Activated release of chlorine dioxide gas from polyvinyl alcohol microcapsule (ethylcellulose/sodium-chlorite) hybrid films for active packaging of litchi during postharvest storage

Current methods of preserving fruit and vegetables are costly with accompanying health risks from preserver residue. ClO2 gas preservatives can regulate the respiration and transpiration of fruit and vegetables, kill bacteria and fungi on their surface, and prolong their postharvest shelf life. Low concentration ClO2 gas preservative will not cause safety problems and is a novel gas preservative. In this study, ethylcellulose (EC) was used as a shell material to encapsulate aqueous NaClO2 to obtain EC-NaClO2 microcapsules with core-shell structures. The microcapsules were inlaid in polyvinyl alcohol (PVA) film, and citric acid in the PVA film enters the microcapsules with water vapor, reacts with NaClO2 and releases ClO2 gas. Film-forming properties of the PVA/EC-NaClO2 film-forming fluids were evaluated considering their viscosity and viscoelastic properties. The mechanical and gas barrier properties of the films were most suitable for the preparation of litchi storage bags when the microcapsule content was 6.0 wt%. Furthermore, the highest ClO2 concentration in the storage bags was 263.22 ± 12.34 mg m−3, which could kill etiological bacteria (E. coli and L. monocytogenes) and inhibit the growth of B. cinerea. The storage bags can extend the post-harvest shelf life of litchis and maintain their sensorial properties, such as color, moisture, hardness, weight, anthocyanins and pH. Therefore, our analysis indicates that the proposed PVA/EC-NaClO2 active package films exhibit significant potential for applications in the field of fruit and vegetable postharvest storage.