Pretreatment of defatted wheat germ proteins (by-products of flour mill industry) using ultrasonic horn and bath reactors: Effect on structure and preparation of ACE-inhibitory peptides

•The ACE-inhibitory activity increased by horn and bath sonication.•Combinations of fixed frequency (bath) produced more ACE-inhibitory peptides.•Changes in structural properties of DWGP after sonication were found.•Horn sonication was efficient in preparation of ACE-inhibitory peptides. The ultrasonic horn and bath reactors were compared based on production of angiotensin-converting-enzyme (ACE) inhibitory peptides from defatted wheat germ proteins (DWGP). The DWGP was sonicated before hydrolysis by Alcalase. Degree of hydrolysis, ACE-inhibitory activity, surface hydrophobicity, fluorescence intensity, free sulfhydryl (SH), and disulfide bond (SS) were determined. The highest ACE-inhibitory activity of DWGP hydrolysate was obtained at power intensity of 191.1W/cm2 for 10min in the ultrasonic horn reactor. The fixed frequency of 33kHz and the sweep frequency of 40±2kHz resulted in the maximum ACE-inhibitory activity. The combined irradiation of dual fixed frequency (24/68kHz) produced significant increase in ACE-inhibitory activity compared with single frequency (33kHz). The ultrasonic probe resulted in significant higher ACE-inhibitory activity compared with ultrasonic bath operating at single or dual fixed and sweep frequencies. The changes in conformation of the DWGP due to sonication were confirmed by the changes in fluorescence intensity, surface hydrophobicity, SHf and SS contents and they were found in conformity with the ACE-inhibitory activity in case of the ultrasonic horn reactor but not in bath reactor.