Tunable thermosensitive-photothermal antibacterial film based on photothermal agent polycaffeic acid for preservation of Scomberomorus niphonius.

This study aims to solve aquatic product deterioration, defects of traditional preservation, and poor biocompatibility of synthetic photothermal agents. A natural thermo-responsive photothermal antibacterial composite film was developed, and a photothermal synergistic green preservation system for aquatic products was established. Polycaffeic acid (PCA) nanoparticles were synthesized via auto-oxidative polymerization, and composite films were prepared using methyl cellulose/methyl glucan as substrates. Their structure and properties were then systematically characterized. Fish preservation efficacy at 4 °C with photothermal assistance was investigated. Results showed that PCA exhibited a unique hexagonal prism structure, with a photothermal conversion efficiency of 38.74% and excellent cycling stability. The film loaded with 1.0 mg/mL PCA was determined to be optimal, which exhibited DPPH and ABTS radical scavenging rates of 60% and 45%, respectively. Bactericidal rates against Staphylococcus aureus and Escherichia coli exceeds 99%. After 8-day storage, fish pH was stable at 6.1, weight loss 11%, total volatile basic nitrogen 23 mg/100 g, thiobarbituric acid-reactive substances 0.5 mg/100 g. Using natural degradable materials and simple preparation, this study first developed PCA as a natural photothermal agent, solving compatibility and performance matching issues. The film inhibited deterioration via photothermal sterilization, physical barrier, and antioxidant protection, providing a new green approach for the food industry.