Glutathione Regulating Aggregation and Depolymerization Mechanism of Whey Protein Isolate

Impacts of glutathione (GSH) at different concentrations (0, 2, 6, 10, 20, 60 mM) on whey protein isolate (WPI) aggregation and depolymerization were investigated at 50, 65, and 80 °C in this work. With GSH increased from 0 to 60 mM at 50 and 80 °C, GSH-induced WPI (WPI-GSH) aggregates depolymerized, resulting in the molecular weight and particle size decreased, while their absolute potential value and endogenous fluorescence gradually increased (P < 0.05). However, as GSH increased from 0 to 60 mM at 65 °C, the molecular weight and particle size of WPI-GSH first increased and afterward decreased, while their absolute potential value and endogenous fluorescence had the converse trend. 2-10 mM GSH drove WPI aggregation through thiol-disulfide bond exchange reactions and 20-60 mM GSH depolymerized it. WPI-GSH exhibited the most extensive cross-linking at 10 mM GSH. LC/MS/MS identified 15 intermolecular, 13 intramolecular, and 11 cyclic cross-linked peptides that were newly formed. The most active intermolecular disulfide cross-linking sites were α-La (91, 120), and β-Lg (66, 160). This study would expound the molecular mechanism of GSH regulation in whey proteins, being beneficial to its potential applications in food industry.