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 mu mol/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 K-sv. and lower hydrophobicity. Total sulfhydryl content in CS and WPI decreased, respectively, from 5.4 to 3.2 mu mol/g and from 21 to 7.8 mu mol/g, and surface hydrophobicity declined by 16.6% and 22.4% with 240 mu mol/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.