ZIF-8/TOCNF carrier coated with pectin “gatekeeper” for pH/enzyme dual-responsive releasing of carvacrol and its preservation effect on fruits

Developing stimuli-responsive on-demand release systems is very important to effectively suppress microbial infections and excessive food decomposition. However, the commonly designed controlled release systems with a single responsiveness cannot accurately response to environmental changes in food packaging scenarios. Herein, a pH/enzyme dual-responsive active packaging was fabricated based on in situ growth of ZIF-8 nanoparticles (ZIF-8 NPs) on TEMPO-oxidized cellulose (TOCNF) film and loading with carvacrol (CAR), after that electrostatic adsorbing pectin as "gatekeeper" for fruit preservation. The developed CAR@ZIF-8/TOCNF/Pec film was able to respond to acidic condition and pectinase produced by microorganisms in the case of fungal infections during food storage, thus possessing a dual-responsive controlled-release function. The release rate of CAR reached approximately 86.83 ± 1.82 % at pH = 5.0 and reached 88.65 ± 1.86 % in the presence of pectinase (1.0 mg/mL) after 168 h. In addition, the CAR@ZIF-8/TOCNF/Pec film performed superior inhibition efficacy against Escherichia coli, Staphylococcus aureus, and Aspergillus niger. The CAR@ZIF-8/TOCNF/Pec film were highly effective in preserving the freshness of fungus-inoculated raspberries and mangoes, and inhibited the spread of fungal spores during storage for 5 and 7 days, respectively. Therefore, this work provided a promising, smart and eco-friendly strategy for on-demand and precise release of bioactive ingredients during food storage and preservation.