Chemical and thermodynamic characterization of antioxidant emulsifiers: The case of complex of sodium caseinate with EGCG

Abstract

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.

Effects of preheat treatment and syringic acid modification on the structure, functional properties, and stability of black soybean protein isolate

“…Tang et al. (2023) observed that hydrophilic hydroxyl groups in the phenol hydroxyl group could form hydrogen bonds with water molecules, potentially improving the hydrophilicity of the protein, which leads to stronger water‐protein interactions. Additionally, the steric hindrance of polyphenols might effectively inhibit protein flocculation (Arzeni et al., 2012).…”

“…The increased trend in protein solubility results from the hydration of polar groups on its peptide chain skeleton (Sui et al, 2018), which reflects changes in protein molecular structure, such as unfolding after SA addition (Table 2). Tang et al (2023) observed that hydrophilic hydroxyl groups in the phenol hydroxyl group could form hydro- gen bonds with water molecules, potentially improving the hydrophilicity of the protein, which leads to stronger water-protein interactions. Additionally, the steric hindrance of polyphenols might effectively inhibit protein flocculation (Arzeni et al, 2012).…”