The effect of carbohydrate supplementation on microbial fibre digestion was
studied in vitro, by measuring the disappearance of cell
wall monosaccharides, bacterial adhesion (mmol purine bases per g residue),
and total (per g residue) and bacterial (per mmol purine bases)
polysaccharidase activity. Straw cell walls (CW, 0.5% w/v) were
cultured in medium supplemented with (0.275% w/v) or without
starch, a sugar mixture, or pectin. Supplementation with these constituents
did not cause a drop in pH below 6.1, and increased all parameters
investigated with the exception of bacterial polysaccharidase activity, which
was higher for CW cultures, suggesting a higher proportion of fibrolytic
bacteria in the adherent population. By comparison with starch and sugar,
pectin supplementation resulted in a lower proportion of residual sugars
remaining from cell walls after 60 and 72 h (P < 0.05), which resulted in
greater bacterial adhesion after 8 and 12 h (P < 0.05) and higher total
cellulase activity after 8 h (P < 0.01). This was perhaps because pectin
may cover particle surfaces, protecting the digestive area from external
factors, or may act as a substrate for cellulolytic bacteria. The lack of
differences in bacterial enzymatic activities suggests the absence of
qualitative or quantitative differences in the adherent fibrolytic population.
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