Response Surface Methodology for Optimization of Genistein Content in Soy Flour and its Effect on the Antioxidant Activity

Biotransformation of isoflavones glycosides into the aglycone form is essential to attain the maximum bioavailability. The factors affecting deglycosylation of genistin in soy flour using commercial β-glucosidase enzyme were evaluated. The presence of genistin in soy flour was confirmed by isolation through chromatographic fractionation and identification by spectral method. Two-levels Plackett-Burman design was applied and effective variables for genistein production were determined. Agitation rate, enzyme concentration, and reaction time, owing to their significant positive effect, and pH, owing to its significant negative effect, were further evaluated using Box-Behnken model. Accordingly the optimal combination of the major reaction affecting factors was ―enzyme concentration, 1 IU; agitation speed, 250 rpm; reaction time, 5 h and pH 4. The concentration of genistein can be increased by 9.91 folds (from 0.8 mg/g in the non biotransformed soy flour to 7.93 mg/g in the biotransformed one) using the determined optimal combination of major reaction affecting factors. The antioxidant activity of the non biotransformed and biotransformed soy flour extracts was determined by DPPH method. It was found that biotransformation increase the antioxidant activity by two folds. The concentration causing a 50% reduction of DPPH absorbance (EC50) were 10 and 5 mg/mL for the non biotransformed and biotransformed soy flour extracts, respectively.