Development of EVA and LLDPE polymer-based carvone and spearmint essential oil release systems for citrus postharvest diseases applications

Abstract

Carvone and spearmint essential oil vapours are suitable candidates for the control of citrus postharvest pathogens due to their strong antifungal activity. However, the high volatility of essential oils remains a hurdle that needs to be overcome before it can be applied as an alternative fungicide. This work investigates the antifungal activity of 20 and 30 wt-% spearmint essential oil or carvone, incorporated into ethylene–vinyl acetate (EVA) and linear low-density polyethylene (LLDPE) strands postharvest pathogens affecting kumquats. Following the melt-extrusion process, an average yield of 16–29 % and 15–28 % of the total carvone and spearmint essential oil, respectively, was determined in the polymer strands. Morphological studies using scanning electron microscopy (SEM) revealed the presence of microporous structures in the internal structure of the strands. The membrane-like skin that covers the polymer strand was also confirmed by SEM. Variations in the release rates were observed between carvone and spearmint essential oils, which was attributed to the difference in the vapour pressure of the neat essential oils. Furthermore, in this study, the results demonstrated that the diffusion exponent ‘n’ of the Korsmeyer–Peppas, Weibull and Log-logistic models exceeded 1.0. In most cases, the Super Case II mechanism was observed. In the case of the Mapossa model, as k2 was ˃> 1, it implies that the outer skin-like membrane covering the polymer strand fully controlled the carvone release. The application of the essential oil-loaded polymer strands resulted in a significant reduction in deterioration, caused by citrus postharvest pathogens, of kumquats kept at room temperature for 21 days. This study indicates that the incorporation of spearmint essential oil or carvone into LLDPE or EVA polymer strands promoted the preservation of kumquat over a 21-day period.