Enzymic transformation of isoflavone phytoestrogens in soymilk by β-glucosidase-producing bifidobacteria

Five strains of bifidobacteria were screened for beta-glucosidase activity using p-nitrophenyl-p-D-glucopyranoside as the substrate, and selected strains were used to ferment soymilk. Enumeration of viable bifidobacteria and quantification of isoflavones using HPLC were performed at 0, 12, 24, 36, and 48 h of incubation. Four strains produced beta-glucosidase. B. pseudolongum and B. longum-a displayed the best growth in soymilk, with an increase of 1.3 log(10) CFU/mL after 12 h. B. animalis, B. longum-a, and B. pseudolongum caused hydrolysis of isoflavone malonyl-, acetyl- and beta-glucosides to form aglycones, and transformed daidzein to equol in soymilk. Fermentation of soymilk with Bifidobacterium sp. resulted in a significant increase (p < 0.05) in the concentration of aglycones.