Generation of hydrolysates from rice bran proteins using a combined ultrasonication-Alcalase hydrolysis treatment

Hydrolysis of rice bran protein (RBP) using a physical-enzymatic combined method (ultrasound-Alcalase) was carried out. The RBP was extracted using an ultrasound-aided alkaline extraction method and then the extract was hydrolysed. Furthermore, ultrasounication was used prior to Alcalase hydrolysis (pH 8.5, 10 min, 55 ◦C). Two variables were considered to operate the ultrasonication: power (50, 100 and 150 w) and duration of the treatment (10, 25 and 40 min). The results showed that the degree of hydrolysis (DH%) was increased with increasing the power and the duration. The highest DH (27.35 ± 0.45%) was associated with the hydrolysates obtained by ultrasonication (150 w, 40 min)-Alcalase combined treatment. The optimal condition for the ultrasonication was found at 50 w-10 min, where the bioactive peptides (BAPs) had the highest 2,2-diphenyl-1- picrylhydrazyl free radical (DPPH• ) scavenging activity (86.55 ± 1.17%) and lipase inhibitory activity (57.57 ± 0.91%). The hydrolysates obtained at the optimized condition were studied in terms of physicochemical and structural properties. The mass distribution of the materials was studied using the high performance liquid chromatography (HPLC) showing a lower molecular weight proteins and peptides for all generated hydrolysates compared to non-hydrolysed samples. The results were in agreement with the results of DH analysis and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Ultrasonication enhanced the effect of enzyme hydrolysis by affecting the structure of the proteins. This was confirmed by the structural investigation using fourier-transform infrared spectroscopy and ultraviolet–visible spectrophotometry. Using ultrasound in different conditions prior to enzymatic hydrolysis influenced in the biological properties of the BAPs generated from RBP.