Structural changes and exposed amino acids of ethanol-modified whey proteins isolates promote its antioxidant potential

Whey protein isolates (WPI) were treated with different ethanol level (20, 40, 60, and 80%, v/v) to promote structural unfolding and subsequent aggregation. In general, protein aggregation gradually increased with increasing ethanol level in a dose-dependent manner, which was implied by notably increased turbidity and gradually decreased solubility. The formation of aggregates, which were confirmed by the results of circular dichroism spectrum and total sulfhydryl content, were promoted mainly through disulfide bonds and intra-molecular hydrogen bonds. Moreover, ethanol treated WPI (E-WPI) had significantly enhanced antioxidant activities over native WPI, which was mainly attribute to the higher contents of specific amino acids (such as hydrophobic amino acids, aromatic amino acids, and sulfur-containing amino acids), and E-WPI prepared with moderate ethanol concentration (40% in our present study) exhibited the highest antioxidant activities. These results reveal that antioxidant activities of WPI can be increased by ethanol treatment and are possibly achieved through molecular unfolding of native WPI.