This study investigated the effects of the interaction of walnut protein isolate (WPI) with epigallocatechin gallate (EGCG), chlorogenic acid (CLA), (+)-catechin (CA), and ellagic acid (EA) on the structural and functional properties of proteins. The results for polyphenol binding equivalents and content of free amino and sulfhydryl groups as well as those from sodium dodecyl sulfate‒polyacrylamide gel electrophoresis confirmed the covalent interaction between WPI and the polyphenols. The binding capacities of the WPI-polyphenol mixtures and conjugates were as follows: WPI-EGCG > WPI-CLA > WPI-CA > WPI-EA. Fourier transform infrared spectroscopy (FTIR) and fluorescence spectrum analysis identified changes in the protein structure. The conjugation process obviously increased the polyphenols' antioxidant properties and the surface hydrophobicity was substantially reduced. WPI-EGCG conjugates had the best functional properties, followed by WPI-CLA, WPI-CA, and WPI-EA. Lycopene (LYC) was loaded into nanocarriers by WPI-EGCG self-assembly. These results indicated that WPI-polyphenol conjugates can be utilized to develop food-grade delivery systems to protect chemically lipophilic bioactive compounds.
Supplementary information: The online version contains supplementary material available at 10.1007/s13197-023-05768-2.
Keywords: Dietary polyphenols; Lycopene; Nanocarriers; Properties; Walnut protein isolate.
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