Physicochemical properties and structure characteristics of different molecular weight peptides from ultrasonic assisted papain hydrolysate of wheat germ albumin

Wheat germ albumin (WGA) has high physicochemical and biological activity after enzymatic hydrolysis. The traditional protease hydrolysis method, due to its low enzymatic efficiency, can no longer meet the needs of efficient production. Adding assisted means to the traditional enzymatic hydrolysis method can improve these shortcomings. In this study, the effect of ultrasonic assisted papain on the hydrolysis degree of WGA and the physicochemical properties and structural characteristics of peptides with different molecular weights (MW) were compared and analyzed. The results showed that the optimal conditions for ultrasonic assisted enzymatic hydrolysis of WGA were determined through Box-Behnken design-response surface methodology (BBD-RSM): hydrolysis time of 20 min, substrate concentration of 2%, papain dosage of 10000 U/g, and ultrasonic power of 180 W. Under this condition, the clearance rate of DPPH could reach 82.29%. After enzymatic hydrolysis β-sheet decreased from 33.74% to 15.64%, β-turn increased from 30.93% to 47.36%, indicating that after enzymatic hydrolysis of WGA, the breaking of peptide bonds lead to the unfolding of the protein secondary structure. The peptides with MW less than 3 kDa exhibited circular particles and a dispersed organizational structure. The peptides with MW less than 3 kDa contained hydrophobic amino acids which could enhance the interaction between different peptides and lipid targets, or allowed peptides to enter target organs through hydrophobic binding. The use of ultrasonic assisted enzymatic hydrolysis of WGA would provide theoretical basis for further industrial application of biologically active wheat germ peptides.