Dietary Fibre Functionality in Food and Nutraceuticals

From Plant to Gut

Farah Hosseinian, B. Dave Oomah, Rocio Campos-Vega, Farah Hosseinian, B. Dave Oomah, Rocio Campos-Vega

• Publisher: Wiley-Blackwell
• Year: 2016
• Print ISBN: 9781119138051
• eBook ISBN: 9781119138082
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Increasing fiber consumption can address, and even reverse the progression of pre-diabetes and other associated non-communicable diseases. Understanding the link between plant dietary fiber and gut health is a small step in reducing the heavy economic burden of metabolic disease risks for public health. This book provides an overview of the occurence, significance and factors affecting dietary fiber in plant foods in order to critically evaluate them with particular emphasis on evidence for their beneficial health effects.

Chapter 1
Do the Physical Structure and Physicochemical Characteristics of Dietary Fibers Influence their Health Effects?

Anthony Fardet

INRA, JRU 1019, UNH, CRNH Auvergne, F-63000 Clermont-Ferrand & Clermont Université, Université d'Auvergne, Unité de Nutrition Humaine, BP 10448, F-63000, Clermont-Ferrand, France

Studies on humans, animals, and in vitro have clearly shown that the way dietary fiber is degraded and fermented throughout the digestive tract depends on both its physical and chemical structure (intrinsic properties such as crystallinity and particle size) and its interaction with the closed environment of the gut (i.e., physical–chemical properties such as porosity, water-holding capacity, and solubility) (Guillon and Champ, 2000). For example, cellulose, which has a compact structure, is only partially fermented whereas soluble pectin is fully fermented, due to its much greater porosity (Fardet et al., 1997; Salvador et al., 1993). Thus, a greater porosity enables enzymes to access their substrate and degrade it more efficiently. This illustrates the interaction between factors such as porosity, solubility, and water-holding capacity.

Although much is known about factors influencing the fermentation of dietary fiber, less is known about the influence of a change in fiber structure, either isolated or within a complex food matrix, on human health. For example, is an increase in the porosity of fibers in a food beneficial? What are the consequences of higher fiber porosity on the short-chain fatty acid (SCFA) profiles generated during fermentation in the colon? Increasing porosity probably increases the rate of fermentation within the colon, yielding a more rapid and massive surge of SCFAs. But does the way the SCFAs are released have any effect on human physiology and health? Do the exact location where SCFAs are released (transverse, ascending, or descending colon) influence human health? These questions are of great interest in terms of the important physiological roles of the main SCFAs: butyric (Blouin et al., 2011), propionic (Hosseini et al., 2011), and acetic (Kondo et al., 2009) acids.

Although today we cannot fully answer these questions, this review will attempt to discuss the physicochemical parameters of fiber that can be modified and their relationship with their effects on human physiology and/or health (e.g., glycemia, cholesterolemia, satiety, microbiota, and fecal bulking). In a recent publication, Monro notably reviewed and discussed the impact of polysaccharide-based structures on nutritional properties in the foregut, focusing on complex foods containing such fiber-based structures (Monro, 2014). This review is more focused on isolated fibers and their structural features; some of the best studied being crystallinity, particle size, solubility, porosity, water-holding capacity, and the ability to adsorb bile acids, complex minerals, and trace elements (Guillon and Champ, 2000).

1.1 Influence of the Chemical and Physical Structure on the Metabolic Effects of Fibers

The intrinsic properties of fibers, their chemical and physical structure, are fundamental to their biological actions. The chemical structure of a fiber greatly influences the rate and extent of its fermentation in the colon. Thus, pectins, hemicelluloses, cellulose, lignin, and resistant starch (all included in the definition of fiber) are not all fermented at the same speed and the same extent. Cellulose has a compact structure, whereas hemicellulose is much more porous and more accessible to bacterial enzymes. Hence, hemicelluloses are almost completely degraded in the colon, but cellulose is only partially fermented and is excreted in the feces. Lignins are almost undegraded in humans (Holloway et al., 1978; Slavin et al., 1981).

Interestingly, Eastwood et al. (1986) showed that there is no obvious correlation between the chemical composition, structure, molecular size, shape, and physical properties of a fiber and its physiological effects in humans. For example, wheat bran and gum tragacanth have very different chemical structures but they have similar physiological effects. However, these findings are only valid for the physiological properties tested: the weight of stool, serum cholesterol levels, and the excretion of hydrogen. From this study, other physiological parameters have been tested.

It is hardly surprising that the chemical structure of a fiber influences its physiological effects, as each type of fiber is a complex mixture of carbohydrates (including pentoses and hexoses). A review has focused on the relationships between the molecular structure of cereal fibers and their physiological effects in humans (Gemen et al., 2011). There appears to be a clear link between the chemical structure of a fiber and blood glucose and insulin responses and satiety. However, the authors emphasize that information on the molecular structure are rarely given in the literature and there are no obvious trends in the relationship between the molecular structures of fibers and their fermentation profiles in humans (Gemen et al., 2011).

1.1.1 Changing the Molecular Weight

Some of the results appear contradictory. Some studies have shown that reducing the molecular weight of a fiber, and hence its potential viscosity in vivo, has no significant effect on the glycemic response (Ellis et al., 1991; Gatenby et al., 1996). These authors concluded that low molecular weight guar gum can be used in bread instead of a high molecular weight guar gum that is more viscous but less palatable (Ellis et al., 1991). Another study showed that reducing the molecular weight of β-glucan in muffins tended to increase the blood glucose and insulin responses in humans (Tosh et al., 2008). Immerstrand et al. (2010) showed that β-glucans with different molecular weights all had the same effect on the plasma cholesterol of mice. However, Kim and White (2010) found that low molecular weight β-glucan from oats produced more volatile fatty acids that did the β-glucan with a higher (4.4 times) molecular weight after fermentation for 24 hours in vitro.

An exhaustive review of the literature on cereal fiber suggests that the molecular weight of the fiber must be above a certain value to significantly increase the viscosity of the digestive effluents and to have a significant effect on postprandial glycemic and insulinemic responses. The authors even suggest that the thresholds value should be above 100 kDa for β-glucans and above 20 kDa for arabinoxylans. However, although low molecular weight fibers are more rapidly fermented, just how the molecular characteristics of a fiber influence its fermentation profile remains unclear (Gemen et al., 2011). Nevertheless, viscosifying fibers with high molecular weights increase the viscosity of the digesta more than do lower molecular weights fibers that tend to be fermented faster (Gemen et al., 2011). It has been shown that the molecular weights of fungal β-glucans significantly influence the secretion of interleukin-8 (IL-8) by HT29 cells in vitro, with lower molecular weight β-glucans producing more secretion than those of high molecular weight (Rieder et al., 2011). Finally, the prebiotic effect of wheat arabinoxylans increases inversely with their molecular weight in the presence of human feces in vitro (Hughes et al., 2007).

The fermentation and prebiotic properties of arabinoses from arabinoxylo-oligosaccharides (AXOS) have also been tested with respect to the degree of polymerization and substitution. Low molecular weight AXOS (average MW <3) produced more acetic and butyric acid and also stimulated an increase in the concentrations of bifidobacteria, whereas the fermentation of higher molecular weight (average MW = 61) AXOS resulted in a lack of the branched volatile fatty acids that are considered to be markers of protein fermentation and had no effect on the production of acetic and butyric acids or on bifidobacteria (Van Craeyveld et al., 2008). The authors used an experimental design that varied both the molecular weight and degree of substitution of arabinose in AXOS and concluded that AXOS with an average molecular weight of 5 and a degree of substitution of 0.27 produces the best effects on intestinal health (Van Craeyveld et al., 2008).

1.1.2 Changing the Degree of Crystallinity

Changes in the crystalline structure of a fiber are best illustrated in cellulose, the most abundant fibrous compounds on Earth. Indeed, like starch, cellulose has a crystalline structure, and by modifying it, it is possible to alter its digestibility/fermentation. This was clearly demonstrated in rats fed celluloses having degrees of crystallinity from ...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• List of Contributors
• Preface
• Chapter 1: Do the Physical Structure and Physicochemical Characteristics of Dietary Fibers Influence their Health Effects?
• Chapter 2: Interaction of Phenolics and their Association with Dietary Fiber
• Chapter 3: Dietary Fiber-Enriched Functional Beverages in the Market
• Chapter 4: Dietary Fiber as Food Additive: Present and Future
• Chapter 5: Biological Effect of Antioxidant Fiber from Common Beans (Phaseolus vulgaris L.)
• Chapter 6: In Vivo and In Vitro Studies on Dietary Fiber and Gut Health
• Chapter 7: Dietary Fiber and Colon Cancer
• Chapter 8: The Role of Fibers and Bioactive Compounds in Gut Microbiota Composition and Health
• Chapter 9: Effect of Processing on the Bioactive Polysaccharides and Phenolic Compounds from Aloe vera (Aloe barbadensis Miller)
• Index
• End User License Agreement