Abstract
Human health benefits are expected of the anti-estrogenic or estrogenic effects of soy isoflavone. Recently, the biological effects of one of the metabolites of soy isoflavone, equol, has been focused. Equol is an active metabolite produced by intestinal bacteria. However, in humans, non-equol producers exist owing to differences in intestinal microbiota among individuals. Therefore, it is considered that non-equol producers will not benefit from soy isoflavone, even when they ingest it. The purpose of this study was to look for the lactic acid bacteria which metabolize daidzein to equol which could be used in foods. We tested 213 strains (Bifidobacterium spp and Lactobacillus spp), screening for the lactic acid bacteria which metabolize daidzein to equol, but none were found. We also tried to isolate human intestinal bacteria capable of metabolizing daidzein to equol using the feces of healthy humans, and succeeded in newly isolating 3 strains of equol-producing bacteria. Only one strain, Lactococcus 20-92, was the equol-producing lactic acid bacterium. It was identified as Lactococcus garvieae by the 16S rDNA homology. It was confirmed that equol production by Lactococcus 20-92 occurrs after the steady state of growth has been achieved. This is the first report of lactic acid bacteria capable of metabolizing daidzein to equol directly, and the itilization of Lactococcus 20-92 is expected in functional foods.
