Abstract: In order to find the appropriate proteases for enzymatic preparation of angiotensin Ⅰ-converting enzyme (ACE) inhibitory peptides from shrimp shell, neutral protease, alkaline protease, bromelin and papain were evaluated for their effectiveness in hydrolyzing shrimp shell based on hydrolysis degree and ACE-inhibitory activity. It was found that both neutral protease and alkaline protease were more suitable for the preparation of ACE-inhibitory peptides from shrimp shell. The process conditions for hydrolyzing shrimp shell with neutral protease or alkaline protease were optimized by orthogonal array design method. The optimized alkaline protease hydrolysis conditions were hydrolysis temperature of 60 ℃, hydrolysis pH of 9.5, substrate concentration of 2.5 g/100 mL, enzyme concentration of 4000 U/g and hydrolysis time of 2.5 h, resulting in an ACE-inhibitory rate of 67.70% and a hydrolysis degree of 69.79%. The optimized neutral protease hydrolysis conditions were hydrolysis temperature of 50℃, hydrolysis pH of 7.0, substrate concentration of 2.5 g/100 mL, enzyme concentration of 2000 U/g and hydrolysis time of 2 h, resulting in an ACE-inhibitory rate of 84.04% and a hydrolysis degree of 26.76%. In conclusion, neutral protease is a superior protease over alkaline protease for the preparation of ACE-inhibitory peptides from shrimp shell.

Key words: shrimp shell, neutral protease, alkaline protease, ACE inhibitory peptide, enzymatic hydrolysis