Effect of Ultrasound-Induced the Structural Changes in Casein on α-Glucosidase Inhibitory Peptide of Its Hydrolysate

The effects of ultrasonic powers on casein structure and the α-glucosidase inhibitory activity of casein hydrolysates were investigated. Potential α-glucosidase inhibitory peptides generated from casein hydrolysate were identified by LC-MS/MS and predicted by in silico. The action mechanism of the potential α-glucosidase inhibitory peptides was further explored based on molecular docking. The results demonstrated that 300 W ultrasound treatment significantly enhanced fluorescence intensity and surface hydrophobicity (P < 0.05), along with a decrease in particle size (P < 0.05), an increase in zeta potential absolute value, and sulfhydryl contents (P < 0.05) of casein. Concurrently, a significant decrease in α-helix and β-sheet content of casein was detected (P < 0.05). Notably, the hydrolysate derived from 300 W ultrasound pretreatment casein exhibited a hydrolysis degree of 24.35% ± 1.28% and α-glucosidase inhibitory activity of 57.43% ± 2.15%, both significantly higher than the untreated group (P < 0.05). Three potential α-glucosidase inhibitory peptides RYPSYGI, SRYPSYGLN, and YQKFPQYL displayed PeptideRanker scores above 0.5, low molecular weight, and were predicted to have good human intestinal absorption and be non-toxic. Molecular docking revealed that binding energies with α-glucosidase were -9.4, -8.6, and -7.4 kcal/mol, respectively. The identified peptides bound to amino acid residues within the active site of α-glucosidase through hydrogen bonding, electrostatic interactions, and hydrophobic interactions. In conclusion, ultrasonic pretreatment-assisted enzymolysis was an effective technique for preparing α-glucosidase inhibitory peptides from casein.