Phage-derived Hol49_Lys19/sodium alginate/chitosan composite green coating: Preparation, performance and preservation...

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/(m²·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 Log₁₀ 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.