezing on raspberry phenolics, ellagitannins, flavonoids, and antioxidant capacity (Mullen et al., 2002), these authors found that the antioxidant capacity of the fruit and vitamin C levels were not affected by freezing. The raspberry cultivar used in this study differed from those evaluated by de Ancos, however, and this

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may have affected the results. Freezing preservation of fruit is less destructive toward some antioxidant compounds, in particular total phenolics and ascorbic acid, than other means of preservation. One illustration of this is a recent publication (Asami et al., 2003a) in which Marionberries, strawberries, and corn were preserved using freezing, freeze-drying, and air-drying methods. The highest levels of both total phenolics and ascorbic acid (reduced form) were consistently found in the extractions of frozen samples, followed by those of freeze-dried and then air-dried samples. Freezing may cause some damage to cell structure, and application of a drying procedure following freezing, even though this is under vacuum at reduced temperatures, may result in even greater losses of beneficial nutrients. Air-drying at temperatures above 60°C may result in oxidative condensation or decomposition of thermolabile compounds, such as (+)-catechin and ascorbic acid. Therefore, the presence of total phenolics and ascorbic acid in the air-dried products was lower than that in either frozen or freeze-dried products.

8.5 Effect of Thawing on Phytochemical Content The quality of the original fruit, preserved by freezing, is retained by quick thawing at low temperature in controlled conditions. During incorrect thawing, chemical and physical damage and microorganism contamination can also occur. Fruit products exhibit large losses of ascorbic acid (up to 40%) and color changes when thawed for an unusually long period, e.g., 24 h at room temperature. Good results in terms of vitamin C and anthocyanins retention (90%) were achieved by thawing small frozen fruits such as bilberry, raspberry, black currant, red currant, and strawberry at room temperature (18–20°C /6–7 h), in a refrigerator (2–4°C /18 h), or in a microwave oven. Color and ascorbic acid retention of fruit was equally affected by thawing temperature and time. Thorough thawing must be determined by taking into account the size of the fruit and/or the type of packaging (Kmiecik et al., 1995). In relation to the control samples (frozen and thawed by traditional methods) freezing in liquid nitrogen and thawing in microwave oven allowed an increase of the retention of polyphenols in all strawberry varieties (1.7–25.7%). The difference between effects of the frozen strawberry preparation and thawing methods explained 68.9% of the total variation in principal component. The samples which were thawed in microwave oven had a much higher phenolic content (anthocyanins, proanthocyanins, (+)-catechin and ellagic acid) than samples which was thawed during 20 h at 20 °C. Probably enzymatic reaction

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Adel A. A. Mohdaly, Abdelrahman R. Ahmed and Iryna Smetanska

could take place in destroyed strawberry tissues during long thawing process. To achieve a higher content of phenolic compounds in strawberries, they should be thawed by faster method in microwave oven (Jan Oszmianski et al., 2009). Yurena et al.,( 2006) who found that, the relative to the content before freezing, differed depending on the thawing method (84 ± 7%, 91 ± 9% and 97 ± 6% when thawing at room temperature, in the refrigerator and in the microwave oven, respectively). There were no significant differences in the initial content and the values measured after microwave thawing. Thawing at room temperature resulted (for both standard solutions and extract) in lower AA content than thawing in the microwave oven. Microwave thawing was chosen on the basis of these results and because it was the most practical method for routine analysis.

9. PACKAGING, STORAGE AND HANDLING PROCEDURES INFLUENCING PHYTOCHEMICAL CONTENT OF FRUIT 9.1 Packaging Materials Used for Processed Fruits Thermally processed fruits have traditionally been packed in metal containers and glass jars. Products stored in glass and metal containers generally maintain their nutritional and organoleptic quality for extended periods of time due to the durability and excellent oxygen and moisture barrier properties of the containers. Plastic packaging materials have recently become more popular due to their light weight, unbreakable nature, and convenience features. Driven by advances in aseptic processing, fruit purees (baby foods) are now available in reclosable, multilayer, barrier-plastic cups that are microwaveable. Plastic polyethylene terephthalate (PET) containers are also becoming more popular for high acid fruit products and many of the containers provide convenience for the consumer through easy dispensing designs. Although the convenience afforded by these products is unquestioned, information is lacking on how processing and storage of fruits in plastic containers affect the retention of phytochemicals. Storage stability of oxygen-sensitive phytochemicals may be an important issue since the plastic packaging materials are not completely oxygen impermeable.

Processing Techniques and Their Effect on Fruit Phytochemicals

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9.2 Storage Factors Influencing Retention of Phytochemicals The stability of carotenoids and phenolics in processed fruits during storage is influenced by temperature, light, oxygen, and chemical interactions, which may or may not be oxidative in nature. The package plays an integral role in protecting food constituents from the adverse effects of oxygen and light, which is especially important for dehydrated powders that are highly prone to oxidation. Although thermally processed fruits are typically stored at ambient temperature, storage at refrigerated temperatures can result in greater retention of color and phytochemicals.

(I) Cold Storage At optimum cold storage conditions vitamin C content is decreasing; whereas most phenolics, carotenoids, glucosinolates and dietary fibers are relatively stable (Table 3). Deviations from optimum conditions may indeed affect the contents of health-related constituents. Suboptimum temperature and humidity usually give rise to enhanced rates of breakdown due to increased metabolism leading to faster maturation and senescence. Some constituents, such as phenolics, can increase their content under dehydration (without change in total amount) or when exposed to visible or UV radiation (with increased total amount). Except for vitamin C and phenolics, storage effects on nutrients and health-promoting phytochemicals have not been investigated to any great extent (Bengtsson, 2008). The biosynthesis of anthocyanins in red small fruits and berries tends to continue after harvest and during storage. Increased content of anthocyanins during cold storage has been recorded in strawberries, blueberries, grapes and pomegranates (Tomás-Barberán and Espín, 2001). (II) Controlled Atmosphere (Ca) Storage CA is a technologically advanced storage method for which temperature, humidity and the levels of oxygen and carbon dioxide are precisely controlled. Low oxygen concentration in the atmosphere during storage leads to reduced rate of respiration with a delayed onset of senescence. This has been exploited commercially for suitable species of fruit using special storage facilities. In addition to typically 1–2 kPa concentration of O2, the CA contains CO2 at an elevated level, for instance 2–6 kPa. The exact concentrations used depend upon the product. CA storage is an extension of cold storage; thus an optimum temperature is also a prerequisite for optimum product quality.

Table 3. General Effects of Storage on Contents of Health-Related Constituents of Fruits and Vegetables

Vitamin C Phenolics, fruits Phenolics, berries Carotenoids, fruits Glucosinolates Dietary fibre

Optimal temp.

Suboptimal temp.

Incident light

Decrease

Decrease

Decrease

Stable

Decrease

Increase

Increase

Increase

Variable

Variable

Variable

Stable or Decrease Stable

(adapted from Bengtsson et al., 2008)

Decrease Variable

Elevated CO2

Reduced O2 Slower decrease Stable or increase Stable or decrease

Stable or increase Stable or decrease

Variable

Increase

Elevated O2

Dehydration Decrease Variable

Increase

Increase

Decrease

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In general, CA storage retards the loss of health-related constituents compared to cold storage in air (Table 3). Some constituents can also increase their content during CA storage, for example some glucosinolates and phenolics. Controlled atmosphere (CA) storage of strawberry fruit did not affect anthocyanin content in external tissues but decreased anthocyanin content in internal tissues (Holcroft and Kader, 1999).

(III) Modified Atmosphere Packaging (Map) Modified atmosphere packaging is an extension of CA to small packages for retail, the main difference being that the gas composition is not controlled by external systems. The atmosphere composition inside the closed package changes with time and is dependent on uptake and release of gases by the food, as well as on transmission of gases through the package. The effects of MAP on healthrelated constituents are very similar to those of CA storage, when similar atmosphere compositions are compared (Table 3). In a study on fresh-cut jackfruit bulbs, it was observed that the total phenolic (TP) content decreased during storage of fresh-cut jackfruit bulbs in dip-pretreated as well as in untreated bulbs. Dip pretreatment coupled with MAP showed a significantly (p < 0.05) lower TP loss as compared to untreated samples which recorded a higher degree of degradation after just 7 days. The percentage phenolics loss in the pretreated samples was found to be 7–15%, as compared to 15–26% in the case of untreated samples kept under MA conditions (Alok Saxena, 2009). Alasalvar et al. (2005) reported that storage under low O2 atmosphere could reduce the accumulation of TP in shredded orange compared to those stored under air and high O2 conditions. Cocci et al., 2006), who reported a restricted degradation in TP, due to the reducing action of AA added in the dip pretreatment given to fresh-cut apple stored under MA conditions. The decrease in TP during storage of fresh-cut commodities could be attributed to enzymatic degradation by peroxidase (POD) and PPO activities. The loss in total flavonoids content was found to be 8–20% in the case of pretreated MA packaged samples as compared to a significantly higher loss of 20– 33% in the control samples under different MA conditions. Total carotenoids content was observed to decrease from the 7th day onwards in the control samples. The overall retention of total carotenoids was found to be in the range of 40–57%, in the case of pretreated samples, whilst the control ones showed a significantly lower retention (5–39%) under the various MA conditions during storage for 35 days (Alok Saxena, 2009). The pretreated samples kept under MA conditions showed a significantly (p < 0.05) higher retention of AA (56–69%), as against 10–49% in the case of untreated samples. Reports exist about higher retention of AA in fresh-cut

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Adel A. A. Mohdaly, Abdelrahman R. Ahmed and Iryna Smetanska

commodities subjected to MAP (Odriozola-Serrano et al., 2008). Lower respiratory activity could be attributed to higher retention of AA content, due to restriction in enzymatic oxidation of AA into dehydroascorbic acid, through headspace oxygen in the MA-packaged samples during storage.

9.3 Influnence of Storage and Handling on Health- Related Properties of Fruit (I) Vitamin C Vitamin C as L-ascorbic acid (AA) and its oxidation product Ldehydroascorbic acid (DHA) is present in all plants. The variation in content between various plant foods and within species is very large (Davey et al., 2000). L-dehydroascorbic acid is present in most fruits in small amounts, usually about 10% of the AA level, but it can increase during storage due to oxidation of AA. The storage stability of AA seems to be related to the initial level (Lee and Kader, 2000). The percentage losses are larger with a lower starting value. After cold storage for several months the AA level of apples is halved or more. Davey and Keulemans (2004) found among 31 Belgian apple cultivars that cultivars low in vitamin C had the largest losses during storage (both for three months at 1°C and for 10 days at room temperature) and these cultivars were also the ones with the worst storage outcome. The effect of storage temperature (4°C) on the AA stability was studied by Silvia Tavarini et al., (2008) in two standard solutions (50 mg/l AA in water and 3% MPA–8% acetic acid, n = 3) and a ripe banana extract spiked with 50 mg/l AA (n = 3), which was selected as the extract model because it had the highest complexity among the extracts. After 24 h, the stability of AA kept at 4°C was 95 ± 5% from the initial AA content; after 4 days it was 75 ± 4% and after 8 days 51 ± 3% (Yurena et al., 2006). In kiwi fruit, the AA significantly decreased after 6 months of cool storage and slightly increased again after a week to ambient temperature. (II) Phenolics Apple is one of the most studied fruits with regard to phenolic content. The phenolic content in apple has been repeatedly reported to be relatively stable during long-term storage at low temperature (1-2 mm, produces a retention in the gastric lumen of the dietary fibers that cannot be reduced to a diameter