Chitosan–Sargassum fusiforme Polyphenol Edible Films: From Physicochemical and Bioactive Characterization to Shelf-Life Extension of Refrigerated Golden Pompano Fillets

The practical application of active food packaging materials is increasingly constrained by performance degradation and functional oversimplification. Although Sargassum fusiforme polyphenols (SP) possess potent antioxidant activity, their potential in edible films remains unexplored. In this study, the effects of incorporating varying proportions of SP (0.5–2.0%, w/v) into Chitosan–Sargassum fusiforme polyphenol edible films (CSFFs) on the physicochemical properties and preservative efficacy for chilled golden pompano fillets were investigated. SP incorporation was found to alter film structure and properties significantly. At SP concentrations ≥ 1.0%, reductions in tensile strength, elongation at break, and water vapor permeability were observed, along with increased opacity and enhanced UV-Vis light barrier capacity. SP concentration-dependent increases in DPPH and ABTS radical scavenging activities were revealed, and the CSFFs exhibited broad-spectrum antibacterial activity against six pathogenic strains. In preservation trials at 4 °C, the 2.0% SP coating yielded optimal results, with total bacterial count (5.63 log CFU/g) and total volatile basic nitrogen (18.45 mg/100 g) remaining below acceptable limits on day 15. Additionally, pH increase was inhibited, weight loss was reduced, and declines in hardness and springiness were prevented. Collectively, this study demonstrates that SP can serve as an effective functional component to enhance chitosan-based edible films, offering a scalable active packaging strategy for refrigerated aquatic product preservation.