Evaluation of antioxidant modification on the functional and structural properties of EWP conjugates

The aim of this present study was to improve the oxidative stability of egg white protein (EWP) through catechin (CT) and epigallocatechin gallate (EGCG) covalent modification via an alkaline method at pH 9.0. Effects of CT and EGCG conjugation on the antioxidant activities, physicochemical and structural properties of EWP were comprehensively studied. The results indicated that CT and EGCG modification altered the isoelectric point value of EWP to lower pH, thus the solubility of EWP conjugates at pH 3.8 decreased, especially after EGCG conjugation. In addition, the antioxidant activities of EWP–CT and EWP–EGCG conjugates were 2.88 and 3.52 fold (2-diphenyl-1-picrylhydrazyl radical scavenging activities), 2.60 and 7.91 fold (ferric reducing powers) higher than that of the unmodified EWP. Moreover, the CT or EGCG conjugation resulted in an increase in alpha-helix formation with a decrease in the β-sheet formation, indicating that the secondary structure of EWP became more compact after CT or EGCG modification, and Trp and Tyr residues were involved into the conjugation reaction of EWP with CT or EGCG. Furthermore, CT and EGCG conjugation obviously improved the emulsifying stability of EWP, due to the improvement of the antioxidant activity after being modified by the CT or EGCG. In conclusion, CT or EGCG conjugation with EWP via an alkaline method was an effective way to improve the utilization value of EWP.