Fermentative Bioconversion of β-Glucoside Like Isoflavones is a Better Indicator of β-Glucoside Hydrolysing Capability in Probiotic Lactic Acid Bacteria (LAB) Due to the Predominant Phosphoglucosidase Activity

ABSTRACT Isoflavones provide multiple health benefits, such as the potential for prevention of cancer and osteoporosis. Isoflavones are naturally present as β-glucosides, rendering them unavailable for uptake in the human gut. In the present study, an attempt was made to understand the mechanism of β-glucoside hydrolysis by probiotic microbes. Six major probiotic-type strains were screened for β-glucosidase activity, and two annotated β-glucosidase genes were cloned and characterized from L. acidophilus. These proteins were more active on phosphorylated pNPG than on pNPG, indicating a Phosphoenolpyruvate (PEP)-dependent pathway involving phosphoglucosidase for the uptake and metabolism of β-glucosides such as isoflavones. The screening of these strains for the bioconversion of isoflavones showed above 90% isoflavone glucoside hydrolysis for four strains, with L. rhamnosus showing the highest hydrolysis. To the best of our knowledge, this is the first report comparing glucoside hydrolysis by whole bacterial cells with cell extracts and purified candidate proteins.