Abstract: The enzymatic hydrolysis of grass carp scales with alcalase for the preparation of antioxidant peptides was optimized by one-factor-at-a-time and orthogonal array design methods. Peptide yield, hydrolysis of degree (DH) and hydroxyl free radical scavenging rate of grass carp scale hydrolysate were investigated with respect to temperature, enzyme dose, substrate concentration, reaction time. The optimal hydrolysis conditions were pH 9.0, hydrolysis temperature of 55 ℃, enzyme amount of 3%, hydrolysis time of 5 h and substrate concentration of 10%, respectively. Under these conditions, the yield of peptides was 55.2% and the resultant hydrolysate presented a hydroxyl free radical scavenging rate of 98.86%. High performance liquid chromatography analysis showed that 91.8% of peptides in the hydrolysate had a molecular weight below 1000 D. The hydrolysate had an isoelectric point of around 2.6 and a solubility of higher than 98 % in the range of pH 2－12 and could thus be extensively used in foods.

Key words: grass carp scales, low molecular weight antioxidant peptide, technology, molecular weight distribution