Prebiotics: Development and Application - Hardcover

Hardcover

ISBN 10: 0470023139 ISBN 13: 9780470023136

Publisher: Wiley, 2006

Synopsis

The prebiotic concept works on the basis that many potentially health-promoting microorganisms are already present in humans. Prebiotics are non-digestible food ingredients that stimulate activity in targeted microorganisms, to improve the health of the individual. Prebiotics can be incorporated into many foodstuffs such as beverages, health and sports drinks, infant formulae, cereals, bread, savoury products and so forth, and are receiving much commercial interest.

Prebiotics: Development and Application is the first book to consolidate research in this emerging area of 'functional food' study. The book takes a broad view approach to prebiotics, from the conceptual stage, definition, production, evaluation of individual food products and their effect on microbial flora, and their potential relation to diseases.

The book starts with an introduction to the prebiotic concept and its development, proceeds to consider the synthesis and manufacture of prebiotics and testing for prebiotic effects, and will then consider different forms of prebiotics (e.g. fructans, galactans, lactulose etc). The book will then look at prebiotic intervention for improving human health (acute and chronic disorders) and animal health. The book closes by considering the sectors for prebiotic foods, development and commercialisation issues, and future developments.

About this title

About the Author

Bob Rastall, University of Reading, UK.

Glenn Gibson, University of Reading, UK.

From the Back Cover

Prebiotics: Development and Application is a one-volume account of the emerging area of prebiotics – non-digestible food ingredients that stimulate the growth and activity of beneficial bacteria in the colon. Prebiotics can be incorporated into many foodstuffs to improve the health of the individual and are receiving much commercial interest.

The book takes a broad view of prebiotics from the conceptual stage, definition, production, evaluation of individual food products and their effect on microbial flora, and their potential relation to diseases. Contents include:

• an introduction to the prebiotic concept and its development
• the synthesis and manufacture of prebiotics
• testing for prebiotic effects
• fructans, galactans, lactulose and other prebiotic forms
• prebiotic intervention for improving animal and human health
• sectors for prebiotic foods
• development and commercialisation issues
• future developments

Prebiotics: Development and Application is an essential guide to this emerging technology for researchers, students and practitioners of food science, biotechnology, nutrition, microbiology, dietary health and food processing.

From the Inside Flap

Prebiotics: Development and Application is a one-volume account of the emerging area of prebiotics – non-digestible food ingredients that stimulate the growth and activity of beneficial bacteria in the colon. Prebiotics can be incorporated into many foodstuffs to improve the health of the individual and are receiving much commercial interest.

The book takes a broad view of prebiotics from the conceptual stage, definition, production, evaluation of individual food products and their effect on microbial flora, and their potential relation to diseases. Contents include:

• an introduction to the prebiotic concept and its development
• the synthesis and manufacture of prebiotics
• testing for prebiotic effects
• fructans, galactans, lactulose and other prebiotic forms
• prebiotic intervention for improving animal and human health
• sectors for prebiotic foods
• development and commercialisation issues
• future developments

Prebiotics: Development and Application is an essential guide to this emerging technology for researchers, students and practitioners of food science, biotechnology, nutrition, microbiology, dietary health and food processing.

Excerpt. © Reprinted by permission. All rights reserved.

Prebiotics

Development and Application

John Wiley & Sons

Copyright © 2006 John Wiley & Sons, Ltd
All right reserved.
ISBN: 978-0-470-02313-6

Chapter One

Human Colonic Microbiology and the Role of Dietary Intervention: Introduction to Prebiotics

Claire L. Vernazza, Bodun A. Rabiu and Glenn R. Gibson

1.1 Acquisition and Development of the Human Gut Flora

The human embryo is virtually sterile, but at birth microbial colonisation of the gastrointestinal tract occurs, with the neonate receiving an inoculum from the birth canal (Fuller, 1991; Zetterström et al., 1994). The microbial pattern that ensues depends on the method of delivery (Beritzoglou, 1997; Salminen et al., 1998a) and hygiene precautions associated with parturition (Lundequist et al., 1985). In addition to characteristic vaginal flora such as lactobacilli, yeast, streptococci, staphylococci and Escherichia coli, the neonate is also likely to come into contact with faecal microorganisms and skin bacteria during birth (Fuller, 1991). Furthermore, inoculation from the general environment and other external contacts may also be significant, especially during Caesarean delivery (Beritzoglou, 1997; Gronlund et al., 1999). During the acquisition period, some bacteria transiently colonise the gut whilst others survive and grow to form the indigenous microflora. Consequently, the neonatal gut experiences a rapid succession of microfloral components in the first days to months of development, selected for, initially, by luminal redox potential (Eh) but more frequently reported as being due to the feeding regime that follows birth (Zetterstrom et al., 1994). Initial colonisers utilise any available oxygen, usually by 48 h, creating an environment sufficiently reduced to allow succession by obligate anaerobes, mainly those belonging to the bifidobacteria, bacteroides and clostridia groups. At this stage, it appears that feeding methods have a significant influence on the relative proportions of bacteria that establish in the infant gut. Historically, breast-fed infants are thought to have relatively higher proportions of bifidobacteria than formula-fed babies of the same age, who possess a more complex composition (Fuller, 1991). Such purported differences have been linked with a lower risk of gastrointestinal, respiratory and urinary tract infections in breast-fed infants (Kunz and Rudloff, 1993). However, as the nature of commercial feeds has altered in recent times, the bifidobacterial predominance seen during breast feeding is less definitive. Nevertheless, such observations demonstrate the ability of diet to influence the gut microbiota composition and the possibilities for influencing health as a result. This has formed the basis for dietary intervention procedures that are extremely popular today (see later).

By the end of weaning there is a drop in the frequency of bifidobacteria. With the introduction of solid foods and by about 2 years after birth, infants start to adopt microflora profiles in proportions that approximate to those seen in adults (Fuller, 1991). The populations then seem to be relatively stable (>99 % anaerobic), aside for perturbations by diet and habit, until advanced ages when a significant decline in bifidobacteria, plus increases in clostridia and enterobacteriaceae are reported (Mitsuoka, 1990).

1.2 The Human Gastrointestinal Tract and its Microflora

Microorganisms occur along the whole length of the human alimentary tract with population numbers and species distribution characteristic of particular regions of the gut (Macfarlane et al., 1997). After the mouth, colonisation is markedly influenced, in part by luminal pH, and by the progressively slower transit of food materials towards the colon. The movement of digesta through the stomach and small intestine is rapid (ca. 4–6 h), when compared with a typical colonic transit time of around 48–70 h for adults (Macfarlane and Gibson, 1994). This allows the establishment of a complex and relatively stable bacterial community in the large intestine (Table 1.1). The near neutral pH and the relatively low absorptive state of the colon further encourages extensive microbial colonisation and growth (Macfarlane et al., 1997; O'Sullivan, 1996).

The human large intestine consists of the caecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum (Macfarlane and Macfarlane, 1997) (Figure 1.1). Through the microflora, the colon is capable of complex hydrolyticdigestive functions (Cummings and Macfarlane, 1991). This involves the breakdown of dietary components, principally complex carbohydrates, but also some proteins, that are not hydrolysed nor absorbed in the upper digestive tract (Macfarlane et al., 1992). Carbohydrate availability subsequently diminishes as dietary residues pass from the proximal colon to the transverse and distal bowel.

For persons living on Western-style diets, the microbial biomass makes up over 50 % of colonic contents. There are more than 500 different culturable species of indigenous bacteria present in the adult large intestine comprising around 10¹² bacteria per gram dry weight (Moore et al., 1978; Simon and Gorbach, 1984). A summary of the principal bacterial groups present is shown in Table 1.2.

In very general terms, intestinal bacteria can be divided on the basis of whether they can exert health promoting, benign or potentially harmful activities in their host (Gibson and Roberfroid, 1995). The most obvious pathogens are strains of E. coli and clostridia. Pathogenic effects include diarrhoeal infections and putrefaction whereas beneficial aspects may be derived simply by improved the digestion/absorption of essential nutrients. This leads towards a consideration of factors that may influence the flora composition in a manner than can impact upon health.

The multiplicity of substrates is probably the single most important determinant for dynamics and stability of species existing in the large bowel (Gibson and Collins, 1999). Whilst these are mainly produced by dietary residues, there is appreciable contribution from host secretions like mucins. The colonic microflora derive substrates for growth from the diet (e.g. nondigestible oligosaccharides, dietary fibre, undigested protein reaching the colon) and from endogenous sources such as mucin, the main glycoprotein constituent of the mucus which lines the walls of the gastrointestinal tract (Rowland and Wise, 1985). The vast majority of bacteria in the colon are strict anaerobes and thus derive energy from fermentation (Macfarlane and McBain, 1999). The two main fermentative substrates of dietary origin are nondigestible carbohydrates (e.g. resistant starch, nonstarch polysaccharides and fibres of plant origin and nondigestible oligosaccharides) and protein which escapes digestion in the small intestine. Of these, carbohydrate fermentation is more energetically favourable, leading to a gradient of substrate utilisation spatially through the colon (Macfarlane et al., 1992). The proximal colon is a saccharolytic environment with the majority of carbohydrate entering the colon being fermented in this region. As digesta moves through towards the distal colon, carbohydrate availability decreases and protein and amino acids become a more dominant metabolic energy source for bacteria in the distal colon (Macfarlane et al., 1992). Overall however, the principal substrates for bacterial growth are dietary carbohydrates. It has been estimated that about 10 to 60 g per day of dietary carbohydrate reaches the colon (Englyst and Cummings, 1986, 1987). A large proportion of this carbohydrate is made up of resistant starch (i.e. starch recalcitrant to the activities of human amylases). Resistant starch is readily fermented by a wide range of colonic bacterial species including members of the Bacteroides spp., Eubacterium spp. and the bifidobacteria (Englyst and Macfarlane, 1986). The remainder of the carbohydrate entering the colon is comprised of nonstarch polysaccharides (about 81–8 g per day), unabsorbed sugars, e.g. raffinose, stachyose and lactose (about 2–10 g per day) and oligosaccharides such as fructooligosaccharides, xylooligosaccharides, galactooligosaccharides (about 2–8 g per day) (Bingham et al., 1990; Gibson et al., 1990; Cummings and Macfarlane, 1991). The degree to which these carbohydrates are broken down by the gut microflora varies greatly. Unabsorbed sugars entering the colon are readily fermented and persist for only a short time in the proximal colon (Hudson and Marsh, 1995). Some sugars such as raffinose may have a more selective fermentation (being mainly assimilated by bifidobacteria and lactobacilli) while others support the growth of a range of colonic bacteria. Similarly, nondigestible oligosaccharides reaching the colon display different degrees of fermentation. Certain oligosaccharides such as fructooligosaccharides, galactooligosaccharides and lactulose may be fermented preferentially by bifidobacteria, which has given rise to the concept of prebiotics (discussed later) (Gibson and Roberfroid, 1995). Nonstarch polysaccharides include pectin, arabinogalactan, inulin, guar gum and hemicellulose, which are readily fermented by the colonic microflora, and lignin and cellulose, which are much less fermentable (Lewis et al., 2001). Endogenous carbohydrates, chiefly from mucin and condroitin sulphate, contribute about 23 g per day of fermentable substrate (Quigley and Kelly, 1995). The main saccharolytic species in the colonic microflora belong to the genera Bacteroides, Bifidobacterium, Ruminococcus, Eubacterium, Lactobacillus and Clostridium (Gibson, 1998). Protein and amino acids are also available for bacterial fermentation in the colon. Approximately 25 g of protein enters the colon daily (Macfarlane and Macfarlane, 1997). Other sources of protein in the colon include bacterial secretions, sloughed epithelial cells, bacterial lysis products and mucins. The main proteolytic species belong to the bacteroides and clostridia groups.

Carbohydrates in the colon are fermented to short chain fatty acids (SCFA), principally, acetate, propionate and butyrate (Cummings, 1981, 1995) and a number of other metabolites such as the electron sink products lactate, pyruvate, ethanol, succinate as well as the gases H₂, CO₂, CH₄ and H₂S (Levitt et al., 1995). SCFA are rapidly absorbed by the colonic mucosa and contribute towards energy requirements of the host (Cummings, 1981; Englehardt et al., 1991). Acetate is mainly metabolised in human muscle, kidney, heart and brain, while propionate is cleared by the liver, and is a possible gluceogenic precursor which suppresses cholesterol synthesis. Butyrate, on the other hand, is metabolised by the colonic epithelium where it serves as a regulator of cell growth and differentiation (Cummings, 1995). Protein reaching the colon is fermented to branched chain fatty acids such as isobutyrate, isovalerate and a range of nitrogenous compounds. Unlike carbohydrate fermentation, some of these end products may be toxic to the host, e.g. ammonia, amines and phenolic compounds (Macfarlane and Macfarlane, 1995). Excessive protein fermentation, especially in the distal colon, has therefore been linked with disease states such as colon cancer, which generally starts in this region of the colon before progressing proximally along the colon. Examples include bowel cancer and ulcerative colitis.

1.2.1 Influence of Diet on Microflora Activity and Health

Metchnikoff (1907) hypothesised that the onset of senility and shortening of life span resulted from putrefaction in the large bowel. In his opinion, the consumption of soured (fermented) milks was a progenitor for improved gastrointestinal health and the prolongation of life in Bulgarian populations. It is now known that bacterial activity in the human colon is involved in a number of disease states. The large intestine can harbour pathogens that are either part of the resident flora or exist as transient members (Gibson et al., 1997). Attachment and overgrowth of the pathogens generally results in acute diarrhoeal infections, however more chronic forms of intestinal disease also occur (Gibson et al., 1997; Gionchetti et al., 2000). These include inflammatory bowel diseases (ulcerative colitis and Crohn's disease) (Chadwick and Anderson, 1995), colon cancer (Rowland, 1988; Rumney et al., 1993) and pseudomembranous colitis (Duerden et al., 1995). To varying extents, each has been linked into microflora composition and activities, and thereby diet as this provides the major source for their growth. The concept of probiotics was developed to influence the gut microbiota in a beneficial manner.

1.3 Probiotics

The word probiotic comes from the Greek 'for life' and is defined as 'a live microbial food supplement that is beneficial to host health' (Fuller, 1989). The definition of probiotics has evolved over the years, but the consensus designates probiotics as 'nonpathogenic, live microbial, mono- or mixed-culture preparations, which, when applied to humans or animals in high enough doses, beneficially affect the host by improving the intestinal microbial balance and its properties' (Fuller, 1989; Havenaar et al., 1992; Havenaar and Huis in't Veld, 1992; Salminen et al., 1998a). Accepted characteristics for probiotics are listed in Table 1.3. Hitherto, evaluating their ability to compete effectively with resident and established microorganisms for available nutrients in a multi-substrate gut environment, is one attribute not thoroughly investigated in the selection and implementation of probiotics. Their survivability may be enhanced greatly in the presence of prebiotic carbohydrates proven to select for useful species of Bifidobacterium and Lactobacillus (Kailasapathy and Chin, 2000). Such a mixture may improve therapeutic potential in the gastrointestinal tract, and are defined as synbiotics (see later).

(Continues...)

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Edition details

• Publisher: Wiley
• Publication date: 2006
• Language: English
• ISBN 10: 0470023139
• ISBN 13: 9780470023136
• Binding: Hardcover
• Edition number: 1
• Number of pages: 264
• Editor: Rastall Bob, Gibson Glenn