In this study, we evaluated the effects of sweeping frequency ultrasound (SFU) pretreatment on the angiotensin-converting enzyme (ACE) inhibitory activity of zein hydrolysates and enzymatic hydrolysis thermodynamics. The solubility, surface hydrophobicity (Ho ), degree of hydrolysis (DH) of zein and ACE inhibitory activity of hydrolysates were determined. After SFU pretreatment, the solubility and Ho of zein were significantly increased. During the hydrolysis process, ultrasonic pretreatment significantly increased the DH of zein and the ACE-inhibitory activity of zein hydrolysates by 19.37 and 133.76%, respectively. First-order kinetics could be used to explain both traditional and ultrasonic-assisted hydrolysis. In contrast to traditional hydrolysis, the reaction rate constants of SFU-assisted hydrolysis were largely increased by 82.76, 17.81, 23.96, and 21.26% at hydrolysis temperatures of 293, 303, 313, and 323 K, respectively. For the thermodynamic parameters, SFU pretreatment decreased activation energy, enthalpy of activation, entropy of activation, and free energy of activation by 19.52, 20.63, 6.16, and 7.02% respectively. In conclusion, SFU pretreatment markedly enhanced the hydrolysis of zein, and this method could be applied to the protein proteolysis industry to produce zein peptides with high ACE inhibitory activity.
Keywords: Angiotensin-converting enzyme inhibitory activity; Hydrolysis; Sweeping frequency ultrasound; Thermodynamics; Zein.