Ultrasound-Assisted Gallic Acid–Embedded Edible Coating for Snakehead Fish Fillet Preservation: Enhanced Hydrophobicity, Mechanical Strength, and Antibacterial Activity

In this study, gelatin films incorporated with gallic acid (GA) were applied to retard the quality deterioration of fish fillets, and ultrasound treatments were employed to enhance the preservation efficacy. Results demonstrated that ultrasound-assisted coating treatment enabled the fillets to meet stricter processing standards (TVB-N < 15 mg/100 g) within 5 days. Specifically, TVB-N values decreased from 27.07 mg/100 g in the control group to 14.47, 11.20, and 10.27 mg/100 g under ultrasound powers of 60, 120, and 240 W, respectively. Furthermore, ultrasound treatment resulted in a more than threefold increase in GA migration, contributing to preservation performance with improved antibacterial activity. Synergy values against Psychrobacter sanguinis , a representative spoilage microorganism on snakehead, were 2.84 for US + 2 mg/mL GA and 4.20 for US + 3 mg/mL GA, respectively, demonstrating a pronounced synergistic effect. Meanwhile, the characterization of the composite material provided crucial insights into the effects of ultrasound, including the enhanced water barrier capacity and mechanical strength. This improvement was attributed to cavitation-induced exposure of hydrophobic groups, as confirmed by the increase in water contact angle from 54.1° to a maximum of 75.1°. Spectroscopic analyses revealed that ultrasound facilitated interactions and increased the crystallinity of the film matrix. However, excessive ultrasound treatment (240 W) led to disordered microstructures and damaged physical properties of films. These findings provide a theoretical foundation for expanding the application of ultrasound technology in food preservation, with enhanced efficacy while minimizing potential adverse effects.