Effects of Catechin Binding on the Structure, Emulsifying Properties, and Antioxidant Activity of Egg White Protein

Abstract

This study addressed the issues of easy aggregation and weak antioxidant capacity of egg white protein (EWP) in emulsion systems, aiming to simultaneously improve the emulsifying properties and antioxidant activity of EWP through non-covalent binding between EWP and polyphenols. Four catechin monomers with different structures—epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC), and epicatechin (EC)—were non-covalently bound to EWP, with catechin concentrations ranging from 0 to 180 µmol/g. Various properties of the EWP-catechin complexes were measured, including bound phenol content, intrinsic fluorescence spectroscopy, Fourier-transform infrared spectroscopy, surface hydrophobicity, particle size, Zeta potential, reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, emulsifying properties, and antioxidant activity. The aim was to investigate the effects of the non-covalent binding of the four catechin monomers on the structure, emulsifying properties, and antioxidant activity of EWP. The results showed that the bound phenol content of the complexes increased with the addition level of catechins. Under the same addition level, the bound phenol content was higher for the EWP-EGCG complex. The average particle size of the complexes initially increased and then decreased with increasing bound phenol content. At an additional level of 60 µmol/g, the particle sizes of the EWP-EGCG and EWP-ECG complexes were 140.43 nm and 135.86 nm, respectively. The Zeta potential of the complexes decreased with increasing bound phenol content, with the most significant effect observed for EWP-EGCG, decreasing from −4.82 mV to −14.80 mV. Compared to EWP, the emulsifying activity of EWP-EGCG and EWP-ECG increased by 2.05-fold and 1.25-fold, respectively, while their emulsifying stability improved by 1.08-fold and 0.67-fold, respectively. Meanwhile, the antioxidant activity of the complexes was effectively enhanced. The Fe3+-reducing capacity of both EWP-EGCG and EWP-ECG increased by 2.7-fold compared to EWP. The ABTS cation radical scavenging rate of EWP-EGCG and EWP-ECG improved by 44.3% and 46.5%, respectively, compared to EWP, while their DPPH radical scavenging rate increased by 16% and 14.4%, respectively. This study provides a theoretical basis for the development of protein ingredients with strong emulsifying stability and antioxidant properties, thereby advancing their high-value applications in functional foods and health products.