Effect of covalent binding of (-)-epigallocatechin gallate on the antibody binding capacity, physico-chemical properties and functional properties of whey isolate proteins: Comparison of ultrasound-assisted treatment and heat-assisted treatment

Polyphenol-modified proteins have been extensively studied, but the long processing time limits their application. This study aims to evaluate the effects of ultrasonic-assisted treatment (UAT) at 0 W (no ultrasound) and 650 W, as well as heat-assisted treatment (HAT) at 25 °C (no heat) and 80 °C, on the physicochemical, structural, antibody-binding capacity and functional properties of whey protein isolate (WPI)-(−)-epigallocatechin gallate (EGCG) conjugates. The results showed that the immunoglobulin E (IgE) binding capacity of WPI-EGCG conjugate prepared by UAT (U650-E) and WPI-EGCG conjugate prepared by HAT (H80-E) was significantly reduced in comparison with the corresponding conjugates without ultrasound-assisted and without heat-assisted. Notably, H80-E exhibits the lowest IgE binding capacity (42.40 %) and demonstrates superior performance in terms of antioxidant capacity, α-glucosidase inhibitory activity, solubility, and emulsifying properties. This is attributed to the effects of heat treatment on the structure of WPI and the binding sites between WPI and EGCG. In addition, the reduction in IgE binding capacity of H80-E can be attributed to the disruption of conformational epitopes and the masking of critical linear epitopes by both heat treatment and the presence of EGCG. However, the foaming characteristics of H80-E were observed to be less favorable compared to those of U650-E, which can be attributed to the decreased surface hydrophobicity and diminished free sulfhydryl group content exhibited by H80-E. This study demonstrates that WPI-EGCG conjugates prepared by HAT have more potential for application in hypoallergenic or functional foods.