Lysozyme-(-)-epigallocatechin gallate covalent conjugates: preparation, structure and functional properties

The development of multi-functional preservatives is a promising solution to food waste caused by microbial spoilage. Therefore, in the present study, lysozyme - (-)-epigallocatechin gallate (Ly-EGCG) covalent conjugates were prepared by a free radical grafting approach. The effects of EGCG concentration on the physicochemical, structural, antioxidant, and antibacterial properties of Ly-EGCG conjugates were investigated. The covalent coupling of Ly with EGCG was confirmed by the generation of new bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles, the decrease in fluorescence intensity (> 85%) shown by multispectral techniques, and the shift of the amide I band in the Fourier transform infrared (FTIR) spectra. Compared to Ly, after adding 0.7 mM EGCG, the thermal denaturation temperature of the Ly-EGCG conjugates was decreased to 68.84 °C, whereas the DPPH scavenging capacity (88.84 ± 0.42%) and total antioxidant capacity (0.94 ± 0.06 U/mL) were remarkably enhanced. The inhibitory effect of Ly-EGCG conjugates on E. coli and S. aureus could be effectively regulated by modifying the EGCG concentration. Furthermore, Pearson correlation analysis revealed a correlation between the structural and functional properties of Ly-EGCG conjugates. These results provide potential strategies for the development of food-grade, multi-functional preservatives.