Chitosan-based composite film incorporated with soybean protein isolate and Auricularia auricular polysaccharide (SPI/CS/AAP) was modified by ultrasonic, microwave, ultraviolet (UV) or their combination to evaluate the effect of different modification methods on the film’s properties. The results showed that the mechanical properties and barrier properties of the film were improved by ultrasonic, microwave and UV modification treatments. Among them, the effect of ultrasonic-microwave synergistic modification was the most pronounced, resulting in the highest tensile strength (TS) and elongation at break (EAB) (21.67 MPa and 78.02%, respectively) and lowest water vapor permeability (WVP) and oxygen permeability (OP) (1.34 × 10^-12 g/(cm·s·Pa) and 0.47 × 10^-2 g/(m²·d), respectively). Furthermore, the synergistic modification could significantly increase the brightness, whiteness and light transmittance of the film. The composite film was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), revealing that the hydrogen bonding between the film matrix molecules was strengthened by ultrasonic, microwave and UV treatments, and the modified film exhibited a dense and stable network structure and improved thermal stability.

In this study, the effects of different freezing methods namely air freezing, cryogenic freezing, freezing after dipping in a refrigerating medium consisting of 20% ethanol (V/V), 20% propylene glycol (V/V), 5 g/100 mL trehalose aqueous solution and freezing after dipping in anhydrous ethanol on the quality of sea bass were investigated. The results showed that the freezing rates of refrigerating medium freezing and anhydrous ethanol freezing were 8.20 and 6.25 cm/h, which were 32.80 and 25.00 times as high as that of air freezing, respectively. The microstructure of frozen sea bass showed that the small ice crystals formed between muscle tissues were small, and the muscle fibers were closely arranged. Refrigerating medium freezing was more conducive to maintaining the water-holding capacity (WHC) of muscle tissues and slowing down the migration of immobilized water, and had a significant effect on maintaining the freshness, texture properties and protein thermostability of fish fillets. In summary, refrigerating medium freezing can effectively slow down the quality deterioration of frozen sea bass. The results of this study will provide a theoretical and practical basis for improving the storage quality of frozen aquatic products.