Phage-derived Hol49_Lys19/sodium alginate/chitosan composite green coating: Preparation, performance and preservation effect on refrigerated salmon

Refrigerated aquatic products are prone to microbial spoilage, while traditional preservation methods have insufficient antibacterial activity or residual risks. To address these issues, this research fabricated a novel composite preservative coating using matrix composed of chitosan (CS) and sodium alginate (ALG), together with bioactive antibacterial phage-derived holin–endolysin(Hol49_Lys19, HL) fusion protein. Structural characterization using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction confirmed that HL formed stable interactions with CS/ALG, and resulted in a dense and uniform structure. The coating exhibited enhanced mechanical properties (tensile strength = 75.5 ± 3.8 MPa), thermal stability (T max  = 286.5 °C), and moisture barrier capacity (water vapor transmission rate = 68.49 g/(m 2 ·d)). It inhibited the growth of 99.97% Aeromonas hydrophila compared with the control and excellent biocompatibility (cell viability >88%). The application of the coating onto refrigerated salmon (4 °C) effectively inhibited microbial proliferation (total viable count <7 Log 10  CFU/g at 12 days), lipid oxidation (thiobarbituric acid reactive substances ≤1.35 mg malondialdehyde/kg), and protein decomposition (total volatile basic nitrogen = 20.72 mg/100 g at 12 days), and it maintained pH stability, high water-holding capacity, and texture integrity. The coating extended the salmon shelf life by at least 6 days. This study integrates the physical barrier of natural polysaccharides with the targeted antibacterial activity of phage-derived proteins, and provides a green and efficient solution to preserve aquatic products and advance the application of phage-derived substances in the food industry.