Dietary-fiber-degrading enzymes from a human intestinal Clostridium and their application to oligosaccharide production from nonstarchy polysaccharides using immobilized cells.

Abstract

The secretion of nonstarchy polysaccharide-degrading enzymes from an anaerobic human intestinal bacterium, Clostridium butyricum- beijerinckii (isolated from human feces), was investigated. Growth of the bacterium was found when laminarin, konjac glucomannan, and pectic acid were added separately to the culture media as sole carbon source. The corresponding degrading enzymes for these dietary fibers, laminarinase (endo-1,3- beta-glucanase), endo-1,4-beta-mannanase, endo- and exo-pectate lyases, and pectin methylesterase, were then purified and characterized. These extracelluar enzymes, which were secreted by the bacterium in the human large intestine, were considered to contribute to digestion of the ingested dietary fibers to their oligosaccharides, following by short-chain fatty acid fermentation by the bacterium. We have developed cell immobilization techniques of the bacterium on cellulose-foam carriers that are effective for continuous production of the oligosaccharides from the dietary fibers in a fed-batch reactor system. From 9 g of pectic acid, a total of 3.96 g of 4,5-unsaturated digalacturonic acid was produced over 40 h in four 500-ml batchcultures. In the same manner, the corresponding oligosaccharides were obtained from konjac glucomannan and laminarin with average conversion rates of around 30-40%.