Effects of multifrequency ultrasound pretreatment on the enzymolysis, ACE inhibitory activity, and the structure characterization of rapeseed protein

In this study, the effects of multifrequency ultrasound pretreatment with various frequency modes on rapeseed protein enzymolysis and its mechanism were studied. Following processing parameters, including substrate concentration, enzyme dosage, power density, pretreatment time and initial temperature on the degree of hydrolysis (DH) and angiotensin-I-converting enzyme (ACE) inhibitory activities of the hydrolysates, were evaluated using single-factorial experiments. The structural characteristics were analyzed using circular dichroism spectra and scanning electron microscopy. The results showed that during the screening of multifrequency ultrasonic pretreatment, combined fixed frequency 24/28 kHz significantly (p < .05) improved the DH and ACE inhibitory activity over the control. The experimental verification test results revealed that the processing factors that were studied had a significant effect on the DH and ACE inhibitory activity, which increased by 19.12 and 35.08% over the control, respectively. The molecular conformation of rapeseed protein indicated that sonication had destroyed the microstructure and increased surface area. Practical applications Multifrequency ultrasound (MFU) technology is a novel and nonthermal physical processing technology in the food industry. Ultrasound pretreatment with various frequency modes has been shown to have remarkable effects on the enzymatic hydrolysis of plant-based proteins. Rapeseed protein is a low-cost and abundant by-product of the oil industry, and it is considered to be a potential resource of bioactive peptides, such as angiotensin-I-converting enzyme (ACE) inhibitory. These peptides are beneficial to patients due to easy absorption as well as being safe and stable. In this article, a combination of MFU pretreatment and enzymolysis were shown to be an effective way to prepare hydrolysates with ACE inhibitory activity from rapeseed protein. Additionally, optimization of ultrasonic pretreatment factors using a single-factorial method provides a good reference for industrial production of ACE inhibitory peptides. Multifrequency sonication with its key factor acoustic cavitation prior to the enzymolysis could induce changes to the protein structure and ultimately increase the accessibility of enzyme to peptide bonds