LAUSR

BACKGROUND Ultrasound pretreatment could improve the angiotensin-I converting enzyme (ACE) inhibitory activity of hydrolysates of wheat gluten (WG). The working mode of ultrasound has an important effect on the enzymatic hydrolysis of protein. RESULTS The results showed that the optimum working mode of ultrasound was alternate dual-frequency mode (20/35 kHz), substrate concentration was 30 g L-1 , initial temperature of the suspension was 30 °C, ultrasound pretreatment time was 10 min and power density was 150 W L-1 . Under optimised conditions, ACE inhibitory activity of WG hydrolysates reached to its maximum value in advance. The surface hydrophobicity (H0 ) of WG and the content of small peptides at the beginning of the enzymolysis were improved by the ultrasound pretreatment. The structure of WG was destroyed by the ultrasound pretreatment. The enzymatic residue of ultrasound pretreated WG were damaged greater than control. CONCLUSION It was concluded that alternate dual-frequency ultrasound pretreatment improved the ACE inhibitory activity. Ultrasonic pretreatment may loosen the tissue of WG aggregate, and help the enzyme alcalase to attack the interior of WG aggregate easily, which resulted in the release of low molecular weight peptides from WG aggregate. © 2017 Society of Chemical Industry.