In vitro ACE-inhibitory and Antioxidant Activities of the Casein Hydrolysates Subjected to Plastein Reaction with Addition of Three Extrinsic Amino Acids

Plastein reaction was used in the present work to modify casein hydrolysates in the presence of extrinsic amino acids to reveal its impacts on two bioactivities. Casein was hydrolyzed by alcalase to a degree of hydrolysis of 12.4%. The prepared hydrolysates exhibited in vitro inhibition on Angiotensin-I-converting Enzyme (ACE) and scavenging activity on DPPH radical. The prepared hydrolysates were then modified by alcalase-catalyzed plastein reaction in the presence of one of three extrinsic amino acids (leucine, valine or phenylalanine). At fixed 35% (w/w) substrate concentration and 6 h reaction time, other conditions were optimized as 0.6 mol/mol amino acid addition, 3 kU g-1 peptides alcalase addition and 30C reaction temperature. The modified hydrolysates exhibited better ACE inhibition for its IC50 value decreased from 42.2 to 21.0-25.1 mg mL-1. The scavenging activity on DPPH (hydroxyl) radical or reducing power of the modified hydrolysates was also better than that of original casein hydrolysates. The results show that alcalase-catalyzed hydrolysis of casein coupled with plastein reaction is capable of preparing casein hydrolysates with better ACE inhibition and antioxidant activity.