Development of an isoflavone aglycone-enriched soymilk using soy germ, soy protein isolate and bifidobacteria

Soymilks comprising soy protein isolate (SPI) and soy germ (SG) at ratios of 9:1 (SPI/SG9:1), 6:4 (SPI/SG6:4) and 3:7 (SPI/SG3:7) were fermented with Bifidobacterium animalis Bb-12. Enumeration of microbial populations, pH measurements and quantification of isoflavones were performed at 12 and 24 h incubation and at 1, 7 and 14 day refrigerated storage. Isoflavone concentrations were 3, 7 and 12 times higher in SPI/SG9:1, SPI/SG6:4 and SPI/SG3:7 than soymilk made from SPI and microbial populations increased, respectively, by 1.2, 1.3 and 0.9 log₁₀ CFU/mL after 24 h. Hydrolysis of isoflavone glucosides increased the concentration of aglycones from 0.819 to 5.645 mg/100 mL (47% of total isoflavone) in SPI/SG9:1 after 24 h (P<0.05), with isoflavone biotransformation less apparent in SPI/SG3:7. Fermented SPI/SG6:4 contained the highest concentration of isoflavone aglycone at 7.801 mg/100 mL (26% of total). Viability of B. animalis and composition of isoflavones were unchanged after 14 day refrigerated storage (P>0.05).