Fermentation by gut microbiota cultured in a simulator of the human intestinal microbial ecosystem is improved by supplementing a soygerm powder

An in vitro model, designated the Simulator of the Human Intestinal Microbi al Ecosystem (SHIME), was used to study the effect of a soygerm powder rich in beta-glycosidic phytoestrogenic isoflavones on the fermentation pattern of the colon microbiota and to determine to what extent the latter metabol ize the conjugated phytoestrogens. Initially, an inoculum prepared from hum an feces was introduced into the reactor vessels and stabilized over 3 wk u sing a culture medium. This stabilization period was followed by a 2-wk con trol period during which the microbiota were monitored. The microbiota were then subjected to a 2-wk treatment period by adding 2.5 g/d soygerm powder to the culture medium. The addition resulted into an overall increase of b acterial marker populations (Enterobacteriaceae, coliforms, Lactobacillus s p., Staphylococcus sp. and Clostridium sp.), with a significant increase of the Lactobacillus sp. population. The short-chain fatty acid (SCFA) concen tration increased similar to 30% during the supplementation period; this wa s due mainly to a significant increase of acetic and propionic acids. Gas a nalysis revealed that the methane concentration increased significantly. Am monium and sulfide concentrations were not influenced by soygerm supplement ation. Use of an electronic nose apparatus indicated that odor concentratio ns decreased significantly during the treatment period. The P-glycosidic bo nds of the phytoestrogenic isoflavones were cleaved under the conditions pr evailing in the large intestine. The increased bacterial fermentation after addition of the soygerm powder was paralleled by substantial metabolism of the free isoflavones (genistein, daidzein and glycitein), resulting in rec overy of only 12-17% of the supplemented isoflavones.