Gastrointestinal or simulated in vitro digestion changes dietary fibre properties and their fermentation

This study evaluated the effect of digestion on the chemical and physicochemical characteristics of dietary fibre and on its behaviour during fermentation. Three dietary fibre sources (wheat bran, barley bran and beet fibre) were recovered from ileal cannulated pigs after in vivo digestion and prepared by in vitro enzymatic treatment simulating digestion. Raw substrates and fibre residues were analysed for their chemical and physicochemical properties as well as their potential fermentation by human colonic bacteria. In vitro and in vivo treatments led to insoluble residues, enriched in cell wall polysaccharides, with similar cell wall sugar composition and physicochemical properties. Degradations of cell wall polysaccharides with losses of sugar residues occurred mainly after in vivo digestion, especially for pectins from beet fibre and B-glucans from barley bran. Solubilisation of B-glucans removed highly fermentable substrates for further fermentation. For beet fibre, removal of pectins led to increased hydration properties and faster fermentation of cell-wall polysaccharides. Enzymatic treatment simulated correctly the passage of fibre through the digestive tract, modifying the cell-wall matrix and predisposing the fibre to further fermentation. (C) 1998 SCI.