Effects of chitosan-gentianic acid derivatives on myofibrillar proteins in sea bass (Lateolabrax maculatus) during refrigerated storage

Phenolic acid-chitosan derivatives have received extensive attention due to their greatly enhanced mechanical, antibacterial and antioxidant properties, especially in food preservation. The chitosan-gentianic acid (CS-g-GA) was prepared and its impact on myofibrillar proteins (MPs) in sea bass ( Lateolabrax maculatus ) during refrigerated storage was investigated in this study. Fish fillets were immersed in distilled water, CS, GA and CS-g-GA solutions, respectively, followed by an 18-day refrigerated storage. MPs were extracted from fish fillets every 3 days, and then the degree of oxidation and conformational changes of MPs were evaluated. The results of myofibril fragmentation index (MFI) and surface hydrophobicity confirmed that CS-g-GA can retard the fragmentation and degradation of myofibrils. Additionally, the total sulfhydryl content of CS-g-GA-treated samples in the later storage was significantly higher than those of other groups, confirming that CS-g-GA treatment protected the structure and function of protein. Results of Fourier transform infrared spectroscopy (FT-IR) and inner fluorescence intensity (IFI) showed that CS-g-GA maintained the secondary and tertiary structure of MPs. The results from scanning electron microscope (SEM) further clarified that CS-g-GA can maintain the tight arrangement of muscle fibers and protect the microstructure of myofibrils. Furthermore, the observation of confocal laser scanning microscopy (CLSM) demonstrated that CS-g-GA can prevent protein cross-linking and aggregation. Therefore, CS-g-GA treatment can effectively protect the structure and delay the oxidation of MPs.