Effects of Ultrasound Pretreatment on the Enzymolysis and Structural Characterization of Wheat Gluten

Ultrasound pretreatment of protein could improve the angiotensin-I converting enzyme (ACE) inhibitory activity of hydrolysates and by alerting the structure of enzyme substrates. In this research the effects on ACE inhibitory activity and enzymolysis efficiency were explored under the optimum counter flow ultrasound (CFU) pretreatment conditions which obtained from our previous studies. The mechanism was studied by microstructure, nano-mechanical properties and secondary structures of wheat gluten (WG), which measured by scanning electron microscopy (SEM), atomic force microscopy (AFM), and flourier transform infrared spectrum (FTIR). The results showed that the CFU pretreatment resulted in significantly (P < 0.05) higher value compared with control, the ACE inhibitory activity was increased by 29.8 % and the value of IC50 was decreased by 36.92 %. CFU pretreatment increased the initial reaction rate by 9.58–20.27 % at a substrate concentration of 10–50 g/L, the KA was increased by 2.90 % and KM was decreased by 15.83 % compared to control. The microstructure revealed that the meshwork structure of WG was loosened and the surface roughness values of Ra and Rq were increased by CFU pretreatment. The nano-mechanical analyses showed that CFU pretreatment redistributed the adhesion map and decreased the stiffness. The secondary structures were less ordered by CFU pretreatment. Intermolecular β-sheet of protein aggregation and random coil were increased, Intramolecular β-sheet, α-helix and β-turn were decreased. It was concluded that CFU pretreatment can remarkably improve the ACE inhibitory activity of hydrolysate and enzymolysis efficiency of WG confirmed by the changes of microstructure, nano-mechanical properties, and secondary structures.