The effect of non-covalent interaction of chlorogenic acid with whey protein and casein on physicochemical and radical-scavenging activity of in vitro protein digests

The effects of the interaction of whey protein isolate (WPI) and casein (CS) with chlorogenic acid (CA; 20, 120 and 240 μmol/g protein) on the structural and functional properties of proteins were investigated. CA induced significant structural changes, increased digestibility, and improved functionalities of CS and WPI. Non-covalent association between CA and treated proteins was detected using Fourier transform infrared spectroscopy (FTIR), intrinsic tryptophan fluorescence, and ANS-augmented fluorescence. The CA binding affinity for WPI was superior to that for CS as indicated by higher Ksv and lower hydrophobicity. Total sulfhydryl content in CS and WPI decreased, respectively, from 5.4 to 3.2 μmol/g and from 21 to 7.8 μmol/g, and surface hydrophobicity declined by 16.6% and 22.4% with 240 μmol/g CA. Enhanced solubility and foaming capacity of the protein-phenol complex were demonstrated. CA at medium and high concentrations displayed a remarkable synergism of radical scavenging activity with peptides in both protein digests.