Regioselective deglycosylation of onion quercetin glucosides by Saccharomyces cerevisiae.

Bioconversion of quercetin glucosides using four generally recognized as safe (GRAS) organisms (Aspergillus oryzae, Bacillus subtilis, Lactobacillus plantarum, and Saccharomyces cerevisiae) was evaluated by measuring changes in the levels of quercetin compounds of onion. Of the four organisms, S. cerevisiae increased the content of quercetin-3-O-β-D-glucoside (III; isoquercitrin) and quercetin (IV), whereas decreasing quercetin-3,4'-O-β-D-glucoside (I) and quercetin-4'-O-β-D-glucoside (II).