Effect of oxidative modification by reactive oxygen species (ROS) on the aggregation of whey protein concentrate (WPC)

The effects of reactive oxygen species (ROS) on the oxidative aggregation of whey protein concentrate (WPC) were studied. Increasing the oxidation time resulted in the accumulation of carbonyl groups, a decrease in α-helix structures, an increase in disordered structures and the aggregation of secondary structures. The surface hydrophobicity decreased and the zeta potential increased at the beginning of oxidation, indicating that electrostatic interactions were the cause of the noncovalent aggregation of the whey protein. Covalent aggregates were examined in terms of the sulfhydryl/disulfide content (total SH/SS), molecular weight and carbonyls, with the results implying that covalent interactions included protein-protein cross-linking, carbonyl cross-linking, and aromatic side chain cross-linking but excluded the cross-linking of sulfur-containing amino acid residues. The solubility and stability of initial aggregations were high due to flexible structures, while upon further oxidation, the solubility and stability worsened, consist with the soluble protein content and stability index.