Underlying mechanisms and effects of EGCG on the interfacial composition and protein-lipid co-oxidation of whey protein isolate-stabilised O/W emulsions

Addition of different (−)-epigallocatechin-3-gallate (EGCG) (0, 100, 200, 500 or 1000 mg/L emulsion) on the interfacial composition and protein-lipid co-oxidation of whey protein isolate (WPI)-stabilised oil-in-water (O/W) emulsions were studied, and underlying mechanisms were also explored. The results indicated that the physical stability of emulsions gradually decreased with the increasing level of EGCG during storage, which clearly verified by decreasing ζ-potential absolute values and increasing droplet size. Moreover, the combination between WPI and EGCG by covalent/non-covalent binding for either adsorbed proteins (AP) or unadsorbed proteins (UAP) led to aggregation and conformational changes in WPI, which confirmed and characterised by electrophoresis, fluorescence quenching, and molecular docking simulation. Meanwhile, the concentration of AP slightly decreased as a function of EGCG level and storage time, however, the UAP showed the opposite change tendency, indicating that EGCG could effectively modulate the interfacial adsorption property of WPI in O/W emulsions. In addition, the incorporation of EGCG efficiently suppressed protein-lipid co-oxidation of O/W emulsions during storage, which was illustrated by hierarchical cluster and correlation analysis between protein and lipid oxidation products. Our results clearly revealed the viability of the EGCG to modulate the interfacial composition and retard the co-oxidation of O/W emulsions with enhanced storability.