Synergistic citric acid cross-linked chitosan/sodium alginate films with porous starch-encapsulated thymol for sustainable pork preservation

To overcome the challenges of volatile active agents and the limited functionality of biopolymer-based packaging, a novel synergistic strategy was devised by constructing a biomimetic “organelle-cytoplasm-cell wall” system within a chitosan/sodium alginate (CS/SA) matrix. This was achieved by simultaneously incorporating citric acid as a covalent crosslinker and porous starch (PS) pre-loaded with thymol (THY) as a sustained-release organelle. The synergistic interplay between the robust cross-linked network and the PS-THY capsules endowed the composite film (CS-c-SA/PS-THY) with exceptional comprehensive properties: a 42.23% enhancement in tensile strength, an order-of-magnitude reduction in water vapor permeability (7.11 g/(m 2 ·24 h)), and a 23 °C increase in thermal decomposition temperature. Crucially, the film achieved sustained and controlled THY release that obeyed Fickian diffusion, which underpinned its potent, long-lasting antioxidant (75.82% DPPH scavenging) and antibacterial (inhibition zones >18 mm) efficacy. In practical pork preservation, the CS-c-SA/PS-THY significantly outperformed the control and the CS-c-SA/THY, effectively inhibiting microbial growth and quality deterioration to extend the shelf life by at least 4 days. This work provides a scalable and fundamental strategy for developing high-performance, sustainable active packaging.