Ultrasound-assisted preparation of ACE inhibitory peptide from milk protein and establishment of its in-situ real-time infrared monitoring model

A scheme for preparing milk ACE inhibitory peptides by in vitro proteolysis and simulated gastrointestinal digestion was constructed. The ultrasonic assisted pretreatment was used to improve the enzymolysis of milk protein. The in-situ real-time infrared was used to establish monitoring model of enzymatic process. Results showed that under the conditions of single frequency 28 kHz, ultrasound time 40 min, ultrasound power density 20 W/L, milk protein concentration 34 g/L, batch ratio 2:4 and initial temperature 30 °C, the ACE inhibition rate of gastric digestion of enzymatic hydrolysate reached 67.20%, which was 22.87% higher than that of non-ultrasound samples. The results of secondary structure studies of proteins showed that after the ultrasonic treatment, the content of α-helix and β-corner reduced, and the content of β-folding and random coil increased. Compared with the control group, the ultrasonic treatment increased surface hydrophobicity and the content of SH while reduced the content of SS in milk protein, thus improving the ACE inhibitory activity of enzymatic hydrolysates. Furthermore, three quantitative prediction models of PLS, iPLS and Si-PLS for ACE inhibition rate of milk protease hydrolysates were established. And all these three different in-situ real-time prediction models had good predictive effect on the ACE inhibition rate of milk proteolysis products and gastrointestinal simulated digestion products.