Abstract:Antioxidant peptides from soybean were prepared by solid fermentation with Aspergillus oryzae and combined with controllable koji hydrolysis. With defatted soybean as nitrogen source and wheat bran as carbon source for Aspergillus oryzae, the koji-making conditions were optimized and the protease activity of koji were evaluated.The degree of hydrolysis, peptide recovery and protein recovery were also analyzed. Then orthogonal test was applied to optimize preparation conditions. It was found that the optimum koji-making conditions were as follows: C/N ratio 1/5, culture time 44 h, and inoculum size 0.05%. The optimum hydrolysis conditions were as follows: pH 7, substrate protein concentration 8%, hydrolysis time 4 h and no additional protein needed. Under these conditions, the alkaline protease activity of koji was 3109.85 U/g and the obtained product showed strong antioxidant activity with high ORAC value (2130.22 μmol Trolox equivalent/g peptide) and DPPH scavenging activity (IC50 =0.29 mg/mL).
