Ultrasound enhanced the conjugation of epigallocatechin gallate on whey protein isolate and its influence on the emulsifying property and allergenicity

The formation of EGCG-WPI conjugates (EW) resulted in a decrease in free amino groups and thiol groups in WPI, accompanied by an increase in size and thermal stability. Consequently, this conjugation inhibited the immunoglobulin E (IgE) binding capacity and improved the emulsifying properties of WPI. Furthermore, ultrasound facilitated the interaction by producing larger size of conjugates (U-EW), increasing the binding affinity from 5.8 × 10⁵ M^-1 to 1.7 × 10⁶ M^-1 and the polyphenol bound equivalent from 80.4 ± 1.3 mg/g to 98.2 ± 1.9 mg/g compared to EW. It induced the greater changes in the secondary structure and surface hydrophobicity, thereby promoting greater participation of β-lactoglobulin (βLg) in conjugation with EGCG, and resulting in a higher inhibition rate of IgE binding capacity, an enhanced emulsifying property of U-EW. These findings will potentially expand the applications of WPI in the food industry.