Improvement of antioxidant, emulsification properties and thermal stability of egg white protein by covalent binding to gallic acid/tannic acid and xanthan gum

This study aimed to improve the functional properties of egg white protein (EWP) by covalent modification of EWP with xanthan gum (XG) and gallic acid (GA)/tannic acid (TA) to form covalent complexes. The structure and functional properties of EWP before and after modification were explored. The results showed that the grafting degree of EWP-GA-XG and EWP-TA-XG reached 37.23% and 44.01% respectively measured by the OPA method. The secondary structure of EWP became loose after reaction with GA/TA and XG, with a decrease in the content of α-helix and an increase in the β-sheet content, thus contributing to the improvement of its functional properties. The DPPH and ABTS radical scavenging rate and iron reduction ability of EWP-GA-XG (44.94%, 56.38%, 18.29 mg VC/μmol) and EWP-TA-XG (85.45%, 88.39%, 39.26 mg VC/μmol) complexes were significantly improved compared with EWP (7.90%, 12.94%, 0.12 mg VC/μmol). The emulsion activity index and emulsion stability index of EWP-GA-XG (10.05 m2/g, 96.43%) and EWP-TA-XG (11.04 m2/g, 96.53%) complexes were also improved as compared to those of EWP (5.94 m2/g, 51.45%). Moreover, the peak transition temperatures of EWP-GA-XG (138.09 °C) and EWP-TA-XG (143.96 °C) complexes were higher than that of EWP (125.00 °C). This study may provide the theoretical basis for improving the functional properties of EWP and expanding its application in the field of food.