Evaluation of enzymic potential for biotransformation of isoflavone phytoestrogen in soymilk by Bifidobacterium animalis, Lactobacillus acidophilus and Lactobacillus casei

Three strains of Lactobacillus acidophilus, two of Lactobacillus casei and one of Bifidobacterium were screened for beta-glucosidase activity using p-nitrophenyl-beta-D-glucopyranoside as a substrate and their potential for the breakdown of isoflavone glucosides to the biologically active aglycones in soymilk. Isoflavones quantification with HPLC and beta-glucosidase activity were performed after 0, 12, 24, 36, and 48 h of incubation in soymilk at 37 degrees C. All six micro-organisms produced beta-glucosidase, which hydrolysed the predominant isoflavone beta-glucosides. There was a significant increase and decrease (P < 0.05) in the concentration of isoflavone aglycones and glucosides, respectively, in fermented soymilk. Based on the concentration of isoflavones during peak beta-glucosidase activity, the hydrolytic potential was calculated. L. acidophilus 4461 had the highest aglycone concentration of 76.9% after 24 h of incubation, up from 8% in unfermented soymilk (at 0 h). It also had the best isoflavone hydrolytic index of 2.01.. signifying its importance in altering the biological activity of soymilk. (C) 2005 Elsevier Ltd. All rights reserved.