Effects and structure-activity relationship of different catechins on properties of myofibrillar protein from beef during frozen storage

Effects and structure-activity relationship of catechins with different structures on the properties of myofibrillar protein (MP) during frozen storage were investigated. Catechins including epicatechin (EC), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and epigallocatechin-3-gallate (EGCG) could reduce the particle size and solubility of MP, increased its surface charge and hydrophobicity, and inhibited protein unfolding and aggregation. Meanwhile, catechins reduced the contents of carbonyl, free amino, and free sulfhydryl groups of MP, and inhibited the oxidative damage of MP during freeze-thaw cycles. Moreover, catechins improved the physicochemical properties of MP gels after freeze-thaw cycles. Multispectral analysis and molecular docking indicated that catechins significantly altered the secondary and tertiary structures of MP due to their strong interactions including hydrogen bonding and hydrophobic interactions, and the action order was: EGCG > ECG > EGC > EC. These results indicated that the structural characteristics, such as the number and position of hydroxyl groups, as well as the presence of galloyl groups in the molecule, significantly affected effects of catechins on the structures and properties of MP during frozen storage. The hydroxyl group located at the 5′-position of the B-ring and the galloyl moiety attached at the 3-position of the C-ring in catechins played an important role in the molecular interactions between catechins and MP, which contributed to their high dipole moments and strong binding affinities with MP. All results suggest that catechins containing galloyl group (ECG and EGCG) showed the stronger power than catechins lacking galloyl group (EC and EGC) to improve the properties of MP during frozen storage.