Antioxidant properties of protein hydrolysate from Douchi by membrane ultrafiltration

Protein extracted from Douchi was hydrolyzed by alcalase based on a single-factor experiment and response surface methodology was employed to optimize hydrolysis conditions. The optimum conditions were determined to be: 63℃ extraction temperature, 1.4% quantities of enzyme and substrate, and 1.7 h extraction time. The optimal protein hydrolysate was subsequently subjected to ultrafiltration, and the fraction of molecular weight 10–50 kDa was identified as the most potent contributor to antioxidant activity. Amino acid analysis indicated that acidic amino acids were the most abundant in all fractions of the protein hydrolysate. Infrared spectroscopy showed there were no significant differences in secondary structure between fractions.