Abstract:The soybean isoflavone was firstly extract from soy sauce residue by ethanol extraction method, and the extraction conditions were optimized. The crude isoflavone extract was further purified by 6 methods including alcohol precipitation, isoelectric precipitation, concentrated centrifugation, n-butanol, dichloromethane, and ethyl acetate extraction. Finally, the composition of isoflavone monomer after purification was identified by high performance liquid phase, and its in vitro antioxidation was evaluated by the pyrogallol oxidation and DPPH methods. The optimized extraction of crude isoflavone yielded the isoflavone content of 1.21% and the extraction rate of (85.36±0.09)%. Among the 6 purification methods, the isoflavone content obtained by the concentrated centrifugation method was 7.75% with best removal of protein. The isoflavone content obtained by the dichloromethane extraction method was 27.74% with best removal of total sugar and ash. The purity of the isoflavone was 44.88% when the two methods combined, and it was composed by genistein, glycintein and daidzein, accounting for 67.37% and 9.33%, 23.30%, respectively. The scavenging rates of purified isoflavones(1 mg/mL) to superoxide and DPPH free radicals were 67.65% and 89.18%, which were significantly higher than isoflavones crude extracts(P<0.05). And their IC50 were 0.34 and 0.26 mg/mL. The isoflavone purified products achieve certain antioxidant activity, expected to be used as potential natural antioxidants in functional foods.
