Effects of covalent binding of different polyphenols on structure, rheology and functional properties of whey protein isolate

In this paper, conjugated four polyphenols (epigallocatechin gallate [EGCG], procyanidine [PA], apple polyphenol [AP], puerarin [PUE]) with whey protein isolate (WPI) was prepared under alkaline condition. The covalent interaction between polyphenols and WPI was confirmed by the determination of polyphenol binding equivalent. Fluorescence spectroscopy and fourier transform infrared spectra analysis were used to identify the changes in whey protein structure. The scanning electron microscopy data and the particle size distribution demonstrated surface changes and increases in the particle sizes of conjugates. Rheology analysis showed that the initial value of apparent viscosity and curve shape of all the samples have certain differences and exhibited a pseudoplastic behavior. Conjugation significantly improved foaming and emulsifying properties of the WPI, while its surface hydrophobicity was greatly decreased.These results provide a new basis of theory for the development of novel protein ingredient.