Abstract: In order to establish an enzymatic method to hydrolyze crude tea residue protein to prepare tea residue polypeptides with higher hydroxyl free radical scavenging activity, the effects of enzymes (acidic protease, neutral protease, alkaline protease and protamex), substrate concentration, enzyme dosage, temperature, pH, hydrolysis time on hydroxyl free radical scavenging activity were studied. Protamex was the best enzyme for the preparation of tea residue polypeptides with hydroxyl free radical scavenging activity, followed by alkaline protease and the optimal substrate concentration, enzyme dosage, hydrolysis temperature, pH and hydrolysis time were 0.5%, 600 U/g, 55 ℃, 8.0 and 5 h for protamex hydrolysis, and 0.5%, 400 DU/g, 8.5, 50 ℃ and 1.0 h for alkaline protease hydrolysis, resulting in a hydroxyl free radical scavenging rate of 27.3% and 25.3%, respectively. Compared with protamex hydrolysis, alkaline protease hydrolysis resulted in a decrease in time consumption by 4 h despite showing no significant difference in hydroxyl free radical scavenging capacity. The polypeptide sample obtained by alkaline protease hydrolysis contained 28.4% protein, 11.0% polypeptide and 1.5% free amino acids and indicated an IC50 of 8.432 mg/mL against hydroxyl free radicals compared with 0.897 mg/mL for vitamin C.

Key words: tea residue protein, protease, hydrolysis, polypeptide, hydroxyl free radical