Interaction Mechanism of Bovine Myosin Oxidation Inhibition by Epicatechin Gallate: Insights from Molecular Docking and Thermodynamic Analysis

Protein oxidation is a critical factor governing meat quality. Although lotus seedpod proanthocyanidins (LSPC) can inhibit protein oxidation in beef during refrigerated storage, the underlying mechanism remains unclear. This study investigated the antioxidant activity and conformation impacts of epigallocatechin gallate (ECG), the principal active constituent of LSPC, on myosin from the perspective of molecular interactions. Isothermal titration calorimetry (ITC), molecular docking, and multispectral analyses were applied to characterize ECG–myosin interactions and unravel the mechanism underlying myosin oxidation inhibition. The results showed that ECG exerted a biphasic, dose-dependent effect on myosin conformation and related functional properties. At 10–30 μmol/L, ECG significantly enhanced the radical scavenging capacity of myosin and alleviated oxidative damage to amino acid side chains. Mechanistically, ECG bound spontaneously to myosin via entropy-driven hydrogen bond and hydrophobic interactions, inducing conformational rearrangement characterized by an α-helix-to-β-sheet transition, reduced surface hydrophobicity, and stabilization of secondary and tertiary structures, thereby inhibiting oxidative denaturation of myosin. However, at 40 μmol/L, ECG still retained antioxidant capacity toward myosin, while it increased surface hydrophobicity and reduced fluorescence intensity. These changes further aggravated the structural disorder, led to protein aggregation and microstructure damage, and ultimately caused the instability of myosin. These findings underscore the necessity of optimizing ECG dosage for reliable application in meat processing and provide experimental evidence supporting ECG and LSPC as natural antioxidants for meat systems.