Study on effects of ultrasonic pretreatment on enzymolysis preparation of ACE-inhibitory peptides from corn germ protein

This study aimed to research the effects of ultrasonic pretreatment of different working modes on the preparation of ACE-inhibitory peptides from corn germ meal. According to protein conversion and proportion of highly active peptides, dual-frequency countercurrent energy-gathered ultrasound, triple-frequency divergence ultrasound and dual-frequency relative vibration ultrasound were used to pretreat corn germ meal and the best ultrasonic mode was selected. The ultrasonic preprocessing parameters were determined by single-factor step optimization method. Under ideal ultrasonic pretreatment conditions, enzymatic reaction conditions were optimized. Results showed that the ACE inhabitary activity of peptides of 300~1000 Da was the highest, IC₅₀ of which was 0.78 mg/mL;the most effective ultrasonic mode was 20/40 kHz alternate dual-frequency and the optimum parameters of the ultrasonic pretreatment were the power density of 100 W/L, the substrate concentration of 8%, ultrasonic time of 20 min, ultrasonic temperature of 30℃. Enzymolysis conditions were enzyme dosage of 2000 U/g protein, enzymolysis time of 2.5 h. Under the optimal conditions, the protein conversion rate was 85.00%, which was 16.42% higher than 73.01% in the control group (without ultrasound), and the proportion of highly active peptides was 29.63%, which was 13.96% higher than 26.00% in the control group. The results showed that dual-frequency ultrasound could effectively improve the yield and the ACE inhabitary activity of the product, which was beneficial to the preparation of ACE inhibitory peptides.