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. s-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 s-glucosidase activity using p-nitrophenyl -s-d-glucopyranoside as a substrate. Six strains were selected on the basis of s-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 s-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) s-glucosidase activity and better stability than that at higher temperatures (24.8°C and 37°C). The stability of s-glucosidase from these microorganisms should be considered for enzymic biotransformation during storage of isoflavone s-glucosides to bioactive isoflavone aglycone forms with potential health benefits.