Thermal processing modulates the interaction between whey proteins with variable hydrolysis and polyphenols: Implications for structural and functional properties.

Thermal treatment ensures food safety, but high temperatures affect the structure and activity of protein-polyphenol complexes. This study used whey protein isolate (WPI) to examine the impact of thermal treatments (pasteurization and sterilization) on the interactions between WPI with varying degrees of enzymatic hydrolysis (WPIHs) and epigallocatechin gallate (EGCG), and the functional properties of the formed complexes. The results indicated that thermal treatment significantly altered the protein structure, promoting aggregation and unfolding. The binding of WPI/WPIHs to EGCG follows a static quenching mechanism, with hydrophobic interactions playing a dominant role. Sterilization (121 °C, 15 min) shifted the primary interaction force of partially hydrolyzed WPI (WPIH1) to electrostatic interactions, while transforming highly hydrolyzed WPI (WPIH2) to van der Waals forces and hydrogen bonds. The binding capacity of WPIH1 with EGCG can reach 3.798 × 105 ± 0.084 × 105 M-1. Under thermal treatment, the number of binding sites was consistently one. In terms of functional properties, WPIH1 combined with EGCG exhibited better antioxidant activity, enzyme inhibitory capacity and emulsifying properties. Specifically, the WPIH1-EGCG complex prepared at 65 °C showed the highest ABTS (94.16 % ± 0.33 %) and DPPH (84.55 % ± 0.45 %) scavenging rates, with α-glucosidase (72.17 % ± 1.00 %) and α-amylase (69.70 % ± 0.46 %) inhibition, and its emulsifying properties increased by 47.49 %. In summary, appropriate thermal treatment and enzymatic hydrolysis render the functional properties of the complexes more stable. This study contributes to understanding the binding mechanism between WPI (varying hydrolysis degrees) and EGCG. It provides insights for optimizing thermal processing parameters of functional foods containing EGCG and whey protein derivatives.