Optimized antioxidant peptides fractions preparation and secondary structure analysis by MIR.

The soybean protein was hydrolyzed by Alcalase Food grade (FG) 2.4 L and the optimal hydrolysis parameters of strongest antioxidant capacity of peptides were obtained using response surface methodology (RSM). The effects of reaction temperature, pH value and ratio of enzyme/soybean protein powder ([E/S]) on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) of the peptides was well fitted to a quadric equation with high determination coefficients. The hydrolysate with optimal DPPH was predicted to be obtained at: temperature of 50°C, pH value of 10.32, and [E/S] ratio of 12%. The hydrolysates were separated by the ultrafiltration membranes in the cut-off MW at 1kDa, 3kDa, 10kDa and 30kDa and molecular weight cut-offs (MWCO) I-V were determined antioxidant activity. And secondary structures of those fractions were investigated by mid-infrared spectroscopy (MIR).