Microbial metabolism of soy isoflavones by human intestinal bacterial strains.

Intestinal bacteria play an important role for the metabolism of soy isoflavonoids. When soy foods are consumed, the soy isoflavone glucosides are metabolized into their aglycones and the related isoflavonoids by intestinal bacteria. We designed an in vitro microbial metabolic system using 29 commercially available human intestinal bacterial strains and elucidated the metabolism of soy isoflavone glucosides. The strains were classified into three categories, which were 14 facultative anaerobes, 13 obligate anaerobes, and 2 aerobes. Almost all facultative anaerobe strains metabolized soy isoflavone glucosides to their aglycones. The ratio of metabolism from glucoside to aglycone was different in each strain. Contrary to the facultative anaerobes, some of the obligate anaerobes did not metabolize soy isoflavone glucosides at all. Both the aerobic bacteria hardly metabolized soy isoflavone glucosides. The bacterial growth speed might show good correlation to the metabolizing speed of both glucosides. Therefore, the speed of metabolism would be different in each bacterial strain, too.