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: 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.

Galactooligosaccharides (GOSs) are nondigestible oligosaccharides and are comprised of 2 to 20 molecules of galactose and 1 molecule of glucose. They are recognized as important prebiotics for their stimulation of the proliferation of intestinal lactic acid bacteria and bifidobacteria. Therefore, they beneficially affect the host by selectively stimulating the growth and/or activity of a limited number of gastrointestinal microbes (probiotics) that confer health benefits. Prebiotics and probiotics have only recently been recognized as contributors to human health. A GOS can be produced by a series of enzymatic reactions catalyzed by β-galactosidase, where the glycosyl group of one or more D-galactosyl units is transferred onto the D-galactose moiety of lactose, in a process known as transgalactosylation. Microbes can be used as a source for the β-galactosidase enzyme or as agents to produce GOS molecules. Commercial β-galactosidase enzymes also do have a great potential for their use in GOS synthesis. These transgalactosyl reactions, which could find useful application in the dairy as well as the larger food industry, have not been fully exploited. A better understanding of the enzyme reaction as well as improved analytical techniques for GOS measurements are important in achieving this worthwhile objective.

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