Ultrasonic Treatment Effect on Enzymolysis Kinetics and Activities of ACE-Inhibitory Peptides from Oat-Isolated Protein

Pretreatment of oat protein with ultrasound showed excellent prospects in increasing the efficiencies of enzymatic hydrolysis and inhibitory activities of peptides against angiotensin converting enzyme (ACE). The mechanism of the ultrasound pretreatment on enhancement of protein hydrolysis rate and the characterization of the enzymolysis process was investigated. The Michaelis-Menten model was used to study the effects of ultrasound on the hydrolysis rate. An ordered sequential bi-substrate reaction mechanism model was applied to describe the characteristics of enzymolysis of the protein with ultrasonic pretreatment. The protein concentration and the enzyme loading were factors in this model. The kinetic parameters of the models were estimated by experimental results and evaluated. The results showed that ultrasonic power, time and enzymolysis time greatly influenced the degree of hydrolysis and ACE inhibitory activities of the peptides. The best conditions for hydrolysis and ACE inhibitory activities were 750 W, 20 min of sonication followed by 60 min of enzymolysis. After the treatment, the hydrolysis rate and the ACE inhibitory activities of peptides were significantly (P < 0.001) increased by 32.1 and 53.8 %, respectively compared to the samples without ultrasonic pretreatment. The Michaelis constant K (m) indicated the ultrasonic treatment enhanced the affinities between the alcalase and oat protein. The enzymolysis kinetic model fitted well the enzyme catalyzed hydrolysis trend for the ultrasonic pretreated oat protein. The model provided a theoretical basis for describing the complex enzymatic process and preparing the ACE inhibitory peptides efficiently.