FERMENTATION OF XYLOGLUCAN BY INTESTINAL BACTERIA

Xyloglucan, a cell wall polysaccharide and part of the dietary fiber f raction of the diet, can be degraded by the intestinal microflora. Deg radation is not common among intestinal bacterial species. Of 138 stra ins (representing 75 species) only nine strains were able to degrade t he xyloglucan polymer. These strains, seven clostridia, one bifidobact erium and one bacteroides, all produced apparent extracellular enzymes , which degraded the glucan backbone. Gas production was detected in t he individual clostridia. The other two strains did not produce any ga s. Selective elimination of bacterial groups from faecal slurries indi cated that clostridia are the main group of intestinal bacteria respon sible for degradation of xyloglucan polymer. In addition to the polyme r-degrading strains, some other strains were able to degrade and ferme nt oligosaccharides produced from tamarind seed xyloglucan with a fung al endo-beta-glucanase. HPAEC analysis showed that the fungal oligosac charides were identical to the oligosaccharides produced by the polyme r-degrading species suggesting the presence of an endo-beta-glucanase in these bacteria. It is proposed that xyloglucan is degraded in vivo by endo-beta-glucanases produced mainly by clostridia, followed by fer mentation of the oligosaccharides by a larger group of bacteria. (C) 1 996 Academic Press.