Regulation of catechins with different structure characteristics on the physicochemical properties of casein and the...

Regulation of catechins with different structure characteristics on the physicochemical properties of casein were investigated, and the structure-activity relationship was further explored. All testing catechins effectively modulated the physicochemical properties of casein, and esterified catechins showed the stronger binding affinity to casein than non-esterified catechins. Catechins significantly altered the secondary and tertiary structures of casein. Fluorescence spectroscopy and thermodynamic analyses indicated that the fluorescence quenching mechanism of casein by the four catechins was static. The Gibbs free energies (ΔG) for the interactions between EC, ECG, EGC, and EGCG with α-casein were - 14.16, -25.41, -22.23, and - 24.48 kJ/mol, respectively. For β-casein, ΔG were - 17.91, -29.85, -17.34, and - 19.33 kJ/mol, respectively. All negative ΔG values suggested that the interactions between catechins and casein occurred spontaneously. At 297 K, the binding constants for catechins with α-casein followed the order: ECG (29.51 × 10³ L/mol) > EGCG (20.23 × 10³ L/mol) > EGC (8.13 × 10³ L/mol) > EC (0.31 × 10³ L/mol). For β-casein, the order was: ECG (177.83 × 10³ L/mol) > EGCG (2.51 × 10³ L/mol) > EC (1.41 × 10³ L/mol) > EGC (1.12 × 10³ L/mol). Molecular docking combined with multispectral analysis further demonstrated that hydrogen bonds, van der Waals forces, and hydrophobic interactions governed the interactions between catechins and casein, and hydrogen bonds were the predominant force. All results indicate that the amount of hydroxyl groups and the presence of galloyl group significantly affect the capability of catechins to interact with casein.