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Dietary Fiber: Properties, Recovery and Applications
 0128164956, 9780128164952

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DIETARY FIBER: PROPERTIES, RECOVERY, AND APPLICATIONS

DIETARY FIBER: PROPERTIES, RECOVERY, AND APPLICATIONS Edited by

CHARIS M. GALANAKIS Research & Innovation Department, Galanakis Laboratories, Chania, Greece Food Waste Recovery Group, ISEKI Food Association, Vienna, Austria

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www. elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN 978-0-12-816495-2 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Charlotte Cockle Acquisition Editor: Nina Rosa de Araujo Bandeira Editorial Project Manager: Laura Okidi Production Project Manager: Prem Kumar Kaliamoorthi Cover Designer: Greg Harris Typeset by SPi Global, India

Contributors Federica Balestra Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy

Aires, Institute of Food Technology and Chemical Processes (ITAPROQ), Buenos Aires, Argentina;

Sheweta Barak Department of Dairy & Food Technology, Mansinhbhai Institute of Dairy & Food Technology, Mehsana, India

A.C. Flores-Gallegos Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico

Isaac Benito-Gonza´lez Food Preservation and Food Quality Department, IATA-CSIC, Valencia, Spain

Adriana Fodor Diabetes and Metabolic Diseases, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

Maurizio Bianchi Italy

Prodotti Gianni srl, Milan,

M. Garcia-Vaquero School of Veterinary Medicine, University College Dublin, Dublin, Ireland

F. Castillo-Reyes Saltillo Experimental Station, National Research Institute for Forestry, Agricultural and Livestock Research (INIFAP), Saltillo, Mexico

Lia Noemi Gerschenson Buenos Aires University, Natural and Exact Sciences School, Industry Department; CONICETUniversity of Buenos Aires, Institute of Food Technology and Chemical Processes (ITAPROQ), Buenos Aires, Argentina;

M.L. Cha´vez-Gonza´lez Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico Teodora Coldea Department of Food Technology, University of Agricultural Sciences and Veterinary Medicine ClujNapoca, Cluj-Napoca, Romania

Wen Han College of Grain and Food science, Henan University of Technology, Zhengzhou, China I˙ncinur Hasbay TUBITAK Marmara Research Center, Food Institute, Kocaeli, Turkey

Angela Cozma Department Internal Medicine, Clinique IV, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

Simona Codruta Heghes Department of Pharmaceutical Analysis, Faculty of Pharmacy, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

M. Cruz-Requena GreenCorp Biorganiks de Mexico, S.A. de C.V, Saltillo, Mexico S.

Cristina Adela Iuga Department of Pharmaceutical Analysis, Faculty of Pharmacy; Department of Proteomics and Metabolomics, MedFuture Research Center for Advanced Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

Escobedo-Garcı´a Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico

Maria Jose Fabra Food Preservation and Food Quality Department, IATA-CSIC, Valencia, Spain

Amparo Lo´pez-Rubio Food Preservation and Food Quality Department, IATA-CSIC, Valencia, Spain

Eliana Noemı´ Fissore Buenos Aires University, Natural and Exact Sciences School, Industry Department; CONICET-University of Buenos

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CONTRIBUTORS

Sen Ma College of Grain and Food science, Henan University of Technology, Zhengzhou, China Marta Martı´nez-Sanz Food Preservation and Food Quality Department, IATA-CSIC, Valencia, Spain

Department; CONICET-University of Buenos Aires, Institute of Food Technology and Chemical Processes (ITAPROQ), Buenos Aires, Argentina

Y. Mora-Cura Biorganix Mexicana SA de CV, Ramos Arizpe, Mexico

Liana-Claudia Salanța˘ Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Deepak Mudgil Department of Dairy & Food Technology, Mansinhbhai Institute of Dairy & Food Technology, Mehsana, India

J.A. Salas-Tovar Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico

Carmen Ioana Muresan Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Adela Viviana Sitar-Taut Department Internal Medicine, Clinique IV, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

Crina Carmen Muresan Department of Food Engineering, University of Agricultural Sciences and Veterinary Medicine of ClujNapoca, Cluj-Napoca, Romania

Sonia Ancuța Socaci Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Massimiliano Petracci Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy

Ramona Suharoschi Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Oana Lelia Pop Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Romina Alina Vlaic Department of Food Engineering, University of Agricultural Sciences and Veterinary Medicine of ClujNapoca, Cluj-Napoca, Romania

Carmen Rodica Pop Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

Dan Cristian Vodnar Department of Food Science, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, ClujNapoca, Romania

R. Rodrı´guez-Herrera Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico

Romana Vulturar Cellular and Molecular Biology, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

Ana Marı´a Rojas Buenos Aires University, Natural and Exact Sciences School, Industry

Preface Since the mid-1970s, interest in the role of dietary fiber in health and nutrition has prompted a wide range of research and received considerable public attention. Today, supplementing foods with dietary fiber can result in fitness-promoting foods that are lower in calories, cholesterol, and fat. The effectiveness of dietery fiber depends on preserving food’s stability, bioactivity, and bioavailability during handling, extraction, and processing. In recent years, researchers have investigated these issues, and the development of dietary fiber in functional food and nutraceutical industries has attracted great interest. Indeed, recent advantages in food processing (e.g., nonthermal technologies, etc.), new developments, and research studies in the field are consistently being released. Modern food chemists and technologists often deal with new product development and functional foods. Thereby, more integral information is needed in a new reference connecting properties and health effects of dietary fiber with recovery and processing issues, as well as industrial applications in the food industry. Following these considerations, this book fills the gap existing in current literature by providing information in the three most relevant parts: properties, recovery, and applications. The ultimate goal is to support the scientific community, professionals, and enterprises that aspire to develop industrial and commercialized applications of dietary fiber. The book consists of 10 chapters. Chapter 1 reviews the history and evolution of the state of dietary fiber with an account of refinements in extraction methods and legal definitions. Although chemical compositions and analytical methods still play an important role in the definition of dietary fiber, physiological activity has also been taken into consideration. The precise definition of dietary fiber is still evolving; one area of particular interest is whether oligosaccharides’ degrees of polymerization 3–9 should be considered as dietary fiber or not. Decades of scientific research have initiated the expansion of the term dietary fiber to include indigestible oligosaccharides with their degrees of polymerization between 3 and 9; hence responding to the positive health benefits of dietary fiber as well as fulfilling the needs in food-labeling regulations. In Chapter 2, classification, technological properties, and sustainable sources of soluble dietary fiber and insoluble dietary fibers are discussed. In Chapter 3, the behavior of dietary fiber in the human digestive tract is discussed and linked to its physiological effect with special attention to the modulation of bioavailability by the plant cell walls, the effect of dietary fiber on the rheological and colloidal state of digesta, the binding of dietary fiber with phenolic compounds, bile salts, mineral ions, digestive enzymes, and dietary fiber fermentation in the large intestine and the corresponding effect on microbiota composition. Chapter 4 revises the current evidence from human trials and epidemiological studies on the impact of fiber-rich foods and isolated dietary fiber on body-weight management and nutritional issues. Chapter 5 discusses the health effects of dietary fiber and its boosting effect on other antioxidant molecules when glycosylated with them.

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PREFACE

The traditional and innovative official methods developed to analyse dietary fiber are discussed in detail in Chapter 6, paying special attention to the recent advances in chromatographic methods (liquid, gas, and thin-layer chromatography), nonchromatographic techniques (field-flow fractionation (FFF) and capillary electrophoresis), and other analytical tools to elucidate the chemical structure of carbohydrates (e.g., nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR)). Chapter 7 discusses the conventional and emerging technologies used for the recovery of dietary fiber from plant agroindustrial by-products. Chapter 8 revises the current knowledge of the health effects of dietary fiber and prebiotic and dairy applications. The positive health effects of specific fibers on defecation, reduction of postprandial glycemic response, and maintenance of normal blood cholesterol levels are generally accepted, but other presumed health benefits of dietary fibers are still debated. Chapter 9 introduces the application of dietary fiber in wheat flour products. It starts by presenting the quality characteristic, including water distribution; textural parameters; loaf volume; cooking properties; staling issues of biscuits, breads, steamed breads and noodles modified by soluble, as well as insoluble dietary fibers. Finally, Chapter 10 discusses the main issues and topics concerning the use of dietary fibers in meat-product formulation and manufacturing. Conclusively, the book supports the modern applications of dietary fiber and reveals those that are under development. It is intended to support food scientists, technologists, engineers, chemists, and new product developers working in the whole food science field, as well as relevant researchers, academics, and professionals. It could be used by university libraries and institutes all around the world as a textbook and as ancillary reading in undergraduate and postgraduate level multidiscipline courses dealing with nutritional and food chemistry, as well as food science, technology, and processing. I would like to take this opportunity to thank all the authors of this book for their collaboration and qualitative work in bringing together all issues of dietary fiber in one integral comprehensive text. I consider myself fortunate to have had the opportunity to collaborate with so many knowledgeable colleagues from Argentina, China, Ireland, Italy, India, Mexico, Romania, and Spain. Their acceptance of the book’s approach, editorial guidelines, and timeframe is highly appreciated. I would also like to acknowledge the support of the Food Waste Recovery Group of ISEKI Food Association; as well as to thank the acquisition editor Megan Ball for her honorary invitation to lead this project; Katerina Zaliva (the book manager); and all the Elsevier team for their assistance during production. Last but not least, is a message for you, the reader. This kind of collaborative project might generate debates upon specific scientific matters. Instructive comments and even criticism are and always will be welcome. Thus, if you find any mistake or if you have an objection to content within the book, please do not hesitate to contact me. Charis M. Galanakis Food Waste Recovery Group, ISEKI Food Association, Vienna, Austria Research & Innovation Department, Galanakis Laboratories, Chania, Greece

C H A P T E R

1

Definitions and Regulatory Perspectives of Dietary Fibers M. Cruz-Requena*, S. Escobedo-Garcı´a†, J.A. Salas-Tovar†, Y. Mora-Cura‡, M.L. Cha´vez-Gonza´lez†, F. Castillo-Reyes§, A.C. Flores-Gallegos†, R. Rodrı´guez-Herrera† *

GreenCorp Biorganiks de Mexico, S.A. de C.V, Saltillo, Mexico †Department of Food Research, School of Chemistry, Universidad Autonoma de Coahuila, Saltillo, Mexico ‡Biorganix Mexicana SA de CV, Ramos Arizpe, Mexico §Saltillo Experimental Station, National Research Institute for Forestry, Agricultural and Livestock Research (INIFAP), Saltillo, Mexico

O U T L I N E 1.1. Introduction

2

1.2 History of DF Concept

2

1.3 Legal Definitions of DF 1.3.1 Definitions of DF: Institutions and Organizations Worldwide 1.3.2 Legal Status of DF Worldwide 1.3.3 Declaration of DF on Label

5 7 8 10

1.4 DF and Its Components 1.4.1 Hemicellulose 1.4.2 Cellulose 1.4.3 Pectin 1.4.4 Gums 1.4.5 Resistant Starch 1.4.6 Oligosaccharides 1.4.7 Lignin

10 10 11 11 11 11 11 12

Dietary Fiber: Properties, Recovery, and Applications https://doi.org/10.1016/B978-0-12-816495-2.00001-0

1

1.5 DF Extraction Methods 1.5.1 Fractionation of Fiber 1.5.2 Dry Processing 1.5.3 Wet Processing 1.5.4 Gravimetric Methods 1.5.5 Enzymatic-Chemical Methods 1.5.6 Physical and Microbial Methods

12 14 14 15 16 16

1.6 Physiological Activity of DF 1.6.1 Satiety Hormones and Obesity 1.6.2 Fermentability and DF 1.6.3 DF and Metabolic Diseases

16 16 16 17

1.7 Future Trends 1.7.1 Source 1.7.2 Quantification Methodologies 1.7.3 Natural Fiber Effect 1.7.4 Applications

18 18 18 18 19

# 2019 Elsevier Inc. All rights reserved.

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1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

19

References

20

1.8 Conclusions

19

Further Reading

25

Acknowledgments

20

1.7.5 Current Intakes

1.1 INTRODUCTION Dietary fiber (DF) comprises highly complex substances including natural and modified materials with substantial variations in physical and chemical properties which are not hydrolyzed by endogenous enzymes in the human small intestine, showing potential physiological effects (Poutanen et al., 2018). DF has been extensively studied due to its beneficial physiological effects, which are directly related to their different physicochemical properties, such as solubility, fermentability, water absorption, binding ability, viscosity, and bulking ability, among others. Indeed, one of the principal classifications of DF is based on water solubility, where fiber is divided in two groups, soluble and insoluble dietary fiber (IDF), which show a different effect on gastrointestinal tract and hence, different physiological health effect. However, until this day, the underlying mechanisms of the beneficial effect of DF are not completely understood (M€ uller, Canfora, & Blaak, 2018). In spite of this, DF intake has been suggested to improve glycemic control, reduce lipid levels, exhibit prebiotic effects, and may be a useful tool for weight management (Khan et al., 2018). Diets differing in quantity of soluble and insoluble fiber may have different effects on body weight gain and carbohydrate metabolism, but a contributing factor may be altering the rate of glucose absorption in the gut (Wang et al., 2007). Both types of fiber, together or separately, have contributed to the improvement of human health. Increasing DF intake may help to reduce weight gain and promote weight loss by decreasing the energy density of the diet (Burton-Freeman, Liyanage, Rahman, & Edirisinghe, 2017). Soluble dietary fiber (SDF) include β-glucan, psyllium, pectins, guar gum, arabinoxylans, and inulin and has been associated with some beneficial effects on human organisms, such as reduction of cholesterol levels, decrease of gastric emptying and small intestine transit time, prebiotic effect, and fecal bulk effect (Surampudi, Enkhmaa, Anuurad, & Berglund, 2016). While iIDF include cellulose, hemicellulose, chitosan, lignin, etc., IDF can have properties such as water insolubility, decreased fermentability, and stool bulk forming (Surampudi et al., 2016).

1.2 HISTORY OF DF CONCEPT The concept of DF has been developing for many years, and even now, there is not a complete agreement on its precise definition, basically because of the discrepancy on the carbohydrates included in the DF, in addition to its physiological effects and the methods employed to determine DF. The term DF arose from the hypothesis that linked the potential effects on a population’s health with the inclusion or exclusion of low-processed foods that are rich in fiber. Hipsley (1953) coined the DF concept after his observations on the relevance of fiber ingestion on the reduction of certain diseases. Even though initially, this idea was not

1.2 HISTORY OF DF CONCEPT

3

given enough relevance, the subsequent publications of Trowell offered a wider vision of DF significance, as well as, a more concrete concept, which encompassed the information regarding this topic at that time. In the beginning, Trowell defined DF as the plant cell wall materials that are nondigestible by human enzymes, including among them cellulose, lignin, uronic acids, hemicelluloses, and others (Trowell, 1972a, 1972b). The latter definition was closely related to the division of carbohydrates in “available” and “unavailable” established by McCance and Lawrence (1929), from which “unavailable carbohydrates” represented those carbohydrates that were not hydrolyzed by human digestive tract enzymes and thus were not directly absorbed. Likewise, Trowell stated that DF and crude fiber were not synonyms (Trowell, 1972a). The crude fiber was a concept established earlier than DF term, the former refers to portion of foodstuffs that is resistant to hydrolysis by boiling acid and later by alkali, which mainly symbolizes the amounts of cellulose and lignin in a product (Cummings, 1973). On the other hand, according to Trowell, the ability to prevent certain disease was attributable to DF instead of crude fiber (Trowell, 1972a). However, recognizing some shortcomings on its initial definition, Trowell et al. (1976) observed that consideration as DF of only those materials of plant cell wall that were not hydrolyzed by human enzymes was excluding all those nondigestible plant materials that were not in the cell wall, but within the cell. Hence, the concept of DF was reestablished as the plant polysaccharides and lignin, which were not hydrolyzed by human digestive enzymes. As aforementioned, an important issue in evolution of DF concept were the methods employed for its determination, because if based on the definition adopted, there would be defined the analytical strategy implemented. It was a difficult target to obtain a generally applicable method for DF analysis, because of the discrepancies existing between food chemists and health experts, along the time. Development of a method for DF analysis by Widdowson and McCance (1935) included determination of available carbohydrates as glucose, fructose, sucrose, and starch by mean of α-amylase (E.C. 3.2.1.1) hydrolysis served as a first step for the subsequent gravimetric estimation of “unavailable carbohydrates” or “roughage,” by subtracting values of starch, protein, and fat (McCance, Widdowson, & Shackleton, 1936). Around the same time, Williams and Olmsted (1935) achieved an approach for simulation of a physiological digestion, and thus to nondigestible compounds determination, with the adaptation of a method for estimation of indigestible residue, based on sample processing with acid and a multienzyme complex, that included α-amylase, pepsin (E.C. 3.4.23.1), and pancreatin. It was in 1975 when Hellendoorn, Noordhoof, and Slagman took back the principles established by Williams and Olmsted to improve the physiological-related digestion process, for the later gravimetric estimation of DF (Hellendoorn, Noordhoof, & Slagman, 1975). The enzymatic-gravimetric method was refined in a series of collaborative studies by Prosky, Asp, Schweizer, DeVries, Furda, and Lee, which included analysis of high molecular weight soluble and insoluble polysaccharides plus lignin (Lee, Prosky, & DeVries, 1992; Prosky, Asp, Schweizer, DeVries, & Furda, 1988), which in turn would be adopted as the AOAC methods 985.29 and 991.43. Likewise, Southgate takes the basis of the “unavailable carbohydrates” for the development of a procedure for DF quantification, with the sequential analysis of sugars, starch, cellulose, lignin, and other noncellulosic polysaccharides with a single sample (Southgate, 1969). Later, the modification of this method by Englyst, Quigley, and Hudson (1994) allowed a more accurate determination of carbohydrates through specific chromatographic methods;

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1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

It also included use of pancreatin, α-amylase, and pullulanase (E.C. 3.2.1.41). In the works of Englyst and coworkers, the term nonstarch polysaccharides (NSP) was used as an alternative expression for DF, since by that time, NSP represented chemically the major portion of DF, taking as a reference mainly the structural components of the plant cell wall. Additionally, in Englyst’s method, resistant starch (RS) was scattered and, like lignin, were not be considered as part of NSP value (Englyst & Cummings, 1984). This method laid the foundations for the enzymatic-chemical determination of DF. In the same way, the determination of NSP was also possible through the Uppsala method (AOAC method 994.13), that unlike Englyst’s method, considered the α-amylase resistant-starch and lignin, which made this a procedure that ˚ man, Westerlund, Andersson, & matched with Trowell’s DF definition (Theander, A Pettersson, 1995). At the same time, there was an increasing attention in non-previously encompassed fractions of DF, which moved away from the analytical methods of that time, but fulfilled the consideration of being not hydrolyzed by human digestive enzymes. In a couple of international surveys conducted by Prosky and Lee, an agreement existed for inclusion of nondigestible oligosaccharides (NDO), as well as, digestion-RS within DF (DeVries, Prosky, Li, & Cho, 1999). This led to the classification of dietary carbohydrates according to its degree of polymerization (DP), composition, and its physiological effect (Cummings et al., 1997). Additionally, this modification in the DF definition allowed for the incorporation of carbohydrates, such as fructans, fructooligosaccharides, galactooligosaccharides (GOSs), polydextrose, resistant-maltodextrins, and RS (McCleary & Rossiter, 2004). The individual quantity of each component could be later estimated by specific methods and added to DF value (Craig, Holden, & Khaled, 2001; De Slegte, 2002; McCleary, McNally, & Rossiter, 2002; McCleary, Murphy, & Mugford, 2000). Resistant-maltodextrin can be assessed by the method proposed by Gordon and Okuma (2002) (AOAC 2001.03). The latter surged after their observation that not all components of DF were fully recovered after ethanol precipitation in Prosky’s method since low molecular weight soluble DF does not precipitate in 78% ethanol. Hence, through the analysis of the filtered after ethanol precipitation, it was possible to estimate the low-molecular–weight-resistant maltodextrins by liquid chromatography. Furthermore, in this method, DF was defined as the nondigestible carbohydrates that preserve a DP of three or higher after enzymatic hydrolysis. In the 27th session of the Codex Committee on Nutrition and Foods for Special Dietary, a definition of DF was resolute as “carbohydrate polymers with a DP not lower than 3, which are neither digested nor absorbed in the small intestine”. When DF came from plant material, this also considered other compounds associated with polysaccharides in the plant cell wall, such as lignin, protein fractions, phenolic compounds, waxes, saponins, phytates, cutin, phytosterols, and others. Likewise, DF has to consist of carbohydrates’ polymers naturally occurring in the food as consumed or have been obtained from raw material by physical, enzymatic, or chemical methods, besides considering synthetic carbohydrate polymers. Additionally, DF must have properties like “decrease intestinal transit time and increase stool bulk, be fermentable by colonic microflora, reduce blood total and/or LDL cholesterol levels, reduce post-prandial blood glucose and/or insulin levels” (Codex Alimentarius, 2006). Some modifications were made to this definition in 2009, concisely DF was considered as “carbohydrate polymers with 10 or more monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans,” where the decision to include

1.3 LEGAL DEFINITIONS OF DF

5

carbohydrates from 3 to 9 monomeric units would be left to each nation’s authorities. Meanwhile, regarding DF sources, they were the same as previously described, but synthetic and modified carbohydrate polymers must be shown to have a physiological effect of benefit to health, demonstrated by scientific evidence (Codex Alimentarius, 2010). The disagreements in the inclusion or exclusion of NDO with DP 3–9 came to arise because it was felt that NDO did not comply with some of the physiological effects associated with DF (Codex Alimentarius, 2008). DF, as defined by Codex Alimentarius, can be assessed according to AOAC methods 2009.01 and 2011.25, which includes break up DF in: high-molecular-weight DF (HMWDF) and low-molecular-weight soluble DF (LMWSDF) (McCleary et al., 2010), as well as, separation of DF according to its solubility in water and 78% ethanol-like water insoluble DF (IDF), water-soluble DF that precipitates in 78% ethanol (SDFP), and the DF soluble in both water and 78% ethanol (SDFS) (McCleary et al., 2012). Furthermore, some improvements to these analytical methods have been made, particularly in order to mimic the human digestion process, which also minimizes over/underestimation of DF content (McCleary, 2014; McCleary, Sloane, & Draga, 2015). Changes within the DF concept by different authors over time are summarized in Table 1.1. Currently, the DF definition of Codex Alimentarius is generally accepted, though there are other definitions that also include animal fibers (e.g., chitosan) (Borderı´as, Sa´nchez-Alonso, & Perez-Mateos, 2005). As mentioned above, DF has been shown to have some specific properties like being able to modify the rate of digestion by different means, such as slowing gastric emptying, preventing specific enzyme activity toward certain diet components (e.g., starch hydrolysis), and by limiting the nutrient availability for absorption (e.g., lipids and glucose), due to the ability of some components of HMWDF to form a gel (Qi, Al-Ghazzewi, & Tester, 2018). Likewise, IDF can increase fecal bulk, while most soluble DF do not, but instead are fermented by gut bacteria for production of metabolites such as short-chain fatty acids (SCFAs). The latter are recognized to be important factors for host metabolism regulation, immune system, and cell growing. On the one hand, DF acts as an energy source for gut microbiota and protects host intestinal mucus by stimulating its production (Makki, Deehan, Walter, & B€ ackhed, 2018). In addition, some fibers can promote the selective development of specific microorganisms through its consumption, conferring health benefits (prebiotic effect) to the host. Disorders like irritable bowel syndrome and diabetes mellitus type 2 can be reduced by the consumption of certain fibers (So et al., 2018).

1.3 LEGAL DEFINITIONS OF DF Different definitions of DF have been considered over the years; however, there is not an accepted universal definition or even an organization that regulates the use of DF in foods or on labels worldwide. On the other hand, there are several institutions that handle their own definitions and that many countries use as a guide. Some of these institutions are: the CAC (Codex Alimentarius Commission), the AACCI—Cereals & Grains Association, the AOAC International (Association of Analytical Communities), the EFSA (European Food Safety Authority), the FDA (Food and Drug Administration), the ILSI (International Life

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1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

TABLE 1.1 Evolution of the Compounds Considered Within the Term Dietary Fiber Year

Components Determined as DF

Author

1929

Cellulose, hemicelluloses, pectin, condensation products of fructose (inulin)

McCance and Lawrence

1935a

Lignin, celluloses, and nonwater soluble hemicelluloses

Williams and Olmsted

1953

Lignin, cellulose, and hemicelluloses.

Hipsley

1969

Water-soluble polysaccharides (gums, mucilage, pectic substances), hemicellulose, cellulose, and lignin

Southgate

1972

Nondigestible plant cell wall material (cellulose, lignin, pentosane, uronic acids)

Trowell

1976

Nondigestible plant polysaccharides (celluloses, hemicelluloses, guar gum, mucilage, storage polysaccharides, and algal polysaccharides) and lignin

Trowell, Southgate, Wolever, Leeds, Gassull, and Jenkins

1982

Non-starch polysaccharides (cellulose, hemicelluloses, pectin, arabinogalactans, arabinoxylans, and other plant cell wall material) and Klason lignin

˚ man Theander and A

1992

IDF (cellulose, resistant starch, some xylans, lignin) and highmolecular-weight water-soluble polysaccharides (β-glucan, guar gum, certain xylanes).

Lee, Prosky, and DeVries

2004

IDF (cellulose, resistant starch, some xylans, lignin), HMWSDF (β-glucan, guar gum, certain xylanes), resistant-maltodextrin, fructans, fructooligosaccharides, galactooligosaccharides, polydextrose, resistant maltodextrin

McCleary and Rossiter

2015

IDF (cellulose, resistant starch, and some xylans), SDFP (β-glucan, guar gum, and certain xylans), SDFS (fructooligosaccharides, galactooligosaccharides, polydextrose, inulin, resistant maltodextrin), and polysaccharide and oligosaccharide associated substances (lignin, protein fractions, phenolic compounds, waxes, saponins, phytates, cutin, phytosterols and others)

McCleary, Sloaneand Draga

a

a

a

Referred as unavailable carbohydrates or indigestible residue instead of DF.

Sciences Institute), the IOM (Institute of Medicine), the FNB (Food and Nutrition Standards) and the FSANZ (Food Standards Australia and New Zealand) (FAO/WHO, 2010; Lunn & Buttriss, 2007; Slavin, 2013). In order to push regulations in food labeling, these institutions have attempted to standardize the definition of DF based on chemical composition and the physiological role in human health (Trowell, 1978; Miller, 2014). In general, DF is considered as a group of carbohydrates and resistant compounds to digestion by enzymes in the small intestine and that they are partially or totally fermented by the gut microbiota with favorable health effects (Fuller, Beck, Salman, & Tapsell, 2016; Jones, 2013). The main differences in definitions are divided into three different areas: 1. Chemical composition, whose definition is highly related to the type of analysis to quantify it. 2. Physiological effects. There are several investigations that report new sources of DF in which its functionality is evaluated in vitro according to its degree of solubility, hydration

1.3 LEGAL DEFINITIONS OF DF

7

capacity, cation exchange capacity (related with mineral absorption), degree of fermentation, fat retention capacity, among other functionalities (Mora et al., 2013; Slavin, 2013). At the same time, the different mechanisms of overweight and obesity regulation, the glycemic index and type II diabetes, colon cancer and constipation, all known as NCDs (noncommunicable diseases) have been identified. 3. Food and food processing. Another topic of discussion is whether the carbohydrates in the fiber should be intrinsically or extrinsically in the food. Those carbohydrates that can be extracted from DFs as edible material are known as intrinsic and those carbohydrates modified or that can be added to foods are the extrinsic ones (Mudgil & Barak, 2013).

1.3.1 Definitions of DF: Institutions and Organizations Worldwide Each source of DF is different due to its chemical complexity. The degree of carbohydrate polymerization has been a subject of debate. In the first related DF investigations, they only included the polymers greater than 10 monomers as DF. However, in 2009, the Codex Alimentarius Commission (CAC) supported by other institutions declared consensus to include the term oligosaccharides from 3 to 9 monomers (DP 3–9) as DF (De Menezes, Giuntini, Dan, Sarda´, & Lajolo, 2013). This definition has been adopted by several regulatory authorities, including the European Union, Australia, Canada, and New Zealand (FAO/WHO, 2010; McCleary, Sloane, Draga, & Lazewska, 2013; Mudgil & Barak, 2013). These carbohydrates are not digested or absorbed by the small intestine but can be fermented by the microbiota of the large intestine. They can also be considered as prebiotics that have been widely studied for the benefit of human health (Gibson & Roberfroid, 1995). As mentioned earlier, a world definition of DF does not exist; Each institution or organization involved has its own definition. Next, mention is made of the main institutions worldwide that have worked and continue to work on the definition of DF. CAC-Codex Alimentarius (2009). Its definition of DF includes polymers of carbohydrates with 10 or more monomer units, which are not hydrolyzed by the enzymes of the small intestine of humans. These polymers can belong to different categories: edible polysaccharides intrinsic in food; polysaccharides obtained from raw food material extracted by physical, chemical, or enzymatic processes; and synthetic polysaccharides. The latter must show a proven physiological human health benefit. The oligosaccharides of DP 3–9 are considered DF. It includes resistant oligosaccharides, RS, and resistant maltodextrins (Miller, 2014). FDA-Food and Drug Administration. DF is considered soluble and insoluble carbohydrates that are nondigestible, intrinsic, isolated, or synthetic and have physiological effects that are beneficial for human health. These effects include the regulation of glucose and cholesterol in the blood, reduction of caloric intake, and increase in the frequency of bowel movements. This includes mixed plant cell wall fibers, arabinoxylan, alginate, inulin, RS, GOS, polydextrose, and resistant maltodextrins (FDA, 2018; FDA et al., 2018). EFSA-European Food Safety Authority (2010). Its definition includes nondigestible carbohydrates including lignin and all nondigestible carbohydrates in the human small intestine and that pass through the large intestine. It also includes NSP, RS, and resistant oligosaccharides. AACC-American Association of Cereal Chemists (2001). Its definition includes those edible parts of plants or similar carbohydrates that are resistant to digestion and absorption in

8

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

the human small intestine with complete or partial fermentation in the large intestine. This definition includes polysaccharides, oligosaccharides, lignin, and associated plant substances. DFs promote beneficial physiological effects including laxation, attenuation of blood cholesterol, and attenuation of blood glucose. It includes resistant oligosaccharides, RS, and resistant maltodextrins (Miller, 2014). IOM-Institute of Medicine (2001). It handles three terms: DF, functional fiber, and total DF. DF consists of nondigestible carbohydrates and lignin that are intrinsically and intact in plants. Functional fiber is composed of isolated nondigestible carbohydrates with beneficial physiological effects in humans. Total fiber is the sum of DF and functional fiber. It includes resistant oligosaccharides, RS, and resistant maltodextrins. HC-Health Canada (2010). The DF consists of natural edible carbohydrates (DP > 2) of vegetal origin are not digested or absorbed by the small intestine, including the new accepted DFs. The new DFs are an ingredient manufactured from DF. This consists of carbohydrates (DP > 2) extracted naturally or produced synthetically that are not digested by the small intestine. It must be shown that these have beneficial physiological effects on human health and belong to one of the following categories: it has not traditionally been used for human consumption to any significant extent; it has been processed so as to modify the properties of the fiber; or it has been highly concentrated from a plant source. It includes resistant oligosaccharides, RS, and resistant maltodextrins (Miller, 2014). FSANZ-Food Standards Australia New Zealand (2001). DF consists of the edible plant parts or their extracts and their synthetic analogues, which are resistant to digestion and absorption and which are generally partially or totally fermented in the large intestine, promoting the following physiological effects: laxation, cholesterol reduction in blood, and modulation of blood glucose. It includes resistant polysaccharides, oligosaccharides (DP > 2), lignin, and RS.

1.3.2 Legal Status of DF Worldwide For DF to be included or legally considered in food labels, it is necessary that it be quantified by a recognized official method (AOAC), and in some cases, that its functionality is also recognized. For now, there are some terms in legal debate such as oligosaccharides, intrinsic compounds, and addition of extrinsic compounds to food, as well as the functionality of DF. Below is a brief discussion of the legal implications of each term. 1.3.2.1 Oligosaccharides (DP 3-9) The inclusion of the term oligosaccharides to the DF definition opened a panorama of debate between those institutions or countries that adopt or did not adopted this term. This is due to the fact that there is not an accepted official analytical method of reference for the determination of oligosaccharides in foods. Countries such as the United States do not consider oligosaccharides as DF because of the fact that there is no official measurement method; therefore, they cannot be included in the label (Slavin, 2013). However, countries such as Taiwan, which consider oligosaccharides 3–9 and lignin as part of their definition of DF, still use the reference method AOAC 985.29, which leads to the underestimation of DF content in a food. It therefore creates a conflict on the label. Table 1.2 shows those institutions and countries that consider oligosaccharides as DF. These countries advocate changes in the labeling systems

9

1.3 LEGAL DEFINITIONS OF DF

TABLE 1.2

Countries and Institutions That Accept Oligosaccharides Term With DP 3–9 as Dietary Fiber

Countries/Authorities Accepting the Definitions With DP 3–9

Countries Not Accepting the Definition With DP 3–9

Countries Awaiting a Decision

American Association of Cereal Chemists (AACC) Association Official Analytical Chemists (AOAC) Codex Alimentarius Commission (CAC) European Food safety Authority (EFSA) Food and Drug Administration (FDA) Food Standards Australia and New Zeland (FSANZ) Institute of Medicine (IOM) International Life Science Institute (ILSI) Healt Canada Brazil Canada China Indonesia Japan Korea Malaysia Mexico Singapore Thailand Taiwan Chile (separates soluble and insoluble DF in food labeling and also includes oligosaccharides (DP 3–9) as DF)

South Africa

FDA USA

(Miller, J. (2014). CODEX-aligned dietary fiber definitions help to bridge the “fiber gap”. Nutrition Journal 13(1), 1–10; Dai, F., & Cahu, C. (2017). Classification and regulatory perspectives of dietary fiber. Journal of Food and Drug Analysis 25, 37–42; Williamson, P. S. (2017). A brief overview and comparison of global fiber regulations. Cereal Foods World 62(3), 95–97.)

based on research advances, their research on DF has measurable bases. For now, however, the analysis methodologies are still under debate. 1.3.2.2 Intrinsic and Extrinsic DF The intrinsic and extrinsic terms are included in some definitions such as that of the FDA, the CODEX Alimentarus Commission (CAC), the Food Standards Australia New Zealand (FSANZ), and Health Canada (HC). The term intrinsic refers to compounds that are naturally contained in the DF. These fibers (intrinsic) occur in foods such as vegetables, whole grains, fruits, cereal bran, flaked cereal, and flours. The fibers are also considered to be “intact” because they have not been removed from the food but can be extracted (physical, chemical, or enzymatic methods). Extrinsic refers to all those extracted compounds (chemical, physical, or enzymatic methods) and synthetic analogues that are incorporated into food and must comply with some physiological effects that are beneficial to human health; these fibers are also known as “added fibers.” 1.3.2.3 DF Functionality It is important to understand why DF is considered a nutriment by some institutions and why it is therefore necessary to incorporate it into the daily diet. There are numerous

10

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

physiological benefits related to the consumption of DF in intestinal health (laxation, improves intestinal transit time, glycemic control, cholesterol reduction, maintenance of weight, reduces the caloric index, increases satiety, increases the absorption of minerals, and some compounds serve as a prebiotic for the beneficial intestinal microbiota known as probiotics) (Grabitske & Slavin, 2009; Howlestt et al., 2010; Jones, 2013). Not all countries or institutes have accepted the beneficial physiological effects of DF (FDA, 2018).

1.3.3 Declaration of DF on Label According to the FDA, the daily consumption of DF reflected in labels is 25 g for a diet of 2000 kcal/day or 30 g for a diet of 2500 kcal/day. In the United States, information on the amount of DF per serving should appear in the nutrition information panel unless the product contains less than 1 g of fiber. The declarations allowed in the United States are the following: Fiber source: Products that contain at least 10% of the recommended daily value or 2.5 g of fiber. High in fiber: Those products that contain at least 20% or 5 g of fiber. The European Union is governed by EU regulation No. 1169/2011 (EU, 2011) that allows the voluntary declaration of fiber content on the nutrition label. The definition of DF in the European Union includes the intrinsic carbohydrates in the food and those that are not naturally in the food as long as they have some proven beneficial physiological effect. These carbohydrates must be measured with the methods proposed by the AOAC so that they can be declared on the label. According to the regulation (CE) 1924/2006 (EC, 2006), the permitted declarations of DF for products of the European Union are the following: Fiber source: Product that contains at least 3 g of fiber per 100 g or at least 1.5 g of fiber per 100 kcal. High in fiber: Product that contains at least 6 g of fiber per 100 g or at least 3 g of fiber per 100 kcal. Most Latin American countries use the FDA and Codex guidelines for the inclusion of DF in food labeling.

1.4 DF AND ITS COMPONENTS As previously mentioned, each source of DF is different due to its chemical complexity, including polysaccharides as hemicellulose and cellulose and oligosaccharides. DF also includes molecules that are not carbohydrates such as lignin.

1.4.1 Hemicellulose Hemicellulose is a heteropolysaccharide that is formed by more of one type of monomer normally of five or six monomeric residues; some of them are glucose, galactose, xylose,

1.4 DF AND ITS COMPONENTS

11

arabinose, mannose, and glucoronic acid, among others (Sj€ ostr€ om, 1993). It can be founded in the cell wall of plants and as part of lignocellulosic biomass, which is considered the second most abundant component of biomass in nature just after cellulose (Farhat et al., 2017).

1.4.2 Cellulose Cellulose is a kind of homopolysaccharide composed by monomers of β-glucose linked by β-1,4-O-glycosidic bonds (Kian, Jawaid, Ariffin, & Karim, 2018). It is perhaps the most abundant organic biomolecule in nature due is the major component in terrestrial biomass and part of the cell walls of all plants. Cellulose, an IDF, is resistant to digestion, but around 50% is fermented in the colon, where partial digestion occurs (Mudgil & Barak, 2013).

1.4.3 Pectin Pectin is a type of heteropolysaccharide conformed by three important domains: homogalacturonanes and ramnogalacturonanes I and II. It can be found in the primary cell wall of all higher plants (Verkempinck et al., 2018). Also, pectin is considered an important hydrocolloid widely used in food production (Kim, Miller, Lee, & Kim, 2016). Pectin can be used like a DF in structural modifications that can be carried out by chemical or enzymatic processes (Ngouemazong et al., 2011).

1.4.4 Gums A variety of gums that could be consider into “DF” term. Guar gum is one of them, it is considering a soluble DF. Structurally, Guar gum is a polygalactomannan that is obtained from seeds of Cyamopsis tetragonalobus; chemically, galactomannan is constituted by monomers of mannose linked by β-D-(1,4)-glycosidic bonds, and monomers of galactose are linked to mannose. Also, this compound is widely used in food processing because it confers textural changes such as thickening and stabilizing (Gupta, Saurabh, Variyar, & Sharma, 2015).

1.4.5 Resistant Starch RS is also part of DF and is defined as starch that is not hydrolyzed in the human small intestine (Buksa, 2018). RS is classified in subgroups: encapsulated starch, resistant granules, retrograded amylose, chemically modified starch, and amylose-lipid complex (Zhao, Andersson, & Andersson, 2018).

1.4.6 Oligosaccharides Oligosaccharides or glycans are defined as carbohydrates that consist of 3–10 monosaccharide units, linear or branched, connected by α- and/or β-glycosidic linkages. The principal monosaccharides components of the oligosaccharides are D-glucose, D-galactose, D-mannose, L-Fucose, L-xylose, N-acetyl-D-glucosamine, N-acetylgalactosamine, D-glucuronic acid, D-galacturonic acid, L-iduronic acid, N-accetyl-D-neuramic acid, N-acetyl-D-muraminic acid,

12

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

and 3-deoxy-α-D-manno-oct-2ulopyranosonic acid; and among the main oligosaccharides are Fructooligosaccharides (FOSs), galactooligosaccharides, lactulose, raffinose, and others (Zhao et al., 2017). A FOS is a linear oligosaccharide composed by 10–20 units of fructose linked by β 1–2 bonds. Examples of fructooligosaccharide are 1-kestose, nistose, and fructosil-nistose (Park, Jang, & Lim, 2016). GOSs are mainly obtained from enzymatic hydrolysis of lactose using β-galactosidase (Lans & Vodovotz, 2018); the product of this reaction is a mixture of GOS with a variable DP (Guo, Goff, & Cui, 2018).

1.4.7 Lignin An organic polymer, lignan’s structure contains functional groups such as phenolic, methoxyl, carboxyl, p-hydroxy-phenyl, and aliphatic hidroxyl (Li, Hua-Min, et al., 2018; Li, Li, et al., 2018). Lignin, considered a highly branched phenolic compound, is in fact the most abundant source of aromatic chemicals in nature, and structurally lignin is composed by phenylpropanoid units linked by carbon-carbon or carbon-oxygen bonds (Chen et al., 2018).

1.5 DF EXTRACTION METHODS DF is a complex mixture of plant carbohydrate polymers that resist digestion by gastrointestinal enzymes and the subsequent absorption in the human small intestine. It includes cellulose, hemicellulose, lignin, pectin, gums, mucilage, and other polysaccharides and oligosaccharides associated with plant cells (Esposito et al., 2005). The most common DF extraction methods include dry processing, wet processing, chemical, gravimetric, enzymatic, physical, and microbial, or a combination of these methods (Maphosa & Jideani, 2016).

1.5.1 Fractionation of Fiber Fiber can be classified as dietary or functional and can further be classified according to its molecular weight as high or low molecular weight (Slavin, 2013; Trumbo, Schlicker, Yates, & Poos, 2002). Moreover, DF can be classified according to its solubility in water as soluble or IDF (Prakongpan, Nitithamyong, & Luangpituksa, 2002). Fiber classification is important to facilitate its study because each part of fiber has different properties; this is possible through extraction of different parts of fiber. Fiber extraction can help to: separate it into individual components, identify/quantify fractions of interest, and eliminate the unwanted components. Numerous extraction methods have been investigated. The basis of all methods of extracting fiber is similar, but the approach differs depending on the desired end product, application, source of fiber, and the equipment used (Maphosa & Jideani, 2016). The extraction method can affect the behavior of fibers in food applications and in the human body. Additionally, other factors related to the extraction method (solvent, treatment intensity, and source of fiber) can affect the properties and composition of fibers after the extraction (Fuentes-Alventosa et al., 2009). The choice of extraction method used to isolate fibers depends on fiber composition, its complexity, chemical composition, DP, and presence of

13

1.5 DF EXTRACTION METHODS

oligosaccharides. In addition, choice of method, contact time, temperature, and solvent are some parameters that highly affect the yield (Al-Farsi & Lee, 2008; Elleuch et al., 2011). The advantages and disadvantages of different extraction methods are presented in Table 1.3. Southgate (1969) was the first to fractionate the unavailable carbohydrates in foods; he outlined and updated a method of extraction for lignocellulosic materials, crude lignin, and cellulose fractions. Fiber can be extracted as a whole, called total fiber, as soluble and insoluble fiber, or as its individual components. It is well known that the physiological and physicochemical effects of fibers depend on their relative amount of individual fiber components, especially the content of soluble and insoluble fractions. Some methods of fiber extraction are used for industrial purposes, while others are used only for research purposes. Furthermore, some extraction methods are closely related with DF analytical methods. The fiber extraction methods are varied; there is not a global method used, and each analyst can modify the method in order to obtain the optimal conditions for its own study (Elleuch et al., 2011).

TABLE 1.3 Method

Advantages and Disadvantages of Fiber Extraction Methods Products

Dry processing

Advantages

Disadvantages

References

Low consumption of water and energy

Only for plants with starch as main storage

Ramı´rez, Johnston, Mcaloon, and Singh (2009)

No reagents used

Low yield

High amount of fiber obtained

Time consuming

Wet processing Conventional wet milling

Soluble fiber

High cost Residues of SO₂

Salehifar and Fadaei (2011)

Alkali wet milling

Less waste water produced

Time consuming

Maphosa and Jideani (2016)

Enzymatic wet milling

Less SO₂ produced

Residues of SO₂ in The final product

Salehifar and Fadaei (2011)

High purity products

Waste water

Modified wet milling

Insoluble and soluble fiber

Low consumption of water No chemicals Enzymaticgravimetric

Total dietary fiber, insoluble and soluble fiber, crude fiber

Higher yield than enzymaticchemical

Dalgetty and Baik (2003) Some insoluble fiber, lignin and all soluble fiber are lost Continued

14

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

TABLE 1.3 Advantages and Disadvantages of Fiber Extraction Methods—cont’d Method

Enzymaticchemical

Products

Hemicellulose, cellulose, total dietary fiber, soluble fiber

Advantages

Disadvantages

References

Quick and easy

Residues contain nitrogenous material

Gordon and Okuma (2002)

Faster and easier than enzymaticgravimetric

Chemical residues in products Time consuming

Nonenzymaticgravimetric

High purity products

Devinder, Mona, Hradesh, and Patil (2012)

Low selectivity Difficult extraction conditions

Mwaikambo (2006) Mwaikambo (2006)

Physical

Preservation of fibers structure

Unreliable

Microbial

Preservation of fibers structure

Production of toxic substances

High selectivity Easy

Mwaikambo (2006)

1.5.2 Dry Processing Dry processing methods have been applied for research and industrial applications. These methods involve disintegration of samples by milling and air classification into starch and protein fractions. Therefore, the powder produced during the milling process contains two different particles, which differ in size and density. To separate those phases, a process called “air classification” is repeated several times to purify fractions (Muehlbauer, 2002). Wang, Suo, De Wit, Boom, and Schutyser (2016) found that dry processing fractionation does not affect the functional properties of defatted rice bran. Also, Termrittikul, Jittanit, and Sirisansaneeyakul (2018) used a dry-process with Jerusalem artichoke (Helianthus tuberosus L.) to prepare a sample for inulin extraction, and they obtained a higher purity with this process than with a wet-milling process.

1.5.3 Wet Processing The wet-milling methods use water for fiber extraction but differ in the reagents and conditions employed. There are different wet-milling methods, such as conventional, alkali, enzymatic, and modified wet milling. The conventional wet-milling process involves the soaking of raw materials in a sulfuric acid solution. Then the co-products and starch are physically separated. Traditional wet-milling processes take up to 36 h to be completed.

1.5 DF EXTRACTION METHODS

15

Wronkowska and Haros (2014) used wet milling for starch extraction and found that this method did not change the properties of starch compared to raw material. Alkali wet milling. This method consists of soaking the raw material in NaOH (pH 13) at 85°C. Then, raw material is de-branded, cracked, and steeped in NaOH at 45°C, then ground to a powder, which is next mixed with NaOH, ground and sieved. Finally, the residue is collected (Eckhoff et al., 1999). The enzymatic wet milling. This process was developed to help with the residues (SO2) generated by conventional wet milling. The most common enzymes used are proteases, which solubilize and hydrolyze the gluten matrix (protein); α-amylase, which gelatinizes, hydrolyzes, and depolymerizes starch; and amylo-glucosidase, which disintegrates starch fragments to glucose. The NSP can be recovered by precipitation with ethanol (Ramı´rez et al., 2009). Modified wet milling. This technique involves the use of water and produces products with a high purity. This method, used for food applications, grinds the raw material in small particles to increase the surface area. Then, the protein is extracted at an alkaline pH and followed by acid precipitation. This method separates insoluble fiber using the differences in swelling properties of the fraction. At room temperature, fiber has a higher swelling capability than starch. Such differences in swelling capability give rise to different particle sizes. The insoluble fraction is dispersed in water and screened through sieves with pore diameters in a range from 30 to 300 μm. The supernatant is mainly a dispersion of starch granules, and the residue is fiber (Maphosa & Jideani, 2016).

1.5.4 Gravimetric Methods Non enzymatic-gravimetric methods were the earliest methods for fiber extraction. These methods include hydrolytic or oxidative chemical decomposition and crude fiber, which is the residue remaining after chemical decomposition. Methods can be classified into two categories: acid-detergent and neutral-detergent extractions. The acid-detergent extraction isolates lignin, cellulose, and acid insoluble hemicellulose; the neutral-detergent extraction isolates cellulose, lignin, and neutral detergent insoluble hemicellulose. The second category makes use of protein and starch-digestive enzymes (Elleuch et al., 2011). The enzymatic-gravimetric method was developed by Prosky et al. (1988) based on the work of Asp (1978). This method involves enzymatic treatments for starch and protein removal, precipitation of soluble fiber components by ethanol, isolation and weighing of the DF residue, and correction for protein and ash in the residue (Devinder et al., 2012). The enzymatic-gravimetric method starts with the use of alkalis and acids to determine crude fiber in plant samples; then, it is modified by the AOAC to include animal feed. Later, this method was modified to include the use of enzymes to remove starch and solubilize the protein fraction. Also, the method includes the removal of fat if present above 10%. Lee, Prosky, and De Vries (1992) adapted this method for insoluble and soluble fiber; then it was simplified using 4-morpholine-ethanesulfonic acid-TRIS buffer instead of the original phosphate buffer. Recently, use of pepsin and pancreatin for protein and starch digestion is suggested because these enzymes mimic digestive enzymes in the human body (Maphosa & Jideani, 2016).

16

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

1.5.5 Enzymatic-Chemical Methods The enzymatic-chemical method was first outlined by Southgate (1969) and developed by Englyst et al. (1994). The removal of starch and protein fractions is an essential step for enzymatic-chemical extraction. Additionally, a precipitation with ethanol or dialysis is required to separate the soluble DF polysaccharides from low-molecular-weight sugars and starch hydrolysis products (Englyst et al., 1994). Nevertheless, the separation by dialysis is preferred to ethanol precipitation to avoid soluble fiber loss (Man˜as, Bravo, & SauraCalixto, 1994).

1.5.6 Physical and Microbial Methods The physical methods preserve the structure of fibers and avoid damage to the polymer chain, whereby the extracted fibers can have a high cation exchange capacity because the side chain group remains almost intact (Yangilar, 2013). Microbial methods involve the fermentation of fibers by microorganisms and enzymes. These methods are specific and precise because of the use of specific enzymes that selectively removed oligosaccharides and polysaccharides (Rodriguez, Jimenez, Ferna´ndez-Bolanos, Guillen, & Heredia, 2006). Microbial methods preserve the structure of fibers and significant hemicelluloses, and soluble fibers are not lost. Also, these methods have a high selectivity and are easy to handle. Moreover, microorganisms can produce toxic substances during fermentation; therefore, the extracted fibers are unsuitable for use in food applications (Yangilar, 2013).

1.6 PHYSIOLOGICAL ACTIVITY OF DF 1.6.1 Satiety Hormones and Obesity Human appetite is controlled by central and peripheral mechanisms that interact with the environment, which are satiety hormones (Rebello, O’Neil, & Greenway, 2016). Satiety hormones as glucagon-like peptide (GLP)-1 located in the L cells of the ileum and proximal colon, peptide tyrosine tyrosine (PYY), secreted from the same L cells, reduce food intake as well as delay gastric emptying (Schroeder, Marquart, & Gallaher, 2013). Likewise, ghrelin is another hormone that stimulates appetite and food intake. It also modulates gastric acid secretion and motility and the endocrine and exocrine pancreatic secretions (Delporte, 2013). Studies related satiety to DF, but not all DF products have the same effects on satiety. An increment of soluble DF intake increases circulating concentrations of the gut-satiety hormones GLP-1 and (PYY) in rats, which is related to weight control (Adam, Williams, Garden, Thomson, & Ross, 2015).

1.6.2 Fermentability and DF Insoluble fibers, such as cellulose, are generally poorly fermented by gut microbes; conversely, soluble fibers that are highly fermentable as β-glucan and pectin also possess high solubility and viscosity (Holscher, 2017). The complex composition of DF, polysaccharides,

1.6 PHYSIOLOGICAL ACTIVITY OF DF

17

and oligosaccharides, composed in turn by monosaccharides (principally glucose, galactose, mannose, fructose, arabinose, xylose, rhamnose, fucose, and some of their uronic acid forms), makes the use of these compounds by gut microbiota difficult, although bacteria have different abilities to cleave linkages in the structure of these complex molecules to obtain simple sugars (Hamaker & Tuncil, 2014). SCFAs are saturated aliphatic organic acids that consist of one to six carbons of which acetate (C2), propionate (C3), and butyrate (C4) are the most abundant (95%), and they are the main metabolites of microbial fermentation of DF (Den Besten et al., 2013). The presence of DF in the gut has beneficial effects on health because there is an increased ratio of Firmicutes and Bacteriodetes, the two most dominant phyla in human gut microbiota. This has been associated with obesity, hypertension, and type 2 diabetes. Also, an increase in Bacteriodetes, which produce primarily acetate and propionate, has been shown to exert a systematic effect on appetite regulation and adiposity (Dahl et al., 2017). SCFA plays a different beneficial role on human health. Butyrate is considered as a major energy source for the colonic epithelium (Puddu, Sanguineti, Montecucco, & Viviani, 2014) and has been studied as stimulant of pancreatic beta-cells, increasing plasma insulin in mice (Lin et al., 2012). On the other side, propionate is primarily utilized on gluconeogenesis in the liver, and acetate enters systemic circulation and reaches peripheral tissues (Puddu et al., 2014). Propionate and butyrate activate intestinal gluconeogenesis via a gut-brain neural circuit, promoting metabolic benefits on body weight and glucose control. For this part, acetate reduces the appetite by changing expression profiles of appetite regulatory neuropeptides in the hypothalamus through activation of TCA cycle (Kasubuchi, Hasegawa, Hiramatsu, Ichimura, & Kimura, 2015).

1.6.3 DF and Metabolic Diseases Metabolic diseases occur when the body’s usual metabolic processes are disrupted. These diseases can be congenital or acquired as diabetes and/or cardiovascular diseases (CVDs). Several studies have mentioned that a high intake of DF is inversely associated with the incidence of CVDs due to the DF reducing blood pressure serum cholesterol. Thus, it is believed that a deficiency in DF might be contributing to the epidemic of CVD (Sanchez-Muniz, 2012). Without a doubt, one of the more extensive studies about the health benefits of DF pertain to diabetes mellitus. IDFs founded in whole grain products are considered to be especially effective in the prevention of type 2 diabetes mellitus (Kaline, Bornstein, Bergmann, Hauner, & Schwarz, 2007). The described mechanisms associated with DF and diabetes’ control are based on the physicochemical features. Soluble fiber reduces glucose absorption about 12.2%. Viscose fibers as psyllium may delay intestinal transit time and lead to a feeling of fullness, retarding the entry of glucose into the bloodstream. It also lessens the postprandial rise in blood sugar and increases absorption of macronutrients due to increased intraluminal viscosity. In this way, the gel-like material formed by soluble fiber traps nutrients inside its gel and slows down considerably while passing through the digestive tract. Nutrients are protected from the action of digestive enzymes and are less likely to reach the intestines wall for absorption. Its lowers the sharp rise of blood sugar after meals and improves the sensitivity of cells to the action of insulin, thus helping with diabetes control (Abutair, Naser, & Hamed, 2016).

18

1. DEFINITIONS AND REGULATORY PERSPECTIVES OF DIETARY FIBERS

1.7 FUTURE TRENDS 1.7.1 Source There are different reports regarding the utilization of DF sources. Li and Komarek (2017) mentioned different conventional and uncommon sources, among them by-products of the agro-food industry processing. Recently, Li, Hua-Min, et al. (2018) and Li, Li, et al. (2018) found a new fiber source in hulls, an abundant and inexpensive by-product of the corn industry that is generally discarded. These authors used hot-compressed water for the extraction of DF and found that temperature and time played critical roles in this process. Thus, it is still important to develop new and more efficient methods for extraction of fiber from both conventional and uncommon sources.

1.7.2 Quantification Methodologies DF, resistant to digestive enzymes, is found mainly in cereals, fruits, and vegetables and € contains a blend of RSs, minerals, vitamins, antioxidants, and phytochemicals (Otles & Ozgoz, 2014). For correct identification of the health benefits of DF, it is necessary to know the composition of each fiber-rich food (Gyurova & Enikova, 2015). In addition, some advanced processing technologies such as enzymatic conversion, micronization, and dry fractionation affect levels of DF in foods (Li & Komarek, 2017). Currently, quantification of DF is a big problem because there is a broad range of fiber sources. Thus, the chemical structure and composition of DF varies, and harmonization of analytical methods for fiber quantification is a need. In addition, reliable data from DF analysis is important to meet regulatory and labeling requirements (Li & Komarek, 2017).

1.7.3 Natural Fiber Effect DF has a positive effect on functions of the large intestine because it helps to regulate glu€ cose, lipid metabolism, and mineral bioavailability (Otles & Ozgoz, 2014). As DF increases, serum cholesterol and blood pressure levels decrease. It has been found in non-diabetic and diabetic individuals that when fiber intake is increased, glycemia and insulin sensitivity are improved (Anderson et al., 2009). DF modifies some gut hormones that affect satiety and energy intake, regulating lipid metabolism and energy expenditure and having have effects on obesity, insulin resistance, and hyperlipidemia (Sanchez, Miguel, & Aleixandre, 2012). Increase of fiber intake in obese individuals significantly enhances weight loss. In addition, a protective effect of DF against different diseases has been reported. Among these health problems are: constipation, gastrointestinal diseases, gastroesophageal reflux disease, obesity, hemorrhoids, diverticulitis, duodenal ulcer, stroke, diabetes, hypertension, CVDs, and colon € cancer (Otles & Ozgoz, 2014). Also, fibers used as prebiotics enhance immune function (Anderson et al., 2009). However, more information is needed to determineappropriate levels of DF to reduce a specific disease. In one instance, it has been mentioned that an increased intake of DF during adolescence and early adulthood may reduce breast cancer (Farvid et al., 2016).

1.8 CONCLUSIONS

19

1.7.4 Applications Because the technological and functional properties of DFs, these can be used in different € applications for formulation of foods (Otles & Ozgoz, 2014). Among these foods are functional foods such as beverages, drinks, bakery, and meat products. Devinder et al. (2012) indicated that food-processing treatments such as extrusion-cooking, grinding, frying, boiling, and canning could alter the DF and physical-chemical properties of foods, which may improve their functionality. In this aspect, there are still opportunities for research, especially on the industrial application of novel sources of DF. In addition, investigation is needed on the difference of the effect of intact vs isolated and refined fibers, which are added to industrial products (Li & Komarek, 2017).

1.7.5 Current Intakes Different authors have pointed out that fiber intake levels are lower than those recommended. Li and Komarek (2017) indicated that in most nations worldwide, the recommended levels of fiber and fiber-rich foods are still low. For example, intake of DF by US children and adults is less than half of the recommended amount (14 g/1000 kcal) for both children and adults (Anderson et al., 2009). In a study on adolescents’ diets, it was found that excessive fat consumption and non-habitual consumption of vegetal sources of fiber, such as beans, negatively affect levels of DF intake in both sexes (Vitolo, Campagnolo, & Gama, 2007). Other factors that affect levels of DF intake are changes in food habit and lifestyle (Sarker & Rahman, 2017). Although the intake of fiber does not reach the recommended level worldwide, only a few countries provide information on the type of fiber sources recommended to achieve the optimum level of required DF (Stephen, Champ, Cloran, & Fleith, 2017). There is a need for more effective communication about the benefits of DF on diet and the optimum recommended daily values. In addition, consumer education is required in order to enhance fiber intake from both foods and/or supplements (Anderson et al., 2009). Each country should emphasize specific food sources that should be part of the diet to obtain optimum health benefits (Stephen et al., 2017). In addition, some countries have stricter regulations about foods or supplements that claim to be “high fiber” (Li & Komarek, 2017).

1.8 CONCLUSIONS Currently, there is not a widely accepted definition of DF. Its definition is still evolving, taking into account its composition, oligosaccharides with different degrees of polymerization, health benefits, and food-labeling regulations. On the other hand, although there are different fiber sources reported, recently abundant and inexpensive byproducts have been focus of attention for this purpose. Actual DF extraction methods need to be adapted for efficient DF extraction from both conventional and uncommon DF sources. There is still a long way to go in the legal realm regarding DF. The inclusion of new terms or components in the definition of DF by institutions such as the CAC reflects the growing progress in research, but at the same time, the delay in the updating of reference methods for its analysis is observed; this is

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undoubtedly what hinders the regulatory part of food labeling and therefore its commercialization in many countries. In addition, DF quantification of DF is a big issue because the different origins of DF affect its chemical structure and composition. Thus, harmonization of analytical methods is a necessity for regulatory and labelling requirements. Huge advances have been made on the beneficial effects of DF on human health, but more research is still needed to determine the best human life step where intake of appropriate DF levels is more effective to reduce disease risks. There are advances on DF technology for industrial applications. However, many research opportunities exist to develop chemical technologies and utilize novel DF sources. This would facilitate research in terms of nutrition and reach a global definition for harmonized nutrition labeling.

Acknowledgments This project was financially supported through the Project: FON.SEC. SAGARPA-CONACYT CV-2015-4-266936. S.E. G and J.A.S.T want to thank CONACYT for the financial support during their postgraduate studies.

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Trumbo, P., Schlicker, S., Yates, A. A., & Poos, M. (2002). Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids. Journal of the American Dietetic Association, 102, 1621–1630. Verkempinck, S. H. E., Salvia-Trujillo, L., Denis, S., Van Loey, A. M., Hendrickx, M. E., & Grauwet, T. (2018). Pectin influences the kinetics of in vitro lipid digestion in oil-in-water emulsions. Food Chemistry, 262, 150–161. Vitolo, M. R., Campagnolo, P. D. B., & Gama, C. M. (2007). Factors associated with risk of low dietary fiber intake in adolescents. Journal of Pediatrics, 83(1), 47–52. Wang, J., Suo, G., De Wit, M., Boom, R. M., & Schutyser, M. a. I. (2016). Dietary fibre enrichment from defatted rice bran by dry fractionation. Journal of Food Engineering, 186, 50–57. Wang, Z. Q., Zuberi, A., Zhang, X. H., Macgowan, J., Qin, J., Ye, X., et al. (2007). Effects of dietary fibers on weight gain, carbohydrate metabolism and gastric ghrelin gene expression in high fat diet fed mice. Metabolism, 56(12), 1635–1642. Widdowson, E. M., & McCance, R. A. (1935). The available carbohydrate of fruits. Determination of glucose, fructose, sucrose, and starch. Biochemical Journal, 29(1), 151–156. https://dx.doi.org/10.1042/bj0290151. Williams, R. D., & Olmsted, W. H. (1935). A biochemical method for determining indigestible residue (crude fiber) in feces: lignin, cellulose and non-water soluble hemicelluloses. Journal of Biological Chemistry, 108, 653–656. Wronkowska, M., & Haros, M. (2014). Wet-milling of buckwheat with hull and dehulled—the properties of the obtained starch fraction. Journal of Cereal Science, 60, 477–483. Yangilar, F. (2013). The application of dietary fibre in food industry: structural features, effects on health and definition, obtaining and analysis of dietary fibre: a review. Journal of Food and Nutrition Research, 1, 13–23. Zhao, C., Wu, Y., Liu, X., Liu, B., Cao, H., Yu, H., et al. (2017). Functional properties, structural studies and chemoenzymatic synthesis of oligosaccharides. Trends in Food Science and Technology, 66, 135–145. Zhao, X., Andersson, M., & Andersson, R. (2018). Resistant starch and other dietary fiber components in tubers from a high-amylose potato. Food Chemistry, 251, 58–63.

Further Reading Dai, F., & Cahu, C. (2017). Classification and regulatory perspectives of dietary fiber. Journal of Food and Drug Analysis, 25, 37–42. EC. (2012). European Commission, Guidance document for competent authorities for the control of compliance with EU legislation on: Council Directive 90/496 EEC (20 September 1990) on nutrition labelling and food stuff and Regulation (EU No 1196/2011, with regard to methods of analysis for determination of the fibre content declared on a label. EC Health and Consumer Directorate General 2012). Slavin, J. L. (2005). Dietary fiber and body weight. Nutrition, 21, 411–418. Williamson, P. S. (2017). A brief overview and comparison of global fiber regulations. Cereal Foods World, 62(3), 95–97.

C H A P T E R

2

Classification, Technological Properties, and Sustainable Sources Deepak Mudgil, Sheweta Barak Department of Dairy & Food Technology, Mansinhbhai Institute of Dairy & Food Technology, Mehsana, India

O U T L I N E 2.1 Introduction

27

2.3.7 Particle Size and Porosity

2.2 Classification 2.2.1 Soluble Dietary Fiber 2.2.2 Insoluble Dietary Fiber

29 30 32

2.3 Physicochemical Properties 2.3.1 Solubility 2.3.2 Viscosity 2.3.3 Water Holding and Binding Capacity 2.3.4 Fermentability 2.3.5 The Binding Ability of Minerals and Bile Acids 2.3.6 Oil-Binding Ability

35 35 36

2.4 Important Sustainable Sources of Dietary Fiber 2.4.1 Cereals as a Source of Dietary Fiber 2.4.2 Legumes as a Source of Dietary Fiber 2.4.3 Fruits and Vegetables and Their Waste as Source of Dietary Fiber

37 39 40 41

41 42 42 46 48

2.5 Conclusion

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References

51

2.1 INTRODUCTION Dietary fibers are the portion of food materials, particularly carbohydrates, that cannot be digested by the human digestive enzymes secreted in the small intestine. Hippocrates in 430 BC mentioned the laxative action of coarse wheat flour over refined wheat flour. J. H. Kellogg in 1920 explained about various health attributes of wheat bran, such as an

Dietary Fiber: Properties, Recovery, and Applications https://doi.org/10.1016/B978-0-12-816495-2.00002-2

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# 2019 Elsevier Inc. All rights reserved.

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2. CLASSIFICATION, TECHNOLOGICAL PROPERTIES, AND SUSTAINABLE SOURCES

increase in stool weight and laxative action (Slavin, 1987). The term “Dietary Fiber” was used by Hispley for the first time in literature for cell wall materials, such as cellulose, hemicellulose, and lignin (Hispley, 1953). In the 1980s, dietary fiber became a topic of extensive research for its role in human nutrition. After this period, the field of dietary fiber research began growing at a fast rate. Several research publications and books were published on various aspects of dietary fiber. Dietary fibers are also termed “roughage” material, which increases the bulk of the food excreted in the stool. These indigestible carbohydrates are called “functional fiber” when extracted from the plants and show physiological health benefits upon consumption. Dietary fibers can be classified into various categories on the basis of their soluble or insoluble behavior in water, their fermentability in the human large intestine, and their physiological actions in human metabolism. Generally, dietary fiber includes nonstarch polysaccharides, some oligosaccharides, lignin, phytic acid, cutin, suberin, etc. (Champ, Langkilde, Brouns, Kettlitz, & Collet, 2003). Another class of compounds that comes under the definition of dietary fiber are resistant starches due to their nondigestibility in the human alimentary canal (Ferguson, Chavan, & Harris, 2001). Resistant starches are further categorized in different classes depending on their sources and properties. Different categories of resistant starches normally occur in whole grains or partially milled grains, legumes, corn flakes, and cooked potatoes. Traditional sources of dietary fiber include cereals, legumes, oilseeds, fruits, vegetables, and some plant portions. Whole grains of cereals and legumes are good sources of dietary fiber. Cereal brans are also reported to have significant amounts of dietary fiber. Wheat bran also shows functionality in bread making (Hemdane et al., 2016). The composition of dietary fiber in plant foods also depends on the portion of the plant used, storage, ripening, and the processing operation used for that food product. All these factors control the composition of native dietary fiber. The main component of dietary fiber in cereals and vegetables is cellulose, whereas lignin is the main component of dietary fiber in fruits and matured root vegetables. Hemicellulose is the main dietary fiber component in wholegrain cereals and cereal bran. Pectin is the main dietary fiber component found in fruits (apples, oranges, etc.). Oats and dried beans, such as guar, are good sources of soluble dietary (Mudgil & Barak, 2013). In the last few decades, comprehensive research studies have been carried out on various aspects of dietary fibers, including their properties and action on different human physiological conditions such as blood cholesterol levels, bowel function, postprandial blood glucose level, insulin levels, etc. Dietary fibers also have interaction with other food components present in food and have potential effects on their absorption and metabolism in human physiology (Buttriss & Stokes, 2008). Based on their solubility in water, dietary fibers are broadly classified into two types, that is, soluble and insoluble dietary fiber (Mudgil & Barak, 2013). Dietary fiber sources may contain both types of dietary fiber in different proportions. Insoluble types of dietary fiber are generally comprised of components such as cellulose, hemicellulose, and lignin. Insoluble fibers are considered good for the human digestive system as these reduce the bowel transit-time, enhance fecal bulk, and cause softer stool. Soluble dietary fibers perform various physiological functions, such as slow gastric emptying, retarded glucose absorption and reduced serum-cholesterol level. When consumed, they ferment in the human colon and produce short-chain fatty acids (SCFA), which inhibit the cholesterol synthesis and

29

2.2 CLASSIFICATION

ultimately reduce serum-cholesterol levels in blood. Food products contain both types of dietary fiber that is, soluble and insoluble fibers in varied proportion. Health benefits of dietary fibers are associated with their physicochemical properties, which are responsible for the ultimate functional behavior of dietary fiber and lead to certain health benefits on consumption (Anderson et al., 2009; Kaczmarczyk, Miller, & Freund, 2012; Redgwell & Fischer, 2005).

2.2 CLASSIFICATION Types of dietary fiber may be categorized according to their sources, composition, solubility, fermentability, site of digestion, products of digestion, and physiological effects. But none of these categories can singly be used for the classification of dietary fibers as they do not completely cover all aspects of dietary fiber. The two most popular classification systems of dietary fibers are based on their solubility (soluble and insoluble) in water and fermentability (fermentable and nonfermentable) in the human colon. Fermentable dietary fibers are considered water-soluble in nature while nonfermentable or least-fermentable dietary fibers are considered water-insoluble (Tungland & Meyer, 2002). Both types have specific effects on human metabolic activities (Table 2.1).

TABLE 2.1 Classification of Dietary Fiber Class

Examples

Insoluble dietary fiber

Celluloses Hemicelluloses Lignins Resistant Starches Arabinoxylans Nonstarch polysaccharides

Soluble dietary fiber

Inulin Pectin β-glucan Galactomannans Glucomannans Polydextrose Psyllium Fructo-oligosaccharides (FOS) Dextrin (resistant)

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2.2.1 Soluble Dietary Fiber Soluble dietary fibers, which are soluble in aqueous solution, show resistance toward the digestion process in the small intestine and undergo the fermentation process in the large intestine caused by intestinal microorganisms. Sources of soluble dietary fiber include fruits, vegetables, pulses, etc. (Mudgil & Barak, 2013). Based on their ability to form viscous gel upon dissolution in water, soluble fibers are further divided into two types, that is, viscous fiber and nonviscous fiber. Soluble dietary fibers enhance the transit time in the human digestive tract and cause delay in gastric emptying, which leads to a reduced rate of glucose absorption. Soluble dietary fibers include beta-glucan, pectin, gums, and inulin. 2.2.1.1 β-Glucan β-Glucan is a polymer with monomer units of glucose attached via glycosidic bonds at β(1 ! 3), β(1 ! 4), and β(1 ! 6). It is commonly found in oats, barley, mushrooms, and some microorganisms. In cereals, it is generally present in the bran portion of the grains. β-Glucans obtained from cereals generally are composed of glucose units with β(1 ! 3) and β(1 ! 4) linkages while β-glucans from yeast and fungi contain β(1 ! 6). The cereal β-glucan components present in endosperm the cell wall portion of the grains (oats and barley) are molecules with linear chain with about 30% (1 ! 3) and 70% (1 ! 4) linkages (Bacic & Stone, 1981). β-Glucan obtained from oats is reported to have high molecular weight as compared to barley β-glucan (Lazaridou & Biliaderis, 2004; Lazaridou, Biliaderis, & Izydorczyk, 2003). β-Glucan generally has an ability to hydrate well in the presence of water and forms very a viscous solution. Rheological properties of β-glucan are controlled by various factors, such as molecular weight, degree of polymerization, chains association, proportion, and arrangement of cellotriosyl/ cellotetraosyl units (Cui & Wood, 2000; Tosh, Wood, Wang, & Weisz, 2004). 2.2.1.2 Pectin Pectin is a naturally occurring fibrous structural component present in cell walls of plant cells and also found in intracellular layers of plant cells. It is mainly found in apples and citrus fruits. In apples, it is present in the peel and pulp; In citrus, it is present in the peel portion. Apple pomace contains 10%–15% of pectin on a dry-weight basis whereas citrus peel contains 20%–30% of pectin on a dry weight basis (May, 1990). Pectin is a linear polymer having galacturonic acid backbone chain in which monomer units attached via α-(1 ! 4)-glycosidic linkage. This backbone chain in pectin molecule is substituted at some points with α-(1 ! 2) rhamnopyranose units, which may lead to side chains of mannose, glucose, galactose, and xylose. In pectin molecule, galacturonic acid molecules are methyl esterified. Depending on methyl esterification, pectins can be divided into two categories, that is, high methoxyl pectin and low methoxyl pectin. High methoxyl pectin are those pectins in which more than 50% galacturonic acid are esterified while in low methoxyl pectins, less than 50% of galacturonic acid is esterified. Pectin molecules have a molecular weight of about 50,000–150,000 Da. Pectin comes in the category of soluble dietary fiber due to its watersoluble nature. It resists the digestive action of human digestive enzymes in the small intestine but undergoes microbial degradation in the large intestine. Pectins are considered to have hypocholesterolemic action because of its gel-forming ability in aqueous systems, but it can be

2.2 CLASSIFICATION

31

fortified in food products up to certain limits; beyond that, it interferes with the sensorial characteristics of the product (Chen et al., 2015). 2.2.1.3 Gums Gums belong to a class of polymers that are water soluble in nature and form a viscous solution when dispersed in water. These gums can be obtained from plant exudates, plant seeds, products of microbial fermentation, and extracts from seaweeds. Examples of some gums include acacia gum, guar gum, locust bean gum, tragacanth gum, carrageenan, alginates, xanthan gum, pullulan gum, gellan gum, etc. (Bajaj, Survase, Saudagar, & Singhal, 2007; Barak & Mudgil, 2014; Campo, Kawano, da Silva Jr, & Carvalho, 2009; Garcıa-Ochoa, Santos, Casas, & Gomez, 2000; Islam, Phillips, Sljivo, Snowden, & Williams, 1997; Leathers, 2003; Mudgil & Barak, 2013; Mudgil, Barak, & Khatkar, 2014a; Saha & Bhattacharya, 2010). Composition and concentration of plant-based gums vary from species to species. Polymeric composition varies depending upon the type of gum. Some microorganisms can also produce gums as a product of their fermentation process, such as xanthan gum, pullulan gum, etc. These gums can be used as dietary fiber sources as they have resistance toward the enzymatic digestion process and act as functional dietary fiber. When added to a food product, it increases the dietary-fiber content of that food product. Apart from their functions as dietary fiber, they are also utilized as food additives for their ability to form viscous solutions in water. Recently, partially hydrolyzed guar gum has been developed from native guar gum via enzymatic hydrolysis to utilize it as a source of soluble dietary fiber (Mudgil, Barak, & Khatkar, 2012; Mudgil, Barak, & Khatkar, 2014b). When added to food products, it not only increases the dietary fiber content but also improves the sensory and textural characteristics of the food products (Mudgil, Barak, & Khatkar, 2016a; Mudgil, Barak, & Khatkar, 2016b; Mudgil, Barak, & Khatkar, 2016c). 2.2.1.4 Inulin Inulin is a water-soluble polymer that falls under the category of indigestible carbohydrate polymers known as fructans. It has GRAS status in the United States. It naturally occurs in around 36,000 plant species (Shoaib et al., 2016). The most abundant source of inulin is chicory roots, which are used for the commercial production of inulin. Apart from chicory roots, dahlia and Jerusalem are also used for the commercial production of inulin (Flamm, Glinsmann, Kritchevsky, Prosky, & Roberfroid, 2001). Inulin is composed of fructose units attached via β-(2-1)-D-frutosyl fructose linkage. The presence of β-configuration of anomeric carbon leads to its indigestible nature in the small intestine but undergoes fermentation by microbial flora in the large intestine (Apolina´rio et al., 2014). Inulin obtained from chicory roots may contain 2–60 fructose units (Roberfroid, 2005). Functionality of inulin is directly related to the degree of polymerization and branching. Inulin obtained from plant sources has a low degree of polymerization (below 200) whereas inulin from bacterial sources has a high degree of polymerization (more than 10,000). Inulin obtained from bacterial sources has more branched structure as compared to inulin obtained from plant sources (Cho & Samuel, 2009). Inulin is also reported to have prebiotic activity, whereas it can be used for fat replacement and texture modification of the food products. In addition, it can be used for the development of novel functional food products having certain health benefits specifically related to the human digestive system (Shoaib et al., 2016).

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2.2.2 Insoluble Dietary Fiber Insoluble dietary fibers are insoluble in water and do not show gel formation because of this behavior. Insoluble dietary fibers do not undergo fermentation in the large intestine by microflora. When consumed, they enhance the fecal bulk, help in elimination of waste, and reduce intestinal transit time. Insoluble dietary fibers include celluloses, hemicelluloses, lignin, cutin, suberin, chitin, and chitosan are included in insoluble dietary fiber. 2.2.2.1 Cellulose Cellulose, the main component of plant cell walls, is the most copious organic material found in nature. Its’ molecules are also associated with other polysaccharides and lignins present in plant cell walls. Cellulose may also be synthesized by some algae and bacteria (Iwamoto, Nakagaito, & Yano, 2007; Klemm et al., 2006). It is composed of glucose units as monomer present in linear structure without any branching. In cellulose molecules, glucose units are attached to each other via β-D-1,4 glycosidic bond. Cellulose in its native form is generally comprised of 10,000–15,000 units per chain. These linear chains of cellulose have an ability to form hydrogen bonding among each other, which leads to formation of micro fibrils that are rigid, nonflexible, and crystalline in nature (McDougall, Morrison, Stewart, & Hillman, 1996). This fibrous structure is responsible for the strength, density, crystallinity, chemical, and enzymatic resistance of cellulose. Ninety percent of cellulose exists in crystalline form whereas about 10% exists in amorphous form. Cellulose is also insoluble in dilute solutions of acid and base. Water absorption capacity of cellulose is very high due to its fibrous structure. Cellulose has resistance toward the human digestive enzymes in the small intestine but can be degraded by the microflora living in the human large intestine. These microflora have cellulase enzymes, which are capable of degrading cellulose via breakage of β-D-1,4 glycosidic linkage. 2.2.2.2 Hemicellulose As compared to cellulose, hemicellulose has a relatively complicated structure. Generally, hemicelluloses have a back bone chain that is composed of various types of monosaccharide units present alone or in combination with each other. Apart from this, hemicelluloses may have various types of side chains attached to the back bone chain, which gives them a more complex structure. Hemicelluloses are soluble in dilute basic solutions, which differentiate them from cellulose. However, like cellulose, hemicelluloses are also insoluble in water and dilute acid solutions. These hemicelluloses can be obtained via basic extraction (base solution) from plant cell walls after the pectin-removal process (McDougall et al., 1996). Complex structure of hemicelluloses is due to the varied monomer back bone chain, which is generally composed of glucose, galactose, xylose, mannose, and arabinose (singly or in combination) attached via β-1,4 glycosidic linkages. Hemicellulose polysaccharide molecules may contain about 50 to 200 monomer units. The side chain attached to the back bone chain may be comprised of uronic acids. The nomenclature of hemicellulose molecules is based on the monosaccharide units present and adding a suffix “an” such as xylan, arabinan, etc. As per this structure-based classification, all glucans should be classified in hemicelluloses category. However, glucans do not fulfill the criteria of the solubility based definition of hemicellulose; hence, they are not considered in this category. Curdlan (β-1,3 glucan), which is

2.2 CLASSIFICATION

33

water insoluble in nature and also insoluble in dilute solutions of acids, is hence categorized under the hemicellulose category (McIntosh, Stone, & Stanisich, 2005). However, water soluble β-glucans, which are obtained from barley and oats and have both types of linkages (i.e., β-1,3 & β-1,4), are not classified in the category of hemicellulose. On a commercial basis, pure hemicelluloses are not available because the extraction and removal of their attached components and the isolation of pure hemicellulose is very difficult and also very expensive. 2.2.2.3 Lignin Lignin is the second largest available raw material in nature (Gosselink, De Jong, Guran, & Ab€ acherli, 2004). Lignin is also referred to as the most copious aromatic polymer in nature (Lora & Glasser, 2002). It acts as a cementing material for cellulose fibers in plant cells. Chemically, it is not a polysaccharide but is a polyphenyl-propane polymer. As a polymer, it has a highly branched three-dimensional phenolic structure composed of phenyl-propane units such as p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Like cellulose, lignin is also insoluble in aqueous solutions. It aids in association of plant cell wall components because of their ability to form cross-links with other saccharide molecules. Lignin molecules show unique resistance toward enzymatic and chemical degradation. It is also resistant toward bacterial degradation. Lignin exhibits greater resistance toward human digestive secretions as compared any other natural compounds. It is responsible for the structural strength of the wood due to its rigid structure. Some high-fiber ingredients, such as oat fiber and cellulose, are processed to remove lignin because of their highly insoluble behavior. Even boiling water is not able to dissolve or soften lignin molecules. Lignin alone is not commercially isolated as a high-fiber ingredient, but it is always associated with the other fiber ingredients, especially from plant cells. Condensation and oxidation reactions during isolation of lignin make it difficult to isolate lignin from lignocellulosic material (Hon, 1996). Lignin as insoluble dietary fiber is reported to be beneficial for gastrointestinal physiology (Anderson & Bridges, 1988). Some examples of lignin sources are celery, carrots, etc. 2.2.2.4 Cutin and Suberin Cutin and suberin are complex polymers present in plant cell walls. These are the polyesters of hydroxy fatty acids. These occur in plant cells with associated waxes comprising the hydrocarbons chain. Both cutin and suberin are water insoluble in nature. They come under the category of insoluble dietary fiber and contribute to a small proportion of plant-based fibers. Despite their very small concentration, they are very significant in protecting against colorectal cancer (Ferguson & Harris, 1998). Just like lignin, these are also not extracted commercially for use as fiber ingredients. In plant cells, cutin, along with associated waxes, constitutes the cuticle, which is present in both sides of the outer-epidermal walls of leaves and fruits. Chemically, suberin is biopolymer obtained from ferulic acid and has polyaliphatic and polyaromatic domain. Suberin is present in the wall portion of cork cells, which are responsible for skin formation in several root vegetables and tubers (e.g., potatoes). After processing, potato peels have been used as specific food additives in cookies and bakery products because of their fascinating baking properties (Arora & Camire, 1994). Cutin and suberin are reported to shield cell-wall polysaccharides from disintegration via bacterial enzymes in the colon (Harris & Ferguson, 1993). The presence of cutin and suberin makes the plant cell wall hydrophobic

34

2. CLASSIFICATION, TECHNOLOGICAL PROPERTIES, AND SUSTAINABLE SOURCES

in nature due to their high water insolubility. This makes them potential absorbers of carcinogens, which are hydrophobic in nature (Harris, Triggs, Roberton, Watson, & Ferguson, 1996). 2.2.2.5 Chitin and Chitosan Chitin and chitosan molecules are the biological polymers composed of glucosamine and N-acetylated glucosamine monomers, which are attached to each other by β-1-4-glycosidic € bonds (Hamed, Ozogul, & Regenstein, 2016). They are found in the shells of arthropods (e.g., crabs and shrimp) (Champ et al., 2003). They are also produced as exopolysaccharides by some fungi and brown algae. Chitin and chitosan are different only due to their level of acetylation and solubility. The Chitosan molecule is deacetylated while the chitin molecule is extensively acetylated. Chitin shows high insolubility in water while chitosan shows little water insolubility as compared to the chitin molecule. Chitosan molecules are soluble in acid. When chitosan is ingested in diets, it markedly decreases the serum cholesterol in human beings. Results of clinical trials reported in literature suggest that chitosan reduces total serum cholesterol and increases serum HDL-cholesterol when ingested in fortified biscuits at dose level of 6 g/day by healthy adult males (Maezaki et al., 1993). Chitosan molecules having at least six glucosamine units with nominal deacetylation degree are adequate to inhibit the lipid and cholesterol absorption in the human alimentary canal. This decrease in cholesterol absorption is related to the gel-forming capacity of chitosan in the alimentary canal (Deuchi, Kanauchi, Imasato, & Kobayashi, 1995; Deuchi, Kanauchi, Shizukuishi, & Kobayashi, 1995). Ascorbic acid is also reported to increase the gel-forming capacity of chitosan, which leads to the increase in its ability of lipid-binding and lowering in plasma cholesterol. 2.2.2.6 Resistant Starch Starch, one of the major polysaccharides, occurs in plant cells and is composed of glucose monomers. Glucose molecules present in starch granules occurs in two polymeric forms i.e., amylose and amylopectin. Amylose is composed of glucose units attached via α-(1-4) glycosidic bonds while amylopectin is composed of glucose units attached via α-(1-4) and α-(1-6) glycosidic linkages; α-(1-6) linkages are responsible for branching in the polymeric chain of starch granules. Starch molecules obtained from plant sources are hydrolyzed by amylases and are digestible in human digestive enzymes in the small intestine. Resistant starch is a term used for the category of starch molecules that resist the action of the amylase enzyme in the human small intestine and shows some extent of bacterial degradation in the human large intestine, similar to other dietary fibers. This property enables them to be placed in the category of dietary fiber (Fuentes-Zaragoza, Riquelme-Navarrete, Sa´nchez-Zapata, & Perez´ lvarez, 2010). Resistant starches are categorized into four different groups, i.e., RS1, RS2, A RS3, and RS4 (Sajilata, Singhal, & Kulkarni, 2006). RS1, the first category of resistant starches, refers to the starch molecules that are physically unavailable or inaccessible, meaning that these embedded or entrapped starches in plant portions (i.e., seeds and partly milled grains) are unavailable and resistant toward enzymatic action. These types of starches can become digestible or available for digestion when their enclosed coating or structure is physically broken. Another category, RS2 type starches, are intact starch granules. Amylase is not able to degrade them without gelatinization of these types of starches. These types of starches occur in unripe bananas, uncooked peas, and potatoes. RS3 type starches undergo gelatinization followed by retrogradation and lose their granular form. This type of starch forms a

2.3 PHYSICOCHEMICAL PROPERTIES

35

crystalline network in their structure and resists the amylase action during their digestion in the human small intestine. Amylase enzymes can only hydrolyze gelatinized starch and are unable to hydrolyze retrograded starch due to their network structure. Their sources include cooked, cooled potatoes, ready-to-eat cereals, and bread in which starches are retrograded during their processing (Yue & Waring, 1998). Finally, RS4 type starches are also referred to as chemically modified starches. The most suitable example of chemical modification is the crosslinking reaction, which modifies the structure and enables the starches to resist the enzymatic action on them during digestion process.

2.3 PHYSICOCHEMICAL PROPERTIES Significant physicochemical properties of dietary fiber include solubility, viscosity, and water-holding capacity, bulking, and fermentability, which are responsible for the physiological functions caused by dietary fiber.

2.3.1 Solubility The solubility of dietary fiber is the most important characteristic, which is directly related to the physiological functions it causes. Depending on their solubility, There are two types of dietary fibers: soluble and insoluble. Soluble dietary fibers have physiological action on the plasma lipids and show protection from cardiovascular diseases. Insoluble dietary fibers are associated with the effects on the human digestive system; their consumption leads to enhanced laxation and protection against colorectal cancer. Solubility of dietary fiber in relation to their action is complex and unclear. For example, soluble dietary fiber is not a single component but is a mixture of different types of polysaccharides having different ranges of molecular weights. Generally, the solubility of dietary fiber refers to its tendency to readily hydrate in water. In favorable conditions, they can also lead to the formation of true solutions. Molecular structure of the polysaccharide is the factor that is responsible for its solubility in water (Morris & Norton, 1983). Polysaccharides are polymers composed of monosaccharides as monomer units (e.g., glucose, galactose, mannose, xylose, arabinose, etc.) Monosaccharide units present in the polysaccharide chain undergo structural changes in solution. They are transformed into ring structure and undergo reversible intra-molecular chemical reactions between dCHO group and dOH groups, which leads to the formation of hemiacetal structure. This hemiacetal may react with dOH groups of other monosaccharide units and forms a glycosidic link, leading to the formation of ultimate polysaccharide and intermediate disaccharide. When the monosaccharide unit is D-glucose, the glycosidic bond may be built among the first carbon of one glucose molecule and the first, second, third, fourth, or sixth carbon of another glucose molecule, which can possibly form different structures. Hence, the determination of polysaccharide structure can be defined via the type of monosaccharide molecules present in it and also via the type of bonds between the monosaccharide units. However, solubility of polysaccharide is more dependent on the type of bonds or linkages present in monosaccharide units as compared to the type of monosaccharide units present in it (Morris, 1979). This can be better understood by considering the example of cellulose and barley β-glucans, both of which are composed of the same monomer units but have different

36

2. CLASSIFICATION, TECHNOLOGICAL PROPERTIES, AND SUSTAINABLE SOURCES

types of linkages among the monomer units that is, glucose units. Due to the difference in types of linkages present, both show different solubility properties in water. Cellulose is insoluble in water whereas β-glucan is water soluble in nature. Cellulose molecules contain β-(1 ! 4) linkages while β-glucan have both β(1 ! 4) and β(1 ! 3) linkages, which is mainly responsible for their different solubilities . Similar types of linkages and regularity are responsible for the crystalline structure of cellulose chains linked via hydrogen bonds which leads to the insoluble behavior of cellulose (Morris, 1989; Rees, 1977). β-glucans are unable to form ordered-crystalline structure due to their irregular structure, which makes them water soluble in nature and classifies them in the category of soluble dietary fiber. The branched structure of polysaccharides is also responsible for their water-soluble behavior, for example, arabinoxylans in wheat, which are not able to form ordered-crystalline structures and hence are water soluble in nature. The electrostatic charge on the polysaccharides due to the presence of charged groups, such as COO– or SO 3 , also shows solubility in water due to electrostatic repulsive force between the charged groups; this makes them unable to form ordered structures via packing of molecules, for example, pectins and carrageenans (Morris, 1989). Hence, it is clear that several structural characteristics of the polysaccharides are responsible for their solubility behavior: branching, presence of ionizing groups, bonding pattern, and nonuniformity in structure (Glass, 1986). The solubility of dietary fibers not only affects the physiological functions in human metabolism but also has technological functions in the food products ( Jimenez-Escrig & Sa´nchez-Muniz, 2000). Consumption of soluble dietary fiber leads to a rise in the aqueous phase viscosity and a decrease in plasma cholesterol levels and glycemic response (McCarty, 2005; Slavin & Greenberg, 2003). Insoluble dietary fibers have unique properties of porosity and low density, which helps in enhancing the fecal bulk and reduction in intestinal transit (Olson, Gray, & Chiu, 1987). Both soluble and insoluble dietary fibers have distinct unique action in human physiology. However, the development of soluble dietary fiber products is the main choice of functional food manufacturers.

2.3.2 Viscosity Viscosity is the resistance provided by fluid toward its own flow and is considered as one of the important characteristics related to soluble dietary fiber (Dikeman & Fahey Jr, 2006). When dispersed in aqueous phase, soluble dietary fiber (e.g., β-glucan, guar gum, psyllium, pectins, etc.) leads to the formation of viscous solutions. The gel-forming ability of dietary fibers is due to their tendency to absorb water, which yields gelatinous mass or viscous or gel-like solutions. When consumed, these types of dietary fibers not only increase the volume of the gastrointestinal tract contents but also the viscosity of the contents in the tract (Olson et al., 1987). This enhanced viscosity and volume of digesta is responsible for delayed gastric emptying and leads to enhanced satiety. It also influences lipid emulsification and assimilation. Dietary fiber increases the viscosity of the food content in the gut and makes gel-like viscous material, which behaves like solid rather than semisolid or liquid. This reduces the rate of the digestion process by decreasing the rate of the diffusion of digestive enzymes toward their substrate. It also slows down the release of hydrolysis products for absorption on mucosal surface. Space or volume taken up by dietary fiber molecules are generally described by intrinsic viscosity (Morris, 1990). Viscosity of digesta having dietary fiber components is not similar to all parts of the gut. These components do not undergo any change in the upper

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region of the gut, but they may be degraded later, e.g., pectin which is solubilized at acidic pH in the stomach or at neutral pH in the small intestine. The degree of dietary fiber degradation may have a nutritional effect caused by decreased viscosity that is ultimately related to the physiological actions. Ionic environment and pH of the gastrointestinal tract also affects the viscosity as well as the solubility of the dietary fiber component in the tract. It is reported for polyelectrolytes, for example, alginate that shows gel formation in the stomach but hydrolyzes in the small intestine portion of the GI tract. Concentration, composition, molecular weight, and structure of dietary fiber components are important factors that influence their viscosity values in the gastrointestinal tract and ultimately the physiological action caused by the dietary fiber. Most of the polysaccharides, which are soluble in water, yield viscous solutions. Physical interactions, such as the entanglements of polysaccharide molecules in aqueous solutions, are the main cause behind the viscous nature of polysaccharides in aqueous solutions (Glicksman, 1969; Graessley, 1974). The characteristics of polysaccharide solutions can be easily described by understanding the concept of space or volume occupied by the polymer in the aqueous solutions (Morris, Cutler, Ross-Murphy, Rees, & Price, 1981). Mostly, polysaccharides occur in solution in disordered conformation forms also referred as random coils, which means that polysaccharide molecules have random fluctuating shapes that are caused by Brownian motions. In dilute solutions, polysaccharide molecules are freely moving due to having a good amount of free volume present between polysaccharides molecules. In case of concentrated solutions, polysaccharide molecules do not have free space or volume; they overlap, interpenetrate, and get entangled with each other. This increase in the concentration of polysaccharides results in increased viscosity of the solution. Hence, polysaccharide concentration is an important factor affecting viscosity of polysaccharide solutions. Another factor that affects the viscosity of polysaccharide solutions is shear rate. Viscosity of concentrated polysaccharide solution decreases as the shear rate increases, which is due to opening the entangled chain of the polysaccharide molecules. This effect is known as shear thinning behavior of the polysaccharides. In dilute solutions, viscosity is slightly dependent on the shear rate. Another factor that affects the viscosity of the polysaccharide solutions is temperature, but in case of dietary fiber for human use, this factor is not so important because of the constant human body temperature (i.e., 37°C). Hence, viscosity values of polysaccharide solution should be reported with specific conditions of concentration, shear rate, etc. at which viscosity is determined. Viscosity of food-based formulations can be measured using rotational-type viscometer and rheometers at specific conditions of concentration, temperature, pH, shear rate, etc. These instruments are based on the principle of resistance to flow and measure the resistance force on rotating spindle by spring.

2.3.3 Water Holding and Binding Capacity Several terms can be used for the interaction of dietary fiber and water, such as hydration, water-adsorption, water-binding, water-holding, water-uptake, etc. All these terms have similar meanings or have very little difference depending on the conditions in which these are described. The most important terms used for dietary fibers are water-holding and waterbinding capacity. Some definitions are mentioned in the literature for these terms, which can be adopted to differentiate between water-holding and water-binding capacity. Researchers suggested a definition based on the principle of the gel-forming action of

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polysaccharides, which is also suitable in case of dietary fibers (Rey & Labuza, 1981). According to them, water-binding capacity is the amount of water in the gel structure withheld by it after exposure to external force or stress. The example of external force may include centrifugal force. Water-binding capacity of dietary fiber is considered more important as different processing operations of food products containing dietary fiber require exposure to external force or stress. Some examples are homogenization (liquid products), high-speed mixing or kneading (bakery products), and extrusion (cereal products), etc. Water-holding and water-binding capacity of dietary fibers is affected by several factors, but the most important factor is the source of dietary fiber, which influences its chemical composition. Other factors that influence the water-holding and water-binding capacity of dietary fibers are microstructure, processing conditions, and the method used for determining water-holding and water-binding capacity. Some researchers also reported that water-binding or holding capacity of dietary fiber is function of origin or source of dietary fiber and the technique used for its measurement. They also suggested that dietary fiber’s structure is more prominent as compared to the chemical composition of dietary fiber (Robertson & Eastwood, 1981). Length of dietary fiber, particle size, and porosity behavior of dietary fiber are associated with its microstructure. Both the source of dietary fiber and conditions of processing operations affect the microstructure of dietary fiber. Hence, manufacturers can transform the waterholding and binding capacity of dietary fiber by altering these above-mentioned factors and prepare tailor-made dietary fiber ingredients as per the requirements of specific food processors. Other factors that influence the water-holding and binding capacity of dietary fiber are the conditions or environment of the food system in which dietary fiber is incorporated. These conditions include ionic nature, pH, dietary-fiber concentration, and other ingredients (such as starch and sugars) present in the food system having high water-binding capacity. All these conditions interfere with the water-binding capacity of dietary fiber. Particularly in the case of soluble dietary fibers, pH and ionic behavior have a direct effect on its interaction with water molecules. Methods of determining water-holding or binding capacity of dietary fibers affect its value, too. There are several methods proposed to determine the water-holding and binding capacity of dietary fibers; however, there is no standard method that is recommended and adopted globally. This restricts the comparisons of water-holding and binding capacity data from different sources. A recent report suggested the adoption of the optimized centrifugal method for waterbinding capacity based on the hydration characteristics of dietary fibers (Robertson et al., 2000). They reported that statistically significant results were obtained for resistant starch and other dietary fibers, such as apple pulp, pea hull, and citrus pulp. Hydration capacity of dietary fibers made up of primary cell walls are higher in comparison to the components made up of secondary cell walls (Thibault, Lahaye, & Guillon, 1992; Thibault, Renard, & Guillon, 1994). The determination of water-binding capacity of dietary fibers generally involves the addition of the known volume of water to the known weight of the dietary fiber sample, which is subjected to separation via filtration or centrifugation. Other conditions such as temperature, time of soaking, centrifugation speed, and duration, etc. should also be mentioned as the water-binding capacity of dietary fibers is influenced by several factors. While determining water-holding or binding capacity of dietary fiber, a small amount of soluble fiber is usually lost, which affects results (Fleury & Lahaye, 1991). Direct and indirect methods for determining water-holding and water-binding capacity of dietary fibers are reported in literature

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(Cho, DeVries, & Prosky, 1997). Several modified methods are also reported for determining water-holding and water-binding capacity of dietary fibers (Dreher, 1987; Thibault et al., 1992). Swelling and water-holding and water-binding capacity of insoluble dietary fibers (cellulose, lignin, etc.), which are unfermentable by microflora in large intestines, causes an increase in fecal bulk (Elleuch et al., 2011). Absorbing and entrapping water in its porous structure and swelling is responsible for the bulking effect of insoluble dietary fiber in the colon. Waterbinding ability of insoluble dietary fiber enables it to diminish the efficacy of toxic materials due to their dilution in the human large intestine.

2.3.4 Fermentability Dietary fibers have resistance toward enzymatic action in the gastro-intestinal tract and undergo slight degradation by colonic microbial fermentation (Topping & Illman, 1986). Fermentability of dietary fiber is its significant property, which makes it able to act as a substrate for the fermentation process. It is reported in literature that a low-fiber diet shows normal excretion of 50 g per day with 800 k joules per day, whereas a high-fiber diet shows normal excretion of 88 g per day with 1700 k joules per day (Langkilde & Andersson, 1998). Different types of dietary fibers show different degrees of fermentation, that is, nonfermented such as lignin and completely fermented such as pectins. Generally, soluble dietary fiber is more fermentable by bacteria present in colons in comparison to insoluble dietary fiber. Various bowel functions, such as fecal weight, frequency of stool, pH of colon, and energy from nondigestive foods depend on the fermentability and pattern of fermentation of dietary fiber (Edwards, 1995). Based on their fermentability in the colon, there are three categories of dietary fiber: rapidly fermentable, slowly fermentable, and nonfermentable dietary fiber. Examples of rapidly fermentable dietary fibers are those that are obtained from fruits and vegetables. These types do not have a substantial contribution to fecal bulk as compared to other types of dietary fibers. Examples of slowly fermentable dietary fibers are those that are obtained from psyllium, wheat bran, etc. These also contribute to fecal weight after fermentation. Nonfermentable or poorly-fermentable dietary fibers are associated with an increase in fecal bulk and fecal weight in human large intestines, which leads to lower risk of constipation-related problems and colon cancer. Due to the production of metabolites as a result of colonic fermentation, fermentable dietary fibers cause physiological changes in mucosa present in the colon (Bingham, 1990). Rapidly fermentable dietary fibers cause postabsorptive action on liver and tissues of other organs (Topping & Pant, 1995). Besides performing these functions, a few dietary fibers are also associated with stimulation of growth as well activity of beneficial bacteria (bifidobacteria, lactobacilli, etc.) present in the human alimentary canal, which perform a protective barrier function and stimulate human immune response (Salminen et al., 1998). The speed of fermentation and degree of fermentation is very much dependent on the structure of the fiber source, which is further associated with the bacterial contact to the fermentation substrate (Guillon & Champ, 2000). Fiber sources having higher numbers of parenchyma tissues, such as fruits and vegetables, are more prone to fermentation as compared to fiber sources having higher numbers of secondary tissues, such as hull and bran portions of cereals and legumes. Soluble types of polysaccharides show a high rate of fermentation as compared to insoluble polysaccharides present in cell wall portion. Results from animal

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studies suggest that dietary fibers having the characteristic to undergo fast fermentation (e.g., pectin and guar gum) are not protective against colorectal cancer; however, dietary fibers having the characteristic to undergo slow fermentation (e.g., wheat bran) show good protection against colorectal cancer (Young, 1991). Polysaccharides having blocked, branched structure favor fermentation in comparison to polysaccharides having more and random branching. The fermentation process is highly dependent on the microflora present in the individual, which varies from individual to individual and also in the cell-population densities of main taxonomic groups (Macfarlane & Macfarlane, 1993). Bacteria capable of hydrolyzing polysaccharides are Bifidobacterium, Ruminococcus, Bacteroides, Clostridium, and Eubacterium. Fructooligosaccharides and inulin have the ability to promote growth as well as activity of one or more types of bacteria in the colon. These nondigestible oligosaccharides, which promote the growth of beneficial bacteria in the human gut, are termed as prebiotics (Mudgil, Barak, Patel, & Shah, 2018). These fermentation processes in the human colon lead to the formation of end products, such as short chain fatty-acids including acetate, butyrate, etc. and gases that are beneficial for humans.

2.3.5 The Binding Ability of Minerals and Bile Acids Besides having water-binding ability, dietary fiber components are also reported to have binding ability for polar and ionic molecules, such as bile acids and minerals. The decrease in availability of minerals and absorption of ionic components are due to the presence of dietary fiber that has binding ability for ions and polar materials (Schneeman, 1986). Presence of free carboxylic group and amount of uronic acid present in dietary fiber components in diet are generally responsible for their minerals and ion-binding ability. These metal ions and polar molecules may be released and absorbed in the colon where some dietary fibers undergo degradation. It has been reported that iron and zinc absorption is increased by sugar-beet fiber, whereas absorption is inhibited by wheat bran fiber due to presence of phytate (FairweatherTait & Wright, 1990). When included in the human diet, dietary fibers from different food sources are reported to enhance bile-acid secretion in human feces via adsorption and entrapment of bile acids, which is considered health beneficial for human beings (Eastwood & Hamilton, 1968; Kritchevsky & Story, 1974). On interaction with water, the soluble type of dietary fiber leads to the formation of gel-type structures and are generally excreted out in feces. These gel structures show that the binding and entrapment of bile acids from the gallbladder are excreted out with the feces. The binding of bile acids by gel structures of soluble dietary fibers is reported to be more prominent in the last portion of ileum in which bile acids from the digesta are generally re-absorbed (Elleuch et al., 2011). This increased excretion of bile acids in human feces causes increased utilization of cholesterol in the body for the formation of bile acids and finally leads to lowering of cholesterol levels in the human body. The accurate mechanism behind dietary fiber’s binding with bile acids is not yet clear. Some researchers suggest that ionic and hydrophobic interaction between bile acids and dietary fiber components are responsible for the binding and adsorption of bile acids by dietary fiber (Thibault et al., 1992). Binding ability of dietary fibers also depends on its composition. When fiber components have more coarse and lignified tissues present, they have an increased binding ability (Robertson, 1998). Adsorption ability of dietary fiber for different

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components can be determined by various methods involved in determining water-binding ability. Retention of these components in dietary fiber cell matrices is due to their entrapment and adsorption. Certain conditions may have influence on the adsorption and binding ability of dietary fiber components. These conditions are pH of digesta in the small intestine and behavior of digesta having dietary fiber in the small intestine. Hence, conditions should be controlled and reported while measuring binding ability of dietary fiber.

2.3.6 Oil-Binding Ability Dietary fiber components have an ability to bind oil in their structure. Chemical composition and structure of dietary fiber components play a role in oil-binding ability. Porosity in dietary-fiber structure is a more prominent factor responsible for oil-binding capacity as compared to chemical composition or its affinity toward oil molecules. In water-binding ability of dietary fiber molecules, chemical composition or affinity is a primary factor. Porous structure of dietary fiber components enables them to bind oil in the pores present in its structure. This oil-binding ability of dietary fiber components can be reduced by simple preprocessing operations, such as presoaking in water. Before adding oil to the ingredients containing dietaryfiber components, their presoaking in water aids in reduced oil uptake by fiber components as a result of occupation of pores by water molecules. This process is very significant for fried food products. This leads to a reduction in the fat content of fried products, which is important from a health viewpoint. Addition of dietary fiber ingredients to comminuted meat products and emulsified meat products leads to emulsification via retention of fat molecules. This property of dietary fiber components is also significant in the formulation of low-fat meat products; the fiber molecules bind the low amount of fat present in the formulation and lead to final products with improved textures (Nelson, 2001).

2.3.7 Particle Size and Porosity Dietary fiber particle size is significant in various important physiological functions in the human intestine, i.e., transit time of digesta, fermentation rate of digesta, and fecal excretion. Surface area of dietary fiber is directly related to dietary fiber fermentation speed. An increased surface area of dietary fiber increases the speed of the fermentation process; more bacteria are linked with substrate, which facilitate the fermentation process (Cherbut, 1995). Coarse particles of wheat bran regulate the transit time of digesta more effectively than fine particles of wheat bran. Dietary fiber in digesta reduces transit time, which protects the human colon from cytotoxic substances, which are harmful for human health. Dietary fiber particle size depends on the type of plant cell wall and the level of processing. Processing operations such as grinding, comminution, mincing, etc. greatly influence the particle size of dietary fiber. Colonic bacteria can degrade the fiber matrix and result in an almost complete breakdown of the particles. The behavior of dietary fiber in the colon is not necessarily associated with particle size of dietary fiber before consumption (Guillon & Champ, 2000). Porosity of dietary fiber is also an important characteristic that affects its bacterial and enzymatic degradation, and it depends on the types of cells, composition of dietary fiber, and the degree of processing. Pectins are considered to have a prominent role in defining porosity of cell walls (Guillon, Auffret, Robertson, Thibault, & Barry, 1998).

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2.4 IMPORTANT SUSTAINABLE SOURCES OF DIETARY FIBER 2.4.1 Cereals as a Source of Dietary Fiber cereal grain consists of different tissues differing in their composition and properties. The cell walls from the outer grain tissues are generally thick and play a protective role in grain. These cell walls are composed of cellulose and complex xylans and may also contain a significant quantity of lignin. However, cell walls of aleurone and endosperm are primarily composed of arabinoxylans and β-glucan, and smaller amounts of cellulose, heteromannans, protein, and esterified phenolic acids (Fincher, 1986; Hemery, Rouau, Lullien-Pellerin, Barron, & Abecassis, 2007; Saulnier & Quemener, 2009) (Table 2.2). 2.4.1.1 Wheat After rice, wheat is the second most consumed cereal by humans. Wheat is a nutritious grain, comprised of different nutritional components including proteins, minerals, B vitamins, and dietary fiber (Sarwar, Sarwar, Sarwar, Qadri, & Moghal, 2013). The fiber TABLE 2.2 Sources of Dietary Fiber Food Source

Examples

Cereals

Wheat Rice Barley Oats Rye Pseudocereals

Legumes

Cluster beans Broad beans Chickpeas, Lentils Soybeans Lupins Mung beans Lotus bean Sprouts Dry beans Green beans Peas

Fruits

Oranges Kiwi fruit Apples Citrus fruits Prunes

Vegetables

Tomatoes Cabbage Alfalfa Carrots Potatoes Lady fingers

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content of whole wheat grain ranges from 11.6% to 12.7% (dry weight). Most of the fiber that is present in the outer layers of the grain is called wheat bran, which constitutes about 13%–17% of total wheat grain weight. The composition of bran varies widely among different crops, and predominantly contains dietary fiber, vitamins, and minerals (Stevenson, Phillips, O’sullivan, & Walton, 2012). Wheat bran is one of the richest sources of fiber; the majority is nonstarch polysaccharide (NSP). The main NSPs present are arabinoxylan, cellulose, and beta-glucan that are respectively 70%, 24%, and 6% of the NSP of the bran (Maes & Delcour, 2002). About 34%–63% of the wheat bran is constituted of soluble and insoluble dietary fiber attached to proteins, lignin, and other substances that escape hydrolytic enzymatic digestion in the upper gastrointestinal tract. Out of this, soluble dietary fiber comprises 5% of total dietary fiber, and comprises of glucan and xylans, which is significantly less than barley (3%–11%) and oats (3%–7%) (Wood, 1997). The water-insoluble fiber of wheat bran is composed of arabinoxylan (19%–25%), starch (17%–29%), protein (14%–18%), lignin (3%), β-glucans (1%–3%), phytic acid, (3%–5%) and ferulic acid (0.3%–5%). β-Are soluble in water and highly viscous. β-glucans correspond about 2.2%–2.7% of the dry weight of wheat bran. Wheat bran has been recommended in the human diet for prevention of different fiberrelated diseases such as constipation and cancer. Wheat bran has been extensively used in the fortification of cereal-based food products. Wheat bran is known to be rich in minerals, fiber, B vitamins, and bioactive compounds, which have shown to possess health-promoting properties (Onipe, Jideani, & Beswa, 2015). Dietary fibers have been shown to improve the gut health, regulate appetite, and lengthen satiety. Prolonged satiety can be attributed to large water absorption by dietary fiber, reduced gut transit time, increased viscosity in the small intestine, increased stool bulk, and short-chain fatty acid (SCFA) production in the colon, as a result of fermentation of the fiber (Brouns, Hemery, Price, & Anson, 2012). Although some work has been cited in literature regarding the role of wheat bran dietary fiber in human weight regulation, not much evidence is available for establishing its role as weight regulator. Around 64% of wheat bran cell walls consist of arabinoxylans, which have been reported to reduce postprandial glycemic response via maintaining viscosity in the gut, thereby reducing the risk of development of type II diabetes. Wheat bran is used as an additive and plays a key role in the preparation of dough and in bread baking (Anson, Hemery, Bast, & Haenen, 2012). 2.4.1.2 Rice Rice is an edible starchy cereal grain that is consumed by a large part of the world population, particularly East and Southeast Asia, which is completely dependent upon rice as a staple food. About 95% of the rice produced in world is consumed by humans and has been a source of food for people for ages. Rice is considered as an excellent food source and is particularly rich in vitamins and fiber. The different layers of rice have different quantities of fat, carbohydrate, protein, and fiber, and removal of these different layers during the milling process affects the nutritional quality of rice. The milling of brown rice involves the removal of the outer bran layer, seed-coat, aleuronic layer, and embryo. This results in substantial loss of fat, crude protein, and neutral detergent fiber in milled rice. After milling of rice, two fractions are obtained, the first being rice bran, which contains an appreciable quantity of crude fiber, and white rice, which is a rich source of starch. Rice bran fiber majorly consists of noncellulosic polysaccharide (24%), cellulose (10.3%), and lignin (10.7%) (Sera et al., 2005). Arabinoxylans and some amount of β-D-glucans present in rice bran form the major components of SDF (soluble dietary fiber) (Rao & Muralikrishna, 2004) present in rice along with

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rhamnose, xylose, mannose, galactose, and glucose while cellulose, hemi-cellulose, insoluble β-glucan, and arabinoxylans constitutes the IDF (insoluble dietary fiber) (Lai, Lu, He, & Chen, 2007). The quantity and amount of these nonstarch polysaccharides in rice are dependent upon the rice cultivar, degree of milling, and water solubility. Rice bran contains about 25.3 g of dietary fiber per 100 g and can possibly meet the recommended dietary fiber intake of an adult, which is about 27 g a day. Dietary fiber in rice bran includes cellulose, hemicellulose (13%), and pentosans (6.5%), which fall under the category of insoluble fibers. In addition, it also contains around 2% soluble dietary fiber. The role of dietary fiber in protecting the body against diabetes and heart disease has been well cited in the literature. However, only limited studies have been conducted to demonstrate the antidiabetic and hypocholesterolemic effects of dietary fiber of rice bran in humans, while this aspect has been well studied in rats and hamsters (Kahlon, Chow, Sayre, & Betschart, 1992). In a study on human subjects (Hegsted, Windhauser, Morris, & Lester, 1993), it was shown that 100 g of rice bran a day could lower plasma cholesterol levels and thus can be considered as good as oat bran. However, an intake of 30 g of rice bran did not show any appreciable effect. Both the full-fat rice bran and defatted rice bran are good sources of dietary fiber, the latter having a considerably higher fiber content (30%). The reported hypocholesterolemic effect of full fat rice bran may be partly due to its oryzanol and phytosterols content. Rice bran has many food applications in prepared foods, nutraceuticals, and functional foods. Some applications are in snack foods, bakery, pasta, gluten–free foods, beverages (Faccin, Miotto, do Nascimento Vieria, Barreto, & Amante, 2009) and meat products (Huang, Shiau, Liu, Chu, & Hwang, 2005). 2.4.1.3 Barley Barley (Hordeum vulgare) plays a significant role in meeting the nutrient needs of the human population. Barley is considered to be an excellent source of some nutrients while it may be poor in others (Newman & Newman, 2006). Barley grain is known to be a good source of dietary fiber and phytochemicals. Whole-grain barley is preferred for its nutritional importance and also for its nutraceutical properties (Lahouar et al., 2014). Nutraceutical property is β-glucan, which is the soluble fiber. β-Glucan is a polysaccharide found principally in the cell walls of the aleurone layer and endosperm of barley kernels. The β-glucan content varies with the cultivar, degree of extract viscosity, and the starch content and type (Andersson et al., 2004). β-Glucan, a soluble fiber, helps prevent hypercholesterolemia, hypoglycemia, and reduces the chances of chemically induced colon cancer (Newman & Newman, 2008). Fiber represents the second major constituent of the grain after starch and is present throughout the kernel (Brownlee, 2011). Fiber has been classified into two classes: soluble and insoluble. The total fiber content of barley ranges from 11% to 34%. Approximately, 3%–20% is soluble dietary fiber, mostly present in the form of β-glucan ( Jalili, Wildman, & Medeiros, 2000; Makeri, Nkama, & Badau, 2013). The β-glucan content of barley ranges from 2% to 11%, which is higher than the β-glucan content of oats (2.2–7.8) and wheat (0.4%–1.4%). The health benefits associated with consuming β-glucan-rich foods are lowered blood glucose levels and lowering of serum total and LDL-cholesterol levels. The abovementioned health beneficial properties of β -glucan are the result of an increase in viscosity of intestinal content, which in turn depends on the molecular weight and solubility of β-glucan (Hashemi, 2015; Smith, Queenan, Thomas, Fulcher, & Slavin, 2008). A certain

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portion of barley escapes digestion and absorption in the small intestine and reaches the large intestine, where it is fermented with the production of short chain fatty acids (Wong & Jenkins, 2007). This starch fraction is termed as resistant starch (RS), which is associated with a reduction of the glycemic index, lower absorption of cholesterol, and the prevention of colon cancer (Le Leu, Brown, Hu, & Young, 2003). RS can be added as a functional ingredient to different food products. Processing increases the RS concentration of barley. The heating and cooling cycles during processing of barley promote the retrogradation of starch, which, in turn, increases RS content. Another method for production of RS involves gelatinization of starch, enzymatic debranching of the gelatinized polymer, deactivation of the debranching enzyme, and separation of the resultant product by either drying, extrusion, or crystallization. The beneficial health property of RS is attributed to its indigestibility in the small intestine. It is fermented in the large intestine by the intestinal microflora and has a prebiotic effect as well by favorably influencing the ecology of the microbial flora in the large intestine. Upon consumption of both resistant starch and probiotics, a symbiotic effect takes place wherein the prebiotic RS protects some of the ingested organisms against their digestion in the colon, thereby effectively increasing the initial levels of the desirable species when they reach the colon (Slavin, 2013; Topping, Fukushima, & Bird, 2003). 2.4.1.4 Oats Oats contain different health-promoting components, including dietary fiber, proteins, and minerals (Butt, Tahir-Nadeem, Khan, Shabir, & Butt, 2008). The health claims by the European Union allow the food producers to market products containing 1 g β-glucan/portion with claims to reduce blood cholesterol levels and to attenuate postprandial glycemic response. Moreover, the intake of oat and barley grain fiber has also been linked to the increase in fecal bulk and pre˚ kesson, & Onning, vention of metabolic syndrome (Cloetens, Ulmius, Johansson-Persson, A 2012). The innermost layer of the aleurone layer of oat grain contains a majority of mixed-linkage (1 ! 3),(1 ! 4)- β-D-glucan, which is also present in the starchy endosperm, that is, β-D-glucan is mainly located in the subaleurone region. Thus, the main dietary fiber components of oats are mixed-linkage (1 ! 3), (1 ! 4) β-D-glucan (β-glucan), and arabinoxylan (AX) (Khan et al., 2016). Both β-glucan and AX are concentrated more in the bran fraction than in the starch-rich endosperm area. About one-third of the insoluble fiber of oats is β-glucan, whereas the majority of the soluble fiber is β-glucan (Manthey, Hareland, & Huseby, 1999). The concentration of β-glucan in whole grain oats varies from 2% to 8.5% and in oat bran between 65 and 9% (Shewry et al., 2008). Oats β-glucan is a linear polysaccharide, composed of β-D-glucopyranose units linked together by (1 ! 4) and (1! 3) linkages (Parrish, Perlin, & Reese, 1960). The ratio of (1 ! 4) and (1 ! 3) linkages is approximately 70:30 and about 90% of (1 ! 4) linked β-D-glucopyranoses exist in groups of three (cellotriose) or four (cellotetraose) units separated by one (1 ! 3) linkage (Doublier & Wood, 1995). The β-(1 ! 3)-bonds increase the flexibility of the chain, which prevents the close packing of cellulose molecules, and increase β-glucan’s solubility in water (Buliga, Brant, & Fincher, 1986). The molecular weight (Mw) of oat β-glucan ranges from 1000 to 3100 kDa (Sikora, Tosh, Brummer, & Olsson, 2013). Several studies and meta-analyses have shown that oat β-glucan can successfully reduce LDL cholesterol levels (low-density lipoprotein) in hypercholesterolemic subjects (Othman, Moghadasian, & Jones, 2011; Ripsin et al., 1992). According to studies by Othman et al. (2011) daily intake of 3 g of oat β-glucan can reduce blood total and LDL cholesterol levels by 5%–10% in normal or hypercholesterolemic subjects.

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2.4.1.5 Rye Rye, considered one of the heartiest of the grains, is known to be more nutritious than wheat. Originally, rye was grown as a wild grass in Central Asia. Rye is a great source of dietary fiber, phosphorous, magnesium, vitamin B1, and has a ratio of 4:1 magnesium-to-calcium ratio. Due to its high-fiber content, rye can help prevent spikes in blood sugar and is beneficial to those with diabetes. The fiber content of rye has also been shown to reduce the symptoms of those suffering from irritable bowel syndrome. Rye’s ability to provide extra soluble and insoluble fiber, as well as increase colonic butyric acid production, can help prevent colon cancer. As it provides water-binding, noncellulose polysaccharides, rye can promote the sensation of fullness and help normalize bowel function (Aman, Andersson, Rakha, & Andersson, 2010). 2.4.1.6 Pseudocereals In botanical terms, amaranth, quinoa, and buckwheat are not true cereals; they are dicotyledonous plants as opposed to most cereals (e.g., wheat, rice, barley) that are monocotyledonous. Referred to as pseudocereals, their seeds resemble those of the true cereals in function and composition. It is generally accepted that the consumption of food naturally rich in dietary fiber is beneficial to the maintenance of health (Champ et al., 2003). However, the intake of fiber in the gluten-free diet is considered to be inadequate, and experts recommend a higher intake of fiberrich whole-grain cereals as opposed to refined grains (Hopman, le Cessie, von Blomberg, & Mearin, 2006; Kupper, 2005; Pagano, 2006; Thompson, Dennis, Higgins, Lee, & Sharrett, 2005). Studies have shown that the pseudocereals amaranth, quinoa, and buckwheat represent good sources of dietary fiber. In particular, dietary-fiber content is significantly higher in buckwheat seeds in comparison with amaranth and quinoa, which have fiber levels comparable to those found in common cereals (Alvarez-Jubete, Arendt, & Gallagher, 2009). Therefore, the incorporation of these seeds in the diets of celiac disease patients should help alleviate, at least in part, the deficit in fiber intake in this sector of the population.

2.4.2 Legumes as a Source of Dietary Fiber The legumes are regarded as one of the earliest food crops grown in the world for over 10,000 years. The legume family consists of pod–bearing, common edible plants, including dry beans, broad beans, dry peas, chickpeas, lentils, soybeans, lupins, mung beans, lotus, sprouts, alfalfa, green beans, peas, and peanuts. The terms “legumes” and “pulses” are used interchangeably because all pulses are considered legumes, but not all legumes are considered pulses. The Food and Agriculture Organization defines pulses as “the crops harvested solely for the dry seed of leguminous plants.” Legumes are a great source of essential nutrients such as protein, low glycemic index carbohydrates, dietary fiber, minerals, and vitamins. Legumes are particularly rich in protein (17%–20% dry weight in peas and beans, 38%–40% in soybeans and lupins) and dietary fiber (5%–37% dry weight) (Kouris-Blazos & Belski, 2016). In general, beans are the conventional legumes possessing the highest DF content with about 60%–85% insoluble and 40%–15% soluble dietary fiber, followed by chickpeas and peas with the lowest amount found in lentils. However, the DF content of each pulse found in the literature is very heterogeneous, owing to the large quantity of legume varieties grown in different countries. Xuan and Azlan (2017) studied the effect of cooking on the dietary fiber content of prominent legumes and reported a total dietary fiber content of 27.66% in kidney bean, 15.88% in

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chick pea, and 19.38% in mung bean. They further reported that cooking led to a decrease in the fiber content of the different legumes studied. Eashwarage (2017) carried out a study to determine the dietary fiber and resistant starch content of locally consumed legumes of Sri Lanka. The dietary fiber of the raw legumes were found to be 13.07%–15.99% in cow pea, 18.51%–19.67% in soybean, 21.38% in horse bean, 14% in lentils, and 6% in peas. The highest content of resistant starch was reported by horse gram (10.68%) followed by cowpea (9.62%). Chavan, Kute, and Kadam (1989) reported a crude fiber content in faba beans ranging from 5.0% to 8.5% while Pritchard, Dryburgh, and Wilson (1973) and Hove, King, and Hill (1978) found dietary fiber values of 15%–30%. These differences in fiber content could be attributed to the different varieties used for the study. Some of the nontraditional, underutilized legumes such as beach bean (Canavalia maritima), marama bean (Tylosema esculentum), rice bean (Vigna umbellata), winged bean (Psophocarpus tetragonolobus), bambara nut (Vigna subterranea), and tepary bean (Phaseolus acutifolius) have recently gained attention as highly nutritive pulses with good productivity (Katoch, 2013). The dietary fiber content of these underutilized legumes has been studied by researchers across the globe. The total dietary fiber content of tepary bean has been reported to be 9.8% with insoluble dietary fiber contributing 9.2% and soluble dietary fiber 0.6%. The dietary fiber content of beach bean has been reported to be 2.26%, marama bean-18-24% (Holse, Husted, & Hansen, 2010), rice bean-5.22-7.43% (Rodriguez & Mendoza, 1991) and winged bean- 12.23% (Amoo, Adebayo, & Oyeleye, 2006). In general, the insoluble dietary fiber of legumes is primarily composed of hemicelluloses and cellulose, though this composition may vary with the species (Rehinan, Rashid, & Shah, 2004). The IDF of chickpea and lentil is chiefly composed mainly of arabinans and cellulose (MartinCabrejas et al., 2006), whereas the main polysaccharides of IDF in peas are cellulose and pectic polysaccharides (Martin-Cabrejas et al., 2003). On the other hand, the soluble dietary fiber is mainly composed of pectin polysaccharides in beans, peas, and chickpeas, while SDF fraction in lentil and cowpeas possess a lower content of pectin polysaccharides (Benitez et al., 2013). Legume fibers possess several advantages over cereal fibers. Legume fibers had a higher content of soluble components, leading to a greater formation of volatile fatty acids, such as acetic acid, propionic acid, and butyric acid. These volatile fatty acids inhibit cholesterol synthesis (Fechner, Kiehntopf, & Jahreis, 2014), and butyric acid has shown to reduce the risk of colorectal cancer (Fechner, Fenske, & Jahreis, 2013). Moreover, current studies show that acetic acid enhances the feeling of satiation from fibers by influencing central homeostatic mechanisms, as well as through the known action on the baroreceptors in the gastrointestinal tract (Frost et al., 2014). 2.4.2.1 Effect of Different Treatments on the Dietary Fiber Content of Legumes People rarely eat raw legumes as they contain antinutritional factors that can adversely affect enzyme activity, digestibility, nutrition, and health. Generally, treatments such as cooking, soaking, and roasting can affect the dietary fiber and phenolic content of legumes (Guillon & Champ, 2000). Cooking is one of the common ways that people process the legumes. Germination has been suggested as an effective treatment to remove antinutritional factors in legumes, mobilizing secondary metabolic compounds that act as reserve nutrients (e.g., phytates and α-galactosides). Vidal-Valverde et al. (1998) studied the effect of processing on the nutrients and antinutritional content of faba beans. Cooking of the presoaked faba beans produced a slight

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decrease in starch, dietary fiber, calcium, and phytic acid. The germination caused a sharp reduction in α-galactoside and phytic acid content after 6 days, while starch and dietary fiber decreased only slightly. Uncooked and cooked germinated seeds of wild legume Canavalia maritima grown on the coastal sand dunes of the Southwest coast of India were evaluated by D’Cunha, Sridhar, and Bhat (2009). The crude fiber decreased upon cooking from 2.26% to 1.70% in ungerminated seeds of the legume while germination of the seeds reduced the crude fiber slightly. de Almeida Costa, da Silva Queiroz-Monici, Reis, and de Oliveira (2006) studied the effect of cooking and freeze drying on the dietary fiber content in conventional legumes. No significant differences were reported between dietary fiber contents of raw and processed legumes. On the other hand, Kutos, Golob, Kac, and Plestenjak (2003) found considerable decrease of IDF and TDF contents upon canning and cooking of beans. The bean IDF content decreased during soaking, while the SDF content increased. Cooking and canning of soaked beans decreased the SDF content. Similar results were reported by Marconi, Ruggeri, Cappelloni, Leonardi, and Carnovale (2000), who reported that cooking of beans achieved by boiling and microwave heating did not modify the total nonstarch polysaccharide content of beans and chickpeas in comparison to the raw legumes, but both processes increased the SDF and decreased the IDF. These changes were due to partial solubilization and depolymerization of hemicelluloses and insoluble pectin polysaccharides. The cooking and microwave heating resulted in softening of plant tissues (Pena, Vergara, & Carpita, 2001). Aldwairji, Chu, Burley, and Orfila (2014) also studied the fiber content of boiled and canned legumes commonly consumed in the United Kingdom. Results revealed that the boiled legumes had higher TDF levels (3.6% in green beans to 11.2% in red kidney beans) as compared to canned legumes (TDF values of 2.7% in canned green beans to 7.4% for canned chickpeas). Thus, it was found that legumes preserved by canning had significantly lower TDF values than boiled legumes. However, canning did not significantly change the proportion of IDF to SDF as compared to boiled legumes. In general, the germination process increases both IDF and SDF fractions and thus the TDF content (Lee, Oh, Yang, & Kim, 2006). Additionally, fermentation of beans decreases the TDF content as a result of both natural and microbial fermentation of DF of beans (Martin-Cabrejas et al., 2004).

2.4.3 Fruits and Vegetables and Their Waste as Source of Dietary Fiber Worldwide nutrition guidelines state that in order to meet their daily dietary fiber intake goals, consumers should include a variety of fruits, vegetables, and whole grains in their daily diet. The examples of cereal fibers include barley, corn germ, rice bran, rye bran, sorghum bran, corn bran, lignin, wheat bran, wheat starch, arabinoxylan, barley bran flour, oat bran, resistant starch, and soluble corn fiber whereas the vegetable group includes tomatoes, alfalfa, cabbage, carrot fiber, fructooligosaccharides (FOS), inulin, and potatoes. Fruit fiber sources include oranges, kiwi fruit, apples, citrus pectin, and prunes. One of the prominent industries of the world, the fruit and vegetable processing industry produces a large amount of by-products, including fruit peel, pomace, etc. Recent research has shown that fruit peels represent about 20%–40% by weight of the total fruit. Usually, these by-products are used as animal feed and fertilizers while they can also be converted to obtain

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more valuable edible products in order to reduce the cost of their transportation and disposal. Thus, there has been an increased interest in exploiting the possibility of using healthbenefiting components and other valuable ingredients of fruit and vegetable peels in the development of functional food. The major components of fruit peels include nonstarch polysaccharide and lignin, which are the important constituents of the plant cell wall. Both the nonstarch polysaccharide and lignin are generally regarded as insoluble dietary fiber that is neither digested nor absorbed in the human small intestine. Therefore, numerous attempts have been made by researchers all over the globe to turn many fruit and vegetable peels into dietary fiber, such as banana (Emaga, Andrianaivo, Wathelet, Tchango, & Paquot, 2007) mango, (Koubala et al., 2008) citrus, (Figuerola, Hurtado, Estevez, Chiffelle, & Asenjo, 2005) and lime (Ubando-Rivera, Navarro-Ocana, & Valdivia-Lopez, 2005). According to literature, the residues of apple (Grigelmo-Miguel, & Martı´n-Belloso, O., 1999) and citrus fruit, including grapefruit, lemon, and orange (Figuerola et al., 2005) from juice extraction and citrus peels, such as Valencia orange, Persa lime, Maxican lime, lemon, and sweet orange, (Marin, SolerRivas, Benavente-Garcia, Castillo, & Perez-Alvarez, 2007) are considered as fiber-rich plant foods since they have more than 50% of total dietary fiber, whereas the peels of pear and peach have comparably lower contents of dietary fiber (35%–36%) (Grigelmo-Miguel, & Martı´nBelloso, O., 1999). Additionally, the dietary fiber from citrus peels possesses better quality than other fiber sources due to the presence of associated bioactive compounds, such as flavonoids, polyphenols, and carotene, with antioxidant activities (Marin et al., 2007). Lim and Rabeta (2013) studied the proximate analysis of three apple species and reported that 83.28%–89.92% of apple consists of water whereas the amount of dietary fiber is only 0.86%–1.81%. However, the apple pomace separated during processing is reported to have 51.10 g/100 g (dry matter basis) of total dietary fiber. Out of this 14.60 g/100 g, DM is soluble while 36.50 g/100 g DM is insoluble dietary fiber. The values depend upon the extent of pressing, use of enzymes, and additional extraction with water and other solvents, etc. Nilnakara, Chiewchan, and Devahastin (2009) studied the crude fiber content of cabbage leaves and reported its range from 19.92–47.47 g/100 g DM. Similar results were reported by Tanongkankit, Chiewchan, and Devahastin (2010) who reported that cabbage leaves possess a total dietary fiber content of 40.89 g/100 g DM. Carrot is another widely used vegetable in the food industry, but its peels or pomace are usually discarded or used as animal feed. Chantaro, Devahastin, and Chiewchan (2008) studied the carrot peels and reported that the peels contained 45.45 g/100 g DM of dietary fiber with a high antioxidant capacity of 94.67%. They further reported that blanching improves the total dietary fiber (TDF) yield and the insoluble dietary fiber (IDF) to soluble dietary fiber (SDF) ratio with no significant effect on total phenolic content. The by-products of coffee bean were studied by Murthy and Naidu (2012) and reported that coffee pulp, husk, silver skin, and spent coffee are rich in natural antioxidant compounds associated with dietary fiber. These by-products possessed 28%–80% of total dietary fiber. Guava (Psidium guajava L.) is a tropical fruit, widely consumed in fresh form and also in processed forms such as beverages, syrup, ice cream, and jams ( Jimenez-Escrig, Rincon, Pulido, & Saura-Calixto, 2001). Positive health effects of fruit and by-products of guava are due to their high antioxidant capacity. Studies by Jimenez-Escrig et al. (2001) and Martinez et al. (2012) further reported that guava concentrate and by-products exhibit high dietary fiber content of up to 69.1 g/100 g DM.

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Grapes are primarily cultivated as Vitis vinifera for production of wine. It is estimated that around 13% of grape pomace results from the total weight of grapes used for wine making as a by-product in this process (Torres et al., 2002). Grape pomace consists of seeds, skins, and stems, which can also be used to extract grape seed oil. Saura-Calixto (1998) carried out a study on the dietary fiber composition of grape pomace. They reported a dietary fiber content of 64.6% DM. Sanchez-Alonso, Jimenez-Escrig, Saura-Calixto, and Borderias (2007) and Llobera and Can˜ellas (2007) studied the fiber content for red grapes and reported that red grapes yielded an even higher value of dietary fiber at about 74%–77.2% DM. These findings are further strengthened by a similar research by Llobera and Can˜ellas (2008) who indicated that white grape pomace and stem possess a total dietary fiber content of 71.5–79.5 g/100 g DM. Mango (Mangifera indica L.) is a popular fruit that is cultivated in various regions, especially in the tropics. The studies by Vergara-Valencia et al. (2007) revealed that mango fiber concentrate (Martinez et al., 2012) and powder from mango peels (Ajila, Leelavathi, & Rao, 2008) possess high dietary fiber content of 28.05–70.0 g/100 g DM. Orange is well known for its high content of vitamin C and phenolic content. Orange juice is particularly rich in these bioactive compounds, contributing effectively to its antioxidant activity (Stella, Ferrarezi, dos Santos, & Monteiro, 2011). A study by Escobedo-Avellaneda, GutierrezUribe, Valdez-Fragoso, Torres, and Welti-Chanes (2014) showed that the flavedo of orange contains higher vitamin C, flavone, and carotenoid content in comparison to orange juice while the albedo is rich in phenolics, flavanones, and antioxidant activity. Fernandez-Lopez et al. (2009) reported that the orange peel has a high dietary fiber content of 71.62 g/100g DM. Martinez et al. (2012) reported that dietary fiber concentrate from by-products of Passiflora contain 81.5 g/100 g DM of total dietary fiber. A similar study by Lopez-Vargas, FernandezLopez, Perez-Alvarez, and Viuda-Martos (2013) on dietary fiber from coproducts of yellow passion fruit, pulp, seed, and albedo yielded 53.51–71.79 g/100 g DM of total dietary fiber. Martinez et al. (2012) also studied the pineapple fiber concentrate, obtained as waste from industrial productions and showed that pineapple-fiber concentrate is particularly rich in total dietary fiber (75.8 g/100 g DM). The pomegranate is regarded as one of the oldest edible fruits. A native of Persia and surrounding areas, the edible part of pomegranate contains juice, pulp, seeds, and represents about 65%–75% of the total weight of the fruit (Tehranifar, Zarei, Nemati, Esfandiyari, & Vazifeshenas, 2010). The pomegranate is a good source of dietary fiber. The total dietary fiber of pomegranate ranged from 0.57 g/100 g to 1.15 g/100 g in different varieties of the fruit with an average of 0.82 g/100 g. The insoluble dietary fiber was the major fraction reported in pomegranate dietary fiber concentrates with an average of 0.64 g/100 g. Thus, the conclusion is that fruits, vegetables, and their waste can be used as a potent source of dietary fiber.

2.5 CONCLUSION Dietary fibers are associated with several health benefits and are classified in two major classes depending on their solubility in water: soluble and insoluble. Dietary fibers are also associated with textural and sensory characteristics of the food products. Some important properties of dietary fibers are solubility, viscosity, water-holding ability, oil-holding ability, particle size, porosity, etc. Dietary fibers can be obtained from various sources such as cereals

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(wheat, rice, barley, oats, etc.), legumes (dry beans, broad beans, dry peas, chickpeas, lentils, soybeans, lupins, etc.), fruits (oranges, kiwi, apples, etc.) and vegetables (tomatoes, carrots, etc.), whereas the recovery of dietary fibers from respective processing by-products is the new trend. In conclusion, dietary fibers are important constituents in food that can be utilized for with health benefits along with desirable improvements in sensory and textural characteristics.

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Tanongkankit, Y., Chiewchan, N., & Devahastin, S. (2010). Effect of processing on antioxidants and their activity in dietary fiber powder from cabbage outer leaves. Drying Technology, 28(9), 1063–1071. Tehranifar, A., Zarei, M., Nemati, Z., Esfandiyari, B., & Vazifeshenas, M. R. (2010). Investigation of physico-chemical properties and antioxidant activity of twenty Iranian pomegranate (Punica granatum L.) cultivars. Scientia Horticulturae, 126(2), 180–185. Thibault, J. F., Lahaye, M., & Guillon, F. (1992). Physicochemical properties of food plant cell walls. In T. F. Schweizer & C. Edwards (Eds.), Dietary fibre, a component of food. Nutritional function in health and disease (pp. 21–39). Berlin: Springer-Verlag. ILSI Europe. Thibault, J. F., Renard, M. G. C., & Guillon, F. (1994). Physical and chemical analysis of dietary fibres in sugar-beet and vegetable. In J. F. Jackson & H. F. Linskens (Eds.), Vol. XVI. Modern methods of plant analysis (pp. 23–55). Heidelberg: Springer-Verlag. Thompson, T., Dennis, M., Higgins, L. A., Lee, A. R., & Sharrett, M. K. (2005). Gluten-free diet survey: are Americans with coeliac disease consuming recommended amounts of fibre, iron, calcium and grain foods? Journal of Human Nutrition and Dietetics, 18(3), 163–169. Topping, D. L., Fukushima, M., & Bird, A. R. (2003). Resistant starch as a prebiotic and synbiotic: state of the art. Proceedings of the Nutrition Society, 62(1), 171–176. Topping, D. L., & Illman, R. J. (1986). Bacterial fermentation in the human large bowel. Time to change from the roughage model of dietary fibre? The Medical Journal of Australia, 144(6), 307–309. Topping, D. L., & Pant, I. (1995). Short-chain fatty acids and hepatic lipid metabolism: Experimental studies. In J. H. Cummings, J. C. Rombeau, & T. Sakata (Eds.), Physiological and clinical aspects of short-chain fatty acids (pp. 495–508). Cambridge: Cambridge University Press. Torres, J. L., Varela, B., Garcı´a, M. T., Carilla, J., Matito, C., & Centelles, J. J. (2002). Valorization of grape (Vitis vinifera) byproducts. Antioxidant and biological properties of polyphenolic fractions differing in procyanidin composition and flavonol content. Journal of Agricultural and Food Chemistry, 50(26), 7548–7555. Tosh, S. M., Wood, P. J., Wang, Q., & Weisz, J. (2004). Structural characteristics and rheological properties of partially hydrolyzed oat β-glucan: the effects of molecular weight and hydrolysis method. Carbohydrate Polymers, 55(4), 425–436. Tungland, B. C., & Meyer, D. (2002). Nondigestible oligo- and polysaccharides (Dietary Fiber): Their physiology and role in human health and food. Comprehensive Reviews in Food Science and Food Safety, 1(3), 90–109. Ubando-Rivera, J., Navarro-Ocana, A., & Valdivia-Lopez, M. A. (2005). Mexican lime peel: comparative study on contents of dietary fibre and associated antioxidant activity. Food Chemistry, 89(1), 57–61. Vergara-Valencia, N., Granados-Perez, E., Agama-Acevedo, E., Tovar, J., Ruales, J., & Bello-Perez, L. A. (2007). Fibre concentrate from mango fruit: characterization, associated antioxidant capacity and application as a bakery product ingredient. LWT-Food Science and Technology, 40(4), 722–729. Vidal-Valverde, C., Frias, J., Sotomayor, C., Diaz-Pollan, C., Fernandez, M., & Urbano, G. (1998). Nutrients and € Lebensmitteluntersuchung undantinutritional factors in faba beans as affected by processing. Zeitschrift fur Forschung A, 207(2), 140–145. Wong, J. M., & Jenkins, D. J. (2007). Carbohydrate digestibility and metabolic effects. The Journal of Nutrition, 137(11), 2539S–2546S. Wood, P. (1997). Functional foods for health: opportunities for novel cereal processes and products. In G. M. Campbell, C. Webb, & S. L. McKee (Eds.), Cereals novel uses and processes (pp. 233–239). New York: Plenum Press. Xuan, T. C., & Azlan, A. (2017). Effects of cooking on the dietary fiber and phenolic contents of selected beans and its combinations. Journal of Food Science and Technology, 1, 1–8. Young, G. P. (1991). Dietary fibre and bowel cancer: Which fibre is best? In Cereals international Proceedings of an international conference held in Brisbane Australia (pp. 379–383). Melbourne: Royal Australian Chemical Institute. Yue, P., & Waring, S. (1998). Resistant starch in food applications. Cereal Foods World, 43, 690–695.

C H A P T E R

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Dietary Fiber and Metabolism Ramona Suharoschi*, Oana Lelia Pop*, Romina Alina Vlaic†, Carmen Ioana Muresan*, Crina Carmen Muresan†, Angela Cozma‡, Adela Viviana Sitar-Taut‡, Romana Vulturar§, Simona Codruta Heghes¶, Adriana Fodork, Cristina Adela Iuga¶,# *

Laboratory of Molecular Nutrition and Proteomics, Institute of Life Sciences, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Cluj-Napoca, Romania † Department of Food Engineering, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Cluj-Napoca, Romania ‡Department Internal Medicine, Clinique IV, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania § Cellular and Molecular Biology, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania ¶Department of Pharmaceutical Analysis, Faculty of Pharmacy, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania k Diabetes and Metabolic Diseases, Faculty of Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania #Department of Proteomics and Metabolomics, MedFuture Research Center for Advanced Medicine, “Iuliu Hațieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania

O U T L I N E 3.1 Introduction

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Dietary Fiber: Properties, Recovery, and Applications https://doi.org/10.1016/B978-0-12-816495-2.00003-4

3.4 The Binding of Dietary Fiber With Phenolic Compounds, Bile Salts, Mineral Ions, and Digestive Enzymes 66 3.4.1 Binding With Phenolic Compounds 66 3.4.2 Binding With Bile Salts (Bile Acids) 68

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# 2019 Elsevier Inc. All rights reserved.

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3.4.3 Binding With Mineral Ions (MI) 3.4.4 Binding With Digestive Enzymes

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3.5 Dietary Fiber Fermentation in the Large Intestine and the Corresponding Effect on Microbiota Composition 70 3.6 Conclusions

Author Contributions

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References

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3.1 INTRODUCTION It is generally known that the population consuming diets rich in dietary fiber (DF) has a lower incidence of chronic diseases. The digestion and absorption in the gastrointestinal (GI) tract of DF is determined by the DF’s structural complexity. Importantly, all plant cell walls are composed by DF that is digested selectively by microbiotic enzymes and not by host enzymes. Thus, complex DF in plant cell walls function as both substrate for the microbiota and as a sustained-release delivery system of other plant-cell derived nutrients and biomolecules for both microbiotic and host utilization. Plant cell wall structure varies from plant to plant and determines the specific site of plant cell wall degradation and nutrient release. A healthy diet is generally considered to include DF as an important element and this has led to dietary recommendations for an optimal consumption level. The DF positive effect on health is related to its behavior in the GI tract. Foods rich in DF are diverse ranging from whole foods (unrefined) to fully refined foods, and currently no official difference based on the degree of refinement is made. Foods with added refined nutrients (e.g., sugar, starch, or oils) or any food that has been structurally disrupted on the macroscopic level are considered as refined. Beneficial effects of DF on human health have been demonstrated, e.g., in immunity, diabetes, cancer, and cardiovascular diseases. Direct effect of DF on boosting the immune response by the interaction of bacterial and fungal β-glucan with specific receptors of epithelial immune cells has been demonstrated (Mikkelsen et al., 2014). However, this is an exception not the rule. The review studies that describe the physiological effect of DF related to behavior through digestion address one or few aspects of this behavior, and a comprehensive and detailed approach is needed. In this chapter, four health-linked aspects of DF behavior in the GI tract are discussed: (1) the effect of plant cell walls on bioavailability; (2) the effect of DF on the rheological and colloidal state of digesta; (3) the binding of DF with phenolic compounds, bile salts, mineral ions, and digestive enzymes; and (4) DF fermentation in the large intestine and the effect on gut microbiota composition.

3.2 THE MODULATION OF BIOAVAILABILITY BY THE PLANT CELL WALLS A widely recognized fact is that the incidence of chronic diseases is inversely proportional to the consumption of dietary fibers (Ljubicic et al., 2017; Makki et al., 2018). Human health is

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modulated through synbiotics’ effects borne from dietary fiber consumption. The pathway to understanding the physiological effect of the dietary fibers is to spotlight their behavior during digestion. A whole mechanism is contributing to human health when dietary fibers are ingested. Usually, dietary fibers belong to the structural system of the plant, namely in the cell wall. The key role of the wall cell is protection, and it is the principal surface of interaction with the external medium and environment. There are two layers that compose the plant cell wall: a primary cell wall that forms during plant growth and a secondary cell wall that forms after plants have completed their growth (Barnes & Anderson, 2018). In most of the cases, the primary cell wall structure has a network of cellulose fibrilshemicellulose (xyloglucan, arabinoxylans, β-glucan, etc.) embedded in a network of pectins (Carpita & Gibeaut, 1993). In this arrangement, there are different roles; namely: cellulose and hemicelluloses function as a load-bearing structure, while pectin confers plasticity and controls the porosity of the cell wall. Dick-Perez (Dick-Perez et al., 2011) in his work propose a new approach of the cell wall characterization with a single structure made from pectin, cellulose, and hemicellulose. The cell wall of plants is different, depending on the plant type. In grains, excepting rice and seeds, cell walls are comparatively poorer in pectins and cellulose where arabinoxylans and β-glucans dominate (Burton & Fincher, 2014). Secondary cell walls are made up of a network of cellulose and lignin whereas pectins are low or absent (Pettolino et al., 2012). From a nutritional point of view, the secondary cell wall is not a significant components of the human diet. Pectins are also the main component of the middle lamella, a thin layer that is responsible for the adhesion of adjacent cells in plant tissues. From the chemical point of view, the cell wall structure is organized in different manners and is related to factors such as plant species and is affected by environmental and developmental factors (Bordenave, Hamaker, & Ferruzzi, 2014; Vanholme et al., 2010). Cell wall structure and composition play an essential role in the bioavailability of micro- and macronutrients for the human body. For these dietary fibers present in the cell wall membrane to be suitable for absorption, intracellular molecules must pass through the physical barrier represented by the cell wall. The nutrients entrapped in the cell are well protected, and their release is dependent on the release ensured by the cell disrupture. However, the entrapped nutrients can be released in small proportions, and depending on the size of the molecules, disrupt the pores of the cell wall. Thereafter, digestive fluids that enter into the cell are able to start the digestion of macromolecules inside the cell. The functions of the plant cell wall are directly influenced by factors such as the wall’s chemical composition, structure, digestion influence, industrial, and home food processing, but also mastication (Brummer, Kaviani, & Tosh, 2015; Edwards et al., 2015a). Dietary fibers that act as prebiotics suffer minor chemical changes to cell walls when exposed to harsh gastric conditions (Millard & Chesson, 1984). Mandalari et al. (Mandalari et al., 2014) discovered a maximization of the cell wall thickness after 2, 6, and 12 h upon digestion and suggested a possible facilitation of diffusion through the swollen cell walls. Broxterman et al. (Broxterman & Schols, 2018) are talking about swelling of cell wall in raw carrots matrix and solubilization of pectins. In fruits and vegetables in their raw state, reduction of particle size by extreme mechanical grinding, milling, or chewing increases the fraction of fractured cells that are exposed on the particles’ exterior. This reveals a frequently reported statement: the lower the particle size, the higher is the bioavailability.

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In raw fruits and vegetables with strong structure where cell adhesion is quite strong, tissue rupture happens mostly through cell walls. In this particular situation under mechanical stress or oral processing, the number of fractured cells considerably increases. In fruits and vegetables with weaker structure after thermal treatment, cell adhesion is weakened, and tissue fraction would happen principally along cell walls, producing, upon mechanical stress, clusters of intact cells. On the other hand, the solubilization of pectins and implicitly of other constituents present in the cell wall may facilitate the permeability of the cell wall by increasing the size of the cell wall pores. Aribas-Agusti et al. (Ribas et al., 2014) demonstrated that permeability of carrot cell wall toward molecules of limited size is facilitated after heat treatment because of the solubilization of native pectin. In conclusion, nutrients that have not been absorbed in the small intestine because of cell entrapment can be released in the large intestine upon fermentation of cell wall material by the local microbiota. Most of these compounds, e.g., polyphenols, may be absorbed by the colon epithelium after conversion by the gut microbiota. The connections among plant cell wall ingestion, effect of processing, microbial fermentation, and bioavailability in the large intestine is a subject that needs further investigation. The understanding of this mechanism is of interest for scientists, health authorities, food engineers, and chefs alike.

3.3 THE EFFECT OF DIETARY FIBER ON THE RHEOLOGICAL AND COLLOIDAL STATE OF DIGESTION Populations that consume a large amount of dietary fiber in their daily diet were reported to have a lower incidence of cardiovascular disease compared to low-fiber consumers (Al-Sheraji et al., 2013; Chua et al., 2017). This also has beneficial effects in preventing and treating obesity (Kobyliak et al., 2018; Saez-Lara et al., 2016), insulin and diabetes mellitus (Al-Sheraji et al., 2013), and cancer (Slavin, 2013). Fiber-rich, grain diets were shown to improve insulin resistance and the risk of diabetes. The effects of fiber-rich grain diets on weight loss seem to be moderate (Al-Sheraji et al., 2013). Systolic and diastolic blood pressures have a decreasing trend under the influence of viscous soluble fiber. Diets that include viscous fiber may play a role in reducing the cardiovascular disease risk, thus contributing to an overall improvement in blood pressure (Khan et al., 2018). Nutritional components are generally recommended for their intrinsic nutritional value and their effect on the human body. The beneficial effect of dietary fibers on human health is due to their behavior in the gastrointestinal tract. The beneficial effects of dietary fiber on human health due to the bacterial and fungal interaction of β-glucan with epithelial immune cell-specific receptors have been reported alongside with their contribution to the stimulation of immunological responses (Mikkelsen et al., 2014). The physiological behavior of dietary fibers in the tract is extremely varied, depending on their interactions (Capuano, 2017). The type(s) of dietary fibers and their content in monosaccharide constituents may be different according to the form of the monosaccharides (α or β); the type of chemical linkage; the length of the linear polymer chain; and the presence, distribution, and composition of branches attached to the linear chain. Oligosaccharides and polysaccharides can be differentiated based

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on the length of the linear chain (Seidi et al., 2018). The polysaccharides that can be found in dietary fibers include resistant starch and non-starch polysaccharides. Resistant starch enters the colon and escapes digestion. The amount of resistant starch from the food differs from that reaching the digestive tract because resistant starch may depend on the meal composition, storage, and cooking conditions and on the physiological factors (Dhital et al., 2014). Particle size, solubility, moisture, and viscosity are the essential features of dietary fibers, which help in understanding their behavior during digestion (Guillon & Champ, 2000). The solubility of the fibers is dependent on their chemical structure and interactions with water molecules. Solubility depends on the pH and the ionic concentration of the environment. Thus, dietary fibers are classified into soluble (pectins, inulin, mucilage, glucomannan, β-glycans, oligosaccharides, etc.) and insoluble fibers (cellulose and hemicellulose, some types of resistant starch, lignin, etc.) (Capuano, 2017; Weickert & Pfeiffer, 2018). The most important sources of soluble fibers are: fruit, berries, certain vegetables (e.g., pectins from guava, carrots, beans, lentils; nuts); germ fraction from oat and barley products; guar; psyllium; and insoluble fiber: whole-grain and bran products; also skins of fruit; cucumbers, tomatoes; hulls of grains; brown rice; legumes; nuts and almonds. Certain food products contain both soluble and insoluble dietary fibers. Generally, soluble dietary fibers are viscous, and the viscous fibers are insoluble (Fig. 3.1; Weickert & Pfeiffer, 2018).

FIG. 3.1 Classification of fibers, typical attributes, and shared effect (Weickert & Pfeiffer, 2018).

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Viscosity is the main rheological property of fibers. This is defined as resistance to flow, and dietary fibers have a variable ability to produce a viscous solution after dissolution in water. This capacity depends to a great extent on the molecular weight, the concentration in dietary fibers, and is positively correlated with its solubility (Capuano, 2017). Despite the fact that dietary fibers are considered to be an inactive material in the digestive tract, they undergo structural and chemical changes, which influence their behavior during digestion as shown in Fig. 3.2. Dietary fibers are part of the cell wall in plant tissues. In the case of preparations or ingredients rich in dietary fibers, they appear as particles of varying size, purity, and composition and are either part of the cell walls or can be isolated from them. During mastication, mechanical processes cause cell wall breakage and reduction to smaller pieces/fragments. The level of fragmentation has a major impact on the bioavailability of nutrients. In their route through the stomach and intestines, the dietary fibers absorb varying amounts of water and swell according to their specific hydration capacity. This swelling is followed by partial solubilization (Capuano, 2017). Solubilization is limited when dietary fibers are part of cell wall structures due to strong chemical interactions with other cell wall components. These interactions may become less strong as digestion occurs and is in progress (Poutanen et al., 2018). Favored by thermodynamic processes, the dietary fibers that are soluble in liquid fraction are easier to absorb in the digestive tract. When in solution, the dietary fiber molecules can remain dispersed or aggregated in varying proportions, and can produce colloidal particles (Ulmius et al., 2012). The rheological and colloidal state of digestion of dietary fibers is determined by their interaction with digestive fluids and other dietary components. The ability of certain dietary fibers to absorb water leads to the formation of certain viscous solutions. This mechanism has the effect of lowering post-prandial blood glucose (Scazzina, .Siebenhandl-Ehn, & Pellegrini, 2013) and serum cholesterol (Vuksan et al., 2011). Recent research findings from in vitro analyses of digestion showed a slight decrease in starch

FIG. 3.2 Changes of structural properties of dietary fiber during digestion (Capuano, 2017).

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hydrolysis rate and diffusion coefficients for glucose (1.5–2.5 times) compared to a 100-fold rise in digesta viscosity. They delayed gastric emptying, which led to a decrease in the postprandial glycaemia (Dhital et al., 2014). Viscosity and enzymatic/absorptive processes do not always have a linear relationship. Following in vitro studies of gelatinised starch/guar gum mixtures on the small intestinal digestion, viscosity during digestion was analyzed, and it was found that it did not decrease alongside with starch hydrolysis (Hardacre et al., 2015). The viscosity of dietary fibers during digestion can be increased together with the liquid fraction and the changes affecting the physical properties in the structure of particles. Soluble dietary fibers have the capacity to increase the viscosity of the liquid fraction during digestion (pectins, gums, arabinoxylans, and β-glucans), and this capacity is influenced by several factors. Rigid or rod-like polymers have a higher viscosity than linear polymers. Thus, branched polymers tend to have a smaller volume than linear polymers (Beysseriat, Decker, & McClements, 2006). High-molecular-weight polysaccharides result in more viscous solutions than their depolymerisation products. During food processing, dietary fibers may become depolymerised. For instance, pectin is hydrolyzed during the process of thermal treatment. β-Glucan may partially become hydrolyzed during baking (e.g., viscosity decreases in the process of baking) (Izydorczyk et al., 2000). Dietary fiber molecules of the same class may largely vary in molecular weight depending on the extraction procedure. Viscosity may also be influenced by differences in the chemical structure of DF from the same class. For instance, viscosity of pectin solutions decreases (Yoo et al., 2006). Viscosity differs substantially depending on the arabinoxylans extracted from rye, and it is related to the molecular weight of water molecules and to the degree of branching (Ragaee et al., 2001). Viscosity of a dietary-fiber solution varies depending on the dietary-fiber type and the dilution of dietary fiber with digestive fluids (Edwards et al., 2015b). For instance, xanthan gum retained its viscosity very well after mixing with digestive fluids as compared to other gums, such as locust bean, guar, fenugreek, and flaxseed (Fabek et al., 2014). Lazaridou et al. (2014) reported that solubility in the intestines of β-glucan from coarse barley flour is lower than that from fine barley flour. The ionic strength and pH of the solution influence the viscosity of polysaccharide solutions. For instance, a multiple-course meal may induce the occurrence of different polysaccharides in the digestive tract. This may have synergic or antinergic effect on viscosity (Edwards et al., 2015b; Zhu et al., 2018). Dietary fibers have the capacity to change the physical characteristics of the material they are part of, depending on the disintegration kinetics of foods or on the distribution of particles during digestion. Thus, insoluble dietary fiber may increase their viscosity during digestion and can slow down nutrients absorption. This was reported for crystalline cellulose (Takahashi et al., 2005), wheat bran particles, and wood particles (Hardacre et al., 2015). According to in vitro studies reported by Houghton et al. (Houghton et al., 2015), the viscosity of alginate is the double of that of an equivalent amount of alginate incorporated or codigested with bread. Bread dietary fiber forms a barrier around starch granules, which denies access to α-amylase (Brennan et al., 1996), but the same fibers may also change the gluten network so that it can protect starch granules against α-amylase (Foschia et al., 2015). In physiological conditions of the gastro-intestinal tract, gels have a solid consistency and are formed of polymers cross-linked to create an interconnected network immersed in water

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or another liquid medium (Saha & Bhattacharya, 2010). From a rheological point of view, a gel is a viscoelastic system (Lorenzo, Zaritzky, & Califano, 2018). The hydrocolloid properties of dietary fiber have mainly been studied in the stomach but also in the small intestine even though evidence was present with regard to the fact that β-glucan and chitosan could form gels there (Ulmius et al., 2012). The gel content formed in the stomach was reported to increase satiety and decrease the gastric-emptying rate (Hoad et al., 2004). Gels have to resist the mechanical stress that the gastric acidic fluids exert. Alginate forms such gels in the stomach. However, its gelation in the stomach is extremely fast, and the properties of the gel are too sensitive to the conditions in the stomach (Hoad et al., 2004; Norton, Cox, & Spyropoulos, 2011). An alternative to alginate can be replaced by gellan gum, a complex bacterial polysaccharide, and pectins (Spyropoulos, Norton, & Norton, 2011). These gels can also be influenced by other nutritional components with which they come into contact, such as: a mixture of whey protein and pectin, which forms an intragastric gel at much lower concentrations of poly saccharides (Pop et al., 2015). Also xanthan gum and carragenans are able to form gels upon mixing with gastric juices, and whey protein isolates. Another effect of dietary fiber refers to their impact on lipid emulsion stability. In the gastric and duodenal compartments, the polymer stabilization/destabilization of emulsions depends on dietary fiber type, concentration, other biopolymers in solution, pH, and ionic strength, and the nature of the emulsion-stabilizing surfactant (Espinal-Ruiz et al., 2014a). Minekus et al. (Minekus et al., 2005) reported the effect of partially hydrolyzed guar gum on full-fat yogurt in which the lipolysis rate was reduced, and cholesterol was absorbed. Beysseriat et al. (Beysseriat et al., 2006) showed that, in the small intestine (neutral pH), positively charged chitosan can destabilize corn oil in water emulsion and induce coalescence through a bridging flocculation mechanism. In contrast, negatively charged pectin cannot adsorb onto lipids, but it can destabilize the emulsion by inducing reduced flocculation. Espinoza-Ruiz et al. (Espinal-Ruiz et al., 2016) also found increased coalescence of corn oil in water emulsions in the presence of pectins extracted from banana, passion fruit, and corresponding decrease in the digestion rate of fats. Another type of DF, namely methyl cellulose, can also induce reduced flocculation in corn oil/water emulsions (Espinal-Ruiz et al., 2016).

3.4 THE BINDING OF DIETARY FIBER WITH PHENOLIC COMPOUNDS, BILE SALTS, MINERAL IONS, AND DIGESTIVE ENZYMES 3.4.1 Binding With Phenolic Compounds The group of phenolic compounds are plant secondary metabolites included in different classes defined by the number of phenol rings, by their linkage, and type of attached functional groups. A great number of compounds belongs to this group: phenolic acids, hydroxycinnamic acids, xanthones, coumarins, acetophenones, flavonoids, etc. From these, the most important ones occuring in plants are phenolic acids, flavonoides, stibenes, and lignans (Crozier, Jaganath, & Clifford, 2009).

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Phenolic compounds, especially polyphenols, have potential health benefits associated with their biological properties like: antioxidant (Hertog et al., 1993), antiestrogenic (Yuan, Wang, & Liu, 2007), immunomodulatory (Ruiz & Haller, 2006), anticarcinogenic (Liu, 2004), and cardioprotective (Cook & Samman, 1996) activities. In addition, an important biological property is the ability to interact and bind the macronutrients found in food. Dietary fibers (DF) represent a vast category of polysaccharides with chemical and structural diversity. DF can bind, adsorb, or entrap other dietary compounds, thus having physiological effects. Phenolic compounds, omnipresent in vegetables, fruits, cereals, and nuts, are found in plant-based foods and beverages (beer, wine, tea, coffee). Their biological properties and health effects will depend on their intake and bioavailability, which in turn are conditioned by different factors including their binding capacity to DF. Phenolic compounds have hydrophobic rings and hydrophylic groups able to bind to DF at different sites (Saura-Calixto, 2011). The nature of interactions between phenolic compounds and DF was intensively investigated and reviewed (Bordenave et al., 2014; Jakobek, 2015; Saura-Calixto, 2011). The interactions between DF and phenolic compounds are driven by a combination of hydrogen bonding, van der Waals forces, electrostatic attraction, hydrophobic contact, strong covalent bonding (esterification), or physicochemical entrapment. For the phenolic compounds, the interactions are shaped by polymerization degree, flexibility of the molecule, and number of reactive groups (hydroxyl, glycosyl, galloyl, etc.). DF interactions are predominatly of electrostatic and ionic nature (Bordenave et al., 2014). Therefore, the DF-phenolic compounds interactions depend on the type of DF and phenolic compounds. Moreover, when considering the physicochemical entrapment of DF, the particle size, porosity, and surface characteristics will influence the amount of entrapted phenolic compounds (Metzler & Mosenthin, 2008). In the case of polyphenols found in apples, the interactions are of ionic nature with pectins and depend on the phenolic compounds molecular weight (Le Bourvellec & Renard, 2005). As for the interactions of bacterial pectin-cellulose composites with anthocyanins and phenolic acids (PA), a two-step process of binding was found in an in vitro assay. In the first step, anthocyanins bound at neutral pH, the binding being slightly higher for nonacetylated compared to acetylated anthocyanins. While in the second step, unspecific stacking of anthocyanins on pectin-cellulose composites occured slowly. PA were binding via noncovalent interactions to cellulose through hydrophobic contact and to pectins through H-binding and electrostatic interaction (Padayachee et al., 2012). The binding between cellulose and phenolic compounds depends on the pH values and the concentration of phenolic compounds (Phan et al., 2015). Regarding the binding between phenolic compounds and β-glucans, it has been shown that the interactions mainly involve H-bonding (Gao et al., 2012; Wu et al., 2011), and they depend on the phenolic compounds structure, namely on the level of hydroxylation, glycosylation, respectively, galloylation of the phenolic compounds. Lo Piparo (Lo Piparo et al., 2008) showed that the binding of flavonoids to β-glucans is positively correlated with flavonoids hydroxylation (being optimal at three hydroxyl groups and having a decrease in binding with four or more hydroxyl groups), that glycosylation generally limits binding (except for myricetin and daidzein) and that in the case of catechins, galloylation increases the binding. Taking into consideration that mainly the interactions between DF and PA are weak (noncovalent), their formation and dissociation kinetics will respond to changes of conditions like pH value and solvent quality (Quiros-Sauceda et al., 2014). Phenolic compounds begin to be

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released from the food matrix in the upper part of the gastrointestinal tract either by direct solubilization at physiological conditions (37°C, pH range between 1 and 7.5) or by enzymatic hydrolysis of the nutrients to which the phenolic compounds are bound. However, an important amount of phenolic compounds pass through the upper intestine undissociated from the DF. Binding to DF modulates phenolic compounds bioavailability, which has important physiological significance, the phenolic compounds that escaped absorption in the small intestine will be released in the colon, while labile phenolic compounds will be protected from the very acidic conditions in the upper part of the gastrointestinal tract (Ribnicky et al., 2014; Saura-Calixto, 2011) (Roopchand et al., 2012). In consequence, DF has the role of being a PA carrier contributing to fiber-rich diet health benefits. Thus, DF was used for the entrapment or encapsulation of phenolic compounds, for example: chitosan-entrapment of green tea polyphenols, nanoparticles composed of arabic gum and maltodextrin with improved EGCG stability, guar gum matrix, and pectinhydroxypropylmethylcellulose tablets for quercetin incorporation, etc. (Bordenave et al., 2014).

3.4.2 Binding With Bile Salts (Bile Acids) Bile acids play an important role in lipid metabolism (Hofmann, 2003). Bile acids are synthesized in the liver from cholesterol and are secreted via the bile in the small intestine. Most of the bile acids are reabsorbed via the enterohepatic circulation by active and passive mechanisms in the ileum (Chiang, 2009), while the unabsorbed ones are excreted in the feces (Lefebvre et al., 2009). The deficit of bile acids is compensated by de novo synthesis in the liver, therefore presumably leading to reduced cholesterol levels (Li & Chiang, 2015). The soluble and insoluble DF have different bile acids’ binding properties (Daou & Zhang, 2014). Gunness (Gunness & Gidley, 2010) reported that DF interact with the bile acids impeding their reabsorption. Kahlon (Kahlon, Chui, & Chui, 2018) evaluated the in vitro bile acids binding of various raw and after different cooking methods of vegetables. High-bile acids binding values were obtained by steaming the vegetables, while the lowest ones were in the case of boiling them. In the case of steaming, the bile acids’ binding values were as follows: beets, 18%; okra, 16%; eggplant, 14%; asparagus, collard greens, mustard greens, and kale, 10%–13%; cauliflower, green beans, carrots, spinach, brussels sprouts, and broccoli, 6%–8%; green bell pepper and cabbage, 4%; and turnips, 1.2%. Under small intestine conditions, the isolated pectins interacted with bile acids (Kritchevsky & Story, 1974). Bile acids’ binding capacity was significantly improved by ultrafine grinding in several DF types: inulin, β-glucan, guar gum, and Konjac glucomannan (KGM). (Huang, Du, & Xu, 2018). Bileacids’ binding to DF was demonstrated by in vivo and in vitro (Feng et al., 2017) studies, respectively clinical trials. The interactions between DF and bile acids are influenced by particle size, its surface, viscosity, pH, and temperature of the media. The DF interaction with bile acids seems to be a complex process involving hydrophobic and hydrophilic effects. Moreover, polyphenols were shown to reduce bile acids solubility during digestion. By using NMR, Ogawa (Ogawa et al., 2016) was able to show that bile acids and tea polyphenols were in close proximity interacting by H-bonding, which could potentially influence the solubility and enterohepatic recirculation of bile acids. It is important that not all bound bile acids are excreted from the body. A part of the DF is fermented by the microflora, and during this process, the bound bile acids are released and

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enzymatically converted. Despite changed physicochemical properties, a part of the bile acids may be reabsorbed even from the large intestine (Baye, Guyot, & Mouquet-Rivier, 2017).

3.4.3 Binding With Mineral Ions (MI) The binding capacity of DF with mineral ions was intensively studied using in vitro and in vivo assays and was recently reviewed (Baye et al., 2017). It was shown that diverse factors may influence the mineral bioavailability: • the amount of different chelators (as phytate, tannins, citrate, and amino acids). • the mineral concentration, size, and valency. • the potential association of phytic acid with proteins; the heat treatment that could affect the binding. • the pH value. • the presence of other metal ions that may compete, and the fermentability of the fiber components in the colon that could lead to a potential uptake of the minerals in the gut, etc. Especially the last factor is of interest as there are discrepancies between in vitro and in vivo studies of DF-mineral ions binding. Davies studied, both in vivo and in vitro, the amount of zinc bound to purified pectin and found that up to 86% of the zinc was bound in vitro; nonetheless no effect on zinc availability was observed in vivo. The different in vivo and in vitro results may be related to the absorption of released minerals from the DF binding following fermentation of DF in the large intestine (Lovegrove et al., 2017). The interactions between DF and MI are driven mainly by electrostatic attraction or complex formation involving the carboxyl, hydroxyl, and amino groups of DF as main functional groups. Nair (Nair et al., 1987) reported that highly metoxylated pectines bind less MI than the low metoxylated pectines due to the number of available carboxilic acid moieties. The electrostatic interactions between DF and MI involve mainly divalent cations (Espinal-Ruiz et al., 2014b). Pectins, xanthan gum, and carragenans bind a higher amount of divalent cations compared to agar and guar gum (Debon & Tester, 2001). Reinhold (Reinhold et al., 1986) reported that FeII and FeIII retention takes place due to the formation of poorly soluble fiber-mineral element polymers. Nevertheless, ionic strength has to be taken into account as the ion exchange capacity will be low in the acidic conditions of the stomach while it will be high in the neutral conditions of the small intestine. For example, a study of Schlemmer revealed that pectins and gums do not bind divalent cations at ionic strength of around 0.1. The interaction between DF and MI leads to various consequences, the most important one being related to the bioavailability of MI. An increased calcium absorption was reported when adolescent girls were supplemented with inulin (Griffin et al., 2003). These findings were supported by a study of Abrams (Abrams et al., 2005) on pubertal girls and boys supplemented with inulin.

3.4.4 Binding With Digestive Enzymes Ji et al. (2018) evaluated the α-amylase and glucoamylase activity inhibition by cellulose nanocrystals (CNCs) using visible absorption spectroscopy. Fourier transformed infrared

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spectroscopy, fluorescence quenching method, and circular dichroism, which showed an interaction between the tested enzymes and CNCs involving changes in the secondary structure of the enzymes. α-Amylase is also inhibited by guar gum (Hardacre et al., 2015). A DF found in brown algae, called fucoidan, has an inhibitory effect on α-amylase and β-glucosidase (Kim, Rioux, & Turgeon, 2014). Hansen (Isaksson, Lundquist, & Ihse, 1982) reported that lignin could totally inhibit the activity of isolated trypsin and chymotrypsin, having no effect on enterokinase. The inhibition effect depends on incubation time, fiber concentration, and enzyme level. In vitro studies and tests on rats showed that pectin has an inhibitory effect on pancreatic lipase and trypsin (Tsujita et al., 2003). The lipase catalytic activity inhibition could be explained by protonation of the enzyme active site by the pectin carboxylic groups (Isaksson et al., 1982). The same mechanism of inhibition was proposed in the case of alginate, which can also inhibit pancreatic lipase. Alginate has an inhibitory effect on pepsin due to electrostatic interaction between the negative net electric charge of alginate and the positive net electric charge of pepsin in the acidic conditions of the stomach. It should be taken into account that some of the digestive enzyme inhibitory effect observed for DF is actually related to the phenolic compounds carried and released under certain conditions in the gastrointestinal tract. Phenolic compounds were reported to possess inhibitory activity toward enzymes such as amylase, glucosidase, pepsin, trypsin, and lipases, and the subject has been studied extensively (Rohn, Rawel, & Kroll, 2002). The inhibition of amylase and glucosidase is leading to a reduction in post-prandial hyperglycemia, while the synergy between DF and phenolic compounds could have an important role to play in the amylase activity inhibition and therefore contribute to the management of type II Diabetes in humans. A recent study of Perez (Perez et al., 2018) evaluated the biological properties of an ethnic food common in Latin America, Prosopis nigra, and reported that the DF-bound phenolics have a potential of lipase activity control.

3.5 DIETARY FIBER FERMENTATION IN THE LARGE INTESTINE AND THE CORRESPONDING EFFECT ON MICROBIOTA COMPOSITION DF was defined as edible parts of the plants or analogous carbohydrates that have the capacity to resist human digestion in the small intestine and can be completely or partially fermented by the microbiome found in the large intestine. The fermentation depends on numerous structural and physicochemical parameters. The fermentation process was associated with lower colonic pH values, increased bacterial mass in the large intestine, a reduced number of harmful bacterial species, vitamins and antioxidant compounds production, and immune system stimulation, etc. Generally, insoluble DF (cellulose, lignin) is poorly fermentable by the large intestine microbiome due to lack of water-retention capacity. Soluble DF (pectin, guar gum, xanthan gum, β-glucan, inulin, oligosaccharides) is fermentable and represents the main source of energy for the microbiome. Both fermentable and non-fermentable DF have beneficial health effects. The nonfermentable DF is lowering the transit time, is increasing the luminal content,

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and has a dilution effect on the toxic and carcinogenic compounds. An increased soluble DF consumption is correlated with an increased microbiome development in the large intestine (Makki et al., 2018). The fermentation of DF by the microbiome leads to production of short chain fatty acids (acetate, propionate, butyrate), amines, phenols, ammonia, water and gases, bacterial mass growth, and energy release (Saura-Calixto, 2011). The human intestinal microbiota is comprising trillions of bacterias that play an important role in the development and function of diverse physiological processes. The microbiome is composed of more than 400 different bacterial species that possess more than 150 times more genes, thus more catalytic enzymes compared to the human genome (Gill et al., 2006; Qin et al., 2012). The key factor influencing the human intestinal microbiota is the nutrition, especially during infancy, but also throughout life. A dietary pattern rich in saturated fat and simple carbohydrates and low in DF was associated with incresed risk of developing cardiovascular diseases, colorectal cancer, obesity, and diabetes (Fu et al., 2015; Karlsson et al., 2012). Some DF (inulin and other oligofructoses) have prebiotic properties that lead to increased colonization of beneficial bacterial species like Bifidobacteria and Lactobacillus in the large intestine, which suppress the pathogenic bacterias (Anderson et al., 2009; Olano-Martin, Gibson, & Rastell, 2002). These bacterial species can produce short chain fatty acids and stimulate the immune system. The DF with prebiotic effect are of great importance for infants. Studies suggest that when supplemented with prebiotic fiber mixture, the postnatal immune system development was promoted, the bowel function was improved, and atopic dermatitis or respiratory infections were reduced (Veereman, 2007). The DF with prebiotic effect was reported to have anxiolytic, (Burokas et al., 2017) antidepressant, and cognitive effects also (Allen et al., 2016; Clarke et al., 2012; Jang et al., 2018; Savignac et al., 2015; Smith, Sutherland, & Hewlett, 2015). Inulin inhibits the growth of harmful bacteria like Salmonella, Escherichia coli, and Listeria (Gibson et al., 1995). Pectin was reported to reduce acute intestinal infection and to slow down diarrhea in infants and children (Rabbani et al., 2001). Guar gum was shown to be fermented in the human colon by the microbiota inducing beneficial effects like improved bowel function and constipation relief (Takahashi et al., 1994). Pectin is releasing mainly acetate in the colon, which is presumed to enter the peripheral circulation leading to altered fibrin quality, a risk factor involved in cardiovascular diseases (Veldman et al., 1999). Short chain fatty acid productions is leading to low colonic pH values that improves the mineral ions solubility, and therefore facilitates their absorption (Coudray et al., 2006; den Besten et al., 2013). Furthermore, the low pH inhibits the growth of potentially harmful bacteria (E. coli, Bacteroidetes) and favors the growth of butyrate-producing Firmicutes (Duncan et al., 2009). The digestion and absorption of phenolic compounds associated with DF are not complete in the small intestine, thus a part enters the large intestine. Perez-Jimenez (Perez-Jimenez, Arranz, & Saura-Calixto, 2009) showed that the procyanidin content in diet is understimated as the non-extractable phenolic compounds (phenolic compounds bound to DF) measurement is crucial in assesing the dietary intake of phenolic compounds. Phenolic compounds are released from the DF by the bacterial enzymes and can be metabolized, thus a major part of the DF associated phenolic compounds (a percentage of 42% of the dietary phenolic compounds) becomes bioaccesible in the large intestine (Saura-Calixto, 2011). The unabsorbed

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phenolic compounds and their fermentation metabolites (urolithins, phenylacetic, phenylpropionic, and phenylbutiric acids) contribute to an antioxidant environment in the large intestine (Gon˜i & Serrano, 2005; Saura-Calixto, 2011; Selma, Espı´n, & Toma´s-Barbera´n, 2009). This free radicals scavenging could be involved in the protection against cancer in the human colon (Ferguson, Chavan, & Harris, 2001). For example, Janicke ( Janicke et al., 2011) studied the effect of hydroxycinnamic acids on colonic cancer epithelial cells (Caco-2 cells) using global gene expression analysis of mRNA with focus on the genes that are responsible for cell proliferation and cycle progression and reported that different functional groups and pathways were indeed affected. The S phase was delayed, and genes regulating centrosome assembly and S phase DNA damage checkpoints were affected. Also, Lizarraga (Lizarraga et al., 2011) studied the effect of grape DF on mice and reported the downregulation of pathways associated with cancer and obesity like nuclear receptor signaling, lipid biosynthesis and energy metabolism, the upregulation of antioxidant and detoxification enzymes, apoptotic, immune system, and tumor supression genes. Therefore, a new concept was introduced, the “antioxidant DF,” which is defined as DF containing an important amount of associated natural antioxidant compounds (Vazquez-Sanchez et al., 2018). Additionally, the DF associated phenolic compounds have positive effects on lipid metabolism.

3.6 CONCLUSIONS There is a general consensus that a diet rich in DF has a health effect by preventing diseases. Compared to other nutrients, the beneficial health effect of DFs depends on the modulation of digestion rather than the nutritional characteristics or the triggering of specific biological activities. In this review, the behavior of DF during food digestion has been discussed and correlated to the physiological effects on health. Despite actual knowledge of DF’s behavior in the GI tract due to the last year realistic and reliable in vitro digestion models, there are still several research directions for future studies. The increasing prevalence of non-communicable diseases with an inflammatory cause has led to the understanding of the gut microbiota as an intrinsec regulator of host immune responses. Diet as a microbiota-modulating factor by the content and composition of DF is hence a health-modulating factor. A revision of the current nutritional guidelines considering both the molecular content and molecular structure of nutrients for sensitive persons (e.g., insulin-resistant and insulin-sensitive individuals, etc.), could be valuable for the restoration of beneficial bacteria and microbiota diversity for the general population.

Author Contributions Conceptualization, R.S.; Writing-Original Draft Preparation, O.L.P., R.A.V., C.I.M., A.V.S.T., and A.C.; WritingReview & Editing, R.S., R.V., C.C.M., S.C.H., O.L.P., C.I.M.; Vizualization: R.A.V., R.V., C.C.M; Supervision: R.S., C.A.I., A.F.

Funding This work was supported by the UEFISCDI, PN research grants PN-III-P2-2.1-CI-2018-1367, PN-III-P2-2.1-CI-20181569, PN-III-P2-2.1-CI-2018-1134.

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Acknowledgment We are grateful to Rosita Gabbianelli, PhD, for her editorial assistance.

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Metzler, B. U., & Mosenthin, R. (2008). A review of interactions between dietary fiber and the gastrointestinal microbiota and their consequences on intestinal phosphorus metabolism in growing pigs. Asian-Australasian Journal of Animal Sciences, 21(4), 603–615. Mikkelsen, M. S., et al. (2014). Cereal β-glucan immune modulating activity depends on the polymer fine structure. Food Research International, 62, 829–836. Millard, P., & Chesson, A. (1984). Modifications to swede (Brassica napus L.) anterior to the terminal ileum of pigs: some implications for the analysis of dietary fiber. The British Journal of Nutrition, 52(3), 583–594. Minekus, M., et al. (2005). Effect of partially hydrolyzed guar gum (PHGG) on the bioaccessibility of fat and cholesterol. Bioscience, Biotechnology, and Biochemistry, 69(5), 932–938. Nair, B. M., et al. (1987). Binding of mineral elements by some dietary fibre components—in vitro (I). Food Chemistry, 23(4), 295–303. Norton, A. B., Cox, P. W., & Spyropoulos, F. (2011). Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach. Food Hydrocolloids, 25(5), 1105–1111. Ogawa, K., et al. (2016). Interaction between tea polyphenols and bile acid inhibits micellar cholesterol solubility. Journal of Agricultural and Food Chemistry, 64(1), 204–209. Olano-Martin, E., Gibson, G. R., & Rastell, R. A. (2002). Comparison of the in vitro bifidogenic properties of pectins and pectic-oligosaccharides. Journal of Applied Microbiology, 93(3), 505–511. Padayachee, A., et al. (2012). Binding of polyphenols to plant cell wall analogues—Part 1: anthocyanins. Food Chemistry, 134(1), 155–161. Perez, M. J., et al. (2018). Prosopis nigra mesocarp fine flour, a source of phytochemicals with potential effect on enzymes linked to metabolic syndrome, oxidative stress, and inflammatory process. Journal of Food Science, 83(5), 1454–1462. Perez-Jimenez, J., Arranz, S., & Saura-Calixto, F. (2009). Proanthocyanidin content in foods is largely underestimated in the literature data: an approach to quantification of the missing proanthocyanidins. Food Research International, 42(10), 1381–1388. Pettolino, F. A., et al. (2012). Determining the polysaccharide composition of plant cell walls. Nature Protocols, 7(9), 1590–1607. Phan, A. D. T., et al. (2015). Binding of dietary polyphenols to cellulose: structural and nutritional aspects. Food Chemistry, 171, 388–396. Pop, O. L., et al. (2015). The influence of different polymers on viability of Bifidobacterium lactis 300b during encapsulation, freeze-drying and storage. Journal of Food Science and Technology, 52(7), 4146–4155. Poutanen, K. S., et al. (2018). Recommendations for characterization and reporting of dietary fibers in nutrition research. The American Journal of Clinical Nutrition, 108(3), 437–444. Qin, J., et al. (2012). A metagenome-wide association study of gut microbiota in type 2 diabetes. Nature, 490, 55. Quiros-Sauceda, A. E., et al. (2014). Dietary fiber and phenolic compounds as functional ingredients: interaction and possible effect after ingestion. Food & Function, 5(6), 1063–1072. Rabbani, G. H., et al. (2001). Clinical studies in persistent diarrhea: dietary management with green banana or pectin in Bangladeshi children. Gastroenterology, 121(3), 554–560. Ragaee, S. M., et al. (2001). Studies on rye (Secale cereale L.) lines exhibiting a range of extract viscosities. 1. Composition, molecular weight distribution of water extracts, and biochemical characteristics of purified waterextractable arabinoxylan. Journal of Agricultural and Food Chemistry, 49(5), 2437–2445. Reinhold, J. G., et al. (1986). Retention of iron by rat intestine in vivo as affected by dietary fiber, ascorbate and citrate. The Journal of Nutrition, 116(6), 1007–1017. Ribas, A., et al. (2014). Investigating the role of pectin in carrot cell wall changes during thermal processing: a microscopic approach. Innovative Food Science and Emerging Technologies, 24, 113–120. Ribnicky, D. M., et al. (2014). Artemisia dracunculus L. polyphenols complexed to soy protein show enhanced bioavailability and hypoglycemic activity in C57BL/6 mice. Nutrition, 30(7–8 Suppl), S4–10. Rohn, S., Rawel, H. M., & Kroll, J. (2002). Inhibitory effects of plant phenols on the activity of selected enzymes. Journal of Agricultural and Food Chemistry, 50(12), 3566–3571. Roopchand, D. E., et al. (2012). Efficient sorption of polyphenols to soybean flour enables natural fortification of foods. Food Chemistry, 131(4), 1193–1200. Ruiz, P. A., & Haller, D. (2006). Functional diversity of flavonoids in the inhibition of the proinflammatory NF-kappaB, IRF, and Akt signaling pathways in murine intestinal epithelial cells. The Journal of Nutrition, 136 (3), 664–671.

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Saez-Lara, M. J., et al. (2016). Effects of probiotics and synbiotics on obesity, insulin resistance syndrome, type 2 diabetes and non-alcoholic fatty liver disease: a review of human clinical trials. International Journal of Molecular Sciences, 17(6). E928. Saha, D., & Bhattacharya, S. (2010). Hydrocolloids as thickening and gelling agents in food: a critical review. Journal of Food Science and Technology, 47(6), 587–597. Saura-Calixto, F. (2011). Dietary fiber as a carrier of dietary antioxidants: an essential physiological function. Journal of Agricultural and Food Chemistry, 59(1), 43–49. Savignac, H. M., et al. (2015). Bifidobacteria modulate cognitive processes in an anxious mouse strain. Behavioural Brain Research, 287, 59–72. Scazzina, F., Siebenhandl-Ehn, S., & Pellegrini, N. (2013). The effect of dietary fibre on reducing the glycaemic index of bread. The British Journal of Nutrition, 109(7), 1163–1174. Seidi, F., et al. (2018). Saccharides, oligosaccharides, and polysaccharides nanoparticles for biomedical applications. Journal of Controlled Release, 284, 188–212. Selma, M. V., Espı´n, J. C., & Toma´s-Barbera´n, F. A. (2009). Interaction between phenolics and gut microbiota: role in human health. Journal of Agricultural and Food Chemistry, 57(15), 6485–6501. Slavin, J. (2013). Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), 1417–1435. Smith, A. P., Sutherland, D., & Hewlett, P. (2015). An investigation of the acute effects of oligofructose-enriched inulin on subjective wellbeing, mood and cognitive performance. Nutrients, 7(11), 8887–8896. Spyropoulos, F., Norton, A. B., & Norton, I. T. (2011). Self-structuring foods based on acid-sensitive mixed biopolymer to impact on satiety. Procedia Food Science, 1, 1487–1493. Takahashi, H., et al. (1994). Influence of partially hydrolyzed guar gum on constipation in women. Journal of Nutritional Science and Vitaminology (Tokyo), 40(3), 251–259. Takahashi, T., et al. (2005). Crystalline cellulose reduces plasma glucose concentrations and stimulates water absorption by increasing the digesta viscosity in rats. The Journal of Nutrition, 135(10), 2405–2410. Tsujita, T., et al. (2003). Inhibition of lipase activities by citrus pectin. Journal of Nutritional Science and Vitaminology (Tokyo), 49(5), 340–345. Ulmius, M., et al. (2012). Gastrointestinal conditions influence the solution behaviour of cereal β-glucans in vitro. Food Chemistry, 130(3), 536–540. Vanholme, R., et al. (2010). Lignin biosynthesis and structure. Plant Physiology, 153(3), 895–905. Vazquez-Sanchez, K., et al. (2018). In vitro health promoting properties of antioxidant dietary fiber extracted from spent coffee (Coffee arabica L.) grounds. Food Chemistry, 261, 253–259. Veereman, G. (2007). Pediatric applications of inulin and oligofructose. Journal of Nutrition, 137(11 Suppl), 2585s–2589s. Veldman, F. J., et al. (1999). Possible mechanisms through which dietary pectin influences fibrin network architecture in hypercholesterolaemic subjects. Thrombosis Research, 93(6), 253–264. Vuksan, V., et al. (2011). Viscosity rather than quantity of dietary fibre predicts cholesterol-lowering effect in healthy individuals. The British Journal of Nutrition, 106(9), 1349–1352. Weickert, M. O., & Pfeiffer, A. F. H. (2018). Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. The Journal of Nutrition, 148(1), 7–12. Wu, Z., et al. (2011). Characterization and antioxidant activity of the complex of tea polyphenols and oat beta-glucan. Journal of Agricultural and Food Chemistry, 59(19), 10737–10746. Yoo, S. -H., et al. (2006). Viscometric behavior of high-methoxy and low-methoxy pectin solutions. Food Hydrocolloids, 20(1), 62–67. Yuan, J. P., Wang, J. H., & Liu, X. (2007). Metabolism of dietary soy isoflavones to equol by human intestinal microflora—implications for health. Molecular Nutrition & Food Research, 51(7), 765–781. Zhu, D. Y., et al. (2018). Effects of extraction methods on the rheological properties of polysaccharides from onion (Allium cepa L.). International Journal of Biological Macromolecules, 112, 22–32.

C H A P T E R

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Dietary Fiber and Nutrition ˙Incinur Hasbay TUBITAK Marmara Research Center, Food Institute, Kocaeli, Turkey

O U T L I N E 4.1 Introduction

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4.2 Effect of Dietary Fiber on Body Weight Management 4.2.1 Effects on Satiety 4.2.2 Effects on Energy Regulation 4.3 Dietary Fiber and Overweight-Related Diseases 4.3.1 Dietary Fiber and Obesity 4.3.2 Dietary Fiber and Type-2 Diabetes

4.3.3 Dietary Fiber and Risk Factors of Cardiovascular Diseases

80 84 103 104 104

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4.4 Fiber Recommendations and Health Claims

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4.5 Conclusion

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References

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4.1 INTRODUCTION Dietary fiber is widely accepted as an important part of the diet and a common component of healthy nutrition. Large epidemiological and clinical studies indicate that dietary fiber can exert a wide range of health benefits, such as decreasing blood pressure, reducing plasma cholesterol, and decreasing the risk of cardiovascular diseases, which mainly results from weight control and a decreased risk of obesity. Overweight and obesity have become very serious worldwide health problems, which bring together the risk of numerous diseases and clinical disorders, including type 2 diabetes mellitus, hypertension, coronary and cerebrovascular diseases, various cancers, liver disease, and asthma. Risk of the above-mentioned diseases and mortality has been reported to be higher for people with a body mass index (BMI) above 25 kg/m2, which is the limit for obesity (Knight, 2011).

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# 2019 Elsevier Inc. All rights reserved.

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Overweight and obesity are diseases that are linked to disturbances in energy intake; therefore, reduced energy intake and increased energy expenditure are crucial for decreasing the risk of many non-communicable diseases related to obesity. Two important keys emphasized by the health authorities to prevent obesity are healthy diet and physical activity. In this respect, foods that promote satiety or dilute energy density provide a possible first line of defense in managing obesity and its associated comorbidities (Kumanyika, Jeffery, Morabia, Ritenbaugh, & Antipatis, 2002; Parnell & Reimer, 2009). Until now, it has been well documented that diets rich in dietary fiber play a key role in body-weight regulation and reduced risk of related diseases such as obesity and diabetes. This is mainly due to the beneficial effects of dietary fibers, such as enhanced satiety and reduced energy intake (Solah et al., 2014). Controlled-intervention studies and large cohort studies have proven the beneficial role of dietary fiber in body-weight regulation through reducing appetite and energy intake (Du et al., 2010; Wanders et al., 2011). Therefore, consumption of dietary fiber gains importance for decreasing the risk of obesity and diabetes, together with the related diseases such as hypertension, high cholesterol, and cardiovascular diseases. Health authorities and advisory committees recommend consumption of 25–30 g dietary fiber/day, mainly through consumption of whole grains, fruits, and vegetables (EFSA, 2010; SACN, 2015; WHO, 2003). The most important reason for increasing dietary fiber intake from natural food sources versus fiber supplements is the additional beneficial micronutrients and phytochemicals supplied by whole foods beyond that of fiber alone (SACN, 2015; Smith & Tucker, 2011). However, the recommended doses of fiber to achieve clinically important health effects may not be met with the actual intakes. This has led to a series of trials investigating the effects of fiber-supplemented foods and the development of fiber supplements or concentrated sources of fibers (Smith & Tucker, 2011). Changes of diet and lifestyle being the front line, specific fiber supplements are most likely to be used in weight-loss programs since they are considered to be effective across a wide spectrum of individuals, are easy to incorporate into the diet, and have minimal unwanted side effects (Chew & Brownlee, 2018). A review study mentioned that the weight of clinical evidence strongly indicates the beneficial effects of dietary-fiber consumption, especially from supplements, on weight management. The authors also reported that the limited number of clinical trials comparing high-fiber foods with lowfiber foods has not provided consistent data toward their higher efficacy over low-fiber control diets for weight loss; however, randomized, placebo-controlled, clinical trials have clearly documented that fiber supplements are accompanied by significantly more weight loss than the use of placebos (Anderson et al., 2009). Contrarily, in a previous systematic review of randomized clinical trials, evidence for most dietary supplements as aids in reducing body weight was reported to be not convincing (Pittler & Ernst, 2004). In a more recent review, it was indicated that the clinical significance of the effects of dietary fiber supplementation on weight loss still remains uncertain, and rigorous studies specific to each fiber analogue are required for negating the paucity of available evidence (Chew & Brownlee, 2018).

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT The increased prevalence of excess body weight and obesity has led to studies on the effect of diet composition on body weight. The causes of excess body weight are multi-factorial, but

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the most important factors are excess caloric intake coupled with limited energy expenditure (Knight, 2011). Although many conventional and alternative weight-loss options are available, their long-term effectiveness is limited or unknown, and detrimental effects are possible. For that purpose, consumers are looking for effective, natural, and non-toxic weight-loss strategies (Keithley & Swanson, 2005). For more promising results, the addition of functional fiber to weight-loss diets is suggested as a tool to improve success (Slavin, 2005). Body weight and fat-mass regulation takes place with the effect of various factors, involving central nervous circuits, peripheral sensation stimuli, mechanical and chemical satiation signals arising in the gastrointestinal tract, afferent vagal input, and adiposity signals from fat tissue and the liver (Papathanasopoulos & Camilleri, 2010). Dietary fiber has been demonstrated to modulate body weight mainly by several mechanisms such as: (i) increased satiety and satiation (Brownlee, Chater, Pearson, & Wilcox, 2017; Chew & Brownlee, 2018; Papathanasopoulos & Camilleri, 2010; Slavin, 2005; Thompson, Hannon, An, & Holscher, 2017), (ii) reduced energy intake due to being indigestible and decreasing the amount of energy absorbed from ingested foods (Brownlee et al., 2017; Chew & Brownlee, 2018; Papathanasopoulos & Camilleri, 2010; Thompson et al., 2017) and increased postprandial energy expenditure (i.e., dietary-induced thermogenesis), which can be attributed to the increase in the gastrointestinal motility (Brownlee et al., 2017; Chew & Brownlee, 2018), (iii) increased bile acid excretion, which drives a metabolic flux in the hepatic production of bile and a mobilization of body-fat stores (Brownlee et al., 2017; Chew & Brownlee, 2018; Thompson et al., 2017), (iv) acting as a substrate that favorably alters the gut microbiota, which alters the energy harvest, storage, and expenditure (Chew & Brownlee, 2018; DiBaise, Frank, & Mathur, 2012; Thompson et al., 2017). Epidemiological studies including the large cohort ones indicate that a higher intake of dietary fiber is associated with lower body weight, smaller waist circumference, lower BMI and body fat. This is also supported by cross-sectional studies and large observational researches (Du et al., 2010; Papathanasopoulos & Camilleri, 2010; Slavin, 2005; Wanders et al., 2011). In a prospective cohort study, 74,091 US female nurses of 38–63 years old and free of known cardiovascular disease, cancer, and diabetes at baseline were followed for 12 years, and their dietary habits were assessed with validated food-frequency questionnaires. Using multiple models to adjust for covariates, the average weight, BMI, long-term weight changes, and the odds’ ratio of developing obesity (BMI 30) were calculated according to the change in dietary intake. As a result of the study, it was shown that women with a higher increase in dietary-fiber intake gained less weight over 12 years, and weight gain was inversely associated with the intake of high-fiber and whole-grain foods (Liu et al., 2003). In a multicenter population-based cohort study (The Coronary Artery Risk Development in Young Adults Study) conducted in four US areas (Birmingham, Chicago, Minneapolis, and Oakland) over 10 years, the role of fiber consumption and its association with insulin levels, weight gain, and other CVD risk factors compared with other major dietary components were examined with the participation of a total of 2909 healthy adults, 18–30 years of age. Dietaryfiber consumption showed linear associations with body weight, waist-to-hip ratio, fasting insulin adjusted for BMI and 2-h post-glucose insulin adjusted for BMI. Fiber intake was also

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associated with blood pressure and levels of triglyceride, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and fibrinogen, being substantially attenuated by adjustment for fasting insulin level (Ludwig et al., 1999). Findings from two prospective cohort studies showed that increased consumption of cereal fiber was inversely related to weight gain. In one of these studies, which was conducted with 89,432 European participants for an average of 6.5 years, Du et al. (2010) investigated the association of total dietary fiber, cereal fiber, and fruit and vegetable fiber with changes in weight and waist circumference. Findings of the study showed that total fiber was inversely associated with subsequent weight and waist circumference change. Another prospective cohort study of 8 years with 27,082 US men also indicated that an increase in whole-grain intake was inversely associated with long-term weight gain with a dose-response relationship. It was determined that for every 40 g/day increment in whole-grain intake from all foods, weight gain was reduced by 0.49 kg. Consumption of bran either by adding it to the diet or obtaining it from fortified-grain foods further reduced the risk of weight gain, and, for every 20 g/day increase in intake, weight gain was reduced by 0.36 kg (Koh-Banerjee et al., 2004). Findings from both studies supported the beneficial role of cereal fiber intake in prevention of weight gain. The inverse relationship of fruit-fiber consumption with weight gain was also shown by Koh-Banerjee et al. (2004); whereas findings from Du et al. (2010) contrarily indicated that fruit and vegetable fiber was not associated with weight change but had a similar association with waist circumference change when compared with intake of total dietary fiber and cereal fiber. An inverse association between whole-grain consumption and BMI, and the risk of overweight and obesity also was found in a cohort study conducted in Netherlands with a total of 2078 men and 2159 women, aged 55–69 years. Fiber and cereal-fiber intake were inversely associated with BMI in men only (Van de Vijver, Van den Bosch, Van den Brandt, & Goldbohm, 2009). Another cohort study with follow-up of 252 women for 20 months also showed that increasing dietary fiber intake significantly reduced the risk of gaining weight and fat in women, and the effect was independent of several potential confounders, including physical activity, dietary-fat intake, and others. The influence of fiber was predicted to be primarily through reducing energy intake over time (Tucker & Thomas, 2009). An inverse relation of fiber intake with body fat was also shown in a cross-sectional study conducted on 203 healthy men chosen from randomly selected districts within Utah. The subjects volunteered for free diet and fitness evaluations with a written questionnaire to provide data on demographic and lifestyle characteristics. The fattest subjects reported eating significantly more dietary fat (P ¼ 0.05), less carbohydrate (P ¼ 0.01), less complex carbohydrate (P ¼ 0.01), and less fiber (0.005) than the leanest subjects (Nelson & Tucker, 1996). A number of interventional human trials also showed that a high dietary fiber intake may help manage body weight by reducing appetite and energy intake. Overweight and moderately overweight patients were treated with a dietary-fiber supplement together with a lowcalorie diet in two randomized, double-blind, placebo-controlled intervention studies of 6 months. After treatment, significant weight reductions in fiber-treated groups were determined. Accordingly, it was suggested that a dietary-fiber supplement in combination with a low-calorie diet is of value to improve success in overweight management (Birketvedt, Aaseth, Florholmen, & Ryttig, 2000; Rigaud, Ryttig, Angel, & Apfelbaum, 1990).

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83

In another open-label clinical trial of 6 months, 141 consecutively enrolled, hypertensive, overweight patients were randomized to the oral ingestion of 3.5 g psyllium powder or guar gum 20 min before the main meals three times a day, or to standard diet. Long-term treatment with studied fibers was associated with a significant reduction of body weight. A significant (P ¼ 0.005) BMI decrease was observed after 4 months of supplementation in psyllium-treated patients, and the decrease continued after 6 months (P < 0.001). In guar gum-treated patients, the BMI decrease was significant (P < 0.001) after the first 2 months of supplementation and progressively continued after 6 months (P < 0.001) (Cicero et al., 2007). Contrasting results were obtained in another clinical trial, which was mainly conducted to determine the plasma-lowering effects of consuming 5 g of psyllium three times a day on lipid and glucose levels in patients with type II diabetes. The study was conducted with 125 subjects for a 6-week period of diet counseling followed by a 6-week treatment period. Psyllium or placebo were supplied to subjects in identically labeled foil packets containing a 5-g dose of product, to consume three doses per day (5 g each), before regular meals. No significant changes were observed in the patients’ weight for psyllium-treated and placebo groups (Rodrı´guez-Mora´n, Guerrero-Romero, & LazcanoBurciaga, 1998). A randomized placebo-controlled study of 5 weeks was conducted to compare the effects of three commercial fiber supplements, which includes glucomannan, glucomannan + guar gum, and glucomannan + guar gum + alginate, on weight reduction in 176 healthy overweight subjects. Fiber supplements together with a balanced 1200 kcal diet induced significant weight loss more than placebo and diet alone. All commercial fiber products tested were similar in their ability to induce weight reduction (approximately 0.8 kg/week); which indicated that glucomannan induced body weight reduction in healthy overweight subjects, whereas the addition of guar gum and alginate did not seem to cause additional loss of weight (Birketvedt, Shimshi, Thom, & Florholmen, 2005). In accordance with these findings, glucomannan has been shown to reduce body weight in many clinical trials that involve body weight loss as the primary or secondary endpoint (Keithley & Swanson, 2005; Sood, Baker, & Coleman, 2008). There are also studies that do not address a direct relation with fiber consumption and body weight. In a meta-analysis of 11 trials, an insignificant difference in body weight reduction of patients receiving guar gum compared with patients receiving placebo was determined. Considering the adverse events, such as abdominal pain, flatulence, diarrhea, and cramps associated with its use, it was suggested that the risks of taking guar gum outweigh its benefits (Pittler & Ernst, 2001). Similarly, findings from a study to determine the effects of consumption of supplements of fermentable and non-fermentable fibers on hunger, energy intake, and weight loss also did not show an association of either fermentable or nonfermentable dietary fibers with body weight and fat loss (Howarth et al., 2003). A systematic review of reviews also concluded that the existing data from reviews of clinical trials did not provide good evidence for the efficacy of food supplements including dietary fiber on clinically relevant weight loss without undue risks (Onakpoya, Wider, Pittler, & Ernst, 2011). However, individual dietary fibers should be considered and evaluated separately, as the physicochemical properties of dietary fibers may affect their biological activity. A recent systematic review of randomized controlled trials also indicated that there was limited evidence from methodologically robust randomized clinical trials for potential benefits of

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long-term supplementation of several dietary fibers on body weight, and findings should be interpreted with caution due to the potential for variations in interventions, participants, and overall methodological quality. The authors recommended rigorous studies specific to each fiber analogue to negate the paucity of available evidence (Chew & Brownlee, 2018).

4.2.1 Effects on Satiety Satiation and satiety are both related to appetite control and inhibition of eating. Satiation is the satisfaction of appetite during eating, which brings it to an end. Satiety is the inhibition of hunger after the end of eating and prevents further eating before the return of hunger (Karalus et al., 2012; Slavin & Green, 2007). The human appetite system has central and peripheral mechanisms that interact with environmental factors, including the nutrient composition of foods (Bludell, Lawton, Cotton, & Macdiarmid, 1996). The stomach signals satiation in response to the volume and calories of the ingested meal (Papathanasopoulos & Camilleri, 2010). Foods with different nutrient composition exert different physiologic effects, including satiety signals (Bludell et al., 1996). Dietary fibers have been shown to provide higher satiety than digestible polysaccharides and simple sugars, as well as nutrients such as protein alone (Papathanasopoulos & Camilleri, 2010; Solah et al., 2014). Therefore, high-fiber foods have well-documented effects on satiety, which is mainly due to their bulking and textural properties (Slavin & Green, 2007). There is a lack of consensus in the literature with regard to the satiety effects of different fiber types. A number of intervention studies showed increased satiety or decreased subsequent hunger when subjects consumed high dietary fiber diets, either under conditions of fixed energy intake or energy intake consumed ad libitum (Table 4.1). There are also studies that reported no significant effects of several fiber types on satiety (Howarth et al., 2003; Weickert et al., 2006). This is due to the fact that the effects of fibers on appetite, energy, and food intake differ according to the type of fiber, the dose consumed, the form of fiber (whether it occurs naturally in the food or is added as isolated fiber), and the form of food (either it is solid or liquid) (Buckley et al., 2006; Carter & Drewnowski, 2012; Karalus et al., 2012; Monsivais et al., 2011; Wanders et al., 2011). In addition, there are no standardized protocols for conducting studies on the effects of dietary fibers on satiety, energy, and food intake; which makes it difficult to compare studies (Slavin & Green, 2007). It has been indicated that studies that have failed to find an association between fiber, satiety, weight loss, and food intake might have used either fiber doses that were too small (5 g)

β-Glucan improves satiety, and release of CCK is likely to be part of the mechanism

Beck, Tosh, Batterham, Tapsell, and Huang (2009)

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT

Subjects

Continued

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Dietary Fiber Used

Study Design

Conclusion

86

TABLE 4.1 Clinical Studies Related With the Effect of Dietary Fibers on Satiety, Body Weight and Energy Intake—cont’d Interventions

Findings

14 adults (7 female, 7 male) Age:23.9  3 years BMI: 22.9  2.8 kg/m2

I˙socaloric breakfasts including a 3% β-glucan-enriched bread or a control bread

References

A significantly higher Satiety effect of reduction of hunger β-glucans are mediated and increase of fullness by ghrelin and PYY and satiety A 19% reduction of energy intake at lunch A 23% lower AUC60–180 of plasma ghrelin and a 16% higher total AUC of PYY response

Vitaglione, Lumaga, Stanzione, Scalfi, and Fogliano (2009)

Kaats, Michalek, and Preuss (2006)

β-Glucan

Cross-over, randomized

Chitosan

8-week randomized, 134 overweight double-blind, adults (111 placebo-controlled female, 23 male)

Treatment group: six 500 mg chitosan capsules per day. Control group: weightloss programs of their choice

More weight and fat mass loss by the treatment group than the control group and the placebo group

Chitosan may facilitate the depletion of excess body fat under freeliving conditions with minimal loss of fat-free or lean body mass

Chitosan

24-week randomized, double-blind, placebo-controlled

250 overweight and obese adults Age: 48  12 years BMI: 35.5  5.1 kg/m2

3 g chitosan/day or placebo. All participants received standardized dietary and lifestyle advice for weight loss

More body weight loss by the chitosan group than the placebo group (but small effects) No significant differences between groups for any of the other measured outcomes

Chitosan treatment did Mhurchu not result in a clinically et al. (2004) significant loss of body weight compared with placebo

Chitosan

3-month randomized, double-blind

12 obese adults with diabetes mellitus Age: 30-50 years BMI: 30-40 kg/m2

6 patients received chitosan (750 mg, 3 times per day) 30 minutes before meals, and the other 6 subjects received placebo.

Decrease of weight, BMI, and waist circumference in the chitosan group.

3-month administration Herna´ndezof chitosan increases Gonza´lez, insulin sensitivity in 2010 obese patients and decreases their weight, BMI, waist circumference, and triglycerides.

4. DIETARY FIBER AND NUTRITION

Subjects

Dextrin

Standard doubleblinded preload study design

36 adults (22 female, 14 male) Age: 20–34 years BMI: 18.0–30.0 kg/m2

Study preloads: a combination of a solid snack and a liquid beverage containing 4 different types of fiber:

Supplementing beverages with soluble fiber dextrin affects short-term energy intake and may have implications for weight control

Monsivais, Carter, Christiansen, Perrigue, and Drewnowski (2011)

No indication for any effect of dextrin on appetite, food intake, and plasma markers of appetite for the first 150 min postconsumption. Further research is required to determine how dextrin influences appetite several hours after consumption

Emilien, Zhu, Hsu, Williamson, and Hollis (2018)

1. An isoenergetic, lowfiber preload 2. A lower-energy, lowfiber preload All preloads were presented twice for a total of 0.35–1.65 MJ and 1–24 g fiber. Each participant took part in 6 study sessions. Dextrin

Cross-over

41 adults (19 female, 22 male) Age: 18–40 years BMI: 19.9–29.9 kg/m2

Lunch with a beverage that contained 0, 10, or 20 g of fiber from soluble fiber dextrin

87

No effect on appetite over the 150 min after consumption of the lunch meal with dextrin After leaving the laboratory: Lower hunger and desire to eat and higher fullness after consumption of the beverage that contained 20 g dextrin No effect of consuming dextrin on food intake at the snack meal or for the rest of the day

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT

Higher fullness and lower hunger ratings with the five higherenergy preloads compared to the lowenergy control (but not 1. Soluble fiber dextrin significantly different (12 g) from each other) 2. Soluble corn fiber Significantly (11.8 g) suppressed energy 3. Polydextrose (11.8 g) intakes with only 4. Resistant starch soluble fiber dextrin (11.2 g) relative to the isoenergetic control Control conditions of equal volume:

Continued

Dietary Fiber Used

Subjects

Interventions

Fenugreek fiber

Single blind, randomized, crossover study

18 subjects (10 female, 8 male) Age: 32  11 years BMI: 36  5 kg/m2

Glucomannan

Findings

Conclusion

References

Three test breakfasts Significantly increased containing 0, 4, or 8 g of satiety and fullness, isolated fenugreek fiber reduced hunger, and prospective food consumption with 8 g fenugreek fiber Significantly lower energy intake at an ad libitum lunch buffet for 8 g than 4 g fenugreek fiber, but not significantly different from control

Fenugreek fiber may have a role in the control of food intake in obese individuals

Mathern, Raatz, Thomas, and Slavin (2009)

8-week double blind, 20 obese women placebo-controlled

1 g of glucomannan fiber or placebo with 8 oz water, 1 h prior to each of three meals per day

Significant weight loss (5.5 lbs) with glucomannan fiber in 8-weeks

Glucomannan may be used for weight loss

Walsh, Yaghoubian, and Behforooz (1984)

Glucomannan

8-week randomized, 53 participants double-blind, (85% female) placebo-controlled Age: 18–65 years BMI: 25–35 kg/m2

1.33 g of glucomannan or identically looking placebo capsules with 236.6 mL (8 oz) of water 1 h before breakfast, lunch, and dinner for 8 weeks

No significant difference between the glucomannan and placebo groups in amount of weight loss (0.40  0.06 and 0.43  0.07, respectively) or other efficacy outcomes or in any of the safety outcomes

Glucomannan Keithley et al. supplements (2013) administered over 8 weeks did not promote weight loss or significantly alter body composition and hunger/fullness

Guar gum (partially hydrolyzed)

Randomized, double Study 1: blind, cross-over 12 healthy adults Study 2: 24 healthy adults Study 3: 6 healthy adults

Three separate studies: Study 1: Partially hydrolyzed guar gum along with breakfast, lunch, and an evening snack Study 2: 2 g of partially hydrolyzed guar gum

Significant acute and long-term satiety effects with the addition of partially hydrolyzed guar gum compared to the control and/or an equal amount of

Partially hydrolyzed guar gum could be an ideal natural soluble fiber for delivering acute and long-term satiety effects for comfortable appetite control

Rao et al. (2015)

4. DIETARY FIBER AND NUTRITION

Study Design

88

TABLE 4.1 Clinical Studies Related With the Effect of Dietary Fibers on Satiety, Body Weight and Energy Intake—cont’d

or dextrin along with yogurt as breakfast for 2 weeks Study 3: 6 g each of either partially hydrolyzed guar gum or indigestible dextrin or inulin along with lunch

carbohydrate or other types of soluble fiber

25 obese but otherwise healthy females Age: 46  6 years BMI: 35  6 kg/m2

A 3.3 MJ (800 kcal) formula containing either 20 g fiber or placebo daily on days 1, 3, and 7 of the intervention weeks. Measurements were taken after an overnight fast The intervention weeks were separated by a 1-week wash-out period

In the fasting state: No effect of the fiber supplement on any of the measured parameters In the 2 h postprandial period following the test meal: No significant difference in any of the measured parameters from that following the non-fibersupplemented meal, except for the CCK response. An overall higher concentration of CCK after the fibersupplemented meal

A partially hydrolyzed Heini et al. guar gum fiber (1998) supplement yields an increased postprandial CCK response, but does not alter other satiety hormones or increase satiety ratings, in either the fasting or the postprandial state

Guar gum (modified)

Randomized, crossover

28 mainly overweight male volunteers Age: 19  56 years; BMI: 29  2 kg/m2

Three treatments of 2 weeks with a lowenergy diet divided over three times a day, consisting of a semisolid meal with or without guar gum or a solid meal with the same energy content (947 kJ) and macronutrient composition, and a dinner of the subject’s own choice. Washout periods lasted 4 weeks

Compared to baseline values, similar reduction in energy intake and body weight loss for all treatments. Increased appetite (hunger, desire to eat, or estimation of how much one could eat) after semi-solid meal without guar gum and in solid meal compared to baseline Similar satiety and fullness

Guar gum addition to a Kovacs et al. semi-solid meal (2001) prevents an increase in appetite, hunger, and desire to eat. However, differences between treatments were not statistically significant

89

Five-week prospective, randomized, double-blind

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT

Guar gum (partially hydrolyzed)

Continued

Dietary Fiber Used

Study Design

Subjects

90

TABLE 4.1 Clinical Studies Related With the Effect of Dietary Fibers on Satiety, Body Weight and Energy Intake—cont’d Findings

Conclusion

References

Two high-energydensity yogurt beverages (440 kcal; 0.9 kcal/g) and two lowenergy-density yogurt beverages (180 kcal; 0.4 kcal/g) with 6 g inulin or without inulin and an equal volume of orange juice (180 kcal). A no-beverage control condition was also used

Higher satiety ratings and reduced energy intakes with yogurt beverages than the orange juice at lunch Comparable satiating power of low-energydensity yogurt with inulin to that of highenergy-density yogurt

Adding fiber to lowenergy-density foods may be an effective way to suppress appetite and control food intake

Perrigue, Monsivais, and Drewnowski (2009)

Cani, Joly, Horsmans, and Delzenne (2006)

Inulin

Within-subject 38 adults (20 preload design with female,18 male) repeated measures Age: 18–35 years BMI: 18–29.9 kg/m2

Oligofructose

Single-blind, crossover, placebocontrolled, pilot study

10 adults (5 female, 5 male) Age: 21–39 years BMI: 18.5–27.4 kg/m2

16 g/day oligofructose (8 g  2 times) for 2 weeks Placebo: Dextrinemaltose for 2 weeks 2 weeks of washout between cross-over phases

With oligofructose treatment: increased satiety following breakfast and dinner, decreased hunger and prospective food consumption following dinner. Decreased energy intake at breakfast and lunch. 5% lower total energy intake per day

Oligofructose supplements may be proposed for the management of food intake in overweight and obese patients

Oligofructose

Randomized, double-blind, placebo controlled

48 adults (overweight and obese but otherwise healthy) (39 female, 9 male) Age: 20–70 years BMI > 25 kg/m2

21 g/day oligofructose for 12 weeks Placebo: Maltodextrin

1.03  0.43 kg of reduction in body weight with oligofructose supplementation 0.45  0.31 kg of increase in body weight of the control group. Lower area under the curve for ghrelin and a higher for PYY with oligofructose coincided with a reduction in self-

Oligofructose Parnell and supplementation has Reimer (2009) the potential to promote weight loss and improve glucose regulation in overweight adults. Suppressed ghrelin and enhanced PYY may contribute in part to the reduction in energy intake

4. DIETARY FIBER AND NUTRITION

Interventions

reported caloric intake No effect on plasma active GLP-1 secretion with oligofructose supplementation 34 healthy adults (24 female, 10 male) Age: 37  1.9 years BMI: 22.9  0.25 kg/m2

Yogurt-based drinks containing 0, 6.25, and 12.5 g of polydextrose mid-morning after a standard breakfast, 90 min before an ad libitum lunch, which was followed by an ad libitum dinner

Increased satiety and decreased appetite with 6.25 and 12.5 g polydextrose compared to control immediately after consumption A reduction in energy intake (218.8 kJ) at lunchtime for 12.5 g polydextrose (This reduction in energy intake was not compensated for at dinner)

Polydextrose may aid in increasing satiety feelings post consumption and reduce energy intake as a result

Hull, Re, Tiihonen, Viscione, and Wickham (2012)

Psyllium (Metamucil)

2 sequential clinical trials: Randomized, double-blind, placebo-controlled cross-over

Study 1: 30 adults (11 female, 19 male) Study 2: 44 adults (19 female, 25 male) Age: 18–55 years BMI: 18.5–32 kg/m2

Study 1: 3.4, 6.8, and 10.2 g of psyllium before breakfast and lunch for 3 days Study 2: 6.8 g (before breakfast and lunch on Days 1 and 2 and before breakfast on Day 3) and received an energyrestricted breakfast for 3 days

Study 1: Directional or statistically significant mean reductions in hunger and desire to eat, and increased fullness between meals with all psyllium doses compared to placebo. Higher doses better than placebo or 3.4 g. More consistent satiety benefits with the 6.8 g dose vs placebo Study 2: Similar satiety results with study 1. A significant decrease in the 3-day mean hunger and desire to eat, as well as an increase in fullness for psyllium relative to placebo

Psyllium supplementation contributes to greater fullness and less hunger between meals

Brum, Gibb, Peters, and Mattes (2016)

91

Randomized, singleblinded, placebo controlled, crossover

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT

Polydextrose

Continued

Dietary Fiber Used

Subjects

Interventions

Psyllium

Singleblind, randomized, crossover

16 subjects (13 female, 3 male) Age: 20–34 years BMI: 17.4–28.8 kg/m2

Psyllium

6-week doubleblind, placebocontrolled

Psyllium Guar 6gum month-randomized, open-label

Findings

Conclusion

References

1 of 5 isoenergetic test Decreased glucose, meals in a randomized insulin, ghrelin, and order on separate days: PYY responses with fiber-enriched meals. Significantly 1. Low in protein (2.8 g) suppressed and fiber (7.6 g) postprandial GLP-1 2. Low in protein (2.6 g) concentration after a and high in soluble fiber- and protein-rich fiber (psyllium, meal, in contrast to the 23.0 g) initial increases 3. High in protein (soy, following the other 19.7 g) and low in meals fiber (6.2 g) Mostly similar 4. High in protein postprandial ratings of (18.4 g) and fiber appetite after the test (23.0 g) meals 5. White wheat bread

Solid meals enriched with psyllium fiber strongly modified postprandial signals arising from the gastrointestinal tract

Karhunen et al. (2010)

125 subjects Age: 30  75 years

Psyllium or plasebo were supplied to subjects in identically labeled foil packets containing a 5-g dose of product, to consume three doses per day (5 g each), before regular meals

No significant changes in the patients’ weight for psyllium-treated and placebo groups

Psyllium’s effects on Rodrı´guezthe improvement of Mora´n et al. glucose and lipid levels (1998) were not explained by weight loss or reduced food intake

141 hypertensive, overweight patients Age: 50–70 years BMI: 25–30 kg/m2

Oral ingestion of psyllium powder or guar gum 3.5 g t.i.d., to be taken 20 min before the main two meals, or to standard diet

In psyllium-treated patients: A significant (P ¼ 0.005) BMI decrease after 4 months of supplementation and a continued decrease after 6 months (P < 0.001) In guar gum-treated patients: A significant (P < 0.001) BMI

Long-term treatment Cicero et al. with studied fibers was (2007) associated with a significant reduction of body weight

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Study Design

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TABLE 4.1 Clinical Studies Related With the Effect of Dietary Fibers on Satiety, Body Weight and Energy Intake—cont’d

decrease after the first 2 months and progressively continued after 6 months (P < 0.001) Resistant wheat starch

Randomized, single- 27 healthy adults blind, cross-over (12 female, 15 male) Age: 18–35 years BMI: 18.5–29.9 kg/m2

Muffins in which 40% of the standard wheat flour was replaced with resistant wheat starch or muffins that contained only standard wheat flour as part of the breakfast meal

No effect of replacing standard wheat flour with resistant wheat starch on subjective appetite or energy intake at the lunch meal. Reduced total daily energy intake (including the breakfast meal) by 179 kcal when participants consumed the resistant wheat starch muffins. No effect of replacing standard wheat flour with resistant wheat starch on plasma glucose, CKK, GPL-1, or PYY concentration

Replacing standard wheat flour with resistant wheat starch reduces energy intake over a 24-h period

Resistant starch

26-weeks placebocontrolled, doubleblinded, cross-over

Two 12-week intervention periods, with one each for resistant starch (30%, v/ v, in flour) and control flour, and a 2-week washout in between the interventions

Lower waist circumference and % body fat post intervention in the resistant starch group compared with the control group

Dietary resistant starch Upadhyaya supplementation et al. (2016) selectively changes the gut microbial and metabolite environment as well as associated host metabolic functions

4.2 EFFECT OF DIETARY FIBER ON BODY WEIGHT MANAGEMENT

20 selected participants from the parent placebocontrolled, double-blinded, cross-over, dietary intervention study

Emilien, Hsu, and Hollis (2017)

Continued

93

Dietary Fiber Used

Clinical Studies Related With the Effect of Dietary Fibers on Satiety, Body Weight and Energy Intake—cont’d

94

TABLE 4.1

Subjects

Interventions

Findings

Conclusion

References

Resistant starch

Acute randomized, single-blind crossover

20 young healthy adult males

The participants consumed either 48 g resistant starch or the placebo divided equally between two mixed meals on two separate occasions

A significantly lower energy intake following the resistant starch supplement compared to the placebo supplement No associated effect on subjective appetite measures

Consumption of 48 g/ day resistant starch may be useful in the management of the metabolic syndrome and appetite. Further studies are required to determine the exact mechanisms

Bodinham, Frost, and Robertson (2010)

Resistant starch, corn bran, Barley β-glucan + oat fiber, Polydextrose

Randomized double-blind, crossover

20 healthy adults (13 female, 7 male) Age: 18–54 years BMI: 19.7–26.9 kg/m2

Four high-fiber muffins (corn-bran, barley β-glucan + oat fiber, resistant starch, polydextrose) (8.0–9.6 g fiber) for breakfast on five separate visits Control: a low fiber muffin (1.6 g fiber)

The highest impact on satiety with resistant starch and corn bran Little effect with polydextrose, which behaved like the lowfiber treatment

Not all fibers influence Willis, satiety equally Eldridge, Beiseigel, Thomas, and Slavin (2009)

20 healthy subjects (10 female, 10 male) BMI: 24  2 kg/m2

Fasting subjects consumed a muffin with 0, 4, 8, or 12 g of mixed fibers and approximately 500 kcal

More satisfied and more full subjects after consuming the 4 g fiber muffin than after consuming the 0 g fiber muffin. The remaining treatments were indistinguishable

Satiety, gut-hormone Willis et al. response, and food (2010) intake did not change in a dose-dependent manner with mixed fibers

Mixed fibers Double-blind, (pectin, barley randomized, crossβ-glucan, guar over design gum, pea fiber, and citrus fiber)

4. DIETARY FIBER AND NUTRITION

Study Design

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95

fiber intake is controlled (Hoad et al., 2004; Karalus et al., 2012). For example, Willis, Thomas, Willis, and Slavin (2011) found that a solid meal with naturally occurring fiber from oatmeal and whole fruits decreased hunger more than a liquid meal with added fiber. The study was a randomized, cross-over one conducted with 14 women. Fasted subjects consumed liquid (fruit juices and skim milk) and solid (oatmeal, blueberries, and apples) breakfasts with 10 g of fiber and 410 kcal each on two separate days. Subjects were less hungry after eating the oatmeal than after the liquids. In addition, satisfaction and fullness were marginally improved with the oatmeal compared to the liquids. Contrarily, there are also studies that indicate that beverages and liquid foods are effective to improve satiety. Carter and Drewnowski (2012) showed that a beverage containing caffeine and green tea catechins in combination with dextrin fiber decreased appetite and energy intake relative to a beverage with equal caloric content. All beverage preloads were presented three times for a total of 0.28–0.35 MJ and 0–30 g fiber. Dependent measures were appetite ratings and calorie intake at a test meal. In another clinical study, dextrin, the same soluble fiber, has been shown to exhibit a progressive and significant impact on short-term satiety, which is time and dosage correlated. The study was a randomized, double-blind, placebo-controlled one on 100 overweight healthy adults in China. Subjects were assigned to receive either a placebo or 8, 14, 18, or 24 g/day of dextrin mixed with orange juice (20 volunteers per group). Their results suggested that dietary supplementation with a soluble fiber can decrease hunger feelings and increase short-term satiety over time when added to a beverage from 8 to 24 g/ day with time- and dose-responses relationship (Guerin-Deremaux et al., 2011). Orange juices including 5 g of pectin have also been shown to increase satiety. In the study, fasted male (n ¼ 49) and female (n ¼ 25) US Army employees within normal weight limits were fed with 448 mL of orange juice on 2 separate days, one day with and one day without pectin. The subjects were fed with 0.473 L of ice cream 4 h later. It was observed that there was a significant effect of juice including pectin on satiety, but the effect was dose-independent. The authors suggested that pectin mixed with orange juice can aid in a program to reduce weight by limiting food intake (Tiwary, Ward, & Jackson, 1997). Lyly et al. (2009) also showed that dietary fibers in beverages can enhance satiety. A total of 19 healthy volunteers were served with one of the sample foods; i.e., a beverage without fiber, a guar-gum beverage, a wheat-bran beverage, an oat β-glucan beverage, and wheat bread as control. Fiber content of the samples was 0 g (beverage without fiber), 2.4 g (wheat bread), 7.8 g (guar gum), or 10.5 g (wheat bran and oat β-glucan beverage) per 400 g/1.000 kJ portion. The perceived satiety was higher and the desire to eat was lower for the guar-gum beverage as compared to the beverage without fiber. The beverage with oat β-glucan also increased fullness and showed a trend of increasing perceived satiety and decreasing the desire to eat more than the beverage without fiber. The chemical structure and physicochemical properties of fibers such as solubility, viscosity, water-holding capacity, and fermentability, are also important for the effects on satiety, long-term appetite and, hence, regulation of energy intake (Lyon & Kacinik, 2012; Wanders et al., 2011). It has been shown that some types of dietary fiber may enhance satiety more than others (Howarth et al., 2003; Monsivais et al., 2011; Wanders et al., 2011; Willis et al., 2009). To assess the validity of this hypothesis, Willis et al. (2009) conducted an acute, randomized, double-blind, cross-over study to compare the effects of four dietary fibers (corn bran, barley β-glucan + oat fiber, resistant starch, and polydextrose) and a low-fiber treatment on satiety. The fasting subjects consumed either a low-fiber muffin (1.6 g fiber) or one of four high-fiber

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muffins (8.0–9.6 g fiber) for breakfast on five separate visits. Resistant starch and corn bran were consistently more satiating than the low-fiber treatment, whereas polydextrose had little effect on satiety and behaved like the low-fiber treatment. Resistant starch and corn bran also influenced the duration of satiety longer than the treatments with low fiber, polydextrose, and barley β-glucan + oat fiber. Results from their study indicate that not all fibers influence satiety equally (Willis et al., 2009). Contrary to the results of Willis et al. (2009), Hull et al. (2012) determined the positive effect of polydextrose on increasing satiety and decreasing the energy intake in their randomized, single-blinded, placebo-controlled, cross-over study. Thirty-four healthy volunteers were provided with a standard breakfast, then consumed the test product (yogurt-based drinks containing 0, 6.25, and 12.5 g of polydextrose) mid-morning, 90 min before an ad libitum lunch, which was followed by an ad libitum dinner. Consumption of polydextrose in both doses increased satiety and decreased appetite compared to control. Accordingly, the authors suggested that polydextrose may aid in increasing satiety feelings post consumption. This study also proved that beverages and liquid foods are effective to improve satiety as well as solid foods. Viscosity of fiber is also thought to play an important role on its satiating power because it determines the ability of fiber to thicken or form gels when mixed with fluids resulting from physical entanglements and hydrophilic interactions among the polysaccharide constituents within the fluid or solution (Lyon & Kacinik, 2012). Regarding the different satiety effects of fiber types, it has been reported that food containing viscous fiber gives higher satiety than that containing non-viscous fiber (Solah et al., 2014). Some trials using non-viscous soluble fibers, such as resistant starch and inulin, have found no effect on satiety or hunger, even when large amounts of the isolated fiber were fed (Slavin & Green, 2007). However, a recent randomized, double-blind, controlled study showed that a scone product (a ready-to-eat baked good) with a resistant starch (Type 4) content of 16.5 g per serving significantly reduced hunger and desire to eat during the 180 min following consumption. The authors indicated that the mechanism of action for this short-term effect is unclear and warrants further research (Stewart, Wilcox, Bell, Buggia, & Maki, 2018). Regarding the effect of viscosity, Hoad et al. (2004) conducted an intervention study to compare the satiating effects of two types of alginates with different viscosities (which gel weakly or strongly on exposure to acid), and guar gum, in which the viscosity was unaffected by acid. Although gastric emptying was similar for all fiber types and the control, the stronggelling alginate and guar meals increased fullness and decreased hunger. The authors suggested that agents that gel on contact with acid may be useful additions to weight-reducing diets and hypothesized that this effect may be due to distension in the gastric antrum and/or altered transport of nutrients to the small intestine. In a double-blind, randomized, controlled and cross-over trial on 31 healthy weight adolescents, Vuksan et al. (2009) assessed subsequent food intake and appetite in relation to the level of viscosity following three liquid preloads, each containing 5 g of either a high (a novel viscous polysaccharide), medium (glucomannan), or low (cellulose) viscosity fiber. The subjects consumed one of the three preloads 90 min prior to an ad libitum pizza meal. The viscosities of preloads were (10, 410, and 700 poise for cellulose, glucomannan, and novel viscous polysaccharide, respectively). As a result, it was shown that pizza intake was significantly lower (P ¼ 0.008) after consumption of the novel viscous polysaccharide compared to the medium-viscosity glucomannan and low-viscosity cellulose preloads with no difference between the

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97

glucomannan and cellulose preloads. In a systematic review of randomized controlled trials, Wanders et al. (2011) investigated the available literature on the relationship between dietary fiber types, appetite, energy intake, and body weight. Fibers were grouped according to chemical structure and physicochemical properties (viscosity, solubility, and fermentability). In terms of satiety effects, their findings showed that 22 out of 37 comparisons (59%) with more viscous fibers reduced appetite and 3 out of 21 comparisons (14%) with less viscous fibers reduced appetite. There are also a number of studies that show that the satiating effects of some dietary fibers are not due to their viscosity (Monsivais et al., 2011; Rao, 2016). In one of those studies, Monsivais et al. (2011) showed that dextrin, a non-viscous soluble fiber, increased the perception of fullness, reduced hunger ratings, and suppressed energy intakes. The authors suggested that supplementing beverages with dextrin affects short-term energy intake and may have implications for weight control, while indicating that the satiating power associated with dextrin is not likely due to viscosity effects. Guar fiber, a near non-viscous soluble fiber, has also been proven for its acute and sustained effects on satiety, appetite control, and energy intake. The acute post-meal perception of satiety for >4 h was observed with intake of 5 g guar fiber. It has been suggested that regular intake of guar fiber (2 g/day) reduced 20% of daily energy intake via snacking (Rao, 2016). Another non-viscous dietary fiber, resistant starch, has been examined for its postprandial effects on appetite regulation and metabolism in an acute randomized, single-blind cross-over study. Twenty young healthy adult males consumed either 48 g resistant starch or the placebo divided equally between two mixed meals on two separate occasions. There was a significantly lower energy intake following the resistantstarch supplement compared to the placebo supplement. However, no associated effect on subjective appetite measures was observed (Bodinham et al., 2010). Fermentable and non-fermentable fibers were also compared in a number of studies for their effect on satiety. In a single-blind, cross-over, placebo-controlled pilot study of 2 weeks on 10 subjects, Cani et al. (2006) determined that addition of 8 g oligofructose (a fermentable dietary fiber) to the diet twice a day increased satiety, reduced hunger, and reduced postmeal food intake. In contrast to these findings, Howarth et al. (2003) found that nonfermentable dietary fiber was more satiating than fermentable fiber. The study was conducted with 11 subjects to compare the relative effects of fermentable (pectin, β-glucan) and non-fermentable fibers (methylcellulose) on ad libitum energy intake, hunger, satiety, body weight, and fat loss. The subjects first consumed non-fermentable fiber and then fermentable fiber for 3 weeks each, with a 4-week washout period between phases. Their findings suggested no role for acceptable amounts of fermentable fiber isolates in enhancing satiety and reducing energy intake in humans consuming a diet ad libitum. Although soluble fibers have been the focus of research for trials on satiety, it has been shown that insoluble fibers often have an impact on satiety as much as or more than that of soluble fibers (Slavin & Green, 2007). As an example, Delargy, O’sullivan, Fletcher, and Blundell (1997) showed that a breakfast high in soluble fiber (psyllium gum) does not reduce motivation to eat as effectively as a breakfast high in insoluble fiber (wheat bran) 1.5–2 h after consumption. The fibers were incorporated into breakfast cereals and consumed at breakfast by 16 healthy, normal-weight males after an overnight fast using a repeated measures, counter-balanced design. The hunger ratings showed that subjects were less hungry, and energy intake from the snack was lower after the consumption of insoluble fiber than the

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soluble-fiber cereal breakfast. Insoluble fibers may alter satiety and hunger cues by different mechanisms compared with soluble fibers. They may affect satiety in the small and large intestines, which may be linked to changes in gut hormones or intestinal transit (Slavin & Green, 2007). It has also been suggested that a mixture of soluble and insoluble fibers may well produce the strongest effect on reducing the appetite (Delargy et al., 1997). There is also an indication that foods with a low-glycemic index are more satiating compared to foods with high-glycemic index (Solah et al., 2014). However, not all studies showed a significant association with glycemic responses and satiety or body weight (Holt, BrandMiller, & Stitt, 2001; Raben, 2002; Weickert & Pfeiffer, 2008). Effects of dietary fiber on satiety have been proposed to be due to several mechanisms, such as increased mastication, gastric distention, prolonged gastric emptying, slower absorption of macronutrients, and enhanced effects of hunger-related hormones (Vuksan et al., 2009). 4.2.1.1 Increased Mastication Foods with dietary fiber are more difficult to process in the mouth since they have denser, compact textures (Fiszman & Varela, 2013). Accordingly, fiber-rich foods generally require greater mastication in terms of effort and/or time, which stimulates the secretion of saliva and induces cephalic- and gastric-phase responses and signals (Burton-Freeman, 2000; Heaton, 1973; Keithley & Swanson, 2005) and reduce the rate of ingestion (Howarth, Saltzman, & Roberts, 2001). When the product stays longer in the mouth, the opportunity for the sensory receptors in the oral cavity to capture taste, smell, texture, and other properties increases (Fiszman & Varela, 2013), which leads to a stronger feeling of satiety and a reduction in the meal size (Babio, Balanza, Basulto, Bullo´, & Salas-Salvado´, 2010; Burton-Freeman, 2000; Howarth et al., 2001; Keithley & Swanson, 2005; Wanders et al., 2011). Zijlstra, de Wijk, Mars, Stafleu, and de Graaf (2009) showed that increased oral processing time and decreased bite size significantly decreased food intake. The study was conducted with 27 healthy subjects who consumed chocolate custard through a tube, which was connected to a peristaltic pump, and the sound signals indicated the duration of oral processing time. Bite sizes were free or fixed to approximately 5 g (small bite sizes) or 15 g (large bite sizes). Oral processing time was free (only in combination with free bite size) or fixed to 3 or 9 s. It was observed that subjects consumed significantly more when the oral processing time was 3 s rather than 9 s. 4.2.1.2 Gastric Distention Perceived food volume can influence satiety independent of its energy density. Air and water can be exploited to increase the perceived portion sizes without increasing the energy content, while also contributing to sensory and other characteristics (Fiszman & Varela, 2013). Because viscous dietary fibers absorb large quantities of water and form gels, they may increase stomach distention, which is suggested to trigger afferent vagal signals of fullness and accordingly increase satiety during meals and satiation in the post-meal period. In addition, the increased mastication of fiber-rich foods may promote gastric distension through the increased production of saliva and gastric acid (Howarth et al., 2001; Vuksan et al., 2009). Addition of gums, for example, could contribute to gastric distention by increasing the volume of food since they absorb large amounts of water (Fiszman & Varela, 2013). Marciani et al. (2001)

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found a good correlation between gastric volumes and satiety. They studied the relationship between the intragastric distribution, dilution, and emptying of meals and satiety using noninvasive magnetic resonance imaging techniques in 12 healthy subjects. Four test meals of varying viscosity and nutrient content prepared by adjusting the locust bean gum content were used. Fullness was found to be linearly related to total gastric volumes for the nutrient meals and logarithmically related for the non-nutrient meals. Fullness was higher for highviscosity meals compared with the low-viscosity ones (P < 0.02), and this was associated with greater antral volumes for the nutrient meals (P < 0.05). It is also worth indicating that the authors determined an increased satiety for high-viscosity meals with the same gastric volume, which suggested that there is another mechanism through which viscosity influences satiety beyond simply delaying gastric emptying. 4.2.1.3 Prolonged Gastric Emptying Separation of solids and liquids within the stomach allows faster gastric emptying of liquids compared with solids, which is known as sieving. Marciani et al. (2012) examined if blending a solid and water meal would prevent sieving, eliminate the early rapid decrease in gastric volume, and thereby enhance satiety. Two separate 2-way, cross-over studies with 18 volunteers who consumed roasted chicken and vegetables with a glass of water or as a blended soup were conducted. As a result, it was concluded that blending the solid/liquid meal to a soup delayed gastric emptying and increased the hormonal response to feeding, which may contribute to enhanced postprandial satiety. Human trials suggest that enhanced gastric retention is the key factor in decreasing appetite and is probably mediated by a combination of intestinal nutrient sensing and increased viscosity in the stomach (Mackie, Rafiee, Malcolm, Salt, & van Aken, 2013). Soluble dietary fibers form a viscous gel matrix as a result of their water-holding capacity. Due to this property, they trap nutrients and delay their exit from the stomach and passage to duodenum, which results with prolonged gastric emptying and hence, increased satiety (Babio et al., 2010;Dikeman & Fahey Jr, 2006 ; Howarth et al., 2001). It has been shown that consumption of high doses of viscous soluble fibers like guar gum, pectin, and psyllium delays gastric emptying due to increased viscosity, which can reduce pyloric flow and increase retention of gastric contents (Rao, 2016). Sanaka, Urita, Sugimoto, Yamamoto, and Kuyama (2006) showed that stirring a gel-forming agent containing 2.6 g pectin into a liquid meal to increase the viscosity significantly delayed gastric emptying. In their following study, the same research group showed that 5.2 g pectin and 2.0 g agar yielded a comparable meal consistency and delayed gastric emptying in healthy adults (Sanaka, Yamamoto, Anjiki, Nagasawa, & Kuyama, 2007). Besides viscosity of the gastric contents, the chemical composition of digesta is also considered to be important for delayed gastric emptying. The form and physicochemical action of dietary fibers drive their physiological actions (Brownlee, 2014). For example, alginates, which are linear copolymers composed of β-1–4-linked D-mannuronic acid and α-1–4-linked guluronic acid, form stronger gels when they are rich in α-1–4-linked guluronic acid residues, which is important for gastric emptying. It has been determined that strong-gelling alginate meal consistently formed larger total volumes of lumps than the weak-gelling alginate (Hoad et al., 2004). In the study of Marciani et al. (2001) on gastric-emptying rates after meals with different locust bean gum and nutrient contents, it has been determined that increasing the

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nutrient content within the meal delayed gastric emptying, while increasing the viscosity had a smaller effect. Torsdottir, Alpsten, Holm, Sandberg, and T€ olli (1991) conducted a study on the effects of a small dose of soluble alginate fiber on gastric emptying and postprandial glycemia in human with type-2 diabetes. The subjects ingested meals of similar amounts of digestible carbohydrates, fat, and protein with or without a 5.0 g sodium alginate supplement on two different mornings in random order. The gastric emptying rate of the meal containing sodium alginate was significantly slower than that of the fiber-free meal. Sodium alginate also induced significantly lower postprandial rises in blood glucose, serum insulin, and plasma C-peptide. The authors suggested that the diminished glucose response after the addition of sodium alginate could be correlated to the delayed gastric emptying rate induced by the fiber. 4.2.1.4 Slower Absorption of Nutrients Soluble dietary fibers are considered to encapsulate the nutrients and delay their absorption (Sanaka et al., 2007). Accordingly, fibers may increase the time for intestinal passage, leading to a more gradual nutrient absorption and prolonged feelings of satiety (Wanders et al., 2011). Availability of circulating nutrients may affect the feeling of hunger and/or satiety, and hence the ability of dietary fibers to extend the period for the absorption of nutrients may reduce hunger and/or increase satiety (Howarth et al., 2001). Viscous fibers have also been associated with reduction in plasma-glucose concentrations after consumption (Dikeman & Fahey Jr, 2006; Howarth et al., 2001). The gel matrix of hydrated dietary fibers can thicken the small intestinal contents, leading to a decrease in the diffusion of cholesterol, sugars, and other nutrients for absorption, and limits contact between food and digestive enzymes, which disrupts micelle formation and contact with the gastrointestinal wall (Beck, Tosh, et al., 2009; Dai & Chau, 2017; Dikeman & Fahey Jr, 2006). They also alter the resistance of digesta to contractile movements within the gastrointestinal tract and hence decrease the transport of glucose to absorptive surfaces. In addition, viscous fibers may thicken the unstirred water layer at the absorptive surfaces, which decreases the diffusion rate of glucose (Dikeman & Fahey Jr, 2006). The slow absorption of nutrients as a result of the consumption of dietary fiber may blunt postprandial glycemic and insulinemic response, which results with reduction in the rate of return of hunger (Howarth et al., 2001). Dietary fibers such as alginates could significantly influence rates of nutrient absorption through decreasing diffusion across the mucus layer. Mackie, Bajka, and Rigby (2016) examined this effect for sodium alginate on mucus permeability. They showed that sodium alginate is able to diffuse into scraped porcine intestinal mucus and the alginate concentration in the boundary region increases. As a result of the entanglement, the apparent diffusion of the alginate through the mucin was gradually decreased over time, which suggests that the permeability of the mucus to large polymers and also to lipid digestion products was decreased. They also showed that the addition of low concentrations of alginate linearly increased the local viscosity of the mucus layer at the micron scale. In another study, the effect of guar gum on delaying the absorption of nutrients and the mechanism of its effect was examined (Edwards, Johnson, & Read, 1988). Measurements of the electrical resistivity of saline solutions were carried out to determine if guar gum delayed diffusion of solutes or inhibited convection of luminal contents. Their results indicated that guar gum had no effect on the mobility of ions in a completely unstirred solution. However, when they were brought into contact inside a vessel that was rotated at a constant speed, guar gum delayed the time taken for saline solutions of different

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resistivity to achieve complete mixing. Their results suggested that guar gum probably reduced absorption by resisting the convective effects of intestinal contractions. 4.2.1.5 Gastrointestinal Hormones Some centrally and peripherally produced and operating hormones and peptides are secreted mainly by the gut in response to different nutrients and have been implicated in the regulation of food intake in the short-term. These humoral signals are called satiety signals since they are related to termination of the meals. These satiety promoting hormones include cholecystokinin (CCK), glucagon-like peptide 1 (GPL-1), peptide YY (PYY), and ghrelin, which play a vital role in gut-derived appetite signaling to the brain and function as physiological regulators of food intake ( Juvonen, Flander, & Karhunen, 2007; Rao, 2016). CCK, GLP-1, and PYY stimulate the perception of satiety, while ghrelin stimulates hunger. Among the satiety hormones, CCK is the mostly studied one, which was found to increase the perception of satiety and inhibit food intake in humans (Rao, 2016). CCK is a peptide hormone and neurotransmitter that regulates gut motility, gall bladder contraction, and pancreatic enzyme secretion; it may mediate the post-prandial glycemic and insulinemic response to viscous fibers (Slavin, Savarino, Paredes-Diaz, & Fotopoulos, 2009). It is released in the upper part of the colon, from endocrine I-cells of the duodenum and jejunum, and thereby also affects the colonic mobility. The influence of CCK on the perception of satiety is mediated by the CCK1-receptors in the vagus nerve (Rao, 2016). GLP-1 has numerous effects including inhibition of food intake, delayed gastric emptying, weight loss, stimulation of insulin secretion, and inhibition of beta-cell proliferation (Parnell & Reimer, 2009). PYY is an anorexigenic hormone belonging to the pancreatic polypeptide family, which is colocatized with GLP-1 in the intestinal L cells and implicated in appetite control (Beck, Tapsell, et al., 2009; Parnell & Reimer, 2009). Conversely, ghrelin stimulates food intake and hence enhances weight gain and promotes adiposity (Parnell & Reimer, 2009). As a result of the effect of dietary fiber on slow digestion and delayed absorption of nutrients, as well as subsequent gel formation of some fibers; nutrients may be bound for longer periods of time, which may slow the release of glucose into the blood. The non-absorbed nutrients reach further into the bowel, inhibiting the gastric hunger hormone ghrelin and stimulating the duodenal satiety hormone CCK along with the appetite decreasing hormones GLP-1 and PYY (Beck, Tosh, et al., 2009; Solah et al., 2014; Vuksan et al., 2009). A direct correlation has been reported between post-prandial levels of CCK and satiety scores after ingestion of foods with varying amounts of fiber (Slavin et al., 2009). In a randomized cross-over design, Burton-Freeman, Davis, and Schneeman (2002) examined the effect of adding fiber or fat to a low-fat, low-fiber meal on CCK release and subjective measures of satiety on 15 subjects. Three isoenergetic breakfast meals were tested: low fiber, low fat; high fiber, low fat; and low fiber, high fat. Blood samples were drawn from fasted subjects before and at different time points after test meal consumption for 6 h and plasma was analyzed for CCK, insulin, glucose, and triacylglycerols. In female subjects, the meals higher in fiber or in fat resulted in greater feelings of satiety and in significantly higher CCK responses than did the low-fat, low-fiber meal. However, the increase in CCK concentration did not differ between meals in male subjects. The effect of dietary fibers on satiety promoting hormones may be dose-dependent. In a study for determining the satiety effects of β-glucan in extruded breakfast cereal foods and

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the dose responsiveness of these effects, a significant relationship was determined between the dose of β-glucan and the CCK response (P ¼ 0.002). CCK was released in response to β-glucan at a minimum dose of approximately 3.8 g. Subjective satiety was increased at a minimum dose of 2.2 g of β-glucan (P ¼ 0.039). Insulin responses relevant to the development of type-2 diabetes were significantly decreased at a dose of at least 3.8 g of β-glucan. β-Glucan did not suppress the secretion of ghrelin at the levels provided (Beck, Tosh, et al., 2009). In an acute meal test, the plasma PYY levels in overweight human adults were evaluated after consuming several doses of β-glucan (Beck, Tapsell, et al., 2009). Fourteen subjects consumed a control meal and three cereals of varying β-glucan concentrations (2.2–5.5 g), and blood samples were collected over 4 h. A significant positive correlation between PYY concentrations and the β-glucan dose (P ¼ 0.003) was determined. The optimal dose of β-glucan was determined to be 4–6 g, with the effects on PYY mediated by viscosity and concentration. It was indicated in the study that longer timeframes may be required to show the full satiety effect of highly viscous fibers such as β-glucan, since the satiety does not necessarily appear initially. Dietary fibers can be fermented in the colon by selected bacterial strains, which increases the concentration of short-chain fatty acids such as butyrate, acetate, and propionate in the gut lumen (Fiszman & Varela, 2013; Parnell & Reimer, 2009; Thompson et al., 2017). It has been shown that short-chain fatty acids stimulate intestinal proglucagon mRNA expression and GLP-1 secretion in rodents and dogs and PYY secretion in the colons of rats (Parnell & Reimer, 2009), and affect the energy intake and adsorption, body weight and glycemic control (Thompson et al., 2017). Theoretically, about 400–800 mmol short-chain fatty acids can be produced per day with a high-fiber diet, assuming that 10 g of dietary fiber fermentation yields about 100 mmol short-chain fatty acids (Canfora, Jocken, & Blaak, 2015). The extent rate and site of fermentation in the gut and nature of the short-chain fatty acid produced can be affected by a number of factors including chemical structure, particle size, surface area, solubility, availability of other more readily fermentable substrates or the composition of the colonic microflora. Soluble fibers are fermented more readily than insoluble ones. Carbohydrates containing α-arabinose or α-galacturonic acid residues are also more susceptible to fermentation. Xylans, pectins, and other gums are fermented significantly in the gut, and resistant starch is completely degraded in the large bowel (Fiszman & Varela, 2013). However, the effect of pectin on CCK secretion was found to be insignificant (Flourie et al., 1985). The study was conducted by adding 3 concentrations of high-methoxy apple pectin (5, 10, 15 g) on solid-liquid meal and tested on 12 healthy men. The gastric emptying of water and carbohydrates is significantly reduced by addition of 10 and 15 g pectin. It was found that pectin does not modify serum concentrations of CCK. Guar fiber was shown to produce significantly higher amounts of butyrate compared to other fibers, which can be related to the production of satiety hormone CCK (Rao, 2016). The effect of adding guar gum to a liquid formula diet on gut transmit time, bowel release, and CCK levels was examined in a randomized cross-over study conducted with 12 healthy male subjects for 7 days. Isocaloric liquid formulas with or without supplementation of guar fiber (21 g/L) were administered to the subjects. During administration of both liquid diets (with or without guar fiber), fasting CCK concentrations were significantly elevated compared with the concentrations in a self-selected diet, and the fasting CCK concentration correlated significantly with the increase of segmental colonic transit time. Colonic transit time was significantly prolonged with guar fiber supplementation compared with the liquid

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diet and the self-selected diet, which was suggested to be caused by the combined effect of increased colonic fermentation and high basal CCK concentrations (Meier, Beglinger, Schneider, Rowedder, & Gyr, 1993).

4.2.2 Effects on Energy Regulation The importance of energy density on satiation and satiety has been extensively studied. Adding fiber to the diet adds bulk, which alters the energy density and palatability. Energy density is defined as the number of kilojoules per unit weight of food (Burton-Freeman, 2000). In general, fiber-rich diets have a reduced energy density compared with high-fat diets, which can be attributed to the bulking property of the dietary fibers. Fiber can displace the energy of other nutrients for a given weight or volume of food (Fiszman & Varela, 2013; Slavin & Green, 2007), which was mentioned to be the major determinant of short-term energy intake (Yeomans, Weinberg, & James, 2005) due to the hypothesis that gastric capacity is key in the regulation of food intake (Burton-Freeman, 2000). Besides, dietary fibers have low-energy value, which leads to reduced energy intake via fiber-rich diets (Babio et al., 2010; Wanders et al., 2011). The effect of dietary fibers on palatability, as well as other sensory qualities such as texture, may also affect the energy intake. Energy density and palatability have been shown to be correlated (Burton-Freeman, 2000; Drewnowski, 1998). Generally, foods with high-energy density are palatable but not satiating, and vice versa (Drewnowski, 1998). Clinical studies indicate that regular appetite control and post-meal satiation in the long-run may subsequently help to reduce the total energy intake and could contribute to maintaining proper body weight in normal healthy subjects (Rao, 2016). Accordingly, effects of dietary fibers on satiety mentioned in the previous part also indirectly affects the energy intake. As an example, increased mastication, which was mentioned to be a factor that affects satiety, may reduce energy intake. The textural properties of high-fiber foods may increase the work effort and time required for mastication. This increase in chewing effort and time may result in an increased satiety due to a variety of cephalic- and gastric-phase responses and signals, reduced meal size, and energy intake (Burton-Freeman, 2000; Wanders et al., 2011). Increased chewing also slows down the intake, which directly decreases food consumption and energy intake (Heaton, 1973). In a cross-over human study, it was investigated that hard foods led to a 13% lower energy intake at lunch compared to soft foods (P < 0.001). Hard foods were consumed with smaller bites, with longer oral duration, and more chewing for the same weight of food compared to the soft foods (P < 0.05). They also determined that the reduction in energy intake was sustained over the next meal and suggested that changes in food texture can be a helpful tool in reducing the overall daily energy intake (Bolhuis et al., 2014). Physicochemical properties of fiber, such as solubility, viscosity, water-holding capacity, and fermentability, affect the satiety and long-term appetite, which in turn regulates the energy intake (Wanders et al., 2011). The modulation of energy intake by dietary fiber is mostly affected by gelling characteristics of the fiber, which influences the gastric distension, nutrient absorption, and, hence, satiety (Paxman, Richardson, Dettmar, & Corfe, 2008; Pelkman, Navia, Miller, & Pohle, 2007). Paxman et al. (2008) used a novel alginate beverage specifically designed to undergo enhanced intragastric gelation in order to evaluate its effect on mean

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daily intake of energy and macronutrients in free-living adults. The beverage was different from other alginate products in that it does not depend on gastric-acid secretion for gelation. The study was conducted on 68 subjects who daily ingested a strong-gelling sodium alginate formulation against a control for 7 days. As a result, daily preprandial ingestion of this stronggelling sodium alginate formulation produced a significant reduction in mean daily energy intake, which was caused by significant reductions in mean daily carbohydrate, sugar, fat, saturated fat, and protein intakes. The authors suggested a possible role for a strong-gelling sodium alginate formulation in management of overweight and obesity (Paxman et al., 2008). Another double-blind, placebo-controlled, within-subjects intervention study was conducted with a novel, two-part beverage, consisting of alginate-pectin (0, 1.0, and 2.8 g) and calcium components that forms a stable, fibrous gel in the stomach to test its effects on subjective satiety and food intake in overweight and obese women. The subjects (n ¼ 29) ingested the beverage twice a day (once before breakfast and once mid-afternoon) for 7 days. A significant reduction in food intake was observed at dinner for both formulations compared with the control formulation (Pelkman et al., 2007). Fiber can also affect the metabolizable energy of the diet by changing the digestibility of fat and protein. Baer, Rumpler, Miles, and Fahey Jr (1997) conducted a study to measure the metabolizable energy content of nine diets with different fat and fiber concentrations. Diets varied in level of fat (18%, 34%, or 47% of energy) and level of total dietary fiber (3%, 4%, or 7% of diet dry matter) and were consumed for 2 weeks by 17 subjects as three diets containing different levels of fiber and one level of fat. As a result, it was shown that increasing fiber intake decreased fat and protein digestibility, and the metabolizable energy content of the diets decreased as fiber intake increased.

4.3 DIETARY FIBER AND OVERWEIGHT-RELATED DISEASES The excess body-weight problem has progressively increased over the past several decades and is a very serious problem all over the world today. Being overweight significantly increases the risk of numerous diseases and clinical disorders, including obesity, type-2 diabetes mellitus, hypertension, coronary and cerebrovascular diseases, various cancers, liver disease, and asthma (Knight, 2011). World Health Organization (WHO) defines a simple index of weight-for-height (BMI) and is commonly used to classify overweight and obesity in adults. It is defined as a person’s weight in kilograms divided by the square of his height in meters (kg/m2). According to the definition of WHO, overweight is a BMI greater than or equal to 25 kg/m2, and obesity is a BMI greater than or equal to 30 kg/m2 for adults (WHO, 2017). As the BMI increases above 25 kg/m2, risk of the above-mentioned diseases and mortality also increases (Knight, 2011).

4.3.1 Dietary Fiber and Obesity Obesity, defined as the excessive accumulation of fatness within the human body, is strongly associated with negative impacts on health and physiological function (Chew & Brownlee, 2018). WHO reported that the worldwide obesity has nearly tripled since 1975

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and that more than 1.9 billion adults were overweight in 2016, including over 650 million of which were obese. In addition, 41 million children under the age of 5 and over 340 million children and adolescents aged 5–19 were overweight or obese in 2016 (WHO, 2017). Although obesity is preventable, it still remains a major challenge in most parts of the world at a publichealth level (Brownlee et al., 2017; WHO, 2017). The increasing prevalence of obesity and its association with most non-communicable diseases further makes the obesity epidemic a major public-health concern (Chew & Brownlee, 2018). Obesity is considered to be a positive energy balance, which is a result of a sedentary lifestyle and/or over-consumption of food. Accordingly, obesity can be reversed by increasing the levels of physical activity and/or reducing the energy intake (Grunberger, Jen, Catherine, & Artiss, 2007). In this respect, increasing the consumption of dietary fiber and fiber-rich foods is considered to be important for weight management and decreasing the risk of obesity (Brownlee et al., 2017; Slavin, 2005). It has been reported that obesity is rare in developing countries where dietary fiber intake is high (Kimm, 1995). Epidemiological studies suggest a strong link between dietary fiber consumption and reduced risk of obesity. A cross-sectional observational study was conducted by Alfieri, Pomerleau, Grace, and Anderson (1995) to examine the fiber intake of three weight groups of 50 subjects each: normal (20.0  BMI  27.0), moderately obese (27.1  BMI  39.9), and severely obese (BMI  40.0). The nutritional data was gathered using the detailed 3-day food records. As a result, it was found that total fiber intake was significantly higher in the lean group (P < 0.05) and was inversely associated with BMI. Miller, Niederpruem, Wallace, and Lindeman (1994) conducted a similar study, which showed that obese men and women have significantly lower dietary fiber intakes than do lean men and women. The subjects were 23 lean (11.1%  2.9% body fat) men, 23 obese (29.2%  3.8% body fat) men, 17 lean (16.7%  3.3% body fat) women, and 15 obese (42.7%  3.9% body fat) women who volunteered for free diet and body composition analyses. It was determined that dietary fiber consumption was lower for obese men (20.9  1.8 g) and women (15.7  1.1 g) than for lean men (27.0  1.8 g) and women (22.7  2.1 g). No differences of energy intake and total sugar intake were found between lean and obese subjects. The authors suggested that alterations in diet composition rather than energy intake may be a weight-control strategy for overweight adults. In the nurses study by Liu et al. (2003), the relation of grain intake to the risk of obesity and major weight gain was also determined. For that purpose, the participants were categorized into two groups in terms of BMI (BMI 30 and BMI < 30) or weight gain (changes in weight 25 kg and changes in weight 25 kg/m2) but otherwise healthy adults, the subjects were randomly assigned to receive 21 g oligofructose/day or a placebo (maltodextrin) for 12 weeks. At the end of the study, there was a reduction in body weight of 1.03  0.43 kg with oligofructose supplementation, whereas the control group experienced an increase in body weight of 0.45  0.31 kg over 12 weeks. Accordingly, oligofructose was suggested as a supplement with a potential to promote weight loss in overweight and obese adults (Parnell & Reimer, 2009). Fermentation of dietary fibers in the colon may lead to production of short-chain fatty acids such as butyrate, acetate and propionate in the gut lumen, which affect the energy intake, energy adsorption, body weight, and glycemic control (Thompson et al., 2017). The fecal shortchain fatty acid levels increase significantly in obese people compared to lean people (Andoh et al., 2016), and the nature and concentration of the short-chain fatty acids produced can be affected by the composition of the colonic microflora (Andoh et al., 2016; Fiszman & Varela, 2013). In this respect, the gut microbiota, i.e., dietary fiber consumption, is linked to obesity and insulin resistance. Upadhyaya et al. (2016) showed that changes in the gut microbiota that were induced by resistant starch were linked to its biological activity in individuals with signs of metabolic syndrome. They investigated the hitherto unknown effects of a resistant-starch (type 4) enriched diet on gut microbiota composition and short-chain fatty acid concentrations in parallel with host immunometabolic functions in 20 individuals with signs of metabolic syndrome. The study was carried out on 20 selected participants, and the duration was 26 weeks, which included two 12-week intervention periods, with one each for resistant starch (30%, v/v, in flour) and control flour, and a 2-week washout in between the interventions. At the end of the intervention period, cholesterols, fasting glucose, glycosylated

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hemoglobin, proinflammatory markers in the blood, waist circumference, and percent body fat were lower in the resistant-starch group compared with the control group. Attenuation of percent body fat combined with a smaller waist circumference indicated a potential reduction in central obesity in these individuals. Two groups of beneficial bacteria are dominant in the human gut, the Bacteroidetes and the Firmicutes (Ley, Turnbaugh, Klein, & Gordon, 2006). It is known that both groups contribute to short-chain fatty acid generation, and a higher Firmicutes/Bacteroidetes ratio is associated with obesity via increased generation of short-chain fatty acids (Andoh et al., 2016). It has been reported that obese subjects have a different composition of gut microbiota than lean subjects, and the microbiota of obese subjects change toward the microbiota of lean subjects when they lose weight (Weickert & Pfeiffer, 2008). In the intervention study of Upadhyaya et al. (2016), a differential abundance of 71 bacterial operational taxonomic units was determined in the resistant-starch group, including the enrichment of three Bacteroides species and one each of Parabacteroides, Oscillospira, Blautia, Ruminococcus, Eubacterium, and Christensenella species. The fecal short-chain fatty acids were higher, including butyrate, propionate, valerate, isovalerate, and hexanoate after resistant starch intake. There were associations of the gut microbiota with the host metabolic functions and short-chain fatty acid levels specific to resistant starch. Findings from both intervention and epidemiological studies indicate that the gut microbiota is a critical environmental factor contributing to the development of obesity, and, hence, obesity has a microbial component, which might have potential therapeutic implications (Andoh et al., 2016; Ley et al., 2006). The relation between gut microbial ecology and body fat in humans was studied on 12 obese people who were randomly assigned to either a fat-restricted or to a carbohydrate-restricted, low-calorie diet. Composition of the gut microbiota of subjects was monitored over the course of 1 year by sequencing 16S ribosomal RNA genes from stool samples. The relative proportion of Bacteroidetes decreased in obese people as compared with lean people, and this proportion increased with weight loss on two types of low-calorie diets (Ley et al., 2006). The gut microbiota related to obesity may differ in different populations. For example, obesity-associated gut microbiota in a Japanese population was shown to be different from that in Western people (Andoh et al., 2016). The gut microbiota profiles of 10 obese and 10 lean Japanese subjects were studied by Andoh et al. (2016). It was found that the Firmicutes and Fusobacteria were significantly more abundant in obese people than in lean people. However, the abundance of the Bacteroidetes and the Bacteroidetes/Firmicutes ratio were not different between the obese and lean groups. The genera Alistipes, Anaerococcus, Corpococcus, Fusobacterium, and Parvimonas increased significantly in obese people, and the genera Bacteroides, Desulfovibrio, Faecalibacte rium, Lachnoanaerobaculum, and Olsenella increased significantly in lean people. Another important finding was that bacteria species possessing anti-inflammatory properties (such as Faecalibacterium prausnitzii) increased significantly in lean people, but bacteria species possessing pro-inflammatory properties increased in obese people.

4.3.2 Dietary Fiber and Type-2 Diabetes With increasing prevalence, Type-2 diabetes or diabetes mellitus is one of the major, common, and costly health problems in the world. The number of adults (age 18–99 years) with

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diabetes was 451 million in 2017, which means that the global prevalence of diabetes was about 8.4% in the adult population. In addition, there was an estimated 374 million people with impaired glucose tolerance (Cho et al., 2018). Unfortunately, the prevalence of diabetes has been increasing rapidly and has nearly doubled since 1980 when the prevalence was 4.7% (WHO, 2016), probably due to the drastic increase of physical inactivity and obesity (Asif, 2014). The prevalence of diabetes was predicted to rise to 9.9% in 2045 with an estimated number of 693 million people with diabetes (Cho et al., 2018). Diabetes can cause a range of complications, such as cardiovascular disease, peripheral vascular disease, nephropathy, changes to the retina, and blindness that can lead to disability and death (Asif, 2014). Approximately 5 million deaths in the world were attributable to diabetes in the 20–99years age range in 2017. In addition, diabetes also imposes important medical and economic burdens (Asif, 2014). The global healthcare expenditures for diabetes were estimated to be 850 billion USD in 2017 (Cho et al., 2018). According to the report of WHO (2016), diabetes prevalence has risen faster in low- and middle-income countries than in high-income countries over the past decade. Although genetic susceptibility and environmental influences seem to be the most important factors responsible for the development of diabetes; obesity and physical inactivity may constitute the main reasons for the increasing risk of diabetes in the world today. Therefore, diet is one of the major factors for decreasing the risk and for the overall the management of diabetes (Asif, 2014). A high dietary fiber intake is usually emphasized in most of the nutritional recommendations for decreasing the risk of diabetes (Weickert & Pfeiffer, 2008). In addition, high-fiber diets offer many health benefits for diabetic individuals (Anderson, 1986). As mentioned before, dietary fiber inhibits macronutrient absorption, reduces postprandial glucose response, and beneficially influences certain blood lipids. These effects are mostly attributed to the viscous and/or gel-forming properties of soluble dietary fiber (Papathanasopoulos & Camilleri, 2010; Weickert & Pfeiffer, 2008). A number of human intervention studies with diabetic and healthy patients gives insights through a relation between soluble dietary fibers and postprandial glucose reduction. Sierra et al. (2001) evaluated the effects of ispaghula husk and guar gum on postprandial glucose and insulin concentrations in a randomized, cross-over study on 10 healthy female subjects with normal body mass indices. An oral glucose load with and without fiber was administered in the morning after an overnight fast. The rate and extent of glucose absorption as well as the mean serum insulin concentrations decreased in the presence of both fibers, but mean glycemic values after ispaghula husk were lower than after guar gum. The same research group studied the effects of psyllium in 20 type-2 diabetic patients who consumed 14 g/ day fiber for 6 weeks. At the end of the study, it was observed that glucose absorption decreased significantly in the presence of psyllium, and this reduction was not associated with an important change in insulin levels. The fiber treatment also reduced total and LDL cholesterol and uric acid significantly (Sierra, Garcı´a, Ferna´ndez, Diez, & Calle, 2002). The results of both studies indicated a potential beneficial effect of ispaghula husk and psyllium in the metabolic control of type-2 diabetics, although long-term studies in diabetic patients would be required for ispaghula husk (Sierra et al., 2001; Sierra et al., 2002). Although most of the intervention studies show the effect of soluble dietary fiber on decreasing the post-prandial glucose levels, insoluble fiber also has been reported to delay glucose absorption from the small intestine (Anderson, 1986). Two recent intervention studies showed the effect of a commercial resistant starch, an insoluble fiber on decreasing the postprandial blood glucose levels (Stewart et al., 2018; Stewart & Zimmer, 2017). The first study

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examined the effects of a high-fiber ready-to-eat baked good (scone) containing a novel resistant starch of type 4, against a low-fiber control. The high fiber scone significantly reduced postprandial glucose and insulin incremental areas under the curves and postprandial glucose and insulin maximum concentrations. In addition, it reduced hunger and desire to eat during the 180 min following consumption (Stewart et al., 2018). Another study of the same group was conducted to determine the effects of a high-fiber cookie containing 24 g of the same novel fiber. The high-fiber cookie reduced the post-prandial blood glucose incremental area, the maximum glucose concentration, and post-prandial serum insulin versus the control cookie. Both studies showed that resistant-starch type 4 can be incorporated into bakery products such as scones or cookies and significantly reduce post-prandial glucose and insulin responses in healthy adults (Stewart & Zimmer, 2017). Epidemiologic evidence points to insoluble dietary fiber, rather than soluble ones, for reducing the risk of type-2 diabetes, which suggests that further unknown mechanisms are likely to be involved ( Jenkins, Kendall, Axelsen, Augustin, & Vuksan, 2000; Papathanasopoulos & Camilleri, 2010; Weickert & Pfeiffer, 2008). In a 6-years prospective cohort study of 35,988 women from Iowa, the relations of baseline intake of carbohydrates, dietary fiber, dietary magnesium, carbohydrate-rich foods, and the glycemic index with incidence of diabetes was examined. As a result of the study, it was shown that intake of insoluble fiber was inversely associated with diabetes risk, whereas intake of soluble fiber did not appear to be strongly related to diabetes risk. The data especially supported a protective role for grains (particularly whole grains), cereal fiber, and dietary magnesium in the development of diabetes in older women (Meyer et al., 2000). Schulze et al. (2007) conducted both a prospective study and a meta-analysis to determine the association between fiber and magnesium intake and the risk of type-2 diabetes. The study was carried out on 9702 men and 15,365 women who were observed for incident cases of diabetes from 1994 to 2005. During the follow-up, higher cereal fiber intake was inversely associated with diabetes risk, while fruit fiber and vegetable fiber were not significantly associated. Meta-analyses showed a reduced diabetes risk with higher cereal fiber intake, but no significant associations for fruit and vegetable fiber. These findings refute the general belief that soluble fiber decreases post-prandial blood glucose concentrations and serum cholesterol; and insoluble fiber increases stool size. Due to the magnitude of physiologic effects of soluble and insoluble fibers and disparities between their chemically measured amounts; the National Academy of Sciences Panel on the Definition of Dietary Fiber recommended that the terms soluble fiber and insoluble fiber gradually be eliminated and be replaced by specific beneficial physiologic effects of a fiber, perhaps viscosity and fermentability (Slavin, 2005).

4.3.3 Dietary Fiber and Risk Factors of Cardiovascular Diseases Obesity is a well-established risk factor for hypertension, plasma cholesterol, and cardiovascular diseases (Knight, 2011; Threapleton et al., 2013). Many observational and experimental studies have examined the relation between dietary fiber and hypertension, elevated plasma cholesterol, and total cardiovascular risk. Besides obesity and insulin sensitivity,

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hypertension and elevated plasma cholesterol are risk factors for cardiovascular diseases (Threapleton et al., 2013). Scientific evidence indicates that a significant proportion of hypertensive persons in the population are overweight, and the risk of hypertension is higher among obese individuals compared to those with normal weight. Comparisons of simultaneous intra-arterial and cuff blood pressure measurements indicate that blood pressure is generally associated with body weight (Chiang, Perlman, & Epstein, 1969; Knight, 2011). Two early prospective studies to examine the relation of nutritional factors with blood pressure and hypertension among US men and women suggested that an increased intake of dietary fiber may contribute to the prevention of hypertension in men. The earlier one was a 4-year follow-up study carried out among 30,681 US male health professionals, 40–75 years old, without diagnosed hypertension. Dietary fiber was significantly associated with lower risk of hypertension, and the effect was independent of the intake of other nutrients, potassium, and magnesium. The relative risk of hypertension was 1.57 with a fiber intake of 24 g/day. It has also been shown that fruit fiber but not vegetable or cereal fiber was inversely associated with incidence of hypertension (Ascherio et al., 1992). A similar study with a 4-year follow-up was also conducted with 41,541 US female nurses, 38–63 years old without diagnosed hypertension, cancer, or cardiovascular disease. Contrarily to the first one, the outcomes of this study showed that fiber was not significantly associated with risk of hypertension, after adjusting for age, BMI, alcohol, and energy intake. However, the results point to the possibility that magnesium and fiber as well as a diet richer in fruits and vegetables may reduce blood pressure levels (Ascherio et al., 1996). The blood pressure lowering effect of dietary fiber was also confirmed by a number of meta-analysis studies of randomized trials. Streppel, Arends, van’t Veer, Grobbee, and Geleijnse (2005) estimated the effect of fiber supplementation on blood pressure with a meta-analysis of 24 randomized placebo-controlled trials published between January 1, 1966 and January 1, 2003. Fiber supplementation (average dose, 11.5 g/day) changed systolic blood pressure by 1.13 mm Hg and diastolic blood pressure by 1.26 mm Hg. Reductions in blood pressure were larger in older (>40 years) and in hypertensive populations than in younger and in normotensive ones. Another meta-analysis was carried out by Whelton et al. (2005) for 25 randomized controlled trials published in English-language journals before February 2004. The dietary-fiber intake was found to be associated with a significant 1.65 mm Hg reduction in diastolic blood pressure and an insignificant 1.15 mm Hg reduction in systolic blood pressure. In hypertensive subjects, a significant reduction in both blood pressures as a result of dietary fiber intake was reported. Both studies indicate that increased intake of dietary fiber may reduce blood pressure and may contribute to the prevention of hypertension. Another meta-analysis was conducted on different fiber types namely: arabinoxylan-rich diets (high in wholegrain foods), β-glucan-rich diets (high in oat and barley fiber), chitosans, mannans, pectins, xylans, and alginates. Analyses of specific fiber types concluded that all fiber types studied reduce the systologic and diagnostic blood pressure, but the highest effect was obtained with β-glucan. Diets rich in β-glucans reduce systologic blood pressure by 2.9 mm Hg and diagnostic blood pressure by 1.5 mm Hg for a median difference in β-glucans

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of 4 g (Evans et al., 2015). A more recent systematic review and meta-analysis study was conducted to determine the effects of viscous soluble fibers on blood pressure. Randomized clinical trials carried out with five types of soluble fiber (β-glucan from oats and barley, guar gum, konjac, pectin and psyllium) for more than 4 weeks duration was included in the study. Their findings demonstrated a modest but significant reduction of systologic blood pressure and diagnostic blood pressure following all viscous soluble fiber supplementations, in particular psyllium. Reduction of systologic blood pressure by psyllium was higher than that of the other fiber types studied (Khan et al., 2018). High cholesterol is another mainly overweight-related risk factor for cardiovascular diseases. It has been well-documented that soluble fibers, especially the viscous ones, decrease serum total and LDL cholesterol concentrations (Brown, Rosner, Willett, & Sacks, 1999; Erkkil€ a & Lichtenstein, 2006; Mudgil & Barak, 2013). The proposed mechanisms include reducing the absorption of cholesterol and bile acids, and alterations in hepatic metabolism and plasma clearance of lipoproteins ( Jenkins et al., 2000; Mudgil & Barak, 2013). An early meta-analysis study of 67 controlled trials quantified the cholesterol-lowering effect of major dietary fibers (pectin, guar gum, oat bran, and psyllium). Soluble fiber consumption of 2–10 g/day was found to be associated with small but significant decreases in total cholesterol and LDL cholesterol. The effect was independent of the fiber type. Triacylglycerols and HDL cholesterol were not significantly influenced by soluble fiber (Brown et al., 1999). Anderson et al. (2009) also reviewed prospective randomized controlled clinical trials and proposed the net LDL cholesterol effects of different fibers weighted by number of subjects per trial. For guar gum, intakes ranging from 9 to 30 g/day, divided into at least three servings/day, were associated with a weighted mean reduction of 10.6% for LDL-cholesterol values. For pectin, consumption of 12–24 g/day in divided amounts was associated with a 13% reduction in LDL cholesterol values. Barley β-glucan intake of 5 g/ day in divided doses was associated with an 11.1% reduction in LDL-cholesterol values. For hydroxypropyl methylcellulose, data indicated that 5 g/day in divided doses decreases LDL-cholesterol values by 8.5%. These LDL-cholesterol changes with soluble fibers occur without significant changes in HDL-cholesterol or triglyceride concentrations. In the double-blind trial of Walsh et al. (1984) conducted in 20 obese subjects for 8 weeks, glucomannan fiber (from konjac root) was shown to reduce the serum cholesterol and LDL cholesterol significantly when given in 1 g doses 1 h prior to each of three meals per day. The cholesterol-lowering effect of fiber is attributed to the increased viscosity of luminal contents ( Jenkins et al., 2000). In fact, it has been shown in many studies that viscosity of the dietary fiber predicts its cholesterol-lowering effect (Ho et al., 2017; Vuksan et al., 2011). In a randomized cross-over intervention study, Vuksan et al. (2011) compared the lipid-lowering effects of low-viscosity wheat bran, medium-viscosity psyllium, and a highviscosity viscous fiber blend. Reduction in LDL cholesterol was greater with the viscous fiber blend compared with the medium-viscosity psyllium and low-viscosity wheat bran. The magnitude of LDL cholesterol reduction showed a positive association with high-viscosity fiber, which lowered LDL cholesterol to a greater extent than lower-viscosity fiber even in smaller quantities consumed (Vuksan et al., 2011). In an older study, a mixture of lowviscosity gum arabic and pectin (4:1) was given to 110 hypercholesterolemic subjects at doses of 5, 9, and 15 g/day as dissolved in apple juice. At the end of the study, the low-viscosity fiber

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mix did not decrease the serum cholesterol levels (Davidson et al., 1998). Psyllium seed husk, on the other hand, was shown to decrease LDL cholesterol given at doses 3.4, 6.8, or 10.2 g/ day. The study was conducted on 286 subjects as a randomized, double-blind controlled one for 24 weeks. In the group that consumed 10.2 g psyllium seed husk/day, LDL cholesterol remained below baseline during treatment with a value 5.3% below that of the control group at week 24 (Davidson et al., 1998). Overall, obesity is one of the main factors that affect cardiovascular disease and coronary heart disease. Obese hypertensive subjects have been shown to experience a greater risk of coronary heart disease than the non-obese ones, and mortality rates for obese hypertensive persons were reported to be higher than for those with obesity alone or hypertension alone (Chiang et al., 1969). In early studies, an association between the consumption of dietary fiber and reduction in the risk of hyperlipidemia and ischaemic heart disease has been proposed (Trowell, 1972). More recent large observational studies also support an inverse relation between dietary fiber intake from natural food sources and cardiovascular risk (Mudgil & Barak, 2013; Papathanasopoulos & Camilleri, 2010). Food sources of mainly insoluble fibers, such as cereal products, have been shown to be the most consistently associated with lower incidence rates of cardiovascular disease. Soluble, gel-forming fibers have also been reported to beneficially affect cardiovascular disease risk factors. The scientific evidence promotes a food-based approach with increased intake of whole-grain cereals, fruits, and vegetables providing a mixture of different types of fibers for decreasing the risk of cardiovascular disease (Erkkil€a & Lichtenstein, 2006). Liu et al. (1999) has also reported the possible role of increased intake of whole grains in protection against coronary heart disease; however, the authors suggested that the lower risk associated with higher whole-grain intake was not fully explained by its contribution to intakes of dietary fiber, folate, vitamin B6, and vitamin E. According to a systematic review and meta-analysis of 22 prospective cohort studies, insoluble fiber and fiber from cereal and vegetable sources were inversely associated with the risk of coronary heart disease and cardiovascular disease. Fruit fiber intake was inversely associated with risk of cardiovascular disease. Overall, it has been shown that total dietary fiber intake was inversely associated with the risk of cardiovascular disease and coronary heart disease (Threapleton et al., 2013). There has been little support for an inverse association between vegetable fiber intake and risk of cardiovascular disease. A pooled analysis of cohort studies to determine the effects of different fiber types (cereal, vegetable, and fruit) on decreasing the risk of coronary heart disease also reported that consumption of dietary fiber from cereals and fruits is inversely associated with risk of coronary heart disease. However, no such associations were observed for vegetable fiber. One possible explanation for this finding was suggested to be the nutrientpoor high glycemic load nature of common starchy and heavily processed vegetables, such as corn and peas (Pereira et al., 2004).

4.4 FIBER RECOMMENDATIONS AND HEALTH CLAIMS The definition of dietary fiber and its measurement method vary among different countries and health authorities, which leads to differences in the daily consumption requirements.

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Between 1972 and 1976, dietary fiber was defined as the remnants of plant components that are resistant to hydrolysis by human alimentary enzymes. Later, the definition was expanded to include resistant oligosaccharides and resistant starch in addition to non-starch polysaccharides and lignin (O’sullivan and Cho, 1998). Today, dietary fiber is referred as both, i.e., non-starch polysaccharides fiber or as Association of Analytical Chemists (AOAC) fiber. Non-starch polysaccharides fiber includes polysaccharides of the plant cell wall components that is characteristic of plant foods, such as wholegrain cereals, fruits, and vegetables. AOAC fiber includes the non-digestible polysaccharides, and also, e.g., lignin, resistant starches, and resistant oligosaccharides, measured with a set of methods developed by AOAC. Therefore, the reported fiber content in foods can vary depending on the definition and/or the method used to quantify it. Accordingly, recommendations for the daily consumption of fruits, vegetables, and whole grains to meet the dietary fiber intake values differ depending on the definition of fiber and its measurement method. Recommended intake values are expressed in the majority of the cases as adequate intakes of AOAC fiber unless differently stated. Some public health organizations also recommend fiber intakes on per-energy requirements basis (grams fiber per MJ or grams per 1000 kcal) ( JRC & SANTE, 2018). The Joint WHO/FAO Expert Consultation report expresses dietary fiber as non-starch polysaccharides and mentions wholegrain cereals, fruits, and vegetables as the preferred sources of non-starch polysaccharides. Accordingly, the recommendation of the Expert Consultation for dietary fiber intake is consumption of fruits, vegetables, and wholegrain foods, which is likely to provide >20 g per day of non-starch polysaccharides (>25 g per day of total dietary fiber) (WHO, 2003). The Scientific Advisory Committee on Nutrition (SACN) defines dietary fiber as all carbohydrates that are neither digested nor absorbed in the small intestine and have a degree of polymerisation of at least three monomeric units, plus lignin. The Committee recommends that the dietary reference value for the average population intake of dietary fiber for adults should be 30 g/day, as measured using the AOAC methods agreed by regulatory authorities (SACN, 2015). European Food Safety Authority (EFSA) uses AOAC fiber as a basis for intake recommendations and considers dietary fiber intakes of 25 g/day to be adequate for normal laxation in adults (EFSA, 2010). To meet the dietary fiber requirements, nutrition guidelines from the United States and Europe recommend eating a variety of fruits, vegetables, and whole grains (de Vries, Birkett, Hulshof, Verbeke, & Gibes, 2016). Intake of dietary fibers from natural food sources is generally considered preferable to fiber supplements, which contain isolated fibers, since whole foods may supply additional beneficial micronutrients and phytochemicals beyond that of fiber alone (SACN, 2015; Smith & Tucker, 2011). However, the large discrepancy between the recommended doses of fiber to achieve clinically important health effects and actual intakes has led to a series of trials investigating the effects of fiber-supplemented foods or concentrated sources of fibers such as β-glucan (Smith & Tucker, 2011). In addition, to define the extracted natural carbohydrate components or synthetic carbohydrate products as dietary fiber, the beneficial physiological effects must be demonstrated by accepted scientific evidence, similar to those demonstrated for the naturally integrated dietary fiber component of foods (SACN, 2015). Some examples for the dietary fibers approved by health authorities and their health effects are given in Table 4.2.

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TABLE 4.2 Approved Health Claims for Some Specific Dietary Fibers Dietary Fiber

Health Effect

Conditions Required for the Claim

References

β-Glucan from oats and barley

Water-soluble fiber from either whole oats or barley, or a combination of whole oats and barley, consumed as part of a low saturated fat, low cholesterol diet, may reduce the risk of heart disease

At least 3 g of β-glucan soluble fiber from either whole oats or barley, or a combination of whole oats and barley Foods carrying the health claim must provide at least 0.75 g of water-soluble β-glucan from oat or barley per reference amount customarily consumed of the food product

FDA (2016)

The Panel concludes that a cause and effect relationship has been established between the consumption of β-glucans from oats and barley and a reduction of post-prandial glycaemic responses

The Panel considers that in order to obtain the claimed effect, 4 g of β-glucans from oats or barley for each 30 g of available carbohydrate should be consumed per meal. The target population is individuals who wish to reduce their post-prandial glycaemic responses

EFSA (2011a)

Oat β-glucan

The Panel considers that the following wording reflects the scientific evidence: “Oat β-glucan has been shown to lower/reduce blood cholesterol. Blood-cholesterol lowering may reduce the risk of (coronary) heart disease”

The Panel considers that, in order to bear the claim, foods should provide at least 3 g of oat β-glucan per day. This amount can reasonably be consumed as part of a balanced diet. The target population is adults who want to lower their blood cholesterol concentrations

EFSA (2010b)

Barley β-glucan

The Panel considers that the following wording reflects the scientific evidence: “Barley β-glucans have been shown to lower/reduce blood cholesterol. High cholesterol is a risk factor in the development of coronary heart disease”

The Panel considers that at least 3 g of barley β-glucans should be consumed per day in order to obtain the claimed effect. This amount can reasonably be consumed as part of a balanced diet. The target population is adults who want to lower their blood cholesterol concentrations. A minimum of 0.75 g of β-glucans per serving is recommended, or one-fourth of the 3 g daily amount specified above, to assist consumers to choose foods to suit their diet

EFSA (2011b)

Soluble fiber from psyllium seed husk

A food product containing watersoluble fiber from psyllium seed husk, consumed as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease

At least 7 g of water-soluble psyllium fiber must be consumed daily. Foods carrying the health claim must provide at least 1.7 g of water-soluble fiber from psyllium per reference amount customarily consumed

FDA (2016)

Resistant starch

On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the consumption of resistant starch from all sources, when replacing digestible starch in baked foods, and a

The Panel considers that in order to bear the claim, high carbohydrate baked foods should contain at least 14% of total starch as resistant starch in replacement to digestible starch. The target population is individuals

EFSA (2011c)

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TABLE 4.2

Approved Health Claims for Some Specific Dietary Fibers—cont’d

Dietary Fiber

Health Effect

Conditions Required for the Claim

reduction of post-prandial glycaemic responses

wishing to reduce their post-prandial glycaemic responses

Arabinoxylan from wheat endosperm

The Panel concludes that a cause and effect relationship has been established between the consumption of arabinoxylan produced from wheat endosperm and reduction of postprandial glycaemic responses

The Panel considers that in order to obtain the claimed effect, 8 g of arabinoxylan-rich fiber produced from wheat endosperm (at least 60% arabinoxylan by weight) per 100 g of available carbohydrates should be consumed. The target population is individuals who wish to reduce their post-prandial glycaemic responses

EFSA (2011d)

Chitosan

On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the consumption of chitosan and maintenance of normal blood LDL-cholesterol concentrations

The Panel considers that in order to obtain the claimed effect, 3 g of chitosan should be consumed daily. The target population is adults

EFSA (2011e)

Pectin

On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the consumption of pectins and maintenance of normal blood cholesterol concentrations

The Panel considers that, in order to bear the claim, foods should provide at least 6 g per day of pectins in one or more servings. The target population is adults

EFSA (2010c)

On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the consumption of pectins and a reduction of post-prandial glycaemic responses

The Panel considers that, in order to bear the claim, foods should provide at least 10 g of pectins per meal. The target population is adults willing to reduce their post-prandial glycaemic responses

EFSA (2010c)

The Panel concludes that a cause and effect relationship has been established between the consumption of HPMC and maintenance of normal blood cholesterol concentrations

In order to obtain the claimed effect, at least 5 g per day of HPMC should be consumed in two or more servings. The target population is adults

EFSA (2010d)

The Panel concludes that a cause and effect relationship has been established between the consumption of HPMC and a reduction of post-prandial glycaemic responses

In order to obtain the claimed effect, at least 4 g of HPMC per meal should be consumed. The target population is adults willing to reduce their postprandial glycaemic responses

EFSA (2010d)

The Panel concludes that a cause and effect relationship has been established between the consumption of glucomannan and the reduction of blood cholesterol concentrations

The Panel considers that in order to bear the claim, a food should provide at least 4 g/day of glucomannan in one or more servings. The target population is the general population

EFSA (2009)

Hydroxypropyl methylcellulose (HPMC)

Glucomannan (Konjac mannan)

References

Continued

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TABLE 4.2 Approved Health Claims for Some Specific Dietary Fibers—cont’d Dietary Fiber

Guar gum

Health Effect

Conditions Required for the Claim

References

On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the consumption of glucomannan and the reduction of body weight in the context of an energy-restricted diet

The Panel considers that in order to obtain the claimed effect, at least 3 g of glucomannan should be consumed daily in three doses of at least 1 g each, together with 1–2 glasses of water before meals, in the context of an energy-restricted diet. The target population is overweight adults

EFSA (2010e)

The following wording reflects the scientific evidence: “Consumption of guar gum contributes to maintainance of normal blood cholesterol levels”

In order to bear a claim, foods should provide at least 10 g per day of guar gum in one or more servings. The target population is adults

EFSA (2010f )

4.5 CONCLUSION Excess body weight and obesity are considered serious health problems, which significantly increase the risk of numerous diseases and clinical disorders, including type-2 diabetes mellitus, hypertension, coronary and cerebrovascular diseases, various cancers, liver disease, and asthma. Obesity is clearly linked to disturbances in energy intake; therefore, reduced energy intake and increased energy consumption are crucial for decreasing the risk of many non-communicable diseases related to obesity. Epidemiological studies as well as controlled human trials have shown that a higher intake of dietary fiber results with reduced energy intake and increased satiety, which leads to lower body weight and smaller waist circumference. The mechanisms for that are mainly proposed as increased mastication, gastric distention, prolonged gastric emptying, slower absorption of nutrients, and regulation of gastrointestinal hormones by dietary fiber consumption. In this respect, dietary fibers provide an important tool for managing obesity and the associated diseases. Therefore, a daily consumption of 25–30 g dietary fiber is recommended by the health authorities and advisory committees, and it is suggested to meet this dietary fiber intake mainly from natural food sources, such as whole grain cereals, fruits, and vegetables rather than fiber supplements.

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C H A P T E R

5

Health Effect of Dietary Fibers Isaac Benito-Gonza´lez, Marta Martı´nez-Sanz, Maria Jose Fabra, Amparo Lo´pez-Rubio Food Preservation and Food Quality Department, IATA-CSIC, Valencia, Spain

O U T L I N E 5.1 Introduction

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5.2 Fruits 5.2.1 Antioxidant Properties 5.2.2 Prebiotic Properties and Body Weight Management 5.2.3 Antimicrobial Properties

129 130

5.3 Vegetables 5.3.1 Antioxidant Activity 5.3.2 Prebiotic and Body Weight Management 5.3.3 Antimicrobial Activity

140 141

137 139

144 145

5.4 Grains and Cereals 5.4.1 Antioxidant Capacity 5.4.2 Prebiotic Properties and Body Weight Management 5.4.3 Antiviral and Antimicrobial Activity

146 146 148 149

5.5 Other Properties (Anticancer, Antiinflammatory, etc.)

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5.6 Conclusions and Future Outlook

152

References

152

5.1 INTRODUCTION Dietary fiber (DF) has been the focus of many studies because of its ability to improve human health. Some of the most representative benefits attributed to DF include the following (Slavin, 2013): • Optimum fiber intake (14 g/1000 kcal) can decrease low-density lipoprotein (LDL) levels and reduce the risk of cardiovascular disease. • Consumption of 15 g fiber/day has been demonstrated to significantly reduce the risk of diabetes II and attenuate the glucose absorption rate, thus reducing weight gain.

Dietary Fiber: Properties, Recovery, and Applications https://doi.org/10.1016/B978-0-12-816495-2.00005-8

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# 2019 Elsevier Inc. All rights reserved.

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• Laxation and regularity are attributes widely associated with optimum fiber intake and are closely linked to optimum body weight management (Kelsay, Behall, & Prather, 1978). • Body weight management is closely linked to fiber intake, as it promotes satiation due to the higher saliva and gastric acid production as a consequence of the increased chewing time (Slavin & Green, 2007). • Lower colorectal cancer prevalence has been traditionally attributed to higher fiber intake diets. However, there is still a lack of clear causal evidence, and further studies need to be carried out to corroborate this. • Prebiotic effects attributed to fermentable fibers (mainly poly- and oligosaccharides) may provide a number of health benefits by altering the composition of the intestinal flora. • Significant antioxidant capacity has been widely reported in DF. In fact, the antioxidant activity attributed to dietary fiber probably comes from phenolic acids, phenylpropanoids, and flavonoids, which in foods are often glycosylated with different sugars, especially glucose or other polysaccharides (Shahidi, 2000). Given the extensive amount of literature available related to the specific health benefits of dietary fiber, the aim of this chapter is to discuss in more detail some of the health benefits of eating high dietary fiber foods, which in most cases are related to phytochemicals associated to the fibers. The methodologies frequently used to assess these attributes will be briefly presented and some practical examples for particular types of fibers (depending on their native source) will be provided in the following sections. Oxidation processes taking place in the body have been widely studied and recognized as vital for human health, since an oxidative metabolism is essential for the viability of cells. A side effect of these oxidative processes is the production of free radicals and other reactive oxygen species that may cause oxidative damages. Several protective enzymes such as catalases and peroxidases can be affected by the excess of free radicals yielding lethal cellular effects (e.g., apoptosis) by oxidizing membrane lipids, cellular proteins, and DNA. Protection mechanisms against the effects of excessive oxidation are provided by the action of various chemical compounds known as antioxidants. Examples of these substances are vitamins (ascorbic acid) present in fruits like orange and pineapple; carotenoids (β-carotene or lycopene) present in carrot, tomato, or watermelon; and polyphenols (tocopherols or flavonoids) found in cereals (such as wheat or rice) and fruits (such as apricot or grapes). Due to great relevance of antioxidant compounds from the human nutrition and health perspective, several methods have been developed and standardized to measure and analyze the antioxidant capacity (Antolovich, Prenzler, Patsalides, McDonald, & Robards, 2002). The most common methodologies used to determine antioxidant capacity in vitro are ABTS+ and DPPH radical scavenging assays. These methods are based on the tested compounds to reacting with highly oxidized radicals, reducing them, and yielding a significant color variation, which can be measured by spectrophotometric analysis. However, these two colorimetric methods present several drawbacks, such as the difficulty of small highly-reactive radicals (e.g., OH•, NO•, O2) that are active in biological tissues and foods reacting with the ABTS+ radical. Moreover, due to the hydrophobic character of DPPH, this assay has to be carried out using hydrophobic solvents, which are typically unsuitable for fiber components. However, strong hydrogen bonding solvents such as methanol can also interfere with the total

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antioxidant capacity of different molecules like some proteins, thiols, and glutathione, so differences between solvents must be also taken into account (Barclay, Edwards, & Vinqvist, 1999; Foti, Daquino, & Geraci, 2004; Schaich, Tian, & Xie, 2015). Results are commonly presented as Trolox Equivalents (TE) or Ascorbic Acid Equivalents (AAE), depending on which compound has been used as the positive control for the experiments. Alternative methodologies avoiding the drawbacks of the radical scavenging assays are available. For instance, the β-carotene bleaching assay is based on the capacity of antioxidant compounds to delay the bleaching of β-carotene solutions or emulsions upon heating (usually 50ºC). In that case, the results are expressed as a percent of bleaching reduction with respect to a negative control. This assay presents the additional benefit of testing a natural widespread molecule of interest in food such as the β-carotene. On the other hand, since the antioxidant capacity of many foods is directly related to the amount of phenolic compounds, an indirect method would be the quantification of these compounds in the samples to be tested. Gallic Acid Equivalents (GAE) and Catechin Equivalents (CE) are commonly used to express the total phenolic content (TPC) in samples, which is typically determined by the Folin-Ciocalteau method (Singleton, Orthofer, & LamuelaRavento´s, 1999). Another common form to present antioxidant capacity results is the halfmaximal Inhibitory Concentration (IC50), which represents the concentration of the tested compound needed to reduce by 50% the oxidation activity of the target radical. It is important to highlight that, as mentioned above, phenolic acids and flavonoids in foods may occur in free form, but are often glycosylated with different sugars, especially glucose or other polysaccharides considered dietary fibers, providing them antioxidant properties (Zhu, 2018a). Moreover, some studies confirmed synergistic interactions between DF and polyphenols whose effects were clearly better than that of individuals, highlighting the potential of these combinations to improve human health although molecular mechanisms and pathways remain to be explored (Gao, Wang, Wu, Ming, & Zhao, 2012; Wang & Zhu, 2016, 2017). It also appears that the linkage of the sugar moieties to phenolic compounds is responsible for their specific characteristics and transport into the body fluids (Shahidi, 2000). Furthermore, it has been recently demonstrated that the use of severe hydrothermal and mechanical processes applied in food processing (like boiling and autoclaving) do not detrimentally affect the binding capacity of polyphenols to cellulose-like matrixes. Thus, these bound compounds will also have an impact on intestinal health as digestion processes within the small intestine are not considered to disrupt this linkage (Liu, Martinez-Sanz, LopezSanchez, Gilbert, & Gidley, 2017; Padayachee et al., 2013). Related to that, it has been found that while many of the bound polyphenols cannot be adsorbed in the small intestine due to their interactions with cell wall polysaccharides, they are subsequently fermented and metabolized in the large intestine (Padayachee et al., 2013; Saura-Calixto et al., 2010; Snelders et al., 2014). Nevertheless, binding between polyphenols and cell walls is not irreversible. Both hydrophilic (hydrogen bonding) and hydrophobic interactions have been demonstrated by the addition of urea or dioxane (Hanlin, Hrmova, Harbertson, & Downey, 2010; Padayachee et al., 2013). Moreover, a significant variation in the environmental conditions may also be able to release phenolic compounds from the complexes (Padayachee et al., 2013). According to that, a better understanding of the different pathways of these complexes along the human intestinal tract is needed for a proper exploitation of these interactions in terms of human health.

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Furthermore, other bioactive properties have been demonstrated for many of the phenolic compounds that are normally bound to dietary fiber, like antiviral and antimicrobial properties. Thus, dietary fiber is an ingredient that many consider to improve food preservation against degradative oxidation processes, as well as preventing food-borne diseases, which are globally recognized as environmental hazards to the food supply and human health. However, it is important to highlight that the biological activity of the compounds bound to dietary fibers may vary upon storage or pH conditions (Konowalchuk & Speirs, 1976). Additionally, some poly- and oligosaccharides are considered to have remarkable prebiotic properties. A prebiotic compound is defined as “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health” (Slavin, 2013). Most of the known and suspected prebiotics are catalogued as carbohydrates, primarily oligosaccharides, which are able to resist the acid digestion processes and reach the colon, where they are fermented by the gut microflora (Slavin, 2013). A large group of fruits and vegetables such as artichokes, onions, garlic, asparagus, or bananas contain these oligosaccharides (e.g., fructooligosaccharides (FOS)) (Manning & Gibson, 2004). However, their concentration may not be enough as some studies suggest that 4 or even 8 g of FOS/day might be needed to significantly increase bifidobacteria levels in the human gut (Gibson, 1998). Several studies have been carried out to analyze beneficial effects of prebiotics in human health. The greatest benefits of prebiotic intake include the following: • Reduce the prevalence and duration of infectious and antibiotic-associated diarrhea, as well as acute gastroenteritis (Park & Kroll, 1993). • Enhance the bioavailability and uptake of minerals, including calcium, magnesium, and possibly iron (Al-Sheraji et al., 2013). • Lower some risk factors for cardiovascular disease and/or cancer (Ito et al., 1990). • Promote satiety, lipid regulation, and weight loss and prevent obesity (Imaizumi, Nakatsu, Sato, Sedarnawati, & Sugano, 1991). Additional research is still needed to completely define the relationship between the consumption of some prebiotics and the improvement of human health (Brownawell et al., 2012); however, several metabolic pathways are being studied and defined. Indeed, even anticancer properties have been demonstrated as inulin and oligofructose intake decreased the risk of colorectal (Verghese, Rao, Chawan, Williams, & Shackelford, 2002) and breast cancer in rats and showed reduced metastases to lungs (Taper & Roberfroid, 2002). Furthermore, propionic acid, produced as a consequence of dietary fiber fermentation in the colon, may also possess anti-inflammatory properties in relation to colorectal carcinoma cells (Munjal, Glei, PoolZobel, & Scharlau, 2009). The following sections highlight the main groups of foods that are well known to be excellent dietary fiber sources; some specific examples of remarkable natural food products are included with a brief description of their associated health benefits. Intake of fruits and vegetables has been related to body weight management and a reduced risk of chronic diseases, including cancer, heart disease, and strokes. (Gandini, Merzenich, Robertson, & Boyle, 2000; Kaczmarczyk, Miller, & Freund, 2012; Kendall, Esfahani, & Jenkins, 2010; Willett et al., 1995). In fact, the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) recommend eating at least five fruits and

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FIG. 5.1 Schematic distribution of the main sources of dietary fiber in diet and their most remarkable health properties.

vegetables per day. Fruits and vegetables have been recognized as an excellent source of vitamins and minerals, dietary fiber, and a host of beneficial non-nutrient compounds including plant sterols, flavonoids and other antioxidants. As antioxidants can be bound to dietary fiber components, eating a variety of fruits and vegetables helps ensure an adequate intake of many of these essential nutrients (Willett et al., 1995). Among the different foods rich in fiber, cereals are one of the main sources of DF and contribute to about 50% of the fiber intake in € western countries (Lambo, Oste, & Nyman, 2005). Approximately 30%–40% of DF comes from vegetables, about 16% from fruits, and the remaining 3% from other minor sources (Gregory, Foster, Tyler, & Wiseman, 1990). Fig. 5.1 represents the main fiber sources in the diet as well as their most significant contributions to human health. According to that, Sections 5.2–5.4 discuss the most relevant health-related properties of dietary fiber in fruits, vegetables, and cereals, respectively.

5.2 FRUITS Much of the fiber that we ingest when we consume fruit comes from the walls of the parenchyma cells (Grierson, 2001). Plant cell walls contain, when fully formed, a collection of complex soluble polysaccharides, including mainly pectic polysaccharides, while

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xyloglucans and cellulose stand out amongst the water insoluble fiber (Dhingra, Michael, Rajput, & Patil, 2012) (Fig. 5.1). Some heteroxylans and galactoglucomannans can be also found in smaller amounts. All these fibers can differ in their abundance and be subjected to minor structural changes among species, as well as suffering structural variations during storage and/or cooking (Smith, 2013).

5.2.1 Antioxidant Properties In general, fruits are a rich source of antioxidant compounds like carotenoids, vitamins, and phenolic compounds. The antioxidant properties of the dietary fiber contained in fruits may be mainly attributed to the presence of bound phenolic compounds, which can also confer these carbohydrates with additional health benefits. However, it is important to emphasize that the antioxidant capacity is usually measured from food extracts, and it is not representative of the activity of all the bioactive compounds present in a certain food since not of all these compounds will be extracted when using a particular solvent. Table 5.1 summarizes the TPC and antioxidant capacity from some fruits analyzed in the existing literature. The following sections provide an overview of the compounds that confer these fruits with the well reported antioxidant properties and which may be responsible for the antioxidant capacity attributed to dietary fiber. Among fruits, watermelon has been traditionally considered as a good source of fiber (>0.5 g/100 g edible portion) with remarkable contents of both soluble and insoluble fibers (Dhingra et al., 2012). However, its antioxidant capacity is not attributed to its fiber content itself but to lycopene, a carotenoid pigment known to provide fruits and vegetables with its characteristic red color. Its protective activity against oxidation processes has attracted a great deal of interest as it is one of the main carotenoids present in the diet of North Americans and Europeans (Clinton, 1998). Although tomatoes have been traditionally considered to be the main natural source of lycopene, further studies suggest watermelons as important sources, even overcoming tomatoes (Perkins-Veazie, Collins, Edwards, Wiley, & Clevidence, 2002). For instance, considerable amounts of cis-lycopene, ranging from 2.3 to 7.2 mg/100 g in wet weight have been found in watermelon, also presenting a relatively high bioavailability (Perkins-Veazie et al., 2002). Lycopene is typically found in its crystalline form in most vegetable cells. In the case of watermelon, however, it has been reported to be directly available after ingestion, and no thermal or chemical treatment is required as it can be easily released from the cell walls (Naz, Butt, Sultan, Qayyum, & Niaz, 2014; Perkins-Veazie et al., 2002). Numerous studies have focused on the determination of lycopene and phenolic contents, as well as antioxidant capacity, of several watermelon varieties (Dia et al., 2016; Kim, Park, Kim, & Cho, 2014; Nagal et al., 2012; Tlili et al., 2011) and have demonstrated the capability of watermelon lycopene as an antioxidant and anti-inflammatory agent even more powerful than tomato’s lycopene. Differences between varieties, localization, irrigation, production yields, and, especially harvesting period, all are known to affect lycopene accumulation in watermelons (Soteriou, Kyriacou, Siomos, & Gerasopoulos, 2014). For instance, Ang, Lam, Sia, Khoo, and Yim (2012) studied watermelon peel phenolic composition and antioxidant capacity in red and yellow varieties. The ripening degree, solvents used, extraction times, size, and color of the fruit also must be taken into account since they may also make lycopene

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TABLE 5.1 Total Phenolic Content (TPC) and Antioxidant Capacity From Different Fruits and Vegetables Analyzed in the Existing Literature TPC

Antioxidant Capacity

Methodology Followed

Seeds, 5.6–8.4 mg GAE/g (Seidu & Otutu, 2016)

0.02–0.04 mg TE/g of seed flour (Seidu & Otutu, 2016) and 40–60 mg AAE/g of seed (Seidu & Otutu, 2016)

ABTS

383.2  18.2 mg GAE/100 mL (Lantzouraki, Sinanoglou, Tsiaka, Proestos, & Zoumpoulakis, 2015) 29.39  1.3–91.54  2.6 gallagic acid Eq (Guo, Deng, Xiao, Xie, & Sun, 2007) Pulp, 24.4  2.7 mg TAE (tannin acid)/g (Li et al., 2006) Peel, 249.4  17.2 mg TAE/g (Li et al., 2006)

90.82  1.96 mg TE/100 mL wine (Lantzouraki et al., 2015) 82.65  0.59 mg TE/100 ml wine (Lantzouraki et al., 2015) IC50s (μg/mL) from peel, 4.01–23.28 μg/mL (Guo et al., 2007) Juice, 0.83–5.56 μg/mL (Guo et al., 2007) Seed 0.033–0.29 μg/mL(Guo et al., 2007)

ABTS

Persimmon flour fraction, 1–1.3 mg GAE/g sample (LucasGonza´lez, Ferna´ndez-Lo´pez, ´ lvarez, & Viuda-Martos, Perez-A 2018) Persimmon peel, 27.2  2.1 mg GAE/100 g (Gorinstein et al., 2001) Persimmon pulp, 19.3  1.4 mg GAE/100 g (Gorinstein et al., 2001) Whole persimmon, 22.1  1.8 mg GAE/100 g (Gorinstein et al., 2001)

Lyophilized peel, 31 mg TE/ 100 g (Martı´nez-Las Heras, Pinazo, Heredia, & Andres, 2017) Lyophilized pulp, 18.9 mg TE/ 100 g (Martı´nez-Las Heras et al., 2017) 3.2 mg TE/g hydrolyzed tannins (Matsumura et al., 2017) 0.68 mg TE/g nonhydrolyzed (Matsumura et al., 2017) Flour fractions persimmon, 0.7–0.9 μg TE/g (LucasGonza´lez et al., 2018) 1.1–2.1 mg TE/g (LucasGonza´lez et al., 2018)

DPPH

6 different varieties, 3–31 μmol TEAC/g (Egea et al., 2006) 3–52 μmol TEAC/g (Egea et al., 2006) Peel, 251.8 mg TE/100 g (Xinguang et al., 2018) Peel 121.7 mg TE/100 g (Xinguang et al., 2018)

ABTS

IC50 15 μg/mL (Nirmala & Narendhirakannan, 2011)

DPPH

FRUITS Watermelon

Pomegranate

Khaki

Apricot

Grape Bagasse

Peel, 43.8–59.3 mg GAE/100 g (Xinguang, Wenxiao, Xiaomei, Jiankang, & Weibo, 2018) Pulp, 16.6–52.2 mg GAE/100 g (Xinguang et al., 2018)

Skin (extracts), 66 184 mg CE/g (Fontana, Antoniolli, & Bottini, 2013)

DPPH

DPPH Scavenging activity O2 ● ●

OH

H2O2

DPPH

ORAC

ORAC

DPPH ABTS

CUPRAC ABTS DPPH

Continued

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TABLE 5.1 Total Phenolic Content (TPC) and Antioxidant Capacity From Different Fruits and Vegetables Analyzed in the Existing Literature—cont’d TPC

Antioxidant Capacity

Methodology Followed

(ethanol/water) Yellow cherry, 5.07/1.55 mgGAE/g (Noor Atiqah, Maisarah, & Asmah, 2014) Red cherry, 4.28/1.35 mgGAE/g (Noor Atiqah et al., 2014 Tomato, 4.25/1.39 mgGAE/g (Noor Atiqah et al., 2014) 18 tomato varieties, 2–3 mgGAE/ 100 g (Frusciante et al., 2007) FW (fresh weight)

(ethanol/water) Yellow cherry, 20.83/17.78 (%) (Noor Atiqah et al., 2014) Red cherry, 10.42/15.55 (%) (Noor Atiqah et al., 2014) Tomato, 8.33/11.11 (%) (Noor Atiqah et al., 2014)

β-Carotene

1371  14 mg GAE/100 g dw Red onion peel(4 ex), 27.3–384.7 mg GAE/g extract (Singh et al., 2009)

80% inhibition (Guil-Guerrero, Martı´nez-Guirado, del Mar Rebolloso-Fuentes, & CarriquePerez, 2006) 90% inhibition (Guil-Guerrero et al., 2006) 90% inhibition (Guil-Guerrero et al., 2006) 40% inhibition (Guil-Guerrero et al., 2006) 95% bleaching inhibition Red onion peel, 24.2%–97.4% (4ext)

DPPH

11.28–19.10 μg TE/g (defatted) (Madhujith & Shahidi, 2007) 181.42  0.86 μmol AAE/g raw grain (Adom & Liu, 2002)

ORAC

150 mg CE/g (Nirmala & Narendhirakannan, 2011) Seed (extract), 213 1652 mg CE/g (Fontana et al., 2013) 628 mg GAE/g (Baydar, € Ozkan, & Sag˘dic¸, 2004) Tomato

β-Carotene β-Carotene

VEGETABLES Pepper (Yellow Lamuyo) (Red California) (Orange California) (Green Italian) Carrot Onion

DPPH DPPH DPPH β-Carotene β-Carotene

CEREALS (barley maltBeer Bagasse) Corn Wheat Oats Rice

1860–1948 μg ferulic acid/g (McCarthy, O’Callaghan, Piggott, FitzGerald, & O’Brien, 2013) 565–794 μg p-coumaric acid/g (McCarthy et al., 2013) 13.6–22.9 mg ferulic acid/g (lyophilisate weight)(Madhujith & Shahidi, 2007) 15.55  0.60 μmol GAE/g raw grain (Adom & Liu, 2002) 7.99  0.39 μmol GAE/g raw grain (Adom & Liu, 2002) 6.53  0.19 μmol GAE/g raw grain (Adom & Liu, 2002) 5.56  0.17 μmol GAE/g raw grain (Adom & Liu, 2002)

76.70  1.38 μmol AAE/g raw grain (Adom & Liu, 2002) 74.67  1.49 μmol AAE/g raw grain (Adom & Liu, 2002) 55.77  1.62 μmol AAE/g raw grain (Adom & Liu, 2002)

Total oxygen scavenging capacity (TOSC) (Winston, Regoli, Dugas, Fong, & Blanchard, 1998) TOSC TOSC TOSC

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values oscillate with reduced extraction times when using yellow varieties as the natural source (Ang et al., 2012). Apart from that, the antioxidant capacity of several watermelon bioactive compounds has also been studied in-vivo. Hong et al. (2015) observed that diets with high amounts of watermelon reduced oxidative processes in rats, which had been fed with an atherogenic diet (where atheroma formation is promoted by a high ingestion of cholesterol, saturated and -trans fats, and salt) (Hong et al., 2015). Mohammad, Mohamed, Zakaria, Abdul Razak, and Saad (2014) demonstrated the antioxidant potential of watermelon juice in radiation-exposed mice (Mohammad et al., 2014). Moreover, Micol, Larson, Edeas, and Ikeda (2007) tested a registered dietetic supplementary (ActiSOD), which was known to be a nanoencapsulated watermelon extract. Their results seemed to show that watermelon derivative antioxidants can represent a current alternative to reduce obesity oxidative stress as a result of stimulating antioxidant enzymes, improving glycaemic and lipidic metabolisms (Micol et al., 2007). Oyenihi, Afolabi, Oyenihi, Ogunmokun, and Oguntibeju (2016) studied the effect of watermelon juice in oxidative stress alcohol-associated in rats. Oral administration of watermelon juice for 15 days prior to ethanol intoxication significantly reduced the concentration of malondialdehyde in the liver and brain of rats. In addition, watermelon pretreatment increased the concentration of glutathione and normalized catalase activity in both tissues in comparison to the ethanol control group (Oyenihi et al., 2016). Tseng and Hong (2016) observed a remarkable improvement in colitis after feeding rats with a watermelon powder during a high-fat dietary program. Colonic alterations were induced in these rats, and the results evidenced that ingestion of watermelon powder upgraded colonic crypts morphology as well as cell homeostasis modulation (Tseng & Hong, 2016). However, the dietary fiber present in watermelon could influence the absorption of this carotenoid as suggested by previous studies showing that pectin strongly decreased the bioavailability of β-carotene (Rock & Swendseid, 1992). The rationale behind the lower rates of antioxidant absorption could also be related to the increase of the viscosity of luminal contents caused by dietary fiber, apart from physically trapping the antioxidants within the fiber matrix in the chime (PalafoxCarlos, Ayala-Zavala, & Gonza´lez-Aguilar, 2011). However, from the in vivo studies, it seems that the combination of both compounds in watermelon does not affect the beneficial effects attributed to the antioxidants present. Watermelon seeds, which are also rich in fiber content and up to 10 times higher when compared to raw watermelon (5%) (El-Adawy & Taha, 2001), have also been widely investigated as a source of antioxidant compounds. Phenolic content varied between 1.41 and 1.55 mg GAE/g with antioxidant values of 36 mg/mL IC50 (Adaramola & Adebayo, 2016). Other authors analyzed and characterized watermelon seeds, finding remarkable levels of saponins (11–32 mg/g), glycosides (10–14 mg/g), alkaloids (47.2–95.8 mg/g), phenols (5.6–8.4 mg GAE/g), and flavonoids (3.5–7.7 mg QE/g). With regard to the antioxidant activity, 0.02–0.04 mg TE/g of seed flour (by ABTS method) and 40–60 mg AAE/g of seed (DPPH) values were determined (Seidu & Otutu, 2016). Pomegranate can be considered another relevant source of fiber in our diets. According to recent studies, its content can be established in 0.6 g/100 g (of the edible part) being the main part insoluble fiber (being the ratio insoluble to soluble of 5:1) (Dhingra et al., 2012b). Fostered by current consumer trends and a demand for foods with additional health benefits, the beverage industry is searching for natural juices rich in bioactive components, which could provide extra benefits over conventional energy drinks that contain lots of artificial sweeteners. Pomegranate juice presents high fiber content with a superior antioxidant capacity over grape

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or blueberry juice, red wine, ascorbic acid, or tocopherol (Ignarro, Byrns, Sumi, de Nigris, & Napoli, 2006). Pomegranate’s antioxidant capacity is mainly due to its considerable phenolic content (up to 383 mg/100 mL of pomegranate juice) and phenolic compounds like ellagitannins, which have also been related to an improvement in sports performance (Gil, Toma´s-Barbera´n, Hess-Pierce, Holcroft, & Kader, 2000). Pomegranate peel has been reported to possess higher antioxidant capacity than seeds or juice because of its increased phenolic and tannin contents with values between 29.39–91.54 GAE and between 13.50–40.74 (w/w) of tannins. Moreover, white pomegranate varieties showed the highest scavenging activities against several oxidative radicals (cf. Table 5.1) (Faria & Calhau, 2010; Guo et al., 2007). Although very few studies have characterized the polysaccharides present in pomegranate, those extracted from the peel were able to show antioxidant and inhibitory activities against tyrosinase (Rout & Banerjee, 2007), which again confirms the binding of phenolic moieties to polysaccharides although a proper and complete characterization is still needed. Another study carried out by Li et al. (2006) showed the higher phenolic content of pomegranate peel extracts when compared to pulp ones (both extracted in the same conditions with the same solvents ratio). These extracts, especially the ones obtained from the peels, displayed remarkable antioxidant activity. This included scavenging or preventive capability against several reactive oxygen species (superoxide, hydroxyl, and peroxyl) (Li et al., 2006), demonstrating the high antioxidant potential of this rich fiber fruit for human health. Khaki (persimmon) can be considered another relevant source of both soluble and insoluble dietary fiber, with a range of approximately 1.5% of total fiber content with a ratio 1:1 of soluble: insoluble (Gorinstein et al., 2001). Similar to the pomegranate, khaki peels seemed to have greater fiber content than the pulp (1.7% vs 1.3%) (Gorinstein et al., 2001). Several studies have demonstrated the potential of the khaki’s antioxidant capabilities that are mainly linked to their high tannin content, which are mainly bound to peel cell walls. A recent study showed the capability of ethanolic extracts and ethanolic acid extracts from astringent khaki to protect Caco-2 cells against oxidative stresses (Kim, Kim, Kwon, & Kim, 2017). Among the great variety of bioactive compounds present in astringent persimmons, tannins showed an excellent affinity to bile salts in the intestine (Matsumoto, Yokoyama, & Gato, 2010), and their high antioxidant capacity has been reported ( Jang et al., 2010). Tannins are usually present in khakis in their condensed form and mostly comprise flavan-3-ols like catechin, catechin-3-O-gallate, gallocatechin, and gallocatechin-3-O-gallate (Li et al., 2010). Khaki flours have also been investigated, particularly in terms of their composition and how particle size affects the antioxidant capacity. The main carbohydrates detected were glucose and fructose with malic acid the most abundant organic acid. The khaki variety directly affected the final composition. The “Shiny Red” variety with the highest phenolic, flavonoid, and carotenoid contents had the highest antioxidant capacity values when measured by different methodologies. In contrast, particle size did not seem to have a substantial effect in any of the measured parameters (Lucas-Gonza´lez et al., 2018). A recent research study evaluated the antioxidant capacity of the leaves, fruits, and fiber extracts during an in-vitro digestion process, showing that leaf extracts were the richest in terms of total antioxidants. However, they were more sensitive to the digestion conditions. Oral digestion considerably affected the antioxidant capacity, while the gastric process provoked an additional decrease. Interestingly, the intestinal phase led to increased phenolic and flavonoid solubility in both fruit and fiber extracts. It is also worth mentioning that the bioaccessibility of phenolic compounds and flavonoids and the

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antioxidant capacity was 1.4, 1.0, and 3.8 times higher in fruits than in leaves, with a total antioxidant value of 31 mg TE/100 g and 18.9 mg TE/100 g of lyophilized peel and pulp khaki fibers, respectively. It is interesting to note that fiber extracts from khaki peels are richer in antioxidant compounds than commercial orange, peach, or lemon fibers, showing their potential as functional ingredients in high-fiber food formulations (Martı´nez-Las Heras et al., 2017). Another fruit considered to be an excellent source of dietary fiber is apricot. Dried apricots can reach dietary fiber values around 7.7% (Al-Farsi et al., 2007). Similarly as previously observed with other fruits, the phenolic compounds responsible for its antioxidant capacity (mainly rutin, catechin, and chlorogenic acid) are usually bound to cell walls with those cell walls being the main source of dietary fiber from these fruits (Madrau et al., 2009). However, although drying processes result in increased dietary fiber contents, it also leads to reduced antioxidant capacity (with reductions up to 90% expressed in ascorbic acid equivalents) (Madrau et al., 2009), probably as a consequence of the high temperatures employed during drying. Although numerous studies have reported on the antioxidant capacity of apricots, the variability in the methodologies used to perform the measurements precludes from establishing comparisons between different studies. Determination of the antioxidant capacity by means of ABTS or CUPRAC methods (Kubilay, Mehmet, Mustafa, Saliha, & Resat, 2006), as well as other methodologies like hydroxyl or superoxide radicals (Egea et al., 2006) resulted in high antioxidant capacities, both in fresh and in processed fruits with antioxidant values between 3–31 μmol TEAC/g and 3–52 μmol TEAC/g sample (determined by ABTS and CUPRAC assays, respectively) depending on the apricot variety and conditioning of the samples. In a recent study, the antioxidant capacity and TPC were measured in both early and late maturing varieties and at different ripening stages. Results evidenced greater polyphenol content and antioxidant capacity in greener fruits with TPC between 43.8–59.3 mg GAE/100 g sample in peels and 16.6–52.2 mg GAE/100 g sample in the pulp with average polyphenol contents 2–4 times lower in the pulp in comparison with the peel (similar to what has been previously commented for other fruits). Catechin and quercetin were the main polyphenols in the case of pulp and peel, respectively. Finally, earlier ripening varieties showed lower polyphenol content and antioxidant capacity (Xinguang et al., 2018). Grapes are another fruit commonly ingested in Mediterranean diet whose fiber content reaches 1.2% (Dhingra et al., 2012). In order to study the colonic fermentation of some polyphenols bound to dietary fiber of red grapes, in vitro models were used as well as humans (in vivo). It was demonstrated that the type of cell wall determined the secondary metabolites production. However, most of the grape production is used in wine production, which significantly alters its characteristics (Saura-Calixto et al., 2010). During the process of wine production, grape peels and seeds are usually separated from the pulp to form a by-product commonly known as grape bagasse whose fiber content can reach 50% in some varieties (Botella, De Ory, Webb, Cantero, & Blandino, 2005). Roughly, its principal component is lignin (around 60%) followed by hemicelluloses and cellulose (25% and 10% approximately) with only 2% of pectin (Chinchilla, 1989). Its antioxidant capacity is mainly due to their tannin content, which is mostly distributed along the peel bound to cell walls (Zhu, 2018a). The high antioxidant capacity of grape bagasse (Larrauri, Ruperez, & Calixto, 1996) has led to the development of a new concept of dietary fiber (Saura-Calixto, 1998). The phenolic content in the pulp and the peel represents less than 10% and 28%–35%, respectively, of that from the whole grape (Shi, Yu,

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Pohorly, & Kakuda, 2003). Drying at high temperatures can considerably reduce the polyphenol content, as well as the antioxidant and free radical scavenging properties of grape bagasse similarly as observed before in apricot (Larrauri, Ruperez, & Saura-Calixto, 1997; Larrauri, Sa´nchez-Moreno, & Saura-Calixto, 1998). A comprehensive review on phenolic compounds, fibers and oils from grapes’ seeds and bagasse has been recently published (Beres et al., 2017) and there are many other studies reporting on grape bagasse bioactive compounds with remarkable antioxidant properties (Teixeira et al., 2014; Yu & Ahmedna, 2013; Zhu, Du, Zheng, & Li, 2015). Finally, it is important to highlight the different composition of the bagasse and seeds. While bagasse is richer in proantocianidins and antocianidin glycosides, seeds usually present higher contents of phenolic acids, flavonoids, lignans, and stilbenes, which display greater antioxidant capacity. TPC values up to 628 mg GAE/g have been reported in grape seed extracts (GSE) (Baydar et al., 2004; Baydar, Sagdic, Ozkan, & Cetin, 2006) and between 213 and 1652 mg CE/g in seeds, while lower values have been determined in the skins (66 184 mg CE/ g) (Fontana et al., 2013; Friedman, 2014). Finally, although tomato classification can be a little controversial (as some authors consider it a vegetable), it can be assumed as a fruit according to its seed content. Regarding the fiber content, its percentage can reach values up to 1.2% of dietary fiber, the insoluble fraction being double the soluble one (Dhingra et al., 2012). With regard to the antioxidant capacity, the most abundant phenolic compounds present in cherry tomatoes are hydroxybenzoic and hydroxycinnamic acids, as well as their conjugated esters (such as chlorogenic acid), showing fiber values between 21 and 27 mg/100 g of fresh weight (FW) (Frusciante et al., 2007; Vallverdu´-Queralt, Arranz, Medina-Remo´n, Casals-Ribes, & Lamuela-Ravento´s, 2011). High content of chalcones and flavonones (particularly in tomato sauce), as well as other more complex phenolic compounds (Vallverdu´-Queralt, Ja´uregui, Medina-Remo´n, Andres-Lacueva, & Lamuela-Ravento´s, 2010; Iijima, Suda, Suzuki, Aoki, & Shibata, 2008; Moco et al., 2006) have also been found. The low bioavailability of these compounds may be an issue in some cases, thus limiting their antioxidant capacity. Tomatoes are also rich in carotenoid compound. Bugianesi et al. (2004) (Raffo, La Malfa, Fogliano, Maiani, & Quaglia, 2006) reported that the lycopene and β-carotene plasma levels were not substantially modified after ingestion of fresh and cooked cherry tomatoes. However, a clear raise of naringenin and chlorogenic acid in plasma was observed after ingestion of cooked cherry tomatoes (Bugianesi et al., 2004). In fact, several studies have quantified carotenoids in fresh and cooked tomatoes and reported greater quantities of them after heating, which is due to the release of these compounds from the vegetable cells. Nevertheless, thermal treatments can isomerize or even degrade some carotenoids, although lycopene was seen to become somehow more stable inside tomato matrixes within a wide range of thermal treatments (D’Evoli, Lombardi-Boccia, & Lucarini, 2013). Similar to other fruits, the antioxidant capacity may vary with harvest season, showing a clear relationship between antioxidant synthesis and ripening degree. Raffo et al. (2006) studied the variability in several antioxidant compounds along six different harvesting periods in one year and observed that the greatest variabilities took place in phenolic compounds such as naringenin, routine, and α-tocopherol (Raffo et al., 2006). Furthermore, other studies suggest a strong relationship between color parameters in cherry tomatoes and their antioxidant capacity and lycopene content, especially in the case of crushed tomatoes (Sipos et al., 2017).

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However, to summarize, more studies are needed to really understand the influence of fiber on the activity and bioavailability of dietary antioxidants.

5.2.2 Prebiotic Properties and Body Weight Management Polysaccharides constitute one of the main components of soluble-fermentable dietary fiber and they are able to stimulate the growth of beneficial colonic bacteria (Di Gioia et al., 2014; Marotti et al., 2012). A balanced composition of this microbiota confers several benefits to their host by an optimum modulation of metabolic and immune functions (Di Gioia, Aloisio, Mazzola, & Biavati, 2014; Tremaroli & B€ackhed, 2012). Low molecular weight carbohydrates are regularly ingested as part of the daily diet since they are widely present in fruits and vegetables, as it will be reviewed in Sections 5.2.2 and 5.3.2. One of the most widespread fruits according to its incidence in global diets and consumption is apple. Its fiber content (unpeeled) varies around 2%, being majority of insoluble one (1.8% vs 0.2% soluble) (Dhingra et al., 2012). Pectin polysaccharides (also called pectins) are considered to be the predominant components of dietary fiber in apples (either within the cell-wall matrix or after ethanolic or aqueous extraction). Pectins are a complex group of heteropolysaccharides, which are mainly found in the middle lamella or primary cell walls in a range from 15 to 25 g/100 g (Sun-Waterhouse, Farr, Wibisono, & Saleh, 2008). Moreover, apple pomace, a food by-product of apple juice industry can reach fiber contents of 51%. Its rheological characteristics and viscosity make it feasible to introduce as a cake ingredient yielding cakes with remarkably high fiber contents with excellent properties for body weight management (Sudha, Baskaran, & Leelavathi, 2007). The polysaccharide content (soluble and non-soluble) in watermelon pulp and peel has been widely studied by many authors. Liu, Huang, and Hu (2018) extracted and characterized polysaccharides from yellow watermelon, being glucose, galactose, mannose, xylose, arabinose, and rhamnose the main ones (Liu et al., 2018). The molecular weight of the extracted polysaccharides was approximately 30 kDa. Jovanovic-Malinovska, Kuzmanova, and Winkelhausen (2014) examined diverse fruits to evaluate their content in fructooligosaccharides (FOS) with demonstrated prebiotic activity. Among the different FOS, 1-kestose, nystose, fructofuranosyl nystose, and raffinose oligosaccharide family have aroused interest in the food industry as they have been associated to an improvement in intestinal health ( Jovanovic-Malinovska et al., 2014). In particular, mannitol (0.12 g/100 g) and 1-kestose (0.29 g/100 g) have been detected in watermelon. Romdhane et al. (2017) extracted polysaccharides from watermelon peel, with the following monosaccharide composition: galactose was the predominant one, but others such as arabinose, glucose, rhamnose, mannose, and xylose; glucuronic and galacturonic acids were also present (Romdhane et al., 2017). These polysaccharides were evaluated as antioxidant and hypertensive agents. Several studies have reported on the prebiotic potential of pomegranates. Zhang et al. (2017) studied the combined effect of inulin and a rich-polyphenol pomegranate extract in mice microbiota function and composition, yielding a significant increase of bacterial diversity, contributing to prevent inflammatory processes (Zhang et al., 2017). Furthermore, an increase in Oscillospira suggested that pomegranate can be used as a weight management food (as Oscillospira has been associated to low body mass indexes). Moreover, this combination

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also led to a significant increase in bacterial diversity, contributing to prevent inflammatory processes (Zhang et al., 2017). In another recent research article, pomegranate polysaccharides extracts obtained by means of ethanol precipitation showed excellent prebiotic activity for Lactobacillus and other Bifidobacteria. The authors attributed this positive effect to a synergistic effect of the extracted polysaccharides and the ellagitannins present in pomegranates (Khatib et al., 2017). Recently, Henning et al. (2017) analyzed the effect of ingesting 1000 mg of pomegranate extract daily during 4 weeks in healthy volunteers. Results showed that the number of bacteria from the genus Akkermansia muciniphila were significantly higher in faecal samples from those volunteers who ingested pomegranate extract. These results have a great relevance since A. muciniphila has been associated to a better metabolic status, reduction of type II diabetes, and insulin resistance (Henning et al., 2017). Similarly, Li et al. (2015) showed that both the extract and juice of pomegranate promoted Bifidobacterium and Lactobacillus growth and inhibited the growth of other less desirable strains like Clostridium or Enterobacteriaceae, supporting the potential of adding pomegranate as a powerful prebiotic component in diets (Li et al., 2015). On the other hand, according to its high dietary fiber and phenolic content, some prebiotic characteristics have been attributed to grape bagasse. Some research articles showed its capacity to promote the growth of probiotic microorganisms, as well as to act as a barrier against disrupting factors in the case of Lactobacillus acidophilus (Hervert-Herna´ndez, Pintado, Rotger, & Gon˜i, 2009). It has been also reported that grape bagasse improved the fermentation process, stimulating lactic acid production and reducing fermentation times (Frumento et al., 2013). Similar effects have been reported in the case of Streptococcus thermophilus along fermentation processes (Aliakbarian et al., 2015). Furthermore, a major resistance of probiotic bacteria against digestion processes was achieved using bagasse flour (Casarotti & Penna, 2015). Khaki fruits, which are traditionally grown in Japan, are very astringent until they reach a completely ripe state, when tannins transform into non-soluble crystals. Khaki is a good natural source of vitamins, polyphenols, and dietary fiber (Gorinstein et al., 1994, 1998). It has also been reported that polyphenol and carotenoid contents are higher in the peel rather than in the pulp. A fortified diet in dry peel can be more useful than using dry pulp in terms of both antioxidant and hypocholesterolemic properties, and is therefore much more efficient in antiatherosclerotic diets (preventing atheroma) (Gorinstein et al., 1998, 2001). Therefore, khaki peel, which presents high antioxidant capacity, can be used in the food industry for the development of new food products. Concluding, with regard to the prebiotic potential of cherry tomatoes, a recent study evaluated the soluble fiber extracted from fresh and processed (80°C, 15 min) cherry tomatoes in samples with or without an additional commercial enzymatic treatment with Viscozyme L (multienzyme complex containing a wide range of carbohydrases, including arabanase, cellulase, β-glucanase, hemicellulase, and xylanase). Adhesion studies were carried out showing that all the soluble fibers improved the probiotic adherence (Lactobacillus rhamnosus and Bifidobacterium bifidum) to epithelial cell walls in the intestine (Caco-2 cells). The thermal treatment did not affect the adherence significantly, while the oligofructose content displayed a positive correlative effect between oligosaccharide content and probiotic adhesion (Koh, Kim, Hwang, & Lim, 2013).

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Several low-calorie tomato jams with high dietary fiber content (up to 20 times more dietary fiber than commercial apricot jam) have been developed using tomato fibers. With different contents of sucrose (replaced by stevioside or fructose) and pectin, the jam has lower amounts of sugar and calories, which makes it especially suitable for diabetic patients. Interestingly, the ones that incorporated pectin in their formulations were successfully tested by the sensory panel, though their water activity was higher and may lead to a shorter shelf-life (Belovic, Torbica, Pajic-Lijakovic, & Mastilovic, 2017). However, these jams seem a promising initial step in the use of high-fiber food in terms of body weight management.

5.2.3 Antimicrobial Properties Flavonoids and other phenolic compounds present in fruits and vegetables are often bound to dietary fiber and are also known to be natural antimicrobials against viruses, bacterial, and fungus. For instance, antiviral mechanisms are based on the ability of phenolic compounds to inhibit essential enzymes, preventing virus linkage to cell walls and its further penetration, as well as activating cellular defense mechanisms (Smulders, Nørrung, & Budka, 2013). Sections 5.2.3 and 5.3.3 summarize the main antimicrobial properties of fruit and vegetable extracts and by-products. Pomegranate has been traditionally considered as a protective food against different infections. Howell and D’Souza reviewed several studies dealing with the antibacterial and antiviral properties from different pomegranate parts. Most of these works demonstrated that the highest activities corresponded to ellagic acid and several hydrolysable tannins like punicalagin (Howell & D’Souza, 2013). Houston, Bugert, Denyer, and Heard (2017) have recently demonstrated the antiviral activity of pomegranate peel extract when combined with zinc ions, identifying catechin and gallic acid as the main compounds responsible for pomegranate’s antiviral properties. Furthermore, the antiviral activity also has been ascribed to the tannins present in pomegranate due to their availability to link to viral proteins, thus affecting their enzymatic activity. These phenolic compounds were able to inhibit viral infections such as type 1 virus of human immunodeficiency, simple herpes, and influenza A (Tanveer et al., 2015). On the other hand, methanolic extracts from pomegranate peel showed antibacterial activity against some food-borne pathogens like Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Yersinia enterocolitica. However, a lower efficiency was found against Salmonella enteritidis. Once again, the phytochemical analysis revealed the presence of active inhibitors in peels, which included phenolics and flavonoids mainly responsible for antimicrobial activity according to its capability of link and inactivate proteins from virus and bacteria (Al-Zoreky, 2009). More studies are needed to ascertain how the interaction of these polyphenols with the dietary fiber present in pomegranate affects their antimicrobial properties. Several studies confirmed that persimmon khaki extracts present antiviral activity against a wide range of virus. Kamimoto, Nakai, Tsuji, Shimamoto, and Shimamoto (2014) reported the antiviral activity from persimmon khaki extracts against human norovirus, with tannins being the main compounds responsible for this activity (Kamimoto et al., 2014). Persimmon khaki (Diospyros khaki) contains condensed tannins (Matsuo & Ito, 1978) that have been

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traditionally used as food additives, in medicine and as antiseptic agents in Japan. Furthermore, persimmon extracts have reached a significant reduction (>4 log) in the infectivity of 12 viruses with and without envelope, such as influenza, poliovirus, and norovirus substitutes like feline calicivirus and murine norovirus (Ueda et al., 2013). Noncovalent interactions between tannins and several cell wall polysaccharides that are considered dietary fiber have been reported (Zhu, 2018a), which could provide these khaki fiber fractions with antiviral capacity. Some polyphenol-rich grape extracts have demonstrated antiviral activity against many types of viruses relevant to food and biomedical areas like human norovirus, murine norovirus 1, rotavirus, adenovirus, or hepatitis-C virus (Bak, Truong, Kang, Jun, & Jeong, 2013; Campagna & Rivas, 2010; Li et al., 2012; Lipson et al., 2011; Matias et al., 2010; Sharaf, El-Deeb, & EL-Adawi, 2012). With regard to antimicrobial activity, two commercial GSE were more active than the well-known phenolic compounds like gallic acid and ethyl gallate. Gram-positive bacteria (Enterococcus faecalis, S. aureus, and Streptococcus pneumoniae) were more susceptible to inactivation than Gram-negative bacteria (Moraxella catarrhalis and Pseudomona aeruginosa) (Baydar et al., 2006). Finally, remarkable antibacterial activity of grape skin extracts was shown in another study against E. coli, E. faecalis, S. aureus, and P. aeroginosa at low concentrations (40 μg/mL) and against Klebsiella pneumoniae (50 μg/mL) (Nirmala & Narendhirakannan, 2011). Whether the presence of dietary fiber in these extracts may play a role in the antimicrobial capacity of the polyphenols present remains to be determined.

5.3 VEGETABLES In terms of nutrition, vegetables have many similarities to fruits. Both are high in fiber as well as vitamins, minerals, and antioxidants. However, vegetables have a higher dietary fiber content than fruits, especially of the insoluble fraction richer in cellulose and lignin, as well as gums and mucilage.; Fruits present higher values of simple monosaccharides or pectins (Dhingra et al., 2012; Elleuch et al., 2011) (Fig. 5.1). This can be relevant not only from a structural point of view but also from a nutritional perspective. Soluble fiber is able to increase the viscosity of the stomach contents, thereby allowing down-mixing and absorption of nutrients; insoluble fiber can reduce intestinal transit time and consequently increase the bulk of the food mass (Olson, Gray, & Chiu, 1987). Commonly eaten vegetables offer a range of cell types with diverse cell wall (CW) structures that comprise the majority of available dietary fiber. For example, a commonly ingested root vegetable like potato contains a large number of thin-walled storage parenchyma. Thick secondary CWs occupy 90% of the cross-sectional area in many xylem sclerenchyma cells. Apart from the tissue types found in tubers, root vegetables like carrots contain a lignified ring of cells that effectively limits water transport through the tissues of the root. Onion bulbs have an elevated content of suberin, waxes, and cutin as a result of complex layers of cells. In contrast, leafy vegetables are comprised of thin-walled photosynthetic parenchyma mesophyll cells sandwiched between upper and lower epidermal layers (McDougall, Morrison, Stewart, & Hillman, 1996).

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5.3.1 Antioxidant Activity Peppers have been traditionally considered one of the main vegetable sources of dietary fiber, as well as vitamins and phenolic compounds. Its dietary fiber values may oscillate between 15% and 25% (g fiber/g FW) depending on the variety analyzed (green, yellow, and red Californian sweet peppers) as shown in a comprehensive study carried out by Herna´ndezCarrio´n et al., being insoluble fiber content higher than 90% with regard to the total fiber (Herna´ndez-Carrio´n, Hernando, & Quiles, 2015). The total dietary fiber content of four Mexican varieties was also evaluated. Values were on a range between 22% and 39% of insoluble fiber with barely a 5% content of soluble fiber (both expressed as a percent of total dry matter) (Hervert-Herna´ndez, Sa´yago-Ayerdi, & GONi, 2010). Pectin has also been isolated and concentrated from hot pepper although it does not represent the major contribution to its dietary fiber (15%). Uronic acids as well as galactose and glucose as the major neutral sugars were the principal constitutives. Interestingly, this pectin showed significant reducing power and hydroxyl radical scavenging capability at low concentrations (0.3% m/v and 1 mg/mL, respectively) demonstrating the antioxidant capacity of pepper dietary fiber and the possibility to be incorporated in novel food formulations (Xu, Tai, Wei, Yuan, & Gao, 2017). The main bioactive compounds present in pepper are capsinoids and capsaicinoids, which have been previously attributed to present antioxidant and anti-inflammatory properties, according to their composition. Capsaicinoids are present in many spicy pepper varieties, while capsinoids are mainly present in the sweet ones. Capsinoids are present in lower concentrations than 1 mg/100 g wet weight (Kobata, Todo, Yazawa, Iwai, & Watanabe, 1998; Wu et al., 2009) and have been attributed a remarkable antioxidant capacity (Rosa et al., 2002). Other major compounds present in peppers include ascorbic acid, carotenoids, or flavonoids. All these compounds, when concentrated in different extracts, show similar antioxidant activities to commercial compounds like BHT or α-tocopherol, demonstrating the high potential of these molecules to reduce oxidative damage (Guil-Guerrero et al., 2006). Flavonoids and other polyphenols are the most abundant compounds in sweet and spicy peppers. Numerous studies have identified and quantified phenolic levels in different pepper varieties (Alvarez-Parrilla, de la Rosa, Amarowicz, & Shahidi, 2010; Bae, Jayaprakasha, Crosby, Jifon, & Patil, 2012; Kim et al., 2010; Sgroppo & Pereyra, 2009; Sim & Sil, 2008). Flavonoids are known to present high antioxidant capacity because of the particular arrangement of hydroxyl groups and double bounds between carbons in positions 2 and 3. According to the relationship between structure and antioxidant properties, myricetin and quercetin derivatives seemed to be the most potent antioxidant flavonoids in peppers ( Jeong et al., 2011; Lu et al., 2006; Tonin, Jager, Micke, Farah, & Tavares, 2005). Flavonoid levels may change as a consequence of genetic factors, ripening, and environmental conditions. Although higher flavonoid contents have been generally reported in red fruits (Materska & Perucka, 2005), the green sweet peppers seemed to possess higher phenolic and flavonoid contents, as well as antioxidant capacity (Blanco-Rı´os, Medina-Jua´rez, Gonza´lez-Aguilar, & Ga´mez-Meza, 2013). As flavonoids represent one of the most relevant antioxidant compounds in peppers due to their relative abundance, it is important to be concerned about their mechanisms of transport and absorption across the human intestinal tract. Briefly, flavonoids are often glycosylated in food matrixes and are rarely ingested in their free form, preventing initial degradation of the

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FIG. 5.2 Human bioabsorption of phenolic compounds in combination with high-fiber intakes.

antioxidant components before intestinal digestion. They can be absorbed in both the small or large intestine depending on the removal of the sugars where the flavonoid skeleton is attached by the action of enzymes like glucosidases or microflora, respectively (Del Rio, Costa, Lean, & Crozier, 2010; Denny & Buttriss, 2007; Palafox-Carlos et al., 2011). However, they are generally poorly absorbed in the small intestine as enzymes present are not able to degrade DF. In that sense, degradation and fermentation of glycosylated flavonoids (and to a high extent, most of the phenolic compounds) mostly occur in the large intestine by the action of colonic bacteria. Finally, it has also been found that the type of glycosylation determines not only the site and extent, but also the mechanisms of absorption (Dhingra et al., 2012b). To sum up, schematic bioabsorption mechanisms of phenolic compounds in presence of DF have been represented in Fig. 5.2. On the other hand, there are some remarkable differences on the antioxidant composition of colored varieties. While carotenoid content is higher in red and yellow varieties, contradictory results have been reported on the ascorbic acid content (Zhang & Hamauzu, 2003). The ripening degree, when expressed in wet weight, seemed to increase the level of bioactive compounds (phenolics, ascorbic acid, and carotenoids) and antioxidant capacity. However, when measured in dry weight, the phenolic content usually diminished along with ripening (Deepa, Kaur, George, Singh, & Kapoor, 2007). These results were confirmed by another ulterior research article (Ghasemnezhad, Sherafati, & Payvast, 2011) where the antioxidant capacity was seen to increase in colored peppers along with ripening, while both phenolic and ascorbic acid contents diminished. Significant differences also have been observed between varieties. Green peppers at low degrees of maturity are the ones with highest

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polyphenolic level while ripe red peppers displayed higher ascorbic acid and provitamin A contents (Marı´n, Ferreres, Toma´s-Barbera´n, & Gil, 2004). In contrast, capsaicin content diminished along with ripening, while total carotenoids, particularly β-carotene levels, increased (Deepa et al., 2007). Regarding the bioavailability of carotenoids, it is important to highlight their hydrophobic nature, which needs solubilization by bile acids and digestive enzymes. For that, a previous release from the food matrixes (mainly cell walls in the case of dietary fiber) is required, which can partly occur during food processing and mastication (Khachik et al., 2002; Palafox-Carlos et al., 2011) but, in contrast with flavonoids, not during digestion (at least in the human ileum) (Hoffmann, Linseisen, Riedl, & Wolfram, 1999; van het Hof, West, Weststrate, & Hautvast, 2000). Furthermore, high dietary fiber contents seem to be able to entrap lipids and bile salts, thus avoiding micelle formation and consequently interfering in the proper absorption of carotenoids, reducing their bioavailability (Palafox-Carlos et al., 2011) (Fig. 5.2). Other relevant vegetables popular in diets are carrots, which are one of the most important root vegetables rich in bioactive compounds like carotenoids and dietary fibers. Contents are above 2.5%, with 90% of this being insoluble fiber (2.3% vs 0.2% soluble) presenting significant health-promoting properties. However, the crystalline form of carotenoids in carrot plus the structure of some pectin-like fibers can reduce its relative bioavailability, ranging only between 19% and 34% of bioavailability with regard to purified β-carotene (Porrini & Riso, 2008; Zhou, Gugger, & Erdman Jr, 1996). In a study carried out in 2008, the antioxidant capacity of high dietary fiber powder produced from carrot peels was evaluated. The different preparation protocols of the samples (hot-air drying and blanching) reduced the content in β-carotene and phenolic compounds (with a significant reduction using the hot-air drying process), hence decreasing the antioxidant capacity of the final product (although only to a low extent). In contrast, these treatments did not have any negative effect in the dietary fiber content. This becomes especially relevant from an industrial point of view since peels, which are an abundant by-product, could be further processed using conventional preparation methods (Chantaro, Devahastin, & Chiewchan, 2008) to add value to the product. Phenolic compounds and their antioxidant properties and distribution also have been analyzed in carrots, finding that hydroxycinnamic acids and their derivatives were the main compounds present. Chlorogenic acid represented 42.2%–61.8% of total phenolic compounds detected. Finally, it is important to highlight that the phenolic contents were distributed distinctly in the different parts of the vegetal tissue, similarly to other fruits or vegetables (peel > phloem > xylem) (Sharma, Karki, Thakur, & Attri, 2012; Zhang & Hamauzu, 2004). However, as it has been previously mentioned in the introduction, bound polyphenols can be released from cell walls as shown in testing by Padayachee et al. (2013) by the addition of some disruptors like acidified methanol or gastric conditions. Methanol released up to 30% of polyphenols as well as 20% of anthocyanins. In contrast, simulated gastric and intestinal digestions released only 2% of phenolic acids, which were protected until colonic fermentation (Padayachee et al., 2013). Onion is another root vegetable widely consumed in Europe, both fresh and in a processed form ( Jaime et al., 2002). As mentioned before, suberin, waxes, and cutin represent the majority of its dietary fiber (McDougall et al., 1996), reaching 31% (in one of the three varieties studied) as a percentage of dry matter ( Jaime et al., 2002). Interestingly, onion DF display a

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higher soluble ratio in comparison with other vegetables. This can explain the differences in the metabolism and physiological effects reaching 1:1 values (soluble:insoluble) in the inner layers of some of the varieties studied, thus presenting higher soluble antioxidant contents that are easily released and absorbed( Jaime et al., 2002). Contrarily, the insoluble dietary fiber (structural carbohydrates, mainly cellulose and polyuronides with relevant glucose, galactose, and xylose contents) was concentrated in the outer layers ( Jaime et al., 2002). The antioxidant content in onions has been the focus of several studies because of its many benefits for human health, like preventing and reducing the associated risks of several diseases (Helen, Krishnakumar, Vijayammal, & Augusti, 2000; Singh et al., 2009). Different solvents have been tested to produce extracts from red onion (Allium cepa) peels, and ethyl acetate showed the highest phenolic and antioxidant capacity (cf. Table 5.1), with similar or even better results when compared to commercial BHT. In contrast, hydrophilic extracts (obtained by water) showed the lowest antioxidant capacities. Furthermore, remarkable free-radical scavenging activities against hydroxyl, superoxide, or nitric oxide radicals (among others) have been demonstrated (Singh et al., 2009). The total phenolic, antioxidant, and scavenging activities of different parts from four onion varieties (red, violet, white, green) have been evaluated. The TPC was much higher in the outer layers and had a narrow correlation with the antioxidant activity measured by the β-carotene assay. The highest values were obtained in the outer layers of red onions, with a TPC of 74.1 mg GAE/g and AOA of 84.1%, while the white variety showed the lowest values (7.6 and 23.4 mg GAE/g respectively in the outer layers). These results were consistent with the IC50 and EC50 obtained by the DPPH method in the same study (Prakash, Singh, & Upadhyay, 2007). A similar work has been reported by Benkeblia et al. (McCarthy et al., 2013). Once again, they found that the green variety had the lowest values (30 mg GAE/100 g), whereas the purple and red varieties had the highest (45 mg GAE/100 g). In all cases, very similar results were obtained in the DPPH assay and H2O2 scavenging activity, suggesting that apart from the phenolic compounds, the presence of sulfur compounds played an important role in the antioxidant capacity (Benkeblia, 2005).

5.3.2 Prebiotic and Body Weight Management In the case of vegetables as prebiotic sources, FOS are the main compounds with prebiotic properties present in a wide range of them, such as artichokes, onions, garlic, or asparagus (Al-Sheraji et al., 2013; Sangeetha, Ramesh, & Prapulla, 2005). Both in vitro and in vivo experiments have been carried out to find out how these FOS are metabolized by bacteria in the large intestine. In vitro experimental studies indicate that several short-chain fatty acids (SCFAs) enhance bacterial survival and activity(Van Laere, 1997). Despite the high-fiber content present in carrot and derived food products, not many prebiotic properties have been associated to this vegetable. However, in a study carried out by Italian researchers, a synergetic effect of carrot juice supplemented with two different strains of Lactobacillus spp. and inulin or FOS was observed. Results showed that both strains were capable of growing in carrot juice, making this juice as a functional health alternative (Nazzaro, Fratianni, Sada, & Orlando, 2008).

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With respect to the prebiotic activity of onions, some optimized ultrasound techniques (varying temperature and extraction times) have been developed to successfully extract significant amounts of FOS with demonstrated prebiotic activity (Bali, Panesar, Bera, & Panesar, 2015; Charalampopoulos & Rastall, 2012; Rastall, 2010), reaching values of 5 g FOS/100 g FW in onion and above 6 g FOS/100 g FW in scallion ( Jovanovic-Malinovska, Kuzmanova, & Winkelhausen, 2015). With regard to prebiotic activity, gourd family vegetables are known to present high dietary fiber contents with prebiotic activity (Sreenivas & Lele, 2013). Gourds are the fruits of some flowering plant species from the Cucurbitaceae family. The five varieties studied were seen to promote in vitro growth of both Lactobacillus and Bifidobacterium strains (Lactobacillus fermentum and Bifidobacterium breve) by the production of high contents of SCFA with prebiotic abilities such as butyric and propionic acids (Sreenivas & Lele, 2013). Continuing with prebiotic capacity, inulin is one of the most relevant carbohydrates in vegetable systems. Inulin is a plant-derived carbohydrate with the benefits of soluble DF. It cannot be digested or absorbed in the small intestine, but is fermented in the colon by beneficial bacteria. Functioning as a prebiotic, inulin has been associated with enhancing the gastrointestinal system and immune system (Lo´pez-Molina et al., 2005). In addition, it has been shown to promote other beneficial aspects for human health (reduced cholesterol levels or increased absorption of ions) (Coudray et al., 1997; Niness, 1999). In particular, artichoke is one of the most relevant sources of inulin as shown in a study where a high molecular weight inulin was isolated from artichoke agro-industrial wastes (Lo´pez-Molina et al., 2005). Its particular health benefits were demonstrated in an extensive microbiological study showing significant effect on B. bifidum as well as in mixed cultures of colonic bacteria. This makes artichoke inulin a versatile ingredient with a wide range of food applications and reduced costs, as it came from an agro-industrial waste (Lo´pez-Molina et al., 2005). On the other hand, capsinoids, traditionally present in several varieties of peppers, may display several health properties like anti-inflammatory activity. The capacity to promote energy and fat consumption and supress fat accumulation makes them very interesting compounds for the nutrition and pharmacology areas as a weight control factor (Ohnuki et al., 2001).

5.3.3 Antimicrobial Activity As mentioned, flavonoids are one of the most representative phenolic compounds present in vegetables; often bound to dietary fiber, they are rarely ingested in their free form (PalafoxCarlos et al., 2011). Flavonoids are classified in a wide range of molecules like flavones, flavanones, or chalcones, among the most representative ones. For example, quercetin, catechin, or rutin, which can be found in several vegetable-like foods, have been shown to possess activity against seven types of viruses, including herpes simplex virus or poliovirus (Middleton Jr, 1986; Selway, 1986). With regard to antibacterial activity, administration of quercetin was able to reduce mortality provoked by Shigella infections (Vijaya & Ananthan, 1996) while some isoflavones were able to protect mice against Salmonella typhimurium (Dastidar et al., 2004). However, it is important to highlight that all these benefits in health were achieved by dosing individuals with concentrations higher than those naturally present

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in food. Moreover, many discrepancies exist between reports of flavonoid antibacterial activity, so more studies are needed to corroborate these results (Cushnie & Lamb, 2005). The antiviral properties of peppers have been mainly attributed to cis-capsaicin, a powerful molecule against several types of viruses (Khan, Mahmood, Ali, Saeed, & Maalik, 2014). However, spicy peppers seemed to have the most powerful antiviral activity. Some methanolic extracts from peppers have been evaluated against simple Herpes virus, showing that low concentrations of these extracts (25 μg/mL) predominantly composed of phenolic compounds, displayed a remarkable antiviral activity, making its combination with commercial treatments feasible (Hafiz, Mubaraki, Dkhil, & Al-Quraishy, 2017). To the best of our knowledge, no antiviral or antimicrobial activity has been tested in high-fiber carrot extracts. However, an interesting compound was identified and isolated from carrot roots. This compound (6-methoxymellein) has a broad antimicrobial spectrum and inhibits the growth of several fungi, yeasts, and bacteria like Alternaria alternata, Botrytis cinerea, or Aspergillus fumigatus (Kurosaki & Nishi, 1983). In the case of onions, a fructan isolated from the hot water extract of a Welsh onion (Allium fistulosum L.) has proved to have antiviral activity against influenza A virus. Although this fructan did not show any antiviral activity in vitro, it seemed to affect virus replication in vivo when administered to mice. However, further studies need to be carried out, as the antiviral mechanism of the polysaccharide seemed to be dependent on the host immune system (Lee et al., 2012).

5.4 GRAINS AND CEREALS Apart from their protein and starch content, cereals play an essential role in our diets because of their high content in dietary fibers like arabinoxylans, arabinogalactans, β-glucans, cellulose, lignin, and other minor micronutrients like phenolic acids, flavonoids, carotenoids, vitamins, and phytosterols (Makowski, Rosicka-Kaczmarek, & Nebesny, 2015). In order to make a first classification of the main types of DF present in grains and cereals, wheat, barley, oats, and maize contribute to approximately 50% of DF intake in Western countries (Belderok, 2000; Lambo et al., 2005). The amount of DF in whole grains range from 12% in oats up to 27% in barley, with a much higher proportion of insoluble vs soluble fiber (7–9:1) (Vitaglione, Napolitano, & Fogliano, 2008) mainly constituted by glucans such as β-glucans, arabinoxylans (AX), xylooligosaccharides (XOS), and lower contents of pectins (Vitaglione et al., 2008) (Fig. 5.1).

5.4.1 Antioxidant Capacity Regarding the antioxidant capacity attributed to phenolic compounds bound to the dietary fiber in grains, some phenolic compounds have been commonly found linked to these structures. Ferulic acid (one of the most abundant, usually found in the outer layers of grains) was bound to arabinoxylans by acid acetylation(Hatfield, Ralph, & Grabber, 1999; Saura-Calixto & Dı´az-Rubio, 2007).

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Phenolic acids are present in all types of cereals and plants, and are mainly derived from hydroxybenzoic and hydroxycinnamic acids like vanillic, gallic, caffeic, ferulic, p-coumaric, or sinapic (Gani, Wani, Masoodi, & Hameed, 2012). Many hydroxycinnamic acids are known to exhibit a high antioxidant capacity (Kikuzaki, Hisamoto, Hirose, Akiyama, & Taniguchi, 2002) and are able to prevent oxidation in processed meals. According to several studies, phenolic compounds present higher antioxidant capacity than carotenoids or even some vitamins like vitamin C or E (Rice-evans, Miller, Bolwell, Bramley, & Pridham, 1995; Rice-Evans, Miller, & Paganga, 1996). However, the phenolic content is quite low in the cereals’ endosperm although it increases considerably in the external layers of the grains (Awika & Rooney, 2004; Fa˘rcaş et al., 2013; Gani et al., 2012; Madhujith, Izydorczyk, & Shahidi, 2006). Whole grains are also a great source of sulphated amino acids, which are also able to increase the antioxidant capacity. The antioxidant capacity of cereals has been mainly tested in vitro and only a few in vivo studies, mostly on colored grains, are available (Fardet, Rock, & Remesy, 2008). Phenolic acids are predominantly linked to cell walls (Adom & Liu, 2002; Liyana-Pathirana & Shahidi, 2006). Linked polyphenols have greater benefits to human health; they are not affected by the gastric digestion and are absorbed with the cell wall components and transferred to blood plasma after intestinal microflora digestion (Andreasen, Kroon, Williamson, & Garcia-Conesa, 2001; Andreasen, Landbo, Christensen, Hansen, & Meyer, 2001) (Fig. 5.2). The amount of phenolic compounds found in wheat is variable in the existing literature, which might be a consequence of the differences in the extraction protocols used (Liyana-Pathirana & Shahidi, 2006; Mattila, Pihlava, & Hellstr€ om, 2005; Zhou, Robards, Helliwell, & Blanchard, 2004; Zhou, Su, & Yu, 2004). According to this, corn, which presented a higher polyphenol content (15.55  0.60 μmol GAeq/g raw grain) than wheat (7.99  0.39 μmol GAeq/g raw grain), oats (6.53  0.19 μmol GAeq/g raw grain), and rice (5.56  0.17 μmol GAeq/g raw grain); corn also had a higher antioxidant capacity (Table 5.1) and was related to the relative abundance of phenolic bounded forms (from 62% in rice up to 85% in corn) (Adom & Liu, 2002). Ferulic contents in corn were also superior to those detected in other cereals (Adom & Liu, 2002). On the other hand, barley is considered as a fundamental ingredient in functional foods. (Holtekjølen, Bævre, Rødbotten, Berg, & Knutsen, 2008) This is because of its high content in bioactive compounds, in particular tocopherols, tocotrienols, and β-glucans ( Jadhav, Lutz, Ghorpade, & Salunkhe, 1998), as well as diverse phenolic compounds derived from benzoic and cinnamic acids, like proantocianidins, flavonols, flavones, and amino-phenolic compounds (Goupy, Hugues, Boivin, & Amiot, 1999; Hernanz et al., 2001). Similar to other cereals, free and conjugated water-soluble phenolic content is lower than the cell-wall linked polyphenols, having a positive effect in intestinal human health (Madhujith & Shahidi, 2009). Many studies show that the water-soluble phenolic fraction in barley presents significantly higher antioxidant capacity than the non-soluble fraction (Goupy et al., 1999; Kim et al., 2007; Madhujith et al., 2006; Madhujith & Shahidi, 2007, 2009; Zhao et al., 2008). Finally, proantocianidins (condensed tannins), which present a remarkable antioxidant capacity, can also be present in cereals. Great diversity and different ranges of concentrations of these compounds have been identified in different types of cereals, especially in colored grains (Zhu, 2018b). Nevertheless, not only whole or raw grains are useful for their antioxidant capacity. A commonly known and generated food by-product, beer bagasse, can present beneficial properties too, which may re-valorise this residue. The most abundant phenolic acids usually

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found in beer bagasse are ferulic and p-coumaric acids, with concentrations ranging between 1860–1948 and 565–794 μg/g respectively; the majority are present in bounded forms (Forssell et al., 2008; McCarthy et al., 2013). It has been reported that most hydroxycinnamic acids (which include caffeic acid, sinapic acid, ferulic acid, and p-coumaric acid amongst others) can show a powerful antioxidant capacity (Kikuzaki et al., 2002). Moreover, it is important to highlight that the variety of malt from which the bagasse is obtained plays a crucial role in the type and quantity of polyphenols extracted (Santos, Jimenez, Bartolome, Go´mezCordoves, & del Nozal, 2003). However, it is important to remark that, as mentioned, some environmental factors like pH, ionic strength, temperature, or polyphenol ratios may disrupt the linkage between cell wall polysaccharides and polyphenols. For example, enzymatic degradation of barley β-glucans greatly diminished the binding capacity with vanillin-derived phenolic compounds (Simonsen et al., 2009). In this sense, it remains crucial to investigate and analyze not only the structure and relative abundance of phenolic compounds bound to DF as well as their antioxidant capacity, but also to take into account external factors that may disrupt the linkage and substantially decrease the final bioavailability.

5.4.2 Prebiotic Properties and Body Weight Management AX is one of the major components in cereals, and it is usually linked to cellulose by hydrogen bonds (Mandalari et al., 2005). A great proportion of the water-soluble fraction of this AX can be fermented in the large intestine by the colonic microbiota (especially Lactobacillus and Biphidobacteria). This hydrolysis yields XOS and arabinoxylooli saccharides with different polymerization degrees, but all of them show remarkable prebiotic activity (Berger et al., 2014; Broekaert et al., 2011; Wang, Sun, Cao, & Wang, 2010). In fact, enzymes specific for this conversion of AX into XOS have been identified in some bacteria (Grootaert et al., 2007). Also of note, the prebiotic effect is closely related to the AX structure. Their possible combinations of the different AX depend on their water affinity and purity, having a remarkable effect in cecal butyrate levels and pH levels (Damen et al., 2011). The majority of the physicochemical characteristics of AX are due to its capability to form ester links with phenolic acids, mainly ferulic and p-coumaric, highlighting the antiinflammatory and antioxidant properties of ferulic acid (Adam et al., 2002). On the other hand, lignin is a major component that must be taken into consideration. Recent studies have assessed an increase in the survival of some biphidobacteria in colonic models with respect to a standard glucose control as substrate (Niemi et al., 2013). Moreover, phenolic intermediates were present in this study, which may be a consequence of the partial degradation of lignin, suggesting the potential of this biphidobacteria to metabolize lignin (Niemi et al., 2013). The importance of the starchresistant fraction should also be considered. This fraction is metabolized by colonic bacteria in the large intestine, yielding SCFAs like acetate, propionate, and butyrate, widely connected with intestinal health (Sajilata, Singhal, & Kulkarni, 2006; Sharma & Yadav, 2008; Tharanathan & Mahadevamma, 2003). Several clinical tests have evidenced the prebiotic capacity of whole grains. Carvalho-Wells et al. (2010) carried a test to evaluate the prebiotic potential of whole corn and observed that, after 3 weeks, there was a significant increase in the biphidobacteria excreted through the stool in comparison with the placebo, confirming the

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raised hypothesis (Carvalho-Wells et al., 2010). Furthermore, Costabile et al. (2007) carried out a similar study testing the capability of whole wheat as well as wheat bran, showing a clear prebiotic effect in both cases with respect to the placebo control (Costabile et al., 2007).

5.4.3 Antiviral and Antimicrobial Activity There is very scarce information regarding the antimicrobial and antiviral activity of cereals related to their fiber content. Some primary metabolites (4-hydroxystyrene, 3-methoxy-4-hydroxystyrene, and 3-methoxy-4-acetoxystyrene) with antimicrobial activity against Bacillus subtilis, E. coli, Aspergillus candidus, and Cladosporium herbarum have been isolated from wheat root exudate together with amino acids and sugars (Kobayashi, Kim, & Kawazu, 1996).

5.5 OTHER PROPERTIES (ANTICANCER, ANTIINFLAMMATORY, ETC.) Apart from the main benefits of DF extensively described in the previous sections, several DNA-protective activities as well as anticancer and anti-inflammatory effects have been attributed to DF to a lesser extent. This will be reviewed in this section because of their relevance for human health. In particular, the scientific community has focused most efforts on cancer due to its particular high incidence in Western countries. Research efforts have led to an expected decline in cancer-related death rates because of early detection and palliative treatment improvement (Edwards et al., 2014). For these reasons, preventive measures, like ingesting diets rich in DF, can diminish several types of cancer such as colorectal or breast cancer (Hague et al., 1993). DF’s link to cancer prevention is mainly related to the formation of some secondary metabolites (SCFAs like butyrate as previously mentioned) that are derived from colonic bacteria fermentation of the DF, which may induce apoptosis in tumoral colonic cells (Hague et al., 1993). However, a large group of studies have failed to demonstrate the relationship between DF and colorectal cancer. In this sense, a prospective study of a population with low fruit and vegetable intake showed significant reduction in colorectal cancer risk when fruit and vegetable intake was increased. No association was seen with cereal DF, even with the consumption of substantially greater amounts (Terry et al., 2001). In the case of breast cancer, reducing the levels of estrogen in blood circulation may decrease breast cancer risk by DF (Goldin et al., 1982). There has been much controversy about the topic as many studies showed no significant reduction of breast cancer risk related to DF intake (Graham et al., 1992; Shikany et al., 2011). A recent complete review of 24 epidemiologic studies revealed a 12% diminished risk of breast cancer with a dairy fiber intake of at least 30 g/day with increased prevalence in postmenopausal women (Chen et al., 2016). Several compounds often present and studied in fruits such as tomato, pomegranate, or khaki showed interesting anti-inflammatory or anticancer properties. Concretely, lycopene (present in watermelon and tomato) can isomerize to its -trans form after light, thermal, or chemical processes, and is potentially capable to prevent numerous chronic diseases like

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diabetes, osteoporosis, or oncogenesis, as well as acting as an anti-inflammatory agent (Kim et al., 2014). Jovanovic-Malinovska et al. (2014) established a prebiotic consumption of FOS (highly present in watermelon) in 8–10 g/day so as to reduce osteoporosis risk while 15–20 g/day has been fixed in order to help prevent constipation ( Jovanovic-Malinovska et al., 2014). In a system developed for evaluating DNA damage by copper, H2O2, and DNA (among other compounds), the reduction of the two peak values and integral areas was observed with increased pomegranate extract (PEs) concentration. Rich in DF, PEs had a powerful DNA damage prevention ability in different experimental systems (Guo et al., 2007). Moreover, the capability of peel and pulp pomegranate extracts to reduce LDL oxidation was tested positively, concluding that pomegranate peel could be considered as a potential source of LDL antioxidants, which may prevent atheroma and cardiovascular diseases (Li et al., 2006). Kawase et al. (2003) obtained different extracts from persimmon peel, also rich in DF, which presented high radical scavenging activity, suggesting their potential as antitumoral agents (Kawase et al., 2003). In the case of vegetables, other relevant compounds previously mentioned present several beneficial properties that are relevant. In particular, capsaicin (found in peppers) has been demonstrated to induce apoptosis in many types of malignant cell lines, including colon adenocarcinoma, pancreatic cancer, hepatocellular carcinoma, prostate cancer, breast cancer, and many others. However, the mechanism whereby capsaicin induces apoptosis in cancer cells is not yet completely elucidated; it involves common apoptosis reactions (like intracellular calcium increase and/or reactive oxygen species generation). In addition, capsaicin shows antitumor activity in vivo by reducing the growth of many tumors induced in mice (Dı´az-Laviada & Rodrı´guez-Henche, 2014). Moreover, aqueous extracts from black pepper have been shown to be potential immunomodulatory agents. Black pepper seemed to play proproliferative and proinflammatory functions, as well as anticarcinogenic effects via promoting the cytotoxic activity of NK cells (Majdalawieh & Carr, 2010). High concentrations of carotenoids, especially β-carotene in carrot roots (traditionally used for making salads and curries in India), may interact with the DF of these vegetables and seems to be responsible for their ability to inhibit cancers, free radical scavengers, cardiovascular disease associated-risks, and mutagenic factors (Madhavi, Deshpande, & Salunkhe, 1995; Sharma et al., 2012). Other authors claim that carrot intake may also enhance the immune system, protect against stroke, osteoporosis, cataracts, arthritis, bronchial asthma, and urinary tract infection due to its high β-carotene and fiber contents (Beom, Yong, & Myung, 1998; Seo & Yu, 2004; Sun, Mihyang, & Song, 2001). As previously mentioned, regular consumption of onions is associated with a reduced risk of neurodegenerative disorders, cancer, cataracts, ulcer development, and symptomatic reduction of osteoporosis as well as heart disease prevention by inhibition of lipid peroxidation and lowering of LDL cholesterol levels (Kaneko & Baba, 1999; Kawaii, Tomono, Katase, Ogawa, & Yano, 1999). Singh et al. demonstrated that methanolic fractions extracted from red onion peels by means of ethyl acetate presented significant antimutagenic properties (Singh et al., 2009). Four onion extracts from different varieties showed the ability to provide protection against DNA damage caused by reactive oxygen species (especially the red onion

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variety). It is important to highlight that the study, in correlation with other previous work, suggested a triple synergistic action of phenols in scavenging ROS, repairing DNA radicals, and metal chelation (Prakash et al., 2007; Zhao et al., 2005). Finally, although cereal DF has not been directly related to prevention of some types of cancer like colorectal cancer (Terry et al., 2001), some other health benefits have been attributed to cereal fiber intake. For example, the intake of a mixture of FOS and inulin has produced significant reductions in disease severity indexes, reduction in proinflammatory immune markers, and a reduction in calprotectin, an abundant neutrophil protein found in both plasma and stool that is markedly elevated in patients with inflammatory bowel disease (Konikoff & Denson, 2006). Furthermore, observation indicates that XOS fermentation takes place in colon’s distal parts where most of colon cancers occur. Therefore, this SCFA production would contribute to palliate the incidence of this type of cancer (Grootaert et al., 2009). Moreover, bound phytochemicals (from 58% bounded phytochemicals in oats to 87%–90% in corn and wheat) could survive stomach and intestinal digestion to reach the colon. This may partly explain the mechanism of grain consumption in the prevention of colon cancer, other digestive cancers, breast cancer, and prostate cancer, which is supported by epidemiological studies. We have seen some controversy with cereal DF and colorectal cancer prevention, so further studies are needed (Adom & Liu, 2002; Terry et al., 2001). Bound polyphenols present in whole barley extracts may explain its protective effect against LDL cholesterol oxidation, which can be in part attributable to the Cu (II) chelation potential of the phenolic acids, thus reducing the chances of developing atheroma in the arteries. These extracts managed to show remarkable inhibition activity of Caco-2 colon cancer cell proliferation after 4 days, consequently reducing colorectal cancer prevalence (one of the highest cancer death indexes in North America) (Madhujith & Shahidi, 2007). Brewer Spent Grain (BSG extracts from barley malt) may present anticancer, antiatherogenic, and antiinflammatory effects as a consequence of a reduction in the DNA damage caused by different oxidative radicals (H2O2, SIN-1, etc.). This could inhibit the oxidation of LDL reducing cardiovascular disease associated-risks (McCarthy et al., 2013). On the other hand, it was reported that hydroxycinnamic acid derivatives (HADs) (which are commonly present in cereals) are inhibitors of NF-κB activation. Phytosteryl ferulates (one of HADs) probably have potential antiinflammatory properties. Tumor promotion is closely linked to inflammation and oxidative stresses, and it is hence likely that such compounds with strong anti-inflammatory and antioxidative activities act as antitumor promoters, although further studies are also needed (Nagasaka et al., 2007). Another interesting study showed a decrease in breast cancer risk in patients with primary breast carcinoma, suggesting cereal fiber intake (as well as a higher intake of onion and garlic) as a protective factor (Challier, Perarnau, & Viel, 1998). In summary, consumption of fiber-rich fruits and vegetables has been seen to improve human health by decreasing the risk of several types of cancer. The intake of cereal fiber has been reported to present anticancer properties, although these results have been more controversial. Furthermore, there are other beneficial properties in the various types of DF contained in foods, like antiinflammatory properties, DNA protective activities, and preventive properties against several cardiovascular and neurodegenerative diseases; therefore, a greater consumption of DF-rich food should be encouraged.

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5.6 CONCLUSIONS AND FUTURE OUTLOOK The most relevant beneficial properties of DF for human health have been reviewed. Fruits, vegetables, and cereals have been shown to make the highest positive contributions of DF in the world’s human population. DF has demonstrated several beneficial properties for human health, highlighting the prebiotic and body weight management ability of the different polysaccharides (especially FOS, XOS, and pectins) mainly present in fruits and vegetables. Moreover, a wide range of phenolic compounds bound to DF have been seen to resist digestion processes and consequently maintain all their beneficial properties (antioxidant, antiinflammatory, and antitumoral mechanisms). Along the whole gastrointestinal tract, these compounds can be released by the action of several intestinal enzymes and/or fermented by probiotic bacteria. Furthermore, some synergistic effects have been reported for the combination of polyphenolic compounds and DF. High intakes of DF (more than 10 g/day) from the different sources mentioned (mainly vegetables and fruits, as cereals can be a little controversial) have been reported to significantly reduce carcinoma risk, although further research must be carried out in order to reinforce this affirmation. Finally, it is important to highlight that the majority of nutrients and antioxidant compounds, such as vitamins in fruits that are often bound to DF, are found in the peels and external layers of vegetables and cereals. This highlights the importance of preserving peels and consuming whole grain alternatives (in the case of cereals) in the final products, so as to have a significant health effect.

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Verghese, M., Rao, D., Chawan, C., Williams, L. L., & Shackelford, L. (2002). Dietary inulin suppresses azoxymethaneinduced aberrant crypt foci and colon tumors at the promotion stage in young Fisher 344 rats. The Journal of Nutrition, 132(9), 2809–2813. Vijaya, K., & Ananthan, S. (1996). Therapeutic efficacy of medicinal plants against experimentally induced shigellosis in guinea pigs. Indian Journal of Pharmaceutical Sciences, 58(5), 191. Vitaglione, P., Napolitano, A., & Fogliano, V. (2008). Cereal dietary fiber: a natural functional ingredient to deliver phenolic compounds into the gut. Trends in Food Science & Technology, 19(9), 451–463. Wang, J., Sun, B., Cao, Y., & Wang, C. (2010). In vitro fermentation of xylooligosaccharides from wheat bran insoluble dietary fiber by Bifidobacteria. Carbohydrate Polymers, 82(2), 419–423. Wang, S., & Zhu, F. (2016). Antidiabetic dietary materials and animal models. Food Research International, 85, 315–331. Wang, S., & Zhu, F. (2017). Dietary antioxidant synergy in chemical and biological systems. Critical Reviews in Food Science and Nutrition, 57(11), 2343–2357. Willett, W. C., Sacks, F., Trichopoulou, A., Drescher, G., Ferro-Luzzi, A., Helsing, E., et al. (1995). Mediterranean diet pyramid: a cultural model for healthy eating. The American Journal of Clinical Nutrition, 61(6), 1402S–1406S. Winston, G. W., Regoli, F., Dugas, A. J., Fong, J. H., & Blanchard, K. A. (1998). A rapid gas chromatographic assay for determining oxyradical scavenging capacity of antioxidants and biological fluids. Free Radical Biology and Medicine, 24(3), 480–493. Wu, S. -J., Chang, S. -P., Lin, D. -L., Wang, S. -S., Hou, F. -F., & Ng, L. -T. (2009). Supercritical carbon dioxide extract of Physalis peruviana induced cell cycle arrest and apoptosis in human lung cancer H661 cells. Food and Chemical Toxicology, 47(6), 1132–1138. Xinguang, F., Wenxiao, J., Xiaomei, W., Jiankang, C., & Weibo, J. (2018). Polyphenol composition and antioxidant capacity in pulp and peel of apricot fruits of various varieties and maturity stages at harvest. International Journal of Food Science & Technology, 53(2), 327–336. Xu, H., Tai, K., Wei, T., Yuan, F., & Gao, Y. (2017). Physicochemical and in vitro antioxidant properties of pectin extracted from hot pepper (Capsicum annuum L. var. acuminatum (Fingerh.)) residues with hydrochloric and sulfuric acids. Journal of the Science of Food and Agriculture, 97(14), 4953–4960. Yu, J., & Ahmedna, M. (2013). Functional components of grape pomace: their composition, biological properties and potential applications. International Journal of Food Science & Technology, 48(2), 221–237. Zhang, D., & Hamauzu, Y. (2003). Phenolic compounds, ascorbic acid, carotenoids and antioxidant properties of green, red and yellow bell peppers. Journal of Food Agriculture and Environment, 1(2), 22–27. Zhang, D., & Hamauzu, Y. (2004). Phenolic compounds and their antioxidant properties in different tissues of carrots (Daucus carota L.). Journal of Food Agriculture and Environment, 2, 95–100. Zhang, S., Yang, J., Henning, S. M., Lee, R., Hsu, M., Grojean, E., et al. (2017). Dietary pomegranate extract and inulin affect gut microbiome differentially in mice fed an obesogenic diet. Anaerobe, 48, 184–193. Zhao, C., Dodin, G., Yuan, C., Chen, H., Zheng, R., Jia, Z., et al. (2005). “In vitro” protection of DNA from Fenton reaction by plant polyphenol verbascoside. Biochimica et Biophysica Acta (BBA)-General Subjects, 1723(1-3), 114–123. Zhao, H., Fan, W., Dong, J., Lu, J., Chen, J., Shan, L., et al. (2008). Evaluation of antioxidant activities and total phenolic contents of typical malting barley varieties. Food Chemistry, 107(1), 296–304. Zhou, J. -R., Gugger, E. T., & Erdman, J. W., Jr. (1996). The crystalline form of carotenes and the food matrix in carrot root decrease the relative bioavailability of beta-and alpha-carotene in the ferret model. Journal of the American College of Nutrition, 15(1), 84–91. Zhou, K., Su, L., & Yu, L. (2004). Phytochemicals and antioxidant properties in wheat bran. Journal of Agricultural and Food Chemistry, 52(20), 6108–6114. Zhou, Z., Robards, K., Helliwell, S., & Blanchard, C. (2004). The distribution of phenolic acids in rice. Food Chemistry, 87(3), 401–406. Zhu, F. (2018a). Interactions between cell wall polysaccharides and polyphenols. Critical Reviews in Food Science and Nutrition, 58(11), 1808–1831. Zhu, F. (2018b). Proanthocyanidins in cereals and pseudocereals. Critical Reviews in Food Science and Nutrition, 1–13. Zhu, F., Du, B., Zheng, L., & Li, J. (2015). Advance on the bioactivity and potential applications of dietary fiber from grape pomace. Food Chemistry, 186, 207–212.

C H A P T E R

6

Analytical Methods and Advances to Evaluate Dietary Fiber M. Garcia-Vaquero School of Veterinary Medicine, University College Dublin, Dublin, Ireland

O U T L I N E 6.1 Introduction

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6.2 Official Methods to Analyze Dietary Fiber

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6.3 Other Methods to Analyze Carbohydrates 6.3.1 Sample Preparation 6.3.2 Chromatographic Techniques 6.3.3 Nonchromatographic Techniques

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6.3.4 Structure Elucidation of Carbohydrates

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6.4 Conclusions

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Acknowledgments

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References

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Further Reading

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6.1 INTRODUCTION Dietary fiber is a terminology that encompasses carbohydrates that are not hydrolyzed, digested, or absorbed in the upper gastrointestinal tract. These compounds can be fermented in the lower gastrointestinal tract, providing multiple health benefits when consumed regularly. Thus, it is considered as an essential constituent of a healthy and well-balanced diet (Elleuch et al., 2011; Tobaruela et al., 2018). There is evidence on the role of dietary fiber regulating a normal bowel function and protecting against metabolic disease and cancer. The protective role of fiber against colorectal cancer was recently emphasized by several governmental scientific reports in Denmark (Nordic Council of Ministers, 2014) and the United Kingdom (Scientific Advisory Committee on Nutrition, 2015). Moreover, the evidences of its protective role against cardiovascular diseases and type 2-diabetes have been used to determine the dietary requirements of fiber in the United Kingdom’s population (Buyken et al.,

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# 2019 Elsevier Inc. All rights reserved.

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2018). The recommended dietary intakes of fiber in different countries vary from 25 to 30 g/day (Buyken et al., 2018) depending on the definition of dietary fiber adopted by those countries as well as the analytical methods used to quantify and identify these carbohydrates. Recent advances in analytical chemistry, nutrition, and physiology influenced the definition of dietary fiber through the years. The Codex Alimentarius Commission updated the definition of dietary fiber in 2008/2009 setting the basis of new analytical methods, food labeling systems, nutrient reference values, and health claims related to these carbohydrates (Macagnan, Da Silva, & Hecktheuer, 2016). The Codex Alimentarius described dietary fiber as “carbohydrate polymers with 10 or more monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans” (Codex Alimentarius, 2008, 2009). This definition includes three main groups of compounds: (1) carbohydrates naturally occurring in food; (2) carbohydrates extracted from food raw material by physical, enzymatic, or chemical methods with beneficial health properties; and (3) synthetic polymers showing favorable physiological effects on health. Moreover, the benefits of these compounds for human health have to be demonstrated by generally accepted scientific evidences to the competent authorities (Codex Alimentarius, 2008, 2009). One of the main controversies of the current definition adopted by the Codex Alimentarius refers to the inclusion of non-digestible oligosaccharides with three to nine monomeric units as dietary fiber. The inclusion of these compounds was left to consideration by the competent national authorities (Codex Alimentarius, 2009). Several countries and institutions updated their official definition of dietary fiber to include these oligosaccharides (see Table 6.1). However, in some cases, these updates in the definition of fiber were not reflected in the analytical TABLE 6.1 Institutions and Countries That Accepted the Inclusion of Oligosaccharides (3–9 Monomeric Units) in Their Definition of Dietary Fiber Institutions

Countries

American Association of Cereal Chemists

Brazil

Association Official Analytical Chemists

Canada

Codex Alimentarius Commission

Chile

European Food Safety Authority

China

Food and Drug Administration

Indonesia

Food Standards Australia and New Zealand

Japan

Institute of Medicine

Korea

International Life Science Institute

Malaysia Mexico Singapore Thailand Taiwan

(Adapted from Dai, F. J., & Chau, C. F. (2017). Classification and regulatory perspectives of dietary fiber. Journal of Food and Drug Analysis, 25, 37–42.)

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methods of reference used to quantify carbohydrates (Dai & Chau, 2017). For instance, the government of Taiwan defined dietary fiber as edible carbohydrates with a degree of polymerization 3, including lignin. However, the national reference method for the analysis of dietary fiber in this country remained unaltered, using the traditional method from the Association Official Analytical Chemists (AOAC) 985.29. This situation led to an underestimation of the dietary fiber contents in different products and conflicts in the food labeling system with respect to other countries (Dai & Chau, 2017). Analytical complications may also derive from the current definition of dietary fiber. The Codex Alimentarius states that carbohydrates have to show health benefits to be considered as dietary fiber (Codex Alimentarius, 2008, 2009). Carbohydrates are normally associated to other bioactive compounds such as phenols, carotenoids, and phytosterols that display beneficial biological activities, i.e., antioxidant activities (Saura-Calixto, 2011). These associated compounds may influence the physicochemical and physiological properties of fiber and thus the health benefits experienced by the population consuming fiber-rich food products (Macagnan et al., 2016). Moreover, when the carbohydrates are extracted from natural matrices, the conditions used during the extraction and purification of these carbohydrates could result in structural modifications of the molecules and affect the biological properties of these compounds (Garcia-Vaquero, Rajauria, O’doherty, & Sweeney, 2017; Garcia-Vaquero, Rajauria, Tiwari, Sweeney, & O’Doherty, 2018). This chapter reviews the current methodological approaches used to analyze carbohydrates, discussing in detail the official methods to quantify dietary fiber together with recent purification and characterization techniques used to gain a better understanding of the chemical structure and functions of this chemically diverse group of carbohydrates included in the current definition of dietary fiber.

6.2 OFFICIAL METHODS TO ANALYZE DIETARY FIBER The classical methods to analyze dietary fiber in food before the change in the definition of this concept in 2008 were the AOAC 985.29 and 991.43. Both official methods are only able to quantify high-molecular-weight dietary fiber (HMWDF), expressed as total dietary fiber in the case of AOAC 985.29 or distinguishing between soluble and insoluble fiber to estimate the total dietary fiber in the methodology proposed by the AOAC 991.43 (Macagnan et al., 2016). The new definition of fiber proposed by the Codex Alimentarius Commission in 2008 included additional carbohydrates (i.e., resistant starch, RS) and opened the possibility to include low-molecular-weight oligosaccharides or low-molecular-weight dietary fiber (LMWDF) such as inulin, fructooligosaccharides, galactooligosaccharides, and polydextrose (Westenbrink, Brunt, & van der Kamp, 2013). Following this update in the definition of fiber, the classical methods AOAC 985.29 and 991.43 underestimate the dietary fiber contents of foods and thus, the energy value of food products made of or containing high levels of starch and LMWDF, inducing errors in food labels and composition tables (Macagnan et al., 2016). Furthermore, the inclusion RS as dietary fiber represents an analytical issue as the classical methods are only able to quantify retrograded starch or RS3, neglecting the RS1 (physical inaccessible starch), RS2 (ungelatinized starch granules), and RS4 (chemically modified starch) (Macagnan et al., 2016).

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TABLE 6.2 Summary of the Official Methods to Analyze Dietary Fiber, as Described by the Association of Official and Analytical Chemists (AOAC), and the Compounds Measured by Each Method AOAC Method

Compounds Measured

985.29

Total dietary fiber (high molecular weight)

991.42

Insoluble dietary fiber in foods

991.43

Total dietary fiber (high molecular weight: soluble and insoluble)

993.19

High-molecular-weight soluble dietary fiber in foods

993.21

High-molecular-weight dietary fiber (when >10% fiber and 50%) or low methoxyl pectin (DM < 50%). High methoxyl pectin can form gels in an acidic medium (pH 2.0–3.5) if sucrose is present at a concentration higher than 55% (w/w), which compromises the amount of water available for pectin’s hydration. Low methoxyl pectin can form gels over a larger pH range (2.0–6.0) if divalent ions like calcium in the case of food systems are present. Pectin has been commonly extracted using strong mineral acids as the acidic extracting agents combined with high temperatures (70–85°C) to reach reasonable yields, being also time efficient. However, pectin extracted through this technique is susceptible to degradation. In addition, high acidity accelerates corrosion of equipment and triggers water pollution problems. Moreover, pectin is commonly used in the food sector, where the use

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of strong mineral acids may leave consumers with a negative impression (Liew, Ngoh, Yusoff, & Teoh, 2018; Liew, Teoh, Tan, Yusoff, & Ngoh, 2018). Pectin is mostly produced ( 85%) from citrus peels (56% from lemons, 30% from limes, and 13% from oranges), and from apple pomace ( 14%), with a minor fraction being obtained from sugar beets. After juice extraction, essential oil and dissolved sugars are removed from the peel prior to drying. The pectin used in food is defined as a polysaccharide containing at least 65% of D-galacturonic acid (GalA) units (Ciriminna et al., 2016). After this precise definition, an alternative to pectin manufacture is the production of crude pectin or pectinenriched fractions, which can be used for the same purposes of pectin. Pectin-enriched fractions can be obtained by various thermal or thermomechanical treatments, whose aim is to increase the soluble fraction of the fiber. The main difference between the pectin-enriched fractions and the purified pectin (standard pectin) is the high level of fiber or associated neutral sugars (Contreras-Esquivel et al., 2010), as well as the presence of proteins and co-extracted phenolics. Early, Rouse and Crandall (1976) extracted pectins from Duncan grapefruit, pineapple, Valencia oranges, and Sicilian lemon peels of the 1975–1976 Florida citrus season with nitric acid at a constant pH of 1.6, which was the optimum for protopectin hydrolysis. Extractions were evaluated at 95°C for 30 and 45 min, 90°C for 30, 45, and 60 min, and 85°C for 60 min, in a proportion of 17 g dry solids per 1100 mL of water and 1.0 N nitric acid up to pH 1.6, with reextraction, washing, and filtration. The pectin was precipitated from each supernatant with two volumes of 99%-isopropyl alcohol, separated and washed with 68% isopropyl alcohol, and finally dried under vacuum at 60°C for 14 h. Pectin yields calculated on the fresh peel basis, whatever the temperature and time of extraction, were of 11.0%, 8.15%, and 6.35% for lemon, orange, and grapefruit, respectively. On a dry solid basis, these yield values varied around 30%. These pectins presented jelly grades of 254, 225, and 263, respectively, which were higher than the 150 jelly grade shown by the commercial pectin used for marmalade, jam, and jelly. Pectin is the traditional gelling agent. Its applications extend to fruit products of the food industry, dairy products, desserts, soft drinks, and pharmaceuticals. May (1990) reported that normal raw materials for pectin production are apple pomace and citrus peels, from which pectin is obtained by acid extraction and precipitation using alcohols or aluminum salts. For a viable pectin production, it is not only necessary to have a raw material of the right quality, but also a sufficient amount to run a cost-effective operation (May, 1990). On the other hand, apple pomace and citrus peel are very perishable, and they can be attacked by molds, which produce a wide variety of de-esterifying (pectinmethylesterase) and degrading (pectin lyases, polygalacturonase) pectin enzymes, which turn the raw material unacceptable for pectin extraction. Particularly, citrus naturally contain significant amounts of native pectinmethylesterase, as orange peels are especially rich in it. This enzyme, in contrast to fungal pectinmethylesterase, produces carboxyl de-esterified blocks that make the pectin more sensitive to calcium ions than indicated by its overall DM (May, 1990). For the same DM, the blockwise distribution of demethoxylated carboxyl groups made the pectin more sensitive to calcium than randomly deesterified pectins by fungal pectinmethylesterase (Willats, Knox, & Mikkelsen, 2006). The mechanical response of these pectins is also different, for the same DM, in the presence of calcium ions. The blockwise deesterified pectins produces more elastic, deformable gels, whereas randomly deesterified pectins produce brittle gels. At least

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14 neighbor demethoxylated carboxyl groups are needed to produce the “egg-box”-like structure of stable ionic calcium-crosslinks between contiguous pectin chains (Braccini & Perez, 2001; Vincken et al., 2003). Pectin can then be extracted from the fruit residue soon after the pressing of the juice, or the residue obtained in this process can be dried, remaining stable for some months and permitting long-distance transportation to pectin factories. Inevitably, some quality is lost in the drying process, as pectin is a fairly heat-labile material, but if the fruit residue (especially if it is citrus peel rich with citric acid) is well washed before drying. It is dried under conditions sufficient to destroy enzymes and molds without destroying the pectin, and very acceptable pectin can be produced from it. Wet raw material will ideally need blanching after pressing as soon as possible and can only be stored for a few days (May, 1990). Sugar beet residues constitute other sources considered for the extraction of commercial pectins. The products were not of very high quality in terms of gelation. Beet suffers from several disadvantages as a competitor to apple and citrus pectins. Most seriously, it is difficult to obtain as high a molecular weight and hence a good quality of gel, while the content of neutral sugars is distinctly higher, often reducing the GalA content below the legally permitted limit. Also, pectins have lower degrees of esterification and the presence of acetyl groups that hinder blocking calcium ions for gelation (May, 1990). However, this differential characteristic permits manipulation of special textures in the food formulations as well as developing emulsifying capacity. Ralla et al. (2017) determined that an isolated sugar beet extract stabilized emulsions. The generated emulsions were negatively charged and had the smallest particle sizes  1.3 μm at a low emulsifier-to-oil ratio of 0.75:10. Important world industries that produce pectins commercialized one obtained from sugar beet pulp as a high esterified pectin that provides stable oil-in-water emulsions and keeps pulp particles in suspension. Beet pectin is capable of being crosslinked through the ferulic acid lateral substituents of Ara residues when treated with peroxidase and hydrogen peroxide to form a thermally stable covalently crosslinked hydrogels, which may for example be dehydrated and rehydrated, and hence be destined for special purposes (May, 1990). Pectic substances were isolated by de Fa´tima Sato et al. (2011) from 70°C-dried pomace that remained after the hydraulic press for production of premium quality juices separately obtained from 11 cultivars of apples. For pectin extraction, the dried apple pomace was dispersed in 100 mM HNO3 at a 1:40 (w/v) ratio and boiled for 10 min. According to the authors, the pectin was precipitated with 66% (v/v) aqueous ethanol from the supernatant after cooling to 4°C. The separated residue was air-dried at 50°C and stored under 0% relative humidity atmosphere for total dehydration. The apple pomace of the cultivars showed average soluble and insoluble fiber contents of 15% and 28.7% (dry basis), respectively, with a low variation (10%). The soluble fiber content can be ascribed to pectins. The uronic acid content of the pectin fractions was between 46.80% and 52.85% (dry basis), with a high degree of methoxylation (DM,  72.3%), being 42.7% the neutral sugars’ content. The latter included L-arabinose (Ara), D-galactose (Gal), D-mannose (Man), and D-xylose (Xyl) as the main neutral sugar components, in proportions between 4.77% and 2.95%. However, the highest content of D-glucose (Glc) (26.8% of the neutral sugars plus uronic acids) found was striking. Their functional properties were not determined. Pectins were extracted by Kaya, Sousa, Crepeau, Sørensen, and Ralet (2014) from commercialized dry citrus peels of orange, lemon, lime, and grapefruit through nitric acid at pH 2.1 (72°C) and pH 1.6 (70°C), or oxalic acid (0.25% (w/v) ammonium oxalate, pH adjusted with

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0.2 M oxalic acid) at pH 3.5 (72°C) and 4.6 (85°C). For the oxalic acid solution, 1 g dry citrus peel to 40 mL of acid was the proportion used for the extraction, and the pectin fraction was not finally obtained by precipitation with alcohol. The dispersion was maintained at 40°C for 30 min, then at 85°C for 30 min and, afterward, reextracted three times at 85°C for 30 min with oxalate buffer. The separated supernatant was finally concentrated by evaporation at 40°C, dialyzed against water, and freeze-dried. At the plant scale, extraction was performed with a 1 g/30 mL hot water proportion, at 72°C, and then enough nitric or oxalic acid was added to achieve the pH required. Cellulose pulp was added to the previous dispersion, mixed and filtered. The filtrated solution was purified for 30 min with the ionexchange AmberliteTM IR-120-H resin, which was then removed by filtration, and the pectin fraction was precipitated into the supernatant by the addition of three volumes of isopropanol. The separated pectin residue was dried (67°C, 24 h) and milled. The yield of pectin extracted was of  31% (w/w) on dry peel basis for lemon and lime, while varied between 16.7% and 24.8% for orange, and 21.6% and 28.0% for grapefruit. The GalA content was low in all fruit peels (24.08%–29.74%), and again, the main neutral sugar was Glc (16.57%–20.21%, w/w, dry peel), while the characteristic neutral sugars of pectins such as Ara (6.66%–8.78%) and Gal (2.87%–5.39%) were notably lower. The content of L-rhamnose was low as expected ( 1.3%). Xu, Tai, Wei, Yuan, and Gao (2017) extracted pectin-enriched fractions from dried hot pepper (Capsicum annuum L. var. acuminatum Fingerh.) residues of oleoresin extraction for their valorization by using hydrochloric acid or sulfuric acid. For hydrochloric acid, the optimal conditions of yield extraction were investigated (pH 0.5–4.5, temperature 50–90°C, extraction time 1–5 h, 1:10–1:50, w/v, solid:liquid ratio). Optimal conditions for the highest yield of pectin extraction with hydrochloric acid (14.63%, dry basis) were a pH of 1.0 at 90°C for 2 h with a liquid:solid ratio of 1 g:20 L. At the end of the isolation, the extract was cooled down to room temperature (23°C), filtered, and the pH led to 3.0. Activated carbon was added for decolorization (90°C, 1 h), filtered, and the separated liquid phase was concentrated at 50°C to onethird. Afterwards, pectin was precipitated at room temperature by addition of ethanol (65%, v/v, final concentration), and separated by centrifugation, with successive washing steps with 75% and 85% (v/v) ethanol. The final pectin solid was dried at 50°C (24 h) into an oven. The pectin-fraction obtained was mainly composed of uronic acids (70.47%, w/w) with high DM (60.26%), and the major neutral sugars were Gal and Glc, followed by Rha, Xyl, Man, Ara, and fructose (Fru). The latter is not a monosaccharide present in pectins. The molecular weight was 79.1 kDa. The optimal conditions found for extraction with hydrochloric acid were then applied for the isolation with sulfuric acid, obtaining a pectin-fraction with 65.49% of uronic acids, a DM of 67.71%, and an average molecular weight of 69.3 kDa. When dissolved in water at pH 4.0 and 0.25%–2.00% (w/v) concentrations, either with or without sucrose and with and without Ca2+, the pectin fractions showed pseudoplastic behavior and very low viscosity values (below 0.8, 0.1, 0.25, and 0.07 Pa  s) at the lowest shear rates ( 0.1 s1) swept. The pectin extracted showed some emulsifying capacity and relevant antioxidant properties. The content of phenolics was not analyzed. As reported by Liew, Ngoh, et al. (2018) and Liew, Teoh, et al. (2018), pectin extractions from various citrus sources showed that citric acid gave a better yield performance in the range of 36.71%–67.30% in comparison to mineral acids such as nitric (19.80%–27.63%) and hydrochloric (19.16%–21.10%) acids. The optimum amount of solvent required and the

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optimum extraction temperature for citric acid-based extraction on pomelo were marginally lower as compared to the extraction using nitric acid. Additionally, the extraction time using citric acid was approximately three-quarter of the time required using nitric acid. In a largescale extraction, the lower operating temperature and solid-liquid ratio together with a shorter extraction time may lead to substantial energy and material savings. Contreras-Esquivel et al. (2010) analyzed the albedo, which constitutes a 49.23% of the passion fruit (Passiflora edulis), as a potential alternative source of pectin-enriched fractions. They were extracted by autoclaving at 121°C for 20 to 60 min from the sugar-exhausted 90°Cblanched dried albedo powder dispersed in 1% (w/v) citric acid (1 g, 80 mL) at pH 2.3. It is important to remark that the autoclave was preheated to 100°C before introduction of the aqueous dispersions, requiring about 10 min to reach 121°C. Pectinmethylesterase, pectatelyase, and polygalacturonase enzymes were used to distinguish between the total-uronic acid and polymeric uronic acid contents when analyzed. Pectin-enriched fractions were obtained by precipitation with 2 volumes of 95%-ethanol, followed by centrifugation, dissolution in water, and freeze-drying. The residual material remaining after pectin extraction represented 60% of the dried albedo powder. This depectinized material could be used as dietary fiber with high cellulose content for human nutrition or as a source for glucose production by enzymatic methods. The best condition of pectin yield (25% on dry fiber basis), with the highest molecular weight, was obtained with 1.0% citric acid and 20 min of autoclaving, producing a pectin with 70% of uronic acids and 75.6% of DM. Total uronic acid content in the extracts did not vary significantly with extraction time, while the content of polymeric-uronic acids (pectins) and, hence, of the molecular weight decreased with the increase in extraction time. A maximum pectin yield of 30% (dry basis) was obtained after 40 min of autoclaving at 121°C. The passion fruit pectin extracted for 20 min showed a significant increase in gel strength after enzymatic demethylation with fungal pectinmethylesterase, improving the pectin functionality. Pinheiro et al. (2008) extracted pectin-enriched fractions with citric acid (0.086%–2.91%, w/v) at varying extraction times (17–102 min) from the skin (flavedo) of passion fruit (Passiflora edulis flavicarpa), dried at 55°C and reduced to a dry 60-mesh size flour. This powder was composed by a 19.2% (w/w) of soluble fiber and a 38% of insoluble fiber. The extraction was performed at 97°C under reflux (1.50, w/v). The supernatant was separated, and pectins were precipitated by addition of 2 volumes of absolute ethanol. Pectins were dried in an air-circulating oven (45°C, 12 h) and then milled to a dry 60 mesh size powder. The citric acid concentration (or pH) was the most important factor that affected the DM, which decreased as the citric acid concentration increased. The best condition was 0.086% (w/v) citric acid for 60 min of treatment to extract a high-methylated (78.59%) passion fruit pectin. Functionality of the pectin and the chemical composition in uronic acids were not evaluated. Tiwari et al. (2017) extracted pectins with citric acid from the orange peels remaining after the oil extraction with a Soxhlet (40°C, 6–12 h, petroleum ether). Citric acid solutions of pH 1.0, 1.5, 2.0, and 2.5 were used for peel powder (16–60 mesh size) dispersion and heated at 65°C for the optimum time of 30 min. After cooling and filtering, two volumes of ethanol were added for pectin separation. A jelly-like precipitate was formed. It was dried in an oven at 40°C for 20 min. Pectin yields ranged between 7.3 and 52.90%, and DM of that varied between 5.1% and 71.0%, respectively. The pH was the most important parameter influencing the yield of extraction, which increased as the pH decreased. Also, the yield decreased as the mesh size

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of peel particles increased from 16 to 60 mesh. The maximum pectin yield of 52.90% was obtained at pH 1.0 and with a particle size of 60 mesh. Fissore et al. (2010) extracted pectin-enriched fractions with citric acid from the cell-wall enriched powders (420–710 μm) respectively obtained from red beets (Beta vulgaris var. conditiva) and butternut squash (Cucurbita moschata Duch ex Poiret), by drying (85°C, convection) and milling of the tissue remaining after juice extraction, and washing with water. Three pH levels were considered (1.5, 2.0, and 3.0) and two times (2 and 3 h) of stirring at 85°C. Since the extraction at pH 3 gave very low yields, this pH condition was finally discarded. After filtration, the pectin fraction was precipitated (12 h, 6°C) from the respective supernatant by addition of 2.5 volumes of ethanol, then filtrated, and the separated pectin-enriched fraction was freeze-dried. The uronic acid contents of the cell-wall enriched powders used for extraction were similar ( 12.5%–13.7%) and with high DM (91%). They contained a 95% of polysaccharides and 5%–7% of proteins. The DA was of 34% for the cell wall powder of pumpkin and 90% for the red beet powder. High Glc content was determined in the pumpkin powder (68.2%, w/w), while the highest levels of the neutral sugars were for Ara (51.7%) and Gal (14.9%) in the red beet powder. Pumpkin pectin yields varied between 21% and 28%, with 23%–41% of uronic acids of low DM (16.8%–39.3%) for pH 1.5 of extraction, while pectin yields of 11%–31% on a dry-powder basis were obtained, with uronic acid contents of 27.3%–44.1% and low DM (17.2%–45%) for pH 2.0. For red beet pectin fractions, the DA varied between 3.1% and 21.7%. The low pH of extraction hydrolyzes the carboxymethyl ester and the acetyl groups. At the lowest pH assayed, pectins were essentially constituted by homogalacturonan. A significant content of neutral sugars was determined at pH 2.0. Neutral sugars were constituted mainly by Ara, Gal, Rha, and Glc in different proportions for each fraction. In general, butternut fractions showed high Glc contents, which probably stems from residual starch. Flow behavior for 2.00% (w/v) aqueous systems of the different pectinfractions was evaluated, showing that samples showed low viscosity and, hence, poor thickening properties. Acid at low pH was detrimental for the functionality of the isolated pectins. In contrast, pectin-fractions obtained at pH 5.20 with the use of citrate buffer show much better rheological performance but are extracted with lower yields. In the extractive processes performed with acids, reasonable yield performance was achieved when low pH was combined with either long extraction time or high temperature or high liquid:solid ratio. This is due to the fact that low pH causes a concentration difference between the extraction medium and the plant matrix, which enables the extraction solvent that was in contact with the insoluble pectin to easily induce hydrolysis of the insoluble pectin into soluble pectin (Prakash Maran, Mekala, & Manikandan, 2013; Prakash Maran, Sivakumar, Thirugnanasambandham, & Sridhar, 2013). Moreover, longer extraction time was needed for the diffusion of pectin across the plant structure to the extractive solvent, as higher temperatures provide the thermal energy required to soften the plant structure. As a result, the target compound can diffuse much easier into the extraction medium, which in turn would speed up the extraction process. High liquid-solid ratio could also promote the diffusion process of the target compounds (Radojkovic et al., 2012). On the other hand, determination of the uronic acid content and DM are not the only analyses required, but, also, the rheological properties should be evaluated since pectins are used as thickeners (high viscosity, with pseudoplastic behavior) and gelling (dynamic mechanical spectrum of a weak or a true gel) agents.

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The enzyme-assisted extraction (EAE) arises as a greener alternative since it uses mild processing conditions (lower-extraction temperature, higher pH). Enzymes catalyze reactions with high specificity and regioselectivity and have the ability to disrupt cell walls enabling the release of bioactive compounds. According to Nadar, Rao, and Rathod (2018), there are two approaches to the EAE of polysaccharides: (1) the use of enzymes that disrupt cell walls and membranes to facilitate the liberation of the desirable compounds and (2) the use of enzymes that partially degrade the target polysaccharides to facilitate their extraction. The most commonly used enzymes for soluble dietary fibers and, in particular, pectin extraction are: cellulase, hemicellulase, xylanase, protease, glucanase, and pectinase, sometimes in combination with amylases and others. Since the combined effects of different enzymes may result in an increased degradation of the cell wall and thus higher extraction yields, many commercial preparations consist of a mixture of different cell wall degrading enzymes (Table 7.1). These enzymes are obtained from bacteria, fungi, animal organs, or vegetable extracts. It is important to consider that each enzyme has its optimum pH and temperature conditions. The temperature of extraction, time, pH of the system, enzyme concentration, particle size of the substrate and substrate to liquid ratio are the most important parameters to be considered. Some of the disadvantages of this technology are the cost of enzymes, the difficulty to scale up the process, and the limited current availability of enzymes (Puri, Sharma, & Barrow, 2012). In the last decade, there has been a huge number of publications regarding the EAE of polysaccharides, of which some of the more relevant ones can be seen in Table 7.2. Most of these publications are focused on the extraction of pectin and explore the use of different enzymes alone or in combination; they also focus on the use of experimental designs in order to find the optimum extraction conditions in terms of temperature, time, pH, enzyme concentration, and substrate-to-liquid ratio (Dominiak et al., 2014; Fissore, Ponce, Stortz, Rojas, & Gerschenson, 2007; Fissore et al., 2011; Jeong et al., 2014; Lim, Yoo, Ko, & Lee, 2012; Ma et al., 2015; Wikiera, Mika, & Grabacka, 2015; Wikiera, Mika, Starzy nska-Janiszewska, & Stodolak, 2015; Yuliarti, Goh, Matia-Merino, Mawson, & Brennan, 2015). Fissore et al. (2007) and Fissore, Matkovic, Wider, Rojas, and Gerschenson (2009) isolated pectin enriched fractions from dried butternut (Cucurbita moschata Duch) mesocarp using cellulase from Aspergillus niger (H2125, SIGMA, USA) and hemicellulase from Trichoderma viride (C9422, SIGMA, USA). Cellulase concentrations tested were 0.05 and 0.15 g/10 g butternut mesocarp/L buffer and for hemicellulase, concentrations tested were 0.25 and 0.75 g/10 g butternut mesocarp/L buffer (Table 7.2). Insoluble solids obtained after digestions were separated through filtration and soluble DF fractions were precipitated through ethanol (96%) addition, filtrated, and freeze-dried. Cellulase hydrolysis produced soluble dietary fiber fractions enriched in pectin (55%–78% galacturonic acid), and hemicellulase produced fiber fractions with lower levels of galacturonic acid (39%–44%). All isolated fractions showed a thickening effect and a pseudoplastic behavior in water, and their effect delaying glucose absorption in vitro was also observed. When the same enzymatic hydrolyses were performed using red beets (Beta vulgaris L. var. conditiva) as a substrate (Fissore et al., 2011), authors obtained DF fractions with very low yields (100 KDa) galactan potato polysaccharides for their use as bifidogenic fibers. EAE is also used to modify DF for improving its technological applications. Laurikainen, Hærk€ onen, Autio, and Poutanen (1998) evaluated the use of enzymes for improving the quality of fiber-enriched wheat bread containing rye bran. The use of hemicellulase, xylanase, or α-amylase containing hemicellulase activity reduced the total fiber content but increased the soluble pentosan content, which caused a decrease of dough stability, increased softening, and improved the baking performance of the fiber-enriched bread. Zhou, Qian, Zhou, and Zhang (2012) applied a sequential treatment with amylase, protease (phosphate buffer pH 7.0, 50°C, 3.5 h separately), and cellulase (citric acid pH 4.6, 55°C, 1 h) on tartary buckwheat bran flour. Amylase increased the DF content, total polyphenols, and total flavonoids of the extract. Also, the WHC and SC increased from 2.22 g/g and 2.33 mL/g in the control sample to 2.38 g/g and 4.67 mL/g, respectively. After cellulase treatment, the proportion of soluble

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dietary fiber with respect to total DF increased and the WHC and SC were 2.58 g/g and 5.13 mL/g, respectively ascribing this effect to a decrease in fiber particle size. Santala, Kiran, Sozer, Poutanen, and Nordlund (2014) studied the modification of wheat bran by enzymatic hydrolysis in order to improve its technological performance in expanded extrudates. A commercial xylanase (Depol 761P, Biocatalysts Ltd., UK) and a commercial cellulase (Veron CP, AB Enzymes GmbH, Germany) were used for extrusion-aided enzymatic bran modification. The enzymatic treatment increased the crispness and decreased the hardness of the extrudates, and this effect was correlated with a decrease in the WHC of the bran when compared to the untreated bran, as well as with an increase in the expansion of the product. Villanueva-Sua´rez, Perez-Co´zar, and Redondo-Cuenca (2013) used a commercial β-glucanase (Ultraflo L, Novozymes, Denmark) to increase the soluble DF content of okara. Enzymatic treatment led to a product with an improved ratio of soluble–insoluble fiber and the physicochemical properties of the modified product were improved (oil retention capacity, WRC, and SC) when compared to unmodified okara.

7.2.2 Inulin, Oligofructose, and Fructooligosaccharides As reported by Khuenpet, Fukuoka, Jittanit, and Sirisansaneeyakul (2017), inulin is a linear mixture of oligo- and/or polysaccharides consisting of D-fructose bonded by β-(2 ! 1) D-fructosyl fructose bonds linkages that are terminated by a D-glucose molecule bonded to fructose by α-D-glucopyranosoyl bond. The DP varies between 2 and 60 units. However, according to Franck and De Leenheer (2005), DP of plant inulin is rather low and depends on plant source, growing stages, climatic conditions, and the duration and conditions of post-harvest storage. Native inulin, which refers to inulin extracted from fresh roots or tubers without a fractionation procedure, has an average DP of 10–12, while inulin from which smaller oligosaccharides have been removed has an average DP of 27–29. Molecules with DP < 10 are called fructooligosaccharides (FOS). Inulin is reported as a dietary fiber because it is not digested or absorbed in the small intestine. It is also a healthy food ingredient, alternative low-calorie sweetener, and fat substitute. Besides those functional properties, inulin and FOS have prebiotic effects because they stimulate activity and growth of beneficial bacteria in the human colon (Khuenpet, Jittanit, Sirisansaneeyakul, & Srichamnong, 2017). Fructans are present as storage polysaccharides in more than 36,000 plant species, including vegetables and fruits. Primary plants containing fructans belong to mono- and dicotyledonous families, either Liliaceae (e.g., leek, onion, garlic, and asparagus), or Compositae (e.g., dahlia, chicory, and yacon) (Kaur & Gupta, 2002). Jerusalem artichoke (Helianthus tuberosus) and chicory (Cichorium intybus) are common sources of inulin (Franck, 2000). Many cereals and other grasses contain high fructans content but are not used for industrial production. Jerusalem artichoke is a native species of sunflower originally found in Canada and then cultivated widely in Europe, North America, and Asia (Khuenpet, Fukuoka, et al., 2017). Chicory is native to Europe and has been cultivated in several temperate areas since the 16th century. Its roots and greens are widely used for human consumption, especially as a coffee substitute

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after roasting. Chicory inulin is mainly stored in the fleshy root, representing about 70%–80% of the root dry weight (Kaur & Gupta, 2002). Globe artichoke (Cynara cardunculus L. var. scolymus), a plant native to the Mediterranean area whose edible part is the enlarged receptacle and the tender thickened bract base on the head (capitulum), is the immature inflorescence used worldwide as both a fresh and canned delicacy product. Only 15%–20% is edible, while the external bracts and the stem (80%) are discarded. They can be sources of inulin and pectin-enriched fractions that are co-extracted with polyphenols, as determined by Fissore et al. (2014). Upgrading of vegetable wastes to biopolymers and bioactive compounds can contribute not only to reduce pollution but also to add value to the commodity production. Khuenpet, Fukuoka, et al. (2017) extracted inulin from Jerusalem artichoke tuber-powder obtained after tuber washing, slicing, immersion in citric acid (0.5%, w/v), blanching (100°C, 2 min), cooling and draining, and final drying at 65°C until less than 8% of moisture content (on dry basis). The powder was submitted to treatment with 85°C-water because inulin is soluble in hot water. After concentration of the aqueous extract under vacuum, the powder was obtained by spray-drying, and 86% of the powder was constituted by total carbohydrates and 75% of the carbohydrates was inulin. Cleaned and peeled chicory roots were used as a source of inulin in the fresh status, and after drying under the sun (30–35°C) or in hot air ovens (90°C) by Gupta, Kaur, and Kaur (2003). The latter were brownish while the sunlight dried roots were a light yellow, off-white color. Fresh and dried roots were crushed, and the dried product was passed through 100 μm sieve for uniform size particles. Five volumes of water were added for the extraction of inulin by boiling for 20 min, dialyzed for elimination of small sugars, and then inulin of different DP were selectively separated by addition of ethanol to the supernatant at concentrations between 40% and 60% (v/v), and the separated residues were dried at 45°C after washing with ethanol. Fresh or dried root powders were also extracted directly with 20% (v/v) ethanol at 25°C for 3 h. Fructan contents of 72.4%, 70.8%, and 58.5% were respectively determined in the fresh, sun- and oven-dried chicory sources, while the respective levels of fructose were 1.4%, 1.8%, and 12.4% (dry basis). Each ethanolic fraction selectively precipitated by 20%, 20%–40%, and 40%–60% (v/v) ethanol produced a powder constituted by 20.5%, 15.6%, and 12.1% of inulin for the sun-dried roots. An 81.2% of FOS was determined in the 20% (v/v) ethanol extracted fraction, which was produced with a yield of 43%, while an inulin content of 87.4% was found in the residue remaining (42% yield) after separation of the 20%-ethanol soluble fraction. For 50% (v/v) ethanol-treated chicory roots, the increase of pH of the hot extracting water from 6.0 to 7.0 gave rise to an increase in yield from 21.6% to 33.4%, while there was not significant increment when pH rose to 9.0. Bract, heart, and stem by-products of globe artichoke were applied to the extraction of biopolymers by Fissore et al. (2014). Washing and drying (85°C) in a convection oven and milling/sieving gave origin to powders enriched in cell-wall materials that were separately dispersed in 0.05 M citrate buffer (pH 5.20) in a 1 g/100 mL ratio and submitted to digestion (30°C, 20 h) under stirring either without or with a cell-wall degrading enzyme (hemicellulase). These digestions were also performed on other powder-dispersed samples but after a previous heating step at 70°C for 5 min. As it is known that the solubility of inulin in water remarkably increases with temperature, the purpose of the heating step was to increase the inulin content in the isolated fractions. The insoluble solid obtained after digestion was separated through vacuum filtration, and cell wall polysaccharides were precipitated

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from each supernatant through addition of two volumes of 96% (v/v) ethanol. The precipitate was collected by vacuum filtration, washed, and freeze-dried. The highest yields of extraction, calculated as g of product obtained per 100 g of powder enriched in cell-wall material, were showed by two fractions obtained from the stem powder, with a pre-heating step and digested in citrate buffer alone (13.6 g/100 g powder) or in buffer with hemicellulase (20.8 g/ 100 g powder). They also showed some of the highest inulin contents (53% and 46%, respectively). Hemicellulase enhanced the extraction of soluble fibers mainly from stems of globe artichoke, and the preheating treatment (70°C-5 min) doubled the enzymatic yield because of the important increase in inulin. Cell-wall network disorganization produced by hemicellulase decisively helped the extraction with or without preheating. All extracted fractions were almost entirely constituted by carbohydrates (70%–96.8%), with variable amounts of proteins (1.8%–20%). Phenolics were coextracted with all fiber fractions (2.1%–8.2%) and, in general, parallel the antioxidant capacity measured as DPPH radical-scavenging activity. Inulin contents varied between 13.2% and 55%. All the isolated fiber fractions contained pectins as indicated by the uronic acid content, which varied between 12.1% and 20% (dry basis) with DM ranging 31%–58% and degree of acetylation between 8.0% and 10.3%. Fractions showed pseudoplastic behavior when evaluated at 2.00% (w/v) concentration in water. In the presence of calcium ion, fiber fractions produced the mechanical spectra of true gels. Fiber fractions extracted with the highest yields from stems and bracts and using the preheating step showed anti-HSV-1 activity. Sa´nchez-Madrigal et al. (2018) evaluated the EAE of fructans from wild sotol plant (Dasylirion wheeleri) using Pectinex Ultra SP-L (Table 7.2) obtaining high fructan (38.58%) with a degree of polymerization of 8–10.

7.2.3 β-Glucans The (1,3; 1,4)-β-D-glucans are widely distributed as noncellulosic matrix phase polysaccharides in cell walls of the Poaceae, which evolved relatively recently and consists of the grasses and commercially important cereal species, but they are less commonly found in lower-vascular plants, such as horsetails, algae, and fungi (Burton & Fincher, 2009). Since β-D-glucans are characterized by a β-(1 ! 4)-linked backbone with an equatorial configuration at C1 and C4, the water soluble β-glucans from oats and barley are hemicelluloses. This kind of biopolymer is a linear β-1 ! 3 and β-1 ! 4 linked polysaccharide formed of β-D-glucopyranosyl monomers, which are restricted to the Poales and a few other groups. Arabinoxylans are present in seeds of dicots such as flax and psyllium and also in cereal endosperm. The cereal endosperm additionally contains β-(1 ! 3,1 ! 4)-glucans (Scheller & Ulvskov, 2011). β-Glucans extracted from oats exhibited higher DPPH radical-scavenging activity and ferric-reducing power, as well as protection against DNA damage than barley β-glucans (Shah, Gani, Masoodi, Wani, & Ashwar, 2017). As reported by Zielke, Stradner, and Nilsson (2018), the physicochemical and structural properties can govern the nutritional functionality of β-glucan. Viscosity is affected by a large number of factors, such as concentration and molecular weight of the β-glucans, as well as different features affecting the β-glucan backbone (Izydorczyk & Dexter, 2008). Therefore, there is a remarkable interest to develop an efficient extraction process of β-glucans from

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cereals. One possibility is the ability of high molar mass β-glucan to form aggregates, whereas this aggregation is highly dependent on the molar ratios of trimers and tetramers (DP3:DP4) in the individual molecules, the hydrodynamic radius, and the conformation. Molecular interactions can form physical cross-linkages between single molecules. In β-glucan from different cereal origins, a considerable diversity exists regarding molar mass and structure, such as the distributions of β-1 ! 3 and β-1 ! 4 linkages. In oat β-glucan, β-1 ! 4 trimers (53%–61%) and tetramers (34%–41%) are the most dominant, whereas the DP3:DP4 (cellotriosyl: cellotetraosyl) ratios range between 1.5 and 2.3. Another often discussed structural characteristic is the ratio between (1 ! 4) and (1 ! 3) β-glycosidic bonds, which has been reported to be 2.3–2.8 for oat β-glucan. As reported by Fincher (2016), the β-1 ! 3:β-1 ! 4 linkage ratio in oat grain is 2:1 and 80% water soluble (40°C); while in barley, it is 2.8:1 and 20% water soluble (40°C). In wheat, the β-1 ! 3:β-1 ! 4 linkage ratio is 3.2:1 and insoluble in water (40°C), being the β-glucan content of 0.5%–2.3% (w/w) grain. While oats are usually subjected to kilning for enzyme inactivation, barley is not usually submitted to heating before further processing. Therefore, β-glucanases in barley flour has been shown to result in β-glucan degradation during processing, which should be considered at the moment of β-glucans’ extraction from residues or by-products. On the other hand, β-glucans are only a minor constituent in grains, while they also contain major amounts of nonstarch polysaccharides, starch, proteins, and lipids that have to be eliminated during the β-glucans extractive process. Hence, the extraction has to be multistep (Kurek et al., 2018). Especially, oats contain more lipids than other cereals, normally 5%–9%, and they are located throughout the kernel, while lipids in other cereals are concentrated in the embryo. In addition, most of the oat fatty acids are unsaturated, being the oleic acid portion of oat lipids, exceptionally high among cereal lipids (Kaukovirta-Norja, Wilhelmson, & Poutanen, 2004). As reported by Rimsten (2003), the solubility or extractability of β-glucans is not only influenced by the structure of the macromolecules but also by temperature and pH. Wood, Paton, and Siddiqui (1977) stated that the amount of β-glucans dissolved depends on fineness of grind, temperature, ionic strength, and pH of the solvent. Therefore, is it important to also state which conditions are used when referring to extractability of β-glucans. In general, the extractability of β-glucans seems to increase with elevated temperatures and pH (Knuckles, Yokoyama, & Chiu, 1997). Also, it seems to depend on the pre-treatments performed, such as drying and heating; for example, a boiling step with ethanol might increase extractability of β-glucans. Strong alkalis like NaOH alone produce a higher yield than water at any temperature. A complete extraction (solubilization) of β-glucan can be accomplished by the addition of enzymes. Lichenase, endo-1,4-β-xylanases, α-L-arabinofuranosidase, and esterase-released β-glucans. It was speculated that an arabinoxylan coating restricts the access of solvating water to β-glucan (Palmer, 1989). However, since lichenase can be accessed, this suggests that the covering of β-glucan by the arabinoxylans is incomplete (Kanauchii & Bamforth, 2001). Some of the solubilizing effect from xylanase might also arise from contaminating β-glucanase. As β-glucan is a minor component (3%–7%) of oat and barley grains, it is necessary to develop a procedure for its isolation and concentration. Stirring rate and particle size were the operational variables that controlled the extractive process of β-glucans from two varieties of waxy barley, evidencing mass transfer limitations to the process (Benito-Roman, Alonso, & Cocero, 2013).

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Wet and dry processes are the main methods for the extraction and purification of β-glucans from cereals (Benito-Roma´n, Alonso, & Lucas, 2011; Vasanthan & Temelli, 2008). In dry conditions, the extraction is performed by milling and sieving, achieving a final product that yields 15.2% in β-glucans as the best result, and includes dry milling and air classification steps. Wet conditions usually imply alkaline solvents, an enzyme-treatment, or ultrasound. As reported by Benito-Roma´n et al. (2011), wet procedures are more complex because they involve at least two or three steps, which begin when the cereal bran or flour used as raw material is put into contact with a solvent (normally water or an aqueous solvent at basic pH or semialcoholic solution), obtaining an aqueous extract. This aqueous extract contains major amounts of other species apart from β-glucans (nonstarch polysaccharides, starch, proteins, and oils) and, hence, an efficient purification steps are needed. For this purpose, β-glucans are precipitated by the addition of an alcohol as anti-solvent, or separated by other procedures, such as freezing-thawing cycles. The precipitate obtained, once isolated and dried, results in a product that contains between 20% and 70% of β-glucans. In general, the extraction of β-glucans through wet processing results in an efficient purification of above 80% of pure β-glucan, and various molecular weight distributions (60–2200kDa) can be obtained depending on the pH and solvents used, as reported by Kurek et al. (2018). β-Glucans are precipitated by the addition of an alcohol as antisolvent. There is a constant demand to extract and purify β-glucans, considering the yield, purity, and molecular weight, since these properties affect the final viscosity obtained in water or buffer solutions. While extracting β-glucans, water or other solvents are used. Protein-based or nonstarch polysaccharides are present in the solutions during enzyme-treatment, and these fine particles can be removed by adding external flocculants, which aggregate solid impurities to form flakes that can be easily removed from solutions (Kurek et al., 2018). Natural flocculants are promising agents in improving food-processing operations due to their safety and ecological benefits. Several flocculants could be used in foods, such as guar gum, alginates, chitosan, or gelatin. Kurek et al. (2018) used barley and oat flours produced from the whole grains and extracted the β-glucans by using natural floculants for further purification. With this aim, each kind of flour was mixed by rotation (1 h) with water of pH 9.5 (1 g/3 mL) due to 10%-Na2CO3 in order to prevent from the extraction of proteins and nonglucan polysaccharides, including the arabinoxylans. After centrifugation, chitosan, guar gum, or gelatin (0.2% or 0.6%) was added to the separated supernatant and left for acting at 45°C for 30 min, being then the residue discarded after centrifugation. Limberger-Bayer et al. (2014) previously reported that β-glucans can be solubilized at 45°C without the risk of starch gelatinization. The collected purified supernatant was treated with a thermostable α-amylase at 80°C at a constant optimal pH of 7.0. When a negative iodine test result was reached and, hence, starch was totally hydrolyzed, the solutions were cooled, and the pH decreased to 3.5 by acetic acid addition to reduce protein solubility, and heated at 95°C for protein denaturation and precipitation. They were discarded after centrifugation, and 1.5 volumes of 96% (v/v) ethanol were added to the separated supernatant containing the solubilized and purified β-glucans. They were left to precipitate for 24 h at 4°C, separated by centrifugation, and dried into a vacuum oven. The protein content of the β-glucans extracted without the addition of flocculants was similar in those extracted from barley and oats (6.76%–5.06%). Similar soluble dietary fiber contents (73.57%–76.01%) were also determined. The addition of chitosan and guar gum as flocculants produced a significant increase in the amounts of soluble dietary fiber yields

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(79%–83%) in barley and oat extracts, with simultaneous low values of protein contents (0.98%–2.99%). The molecular weights of the β-glucans extracted without flocculants’ addition from barley and oats were 64,873 Da and 28,000 Da, respectively. Chitosan, guar gum, and gelatin led to isolate β-glucans of lower molecular weights from barley (37,362–46,931 Da), whereas the molecular weights of the β-glucans obtained from oats were increased after purification (34,743–55100 Da). The apparent viscosity measured at 20°C and a shear rate of 202 s1 for 1% β-glucan in aqueous buffer phosphate (pH 6.5) solution was 18.31 and 12.80 Pa s for the β-glucans extracted without a flocculant from barley and oats, respectively, which are relevant values. Chitosan and guar gum were permitted to isolate β-glucans that produced 1% solutions with similar or slightly higher apparent viscosity, while gelatin led to extract β-glucans whose 1% solutions showed lower apparent viscosity (8.08–9.62 Pa s). The solutions showed flow-index values of the Ostwald’s law of 1.0 or slightly lower (0.917–0.989), which means that the solutions were Newtonian or slightly pseudoplastic. These flow behaviors mean that the hydrated macromolecules almost did not change their interactions with the water (solvent) flow, which could be due to that β-glucans are not laterally substituted and, hence, there is a low probability of macromolecular entanglements. Only the β-glucans extracted from oats with gelatin as flocculant in phosphate buffer aqueous solution produced a clear pseudoplastic behavior, with a flow index value of 0.762 and 0.702 Pa s. The structure of β-glucan is the same as for cellulose except for the β-(1 ! 3)-linkages, which introduce a kink to the chain. Molecules with less order have a reduced tendency to aggregate, and β-glucan is therefore a molecule that it is partially soluble in water. How solubility of β-glucan is influenced by the order and frequency of these linkages is under investigation. Some studies have shown that longer sequences of β-(1 ! 4)-linkages produce less soluble β-glucans because of intermacromolecular associations. However, Izawa, Kano, and Koshino (1993) suggested that even if there are long blocks of β-(1 ! 4)-linkages, their influence on solubility would not be significant compared to that of long blocks of contiguous cellotriosyl residues. More recent data support this latter conclusion that structural regularity, arising from increasing proportions of β-(1 ! 3)-linked cellotriosyl units, reduces the solubility and also increases the tendency to gel. Cereal β-glucan is able to form gel structures, but gelation has been shown to require quite high β-glucan concentration when compared to the concentrations that would be relevant in food products. Critical concentration for gelation was reported to be 3.5% and 4.4% for oat β-glucans with a molar mass of 35,000 and 110,000 Da, respectively. Also, acid-hydrolyzed oat and barley β-glucans with a molar mass of 40,000–70,000 Da was determined to gel at a concentration of 6%. On the other hand, gelation of oat and barley β-glucans was reported to occur at low concentrations (1%) through repeated freeze-thaw cycles or cryogelation, and thus, indicated that gelation may take place in frozen products. Gelation was suggested to require partial dissolution of β-glucans, which depends on molar mass, and aggregation state of the macromolecules (M€ akel€ a, Maina, Vikgren, & Sontag-Strohm, 2017). Shah et al. (2017) extracted β-glucans according to the procedure previously explained by Temelli (1997). Barley and oat flours separately obtained by milling of the whole grains in a high-speed electric mill and passed through a 0.50 mm mesh was suspended in water (1 g:10 mL), the pH adjusted to 7.0 with sodium carbonate, left under stirring (30 min; 55 °C), and the residue separated by centrifugation. For protein precipitation, the separated supernatant was led to pH 4.5 with 2M-HCl and centrifuged. The separated supernatant was

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then treated with one volume of absolute ethanol for precipitation of β-glucans. The pellet was recovered by centrifugation, resuspended in ethanol, and the mixture was homogenized at room temperature, followed by filtration for recovering of the residue, ethanol washing, and air drying. Shah et al. (2017) determined that these β-glucans extracted from oats and barley have a purity of  95%, with residual amounts of proteins (1.99%–1.64%), as well as 2000 and 1790 kDa average molecular weights, respectively. The flow index of the HerschelBulkly’s model (25°C) was 0.849 for oat and 0.831 for barley β-glucan solutions in water at 6% (w/v) concentration, demonstrating a pseudoplastic behavior. Only the oat β-glucan solution showed yield stress, with a value of 1 Pa. The mechanical spectrum of the oat β-glucan solution at 25°C corresponded to a physical weak gel at 6% (w/v) concentration, while the barley β-glucans showed, at the same concentration, the mechanical spectrum of a dilute solution. Macromolecular entanglements were then not produced in the latter case by the barley β-glucans. The (1,3;1,4)-β-D-glucans consist of unbranched and unsubstituted chains of (1,3)- and (1,4)-β-glucosyl residues, in which the ratio of (1,4)-β-D-glucosyl residues to (1,3)β-D-glucosyl residues, appears to influence not only the physicochemical properties of the polysaccharide and therefore its functional properties in cell walls, but also its adoption by different plant species during evolution (Burton & Fincher, 2009). As a conclusion, it can be remarked that a better procedure for β-glucan separation with higher purity from oats and barley can be summarized in Fig. 7.1, according to that explained by Kurek et al. (2018). Flours are used for extraction in water of pH 9.5 (Na2CO3) to avoid the isolation of proteins and non-glucan polysaccharides, including the arabinoxylans. All these compounds are solubilized in the alkaline water, with the exception of starch and proteins. The separated residue is liberated from the starch by treatment with a thermostable α-amylase

FIG. 7.1 β-Glucan separation from oats and barley. According to Kurek et al. (2018).

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at 80°C (pH 7.0), after which the supernatant containing all glucose produced from the enzyme activity is discarded. The residue is then suspended in water of pH 3.5 (acetic acid) together with heating to 95°C for proteins’ denaturation and precipitation. The final supernatant obtained only contains the β-glucans, which are then separated from the solution for additional purification through precipitation with 1.5 volumes of 96% (v/v) ethanol.

7.2.4 Other Hemicelluloses Arabinoxylan (AX) is the predominant polysaccharide in the cell wall of wheat grain. It consists of a typical hemicellulose backbone of equatorial β-(1 ! 4)-linked xylose residues, which are substituted with Ara residues on the C(O)-2 and/or C(O)-3 position. Since AX is mainly composed of Xyl and Ara, it is commonly referred to as pentosans. Phenolic acids such as ferulic acid can be ester linked on the C(O)-5 position of Ara. Xylans lack Ara substituents (Scheller & Ulvskov, 2011). Arabinoxylan-rich fiber (hemicellulose B) has drawn special attention because of its unique acceptability and palatability. As the rest of hemicelluloses, arabinoxylan has an equatorial-equatorial β-1 ! 4-linkage that cannot be hydrolyzed by human digestive enzymes, and thus is a good dietary fiber (Yadav & Hicks, 2018). When studying the structure of the hemicellulose fractions of seeds of grape (Vitis vinifera cv. Palomino), Igartuburu, Pando, Rodrı´guez-Luis, and Gil-Serrano (1998) gave the definition of the different components of woods and straw as a function of the extracted steps needed. The residual solid obtained after delignification with sodium chlorite-acetic acid of raw materials with high lignin contents is known as holocellulose. It is the total polysaccharide fraction constituted by cellulose and all of the hemicelluloses. The hemicelluloses can then be extracted from the holocellulose by dissolution in 10%-NaOH aqueous solution under nitrogen to avoid oxidation, and hemicellulose A is then precipitated from the supernatant by acidification to pH 5.0 (acetic acid). After centrifugation, the residue is recovered (hemicellulose A) while the separated supernatant is treated with ethanol for precipitation of the so-called hemicellulose B, soluble in acids, which is in general dialyzed against running water. Yadav and Hicks (2018) obtained hemicelluloses A and B from low-valued grain processing by-products, agricultural residues, and energy crops by an alkaline extraction followed by ethanol precipitation. Corn bran and stover, rice fiber, wheat bran and straw, switchgrass, miscanthus, and sugarcane bagasse were oven dried and ground (20-mesh particle size) and used as fiber sources.. The hemicellulose A and hemicellulose B were extracted from the plant material by boiling for 1 h at 85°C under efficient mechanical stirring in the presence of thermostable α-amylase (pH 6.8) for starch hydrolysis. The pH was then raised to 11.50 (50%-NaOH), and the total volume of reaction was maintained constant by NaOH or water addition, while stirring for other 30 min. The hot slurry was then immediately sheared under high speed (10,000 rpm; 30 min) and cooled to room temperature. Afterward, the solid residue separated by centrifugation was discarded, while the supernatant was collected. The pH was adjusted to 4.0–4.5 (concentrated HCl) to precipitate the acid insoluble fiber fraction of “hemicellulose A,” which was collected after centrifugation. The supernatant was then separated, and two volumes of ethanol were gradually added under stirring to precipitate the acid soluble fraction of “hemicellulose B,” which was recovered after centrifugation. The isolated products were obtained with yields that varied between 2.33% for rice fiber to 25.13% for

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corn bran. All the plant materials analyzed contained a high proportion (11.20%–22.63%) of acid insoluble hemicellulose (hemicellulose A), except corn bran, which has only 3.98%. The hemicellulose A fraction obtained from corn bran, corn stover, and wheat bran were very rich in protein (24.58%, 13.51%, and 37.85%, respectively), but the hemicellulose A isolated from the remaining five sources contained only 2.72%–4.41% of protein. Corn and wheat brans had between 0.391% and 1.43% of residual starch, but in the rest of the samples, the starch content was below 1%. The crude fat content varied from 0.65 for sugarcane bagasse to 13.30% for wheat bran, excepting Miscanthus fiber, which showed absence of fats. The neutral detergent fiber content varies between 0% and 0.69%, except that obtained from corn stover, with 4.98%. As the hemicellulose A extracted from all the sources studied by Yadav and Hicks (2018) showed high levels of combined amounts of ash, protein, and fat, they do not contain very high levels of insoluble (1.6%–22.5%), soluble (11.2%–35.6%), and total (15.6%–54.0%) dietary fibers. The hemicellulose B fraction showed high ash contents (2.97%–24.39%). Their protein content was between 0% and 1.27% except the hemicellulose B of wheat bran, which was rich in proteins (8.37%). The hemicellulose B of the different sources analyzed had low residual starch (0.54%–2.43%) and crude fat (0.14%–1.37%). These fractions had 0% or very low levels of neutral detergent fiber (0.00%–1.92%) and insoluble dietary fiber (0.00%–3.2%). They were essentially constituted by soluble dietary fiber, ranging from 87.2% to 93.6%, except for the hemicellulose B isolated from wheat bran and sugarcane bagasse, which had 60.3% and 55.5%, respectively. Hence, the hemicellulose B extracted from most of these sources was almost pure soluble dietary fiber, which can be useful functional ingredients in food formulation. The neutral sugar composition of the fibers extracted demonstrated typical arabinoxylans composed by a high molar ratio of Ara to Xyl. Other neutral sugars found were Gal and Glc. D-Galacturonic and glucuronic acids were found. Except the fiber fraction obtained from wheat bran, the rest of the fractions were very good emulsifiers and showed antioxidant activity. The latter was higher for the isolated fiber-fractions than for their respective original plant material. Heteropolysaccharides were extracted by Rosicka-Kaczmarek, Komisarczyk, and Nebesny (2018) from several types of rye and wheat brans that differ in their particle size (fine and coarse granularity, and wholegrain), which were the by-products of industrial flour milling. The predominant size for each granulometry depended on the origin of brand. The extraction of heteropolysaccharides was performed with water (1 g:15 mL) at room temperature (20–25°C) with constant stirring for 1 h. Each step of this two-step procedure was performed for 1 h. The supernatant containing soluble components were separated by centrifugation and pooled. Starch was hydrolyzed by using thermostable (95–100°C) α-amylase (pH 5.0–5.2) and glucoamylase (60°C, pH 4.0–4.2), while proteins were digested by a Bacillus licheniformis protease (60°C, pH 8.1). Afterwards, the final supernatant of each raw material was collected, adjusted to 25°C and pH 4.0 (HCl), and concentrated twofold under vacuum. The concentrated extracts were dialyzed through 12,000 Da membranes, and finally frozen and freezedried. The properties of heteropolysaccharide products depended on their botanical origin and bran granularity. Phenolic acid content was 0.98, 1.57, and 1.98 g/100 g dry mass for rye bran extracted fiber product from fine and coarse granularity, and wholegrain, respectively, while it varied from 2.02% to 2.38% and 2.22% for the same particle sizes of wheat bran extracted fiber product. On the other hand, the free ferulic acid content varied between 49.03 and 63.63 mg/100 g fiber product (dry basis), while the esterified ferulic acid content varied

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between 98.14 and 269.60 mg/100 g. The protein content of the fiber products was from 10.20% up to 28.86% (dry mass). The neutral sugar composition was in general dominated by Xyl (27.94%–40.40%) and mannose (Man; 25.72%–41.72%) monomers, while some lower or similar contents of Ara (17.94%–29.86%) were also found. The Glc content varied between 5.26% and 12.35%, that may form part of glucomannan, which is a linear polysaccharide composed of both (1 ! 4)-β-linked D-mannose and D-glucose residues in a nonrepeating pattern (Scheller & Ulvskov, 2011). Glucomannans are minor constituents of walls of most aleurone and starchy endosperm cells of cereals, but in certain Oryza indica rice cultivars, values of up to 17% of glucomannan have been reported in the endosperm walls (Fincher, 2016). The fiber products extracted from rye bran contained more arabinoxylans than those derived from wheat bran and exhibited higher antioxidant capacity, measured as DPPH radical scavenging activity, despite having lower total polyphenolic levels. Yadav, Kale, Hicks, and Hanah (2017) extracted a cellulosic arabinoxylan fiber from corn bran and stover, rice fiber, wheat bran, wheat straw, switch grass, sugarcane bagasse, sorghum brans, barley hulls, barley straws, and carrot pomace, which were by-products, agricultural residues, and energy crops. The plant material was extracted under stirring with water (2 g:11.5 mL) at 85°C. The pH was led to 6.8 (NaOH) and thermostable α-amylase was then added and stirred for 1 h for starch hydrolysis. Afterward, the pH of the dispersion was raised to 11.5 (NaOH) and maintained constant as the total volume, while stirring at 85°C for 30 min. In this step, hydrolysis of diferulate bridges that crosslink hemicelluloses occurs. The hot dispersion was immediately sheared using high speed (10,000 rpm; 1 h). The solid disaggregated residue was separated by centrifugation, suspended in 2 L of boiling water and stirred for 5 min. The hot suspension was again sheared (10,000 rpm; 5 min), then left for cooling at room temperature, and centrifuged to separate the solid residue, repeating hot water washing and shearing cycles (two or three times) until a clear supernatant was obtained. The final solid residue was collected, suspended in water and dried by drum or spray drying to obtain the final products. The yield varied between 14.30% and 59.90% for wheat bran and rice fiber products, respectively. Wheat straw, Miscanthus, sugarcane bagasse, barley straws, and corn stover were those raw materials that led to higher yields (56.70%–40.20%) of the final product. In general, very low amounts of proteins (0.56%–2.2%) and starch (0.06%–0.36%) were found, with the exception of the products obtained from three samples of sorghum brand, Black, Sumac, and Burgundy (16.49%, 23.82%, and 5.37% for proteins and 2.51%, 5.42%, and 0.91% for starch, respectively). The final products obtained from all sources were almost entirely constituted by insoluble dietary fiber (91.80%–99.61%), with the lowest amounts (77.88% and 77.62%) for the products obtained from the sorghum brands Black and Sumac. As a consequence, very low and nondetectable amounts of soluble dietary fiber were found in the fiber products extracted. Excepting the wheat straw and sorghum brand Sumac final products, the rest showed very high antioxidant capacity, as determined through the ORAC assay with notably highest values for the corn brand products. The water-holding capacity of the fiber products varied between 13.80 for barley hulls’ product and 74.30 (g water/g product) for the spray-dried corn bran. The drying process used (drum drying or spray-drying) greatly affected the water-holding capacity of the fiber product obtained. The 4% (w/v) aqueous dispersions of each fiber fraction showed pseudoplastic behavior, with the flow index (n) values ranging

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225

from 0.25 to 0.5. In relation to the neutral sugar composition, the highest contents corresponded to Glc (34.78%–66.80%), followed by Xyl (11.69%–31.97%), and Ara (2.04%–12.29%).

7.2.5 Total Dietary Fiber One of the few studies that used EAE for total dietary fiber extraction was performed by Ma et al. (2015). They evaluated the extraction of DF from cumin (Cuminum cyminum L.) by shear emulsifying assisted enzymatic hydrolysis (SEAEH). For this purpose, cumin was mixed with distilled water, shear-emulsified (7000 rpm, 30 min), and treated with Alcalase 2.4 L (Table 7.2). Under optimal conditions, total DF yield was 84% with 12% soluble DF (5% pectin) and 72% insoluble DF (37% hemicellulose, 33% cellulose, 24% lignin). Authors found that decreasing DF particle size from 100 to 51 μm generated DF with greater capacity to absorb oil, glucose, and bile acids but with a particle size of 26 μm, the capacity to absorb oil and glucose decreased.

7.3 EMERGENT METHODS FOR DIETARY FIBER EXTRACTION 7.3.1 Pectins Ultrasound assisted extraction (UAE) is one of the most used emerging technologies for sustainable soluble dietary fiber extraction. When ultrasound (US) waves pass through a solvent medium, it generates small vaporfilled bubbles that collapse violently causing cavitation, which disrupts vegetable cell wall and membrane integrity increasing cell wall permeability, facilitating solvent access to the cell internal structure, and thus favoring the extraction of compounds into the solvent. Frequency, amplitude, power input, reactor design, shape of the probe or sonotrode, solvent, matrix, and temperature are the most important parameters to be considered for UAE (Chemat et al., 2017). There are two types of US devices: ultrasonic baths (for indirect sonication), which usually operate at a frequency of 40 kHz and probe-type ultrasound equipment (for direct sonication), which usually operate at a frequency of 20 kHz (Chemat et al., 2017). The latter is preferred for extraction application. Some of the benefits of this technology are lower extraction times, less amount of energy and solvents used, and CO2 emissions (Chemat et al., 2017; Chemat, Huma, & Khan, 2011). As it can be observed in Table 7.3, most of the available publications on UAE of dietary fiber refer to pectin extraction. The majority of these publications are dedicated to optimizing extraction conditions for obtaining higher yields or for comparison with conventional extraction techniques. Freitas de Oliveira et al. (2016) used response surface methodology for pectin UAE from passion fruit peel in order to optimize pectin yield, galacturonic acid (GalA) content, degree of methylation (DM), and compared it to conventional extraction (CE). Under optimum UAE conditions (Table 7.3), they obtained a pectin fraction with 66.65% GalA and a DM of 60%. Authors observed that extraction yield increased 1.6-fold when using US, and both GalA content and DE were affected by temperature and power intensity.

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TABLE 7.3 Ultrasound Assisted Extraction of Dietary Fiber From Different Sourcesa Source

Extraction Conditions

US Parameters

Yielda

Type of DF

References

Barley

L: water S/L: 20 g/200 mL T: 55°C

Direct sonication F: 24 kHz P: 400 W A: 60%–100% (80) p: 0.8–1.0 (1.0) t: 3–17 min (17)

66.1

β-Glucans

Benito-Roman et al. (2013)

Brewer’s spent grain

L: potassium hydroxide 0.3–3.7 M S/L: 2 g/50 mL

Direct sonication F: 20 kHz P: 750 W A: 8%–100% p: 5 s on-5 s off t: 3.3–11.7 min

20

Arabinoxylans

Reis et al. (2015)

Burdock root

L: water L/S: 5 g/75 mL T: 20–60°C (36.76)

Direct sonication F: 25 kHz A: 20%–100% (83.22) t: 5–25 min (25)

24.31

Inulin

Milani, Koocheki, and Golimovahhed (2011)

Chinese chive

L: water S/L: 1:20–1:50 w/v (1:32) T: 303–343 K (310.15 K)

Direct sonication P: 160–480 W (458) p: 5 s on-1 s off t: 0–80 min (30)

3.66

Polysaccharides

Zhang, Zhang, Lu, Luo, and Zha (2016)

Eremus spectabilis root

L: water L/S: 30–50 v/w (50) T: 30–70°C (60)

Direct sonication F: 24 kHz P: 200 W

62 (direct sonication)

Pectins

Pourfarzad et al. (2014)

Indirect sonication F: 25 kHz P: 500 W A: 20%–100% (79.97) t: 5–40 min (29.3) Ganoderma mushroom

L: water S/L: 10 g/250 mL T: 40°C

Direct sonication F: 20 kHz P: 600 W t: 20–80 min (60)

0.81

β-Glucans

Alzorqi et al. (2017)

Grape pomace

L: citric acid S/L: 10 g/100 mL pH: 1.0–2.0 (2.0) T: 35–75°C (75)

Indirect sonication F: 37 kHz P: 140 W t: 20–60 min (60)

32.3

Pectins

MinjaresFuentes et al. (2014)

Grape pomace

L: 2 and 4 M potassium hydroxide S/L: 1:50 g/mL T: 20°C

Indirect sonication F: 37 kHz P: 140 W t: 1–5 h (2.6)

7.9

Hemicelluloses

MinjaresFuentes et al. (2016)

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7.3 EMERGENT METHODS FOR DIETARY FIBER EXTRACTION

TABLE 7.3

Ultrasound Assisted Extraction of Dietary Fiber From Different Sourcesa—cont’d

Source

Extraction Conditions

US Parameters

Yielda

Type of DF

References

Grapefruit albedo

L: hydrochloric acid S/L: 6 g/300 mL pH: 1.5 T: 50–70°C (70)

Direct sonication F: 24 kHz P: 200 W t: 4–30 min (25)

17.92

Pectins

Bagherian et al. (2011)

Grapefruit peel

L: 0.5 M hydrochloric acid S/L: 1:30–1:70 g/mL (1:50) pH: 1.5 T: 30–80°C (60)

Direct sonication F: 20 kHz P: 30–80 W (60) A: 30%–80% (50) t: 10–60 min (25.9)

26.74

Pectins

Xu et al. (2014)

Grapefruit peel

L: hydrocholic acid S/L: 3 g/150 mL pH: 1.5 T: 60–80°C (66.71)

Direct sonication F: 20 kHz P:

10.18–14.26 W/cm2 (12.56) p: 2 s on-2 s off t: 20–40 min (27.95) L: citric acid S/L: 1:40 pH: 2.5 T: 20–80°C (80)

27.34

Pectins

Wang et al. (2015)

Direct sonication F: 20 kHz P: 500 W p: 5 s on-5 s off t: 15 min

17.15

Pectins

Wang et al. (2016)

Mango peels

Musa balbisiana

L: citric acid S/L: 1.5–1.25 g/mL (1:15) pH: 1.0–5.0 (3.2)

Direct sonication F: 20 kHz P: 100–500 W (323) t: 5–45 min (27)

8.99

Pectins

Prakash Maran et al. (2017)

Papaya peel

L: 0.6%–3.0% sodium hydroxide S/L: 1:10–1:36 w/w T: 30–80°C

Direct sonication P: 125–250 W (175) t: 10–60 min (30.76)

36.99

Pectins

Zhang et al. (2017)

Passion fruit peel

L: 1 M nitric acid S/L: 1:30 g/mL pH: 2.0 T: 45–85°C (85)

Direct sonication F: 20 kHz P: 132–664 W/cm2 (644) t: 3–20 min (10)

12.67

Pectins

Freitas de Oliveira et al. (2016)

Pomegranate peels

L: water S/L: 1:10–1:20 g/mL (1:18) pH: 1.0–2.0 (1.27) T: 50–70°C (61.9)

Direct sonication F: 20 kHz P: 130 W t: 12–35 min (28.31)

23.9

Pectins

Ganesh Moorthy, Prakash Maran, Muneeswari Surya, Naganyashree, and Shivamathi (2015) Continued

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TABLE 7.3 Ultrasound Assisted Extraction of Dietary Fiber From Different Sourcesa—cont’d Source

Extraction Conditions

US Parameters

Yielda

Type of DF

References

Pumpkin

L: water S/L: 1:10–1:20 g/mL (1:10) T: 50–70°C (70)

Direct sonication F: 20 kHz P: 50–70 W (70) t: 15–25 min (23)

16

Soluble DF

Prakash Maran, Mekala, and Manikandan (2013) and Prakash Maran, Sivakumar, et al., 2013

Wheat straw

L: 0.5 M potassium hydroxide S/L: 9.78 g/300 mL T: 35°C t: 2.5 h (after sonication)

Direct sonication F: 20 kHz P: 100 W t: 0–35 min (35)

25.5

Hemicelluloses

Sun and Tomkinson (2002)

White mushroom

L: water S/L: 3 g/30 mL

F: 24 kHz P: 400 W A: 20–100 μm (100) t: 0–15 min (15)

Soluble DF

Aguilo´Aguayo, Walton, Vin˜as, and Tiwari (2017)

4.7

a

Yield is expressed as g DF/100 g dried substrate. Values between parentheses are the optimum conditions found. DF, dietary fiber; L, liquid (extractant); S, substrate; t, time; T, temperature; F, frequency; P, ultrasonic power; A, amplitude; p, pulses.

Wang et al. (2016) compared UAE (Table 7.3) with CE of mango peel pectin. Both extraction methods performed at 80°C resulted in higher pectin yield than those performed at 20°C, while the extraction time for UAE-80°C (15 min) was significantly shorter when compared to CE-80°C (2 h) with equivalent pectin yield. Additionally, UAE-80°C pectins had higher GalA and protein content, higher molecular weight, higher viscosity, better emulsifying capacity and stability, as compared to UAE-20°C. Zhang et al. (2017) extracted soluble dietary fiber (SDF) from papaya (Carica papaya Linn.) peel through ultrasound-assisted alkaline extraction (u-SDF) and compared it with alkaline extraction (a-SDF) in terms of composition, structure, and properties of the extracts. Table 7.3 shows u-SDF extraction conditions applied. Authors observed that GalA content increased substantially, from 15.63% to 27.36%, after ultrasonic treatment. In addition, the waterholding capacity (WHC) of u-SDF (5.26 g/g) was greater than that of a-SDF (4.93 g/g). The oil-holding capacity (OHC) of a-SDF was 1.15, and for u-SDF, it was 1.40 g/g, while u-SDF had a higher swelling capacity (4.54 mL/g) than a-SDF (4.05 mL/g). Moreover, u-SDF presented higher percentages of essential amino acids and essential trace elements and higher thermal stability than a-SDF. Li, He, Lv, and He (2014) extracted water-soluble DF from apple pomace (AP) using cellulase and ultrasound (US) assisted methods in comparison with conventional acid method (20 g AP powder in 400 mL of pH 2.0 sulfuric acid solution heated for 4 h at 80°C using a water bath). For US extraction, the same acid method was applied, but instead of using a water bath, they used an ultrasonic cleaning bath. The highest soluble DF yield (16.4%) was obtained after 40 min of sonication at 400 W; while for conventional acid extraction, the yield was 10.3%. For EAE, they used cellulase from Aspergillus niger (Table 7.2), and they obtained a soluble DF

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229

yield of 18.7%, which was higher than the yields obtained by acid and US methods. The water-retention capacity (WRC) and swelling capacity (SWC) of DFs extracted from AP were all improved by US and cellulase extraction in comparison with conventional acid method (3.0 g/g of WRC and 2.5 mL/g of SWC). The SWC values of DFs extracted by cellulase and UAE methods were comparable ( 7.0 mL/g), whereas the cellulase hydrolysis of AP produced a soluble DF with the highest WRC value (8.9 g/g). Minjares-Fuentes et al. (2014) developed a US-assisted optimized procedure for the extraction of pectins from grape pomace using citric acid as the extracting agent. They used a statistical design for obtaining high yields of pectins of high molecular weight (Table 7.3). The yield obtained after US extraction (Table 7.3) with the optimal conditions was 20% higher than the yield obtained when the extraction was carried out, applying the same conditions of temperature, time, and pH, but without ultrasonic assistance. In addition, pectins from UAE also exhibited a higher average molecular weight. Xu et al. (2014) evaluated the effect of using ultrasound and/or heating on the yield (Table 7.3) and swelling behavior of pectin extracted from grapefruit peel. Authors concluded that the optimized combined method significantly increased the yield of pectin by 14.08%, shortened the extraction time by 39.53%, and reduced extraction temperature by 20°C. Furthermore, image studies showed that US heating extraction disrupted the vegetal tissue and significantly improved its swelling behavior when compared to hot (60°C) extraction without US. Bagherian, Zokaee Ashtiani, Fouladitajar, and Mohtashamy (2011) compared UAE (Table 7.3) and CE of pectin from grapefruit. Results showed that UAE obtained higher yields than CE (at equal times of extraction). The GalA content increased with the sonication time, while DE and molecular weight decreased with increasing sonication time. When comparing the effect of temperature in UAE, authors observed that the pectin molecular weight decreased with increasing temperature because of pectin degradation. Deep eutectic solvents (DES) are commonly composed of two nontoxic components, one of them with the capacity to be a hydrogen bond acceptor (quaternary ammonium, tetralkylammonium, or phosphonium salts) while the other (acids, alcohols, amines, or carbohydrates) possesses hydrogen bond donor HBD properties. They have much lower melting points than that of any of its individual components, which can be attributed to the formation of intramolecular hydrogen bonds between them. DES as well as the natural deep eutectic solvents (NADES), which are prepared using natural components produced by cell metabolism, are eco-friendly, nontoxic, and biodegradable. Their low cost and possibility for production in the laboratory allow considering them as an emergent tool for the development of sustainable extraction procedures instead of organic solvents (Cunha & Fernandes, 2018; Zhang, de Oliveira Vigier, Royer, & Jerome, 2012). Lynam, Kumar, and Wong (2017) studied different DES (formic acid: choline chloride, lactic acid: choline chloride, acetic acid: choline chloride, lactic acid: betaine, and lactic acid: proline) in relation to their capacity of preferentially dissolving lignin at 60°C in a process under agitation at 200 rpm for 20 min from pine biomass. This effect can help to the fractionation or concentration in some preferential components of dietary fiber fractions isolated from food wastes. Jablonsky´, Sˇkulcova´, Malvis, and Sˇimac (2018) revised the application of DES and NADES for the extraction from various substrates of different compounds. The actualized information reported allow conclusions that delignification is a process habitually present when these solvents are used and that it is a key

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tool for the extraction desired. Results from the Master Thesis of Ryan Bogaars (2015) reviews the possibility of extraction of pectin, a soluble dietary fiber, from orange peel using NADES. The yield obtained was 15.5% (w/w, dry weight) using proline:malonic acid:water (1:1:6) and 0.56% (w/w, dry weight) for 1,2-propanediol:choline chloride:water (1:1:1). Liew, Ngoh, et al. (2018) and Liew, Teoh, et al. (2018) extracted pectin-fractions from 60°C-dried pomelo peel (250–355 μm particle sizes) using DESs (1:29 mL/g, 88°C, 141 min; lactic acid-glucose-water 6:1:6 and 5:1:3, lactic acid-glucose 5:1, lactic acid-glycine-water 3:1:3, lactic acid-glycine 9:1; pH 0.31–2.52; 68.99–416.90 mPa s viscosity). The presence of water in acid-water based DES can decrease the viscosity. This implies that a proper selection of mixture components for DES preparation is important as it could directly affect the versatility for chemical usage, and also the extraction performance. After DES’s extractive treatments, each dispersion was centrifuged and the pectin-enriched fraction precipitated from the separated supernatant by addition of 95%-ethanol. The filtrated pectin-fraction was dried at 65°C in an air oven. The yield of the extracted pectin from pomelo varied greatly from 4.47% to 39.57%, and the DM values ranged between 49.71% and 67.50%. The pH exerted the most significant influence on pectin yield, followed by temperature, and liquid:solid ratio, while the time involved in the acid-extraction had the lowest effect. The 6:1:6 lactic acid-glucose-water solution of pH 0.56 and 68.99 mPas of viscosity permitted to extract pectin-fractions with the highest yield (23.04%) among the other DESs used, and high DM (79.15%). The pectin-fractions obtained showed very poor rheological functionality since the Ostwald law flow index was around 1.0, which corresponds to a Newtonian fluid, and the viscosity values were also low. According to Johnson (2007), an ionic liquid is characterized by a cation and or anion quite large, specific conductivity usually 22%, w/w) than those obtained from AIR obtained by convective heating (galacturonic acid >13%, w/w). The fractions formed gels in the presence of calcium ions and were considered to be adequate for their use in the food industry as ingredients or additives. Moderate electric field (MEF) is a process of controlled and possibly reversible permeabilization characterized by the use of electric fields typically bellow 1 KV/cm. Heating usually occurs in these applications, but controlled studies have shown enhanced mass transfer effects that are nonthermal in nature. Freitas de Oliveira, Giordani, Gurak, Cladera-Olivera, and Ferreira Marczak (2015) studied the moderate electric field extraction of pectin from passion fruit peel (Passiflora edulis Sims) and compared the results with those obtained with direct boiling, the conventional method of extraction, which takes around 2 h to obtain a good yield of pectin using strong acid solutions. Experiments were performed in a batch-stirred reactor with a moderate electric field at 60 Hz. When dried peel/extractant ratio, extraction temperature, and voltage/time were maintained at 1:30 (w/v), less than 45°C, 50 V and 15 min, it was observed that at pH 2.0 the pectin isolated had a galacturonic acid content of 69% (w/w, dry matter), an esterification degree of 91% (w/w, dry matter), and a yield of 5% (w/w, dry matter), which were found to be the highest among the different extraction conditions studied. The extraction yield was lower than that of the traditional extraction (higher temperature, longer times), but galacturonic acid content and esterification degree of the pectin obtained were similar. According to the authors, MEF is an efficient, time-saving, and eco-friendly method for the extraction of pectin with a high esterification degree and galacturonic acid content higher than 65 g/100 g of pectin. More research must be performed to evaluate the convenience in relation to energy expenditure and investment costs. The proposed procedure can be also used as a pre-treatment to increase the yield during traditional heating because it induces cell-wall damage, increasing the permeability. Subcritical water extraction (SWE) is an extraction and fractionation technique that uses water at temperatures between 100°C and 374°C and under pressure to maintain the liquid state (critical point of water, 22.4 MPa and 374°C). This extraction is environmentally friendly because it does not use organic solvents. But Kanmaz (2018) and Jokic, Gagic, Knez, Sˇubaric, and Sˇkerget (2018) informed that the use of an elevated temperature in subcritical water at higher temperatures might generate unwanted compounds such as 5-HMF, which can be

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extracted. Because of that, it is important to optimize the extraction procedure. Khuwijitjaru (2016) stated that decomposition reactions of several natural compounds during subcritical water treatment of plant tissues can occur. In this direction, the conversion of polysaccharides to oligosaccharides with health benefits seems to be a promising application of this technique. Subcritical water was used to extract pectin from citrus peel and apple pomace (Wang, Chen, & L€ u, 2014), and the effect of extraction temperature on properties of the pectins was investigated. The maximum yield of citrus peel pectin and apple pomace pectin were 22% and 17% respectively. The pectin solutions exhibited shear-thinning properties, showed viscoelastic behavior, antioxidant activity, and inhibition of colon cancer cell HT-29. Chen, Fu, and Luo (2015) extracted pectin-enriched material (PEM) from sugar beet pulp using subcritical water combined with ultrasonic-assisted treatment. Ultrasonication was carried out as a pre-treatment in water using a sonic frequency of 25 kHz and a time of 10 min. Optimization of the reaction parameters for maximum extraction yield of PEM by means of subcritical water extraction was carried out using response surface methodology. The conditions for the maximum yield obtention (25%) were: liquid/solid ratio 44, extraction temperature 120°C, extraction time 30 min, and extraction pressure was 11 MPa. The material obtained showed a galacturonic acid content of 59%. Klinchongkon, Khuwijitjaru, Wiboonsirikul, and Adachi (2015) studied the treatment by means of subcritical water of passion fruit peel, a major by-product of the fruit processing. The treatment was performed under nonisothermal conditions in batch-type reactor containing the dried peel and water in the ratio 1:16 (w/w), with maximum temperatures in the range of 100–245°C. They observed the decomposition of the polysaccharides giving origin to mono- and oligosaccharides with high degree of polymerizations (DP > 7). The treatment involving a heating at 150°C for 4.5 min and to 175°C within 5.5 min, respectively, yielded the highest amount of oligosaccharides (21%) with galacturonan as a main component (65%), indicating that pectin was predominantly hydrolyzed and extracted under these conditions. The study showed that subcritical water treatment is an effective method for producing oligosaccharides, which may be useful as dietary fiber. Liew, Ngoh, et al. (2018) and Liew, Teoh, et al. (2018) extracted low-methoxyl pectin from pomelo peels using subcritical water. Extraction yield and the rate of extraction were found to be predominantly influenced by temperature. Optimized operating condition of 120°C and 30 bar produced a yield of 19.6%. The absence of acid and a prolonged exposure to pressure under dynamic SWE conditions facilitated the formation of LM pectin rather than HM pectin. Mango peel is the major by-product of mango processing. Xia and Matharu (2017) extracted pectin from mango peel waste by using subcritical water extraction in the absence of mineral acid obtaining. The highest pectin yield (18%) was achieved at a temperature of 175°C, flow rate of 3 mL min1 for 15 min. The pectin showed a degree of methylation higher than 70%. Sasaki et al. (2013) studied the application of subcritical water extraction to deoiled peels of sour Citrus junos (yuzu) cultivated in Japan, which account for approximately 50% of whole fruit. The target compound was pectin, and the yield was greater than 75% at a temperature range of 120–140°C and pressure range of 4–30 MPa. The molecular weight of extracted pectin decreased with increasing temperature. Furthermore, it was suggested that the elimination of methyl groups in the pectin molecule was enhanced by the increase of the extraction temperature.

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7.3.2 Inulin, Oligofructose, and Fructooligosaccharides Pourfarzad, Najafi, Khodaparast, and Khayyat (2014) isolated fructans from the roots of Eremurus spectabilis through optimized water extraction, direct and indirect UAE (Table 7.3). Authors found that among the three methods examined, direct sonication gave the highest fructan yield (62%) and purity (37%) but with a decrease in the degree of polymerization and particle size and an increase in the magnitude of the zeta potential. Pulsed electric fields (PEF) technology involves a short time treatment (several nanoseconds to several milliseconds) with strengths from 100 to 300 V/cm to 20–80 kV/cm. At electric fields higher than 20 kV/cm, it can inactivate microorganisms and enzymes, with minimally modifying the quality of food products because it is essentially a non-thermal treatment. PEF induces electroporation of the cell membranes enhancing the diffusivity of valuable components in plant tissues at ambient temperatures (Barba et al., 2015). This technique has been studied specially for improving the isolation of antioxidants form plant tissues (Bromberger Soquetta, de Marsillac Terra, & Peixoto Bastos, 2018) but in relation to dietary fiber extraction, information is scarce. Loginova, Shynkaryk, Lebovka, and Vorobiev (2010) studied the effect of pulsed electric field treatment on efficiency of soluble solids extraction form chicory with the objective of inulin extraction. Field strength in the range 100–600 V/cm, treatment times of 103–50 s and temperatures between 20°C and 80°C, were assayed. The treatment enhanced the membrane permeabilization even at room temperature accelerating diffusion of soluble matter. The activation energy resulted to be 30–40 kJ/mol, which means that it was inferior to the one usually observed when thermal tratments were applied (263 kJ/mol). They observed a synergic effect between thermal and pulse treatment. The authors concluded that the technique has ample possibilities for cold extraction of soluble solids, potentially improving the rendering of inulin production. Pulsemaster Bladel (2018) designed industrial scale equipment with treatment capacities of 1000–50,000 kg/h with the purpose of producing cell disintegration and favoring an improved extraction of inulin from chicory root. They informed a cost of 0.056 US dollars per lb of tissue treated.

7.3.3 β-Glucans Benito-Roman et al. (2013) optimized the UAE of β-glucans from barley to maximize both extraction yield and molecular weight. They observed that the extraction yield depends on both amplitude and time and that higher extraction times give lower molecular weight. The highest yield (66.1%) and lowest molecular weight (269 kDa) were obtained with the maximum amount of energy delivered (962.5 kJ/L). Authors concluded that UAE is an efficient process to extract high molecular weight β-glucans from barley in very short extraction times (3–10 min) and consuming low amounts of energy ( 2), and lignins. Dietary fiber promotes one or more of these beneficial physiological effects: laxation, reduction in blood cholesterol, and/or modulation of blood glucose. They are accepted by use of AOAC methods 985.29 and 997.08 (fructan method) for labeling

National Academy of Science (NAS) (Gibson et al., 2017)

Dietary fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. Functional fiber has beneficial physiological effects in humans, and total fiber is the sum of dietary fiber and functional fiber

Food and drug administration FDA (FDA, 2006)

1. Nondigestible soluble and insoluble carbohydrates (with 3 monomeric units) and lignin that are intrinsic and intact in plants 2. Isolated and synthetic nondigestible carbohydrates (with 3 monomeric units) that the FDA has granted to be included in the definition of dietary fiber, in response to a petition submitted to the FDA demonstrating that such carbohydrates have a physiologic effect that is beneficial to human health 3. Isolated and synthetic nondigestible carbohydrates (with 3 monomeric units) that are the subject of an authorized health claim

Canadian Food Inspection Agency (Canada, 2016)

Prebiotics “stimulate the growth of friendly intestinal microflora” and “promote healthy/beneficial bacteria in the large intestine.” When included on food labels and in advertising, these claims suggest that food confers a health benefit and are considered to be implied health claims

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Marine algae are extremely rich in polysaccharides that are nondigestible by the human body and are rich sources of soluble fiber. Total fiber found in seaweed ranges between 25% and 75% (based on dry matter), of which water-soluble fiber are between 51% and 85% ( Jimenez-Escrig & Sa´nchez-Muniz, 2000). In Asian countries, algae are consumed in significant quantities since ancient times due to their high vitamin content. Also, the algae are used to produce hydrocolloids, such as agar, alginate, and carrageen (Dawczynski, Schubert, & Jahreis, 2007). The benefits of eating dietary fiber from algae are growing and protecting intestinal microflora, eating them together with foods with high glucose content for a reduced glycemic response, fiber acting as a hypoglycemic factor, stool volume increases significantly, and a reduced risk of colon cancer. Also, there are no significant differences between the dietary fiber content of red and brown algae (Dawczynski et al., 2007).

8.2.3 Dietary Fibers Compounds Dietary fiber is defined as a fraction of the edible parts from herbs or plants extract or those analogue carbohydrates that are resistant to the digestion process and absorption in small intestine, thus having their partial or total fermentation in the colon. The term includes polysaccharides, OS, and lignin (Dhingra et al., 2012). Another definition, given by Codex Alimentarius, states that dietary fibers are carbohydrate polymers formed from 10 or more monomeric units that are not degraded by human endogenous enzymes. These fibers that come from plants may contain fractions of lignin or other compounds, as fractions of proteins, phenolic compounds, waxes, saponins, phytate, cutin, vitamins, phytosterols, minerals, etc. By binding to the polysaccharides in the wall cells, they are extracted together. Also, Codex Alimentarius includes in the term dietary fiber those carbohydrate polymers extracted by physical, chemical, or enzymatic methods from various natural matrices that have been shown to have positive effects on the human body or synthetic carbohydrate polymers that are shown to have positive effects on health. A similar definition provided by the American Association of Cereal Chemists International is that dietary fiber is an edible part of a plant or an analogue of carbohydrates that resists digestion and absorption in the human digestive tract with incomplete or total fermentation in the large intestine. The definition of prebiotics embody polysaccharides, OS, lignin, and various substances related to plants. They are recognized for effects in the laxation process and in the level of cholesterol in blood and glucose levels (Anderson, Grande, & Keys, 1973; Rouhani et al., 2018). These are divided into two categories: soluble fiber (pectin, gums, and mucilages that when in contact with water have a gummy texture) and insoluble fiber (cellulose, hemicellulose, and lignin) (Vidal-Valverde, 1991). Another classification provided by the literature divides dietary fiber into four categories: 1. Starch-free polysaccharides and resistant OS (cellulose, β-glucans, hemicellulose— arabinoxylans, arabinogalactans, polyfructose—inulin, oligofructans, GOS, gums, mucilages, and pectins)

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2. Analogue carbohydrates (nondigestible dextrins, resistant maltodextrins from maize or other sources, potato-resistant maltodextrins), carbohydrate-synthesis compounds (polydextrose, methylcellulose, hydroxypropyl methylcellulose) 3. Lignins 4. Substances associated with starch-free polysaccharides and plant lignin complex (waxes, pith, cutin, saponins, suberines, polyphenols, tannins, vitamins, carotenoids, minerals) The importance of dietary fiber in nutrition has led to the development of products with high fiber content and to the design of new products by supplementation of products already on the market (Dhingra et al., 2012). Dietary fibers may be classified after several criteria, but the most commonly accepted form is classification based on their solubility in water. Water-insoluble fibers are those fibers that do not ferment in the colon. These are water-insoluble cellulose, lignins, and arabinoxylans. Cellulose is the main component in the cell wall of plants, being rooted in long glucose chains linked by β-1,4 glycosidic bonds. It provides the cell wall with mechanical resistivity, resistance to biological degradation, and acid hydrolysis resistance. It cannot be digested by human’s digestive tract enzymes. Hemicellulose is a polysaccharide in the plant cell wall, containing lower glucose chains compared to cellulose, linked by β-1,4 glycosidic bonds. In addition to fructose, it also contains xylose, galactose, mannose, arabinose, and other carbohydrates. It is especially found in cereal cell walls. Lignin is a non-carbohydrate polymer, containing about 40 units of phenylpropane oxygenated, which is susceptible to bacterial degradation. It is especially common in woody plants (Singh et al., 2018). Water-soluble fibers are those fibers that have an active fermentation (Delgado-Ferna´ndez et al., n.d.). Pectins, gums, OS, water-soluble arabinoxylans, β-glucans, galactomannans, psyllium fiber, and alginates are introduced into this category (Fazilah et al., 2018). Pectin substances are a complex polysaccharide group, where D-galacturonic acid is the main component. Pectin is highly soluble in water, almost completely degraded by intestinal microflora. Due to the gelling process, it is a positive influence on laxation. It is mainly found in fruits and vegetables. Gums and mucilages are not components of cell wall; they are formed in the specialized secretory cells of plant. Through the gelling process, they bind water and other organic substances. Gums are secreted in response to the plant injury, and the mucilages are secreted to avoid dehydration (Dhingra et al., 2012). OS are low molecular weight, degradable or nondegradable carbohydrate polymers. The main classes of nondegradable OS include carbohydrates where the monosaccharide residue is fructose, galactose, glucose, and/or xylose. OS are cyclodextrins, FOS, GOS, gentioligosaccharides, glycosyl sucrose, isomaltooligosaccharides, isomaltulose, lactulose, lactosucrose, maltooligosaccharides, and rafinosis (Glibowski & Skrzypczak, 2017). These dietary fibers are found in grains (a significant amount), fruits, vegetables, and legumes. There are many characteristics (Fig. 8.1) that influence the physiological actions of dietary fiber and their dependence consist in the nature of compound, the viscosity, the size and molecular weight, the solubility, the water binding capacity, the fermentation by the intestinal microflora. Consumption of dietary fiber improves blood cholesterol and glucose levels, reduces the risk of cardiovascular diseases, regulates weight by increasing satiety, improves insulin

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FIG. 8.1 The influence of dietary fibers on human health and on food characteristics.

sensitivity, reduces risk of type 2 diabetes, improves gastrointestinal function, improves laxation, lowers the risks of developing colon and breast cancer, improves immunity, and helps increase longevity. Also, some dietary fiber, through the fermentation process, serve as prebiotics for intestinal microflora. With all these benefits, consumption in excess above recommended dose can lead to a series of imbalances by reducing the absorption of some vitamins, minerals, proteins, and energy through the occurrence of diarrhea, flatulence, bloating, and abdominal discomfort (Roberfroid, 1998).

8.2.4 By-products as Prebiotics It has been demonstrated that prebiotics have a significant effect on human health and have greater possibilities for incorporation into a wide range of common foodstuffs. Their role is played by fermentable carbohydrates, which stimulate, preferentially, the growth of probiotic bacteria (bifidobacteria and lactic acid bacteria), thus enhancing the gastrointestinal and immune systems (Al-Sheraji et al., 2013). Prebiotics have great potential as agents to improve or maintain a balanced intestinal microflora to enhance health and well-being (Dwivedi, Puppala, & Ortiz, 2016). Therefore, prebiotics have been associated with a variety of health benefits including an increase in the bioavailability of minerals, particularly calcium, modulation of the immune system, prevention of the incidence or improvement in the severity, duration of gastrointestinal infections, and the list goes on (Singla & Chakkaravarthi, 2017). Prebiotics can be incorporated into many foodstuffs. It must be mentioned, however, that fiber can be a prebiotic, but it is important to note that all fibers are not prebiotic (Samanta et al., 2015). Prebiotics have shown and are still showing an increased interest as they have a significant effect on human health and have greater possibilities for incorporation into a wide range of common food products.

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8.3 DAIRY FOODS Dairy food (Fig. 8.2) products, namely, yogurts, dairy-based beverages, and fermented milks, are among the top probiotic foods consumed worldwide. Fermented beverages represent an important contribution to the human diet, with fermentation dating since ancient times as the most used preserving method. Fermentation is the least expensive food technology for improving products’ nutritional value and sensory properties (Liu, Han, & Zhou, 2011; Settanni & Moschetti, 2010; Shiby & Mishra, 2013).

8.3.1 Milk Milk is one of the most precious natural materials and has been a fundamental element of human food for a long time. It is one of the oldest foods, and at the same time, the most important one. Its color is influenced by the animals feeding method, from white-opaque to a yellowish liquid. It is supposed to have a typical, clean, full, slightly sweet taste and should also have a typical clean smell. The consistency is homogeneous, without clot formation or flocculation. Milk is a food rich in nutrients, a great source of essential amino acids, vitamins, and minerals, particularly calcium (Ritota et al., 2017).

FIG. 8.2 Most common produced dairy foods.

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FIG. 8.3 The general flow chart of dairy foods.

With more than 400 fatty acids found in milk fat, only 10 determine the physical characteristics. Among them are the short-chain fatty acids C4, C6, C8, C10, and C12, as well as the long-chain fatty acids C14, C16, C18, C18:l(cis), and C18:l(trans). The long-chain fatty acids exist in both the saturated and the unsaturated state. The ratio of saturated to unsaturated fatty acids is influenced mainly by feeding; in the summer, the ratio of unsaturated ones is higher than during winter, which also explains the fat content evolution with the seasons (Tavares & Xavier Malcata, 2019). Due to this capacity to nourishing and its low acidity, milk is an optimum environment for the multiplication of many microorganisms. As so, heat treatments represent an essential stage in the milk processing flow diagram (Fig. 8.3), representing the ordinary technique to inhibit the microbial growth in milk (Ritota et al., 2017). High-temperature interventions applied to milk have the dual purpose of making the product more safe for human consumption and extending its shelf life. Though some modifications may occur during milk pasteurization, in order to measure the pasteurization efficiency, there are some rapid, cost-effective tests. Alkaline phosphatase is an enzyme present in raw milk that is inactivated during pasteurization (heat treatment of 72°C for 15 s, or any other temperature-time combination producing an equivalent effect). For this reason, the determination of this enzyme in milk is considered an index of the effectiveness of pasteurization. Lactoperoxidase is another milk native enzyme that is more heat-stable than the one specified above, which is inactivated at temperatures higher than 75°C. Whey proteins are the most heat-sensitive among the milk constituents. They tend to denaturize and to form complexes with casein; the stronger heat treatment it is, the higher complexation degree will be. The Maillard reaction compounds are formed during heat treatment of milk, where Maillard reaction occurs between the free aldehyde group of the glucose unit in the lactose

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molecule and the amine group of lysine residues, generating ε-lactulose-lysine as the first stable product. Lactulose, a molecule not present in raw milk, is formed by epimerization of lactose due to heat treatment. The isomerization process is determined by the pH, time, and temperature of the thermal treatment. Mechanisms and implications suggest that people who live where raw milk is consumed exhibit fewer allergies. This protection is associated with the consumption of raw farm milk. Still, heat-treated farm milk does not present the same effect, indicating that nondenaturated milk proteins can be responsible for this protection. But, as raw milk is not commercially available, alternative milk-processing technologies are needed to preserve the immune active milk proteins. Thermal treatment, pasteurization, or ultra-high-temperature (UHT) processing are widely used to inactivate pathogenic microorganisms and enzymes in commercialized milk, but destroy the bioactive proteins. The disadvantage of mild heat treatment (e.g., low-temperature pasteurization) is the shorter shelf life of around five days. Advanced technologies are becoming available, though more expensive. Bactofugation (centrifuging out the microbes and spores), or membrane filtration (filtering off the spores and microbes), are technologies currently used for specialty products, being capable of protecting the bioactive proteins with immune functionality (van Neerven, 2014). The major source of microorganisms in raw milk is external contamination. Milk composition provides an excellent medium for growth of bacteria. The most common bacteria found in spoiled milk and dairy products are Streptococcus, Lactobacillus, Microbacterium, Achromobacter, Pseudomonas, Flavobacterium, and Bacillus (Michalac et al., 2003). Among all milk preservation methods, UHT treatment and microfiltration can be also mentioned. Cow’s milk allergy is a problem among milk consumers. The main processing technologies used to prevent and eliminate it are heat treatment, glycation reaction, high pressure, enzymatic hydrolysis, and lactic acid fermentation (Bu et al., 2013). Heating is an important process in the manufacturing of most dairy products. During the heating processes, important structural and chemical changes in proteins occur, such as denaturation, aggregation, and the Maillard reaction with other molecules. These alterations may have significant impacts on the antigenicity of milk protein allergens. High pressure is one of novel processing techniques applied in food production. High-pressure treatment can produce structural changes in milk proteins, such as denaturation and formation of aggregates decreasing the allergenic potential of milk proteins. Fermented milks can be divided into three categories depending on the ferments used and temperatures applied in their production: thermophilic sour milk, where the fermentation is conducted at 42–45°C (with lactic acid production); mesophilic sour milk, where the fermentation takes place at 20–30°C (with lactic acid production); and acid and alcoholic milks, where the fermentation is conducted at 15–25°C (with the production of some alcohol, less € € than 0.3%, w/v) (Ozdestan & Uren, 2010) in addition to lactic acid and carbon dioxide (Macori & Cotter, 2018).

8.3.2 Yogurt Yogurt processing includes initial treatment of milk (centrifugal clarification to remove somatic cells and other solid impurities), standardization of milk components, homogenization,

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FIG. 8.4 Flow diagram of the manufacture of yogurt.

heat treatment, fermentation process (the most important in yogurt processing), cooling, and storage. Flow diagram of the manufacture of yogurt is presented in Fig. 8.4. Raw milk is firstly subjected to centrifugal clarification and then a mild heating is performed in range 60–69°C for 20–30 s aiming to kill many vegetative microorganisms and causing the partial inactivation of some enzymes. The standardization of milk refers to the standardization of fat and solid non-fat content. This step is important for the further sensory characteristics of yogurt. The fat content of the milk influences the yogurt characteristics. By increasing the milk fat content, an increase of the consistency and viscosity of yogurt is produced. Milk powder, whey protein concentrates, and casein powder can be added in this phase to increase the firmness of the yogurt. A key stage in yogurt processing is the heat treatment of milk. It reduces the number of pathogenic microorganisms to safe limits for consumers’ health. Various heat treatments can be applied, which are classified based on the duration and the temperature (Sfakianakis & Tzia, 2014) thermalization (heating at 60–69°C, for 20–30), low pasteurization (63–65°C for 20 min/72–75°C for 15–20 s), high pasteurization (85°C for 20–30 min/90–95°C for 5 min), sterilization (110°C for 30 min/130°C for 40 s), ultra heat treatment (145°C for 1–2 s). In the fermentation stage, the yogurt curd is formed, and its textural characteristics and distinct flavor are developed. The starter culture is one decisive ingredient for establishing the yogurt’s flavor. For a fermented dairy product to be labeled as “yogurt,” it should contain the two live bacterial strains of Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus (Sfakianakis & Tzia, 2014). Yogurt starter cultures may include other microorganisms: Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus lactis, Lactobacillus jugurti, Lactobacillus helveticus, Bifidobacterium longum, Bifidobacterium bifidus, and Bifidobacterium infantis. Streptococcus thermophilus ssp. thermophilus is the only species in the streptococcus genus that is used in dairy starter cultures. The optimal fermentation

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temperature ranges between 40°C and 44°C and is stopped by cooling (5°C) the yogurt at a pH of 4.7–4.3, in order to inhibit the growth and metabolic reaction of the starter culture and to prevent the rise in acidity. Among the above mentioned manufacturing stages, the most important stages are homogenization, pasteurization, and fermentation. Apart from these conventional processes, new trends in milk processing that involve the utilization of ultra high pressure, ultrasound, pulsed electric field, and microfluidization are being discussed in literature or are already applied in industry. Last decades’ studies proved the beneficial effects of probiotics and prebiotics on human health and have extensively been utilized in the dairy industry.

8.3.3 Butter and Cheese Primarily, butter technology (Fig. 8.5) involves the following steps: cream separation, heavy mixing for water separation, and packaging. Additionally, milk can be pasteurized to be processed (Oeffner et al., 2013). The feeding method strongly influences the quality of the resulting milk, mozzarella cheese, and butter, in respect to fatty acid composition and butter spreadability, respectively (Hurtaud & Peyraud, 2007). During the butter-making process, the majority of the milk/water-soluble components are separated from the fatty matter. Lactose, being a water-soluble molecule, is largely expelled in the buttermilk, but some lactose remains in small quantities in the butter unless it is also fermented to produce cultured butter. Clarified butter, however, contains very little lactose and is safe for most lactose-intolerant people (Silanikove, Leitner, & Merin, 2015). Cheese technology usually refers to the following phases (Oeffner et al., 2013): milk pasteurization, acidification, curd formation, cutting, resting, fermentation, whey disposing,

FIG. 8.5 Butter-processing scheme.

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FIG. 8.6 The general flow chart for obtaining cheese.

curd softening by immersion in hot water, cooling, storage at refrigeration temperature, and packaging (mostly vacuum packaging) (Fig. 8.6). In the cheese-making process, first the milk is divided into a highly moist gel, named curd and milk serum, i.e., whey. With a micelar form, the main protein is from the milk: casein. Milk of cows, goats, and sheep are composed of five sub-types of caseins: α-, β-, αs1-, αs2-, and κ-casein. The fraction κ-casein helps the casein micelles avoid binding to each other by ionic charge repulsion. Acidifying the milk or processing it with a coagulating enzyme, such as rennin (a mix of enzymes obtained in the stomachs of ruminant mammals) or a combination of the mentioned treatments, anulates the protecting effect of κ-casein from the micelles and induces its collision to form a fine coagulum that encapsulates the milk fat globules. After disturbing the coagulum by mechanical force, more than 80% of the milk is thrown out as whey, and a curd (casein, calcium, and other minerals) is formed. Around 45 g of fresh cheese, such as cottage cheese, contains approximately 12 g of lactose. The content of lactose in hard-matured cheeses can be very low and thus can be tolerated by most people suffering from congenital lactose intolerance (Silanikove et al., 2015). Cheese is the most appreciated fermented milk product. Both soft and hard cheeses are produced by culturing milk for a specific period of time. Certain types of cheeses can be made simply by straining the moisture out of sour cream or yogurt, while others, more complex cheeses require additional steps in the culturing and fermentation process (Macori & Cotter, 2018).

8.3.4 Ice Cream The process of ice cream production is represented in Fig. 8.7. The conventional ice creammaking process include: blending of ingredients, pasteurization, homogenization, cooling to

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FIG. 8.7 Ice cream general processing line.

refrigeration, adding flavorings, freezing, and packaging. Significant improvements on the ice cream quality were obtained in the ice cream processing without emulsifiers (Bolliger, Goff, & Tharp, 2000). The influence of emulsifiers on ice cream produced by conventional freezing and low-temperature extrusion processing demonstrated that ice creams with low content or without emulsifiers pose a higher level of agglomeration, responsible of low melting rates and good shape retention. The flavorings added to ice cream may have a bad influence to the viability of probiotic bacteria. Still, the addition of inulin and oligofructose were proved to have good results in increasing the sensory and physicochemical characteristics of symbiotic ice cream (Mohammadi et al., 2011).

8.3.5 Dairy Desserts The production phases of dairy desserts can be summarized to: the addition of flavorings and gelling agents to milk, homogenization, sterilization, and sealing (Dirk et al., 2016). Milk proteins, along with gelling agents (such as carrageenan), contribute to the physicochemical properties of the desserts. Polysaccharides, such as starch, act as noninteracting fillers and cause a concentration of the other ingredients in the continuous phase as a result of the exclusion effect. These granules, importantly, affect the rheological behavior of the dessert under shear, but seem to be easily deformed when subjected to large, uniaxial forces (Buriti & Saad, 2014). Most studies show that probiotic desserts present enough populations of viable cultures during their shelf lives because insufficient doses during consumption might not provide the aimed health benefit. Nevertheless, results of the viability of probiotic strains

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incorporated in dairy desserts need to be complemented with probiotic functionality in adverse conditions (e.g., survival in simulated gastrointestinal stress). A current trend in the dairy industry is to transform traditional food products into functional ones with the potential to modulate the intestinal microbiota (Shiby & Mishra, 2013). Several studies have shown that probiotic microorganisms and prebiotic fibers might be successfully employed in different milk-based food matrices, such as yogurt, cheese, ice cream, beverages, desserts, and others. Of these, dairy desserts may be considered an interesting option for the incorporation of these functional ingredients for several reasons. The addition of probiotic and prebiotic ingredients for the preparation of milk-based desserts is especially attractive to consumers interested in healthy food, in addition to enhancing the products’ image and value (Morais et al., 2016). Most of the milk-based desserts are composed of ingredients that interact with milk proteins and influence their stability and consistency, including starch and/or several hydrocolloid types. Native and modified starches from different sources, especially from maize, rice, and tapioca, are widely employed for the production of probiotic and/or prebiotic milk-based desserts, due to their thickening and gelling properties. When discussing a dairy dessert, in order to select the most appropriate hydrocolloid, the composition of the dessert should be considered, especially its protein content, its pH, and the conditions employed during the dessert’s production steps. In order to adjust the product’s consistency and stability, combinations of different gums and collagen proteins are frequently used by the food industry. The availability and viability of added probiotic bacteria to frozen dairy desserts is limited during shelf life when compared to their availability during fermentation, for example. Therefore, the microorganism activation is an important step during the production of a dessert. Moreover, it is important for probiotic bacteria to be inoculated in high enough levels to provide health benefits to consumers during the entire shelf life. Inevitability, some factors in the food matrix affect the probiotic viability, including acidity, hydrogen peroxide, oxygen content, storage temperature, sugar concentration (osmotic stress), water activity (aw), and the interaction to other ingredients. Food ingredients and additives that contribute specific flavor features, appearance, and consistency are essential in the preparation of milk-based desserts. These ingredients and additives include sweeteners, fruit, natural/artificial colorings and flavoring agents, thickeners, stabilizers, and acidifying agents, among others. These additives should not interfere with the probiotic viability during the products’ storage. Therefore, it is important to consider these interactions when establishing the product’s recipe. Sucrose, commercial flavorings of strawberry, vanilla, banana and a flavoring-coloring commercial mixture of peach inhibited the tested cultures of bifidobacteria, L. acidophilus, and of the L. casei group (L. casei, Lactobacillus paracasei, and Lactobacillus rhamnosus) when used at high concentrations (15%–20% sucrose concentrations). Natural colorings, including carmine, curcuma/bixin, and bixin did not negatively influence the growth of the above-mentioned probiotic bacteria. However, the L. acidophilus CNRZ 1881 and B. longum A1 strains were inhibited by some fruit juices. When the pH of fruit juices was adjusted, they did not affect these strains’ viability. Another explanation for the inhibitory effect of flavoring agents is the antimicrobial activity of essential oil or polyphenols contained in these ingredients. The addition of passion fruit as concentrated juice or pasteurized frozen pulp reduced L. acidophilus La-5 viability. Oxygen sensitivity is also considered an important problem in the production and storage of probiotic foods, particularly for highly aerated products containing bifidobacteria.

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Microencapsulation, for example, has been proven to be one the most effective methods for maintaining probiotic viability because it protects probiotic microorganisms during food processing and storage, as well as toward gastric conditions (Brinques & Ayub, 2011; Pop et al., 2015). Various protective compounds as dietary fibers may also improve viability of probiotic cultures during manufacture. Examples include glucose to energize cells on exposure to acid and cryoprotectants, such as inulin, to improve survivability during freeze-drying. So the use of ingredients that result in a protective effect toward these microorganisms should be encouraged. For example, the addition of low percentages (1%–4%) of inulin in dairy mousses (chocolate, fruit, yogurt, or fresh cheese-based) increases the ability for extended storage periods and confers quality upgrades, in comparison with conventional mousses. As an alternative to synthetic food ingredients, food industry by-products can be added to dairy products as a natural source of bioactive compounds and nutrients (Iriondo-DeHond, Miguel, & del Castillo, 2018). Many studies have focused on the extraction of functional compounds, such as polyphenols, dietary fibers, vitamins, and others. Yogurt and fermented milks were developed by the addition of polyphenols derived namely from the wine industry (Tseng & Zhao, 2013). Different flours and extracts from grape pomace, skins, and seeds were successfully used in dairy products (Marchiani et al., 2016). Grape pomace represents a sustainable source of polyphenols, possessing a high antioxidant effect, high digestibility, and an absorption degree of biocompounds at gut level (Del Pino-Garcia et al., 2016; Lakhani & Ibrahim, 2016). With grape pomace having a bitter, astringent taste, product development of grape pomace-based functional products involves establishing a balance between functional properties and sensory acceptance (Dos Santos et al., 2017; Marchiani et al., 2016). As alternatives, other ingredients such as sucrose, oligofructose, or fruit juices can be added in order to improve the acceptance scores and maintain the probiotics viability (Cardarelli et al., 2008; De Castro et al., 2009). Other plant byproducts, such as seeds powders, skins, peels, pomace, husks, etc., were tested as new sources of dietary fibers. (Elleuch et al., 2011). These sources have the advantage of being cost-effective and low calorie. As a marketing strategy, the final advantage is adding a nutritional claim to the food package. Product development using by-products as a source of dietary fiber has mostly been carried out in yogurt and fermented milks because of better integration. Orange by-products were added in ice cream for the reduction of fat, and in yogurt, respectively (de Moraes Crizel et al., 2013). Apple, banana, and passion fruit byproduct fibers were used to preserve viability of L. acidophilus and Bifidobacterium animals ssp. lactis strains in yogurt during the shelf life of the products (do Espirito Santo et al., 2012), this being prolonged to four weeks.

8.4 FOOD TECHNOLOGY—INFLUENCE OF DIETARY FIBERS ON DAIRY FOODS’ PROPERTIES Manufacturing of innovative food products brings together the work of scientists and food researchers, food technologists, biotechnologists, food providers, and, last but not least, consumers. Globalization has brought many advantages regarding the spread of food traditions

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and habits, but, with all good things, the spread of diseases and illnesses was unfortunately inevitable. Consumers, along with food specialists and health authorities, are concerned not only about food safety and nutrient values, but the health benefits are now under the spotlight. Fair and sustainable production is the concern of each of us. Due to these innovations, food products now have an extended shelf life and are easy to purchase. In the food-production process, dietary fibers are utilized as food-product stabilizers, as food for beneficial gut bacteria, and for their ability to sustain their multiplication and ensure implicit health benefits. Among all these influences, the big players from the food industry and small food producers are most interested in the influence of prebiotics on food technology, the structure of the final product, and influence on the shelf life. An interesting study reveals the fact that the presence of inulin and FOS in cheese influences the fatty acids’ profile, specifically conjugated linoleic acid. Due to prebiotics in manufactured cheese, an improvement related to a lower index regarding atherogenicity was detected. In addition, Oliveira et al. (De Souza Oliveira et al., 2011) proved in his study that the presence of inulin in the technological process intensifies the growth rate of bacterial cultures and, in a minor way, expanse the enumeration period of S. thermophilus and L. acidophilus. Inulin improves the fermentation process of milk when Lactobacillus cultures are utilized. Herfel et al. (Herfel et al., 2011) demonstrated the fact that the presence of polydextrose in baby formulas fed to 18-day young piglets, led to several modifications. Namely, the modifications included an increase of Lactobacillus counts in the small intestine, a boost in shortchain fatty acids (i.e., propionic acid), and a diminution in pH value. The stability of prebiotics in the food-manufacturing process is essential for their further utilization in the gut. Processing conditions, such as low pH, high temperature, Maillard reactions, etc., alone or in combination can negatively influence the prebiotic action. The fact that many of the prebiotics are stable in the mentioned conditions (B€ ohm, Kleessen, & Henle, 2006) is one more reason to incorporate them in dairy products and other food products.

8.5 PREBIOTICS AND DAIRY FOODS The food industry is in continuous research for new and different products with better functionality and higher quality (Buriti & Saad, 2014). To be functional, foods need to contribute with additional properties other than nutritive values. Dairy products are recognized as healthy, natural products, and their regular consumption can have positive effects in the prevention of disease because they contain a number of bioactive compounds, such as minerals, fatty acids, prebiotics, probiotics, carbohydrates, and proteins/peptides. Prebiotics were accepted for their capacity to modulate the balance of the host microflora and, therefore to induce health benefits, over 20 years ago. Compounds like fructans (inulin), FOS, and galactans: GOS got the main attention. GOS and FOS are used as prebiotic compounds in food products such as infant formula and dairy products to increase the mineral absorption, prevent metabolic disorders, and slow gastric emptying (Chen & Karboune, 2018). Lactulose (i.e., lactose isomer) is a dietary fiber used for the treatment of constipation and systemic portal

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encephalopathy (Ferreira-Lazarte et al., 2017). The prebiotic concept has developed because of advances in approaches for microbiome research, which have improved the knowledge in the field regarding the content of the microbiota and the recognition of additional substances influencing colonization. Prebiotic compounds can possibly improve human health and reduce the risk of issues mediated by microbiota infections (Gibson et al., 2017). Prebiotics can be used to equilibrate the microbiota in the colon, thereby providing beneficial systemic effects. The combination of prebiotics and probiotics has a symbiotic effect manifested to regulate the microbiota (Fernandez & Marette, 2017). While prebiotics are lesser-known than probiotics, they may be equally (if not more) important for consumers’ overall health. The addition of prebiotic into dairy products is a common technological practice, in part to enhance their beneficial health effects and also to improve the physicochemical and sensory properties, replace fat components, and increase the fiber content. To acquire these properties, prebiotics demand stability during food processing, including conditions of low pH and high temperature and conditions favoring Maillard reactions. Prebiotics compounds come in powders, capsules, or as syrup and are sold as supplements, or they can be integrated into food products (Glibowski & Skrzypczak, 2017). Various studies have shown that prebiotic fibers might be successfully employed in different milk-based food matrices, such as yogurt, cheese, and dairy desserts.

8.5.1 Prebiotics in Yogurt Attention has been focused on developing products and food containing prebiotics, which are fermentable fibers that nourish beneficial gastrointestinal microflora and enable the development of probiotics. Yogurt is the most common dairy product consumed around the world (Allgeyer, Miller, & Lee, 2010) and is known for its therapeutic, nutritional, and probiotic effects. It is produced by fermentation of milk with the thermophilic homofermentative lactic acid bacteria S. thermophilus and Lactobacillus delbrueckii ssp. Bulgaricus (Fazilah et al., 2018). The inclusion of specific lactic acid bacteria into milk used in the production of yogurt increases the biological value and the degree of digestibility. Dairy products are not a good source of fiber; however, they can provide an alternative vehicle for the development of fiberenriched foods. For example, supplementation of β-glucan in yogurt was found to improve the viability and metabolic activity of Bifidobacterium bifidum by displaying a prebiotic effect. Prebiotic OS influence the evolution and colonization of probiotic bacteria having useful health effects when ingested. Inulin prebiotic compounds have been included in different food products since 1990. They have improved the physical sensations in the mouth, added creaminess, reduced fat, improved texture, and grown viscosity, especially in yogurt. In research, classical yogurt without added prebiotics was compared with yogurts obtained from milk with added inulin (l0.5% and 1.0%) or with lactulose (0.25% and 2.5%). The results revealed that inulin and lactulose did not have significant effects on the growth of yogurt starter bacteria, but did sustain the growth of B. bifidum BB-02 to a great € € extent (Ozer, Akin, & Ozer, 2005). In yogurt with 4% fat, the addition of FOS and inulin increased the smoothness and made it thicker. FOS (on a wet/weight basis) had a good overall acceptability (Nagpal et al., 2012). Inulin is added in low-fat yogurts as a fat replacer to improve sensorial characteristics and can stabilize emulsions systems (Tungland, 2018).

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Gustaw et al. (Gustaw, Kordowska-Wiater, & Koziol, 2011) conducted research on the influence of the prebiotics FOS, inulin, and resistant starch on the increase and viability of bacteria for bio-yogurt production. They established that the most beneficial probiotic-prebiotic mix should contain 106 cfu/mL (g) for all storage periods of the synbiotic products. A high percent (97%) from the samples taken in the study were in accordance to FAO/WHO regulations, regarding the numbers of lactic acid bacteria in the bio-yogurts (106–109 cfu/g). During refrigerated storage, viability of bacteria decreased (not below 106 cfu/g) without affecting the functional properties of yogurts. Prebiotics added to yogurt samples demonstrated stimulatory effect on the L. acidophilus and Bifidobacterium sp. growth. In addition, inulin supplementation can improve the physicochemical properties of frozen yogurt, as evidenced by Muzammil et al. (Muzammil, Rasco, & Sablani, 2017). The results showed that 4% and 6% inulin supplementation increased the overrun by 3% and 5% and the glass transition temperature by 3.3% and 2.8%. The supplementation decreased the hardness by 7% and 11%. Oligofructose, a prebiotic compound, is a dietary fiber with sweet taste and no negative effects reported. When used in food products, oligofructose enrichesthe sensorial profile and texture. The quality can be compared with that of sugar or glucose syrup, but it has the advantage of lower calories and can be used as a sugar or fat substitute (Ahmadi et al., 2014). Combining yogurt with fruit can have a positive impact for prebiotics from fruit in order to maintain the survival of probiotic bacteria in yogurt. On the other hand, it can provide additional substrate for growing activity once in the colon (Fernandez & Marette, 2017). Thereby, the study followed by Anh^e et al. (Anhe et al., 2015) revealed that polyphenol-rich fruits can have prebiotic effects. Animals with a fat and high-sugar diet were fed with an extract from polyphenol-rich cranberries, which influenced the microbiota with an increase in the relative abundance of Akkermansia spp. population. Seeds like legumes, chickpeas, lentils, mallow composite, peas, beans, and mustard contain compounds from the OS family. The main representatives are raffinose, stachyose, and verbascose. Marinaki et al. (Marinaki, Dimitrellou, Zakynthinos, & Varzakas, 2016) have studied the effect of additional raffinose on the principal physicochemical properties of yogurt after refrigerated storage. Yogurt samples were obtained by mixing the probiotic microorganism L. casei ATCC 393 with the traditional yogurt culture Lactobacillus delbrueckii ssp. bulgaricus and S. thermophilus. Four samples of yogurt were produced with the addition of 0%, 0.5%, 1%, and 2% (w/v) raffinose. In the samples with the added raffinose, physicochemical characteristics (syneresis, pH, water-holding capacity, and titratable acidity) were not affected. The viability of probiotic culture was maintained by the use of raffinose. The author reported a high value (>108 cfu/g) after four weeks of storage. Also, sensory properties of yogurt with the addition of 1% (w/v) raffinose showed positive influence. From the referenced studies, we can conclude that the addition of prebiotics improves the chemical, microbiological, and organoleptic properties of yogurt.

8.5.2 Prebiotics in Cheeses/Cream Cheese Cheese is considered the most popular fermented milk product, and it is consumed by a wide audience (Granato et al., 2010) Cheese is also one of the most efficient food matrices to

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keep the probiotic bacteria viable and enter them in the human diet (Ong & Shah, 2009). Processed cheese has high-sodium and fat content in its formulation. Cheese may undergo a reformulation to provide functional components or to meet specific dietary needs for consumers (Ferra˜o et al., 2016). Prebiotics can be used as a substrate for a limited number of bacteria, mainly probiotic Lactobacillus sp. and Bifidobacterium sp. Bacteria are capable of utilizing some prebiotics as a carbon source. The global prebiotics market is supposed to achieve around 12.7% in the next 8 years; thus, manufacturers are trying to develop new alternatives to obtain sustainable and efficient processes for application in food sector (Mano et al., 2018). Rodrigues (Rodrigues et al., 2012) reported in a study the nutritional advantages of including prebiotic ingredients in the probiotic cheese manufacturing process. Research by ModzelewskaKapituła et al. presents the effects of some prebiotic compounds (inulin HPX and maltodextrins) on the gastrointestinal microflora of Wistar rats. Prebiotics were included in cheese in 2.5%. Synbiotic and probiotic cheese contained 107 CFU/g of live L. plantarum cells. In the group fed with the cheese containing the potentially probiotic strain and inulin HPX, positive changes on anaerobic proteolytic bacteria spores were observed. Also, El-Baz and Azza (2013) investigated the supplementation of low fat in synbiotic ultra-filtered soft cheese manufactured from ultra-filtered milk retentate with inulin as a source of dietary fiber and a mixed probiotic culture, namely L. acidophilus-5, Bifidobacterium BB-12, and S. thermophilus. Inulin was used at levels of 1%, 3%, 5%, and 7%. The results revealed that the addition of inulin led to an increased moisture, ash content, and acidity in the stored cheese and decreased protein content and pH. The addition of inulin was reported as an improvement in the cheese mouth feel, which can be explained by the capability of inulin to form micro-crystals when dissolved in liquid (water or milk). Also, inulin improved the creaminess. Synbiotic soft cheese of good quality could be made with inulin at levels of 5% or 7% (w/w) from the original retentate weight (El-Baz, 2013). The study conducted by Kınık et al. (Kınık et al., 2017) on symbiotic goat cheese showed that the use of prebiotics and probiotic cultures in cheese production has a great impact on the textural profile. The addition of Enterococcus faecium and oligofructose was responsible for the most popular cheeses. In a following study by Slozhenkina et al., a new cheese product with chickpea flour in combination with prebiotic components has been developed. The authors concluded that prebiotic and vegetable components increased the nutritional and energy contents of the cheese product (Slozhenkina et al., 2017). Speranza et al. evaluated the development of a functional fresh cream cheese through the supplementation of probiotic bacteria (B. animalis ssp. lactis DSM 10140 and Lactobacillus reuteri DSM, 2016) and prebiotic compounds (inulin, FOS, and lactulose). B. animalis ssp. lactis DSM 10140 growth was positively affected by lactulose, whereas FOS was the prebiotic ingredient capable to prolong L. reuteri DSM 20016 viability (Speranza et al., 2018). Furthermore, the addition of a probiotic microorganism and prebiotic ingredient did not negatively affect the product’s sensory acceptability. The addition of prebiotic compounds into cheese is a normal technological practice to enhance their health effects and to enhance the final texture and organoleptic properties, replace fat components, and increase the fiber content.

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8.5.3 Prebiotics in Dairy Desserts Dairy desserts (milk-based desserts, ice cream, frozen desserts, etc.) are well received all over the world. The dairy dessert market has increased with many ready-to-eat milk-based desserts available for consumers (Buriti & Saad, 2014). Dessert, widely used in daily diets, has fine taste and mouthfeel; an efficient supplementation’s program with significant nutrients can be achieved. Some prebiotic fibers can confer gelling properties to dairy desserts. Native and modified starches extracted, in particular, from maize, rice, and tapioca are broadly involved for the production of probiotic and/or prebiotic milk-based desserts due to their properties as hydrocolloids (thickening and gelling). Prebiotic fibers are employed in milk-based desserts as body and texture agents, stabilizers, and fat and/or sugar substitutes. Chilled dairy desserts are seen as attractive options for the incorporation of probiotic cultures and prebiotic ingredients, as can be seen in the growing number of scientific papers in the field (Buriti & Saad, 2014). The purpose of prebiotic additions in chocolate dairy desserts is to have dairy desserts with lower calories (Morais et al., 2016). Milk chocolate has a significant amount of natural antioxidants, and the nutritional value of it can be further enhanced by the incorporation of prebiotics and/or probiotics or dietary fibers (Gadhiya, Patel, & Prajapati, 2015). Prebiotic ingredients (inulin, FOS) may improve the quality of the ice cream by increasing the firmness and improving the melting properties. Hence, ice cream with the prebiotic ingredient may have a longer storage period and a higher sustainability of texture (Wood, n.d.). Oligofructose is employed in the production of desserts and is very promising when used together with fruits, improving aroma and flavor mouth perception. It also helps to reduce the use of synthetic additives like sweetners. Prebiotic ingredients (inulin and fructo-oligosaccharide) were used for the replacement of sheep’s milk fat to obtain sheep’s milk ice cream in a research study conducted by Balthazar et al. (2017a). Prebiotics have been shown to be a good option as fat replacement in sheep’s milk ice cream, due to the rheological characteristics and sensory attributes (Balthazar et al., 2017a). Another following study by Balthazar et al. (2017b) revealed the effects of different prebiotic dietary OS (inulin, FOS, GOS, resistant starch, corn dietary OS, and polydextrose) in non-fat sheep’s milk ice cream. The fat substitute by prebiotic OS significantly decreased the melting time/temperature, while accentuating the white intensity and glass-transferring temperature (Balthazar et al., 2017b). The inclusion of inulin in low proportions (2%–3%) in low-fat dairy desserts confers a better-balanced round flavor and a creamier mouthfeel. More than that, inulin is the most used ingredient to obtain prebiotic milk-based desserts due to its advantageous technological properties (Buriti & Saad, 2014). The addition of prebiotics in dairy desserts represents an important choice to increase nutritional properties and develop a functional food. Also, it is advantageous because prebiotics as inulin and FOS showed good stability during the usual food-processing steps, especially during heat treatment. The development of functional foods, mainly those in the prebiotic category, plays an important role in the modern food industry, especially in the dairy category. Future studies may focus on the evaluation of the symbiotic effect of prebiotics and probiotics on various pathogens in dairy products.

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8.6 HEALTH BENEFITS OF DAIRY FOODS CONTAINING PREBIOTICS Improving the human health through probiotic, prebiotic, and synbiotic consumption is well sustained by scientific literature. All three alternatives merge toward producing nutrients that sustain the viability and the growth of good microbes that populate the gut (Fig. 8.8). Products that contain prebiotics and/or probiotics as ingredients fall under the umbrella of functional foods, being the so-called beyond nutrition ingredients due to the fact that by ingesting them nutrients are provided (Gibson & Roberfroid, 1995). The beneficial effect of prebiotic ingestion is not restricted to intestinal wellbeing; their favorable consequences switch on other mechanisms that have an impact on other areas (i.e., allergies, lipid metabolization, insulin secretion, etc.). Nondigestible carbohydrates have come forth as a major nutritional element for the prophylaxis and cure interventions in chronic diseases. Major advantages associated with nondigestible carbohydrates include: improving control of the level of glycemia, balancing the blood pressure, ensuring body weight management, protecting the cardiovascular system, lowering the incidence of certain forms of cancer, reducing the LDL cholesterol level, and sustaining and improving gastrointestinal health. Up-to-date health authorities recommendations are related to doubling of dietary fiber ingestion. This goal to increase the amount of ingested fibers can be achieved by increasing the consumption of fruits and vegetables, non-processed grains, and dehydrated beans and peas (Anderson et al., 2004). The exact mechanism and action of pre- and probiotics after ingestion is not elucidated yet. Due to the fact that the in vivo model involves the complexity of microbes’ interaction, more work is needed in this direction. The most common possible beneficial health effects of prebiotics are covered next.

FIG. 8.8 Prebiotic effect on gut microbiota and human health.

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8.6.1 Cardiovascular Health Different studies have demonstrated the activation of hypocholesterolemic activities through the prebiotic intake. Cardiovascular health is related to factors such as lipid metabolization, triglyceride level, and blood pressure. Several mechanisms can be influenced by the consumption of inulin and OS: metabolization of the lipids at hepatic level and a decrease of serum cholesterol and triglyceride balance (Yasmin et al., 2015). Hsus et al. registered an almost 30% reduction total of triglyceride levels in a study conducted on rats, influenced by the consumption of xylo-oligosaccharide (Hsu, Anen, & Quartz, 2008).

8.6.2 Weight Management Excess body weight can be cataloged in different ways (e.g., body mass index, waist circumference, and body fat percentage estimated by a number of means). All these measurements can predict different illnesses. An increased tendency for a high body mass index and a high level of body fat can be observed even as teenagers and can lead to more and more overweight adults. The scientific evidence tends to link plant-based food consumption to reduced weight in adults for the long-term. Prebiotics are an important ingredient in these types of foods and an important factor in the diets meant to maintain a healthy weight (Delgado-Ferna´ndez et al., n.d.).

8.6.3 Obesity A significant change can be observed regarding the composition of gut microbiota in obese individuals. For example, people born with a low count of Bifidobacterium tend to become obese after childhood (Salazar et al., 2015). Eating a large amount of fruit rich in dietary fructans and OS, which sustain the growth and multiplication of Bifidobacterium in the human gut, is a strategy in the fight against obesity. Moreover, prebiotics also play a significant role in the inactivation of the overexpression of those genes responsible for inflammation and adiposity (Delgado-Ferna´ndez et al., n.d.).

8.6.4 Hyperglycemia In diabetes management, nutrition plays an important role, influencing the glucose response after meals. Active ingredients, such as dietary fibers and polyphenols, present in fruits, vegetables, cereals, and spices are able to positively influence the insulin immune response and the blood level of glycemia. Factors such as the type of fibers, source, and the ingested amount directly influence the postprandial glucose level. Cani et al. (Cani et al., 2007) are discussing the mechanism involved in the reduction of glycemic levels activated by the consumption of inulin. The inulin intake boosts the count of endocrinal L cells in the colon and enhances the release of GLP-1 alive forms, which decrease glycemic levels. Another example of prebiotic involved in the reduction of glycemic levels is arabinoxylan, present in wheat and bran. Alive microbes ferment arabinoxylan in the colon and have a positive effect on hyperglycemic levels.

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8.6.5 Constipation Symbiotic intake of prebiotics can manipulate the communal gut bacteria and accelerate their growth. Evidence from animal studies and human trials suggests that probiotics decline the occurrence of constipation. Furthermore, a study by Scalabrin et al. (Scalabrin et al., 2012) reported that a blend of GOS and PDX produced soft stools in young infants. Similarly, FOS incorporation into many food products and infant preparations has increased due to its laxative effects, whereby the intake of these formulations can increase stool frequency and reduce instances of constipation. There is abundant investigational information to support the hypothesis that prebiotic combinations have largely contributed to advancements in infant formulations. For example, prebiotic supplemented preparations increased the colony totals of bifidobacteria and lactobacilli in stools of premature babies (Srinivasjois, Rao, & Patole, 2009).

8.6.6 Colon Cancer Colorectal cancer (CRC) is a type of disease that affects more and more people, being one of the most usual causes for mortality in the United States (Kumar et al., 2015). Many factors contribute to the increased incidence of this type of cancer, such as a diet high in fat and meat, smoking, alcoholism, and genetics. Research studies propose that ingestion of prebiotics is excellent in prophylaxis and amelioration of CRC. Tending to inhibit or prevent the activity of the colon neoplasm effect of prebiotics is due their ability to sustain the growth of favorable gut bacteria, to produce short chain fatty acids, to modulate the gene expression in the colon and favorise absorption of micronutrients in the colon. Prebiotics change the gut microbiome positively and enhance the production of Lactobacillus and Bifidobacterium, which eliminate carcinogens from the host’s gut system. Many animal studies have shown the effect of prebiotics on the prevention of CRC. Feeding with dietary fibers enhanced the Bifidobacterium count, lowered pH, changed the immune response, and also decreased colon neoplasms induced by azoxymethane, tumors in the colon, and in the small intestine (Rezasoltani et al., 2018). However, the effects of prebiotics on humans were far less. Therefore more clinical studies with improved study designs are needed to build strong evidence for the effect of prebiotics on CRC.

8.7 HUMAN HEALTH MODULATION THROW A SYMBIOTIC EFFECT Any unbalance in the gut microbial population may cause the pathogenesis of certain chronic or metabolic illnesses. Modification in the gut microbiota was linked to obesity, diabetes, fatty liver illness, foodborne diseases, diarrhea, constipation, and inflammatory bowel diseases (Bal, Nayak, & Das, 2017; Brownawell et al., 2012). Restoration of intestinal microbiota can be achieved by probiotic and prebiotic ingestion. Diet supplementation with inulin, FOS, and GOS helps this restoration by sustaining the growth of favorable microbes in the gut. Certainly, prebiotic supplementation can be applied for the health of other parts of the body (i.e., oral cavity, skin care) (Foolad & Armstrong, 2014). The nonactivity of prebiotic

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ingredients and their capacity to reach the colon and selectively be fermented by prebiotic cells are the most important characteristics of the prebiotics. These fibers are ingredients that get in the large intestine and perform as substrates for the local bacteria; mainly for the Lactobacillus and Bifidobacteria species. The growth and multiplication of these beneficial bacteria lead to several benefits for the host. Short-chained dietary fibers with low molecular weight that are not digested by the human enzymes and that selectively improve the growth and activity of the colonic microbiota are referred to as prebiotics. Human health benefits come with their consumption, and their activity is in antagonism with pathogens. A funded affirmation is that gut population has a great impact on human health. Thus, the prebiotic intake utilization for positive influence on the gut microbiota seems to be a reasonable approach. This approach was analyzed and documented in technical papers that underline the importance of prebiotic ingestion and their influence on human health (Sheridan et al., 2014). These links, between pro- and prebiotic intake, have lead to the development of new dairy and nondairy food products with symbiotic effects, putting together the effort of scientists, food engineering, and biotechnologists (Wang et al., 2009). Stimulating the growth and metabolism of a particular class of gut microbes and thus improving human health can be done using synbiotics. When talking about synbiotics, we can discuss a synergic relation, namely, prebiotics selectively sustain the growth of probiotics (de Vrese & Marteau, 2007). Beyond the growth stimulation, the amelioration regarding the survival of probiotic cells when passing the GIT can also be attributed to synbiotic. When probiotics are ingested through dairy products, factors such as the concentration of hydrogen peroxide, pH, water activity, and oxygen can negatively affect the cells viability. This fact can be attenuated by incorporation of prebiotics into the dairy products. The most common probiotic strain utilized to develop synbiotics contains Bifidobacterium spp., Lactobacilli, Bacillus, and Saccharomyces boulardii. The probiotic species that are used to formulate include inulin, FOS, GOS, XOS, and all the prebiotics that are extracted from natural plant sources. An optimum assimilation of minerals (Mg, Ca, K, and Fe) is associated with an optimum functioning of the human body. Probiotic intake was related to a good absorption of these minerals. Lately, it was demonstrated that the prebiotic intake (i.e., fructans) sustain the absorption of Ca. Abrams (Abrams et al., 2007) conducted a study on 100 adolescents whose diet was supplemented with 8 g/day with inulin-type fructans, resulting in a better absorption of Ca and an improvement regarding the bone mineral density. This reaction can be an explanation of the fact that through intestinal fermentation, short-chain fatty acids are produced, leading to a lower pH, causing a hypertrophy of mucosal cells and an enlargement of the intestine, leading to a higher absorption surface (Whisner & Castillo, 2018). The synergistic mixture of prebiotics and probiotics found in food products, but also in pills, syrups, and any supplements, is well known as “synbiotics” (live cells of the useful microbes/probiotics and a selective substrate/ prebiotic). Put differently, synbiotics is defined as “a combination of probiotics and prebiotics that beneficially affects the host by improving the survival and implementation of live microbial dietary supplements in the GIT.” Synbiotics have an increased efficiency compared to the consumption of either probiotic or prebiotic used individually. Dairy foods such as Swiss cheese and functional ice creams can be found as sustainable and appreciated synbiotic food products. Different combinations of pro and prebiotics—synbiotics—have proven therapeutic effects against illnesses such as gastrointestinal disease, respiratory infections, hypercholesterolemia, atopic dermatitis, allergy, diabetes, liver diseases, and cancer.

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8.8 PERSPECTIVES When speaking about prebiotics as functional foods, the improvement of the good microbes’ population in the gut, the antagonist effect of pathogens, and all the associated health benefits come to mind. Thus, the interaction between prebiotics, a culture of microorganisms, and interaction between gut microbes when prebiotics are present are among the mechanisms by which the microbiota involve the immune modulation needed to be fully elucidated. This fact can definitely improve the approaches meant to treat, ameliorate, or prevent human illness through the ingestion of prebiotics (Hardy et al., 2013). Prebiotics in dairy products, constituted of nutritive attributes (Huebner et al., 2008), need to be analyzed from the technological point of view. Among all the health benefits, the improvement of dairy product characteristics, besides the presence of dietary fibers, are not to be overlooked. The activity of these valuable dietary fibers indicates the capacity of a specific substrate to back up the multiplication of good bacteria that populate the gut. Both in vitro and in vivo techniques and studies certify the prebiotic quality. Therefore, stimulation of beneficial bacteria activity has been catalogued as the most important characteristic of prebiotic selection and consumption.

8.9 CONCLUSIONS In accordance with the health and dietary authorities, prebiotics are the most essential component required for human ingestion, recommended to be consumed daily. This fact comes with the necessity of some appropriately validated standards regarding their utilization in foods. Prebiotics’ direct or indirect influence on human well being is related to the production and action of short fatty acids (acidifying the colonic lumen, stimulating metabolic pathways, and constraining pathogen growth). Moreover, studies showing that the incorporation of dietary fibers in dairy products improved food properties, such as texture, mouth fullness, and structure, and sustained the growth of incorporated microorganisms. This information is meant to help scientists link health implications, costs, influences, and technological issues regarding the presence of probiotics in food products.

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C H A P T E R

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Application in Bakery Products Sen Ma, Wen Han College of Grain and Food science, Henan University of Technology, Zhengzhou, China

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9.2 Supplementation of Wheat Flour Products With DFs 9.2.1 Effects of DF Enrichment on the Quality of Biscuits 9.2.2 Effects of DF Enrichment on the Quality of Bread 9.2.3 Effects of DF Enrichment on the Quality of Steamed Bread 9.2.4 Effects of DF Enrichment on the Quality of Noodles 9.3 Effects of DF Enrichment on the Dough Properties and Gluten Network

9.3.1 Effects of DF Enrichment Dough Mixing Properties 9.3.2 Effects of DF Enrichment Dough Elastic Properties 9.3.3 Effects of DF Enrichment Dough Pasting Properties 9.3.4 Effects of DF Enrichment Gluten Network

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9.1 INTRODUCTION Wheat flour products have long been considered as an energy source for people worldwide. People prefer to consume flour products with both desirable sensorial characteristics and rich nutrient components. Such consumption change has brought enormous challenges to the traditional food industry. Therefore, the food industry has been focusing on developing new healthy foods to better adapt to the new demands of the fast-changing food market.

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Due to the fast-growing cereal industry, wheat grains have been highly processed to yield better sensory quality, which in turn also yields a great loss of nutrients. During the peeling and fine-grinding process, most of the nutrients, essential amino acids, as well as dietary fiber (DF), are discarded along with wheat bran to obtain whiter and finer flour particles. As a by-product derived from the roller milling process during wheat flour production, wheat bran contains 44%–50% of DF but was frequently discarded as waste or used as animal feed (Onipe, Jideani, & Beswa, 2015). Whole grain foods have been shown to reduce chronic disease risk and obesity largely due to the presence of DF. Many studies have confirmed the positive effects of DF on the prevention and cure of a diverse range of diseases, including colon cancer, diabetes, cardiovascular disease, and obesity. Accordingly, the proper intake of DF will assist in reducing the incidence as well as the risk of common and chronic diseases. However, due to the lack of DF in highly processed wheat flour products, extra DF additives are greatly needed to meet nutritional needs. Various fiber-fortified flour products, including cakes, breads, steamed breads, pastas, cookies, noodles, etc., have been developed by incorporating extracted DFs or fiber concentrates. This chapter reviews the application of DFs from various sources, including whole grain flour (rich in DF), bran products, extracted insoluble dietary fiber (IDF), as well as soluble dietary fiber (SDF) in wheat flour products. The quality indices include moisture mobility and distribution, expansion behavior, texture, appearance property, crumb volume, and sensory properties. Since dough properties and gluten network formation are closely linked with the texture, appearance, and quality of the final wheat flour products, this review particularly focuses on the effects of DF on dough properties, including mixing, viscoelasticity and pasting properties, as well as the interaction between DF and the gluten network. However, incorporation of DF in foods remarkably changes the resultant rheological, textural, and sensory properties of the developed products (Guillon & Champ, 2000). Problems related to dark color, rough texture, and small volume have greatly limited the popularity of fiber-enriched flour products. Hence, relevant solutions are gathered and discussed at the end of the chapter to help relief this situation.

9.2 SUPPLEMENTATION OF WHEAT FLOUR PRODUCTS WITH DFS Low DF intake has been shown to be associated with the development of a variety of diseases. Hence, a wide variety of fiber sources have been developed for use in various foods. As DF-fortified foods, wheat flour products, such as bread, biscuits, steamed bread, and noodles, enjoy preference. Bread has a long history in the West and has been the most common principle food. Biscuits, as a kind of leisure and convenience food, have been popular all over the world. Steamed bread and noodles, which are two of the oldest main foods in China and Asia in general, have evolved into thousands of varieties. Thus, the enrichment of wheat flour products with DFs would be very useful and deserves to be studied in detail.

9.2.1 Effects of DF Enrichment on the Quality of Biscuits Compared with bread, cookies contain a very low amount of water, which in turn results in crispy texture. The crispiness of low-moisture foods like biscuits is closely related to their

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water content and/or water activity (Katz & Labuza, 1981; Nicholls et al., 1995). Water plays a complex role in affecting the interactions among ingredients, determining the degree of connection between biopolymers and contributing to the unique sensory parameters of biscuits. Nuclear magnetic resonance proton relaxation measurements have been widely used in the rapid and nondestructive testing of food moisture distribution. During heating from 30°C to 80°C, many simultaneous physicochemical phenomena occur, among which the most significant is the evaporation of water. The free water molecules and those components in close interaction with water, which are assigned to the mobile proton signal, decrease with temperature. In contrast, the rigid CH proton groups of starch and gluten, which are assigned to another signal with short relaxation time, gradually increase. As the biscuit dough becomes dryer, less water molecules interact with starch and gluten molecules, thus leading to fewer mobile protons. At the initial heating stage, adding both oat and inulin fibers causes no noticeable effect on all proton signals, indicating fewer changes in water distribution in cookie dough (Serial et al., 2016). The temperature at which the content of free water or highly mobile bound water loses its primary position is 50°C. At this temperature, water evaporates rapidly and causes a loss in free proton content. Also, the heating process induces strong changes in water distribution in biscuit dough. At this stage, the incorporation of oat fiber helps to reduce the increasing mobility of the free water fraction. This can be related to the high β-glucan content in oat fiber that forms a gel and attracts more water molecules (Serial et al., 2016). During the baking process, the biscuit diameter increases linearly at first until it reaches a maximum value and shrinks slightly (Abboud, Hoseney, & Rubenthaler, 1985). The standard biscuit dough can expand constantly up to 100°C when it reaches its maximum diameter. The obtained biscuit usually has the characteristics of appropriate width/thickness aspect ratio and hardness. Enrichment of biscuit dough with inulin fiber affects the biscuit maximum diameter minimally during baking, but produces half less hardness and larger width/thickness aspect ratio, indicating a tender final product (Serial et al., 2016). However, the oat fiberfortified biscuit dough stops expanding at a lower baking temperature than the stand biscuit dough and thus yields a smaller, thicker, and harder biscuit (Serial et al., 2016). Similar findings were also observed in wheat bran- and rice bran-fortified biscuits whose spread ratio significantly reduced as the bran content increased (Sudha, Vetrimani, & Leelavathi, 2007). It is generally accepted that a good biscuit formulation produces biscuits with large diameter and uniform surface-cracking pattern. Thus, the cooperation of cereal bran fibers can adversely affect the expansion property of the biscuits. Besides the smaller biscuit size, the grain bran, including wheat bran, rice bran, barley bran, and oat bran, also yield hard biscuit texture (Sudha et al., 2007; Uysal et al., 2007). At 10% level, the bran incorporation may not affect the biscuit quality significantly. However, with increasing bran content, the texture and surface characteristic values of biscuits dropped significantly (Sudha et al., 2007). The taste and mouthfeel of the biscuits was affected at the 20% bran level, and extremely hard biscuit texture was obtained at the 30% and 40% levels of bran, suggesting unacceptable biscuit quality with high bran content. Nevertheless, the biscuits remained crispy even at the level of 40%, as indicated by the breaking strength values (Sudha et al., 2007). The increased biscuit hardness may be related to the lower level of gluten available to bind the water due to the competition for water between the DF and flour components (Mudgil, Barak, & Khatkar, 2017). The mechanical properties of the bran-enriched biscuit system can be affected by both bran particle size and the level of bran addition. It was observed that the fine bran caused similar changes to biscuit texture parameters, such

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as spread ratio, bulk density, width, length, and height to coarse bran at the same addition level (Sozer et al., 2014). The reduction of the bran particle size yields higher elastic modulus and fracture stress of the biscuits due to their incorporation into the butter, which improved its overall strength (Reynaud et al., 2001; Singh, Zhang, & Chan, 2002). The tensile strain at failure indicates how much the sample elongates upon failure. The smaller the bran particle size, the harder the biscuit texture (Sozer et al., 2014). Moreover, the replacement of the biscuit flour with fiber-rich flours also brings texture changes to the biscuit quality. Adding barley flour from 10% to 40% to wheat flour caused a similar reduction in the biscuit spread ratio compared with that of barley bran (Gupta, Bawa, & Abu-Ghannam, 2011). However, unlike barley bran, barley flour conferred biscuits a lower breaking strength and tender texture. The flavor of the biscuits is malty and sweet at 20% and 30% levels of barley flour substitution (Gupta et al., 2011). Accordingly, compared with barley bran, the use of a relatively high content of barley flour is more acceptable. Many water-soluble dietary fibers (SDFs), such as guar gum, inulin, and other oligosaccharides, have been widely used as thickener, stabilizer, and texturizer in many processed food products. While the fortification of biscuits with increasing levels of SDFs also makes biscuits harder and more difficult to chew, it seems that both SDFs and IDFs could enhance the mechanical properties of biscuits (Huang et al., 2018). The most attractive to consumers in terms of appearance, texture, sweetness, and taste are the biscuits with proper level of SDFs. The large substitution of SDFs also contributes to biscuit quality degradation. Apart from the textural properties, SDFs are likely to produce lower biscuit lightness value than IDFs by facilitating the Maillard reaction. Nonreducing sugars like cellulose do not react with amino acids in the Maillard reaction until they are hydrolyzed to glucose and fructose (Mieszkowska & Marzec, 2016). In contrast to IDFs, the SDFs are characterized by lower polymerization degree and randomly bonded monosaccharides. Upon heating and hydration, SDFs like polydextrose might provide additional reducing sugars for the Maillard browning reaction and produces dark biscuits.

9.2.2 Effects of DF Enrichment on the Quality of Bread Sugar-snap biscuits are characterized by a formula with a high level of fat and sugar, lowwater content, and no yeast. When the cookie dough undergoes the heating process, the development of the gluten network is hindered. Instead, bread requires high moisture and yeast to ensure a well-formed gluten network. The discrepancy between the formulas for biscuits and breads allows the different performance of DFs. The moisture content and water dynamics of the bread are strongly linked with the bread quality and are governed not only by the processing parameters but also by the presence of diverse ingredients. The binding strengths between bran constituents and water molecules can be distinguished. It was believed that fibers mainly bound water molecules through strong and weak hydrogen bonds, dipole-dipole interactions, ionic interactions, and enclosure effects through capillary forces (Chaplin, 2003). However, due to the external forces, weakly bound water is not present in the dough system ( Jacobs et al., 2015). Less weakly bonded water was found in ground bran than in coarse bran due to the discrepancies in particle size and fiber composition (Hemdane et al., 2017a). The substitution of flour with wheat

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bran greatly helps in maintaining the water content in bread dough as evidenced by the increased mobile proton and rigid proton amplitude. After a two-hour resting period, both the proton amplitude and relaxation time decreased, indicating the reduction of the water content and a closer interaction between the dough ingredient and water molecules (Hemdane et al., 2017b). Noticeably, the dough with 20% ground wheat bran performs better in water holding than coarse bran during dough resting, which may be attributed to the difference in affinity for water. Staling can result in low consumer acceptance of bakery products and considerable economic losses. During long-term storage, the crumb moisture decreased dramatically within 30 days and then remained essentially constant (He & Hoseney, 1990). It was proposed that DFs could effectively prolong the shelf-life of bread mainly by maintaining the water content in the bread system. Other studies contended that the presence of DFs could compete for water with the dough matrix (Bock & Damodaran, 2013; Collar, Santos, & Rosell, 2007). For one thing, DFs could bind water and prevent evaporation of water from the dough system during processing and storage. For another, a proportion of the free water exhibits a negative correlation with the amount of DF added due to the higher affinity for water of nonstarch biopolymers than flour components ( Jacobs et al., 2016).] In general, the incorporation of DFs leads to water retention, as well as the transformation of free water to confined water. However, the level of added DF should be carefully selected in case they threaten the hydration and proper formation of the gluten network (Bock, Connelly, & Damodaran, 2013; Li et al., 2012). Some hydrocolloids, like guar gum, trehalose, and carrageenan, have been shown to be effective antistaling agents and were successfully used in the industrial manufacturing of bread (Das, Raychaudhuri, & Chakraborty, 2015; Peng et al., 2017). During baking, the free water molecules migrate from fresh bread crumbs to the crust and evaporate. Due to the very low moisture content of the crust, almost all protons present are low mobility (Bosmans et al., 2012). The application of the low level of hydrocolloids could effectively form a gel network and fill the gaps in bread crumb, thus retaining moisture in bread during baking and storage. Bran, as a fiber-rich product, has been widely used in bread for nutrition purposes. Also, the incorporation of bran into bread leads to changes in organoleptic properties related to volume, crumb softness, color, etc. Wheat bran with higher water-holding capacity could produce larger bread mass. However, a significant negative correlation between bran waterholding capacity and bread volume were found (Hemdane et al., 2018). Furthermore, the height of the bread after baking also exhibited a downtrend with increasing water-binding capacity of bran (Hemdane et al., 2018). The gas cells were initially introduced into the bread dough during mixing, and the final gas cell volume can even take over 70% of the loaf volume (Scanlon & Zghal, 2001). The number and dimension of gas cells vary greatly among bread and will change the sensory properties of bread. A tin loaf with numerous small gas cells is generally accepted as a standard loaf of bread (Upadhyay, Ghosal, & Mehra, 2012; Wilde, 2003). The deleterious effect of wheat bran on the bread volume may blame for the restraint of optimal gas cell expansion. The light micrographs of bread containing bran also added to growing evidence of the steric hindrance induced by bran fibers. It was observed that bran particles formed a physical barrier around the gas cells and hindered their continuous expansion (Gan et al., 1992; Hemdane et al., 2015, 2018). Thus, it is more likely that bran particles make the gas cell more susceptible to breakage. However, such phenomenon was believed to only have a limited impact on bread loaf volume. The strong correlation between the

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water-binding potential of bran and bread loaf volume indicates the important role that water plays in determining the bread volume. Several studies have suggested the redistribution of water in gluten network induced by DF resulted in viscoelastic changes of the doughs (Bock & Damodaran, 2013; Li et al., 2012). Fermentation is a critical process in bread making, where the expansion of air bubbles provides the characteristic aerated structure of bread. During proof and baking, the growth of gas cells determines the degree of the dough expansion and thus the ultimate texture and volume of the bread (He & Hoseney, 1991). The gas cell dimension is directly related to their stability due to the combination and rupture of gas cell walls. Accordingly, the rheological properties of the bubble walls are of great importance in maintaining their stability against premature failure during baking (Dobraszczyk, Campbell, & Gan, 2000; Dobraszczyk & Morgenstern, 2003). Therefore, for bran-rich breads, the modifications of bread rheological properties induced by DFs should be responsible for the unstable gas cells during proofing. Thus, it is more likely that bran fibers influence bubble expansion not only by physical interference but also by altering the bread rheological properties. Additionally, it was also observed that the bread volume was not significantly affected by the size of the bran, as both coarse and fine bran resulted in similar shrinking of the bread volume (Hemdane et al., 2017b). This suggests that irrespective of its particle size, the presence of bran particles can restrain optimal gas cell expansion to a limited extent. Besides the observed hard formation of gas cell in bran-enriched bread, the presence of bran may also produce larger gas holes as observed in the images of the crumb morphology of bread with different bran content (Irakli, Katsantonis, & Kleisiaris, 2015). The formation of unequally distributed big gas holes was theoretically demonstrated to be mostly linked with the physical destruction effects of bran fibers (mainly IDFs). On the one hand, the rod-like bran fibers can pierce the adjacent bubble walls and transform them into a bigger one. This interpretation is consistent with the observations of the dough microstructure by X-ray microtomography (Turbin-Orger et al., 2012). On the other hand, bran fibers have been widely reported to disturb the uniformity of the gluten network to a certain extent. The partial rupture of the gluten filaments thus results in the impaired gas-holding capacity of the bread. Accordingly, the enrichment of bread dough with bran fibers may cause great damage to bread volume by imposing restrictions on the growth of gas cells during proofing. Unlike cookies, breads have the characteristic of gentle texture, which is mainly conferred by the high moisture and yeast addition. The presence of DFs may influence the bread texture by altering moisture distribution in the bread system. A negative correlation was found between the bran water-binding capacity and bread crumb hardness (Hemdane et al., 2018). Previous studies found softer textures in moister bread crumbs, especially during staling (Baik & Chinachoti, 2003). Although the bran-fortified breads had higher water content, they also had higher hardness, indicating that in this case the moisture content was not the only factor influencing hardness. There is a significant correlation between the increase of the porosity during proofing and the final bread density: the higher the porosity during baking, the lower the bread density (Le Bleis et al., 2015). It was reported that the restriction of gas-cell expansion contributed to the reduction of bread porosity and thus resulted in small-sized bread with lower height (Hemdane et al., 2018). It is possible that the bran DFs affect the bread hardness by modifying its texture properties. An uptrend in bread firmness upon increasing the rice bran concentration was observed by various researchers (Tuncel et al., 2014; Turbin-Orger et al., 2012). They attributed this effect to the thickening of the air bubble walls in the crumb (Go´mez et al., 2011). Nevertheless, the thickening effect of DF fails to explain the

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formation of large gas cells with irregular and polyhedral shape. Thus, the hardening effect induced by bran fibers could be attributed to other reasons, i.e., filler effect (Le Bleis et al., 2015). In the case of SDFs, different effects on bread quality characteristics were observed. The inulin with good water solubility tends to yield smaller and harder bread, while the poorly soluble inulin produces larger bread with a softer crumb texture (Peressini & Sensidoni, 2009). The polymerization degree can also influence the loaf volume by altering the solubility of DFs. Inulin substitution with a high polymerization degree resulted in a gradually decreased bread loaf volume (Meyer & Peters, 2009). In addition, the soluble inulin produced finer crumb texture (smaller gas cells) than the reference and insoluble inulin-enriched samples. The bread crumb structure is mainly affected by the formation of the gluten network during the proofing stage. The gluten-starch matrix and liquid film layer are important to keep the gas cells during mixing (Gan, Ellis, & Schofield, 1995). SDFs are believed to contribute to gas retention by stabilizing the film layer so that the gas cells can expand without rupturing or coalescing (Scanlon & Zghal, 2001). It was observed that soluble arabinoxylan can increase dough viscosity and thicken the cell wall, thus resulting in prolonged oven rise and increased loaf volume (Koegelenberg & Chimphango, 2017). Instead, water insoluble arabinoxylan exerts the opposite effects on gas-cell formation by promoting gas-cell coalescence, which in turn leads to loss of gas retention (Gan et al., 1995). Both SDFs and IDFs can produce darker bread crumbs despite their characteristic difference. However, crust browning is more intense for bread enriched with soluble inulin than with insoluble inulin at the same concentration, which is a reasonable result as the soluble inulin contains a higher content of reducing sugars that are involved in the Maillard reaction during baking (Garcı´a-Ban˜os et al., 2004). Arabinoxylan is one of the most important functional DF in wheat bran and can affect the physical and chemical properties of wheat flour products. Arabinoxylan can influence the dough water absorption, mixing, and rheological properties due to its excellent water-binding capacity and oxidative crosslinking ability (Gan et al., 1995). Such behavior may be of interest in bread making as the water content is a key factor that governs final bread characteristics (Scanlon & Zghal, 2001). For this reason, the proper dosage of arabinoxylan should be used to minimize the negative effects on bread moisture distribution. Usually, the use of arabinoxylan in bread is limited to a small dosage, as studies have found unacceptable bread quality with high levels of arabinoxylan (Koegelenberg & Chimphango, 2017). Research indicates that the addition of arabinoxylan at 0.8 g/100 g contributes to fine bread without apparent quality deterioration (Sivam et al., 2010). At the optimal level of arabinoxylan, the bread volume is similar to that of the control. Accordingly, the differences in the characteristic of the DFs determine their application dosage, as well as quality of the final product. However, due to the excellent water-binding capacity, the dosage of SDFs should be kept much lower in bread than that of other IDFs. To further meet the nutritional needs, the level of DFs should be increased. In contrast with cellulose and hydrophilic colloid, rice bran hemicellulose has a moderate water-holding capacity and swelling capacity. In addition, as a kind of IDF, it also produces lower loaf volume and firmer texture of bread, as bran does. However, the bread color, texture, taste, and overall acceptability were not significantly different than those of the control bread when 1%–3% of rice bran hemicellulose was added (Hu et al., 2009). We can draw inspiration from the previous studies that both SDFs and IDFs have advantages, as well as disadvantages in bread fortification and the selection of the addition level and DF species is of utmost importance.

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Currently, with the growing number of celiac disease patients, the gluten-free products are in great demand, as the only way to prevent this disease is to follow a strict gluten-free diet. However, despite the rapid growth of the gluten-free market, patients with celiac disease still have troubles finding gluten-free wheat flour products due to their high prices, poor sensory properties, and limited variety and availability (Capriles, dos Santos, & Ar^eas, 2016). This is largely because of the lack of gluten proteins in gluten-free products, as gluten is of utmost importance in the determination of the flour products texture parameters. Rice flour is one of the frequently used ingredients in gluten-free products due to its low level of protein and high amount of easily digestible carbohydrates (Gujral & Rosell, 2004). As a result, additional gum or emulsifier is necessary to impart desired viscoelastic properties to gluten-free cereal products. The improvement effect of several hydrocolloids, such as hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose (CMC), locust bean gum, guar gum, xanthan, and β-glucan, on gluten-free breads has been widely reported (Gallagher, Gormley, & Arendt, 2004; Haque & Morris, 1994). A possible explanation to such effect is that hydrocolloids allow the entrapment of air bubbles in dough and help stabilize the dough mixture during baking by improving dough viscosity (Delcour, Vanhamel, & Hoseney, 1991). In general, the gluten-free bread without any extra additives has relatively firm structure with poor physical appearance. Adding selected hydrocolloids could reduce the firmness at different levels (Lazaridou et al., 2007). Lee and Lee (2006) reported that the addition of xanthan gum decreased crumb hardness of fresh and stored rice flour formulated breads (Lee & Lee, 2006). Sabanis, Lebesi, and Tzia (2009) found that maize DF imparted gluten-free breads with significantly higher loaf volume and crumb softness compared with the control non-fiber gluten-free breads (Sabanis et al., 2009). Korus et al. (2006) reported larger and tender gluten-free bread containing inulin (Korus et al., 2006). Haque and Morris (1994) made rice bread with HPMC as well as psyllium gum and obtained loaf volumes up to 450 (cm3/100g) by combining the two DFs, but when using only one of the DFs, the loaf volume was reduced to the range of 150–220 (cm3/100 g) (Haque & Morris, 1994). In the case of xanthan-guar fortified gluten-free breads, the firm structure was significantly altered, and produced notably larger bread specific volume (Martı´nez, Dı´az, & Go´mez, 2014). Accordingly, it seems that the composite gel is to some extent more effective in promoting gluten-free bread texture than the single gel. The crumb details of the final gluten-free bread products clearly revealed more delicate breads with SDFs than with IDFs (Martı´nez et al., 2014). Such influence could be attributed to their effect on the internal structural of the dough as observed by the environmental scanning electron microscopy images of glutenfree doughs with diverse fibers (Martı´nez et al., 2014). IDFs remained almost unchanged in the dough and embedded in the dough matrix, whereas SDFs dissolved in the aqueous solution. The aqueous-like SDF enveloped the starch granules and lubricated the final dough (Martı´nez et al., 2014). The gluten-free breads with SDFs like polydextrose had the highest specific volume, lowest hardness, and largest cell density. Whereas coarse IDFs, such as bamboo fiber, generated small and hard gluten-free breads (Martı´nez et al., 2014).

9.2.3 Effects of DF Enrichment on the Quality of Steamed Bread Steamed bread (Mantou), which is made by fermenting wheat flour, water, yeast and then cooking by steaming, is one of the traditional staple foods in Asia (Huang et al., 1996).

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Compared with bread, steamed bread is covered with a smooth, white layer. Researchers drew inspiration from whole grain bread and enriched steamed bread with whole grain flour to improve their nutritional properties. Both the whole oat flakes and brown rice grains significantly decreased the brightness and whiteness of steamed bread, while their influence on steamed bread is weaker than on baked bread at the same addition level, due to lower occurrence of the Maillard reaction (Hsieh et al., 2017). A high brightness value is generally an indicator of better acceptance and quality of the steamed bread (Rubenthaler, Huang, & Pomeranz, 1990). The decrease of this value implies the impaired acceptance of the wholegrain-enriched steamed bread. In addition, it was observed that whole grains increased the hardness, adhesiveness, gumminess, and chewiness, but decreased the degree of cohesiveness and springiness of steamed bread (Hsieh et al., 2017). Because of the gas-steaming procedure and adequate moisture, the final steamed breads are characterized by softer textures than non-steamed bread due to the full formation of the gluten network and starch gelatinization. Thus, springiness is an important evaluation index for steamed breads. The loss of the springiness of steamed bread may also be one of the barriers that hinder its popularity. A positive correlation between whole grain flour particle size and steamed bread hardness was reported in a study, which found that the finer whole wheat flour produced steamed breads with softer textures than steamed breads made with coarse whole wheat flour (Wang, Hou, & Dubat, 2017). However, such benefit seems limited as whole-grain flour yields significantly harder steamed bread regardless of the flour type and particle size, as well as addition level. The chewiness and gumminess of steamed bread are significantly related to hardness (Sun et al., 2015); thus, the undesirable hardness value results in harmful mouthfeel. Additionally, the specific volume of steamed bread decreased with the increasing addition level and particle size of the whole-grain flour. The specific volume is one of the most important visual characteristics of steamed bread, which is strongly influenced by the particle size of the whole grain flour. Overall, smaller steamed breads with larger gas cells were observed in the whole-grain flour substituted samples (Wang et al., 2017). The mouthfeel of bread is known to be strongly influenced by the cell characteristics. For instance, higher value of the gas cell area indicates a more open texture (Hager & Arendt, 2013). Finer, thin-walled uniform gas cells yield softer and more elastic texture than coarse, thick-walled cell structure (Scanlon & Zghal, 2001). Reduction of the whole grain particle size helps yield larger steamed bread volume with smaller gas cell diameter and thicker cell wall (Wang et al., 2017). The observed inferior quality of whole grain flour-enriched steamed bread was reported to be related to the detrimental effects of the high content of IDFs. Considering the enhancing effects of SDFs on the quality of baked goods, they were also applied to steamed bread for further quality improvement. However, it was observed that the spread ratio and specific volume of the steamed bread decreased upon addition of sodium alginate and konjac glucomannan at both the 0.2% and 0.8% levels (Sim, Noor Aziah, & Cheng, 2011). Such observation is consistent with the tensile behavior of the gum-enriched dough. The appropriate balance between the dough resistance and extensibility is important in determining the dough properties. The enhanced maximum resistance of the dough may cause difficulties in the processing of steamed bread and result in shrinkage of the finished products (Sim et al., 2011). In another study, however, adding inulin with a different degree of polymerization increased the specific volume of steamed bread (Luo et al., 2017). This phenomenon was attributed to the yeast activity, which is known to utilize the low molecular sugars during the

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fermentation of dough, including short-chain inulin (Meyer & Peters, 2009). Also, the oligomeric inulin was dissolved and integrated into the bread cell structure, thus strengthening the stability of the gluten network structure and gas-holding capacity (Ziobro et al., 2013). The steaming method yields products with thin, smooth, white skin rather than the brown crust of traditional bread; thus the whiteness of the steamed bread is of utmost importance. Many DFs were found to darken both the crumb and crust of the wheat flour products. Instead, the brightness and whiteness values of the crust and crumb of steamed bread enriched with lower inulin content were higher than those of the control, which may be due to the whiter color of inulin compared to other DFs (Luo et al., 2017). The most significant browning effect occurs with a higher content of inulin with a low degree of polymerization (Luo et al., 2017). This should be blamed for the reinforced Maillard reaction caused by the presence of low molecular weight glucose and fructose in inulin. Compared to baked bread, the non-enzymatic browning rarely occurs during steaming due to the lower temperature required for steaming compared with the baking temperature. It was reported that the shelf life of Chinese steamed bread was 1–3 days at room temperature, and the shelf life becomes even shorter at a higher storage temperature or lower storage relative humidity (Peng & Cheng, 2007). It is widely recognized that starch retrogradation is the main factor responsible for bread staling (Gray & Bemiller, 2003). During storage, the change in firmness usually serves as an index of bread staling (Hareland & Puhr, 1998). Adding 0.8% sodium alginate or konjac glucomannan results in a drastic drop in the firmness increase rate of steamed breads upon storage, which indicates the inhibition of the staling rate of steamed breads (Sim et al., 2011). Adding inulin with a varying degree of polymerization restrains the hardening rate and reduces the change rate of the relative recovery and cohesiveness of steamed bread (Luo et al., 2017). Together, the results of the relative water vaporization enthalpy of inulin-fortified steamed bread demonstrated that inulin hindered the release of water from starch granules and accelerated the water migration to the crust of the steamed bread, which ultimately affected the extent of starch degradation (Kerch et al., 2008).

9.2.4 Effects of DF Enrichment on the Quality of Noodles Noodles, which are made with wheat flour and cooked in boiling water, are another important main food for Asian people. Due to their unique cooking method and lower moisture, noodles are characterized by a smooth layer and compact structure. However, owing to its limited nutrition properties, whole-wheat flour has been added to encourage the consumption of high-fiber noodles. For whole-grain noodles, the significantly higher cooking yield observed was mainly caused by the high-water holding capacity of fiber in wheat bran and the increased starch damage, which picked up more water than intact starch granules (Niu et al., 2014a). Meanwhile, the coarser bran has a more disruptive impact on the gluten matrix and results in cooking loss of noodles. Cooking loss is defined as the amount of solid that dissolves in the water during cooking, and may be regarded as an indicator of the noodle’s structural integrity during cooking (Liu et al., 2012). In another study, the dry noodles with the bran addition showed reduced cooking loss, which may be attributed to the increased noodle firmness (Song et al., 2013). Regarding the impaired cooking loss of bran-enriched fresh noodles, the combination of hydrocolloids may assist in improving such deficiency. With an addition

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level of 4% guar gum and xanthan gum, a significant downtrend in cooking loss and turbidity was observed, indicating the possibly favorable influence of hydrocolloids on the proper whole-grain noodle structure ( Jang, Bae, & Lee, 2015). As for the texture properties of fresh noodles, whole-wheat flour yields harder noodles with low springiness, cohesiveness, and resilience. It was reported that the textural properties of cooked fresh noodles are closely related to the peak viscosity and final viscosity of the flour (Niu et al., 2014b; Wang et al., 2011). High peak viscosity and final viscosity result in softer noodle texture, but whole grain flour is more likely to have low-peak viscosity and final viscosity, which lead to the hard noodle texture (Niu et al., 2014a). Observations from the cross-section microstructures of noodles made from whole-wheat flour showed a thinner gluten matrix and loose structure, further indicating the destructive effects induced by wheat bran (Penella, Collar, & Haros, 2008). Actually, not all the components in wheat bran contribute to the inferior noodle quality. The application of 0.25%–1.0% arabinoxylans was reported to increase both the nutrition and quality of Chinese noodles (Fan et al., 2016). At such an addition level, the cooking loss rate was greatly decreased because of the relatively stable arabinoxylans-starch-protein matrix. The matrix could hinder the swelling and diffusion of starch polymers to some extent when undergoing the heating process. Similar results were also reported by other researchers, who suggested that the cooking properties of noodles were strongly affected by the hydrocolloid content (Zhou et al., 2013). During cooking, starch granules begin to swell and rupture, and in turn affect water uptake during heating (cooking yield). In the conventional preparation of noodles, the cooking yield is mainly attributed to starch gelatinization and gluten network swelling (Majzoobi, Ostovan, & Farahnaky, 2011). Therefore, the increased cooking yield of SDF-fortified noodles may be greatly related to the water-binding capacity of SDFs (Silva et al., 2013). The discontinuous gluten network or weak starch-gluten matrix allows a greater quantity of water-soluble components, especially amylose, to be dissolved into the hot water upon cooking, which contributes to the cooking loss (Zhou et al., 2013). The lower cooking loss of konjac glucomannan fortified fresh noodles suggested that the reinforced gluten-starch network protected starch granules from separating from the gluten matrix. This perspective was further verified by the microstructure of both raw and cooked noodles enriched with konjac glucomannan (Zhou et al., 2013). In the starch-proteinkonjac glucomannan complex, the konjac glucomannan is integrated into the matrix and adheres to discrete starch granules, thus achieving a stronger connection with damaged starch granules, as well as the fractured protein filaments. After cooking, a large number of cavities enmeshed in the network are formed and might serve as containers for noodle waterabsorbing behavior. Increasing konjac glucomannan substitutions led to the reduction of the average pore-size and improved the continuity of the sheets (Zhou et al., 2013). The above findings by scanning electron microscope analysis were successfully correlated with the noodles’ texture parameters. Fresh noodles with the arabinoxylans formula exhibited chewy property with high springiness, cohesiveness, gumminess, chewiness, and resilience values. These textural parameters were closely linked with the reinforced breaking strength and flexibility of cooked arabinoxylan-containing noodles (Fan et al., 2016). Texture profile analysis of cooked noodles made from reconstituted flour with 1%–4% konjac glucomannan also showed improved springiness and cohesiveness. Upon cooking, a semisolid network quickly formed consisting mainly of highly hygroscopic konjac glucomannan, which might form a viscous water layer at

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the surface of the noodles (Zhou et al., 2013). Another study added growing evidence to the formation of such “starchy” film by using inulin in fresh noodles (Qin et al., 2010). Notably, noodles made from IDFs and SDFs received higher scores in terms of hardness than the plain noodles. Thus, it seems that the replacement of wheat flour by DFs can yield fresh noodles with harder textures regardless of the type and solubility. Overall, noodles made with SDFs have higher overall acceptability than those made with IDFs (Mudgil, Barak, & Khatkar, 2018). The improved sensory quality may be due to the addition of hydrocolloids that imparts smoothness and a little gumminess to the noodles preferred by consumers. This further suggests that using low concentration of SDFs can effectively improve the noodle sensory properties, especially the textural related attributes.

9.3 EFFECTS OF DF ENRICHMENT ON THE DOUGH PROPERTIES AND GLUTEN NETWORK As reported by numerous studies, the dough properties are closely linked with the texture, appearance, and quality of the final wheat flour products. For instance, during the breadbaking procedure, the bread dough expands with time and baking temperature, which is a phenomenon closely related to the dough extensibility. The higher extensibility is more likely to impart the bread with a larger volume. Therefore, the fiber-fortified dough properties may be good indicators to evaluate and predict the quality of wheat-flour products enriched with DFs. According to the observations of the impact of DFs on wheat-flour products concerning cookies, breads, steamed breads, and noodles, it is of high significance to understand the effects of DF on the dough properties including the mixing, elastic, and pasting properties, as well as the interaction between DFs and the gluten network.

9.3.1 Effects of DF Enrichment on the Dough Mixing Properties The addition of fibers promoted differences on the dough mixing behavior as measured by the farinograph or Mixolab. Among all the indices, fiber addition markedly modifies the dough water absorption. Such changes are usually divided into two trends, largely based on the fiber type and content. A remarkable increase was usually produced by the addition of fibers that have a large number of hydroxyl groups, such as pea fiber and carob fiber (Wang, Rosell, & Benedito de Barber, 2002). Similar effects on water absorption were also observed when bran from different sources was added at different levels (Sudha et al., 2007). By increasing the bran level from 10% to 40%, a huge increase in water absorption from 63.88% to 76.28% was found with the addition of barley bran (Sudha et al., 2007). The analysis of the chemical characteristics of the bran sources revealed that barley bran had the highest SDF content compared with oat bran, rice bran, and wheat bran. Accordingly, the water absorption of fiber-enriched dough may rely on its SDF content. The availability of hydroxyl groups allows more water interactions through hydrogen bonding, as previously found by Rosell, Rojas, and Benedito De Barber (2001) who worked with different hydrocolloids (Rosell et al., 2001). However, a downtrend in dough water absorption was observed upon addition of different inulin types at different levels (Peressini & Sensidoni, 2009). Thus, it seems that no

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relationship was established between water absorption and inulin content. Inulin has high affinity for water molecules and is thought to compete for water with other flour constituents. However, inulin-enriched dough has low water absorption mainly due to the presence of low-molecular-weight sugars and oligosaccharides in commercial inulin, which reduces the dough consistency (Rouille et al., 2005). The dough development time and stability value are another two important indicators of the flour strength, with higher values suggesting stronger doughs. Normally, bran fibers result in longer development time and shorter stability time of the doughs. Doughs with 40% rice bran had development time as long as 13 min (Sudha et al., 2007). Therefore, the bran fiber-fortified dough usually required more mixing time to guarantee the formation of a suitable gluten matrix. Also, the extent of decrease in dough stability was relatively marginal in the case of wheat and rice bran compared to oat and barley blends, which cause significant reduction in the dough stability time from 8.5 to 4 and 7.0 to 3.5 min, respectively (Sudha et al., 2007). Such findings imply the hard formation of bran-enriched dough and vulnerable gluten network. The easy collapse of the gluten network may be responsible for the flat and less elastic final products. However, not all DFs adversely affect the gluten matrix formation. For example, stronger dough was obtained by the addition of xanthan and alginate, which was reflected in the high dough stability (Rosell et al., 2001). Meanwhile, the development time also exhibited an uptrend from 2.8 to 9.0 and to 11.5 min in the case of alginate- and xanthan-fortified doughs (Rosell et al., 2001). Findings described in Section 9.2 suggested a positive impact of some hydrocolloids on the wheat flour products. This may be one of the results from the enhanced dough stability.

9.3.2 Effects of DF Enrichment on Dough Elastic Properties Dough texture properties play an important role in determining the overall acceptance of flour products, such as bread (McCann, Le Gall, & Day, 2016). During the dough-kneading stage, the dough undergoes different mechanical deformations, which mainly include compression and extension. The extension property of dough is primarily determined by the polymeric network of gluten proteins, which is influenced by the content and composition characteristics of gluten, such as molecular dimension, the entanglement and aggregation of chains, as well as the ratio of glutenin to gliadin (Singh & MacRitchie, 2001). At the early stage of extension, the gluten material displayed a linear response to resistance with the increasing strain (McCann et al., 2016). Then, the resistance force reached the maximum, and the gluten network was fractured when further strain was applied. Thus, the strength of the gluten protein branches greatly affects the dough tensile property. Regarding the effect of DFs on the dough extensibility, different conclusions have been reached. Generally, there are three patterns: the dough extensibility decreases with DF addition, the dough extensibility increases with DF addition, and the dough extensibility first increases and then decreases with DF addition (Ahmed, 2015). The discrepancies may be attributed to the flour quality as well as the variety and level of added DF. For most cereal bran fibers, like wheat, rice, oat, and barley, the extensibility values decreased to a great extent, suggesting harder dough in the presence of bran fibers. Interestingly, oat bran fortified-dough had the highest extensibility and the lowest resistance to

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extension value mainly due to its unique DF composition (Sudha et al., 2007). The chemical characterization findings revealed that oat bran had the lowest total DF content (20.4%) compared with wheat bran (47.5%), rice bran (40.28%), and barley bran (45.0%). Additionally, the ratio of soluble DF in oat bran also was the highest (Sudha et al., 2007). According to findings presented in Section 9.2, high SDF content causes less damage to the gluten network than IDF content, which makes oat bran a more suitable additive than the other three cereal brans. The most important fiber constituent in oat is β-glucan—a soluble fiber beneficial in preventing cardiovascular disease. However, the improper incorporation of β-glucan concentrate negatively affects the gluten network as evidenced by the decreased dough extensibility from 168 to 126 mm at 10% β-glucan level (Ahmed & Thomas, 2015). Thus, a proper DF composition may help enhance the dough elastic property. A combination of good resistance and good extensibility results in desirable dough properties. It was observed that the incorporation of different hydrocolloids in relation to alginate, carrageenan, xanthan, and HPMC at 0.5% addition level produced an increase in the dough extensibility and a decrease in the resistance to extension measured using an extensograph (Rosell et al., 2001). An enhanced dough elasticity was also observed with 1%–5% trehalose addition (Peng et al., 2017), which is consistent with a previous study in which the presence of sucrose increased dough extensibility and conferred dough with more viscous texture (Mariotti & Alamprese, 2012). Therefore, this indicated that low hydrocolloid concentration helps produce softer dough, which may be one of the reasons that low levels of hydrocolloids were frequently used to improve the quality of wheat-flour products. Additionally, doughs containing hydrocolloids exhibited higher stability to changes with time. For instance, alginate-fortified doughs showed almost continuous resistance with time, indicating excellent dough stability (Rosell et al., 2001). As a result, doughs containing hydrocolloids usually exhibit good handling behavior and large tolerance in the fermentation stage. The tensile property is closely related to dough expansibility during fermentation and baking. Alginate caused a notable downtrend in the dough height, which was in line with the lower extensibility and the almost continuous resistance with increasing resting time from 45 to 135 min (Rosell et al., 2001). Likewise, the addition of pea fiber, whose IDF content is 79.8%, also resulted in a remarkable drop of the maximum dough height (Wang et al., 2002). As presented in Section 9.2.2, the incorporation of DFs adversely affects the loft volume, which could be further explained by the changing dough viscoelasticity during the fermentation stage. The interaction between gluten proteins and hydrocolloids may limit the free expansion of the dough throughout the proofing. Moreover, findings from analysis of the tensile property of doughs enriched with hydrocolloids indicated the improved dough stability during fermentation (Rosell et al., 2001). Thus, doughs containing hydrocolloids require slower and longer fermentation. However, the time to reach the maximum dough development was negatively affected by the addition of pea fiber, which was further confirmed by the significantly less time taken for the maximum gas formation (Wang et al., 2002). This suggests that the fermentation of doughs containing more IDF requires less time to reach the maximum gas formation than does the control, which is contrary to the findings in doughs fortified with hydrocolloids. The application of DFs (mainly SDF) in gluten-free bread was reviewed at the end of Section 9.2.2. The rice breads formulations with various DFs like HPMC, guar gum, carrageen, and xanthan gum to produce more elastic gluten-free breads have been widely studied

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(Cato et al., 2004; Kang, 1997; Lee & Lee, 2006; Nishita, 1976). Wheat dough was found to have excellent extensional viscosity, which imparts breads’ high specific volume. In the case of the gluten-free breads, the extensibility was relatively low, resulting in the low specific volume of the rice flour samples compared with the wheat dough. The addition of 0.5% xanthan to rice dough produced high consistency index and apparent viscosity values, which indicate the strengthened thickening behavior of gluten-free samples (Demirkesen et al., 2010). It has been reported that xanthan gum led to high consistency and low-flow behavior indexes due to the complex aggregates formed by semi-rigid molecules (Mandala, Savvas, & Kostaropoulos, 2004; Sworn, 2000). Accordingly, the rice flour dough containing xanthan gum resulted in relatively higher apparent viscosity than common rice flour dough samples. The gluten-free formulations displayed a shear-thinning (pseudoplastic) behavior. For pseudoplastic materials, the viscosity decreases upon increasing the shear due to the breakdown of the interactions between components of the formulations by the shear. Observations from the flow curves revealed that all the gluten-free doughs containing pectin, guar, xanthan, or HPMC exhibited higher shear stress when the same shear rate was applied, indicating the active role of gums in stimulating the aggregation behavior of components in gluten-free formulation (Demirkesen et al., 2010). Therefore, hydrocolloids are widely used to enhance dough viscosity by preventing settling, phase separation, foam collapse, and crystallization (Mir et al., 2016). The viscoelasticity of rice-based gluten-free formulations showed great dependence on the frequency due to the lack of strong elastic gluten matrix. Findings from the linear viscoelastic modulus of wheat dough and rice dough samples revealed the extremely higher elastic and loss modulus values and weak frequency dependency of the wheat dough compared with the rice dough samples (Demirkesen et al., 2010). A significant increase in the storage modulus of doughs containing 0.5% carrageenan, xanthan, guar, and HPMC that led to an increase in the specific bread volume was reported (Demirkesen et al., 2010; Sciarini et al., 2012). Rheological measurements from oscillation tests and creep tests showed that rice dough with 1.5% and 3.0% HPMC had similar rheological properties to those of the wheat flour dough (Sivaramakrishnan, Senge, & Chattopadhyay, 2004). The effect of HPMC on the viscoelastic properties of zein-starch doughs for leavened gluten-free breads has also been studied. For instance, it was shown that HPMC helped stabilize the gas bubbles and significantly improved the quality of the dough, producing a loaf that resembled wheat bread (Schober et al., 2008). In general, the replacement of gluten is a major challenge for food technologists to produce gluten-free breads, and the hydrocolloids are a group of additives that successfully fulfills this need. Unlike gluten-free doughs, different hydrocolloids produce different effects on the viscoelastic properties of ordinary wheat doughs. It was observed that the dough containing trehalose had lower elastic and loss modulus than doughs without trehalose in the frequency sweep range from 0.1 to 100 Hz (Peng et al., 2017). The increase of trehalose addition level from 1% to 5% resulted in the gradual reduction in both elastic modulus and loss modulus, indicating the weakening effect of trehalose on the dough structure and gluten network (Peng et al., 2017). This may blame the beneficial interaction of trehalose with water molecules, which negatively affect the formation of a proper gluten matrix (Lerbret et al., 2005). However, the tan δ value exhibited a downtrend with increasing trehalose content, revealing the more solid-like property of doughs (Peng et al., 2017). For inulin-enriched doughs, different trends were observed during the frequency sweep test. The elastic modulus increased

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with increasing inulin level from 0% to 7.5%, suggesting the enhanced dough elastic property. The decreased tan δ value with increasing inulin addition also contributed to growing evidence to such effect (Peressini & Sensidoni, 2009). Bonnand-Ducasse et al. studied the viscoelastic behavior of doughs containing water-unextractable and water-extractable arabinoxylans fractions through the frequency sweep test and found that both DFs at a 0.1% addition level produced higher elastic modulus and loss modulus (Bonnand-Ducasse et al., 2010). For IDFs, the increase viscoelastic moduli may be attributed either to the lack of water lubrication due to the competition for water absorption between gluten and fiber (Izydorczyk, Hussain, & MacGregor, 2001; Wang et al., 2003), or to the fibers acting as a filler in a viscoelastic matrix (Uthayakumaran et al., 2002). Accordingly, from the changes of tan δ value, both SDF and IDF can result in solid-like properties of wheat doughs, which is in accordance with the findings described in Section 9.2.

9.3.3 Effects of DF Enrichment on Dough Pasting Properties Dough is a combination of starch and protein in aqueous medium. Upon heating, starch gelatinizes and protein denatures, thus causing changes in the dough viscoelasticity. However, the rheological properties of wheat gluten do not change during heating (Dreese, Faubion, & Hoseney, 1988), and the rheological properties of wheat dough during thermal treatment are predominantly determined by starch gelatinization. As mentioned in Sections 9.2.3 and 9.2.4, the texture of steamed bread and cooking properties of noodles were closely related to the starch gelatinization behavior. It is recognized that swollen gelatinized starch granules form a closely packed structure during the heating stage, resulting in an increase of viscosity (Min et al., 2010). The incorporation of non-starch compounds from wheat bran could adversely affect the dough viscosity due to the inadequate gelatinization of wheat starch granules. The peak viscosity is a parameter related to the capacity of starch to absorb water and the swelling of starch granules during heating (Oro et al., 2013). Increasing the level of wheat bran from 0% to 25% dramatically decreased the dough maximum viscosity. The findings from the study of the water hydration properties of whole wheat flour also showed a significantly lower swelling power at 100°C than ordinary wheat flour (Bae et al., 2014). Therefore, the lower peak viscosity of the whole wheat flour could be correlated to its low swelling power at 100°C. Moreover, the addition of wheat bran also resulted in a restriction of available water for starch granules, which negatively affected the starch pasting properties (Boita et al., 2016). The decreased viscosity of wheat bran-fortified dough system upon heating may be one of the reasons responsible for the impaired adhesiveness and chewiness of the corresponding breads as described before. Despite the changes in dough viscosity, the IDF incorporation significantly increased the mechanical strength of the dough as evidenced by the remarkable increase in the dough elastic modulus obtained by the temperature sweep from 30°C to 95°C (Ahmed et al., 2013). Thus, it can be concluded that IDFs weaken the dough viscosity but reinforce the mechanical strength of the blended dough. According to the observations made in Section 9.3.1, the addition of hydrocolloids produces higher viscosity in both gluten-free doughs and wheat doughs mainly due to the formation of the viscous gel network at room temperature. Upon heat treatment, the hydrocolloids-enriched dough viscosity including peak viscosity, hot paste viscosity, cold

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paste viscosity, final viscosity, and breakdown viscosity also exhibited notable uptrend with increasing hydrocolloid level (Ahmed & Thomas, 2018). The viscosity increase in the starchhydrocolloid blend is mostly attributed to the interaction of the hydrocolloid with the leached amylose and low molecular weight amylopectin from the starch granule (Correa et al., 2013). In addition, the observed drop in the paste temperature may be linked with the increasing interaction between leached starch molecules and hydroxyl groups in hydrocolloid molecules that occurred before granule pasting (Ahmed & Thomas, 2018; Martı´nez et al., 2015). Accordingly, the impact of hydrocolloids on the dough-pasting properties may strongly affect the dough viscoelasticity and thus result in final products with fine structure.

9.3.4 Effects of DF Enrichment on Gluten Network It is generally recognized that the quality of wheat flour products is largely dependent on the proper formation of the gluten network, which can also be called gluten aggregation behavior. Gluten has a viscoelastic behavior in which the glutenin and gliadin fractions represent elastic and viscous behavior, respectively (Wieser, 2007). During kneading, peptide chains gradually stretch and unfold, promoting the breakage and reformation of some SdS and secondary bonds, and thus develop a network structure. Various technologies including Fourier transformed infrared spectroscopy, Raman spectroscopy, sodium dodecyl sulfate polyacrylamide gel electrophoresis, -SH content, as well as microscopy and imaging techniques have been employed to study the effects of DFs on gluten aggregation behavior (Nawrocka et al., 2017; Nawrocka, Mis, & Niewiadomski, 2017; Nawrocka, Mis, & Szyma nska-Chargot, 2016; Xiong et al., 2017). These studies specifically focused on the interactions between DFs and the gluten network and deepened our understanding of the effects of DFs on wheat doughs. To study the secondary structure of gluten, spectroscopic techniques are widely used. Chokeberry, cranberry, apple, carrot, cacao, oat, and flax fibers were added to the wheat gluten-wheat starch complex to examine the structural changes in gluten protein as a result of fiber fortification (Nawrocka, Mis, & Niewiadomski, 2017). The results confirmed that the addition of DFs caused aggregation of gluten proteins and led to a stronger and more complex network. The aggregates mainly consist of β-sheets or antiparallel-β-sheets formed by interactions between complexes of peptides or peptides and polysaccharides chains. The observed increase in the aggregated β-sheets content was in line with findings from another study (Nawrocka et al., 2015). Regarding the fiber-gluten mixture, the incorporation of DFs also resulted in aggregation or abnormal folding of gluten proteins (Nawrocka et al., 2016). The main changes involve the formation of β-like structures from the α-helices. Additionally, the comparison of the secondary structure changes in the gluten-fiber system and gluten-starch-fiber system also revealed the importance of starch in the flour. It was claimed that the starch molecules can protect the gluten protein against undesirable changes in its structure (Nawrocka et al., 2016). Indeed, it was observed that the incorporation of DFs is likely to produce more β-like structures, especially β-sheet configuration. In addition, many researchers also observed a downtrend of β-turn conformation (Bock & Damodaran, 2013). The β-turn conformation in the gluten dough might be related to the β-spiral domains in glutenin polypeptides (Wellner et al., 2005). The repetitive β-turn structure was reported

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to form a β-spiral structure, which can extend to 130% of its original length (Urry, Venkatachalam, Long, & Prasad, 1983). The β-spiral conformation represents an energetically favorable state that would be affected by external forces. Upon the removal of stress, the stable conformation would reform, resulting in an elastic recoil. Thus, the formation of the β-spiral structure may be one of the factors directly responsible for the changes of the dough springiness (Belton, 1999; Wellner et al., 2005). The greater the amount of this structural element in the dough, the greater the ability of the dough to trap gas bubbles and the greater the bread loaf volume would be (Bock & Damodaran, 2013). As was observed, the increase level of β-sheet structure at the cost of β-turn induced by DFs may adversely affect the dough elasticity due to the reduction in β-spiral structure. It is well established that the β-sheet conformation is formed through intermolecular hydrogen bonds. Other studies contend that the formation of intermolecular hydrogen bonds leads to a more rigid structure (Tatham, Miflin, & Shewry, 1985). The orderly assembled peptide chains induced by wheat bran dietary fiber are schematically illustrated in Fig. 9.1 (Han et al., 2019). The schematic description shows that flexible peptide chains turned into a stretched structure for the lack of β-turns and thus led to the formation of layered structure rather than agglomerated structure of fiber fortified gluten. Replacement of inelastic intermolecular β-sheets in the gluten network might decrease the viscoelasticity of the dough and result in quality deterioration of flour products. Despite the changes of the gluten secondary structure caused by the addition of fiber, there is another polysaccharide-gluten interaction model called “Loop and Train” that has been widely used (Belton, 1999; Sivam et al., 2013; Zhou et al., 2014). The “Loop and Train” model proposes that protein–protein interactions occur though H-bonding of glutamine residues in the β-spiral structures upon hydration. The “train” region is associated with β-sheets while the “loop” is associated with extended hydrated β-turns (Belton, 1999). When the water level increases, the system becomes plasticized allowing β-turns in adjacent β-spirals to form interchain β-sheets. Further hydration breaks some interchain hydrogen bonds between glutamine residues, leading to the formation of loops. Such a model is schematically shown in Fig. 9.2A and B (Sivam et al., 2013). The schematic shows the possible Loop and Train model for (A) the control bread and (B) bread with 3% of high methoxyl pectin and 3% of

FIG. 9.1 Schematic description of proposed hypothesis of gluten conformational changes induced by wheat bran dietary fiber (WBDF) (Han et al., 2019).

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FIG. 9.2 Schematic representation of possible Loop and Train models for (A) the control bread and (B) bread with 3% high methoxyl pectin and 3% blackcurrant polyphenol extract (Sivam et al., 2013).

blackcurrant polyphenol extract. As can be seen, in the control bread, the doughs get sufficient water and thus form the “loop” region where protein-water-protein interactions (β-turns with helices) occur, and the “train” region where protein-protein interactions (β-sheets) also occur. The hydrated “loop” region would increase at the expense of the “train” region in the β-sheet conformation as the hydration proceeds. Upon addition of the polyphenol compounds, the mobility of the hydrated segments, which is initially high, will be reduced. Moreover, there will be a competition among the protein, polyphenol, and starch for water. It is

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likely for the polyphenol or pectin compounds to increase the intermolecular contacts and binding sites for H bonding to form extended chains due to their interference with the initial bonding (Sivam et al., 2013). The replacement of wheat flour with diverse DFs was also found to increase the concentration of free -SH (Zhou et al., 2014). It is commonly accepted that the free -SH level is a reliable indicator of variation in SdS bonds (Wang et al., 2014) which contributes to a proper gluten network. The SdS content was reported to be positively related to the formation of a stable polymeric protein, as glutenin has more cysteine and can form both inter-/intramolecular disulfide linkages (Wieser, 2007). Therefore, the disulfide bonds play an important role in determining the structure and properties of the gluten network. The increase in -SH content induced by konjac glucomannan indicated the interference effect of konjac glucomannan on the protein tertiary structure (Wang et al., 2014). Results from SDS-PAGE analysis also suggested that konjac glucomannan induced a depolymerization effect as supported by the lower proportion of aggregates (>120 kDa). The incorporation of microcrystalline cellulose and carboxymethyl cellulose into the dough also resulted in lower band intensity for the high molecular mass species of high-molecular-weight glutenin subunits and aggregates (Correa et al., 2014). Therefore, the presence of some DFs can impede glutenin aggregation, thus producing a weaker gluten network due to the rupture of intermolecular cross-linking. The microscopical techniques for imaging the fiber-enriched doughs allow us to visualize the microstructural changes in the gluten network. Doughs with low methoxyl pectin exhibited a disaggregated gluten network (Correa et al., 2014). The coarse bran with large particle size was also found to promote an open and disaggregated gluten structure (Xiong et al., 2017). With the reduction of bran particles, the connectivity of the gluten network was increased. This can be attributed to the reduced steric hindrance action of bran particles and the enhanced polymerization behavior of gluten proteins. The ordinary light microscope observations allow selective staining of different chemical components including wheat starch, wheat gluten, and DFs (Roman-Gutierrez, Guilbert, & Cuq, 2002). Hemdane et al., studied bran-enriched doughs using ordinary light microscopy and contended that the bran particles make the gas cell walls more brittle and susceptible to rupture, or that they form a physical barrier around the gas cells, forcing them to expand in a particular dimension (Hemdane et al., 2018). It is possible that the bran particles align around the expanding gas cells during fermentation and result in a low gas retention capacity or a suppression of gas cell expansion.

9.4 PROBLEMS AND SOLUTIONS OF FIBER-ENRICHED FLOUR PRODUCTS DFs have been applied in flour products for few decades; however, to date, there has been low consumer acceptance of fiber-enriched grain products compared with fine flour products. Various studies have revealed that wheat bran-enriched foods with undesirable texture and taste mainly involving dark color, rough crumb texture, and small loaf volume were responsible for the limited consumption of whole grain products (Bakke & Vickers, 2007;

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Collar et al., 2007). Accordingly, numerous methods have been proposed to resolve the issues with unsatisfactory fiber-enriched grain products. Among these methods, the treatment and modification of DFs were mostly considered. Moreover, the improvement of the process and the selection of materials were also combined to further improve the popularity of fiber-fortified wheat products.

9.4.1 Dark Color The darker color of wheat products caused by the addition of DF has been frequently reported in the literature. For main foods like noodles, steamed buns and bread, the presence of undesirable color may get in the way of their popularity and promotion to the public. Due to the perniciousness of residual chlorine caused by hypochlorides, hydrogen peroxide is more frequently used in the food industry. It was also observed that treatment with alkaline peroxide resulted in better bleaching effect compared with sodium chlorite when bleaching apple DF (Renard et al., 1997). To avoid the excessive addition of peroxide and improve bleaching efficiency, chitosan was used in conjunction to absorb some transition metals, such as iron, copper, manganese, and inhibit the degradation of peroxide (Li et al., 2015). In addition, white-like DFs like inulin could yield brighter and whiter crust as well as crumb for steamed bread at low concentration (Luo et al., 2017). However, the presence of low molecular weight glucose and fructose in inulin that enhances Maillard reaction, which leads to significant browning effect, should not be neglected.

9.4.2 Rough Texture Numerous studies have revealed varying degrees of modification of bread texture upon DF incorporation. The texture of grain products is closely associated with their mouthfeel and thus their acceptance. As described above, the SDFs produced harder bread mainly due to their good water-binding capacity, while the IDFs produced harder bread mainly as a result of their hard texture and poor solubility. Hence, poorly soluble SDF may be developed to reduce ability to compete with the gluten network for water. As it has been reported, poorly soluble inulin produced softer crumb texture than highly soluble inulin species (Peressini & Sensidoni, 2009). Other than that, low levels of SDF still have advantages over IDF as they effectively assist in the production of fine texture. For this reason, special efforts have been made to soften the hard texture of IDFs and increase their solubility to help reduce their harmful effects on the dough texture. The commonly used techniques include mainly micronization, extrusion, and enzyme treatment. These methods are believed to modify the physicochemical property of IDFs and soften their texture. Among them, various micronization methods have been widely studied and applied for their great potential in processing functional food. Usually, ball milling is more efficient, but it takes considerably more time than jet milling (Chau, Wang, & Wen, 2007). Highpressure micronization treatment can pulverize a finer soybean IDF powder to 1.6 μm particle size using high-velocity impact, high-frequency vibration, instantaneous pressure drop, cavitation, ultra-high pressure, and intense shear within 5 s (Liu et al., 2009, 2016). Analysis by

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bright field microscopy and confocal laser scanning microscopy added to the growing evidence on the effectiveness of microfluidization in reducing the corn bran particle size (Wang et al., 2013). It was also observed that the original cell wall structure was almost completely disintegrated, and the dissociation of different bran tissues was more pronounced (Wang et al., 2013). Bulk density results revealed that the microfluidization process can dramatically alter the microstructure, thus leading to a significant increase in porosity and surface area of corn bran particles (Wang et al., 2013). Extrusion is a thermal processing technique that involves the application of high pressure, high temperature, and shear forces to cereal foods. This treatment is advantageous over others due to its low cost, high productivity, energy savings, and versatility (Faraj, Vasanthan, & Hoover, 2004; Kim, Tanhehco, & Ng, 2006). It was contended that the extrusion treatment could induce effective extraction of high-molecular weight soluble DF from oat bran (Zhang et al., 2009). Another study also observed higher SDF and β-glucans content in extruded barley flour (Honcu˚ et al., 2016). The extra SDF components may include the soluble part of arabinoxylans, hemicelluloses, fructans, etc. The increase in the SDF content after extrusion is in agreement with the results from Vasanthan et al. (2002), who reported the transformation of some IDF into SDF during extrusion and suggested that the formation of additional SDF was caused by transglycosidation (Vasanthan et al., 2002). Except for the frequently used extrusion processing, there is also a modified technology named blasting extrusion processing, which is a novel technique and have shown great potential in extracting SDFs from wheat bran and soybean residue (Chen et al., 2014; Yan, Ye, & Chen, 2015). After blasting extrusion, a significant increase in the SDF content of wheat bran from 9.82  0.16% (w/w, %) to 16.7 0.28 (w/w, %) was detected (Yan et al., 2015). Scanning electron microscope images also revealed that the surface of wheat bran particles upon blasting extrusion treatment is more irregular, coarse, and full of holes, indicating the looser texture of IDF. Enzymatic treatment has been shown to be effective in the quality improvement of various DFs by modifying the structure or redistributing the composition (Lebesi & Tzia, 2012; Santala et al., 2014). Besides, it has been reported that enzymatic hydrolysis of non-starch polysaccharides improved the rheological properties of fiber-enriched doughs (MartinezAnaya & Jimenez, 1997). The xylanase and cellulase enzymes were frequently used for bran modification to increase its crispiness and decrease its hardness (Martı´nez-Anaya & Jimenez, 1997). The use of xylanase increased the SDF content of oat bran, while reducing its water binding and holding capacity due to the lower molecular weight (Lebesi & Tzia, 2012). The moisture content of doughs directly influences the softness of the baked products. The incorporation of xylanase significantly increased the whole wheat bread moisture from 32.3% to 40.5%, suggesting that xylanase-fortified whole grain bread has a softer texture. The sensory evaluation further confirmed this finding by showing high texture score for whole wheat bread supplemented with xylanase (Shah, Shah, & Madamwar, 2006). For steamed breads, the xylanase, cellulase, and α-amylase increased their extensibility and stickiness. Furthermore, the combination of the three enzymes was more effective than each single enzyme, implying a synergetic effect of their combination on the dough rheology (Liu et al., 2017). Despite the effective transformation of IDF to SDF by enzymatic processing, this method is not cost-effective and is time consuming. Therefore, physical methods like high hydrostatic pressure treatment and extrusion have been combined to assist enzymatic treatment methods (Ma & Mu, 2016; Santala et al., 2014).

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Sourdough is obtained by spontaneous fermentation of a mixture of flour, water, liquids, and microbes, such as lactic acid bacteria and yeast in an active state. The use of sourdough has a long tradition and still plays an important role in bread making, mainly due to its ability to improve the quality and extend the shelf life of bread (Arendt, Ryan, & Dal Bello, 2007; Gocmen et al., 2007; Katina et al., 2006). The lactic acid bacteria produce a number of metabolites that have been shown to have a positive effect on the texture and staling of bread. Another study also attributed the impact of sourdough on wheat bread to the acidity-induced activation of proteolytic enzymes present in the wheat flour (Clarke, Schober, & Arendt, 2002). The acidity and proteases solubilize gluten, thus decreasing the firmness of dough (Clarke et al., 2002). To promote the acceptability of breads substituted with high levels of whole grain oat flour, the sourdough was added to produce new types of oat bread that meet the requirements of a health claim. At the most favorable sourdough condition, the crumb texture parameters and bread flavor were enhanced, indicating that the combination with sourdough represents a potential method to produce fiber-enriched wheat flour products (Flander et al., 2011). Researchers have been exploring DFs from different sources that are suitable for wheat flour products. However, with the increasing addition of DFs, a gradual significant quality deterioration of flour products was observed in many cases regardless of the fiber solubility, composition, and structure (Eshak, 2016; Fendri et al., 2016; Huang et al., 2016). Hence, the regulation of proper fiber addition is of utmost importance to produce fine flour products. On the other hand, the appropriate choice of DF substitution in wheat flour products does assist in meeting the daily DF demand of consumers without significantly lowering the final-product quality. Therefore, more efforts are needed to explore more suitable DFs. As shown above, fiber-fortified wheat doughs mainly required more water absorption as measured by the farinograph or Mixolab. Additionally, the gluten analysis also revealed the competition for water between DF and the gluten matrix, which may be responsible for the rough texture. As a result, proteins link only with the available water molecules, and only a fraction of the gluten is developed (Osorio, Gahona, & Alvarez, 2003). Such behavior directly led to the increase of the hardness as well as the decrease of springiness and cohesiveness (Hsieh et al., 2017). Findings by Hemdane et al. supported such conclusion by studying how the water binding capacity of bran affects bread quality (Hemdane et al., 2018). The moisture content and bran addition affect the amount of both the bound and monomeric water populations in gluten dough. Secondary structure profile of gluten induced by bran addition revealed the transformation from a β-spiral structure to a β-sheet structure (Bock & Damodaran, 2013). Such conformational change in gluten might be responsible for the poor quality of bran-fortified bread. However, the undesirable change was minimized as the water content increased, implicitly suggesting that the adverse effects of bran on bread quality could be overcome in this way (Bock & Damodaran, 2013). Jasim et al. (Ahmed & Thomas, 2015) also observed better extensibility in the β-glucan enriched doughs with more water addition. Therefore, to meet the moisture requirement, the mixing property was initially measured to obtain the absorption value. Afterwards, the fiber-enriched doughs were prepared according to the optimal water absorption. Moreover, to minimize the dilution of gluten protein by the addition of fibers and the detrimental influences on the grain products, the flour blend was supplemented with vital gluten for better end-product quality (Ma, Lee, & Baik, 2018).

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9.4.3 Small Volume From the observations made in Section 9.2, volume and gas cell distribution are key parameters for the fermented products like bread and steamed bread, which are adversely affected by addition of DFs. During the proofing and baking processes, the formation of gas cells with varying dimensions greatly influences the ultimate dough volume and thus the baked product quality as the increase in the dough height have been found to correlate well with the volume expansion of the dough (Ktenioudaki, Butler, & Gallagher, 2010). The under-fermented dough, in which the carbon dioxide is not properly distributed, results in a very dense loaf with thick cell walls and a tough crust (Upadhyay et al., 2012). Ozkoc et al. suggested that gums may influence the stability of gas bubbles by forming a thick layer on their surface and preventing the coalescence of individual gas cells. Thus, each bubble remains a separate, discrete structure leading to a “stable morphology” (Ozkoc, Sumnu, & Sahin, 2009). Bran particles were also suggested to impede gas cell expansion, restrict the dimension of gas cells, or to pierce gas cells due to their particular shape (Gan et al., 1989, 1992). Therefore, to obtain fiber-enriched products with ideal volume, efforts should be made to enhance the expansion of gas cells and the gas retention capacity. Bread quality largely depends on the wheat gluten quality, thus selecting wheat flour with suitable gluten content is of utmost importance to produce delicate bread products. The dough rheological properties play an important role in maintaining bubble stability so as to protect against premature rupture during baking, which makes moderately strong wheat flour more suitable for bread making than weak flour. For breads made with weak flour, the addition of both soluble and insoluble inulin results in a significant smaller bread volume and higher hardness (Peressini & Sensidoni, 2009). With the addition of inulin, the textural parameters of breads made from weak flour are more sensitive than breads with moderately strong flour. More gas cell coalescence occurred in dough made with weak flour during processing due to the low-strain hardening and poor gas cell stability of the weak flour (Dobraszczyk, 2004; Zghal, Scanlon, & Sapirstein, 2001). Since strong doughs can entrap more gas than weak doughs, they can be stretched up to a certain loaf volume (Sim, Noor Aziah, & Cheng, 2015). However, when the dough is too strong and rigid, the rising can be hindered (Goesaert et al., 2005). On the other side, a dough that is too elastic also produces undesirable products (Goesaert et al., 2005). Thus, flour with a suitable gluten content should be taken into consideration. Numerous studies have revealed that partial replacement of the wheat flour with barley products resulted in a deterioration of the bread quality, especially its volume (Blandino et al., 2015; Collar & Angioloni, 2014; Jacobs et al., 2008). The deterioration of the bread volume is a result of the weakening of the gluten network, which results in lower gas retention capacity (Collar & Angioloni, 2014). Adding sourdough to barley breads produced higher volume than those obtained with a direct method (Pejcz et al., 2017). The positive impact on the bread volume by addition of lactic acid-producing bacteria was previously reported (Tamani, Goh, & Brennan, 2013). Another study observed that a similar specific volume of sourdough-enriched oat breads compared with the ordinary breads, indicating the favorable influence of sourdough on the maintenance of the bread volume (Flander et al., 2011). It is well known that flour lipids significantly affect the bread quality. There is no interfacial adherence of the starch granules to the protein network at the beginning of the mixing

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process, despite that starch and gluten are the two major components of the wheat flour system (Koksel & Scanlon, 2012). Presumably, lipid functionality is associated with their effect on the stability of the gas cells. During heating, the lipid crystals melt and allow the bubbles to grow without rupture, thus giving the bread a large volume and a fine crumb structure (Autio & Laurikainen, 1997). It was reported that the ratio of nonpolar to polar lipids and the galactolipid content of the free non-starch lipid are strongly correlated with bread volume (Matsoukas & Morrison, n.d.; Gan et al., 1995). Some lipids like lecithin and glycolipids were shown to increase the loaf volume of bread (Pomeranz, Shogren, & Finney, 1969; van Nieuwenhuyzen & Szuhaj, 1998). A comparative study of the impact of phosphatidylcholine on doughs made from native wheat flour and delipidated flour suggested that phosphatidylcholine has the ability to increase the specific dough volume, and the existence of wheat flour lipid could strengthen such effect (Ukai & Urade, 2007). The incorporation of emulsifiers in dough was reported to have several benefits. First, they contribute to increase the dough strength. Second, they aid dough stability and gas retention, thus increasing loaf volume. Third, they improve crumb softness (Autio & Laurikainen, 1997). The mechanisms whereby emulsifiers improve dough quality have been attributed to their ability to bind to gluten (Inoue et al., 2009), as well as to form complexes with starch particles (Krog et al., 1989). Emulsifiers can bind the protein hydrophobic surface to produce more aggregates, and thus enhance the strength of protein filament (Kamel & Ponte, 1993). Hydrophilic emulsifiers may also form lamellar liquid-crystalline phases in water, which is associated with gliadin. Such structure contributes to dough elasticity and allows gas cells to expand, thus contributing to increase the volume of baked food (Tamstorf, Jonsson, & Krog, 1986). For whole wheat doughs, increasing level of sodium stearoyl lactylate effectively reduced their hardness (Niu et al., 2017). The rheological changes that occur during fermentation are mainly due to the carbon dioxide produced. Therefore, the presence of yeast is crucial for a better bread texture and volume. During proofing, the rate of gas production depends on the activity as well as the variety of baker’s yeast. Increasing yeast concentration resulted in smaller gas cell size from 23 to 17 μm (Upadhyay et al., 2012). This may be attributed to the increased production rate of CO2 and higher supersaturation that resulted in higher nucleation rate of gas cells. Such behavior led to lower mean bubble size (Upadhyay et al., 2012). The expansion profiles of wheat doughs fermented by different yeast levels revealed that the doughs containing low yeast concentration had markedly lower kinetic rate constants and hence longer fermentation time compared with dough fermented with higher yeast concentration (Birch, van den Berg, & Hansen, 2013). A short fermentation time achieved by higher yeast levels may be economically beneficial for the baker. Mareile et al. used different beer yeasts to make bread and found that, compared with the common baker’s yeast, Lager yeast s-23 and Ale yeast T-58 conferred bread with significantly larger specific volume, slice area, as well as number of gas cells (Heitmann, Zannini, & Arendt, 2015). Hence, for doughs fortified with DFs, the yeast species may be explored and applied, and the yeast concentration needs to be acceptably evaluated. Usually, the bubble height and limiting strain increase with water addition due to the plasticization of the dough. Additional water makes the dough soft and thus the deformation energy and maximum stress values decreased accordingly (Ahmed & Thomas, 2015). Rutuja et al. (Upadhyay et al., 2012) also observed decreased values of moduli and suggested that there was a reduction in the dough firmness and elasticity upon water addition. The reason

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for this is that adding water softens the dough and decreases the hydration time as well as the energy required for mixing (Farahnaky & Hill, 2007). Examination of the dough microstructure and bubble size distribution revealed increased bubble size with increasing moisture content, suggesting that water addition promotes the growth of gas cells (Upadhyay et al., 2012). Such phenomenon was attributed to the increase in the surface tension (Salt et al., 2006). Fiber-enriched breads were reported to have hard texture and small gas cells. Therefore, higher water concentration may be adopted to produce larger gas cells and thus larger bread volume.

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C H A P T E R

10

Applications in Meat Products Federica Balestra*, Maurizio Bianchi†, Massimiliano Petracci* *

Department of Agricultural and Food Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy †Prodotti Gianni srl, Milan, Italy

O U T L I N E 10.1 General Overview of World Meat Production 313 10.2 Role of Functional Ingredients in Meat Products

316

10.3 Functional Properties of Dietary Fibers

321

10.4 Main Dietary Fibers for Meat Processing 10.4.1 Classification

324 324

10.4.2 Sources

325

10.5 Main Applications in Meat Products 10.5.1 Minced Meat and Finely Comminuted Meat Products 10.5.2 Chicken Nuggets and Poultry Breaded Items 10.5.3 Marinated or Injected Meats References

329 338 339 339 340

10.1 GENERAL OVERVIEW OF WORLD MEAT PRODUCTION Demand for meat has been increasing during the last decades because of population growth, rising income, and urbanization. Poultry meat has shown the fastest growth over the last years (Smil, 2013, Fig. 10.1). In 2016, the total yearly production of meat has been estimated to be approximately 350 million tons, and dominant livestock types are poultry, bovine, pig, and sheep. The species produced is quite variable, based on the region with the United States (17.4% and 17.9%), Brazil (14.1% and 12.1%), and China (10.6% and 15.0%) leading the production of beef and poultry, respectively. China (45.8%) also leads in pork production (OECD/FAO, 2018). In addition, the production of all major meat types has been increasing in absolute terms as well as in relative terms. The share of global meat types has changed significantly over the last 40 years. In 1970, poultry meat accounted for only

Dietary Fiber: Properties, Recovery, and Applications https://doi.org/10.1016/B978-0-12-816495-2.00010-1

313

# 2019 Elsevier Inc. All rights reserved.

300

FIG. 10.1 250

Beef and buffalo meat

200

Pigmeat

150

100

50 10. APPLICATIONS IN MEAT PRODUCTS

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

Production (millions of tons)

314

350

Others

Poultry meat

0

Evolution of global meat production from 1970 to 2016. (Own authorship, data source: FAOSTAT.)

Year

315

10.1 GENERAL OVERVIEW OF WORLD MEAT PRODUCTION

kg/person/year 40 35 30

Poultry

25

Pork Sheep

20

Beef 15 10 5 0 2015–17

2027

FIG. 10.2

Annual growth in world consumption of meat 2015–2017 and 2027. (Own authorship, data source: OECD/ FAO (2018). OECD-FAO Agricultural Outlook, OECD Agriculture statistics (database), https://doi.org/10.1787/agr-outldata-en.)

15% of global meat production; by 2017, its share has approximately tripled to around 37%. In comparison, bovine meat’s share of total meat production has nearly halved, now accounting for around 22%. Pork share has remained more constant at approximately 35%–40%. The total meat production is projected to expand by slightly more than 48 million tons by 2027, reaching nearly 367 million tons with developing countries being projected to account for majority of the total increase (OECD/FAO, 2018). Poultry meat is the primary driver of the growth in total meat production in response to expanding global demand. As a more affordable animal protein compared to red meats, poultry meat has low production costs, and its lower product prices have contributed to making poultry the meat of choice both for producers and consumers in developing countries (Windhorst, 2017). In context of consumption, the global meat apparent consumption per capita is expected to stagnate at 35.4 kg by 2027. Within this, the consumption of poultry meat is expected to increase regardless of region or income level. Per capita consumption will grow, even in the developed world, but the growth rates will remain slightly higher in developing regions. Worldwide, poultry has grown rapidly and surpassed pork as the preferred animal protein in 2016. This should remain the case until 2027 and, of all the additional meat consumed over the next decade, poultry is expected to account for almost 45% (Fig. 10.2, OECD/FAO, 2018). In recent years, the meat industry in general is moving toward the introduction of even more attractive and convenient product formulations, especially for consumers having limited time for meal preparation (Font-i-Furnols and Guerrero, 2014; Leroy & Degreef, 2015). Indeed, the way in which the meat is marketed and consumed has been dramatically modified, and therefore, technologies have become part of the meat industry. Most of the present meat production is marketed in the form of ready-to-eat and ready-to-cook products (Barbut, 2015; Petracci, Soglia, & Leroy, 2018). Currently in the United States, almost half of poultry meat is marketed as further-processed products, and there has been a concomitant increase of out-of-home food consumption as proven by the increase of food-service market share (Table 10.1, US NCC, 2018).

316

10. APPLICATIONS IN MEAT PRODUCTS

TABLE 10.1 Evolution of Market Segments and Forms of Chicken Meat in the United States of America Market Segments

Market Forms

Year

Retail Grocery (%)

Food-Service (%)

Whole Carcass (%)

Cut-up Parts (%)

Further Processed (%)

1965





78

19

3

1975

75

25

61

32

7

1985

71

29

29

53

18

1995

58

42

10

53

36

2005

55

45

11

43

46

2015

55

45

11

40

49

(Data source: US NCC (2018). US National Chicken Council, (accessed 31.10.2018).)

10.2 ROLE OF FUNCTIONAL INGREDIENTS IN MEAT PRODUCTS Changes in consumer demand and growing market competition have prompted a need to improve the quality and image of meat. This is not only to prevent the loss of market share based on a negative perception of meats, but also to achieve a much-needed diversification in the activity sector through the development of products with health-benefits. Over the past few decades, the meat and poultry industries have been very active in introducing new meat products. The continuous success of marketing meat depends on the innovation and consistent production of high-quality products (Fletcher, 2004; Henchion, McCarthy, Resconi, & Troy, 2014; Jimenez-Colmenero & Delgado Pando, 2013). Consumers are looking for convenient meat products with new/exciting flavors, textures, etc. (Font-i-Furnols & Guerrero, 2014; Leroy & Degreef, 2015). Fiber-enriched meat products are an opportunity to improve “meat image” as well as to update the recommendations related to dietary fiber goals ( Jimenez-Colmenero & Delgado Pando, 2013). All these developments created a market for various innovative further-processed meat products. Based on the final destination of meat muscle and the degree of size reduction applied on the muscle, processed meat products could be grouped in four categories: (i) whole muscle products such as marinated/injected whole muscles, cut-ups, or carcass where the cyto-architectural design and geometric distribution of intra- and extracellular water are maintained intact; (ii) formed/restructured products manufactured by chunks or pieces of meat bonded together such as rolls and hams; (iii) ground products made of coarse-minced meat, such as burgers and sausages where meat fibrous structure is still detectable to some extent; (iv) emulsified products such as frankfurters that are made of finely comminuted meat slurry in which meat fiber structure is not intact (Fig. 10.3, Petracci et al., 2013). The functional properties of raw meats depend mainly on chemical composition, which vary according to the anatomical position of the muscle, genotype and age of animal, and feed composition, which have great impact on the quality of processed meat products (Barbut,

Formed/restructured

Coarse ground

Finely minced/emulsified

Intact muscle cells with water entrapped in cellular and extracellular spaces

Chunks or pieces of meat that are bonded or glued together

Ground meat with still recognizable meat fibrous structure

Meat batters are complex systems consisting of solubilized muscle proteins, muscle fibers, fragmented myofibrils, fat cells and droplets

Main goals to achieve with the addition of technofunctional ingredients • Brine retention during marination/injection • Increase cooking yield • Optimal texture

FIG. 10.3

• Binding among meat pieces • Brine retention during marination/injection • Increase cooking yield • Optimal texture

• Binding among meat pieces • Water retention during processing • Optimal texture

• Stabilize water/fat components in meat emulsion during processing • Optimal texture

Classification of meat products according to raw meat materials used in its manufacturing and different roles played by technofunctional ingredients. (Modified from Petracci, M., Bianchi, M., Mudalal, S., & Cavani, C. (2013). Functional ingredients for poultry meat products. Trends in Food Science & Technology, 33(1), 27–39.)

10.2 ROLE OF FUNCTIONAL INGREDIENTS IN MEAT PRODUCTS

Whole muscle

317

318

10. APPLICATIONS IN MEAT PRODUCTS

2015; Givens, Gibbs, Rymer, & Brown, 2011). The quality of raw meat can vary also due to preslaughter, post-mortem, and processing factors (Chauhan & England, 2018; Petracci, Bianchi, & Cavani, 2009; Petracci, Bianchi, & Cavani, 2010) along with increasing rates of meat defects or abnormalities, especially in pork as well as in broiler and turkey meat. These defects, like pale, soft, and exudative (PSE) meat, acid meat, muscle-growth abnormalities (i.e., white striping, wooden breast, and spaghetti meat), and destructuration that impairs waterbinding capacity, color and appearance of meat, are mainly due to the improvements used for growth rate and muscle yield (Matarneh, Eric, England, Scheffler, & Gerrard, 2017; Petracci, Mudalal, Soglia, & Cavani, 2015; Petracci, Soglia, & Berri, 2017). Integrated approaches can be employed to manage the aforementioned obstacles and challenges to alleviate their consequences on functional properties of processed meat products. The employment of functional ingredients to optimize the functional properties of processed meat can reduce the effect of natural quality variability in meat origin. Simultaneously, they can provide more flexibility for the processed meat producers to introduce a broad spectrum of products to meet consumer demands and to optimize costs formulation (Barbut, 2017; Petracci et al., 2013). In order to develop healthier foods, different strategies can be used to increase the presence of beneficial compounds and limit those with negative health implications in meat and meat products. These strategies may basically affect animal production (genetic and nutritional) and meat-processing strategies (reformulation). Through the changes affected in the ingredients (raw meat material and non-meat ingredients) used in the making of meat products, the reformulation process offers an excellent opportunity to remove, reduce, increase, add, and/ or replace different components, including those with health implications ( JimenezColmenero & Delgado Pando, 2013). Various types of non-meat ingredients and additives are used by meat processors to achieve different technological requirements and to meet consumer expectations (Table 10.2). Raw, partially or fully cooked, ready-to-eat, fermented, dried, injected, marinated, and dry-cured meat products are those that all derive characteristic properties from usage of non-meat ingredients. Further, most of the non-meat ingredients are used in processed meats, resulting in a wide variety of products. While water is a major component of lean meat, it is also commonly added to many processed meat products, and, as such, becomes a non-meat ingredient. Water plays an important functional role in processed meats, which is likely to be modified if other ingredients are changed (Sebranek, 2015). Non-meat ingredients include a variety of inorganic salts and organic compounds of vegetable, animal, and microbial origins playing different roles. These include meat protein functionality enhancers (i.e., sodium chloride, phosphates), fillers (i.e., starches and flours), binders and extenders (i.e., vegetable and animal proteins), gums (i.e., carrageenan), curing salts (i.e., nitrates/nitrites), sweeteners (i.e., dextrose, corn syrup solids), antioxidants (i.e., ascorbic acid, tocopherols), antimicrobials (i.e., lactates, acetates), flavor enhancers (i.e., hydrolyzed proteins, sodium glutamate), colorants (i.e., red cochineal), spices, and flavoring (Feiner, 2006a, 2006b; Keeton, 2001; Xiong, 2012). Plant and animal proteins, starches or modified starches, hydrocolloids and gums alone or coupled with other common cheap fillers (bread crumbs, potato flakes, cereal flours, texturized proteins, and protein-rich flours) are the most frequently used ingredients in the meat industry ( Jimenez-Colmenero & Delgado Pando, 2013). However, due to increasing marketing requests for more natural perceived formulations and nutrition-related claims, a new

10.2 ROLE OF FUNCTIONAL INGREDIENTS IN MEAT PRODUCTS

TABLE 10.2

319

Main Non-meat Ingredients Used in Meat and Poultry Processing

Non-meat Category

Examples

Functional salts (able to enhance meat protein functionality)

• • • •

Protein-rich extenders and binders/Gelling agents (substances of vegetable or animal origin with substantial high protein content that can serve for partial replacement of meat and/or improve binding, water, and fat holding capacity)

• Leguminous plant (pulse) flours, concentrates, and isolates (i.e., soy, pea) • Cereal proteins (i.e., wheat, barley, rice) • Oilseed proteins (i.e., sunflower, rapeseed) • Dairy proteins (i.e., sodium caseinate, whey proteins) • Meat proteins (i.e., gelatin, collagen rich derivates, blood plasma) • Egg proteins (i.e., albumen)

Fillers (substances of vegetable origin with substantial high carbohydrate content used to lower the amount of meat without restoring the protein content of the recipe)

• • • •

Cereal flours (i.e., wheat, corn, rye) Rusk and breadcrumbs Starches (i.e., wheat, rice, corn, potato, cassava) Cereal and pulses brans

Hydrocolloids (gums) (heterogeneous group of long chain polymers mostly of vegetable origin used as thickening and gelling agents)

• • • • • • •

Carrageenan Alginate Agar-agar Locust bean gum Guar gum Xantan gum Konjac gum

Vegetable fibers (soluble and insoluble indigestible parts of plants foods with multifunctional properties such as water bind ability and texture modulators)

• Cereal fibers (i.e., oat, wheat, rye) • Leguminous plant fibers (i.e., soy, pea) • Other vegetables fibers (i.e., carrot, potato, bamboo, sugar cane, psyllium, sugar beet, inulin, etc.) • Fruit fibers (i.e., citrus, apple)

Curing agents and accelerators

• Nitrates and nitrites • Ascorbate/erythorbate

Preservatives

• Organic acids (i.e., lactates, acetates, sorbates) • Nitrates and nitrites

Flavor enhancers

• • • • •

Sodium and potassium chloride Phosphates Citrates Carbonates

Monosodium glutamate (MSG) Inosinate + guanylate (I + G) Hydrolyzed vegetable proteins (HVP) Yeast extracts Flavors Continued

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TABLE 10.2 Main Non-meat Ingredients Used in Meat and Poultry Processing—cont’d Non-meat Category

Examples

Colorants and coloring foodstuff

• • • • •

Paprika extracts Red beet juice/betaine Turmeric Beta-carotene Cochineal extract

Sweeteners

• • • • •

Sucrose Lactose Dextrose Corn syrup Sorbitol

Antioxidants

• Ascorbic acid and sodium ascorbate • Butylated hydroxyl anisole (BHA) and butylated hydroxyl toluene (BHT) • Vitamin E and tocopherols rich extracts • Plant natural extracts (i.e., rosemary, mint, green tea, sage, lemon balm, etc.)

Herbs, spices and plant extracts (used for flavoring, and to exploit antioxidant and/or antimicrobial effect)

• Root and rhizomes (i.e., ginger, turmeric, horseradish) • Bulb (i.e., onion, garlic) • Fruit (i.e., chili peppers, bell peppers, paprika, caraway, pimento) • Leaves and herbs (i.e., sage, marjoram, rosemary, oregano, mint, thyme, basil) • Flowers (i.e., clove, saffron) • Bark (i.e., cinnamon, cassia) • Berry (i.e., black pepper, juniper) • Seeds (i.e., mustard, coriander, cardamom, nutmeg)

trend in food ingredients has also emerged. This new trend, which is often summarized under the umbrella of “clean label,” is defined as being free of “chemical” additives, displaying easy-to-understand ingredient lists and being produced by the use of traditional techniques with limited processing (Asioli et al., 2017; Cheung et al., 2016). In addition, the use of nonmeat ingredients in industrialized societies is also strongly affected by sustainability concerns (Balestra & Petracci, 2018). Sustainability concerns originated due to the growing awareness of environmental pollution caused especially by meat production and processing. These trends of health consciousness and sustainability push consumers to consider which ingredients are present in the food products (Asioli et al., 2017). The use of dietary fibers for their technological properties and health benefits opens up interesting possibilities in functional meat product development ( Jimenez-Colmenero & Delgado Pando, 2013; Talukder, 2015). Within this context, functional vegetable fibers offer significant texture and nutritional functionality (Ponnampalam et al., 2017). Modern consumers, increasingly

10.3 FUNCTIONAL PROPERTIES OF DIETARY FIBERS

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concerned with their wellness, prefer foods to be beyond tasty and attractive, but also safe and healthy. Meat products are known as valuable sources for essential amino acids, fats, certain vitamin and minerals, and some minor nutrients. Recently, healthier meat products have been answering consumer demands, including low fat, well balanced fatty acids composition, and € lower levels of both sodium chloride and nitrite in meat products worldwide (Ozbaş & Ardic¸, 2016). The nutritional profile of meat products could be further improved by the addition of potentially health-promoting ingredients. Dietary fiber as a functional ingredient can be incorporated with meat products to improve the health view of meat products (Kim & Paik, 2012; Ponnampalam et al., 2017; Talukder, 2015). Furthermore, there are not special sustainability issues concerning the use of food fibers in the meat sector because they are usually obtained by sources that also include by-products and renewable materials (Balestra & Petracci, 2018). The addition of dietary fibers in product formulation is useful to improve meat’s functional properties (Ahmad & Khalid, 2018). In particular, dietary fiber can be incorporated in processed meat products as binders, extenders, and fillers. They can significantly replace the unhealthy fat component from the products, increase acceptability by improving nutritional components, water-holding capacity, emulsion stability, texture, sensory characters, etc., of finished products. The addition of dietary fiber in the meat products can increase the cooking yield, contributing to economic gain as well (Ponnampalam et al., 2017; Talukder, 2015). In this context, the rest of the chapter deals with the main dietary fibers used in the meat industry to retain moisture and modify texture. We also examine their implications on product quality as well as their usage according to current market trends.

10.3 FUNCTIONAL PROPERTIES OF DIETARY FIBERS From a technological point of view, the use of vegetable fibers from different botanical origins to improve the quality of meat products is a promising trend. Supplementation of dietary fibers in meat products has acquired higher prestige. Due to perceived advantages, € dietary-fiber supplementation in foods is rising. (Ozbaş & Ardic¸, 2016). Fibers have multifunctional properties: (i) improves the water holding capacity and retain extra added water thus acting as a kind of extender (i.e., in meat batters for patties or sausages); (ii) improves binding and forming of comminuted meat products (i.e., burgers and breaded patties); (iii) improves the emulsion stability and fat retention of emulsified meats (i.e., frankfurters and bologna style products), as well is a powerful tool to modulate texture and sensory properties of finished product toward the desired profile (i.e., to add bite and knack to frankfurters or increase tenderness and juiciness of lean meat burgers). Moreover, some soluble fractions can be useful for the formulation of low-fat meat products because of their “fat mimetic” behavior. In recent decades, fiber manufacturers have offered new tailor-made products for processed meat applications and have promoted additional ways to nutritionally enrich processed meats ´ l(Bodner & Sieg, 2009; Ferna´ndez-Gines, Ferna´ndez-Lo´pez, Sayas-Barbera´, Sendra, & Perez-A varez, 2004; Ponnampalam et al., 2017; Toldra´ & Reig, 2011). In addition to the nutritive aspects

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of fat reduction or fiber enrichment, the second model is driven by economics. High water binding and significant water retention can help decrease cooking losses or purge in vacuum packages (Bodner & Sieg, 2009). Variable chemical composition and physical characteristics of dietary fiber are the major hindrance in defining dietary fiber. The variability in composition is also responsible for variability in physicochemical parameters of dietary fibers, such as viscosity, water-holding capacity, foaming capacity, solubility, fat-holding capacity, swelling, and fermentation capacity (Ahmad & Khalid, 2018). Some dietary fibers can be incorporated into meat products as noncaloric bulking agents because they are sourced from common agricultural by-products that are relatively cheap, and their incorporation in meat products may reduce overall production costs (e.g., cereal bran) (Han & Bertram, 2017; Jimenez-Colmenero & Delgado Pando, 2013). Along with health and nutritional benefits, dietary fiber has various functional properties that affect the quality and characteristics of food products (Kim & Paik, 2012). Dietary fibers provide technological functions such as water binding and water retention, thereby reducing cooking and drip loss during storage, minimizing production costs, and offsetting the undesired textural changes of formula alterations without affecting sensory properties of the final product (Han & Bertram, 2017; Ponnampalam et al., 2017). The following functional properties should be considered when various sources of dietary fiber are incorporated into meat products (Kim & Paik, 2012). Water-holding capacity is the ability of meat to hold fast onto its own or added water during processing. Good waterholding capacity is essential as it provides desirable characteristics to meat products (Petracci et al., 2013). Fiber is suitable for addition to meat products and has been widely used in raw and cooked meat products to increase the water-holding capacity (Mehta, Ahlawat, Sharma, & Dabur, 2015; Talukder, 2015). The hydration properties of dietary fibers are related to the chemical structure of the polysaccharide components and to other factors such as porosity, particle size, ionic form, pH, temperature, ionic strength, type of ions in solution, and stresses upon fibers. Depending on type and conditions of use, fibers can bind considerable amounts of water (Fig. 10.4, Jimenez-Colmenero & Delgado Pando, 2013). By hydrating a fiber, the water occupies the fiber pores and increases cooking yield, possibly reducing the caloric content of meat products. The length, particle size, and porosity of dietary fiber components may affect the water-holding capacity, and these can contribute to the mouthfeel of the final products (Kim & Paik, 2012). As well as their hydration properties, fibers possess the capacity to hold oil. The ability of fibers to bind water and fat has been used in the manufacture of processed meat products. These properties contribute to final cooking yield. In addition, a high water-holding capacity can control moisture migration and ice crystal formation. This increases the stability during the freezing/thawing process and can also contribute to the final quality of the product (appearance, texture, color, juiciness, and flavor) ( Jimenez-Colmenero & Delgado Pando, 2013; Kim & Paik, 2012). Both properties, in turn, also affect the possibility of fibers’ use as ingredients in meat products. For example, dietary fiber with high oil-holding capacity allows the stabilization of fat in emulsion-based products. The dietary fibers with high waterholding capacity can be used as functional ingredients to avoid syneresis and to modify the viscosity and texture of some formulated meats (Mehta et al., 2015). Moreover, dietary fibers have been used by the meat industry for their gelling properties. Many soluble fibers (e.g., carrageenans, pectins, konjac, and similar compounds) form gels. Their capacity to form a gel and the characteristics of that gel will depend on several factors, including concentration, temperature, presence of certain ions, and pH ( Jimenez-Colmenero

10.3 FUNCTIONAL PROPERTIES OF DIETARY FIBERS

323

FIG. 10.4

Example of water effect on the structure of citrus fiber, causing the fiber structures to expand. The different times indicate the time after the water was added. (Modified from Lundberg, B., Pan, X., White, A., Chau, H., & Hotchkiss, A. (2014). Rheology and composition of citrus fiber. Journal of Food Engineering, 125, 97–104.)

& Delgado Pando, 2013). Fiber’s gel-forming ability can contribute to the increased thickness or viscosity of products, thus stabilizing or modifying the physical structure of meat products and helping to minimize shrinkage and improve product density (Kim & Paik, 2012). Because of their ability to form highly viscous solutions, fibers have been used as thickeners in meat systems, with plant-derived gums being the most widely used ( Jimenez-Colmenero & Delgado Pando, 2013). As the molecular weight or chain length of the fiber increases, the

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viscosity of fiber in the solution increases (Kim & Paik, 2012). Fibers can help modify textural properties in meat processing, including restructured meats. Thermo-irreversible gels, which form sodium alginate in the presence of calcium ions, are used to bind comminuted or diced meat pieces and make restructured meat products ( Jimenez-Colmenero & Delgado Pando, 2013). Fat reduction in processed meats is another area where the functional properties of fibers can make important nutritional contributions (Bodner & Sieg, 2009). Fat reduction has generally been considered an important strategy to produce healthier products. This aspect is especially relevant to the meat industry since some meat products contain high proportions of fat, and fat from meats has often been assumed to be a risk factor in consumer health ( Jimenez-Colmenero & Delgado Pando, 2013). As fat is not just a simple caloric filler hidden in a protein matrix, a fat-replacement strategy for processed meats must hence address the diverse influence of fat on structure, texture, and mouthfeel. Fat reduction in meat products is usually based on two main criteria: the use of leaner raw meat materials and the reduction of fat density (dilution) by adding water at higher levels than traditional products and adding other ingredients with little or no caloric content. Using dietary fiber, alone or in combination, as a fat replacer not only reduces the fat content but also enhances the nutritional attributes of the product while also reducing caloric content by fat substitution (Han & Bertram, 2017; Ponnampalam et al., 2017). Since the addition of a single fiber cannot solve the problem, combinations of fibers and other ingredients with unique and complementary properties may be used in order to take advantage of synergistic effects, in terms of water binding, creaminess, and structure (Bodner & Sieg, 2009).

10.4 MAIN DIETARY FIBERS FOR MEAT PROCESSING 10.4.1 Classification A plethora of vegetable fibers are available in the market as single vegetable source (e.g., bamboo, wheat, pea, potato, citrus) as well as proprietary fibers blends developed to better perform in the final application by exploiting the synergies among different fiber fractions (i.e., insoluble and soluble). The functional properties of vegetable fibers are strongly influenced by the vegetable source (i.e., bamboo, pea, carrot), the botanical part used for extraction (i.e., husk/peel vs inner part), physical status (i.e., granule size/fiber length), and production technology (e.g., isolation of selected fractions, physical modification). Each commercial product has to some extent a special functional behavior, and therefore it is not easy to find different commercial products having the same fingerprint of functional properties. In some cases, they are also produced under patented technologies so that they are quite unique materials (Petracci et al., 2013). Citri-Fi® branded product by Fiberstar, Inc., an example of these innovative fibers, patented a unique technology to physically increase the citrus fibers functionality by expanding the natural structure of fibers and obtaining an innovative functional clean label as citrus fiber (also defined citrus flour or dried citrus pulp according to the country legislation) with increased capabilities to bind water and emulsify fats.

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10.4 MAIN DIETARY FIBERS FOR MEAT PROCESSING

The most common fibers available in the market include: • Insoluble purified cellulose fibers, mainly obtained from bamboo, wheat, oat, and sugar cane by extracting and purifying the cellulose parts and grinding this material at different particle sizes (i.e., from 30 to 200 μm). • Insoluble “not purified” cellulose fibers obtained with a simple grinding of pulse hulls (i.e., pea hulls) or cereal brans (i.e., oat, rice, wheat bran) grinded or finely micronized (i.e., to yield a very fine material with 10–20 μm particle size). • Insoluble fibers with a minor content of soluble fibers and residual native starch, obtained from pea (after removal of starch and proteins) and potato (obtained from the by-products of starch production and composed of both inner cell walls and external potato peel). • Citrus fibers (i.e., from lemon, orange, lime, mandarin, and tangerine) with different levels of residual soluble fibers (mainly pectin) according to the production technology and raw material used for their fabrication (i.e., juice cells, albedo, segment, or external peels). • Carrot fibers obtained as by-product of carrot juice production and composed of a mix of insoluble and soluble fractions. • Psyllium (Plantago ovata) husk, obtained by finely grinding (i.e., to 80–100 mesh) the psyllium seed husk in order to obtain a soluble fiber very rich in mucilage fractions. • Inulin and fructooligosaccharides (FOS) commercially extracted from chicory roots and agave to yield a family of different products with different technological behavior (i.e., from short chains and weak gelling behavior to longer chains and stronger gelling behavior used for fat replacement and mouthfeel improvement). • Other fibers derived from soy, beetroot, apple, and other vegetables.

10.4.2 Sources Various types of fibers have been studied singularly or in combination with other ingredients to formulate mainly minced meat products. These products include burgers and sausages, coarse ground/restructured products (i.e., restructured deli meats and roasts), marinated or injected parts, emulsified meat products like frankfurters and bologna style products as well as reduced-fat meat products (Table 10.3). TABLE 10.3

Main Applications of Vegetable Fibers Used in Meat and Poultry Processing

Type

Fiber Size

Main Applications

Typical Dosages

Insoluble fibers (i.e., bamboo, wheat, oat)

30–40 μm

Injected products

0.5%–2%

90–200 μm

Restructured, coarse/ground or emulsified products

0.5%–2%

Soluble fibers (i.e., inulin)

Not relevant (fully soluble)

All categories

up to 6% for fiber enrichment and fat mimetic

Intermediate fibers (i.e., pea, potato)

100–400 μm

Restructured, coarse/ground or emulsified products

0.5%–2%

Soluble rich citrus fibers (i.e., lemon, orange)

40–100 μm

Injected products (40 μm)

0.3%–0.5%

All granular size

Restructured, coarse/ground or emulsified products

0.3%–1.0%

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TABLE 10.4 Chemical Composition of Various Fibers Commonly Used in Processed Meats Dietary Fiber (%) Food Groups Cereals

Purified cellulose

Legumes

Fruit and vegetables

Type

Total

Insoluble

Soluble

Oat fiber (minimal extraction)

85

81