Abstract: Angiotensin converting enzyme (ACE) inhibitory peptides from oyster were prepared by the combined use of enzymatic hydrolysis and Plastein reaction. Papain, pepsin, alcalase, neutural protease and trypsin were tested for their efficiencies in hydrolyzing oyster based on ACE inhibitory activity and degree of hydrolysis and it turned out that papain was the optimal choice. The hydrolysis conditions were optimized by one-factor-at-a-time method and orthogonal array design as follows: solid-to-liquid ratio (g/mL), 1:8; concentration of papain, 2.0%; hydrolysis time, 1.0 h; hydrolysis temperature, 65 ℃; and initial pH, 6.0. Under these conditions, the percentage inhibition of ACE activity by oyster hydrolsate was 63.30%. The hydrolysate was modified via the Plastein reaction. Based on ACE inhibitory activity and reduction in free amino acid content, the optimal values of Plastein reaction parameters including the type of enzyme, enzyme dosage, substrate concentration, temperature and reaction time were determined to be papain, 1.0%, 40%, 2.5 h and 30 ℃ for hydrolysis at an initial pH of 7.0, respectively. The modified product showed maximum percentage inhibition against ACE activity of 82.31%, which was increased by 19% compared to that before modification.

Key words: oyster, hydrolysis process, angiotensin converting enzyme (ACE) inhibitory activit, Plastein reaction