Chitosan-grafted-caffeic acid combined with ultrasound inhibits the oxidation and degradation of myofibrillar proteins in pompano (Trachinotus ovatus) during ice storage

This study aimed to investigate the impact of chitosan-grafted-caffeic acid (CS-g-CA) and ultrasound (US) on myofibrillar proteins (MPs) in pompano (Trachinotus ovatus) during 24 days of ice storage. Fresh fish slices were treated with US (20 kHz, 600 W), CS-g-CA (G), and US combined with CS-g-CA (USG) for 10 min, respectively. Samples treated with sterile water served as study controls (CK). All samples were then stored in ice at 4 °C. The oxidation and degradation of MPs were evaluated at 4-day intervals. The results showed that US slightly accelerated the fragmentation of myofibrils, as confirmed by the increased myofibril fragmentation index (MFI). However, on day 24, the surface hydrophobicity (SH) of USG samples was 4.09 μg BPB bound/mg protein lower than that of G samples, and the total sulfhydryl content of USG samples was 0.50 μmol g-1 higher than that of G samples, suggesting that US could reinforce the antioxidant capacity of CS-g-CA. Regarding degradation of MPs, USG treatment maintained the secondary and tertiary structure of MPs by reducing the transition from ordered to disordered structures and by reducing the exposure of tryptophan residues. Sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS-PAGE) showed that the inhibitory effect of USG on protein degradation may be related to the binding of CS-g-CA to MPs. The results of scanning electron microscopy (SEM) further clarified the fact that the USG treatment can protect the myofibril microstructure by maintaining the compact arrangement of muscle fibers. Additionally, USG treatment could improve the sensory properties of pompano. Overall, the synergistic effects of US and CS-g-CA can effectively delay the protein oxidation and degradation. The results provided in this study are valuable for the quality maintenance of marine fish.