Interaction of Whey Proteins with Phenolic Derivatives Under Neutral and Acidic pH Conditions

Integration of gallic acid (GA) and its derivative epigallocatechin gallate (EGCG; 20, 120, and 240 mol/g, protein basis) into whey protein isolate (WPI) at room temperature and pH 3.0 and pH 7.0 was investigated. At pH 7.0, both phenolics caused significant structural changes and EGCG induced greater digestibility of WPI. Total sulfhydryl in WPI decreased from 28.6 to 7.6 mol/g and surface hydrophobicity declined by nearly 50% with 240 mol/g EGCG at pH 7.0. Similar but less appreciable changes were produced by GA and at pH 3.0. Isothermal titration and fluorescence quenching tests showed moderately weak binding of WPI with GA but strong binding with EGCG at pH 7.0. Both phenolics at high concentrations lowered the thermal transition temperature of -lactoglobulin by 0.5 degrees C to 1.4 degrees C and promoted its digestion. The phenolics also displayed a remarkable synergism with peptides in the WPI digest exerting radical scavenging activity. Practical Application Structural modification of whey protein by gallic acid and epigallocatechin gallate and their association at acidic and neutral pH conditions promote in vitro protein digestion and elicit synergistic antioxidant activity of the mixed digest, making phenolic-treated whey protein an attractive ingredient in food processing over the acidic-neutral pH range.