Stability of β-glucosidase Activity Produced by Bifidobacterium and Lactobacillus spp. in Fermented Soymilk During Processing and Storage

ABSTRACT: Microorganisms possess endogenous enzymes, however the stability of these enzymes during storage in soymilk has not been studied. β-glucosidase is an important enzyme that could be used in the bioconversion of the predominant soy isoflavone glucosides to their bioactive aglycone forms. Fifteen probiotic microorganisms including bifidobacterium, Lactobacillus acidophilus , and Lactobacillus casei were screened for β-glucosidase activity using p-nitrophenyl-β-d-glucopyranoside as a substrate. Six strains were selected on the basis of β-glucosidase activity produced during fermentation of soymilk. The stability of the enzyme activity was assessed during incubation for up to 48 h and storage for 8 wk at frozen (-80°C), refrigerated (4°C), room (24.8°C), and incubation (37°C) temperatures. L. casei strains showed the highest β-glucosidase activity after 24 h of incubation followed by L. acidophilus strains, whereas bifidobacterium strains showedleast activity. However, p-glucosidase from Bifidobacterium animalis BB12 showed the best stability during the 48 h fermentation. Lower storage temperatures (-80°C and 4°C) showed significantly higher ( P < 0.05) β-glucosidase activity and better stability than that at higher temperatures (24.8°C and 37°C). The stability of β-glucosidase from these microorganisms should be considered for enzymic biotransformation during storage of isoflavone β-glucosides to bioactive isoflavone aglycone forms with potential health benefits.