Effect of non-covalently bound polyphenols on the structural and functional properties of wheat germ protein

This study investigated the effects of epigallocatechin-3-gallate (EGCG), chlorogenic acid (CA), piceatannol (PIC) and ferulic acid (FA) on the conformational and functional properties of wheat germ protein (WGP). The WGP-polyphenol interaction was confirmed by native polyacrylamide gel electrophoresis and detection of polyphenol content in the complex. Among the four polyphenols, EGCG showed the highest binding affinity to WGP. Moreover, FT-IR analysis indicated that the polyphenols changed the secondary structure of WGP, inducing an enhancement in alpha-helix content and a reduction in β-sheet structure. Fluorescence spectrum analysis demonstrated the presence of polyphenols induced tertiary structure change of WGP, leading to the deconstruction and unfolding of protein. In addition, the main interaction force for WGP-EGCG was hydrogen bonding and van der Waals forces, and for WGP-CA complexes was electrostatic interaction, while interaction force for WGP-PIC and WGP-FA complexes were hydrophobic interaction. Moreover, the addition of polyphenols significantly increased the absolute value of zeta potential while decreased surface hydrophobicity and free sulfhydryl content of WGP. The solubility and functionality of WGP were mainly improved by CA and EGCG. The findings in this study suggest that WGP-polyphenol complexes have the potential to be applied as novel functional food ingredients.