Bioactive PVA/SDES propolis extracts composite films for extending oyster shelf life: Structure, functionality, and preservation performance

Oysters are highly nutritious but extremely perishable due to rapid microbial growth and biochemical deterioration after shucking, leading to undesirable off-odor and textural degradation during storage. To address this challenge, a series of poly(vinyl alcohol) (PVA)-based composite films incorporating propolis polyphenols extracted using supramolecular deep eutectic solvents (SDES) were developed as multifunctional active packaging materials. Comprehensive characterization confirmed good compatibility between PVA and DES propolis extracts (DPT), as Fourier transform infrared spectroscopy and X-ray diffraction revealed strong hydrogen bonding interactions and reduced crystallinity in the composite films. The incorporation of DPT markedly enhanced functional performance, including outstanding UV-blocking ability (UV transmittance at 280 nm decreased from 68.2% to 4.6%), improved flexibility (elongation at break increased from 178.7% to 471.1%), and enhanced thermal stability (maximum degradation temperature increased from 285 °C to 360 °C). The PVA/DPT50 film also exhibited excellent antioxidant activity (77.4% DPPH radical scavenging) and strong antibacterial effects against E. coli and S. aureus . When applied to oyster preservation at 4 °C, the PVA/DPT40 film effectively inhibited quality deterioration by reducing lipid oxidation, suppressing microbial growth, and maintaining lower pH and TVB-N values after 10 days of storage. These results demonstrate that PVA/DPT composite films provide an efficient and eco-friendly strategy for extending the shelf life of highly perishable seafood products.