This paper results from the final phase of the ENDO project (DGXII AIRII-CT94-1095), a European Commission-funded project on non-digestible oligosaccharides (NDO). All participants in the programme met to perform a consensus exercise on the possible functional food properties of NDO. Topics studied during the project (including a workshop on probiotics and prebiotics) and related aspects, for which considerable evidence has been generated recently, were evaluated on the basis of existing published scientific evidence. There was a general consensus that: (1) there is strong evidence for a prebiotic effect of NDO in human subjects. A prebiotic effect was defined as a food-induced increase in numbers and/or activity predominantly of bifidobacteria and lactic acid bacteria in the human large intestine; (2) there is strong evidence for the impact that NDO have on bowel habit; (3) there is promising evidence that consumption of inulin-type fructans may result in increased Ca absorption in man; (4) there are preliminary indications that inulin-type fructans interact with the functioning of lipid metabolism; (5) there is preliminary evidence in experimental animals of a preventive effect against colon cancer. Human nutrition studies are needed to substantiate these findings. It was concluded that the nutritional properties of NDO may prove to be a key issue in nutritional research in the future. Functional foods: Non-digestible oligosaccharides: PrebioticsDietary carbohydrates represent a complex group of food components which, besides their usefulness for food technologists, have a variety of physiological and nutritional properties in man. According to the scientists who participated in the discussion, it has become clear over the last decade that the group of non-digestible oligosaccharides (NDO) play, or are likely to play, an important nutritional role (Cummings et al. 1997). As is shown in Table 1, NDO are composed of a variety of monosaccharides that are linked in several ways (type of bond and chain length) and typically are composed of a polydisperse set of comparable molecules differing only in chain length. The available NDO preparations are either (1) extracted from natural sources (e.g. inulin, soyabean oligosaccharides) followed by partial enzymic hydrolysis (e.g. xylo-oligosaccharides, oligofructose, malto-oligosaccharides), or (2) synthesized by subjecting disaccharides such as lactose or sucrose to the action of transferases (e.g. transgalacto-oligosaccharides).NDO such as the fructans and oligosaccharides from beans have always been present naturally in human plant foods, although total daily intakes are largely unknown. In populations consuming a Western-style diet, the intake of inulin-type fructans has been estimated to range between 1 and 4 g/d (Van Loo et al. 1995).Although differing in their chemical characteristics, all the NDO resist digestion in the human small intestine and they are potential substrates for the bacteria that colonize the large intestine.Here, we report the consensus reached b...

The composition and metabolic activities of the human colonic microbiota are modulated by a number of external factors, including diet and antibiotic therapy. Changes in the structure and metabolism of the gut microbiota may have long-term consequences for host health. The large intestine harbors a complex microbial ecosystem comprising several hundreds of different bacterial species, which complicates investigations on intestinal physiology and ecology. To facilitate such studies, a highly simplified microbiota consisting of 14 anaerobic and facultatively anaerobic organisms (Bacteroides thetaiotaomicron, Bacteroides vulgatus, Bifidobacterium longum, Bifidobacterium infantis, Bifidobacterium pseudolongum, Bifidobacterium adolescentis, Clostridium butyricum, C. perfringens, C. bifermentans, C. innocuum, Escherichia coli, Enterococcus faecalis, Enterococcus faecium, Lactobacillus acidophilus) was used in this investigation. Ampicillin [9.2 g (ml culture) ؊1 ] was added to two chemostats operated at different dilution rates (D; 0.10 h ؊1 and 0.21 h ؊1 ), and metronidazole [76.9 g (ml culture) ؊1 ] was added to a third vessel (D ‫؍‬ 0.21 h ؊1 ). Perturbations in bacterial physiology and metabolism were sampled over a 48-h period. Lactobacillus acidophilus and C. bifermentans populations did not establish in the fermentors under the imposed growth conditions. Ampicillin resulted in substantial reductions in bacteroides and C. perfringens populations at both dilution rates. Metronidazole strongly affected bacteroides communities but had no effect on bifidobacterial communities. The bacteriostatic effect of ampicillin on bifidobacterial species was growth rate dependent. Several metabolic activities were affected by antibiotic addition, including fermentation product formation and enzyme synthesis. The growth of antibiotic-resistant bifidobacteria in the large bowel may enable them to occupy ecological niches left vacant after antibiotic administration, preventing colonization by pathogenic species.

Human faecal microorganisms were grown on mixtures of chemically diverse polymerised C‐sources (starch, pectin, xylan, mucin, arabinogalactan, inulin, guar gum) in a three‐stage continuous culture model of the colon. The effects of retention time (R= 27.1 h, R= 66.7 h) on bacterial populations, their expression of hydrolytic enzymes involved in substrate depolymerisation, carbohydrate utilisation and short chain fatty acid formation were investigated. Eleven bacterial marker groups were studied in the fermenters. Strictly anaerobic bacteria predominated including bacteroides, bifidobacteria, clostridia and anaerobic Gram‐positive cocci. Changing system retention time from 27.1 to 66.7 h did not significantly affect the predominant bacterial populations in V1, however, enterobacterial cell numbers increased in V3, while saccharolytic anaerobe recoveries declined markedly, reflecting their greater dependence on polymerised carbon sources in the fermentation system. The majority of polysaccharide degrading activity in the colon model was cell‐associated, under all culture conditions. Increasing R from 27.1 to 66.7 h did not substantially change overall polysaccharidase (amylase, polygalacturonanase, xylanase, arabinogalactanase, galactomannanase) profiles, however, synthesis of some glycosidases was enhanced (e.g. α‐glucosidase, N‐acetyl‐β‐glucosaminidase, neuraminidase), whereas reduced expression of other enzymes such as β‐galactosidase, N‐acetyl‐α‐galactosaminidase, α‐fucosidase and α‐arabinofuranosidase occurred. These observations demonstrate that catabolite regulation is an important control process in the colonic microbiota, with respect to the induction and repression of enzyme synthesis, and that substrate availability plays a major role in regulating bacterial metabolism. Measurements of carbohydrate utilisation demonstrated that while all polysaccharides in the feed medium were digested extensively by bacteria growing in the fermentation system, specific rates of carbohydrate utilisation were maximal at R= 27.1 h. These data also provided evidence of bacterial substrate preferences in the colon model, particularly in relation to xylan and inulin digestion, demonstrating that catabolite regulatory mechanisms were also involved in controlling the assimilation of carbohydrate in the microbiota. Short chain fatty acid measurements showed that fermentation was more efficient at R= 27.1 h compared to R= 66.7 h, with putative conversion of carbohydrate to short chain fatty acids being approximately 60% and 40%, respectively. This was probably due to increased maintenance energy requirements at low bacterial growth rates. Differences were also observed with respect to short chain fatty acid molar ratios, with more propionate, branched chain and longer chain fatty acid production at R= 66.7 h, demonstrating the increasing importance of amino acid fermentation under these culture conditions.

), Bact. thetaiotaomicron and Bact. vulgatus, with lesser numbers of facultative anaerobes, Cl. perfringens and Bif. longum. Wall growth was associated with a reduction in planktonic cell mass and increased acid production by the cultures. Chemotaxonomic study of chemostat microbiotas, on the basis of cellular fatty acid methyl ester (FAME) analyses, showed the existence of characteristic bacteroides (C 15 ) and bifidobacterial (C 18 ) markers, but desulfovibrio markers (i-C 15:0 , C 16:0 , i-C 17:1 ) could not be identified. The metabolic activities of saccharolytic organisms were altered in the SRB chemostat, including synthesis of a number of hydrolytic enzymes involved in carbohydrate breakdown, such as a-galactosidase, a-glucosidase and b-galactosidase, together with several mucinolytic enzymes. High concentrations of sulphide (8·2 mmol l −1 ) were detected in the SRB chemostat, suggesting that this metabolite may have been inhibitory to some species. Saccharolytic organisms growing in the SRB fermenter utilized more starch, but less galactose-containing polymers, which correlated with the observed glycosidase activities. Profound differences were also recorded with respect to fermentation product formation in the chemostats, where a major switch to acetate production occurred in the SRB culture, with concomitant reductions in propionate, butyrate and lactate, which is an important electron donor for desulfovibrios.