Chemical and Thermodynamic Characterization of Antioxidant Emulsifiers: The Case of Complex of Sodium Caseinate with EGCG
Tang, Wei, Minghui Li, Christos Ritzoulis, Yefeng Liu, Yuting Ding, Weilin Liu, and Jianhua Liu
In this study, complexes formed by sodium caseinate (CS) and different concentrations of (−)-epigallocatechin-3-gallate (EGCG) were successfully prepared. The structures of the CS–EGCG complexes were then analyzed by fluorescence spectroscopy, circular dichroism, and Fourier transform infrared spectroscopy (FTIR). Their thermodynamic features were also analyzed by Van’t Hoff equation before evaluating antioxidant properties as well as emulsion stability. The results showed that EGCG grafting significantly altered the CS structure, primarily due to their interactions. However, besides the covalent bonding within CS–EGCG, thermodynamic analysis further highlighted the presence of slight interactions driven by hydrophobic and entropic changes. The EGCG grafting also decreased the surface hydrophobicity of CS while increasing its solubility, thus improving the stability of the protein in water. Finally, the grafting process significantly improved the thermal and emulsifying stability of CS as well as its antioxidant properties, especially 3-ethylbenzothiazoline-6-sulfonic acid and 2,2-diphenyl-1-picrylhydrazyl scavenging properties and ferric ion reducing power. These findings can contribute to the study of protein and polyphenol interactions in food fields.
protein and polyphenol interactions