Self-enhanced multifunctional composite membranes based on metal-organic frameworks embedded with thymol nanoparticles for post-harvest preservation of fruits

Given the growing alarms about food safety hazards and the pollution caused by plastic packaging, biodegradable active packaging materials have garnered considerable attention in research circles. In this study, polysaccharide-based metal–organic frameworks were used to produce a composite packaging film as a non-polluting, biodegradable, and active food packaging material with sustained antimicrobial activity. More specifically, chitosan–proanthocyanidin (CS-PA) affixes were prepared by appending proanthocyanidins onto chitosan via free-radical grafting. ZIF-8 nanoparticles loaded with thymol (denoted as Thy@ZIF-8) were then incorporated into the network architecture of the CS-PA matrix. By utilizing intermolecular hydrogen bonds and Zn 2+ ligand interactions, a novel active packaging film was designed. The CS-PA/Thy@ZIF-8 composite film exhibited good microstructural and physicochemical properties. Significantly, the integration of Thy@ZIF-8 within the CS-PA matrix remarkably enhanced the UV-blocking capacity of the composite film and increased its elongation at break. Furthermore, it augmented the water resistance attributes of the film, decreased its water vapor transmission rate, and increased its thermal stability. The slow release of Thy endowed the CS-PA/Thy@ZIF-8 composite film with an excellent antioxidant activity, along with long-lasting antimicrobial performances against Escherichia coli and Staphylococcus aureus . Moreover, preservation tests showed that the CS-PA/Thy@ZIF-8 film slowed the spoilage of strawberries by inhibiting bacterial growth, extending the shelf life by 50% at 25 °C. A comparable freshness preservation effect was also observed in cherry tomatoes. These results demonstrate that the CS-PA/Thy@ZIF-8 film exhibits good application prospects as a novel biodegradable active packaging material for food preservation.