15E-6 |
Solid-state bioconversion for isoflavone enrichment in genetically-modified soybean by beneficial fungi |
P. MCCUE, Dept. of Food Science, University of Massachusetts, 340 Chenoweth Laboratory, 100 Holdsworth Way, Amherst, MA 01003 and K. Shetty. Soybean is a rich source of the isoflavone genistein, which occurs naturally as a variety of carbohydrate conjugates (glycosides) and has many health-promoting food uses as a phyto-estrogen, an antioxidant, and a nutraceutical. Based on previous successful research with cranberry pomace, we hypothesized that these glycosides in soybean could be hydrolyzed by b-glucosidase produced by the beneficial fungi, Rhizopus oligosporus and Lentinus edodes during solid-state fermentation. Our objective was to investigate the potential of using a high-phenolic-producing, genetically-modified soybean variety as a substrate for the production of free genistein through solid-state fermentation by food-grade fungi. To this end, we analyzed genistein content, antioxidant activity via DPPH quenching, and b-glucosidase activity in extracts of soybean following solid-state fermentation. Our results suggest that fungal b-glucosidase played a major role in release of antioxidant phenolic aglycones from genetically-modified soybean during solid-state fermentation. In Rhizopus-based fermentation, maximum b-glucosidase activity (24 U per mg dialyzed extract protein) correlated with maximum genistein content in water extracts (2.4 mg per gram dry seed weight) and maximum antioxidant activity in ethanol extracts (100%), whereas in Lentinus-based fermentation, similar b-glucosidase activity (23 U) correlated with maximum antioxidant activity in water extracts (91.25%), and high, but not maximal genistein content. The positive correlation of b-glucosidase activity with antioxidant activity, but not necessarily with genistein content suggests that other phenolic profiles of solid-state fermented soy extracts may be relevant. Therefore, solid-state fermentation provides an exciting strategy to naturally or biochemically enhance nutraceutical value of soy compared to any other approach.
Session 15E, Nutraceuticals & Functional Foods I
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