Polysaccharide breakdown by mixed populations of human faecal bacteria

Abstract

Measurements of polysaccharide‐degrading activity in different fractions of human faeces showed that bacterial polysaccharidases and glycosidases were primarily associated with the washed bacterial fractions. Amylase, pectinase and xylanase were the major polysaccharide‐hydrolysing enzymes detected, whilst α‐L‐arabinofuranosidase, β‐D‐xylosidase, β‐D‐galactosidase and β‐D‐glucosidase were the most active glycosidases. Starch and 3 non‐starch polysaccharides (NSP; pectin, xylan and arabinogalactan) were fermented by mixed populations of human faecal bacteria in batch culture. Detailed carbohydrate analysis demonstrated that starch and pectin were the most rapidly degraded substrates and that arabinogalactan and the relatively insoluble polysaccharide xylan were broken down more slowly. Free sugars and oligosaccharides did not accumulate in culture media with any polysaccharide tested. Time‐course measurements of polysaccharide remaining in the batch culture fermentations showed that the arabinose side chains of pectin, xylan and arabinogalactan were co‐utilised with the backbone sugars. In these cultures, polysaccharide‐degrading activity was mainly cell‐associated, but extracellular polysaccharidase activity increased as the fermentations progressed. Molar ratios of acetate, propionate and butyrate produced in these experiments were dependent upon the polysaccharide substrate tested. Molar ratios of acetate, propionate and butyrate in the starch, arabinogalactan, xylan and pectin fermentations were 50:22:29, 50:42:8, 82:15:3, and 84:14:2, respectively. The presence of starch did not inhibit the breakdown of arabinogalactan, xylan or pectin by faecal bacterial, providing evidence that multicomponent substrate utilisation occurs when complex populations of faecal bacteria are provided with mixed polysaccharide substrates.

Effects of Dietary Arabinogalactan on Gastrointestinal and Blood Parameters in Healthy Human Subjects

“…Vince and colleagues [11] also did not find increases in fecal short-chain fatty acid production following arabinogalactan consumption. However, their work as well as the work of Englyst and colleagues [12] did report increases in SCFA production following arabinogalactan supplementation of fecal incubates.…”

“…In addition, arabinogalactan is fermented at a slower rate than other carbohydrates due to its branched structure [12]. Fermentation is evidenced by the ability of human intestinal microflora to degrade arabinogalactan and produce short-chain fatty acids [13,14].…”

The ciliate, Troglodytella abrassarti, contributes to polysaccharide hydrolytic activities in the chimpanzee colon

“…We suspect that the fecal bacterial fractions we obtained might contain a low number of bacteria coming from solid-associated bacterial population, which has dominant role in the fiber digestion of herbivorous mammals. Alternatively, the washing procedure during preparation of bacterial fraction might be responsible for removal of the extracellular CM-cellulase activity (Englyst et al 1987). On the contrary, total fecal specific CM-cellulase activity was similar to respective specific activity of rumen solid-associated bacteria (Martin et al 2001).…”

In vitro availability of starch in heat‐treated potatoes as related to genotype, weight and storage time

“…15 It has been suggested that RS promotes higher colonic levels of butyric acid than other sources of indigestible carbohydrates. 16,17 Furthermore, RS from different sources seems to vary in the proportion of SCFA formed. In rat models, fermentation of potato starch has produced comparatively high amounts of butyric acid.…”