Ultrasonic-induced Structural Modification of Whey Protein and Effect on α-Glucosidase Inhibitory Activity of Fermentation Products

To improve the bioavailability of whey protein hydrolysates, the effects of different ultrasonic power treatments (100, 200, 300, 400 W) on the structural characteristics of whey protein were investigated, along with their effect on the degree of hydrolysis, peptide content, and α-glucosidase inhibitory activity of the hydrolysates. The results demonstrated that moderate ultrasound treatment expanded the whey protein structure. Compared to the untreated sample, at 300 W for 25 min, the intrinsic fluorescence intensity reached its peak, and the average particle size decreased by 62% (P<0.05). Additionally, surface hydrophobicity and free sulfhydryl content increased by 35% and 36%, respectively. Secondary structure analysis revealed a reduction in α-helix (42%) and β-sheet (20%) content, while β-turn and random coil increased by 26% and 77%, respectively (P<0.05). Scanning electron microscopy (SEM) further confirmed structural changes, showed a transition from large, rough-edged sheets to smaller, smooth-edged fragments. Lactiplantibacillus plantarum C11 was used to ferment whey protein after ultrasonic treatment. Compared with non-ultrasonic fermented whey protein, the degree of hydrolysis, peptide content and α-glucosidase inhibition rate were increased by 26%, 15% and 32%, respectively (P<0.05). Moderate ultrasonic pretreatment can enhance the α-glucosidase inhibitory activity of whey protein fermentation products, which provides a new strategy for synergistic preparation of whey protein bioactive peptides.