Effects of multi-mode S-type ultrasound pretreatment on the preparation of ACE inhibitory peptide from rice protein.

The effects of ultrasound working modes using multi-mode S-type ultrasound on the preparation of bioactive peptide from rice protein (RP) were studied with the ACE inhibitory activity of protein-hydrolysate after gastrointestinal simulated digestion as the index. The structure characterizations of protein and enzymolysis products were also studied. Results showed that all the ultrasound working modes pretreatment increased the ACE inhibitory activity significantly (p < 0.05) and 20/40 kHz dual-frequency ultrasound showed the most significant impact, which increased by 38.28% and 27.47% compared to control and ultrasound cleaning machine, respectively. After pretreated by 20/40 kHz dual-frequency ultrasound, the soluble and hydrophobic protein contents, free sulfhydryl content and surface hydrophobicity of RP increased. And the peptide content and hydrophobic amino acid content of protein-hydrolysate after gastrointestinal simulated digestion showed higher value (p < 0.05). In conclusion, the multi-mode S-type ultrasound pretreatment is an effective way in preparation of ACE inhibitory peptide from RP.