In vivo control of Aspergillus flavus on stored rice by slow-release formulations of cinnamon and lemongrass oil

Abstract

Aspergillus flavus is one of the major storage fungi producing aflatoxins on stored grains. Consumption of such foods causes serious health problems in humans due to aflatoxin contamination. The use of plant essential oils is gaining increased attention due to their wide acceptance by consumers and their natural and safety and efficacy. In this study, cinnamon leaf oil and lemongrass oil were microencapsulated using chitosan to obtain controlled release of the oils. Essential oils were microencapsulated using ionotropic gelation method with sodium tripolyphosphate as the crosslinking agent. Both oils were obtained from the local market and analysed using GC-MS. The paddy samples (Bg11-11) were obtained from the Rice Research Institute Bathalgoda, Sri Lanka. A. flavus was isolated from an old rice sample and identified based on morphological and molecular characteristics. The minimum inhibitory dose and the minimum lethal dose of each oil against A. flavus was determined on stored rice. According to GC-MS analysis, the major constituents of cinnamon oil were eugenol (56.49%) and beta-caryophyllene (9.03%) whereas lemongrass oil has Citral-A (45.55%) and Citral-B (36.26%) as major constituents. According to the in-vivo assay, the antifungal activity of both free oils was higher than that of corresponding microencapsulated oils, indicating the controlled-release of oils from microcapsules. Cinnamon oil chitosan microcapsules (CNO-CS-MCs) showed higher antifungal activity against A. flavus than that of lemongrass oil chitosan microcapsules (LGO-CS-MCs). The minimum inhibitory dose of CNO-CS-MCs was 5 mg per 2×107 spores, and that of LGO-CS-MCs was 7.5 mg per 2×107 spores. The minimum lethal dose of CNO-CS-MCs was 12.5 mg per 2×107 spores. Furthermore, the inhibition duration of the fungi by CNO-CS-MCs was longer than that of LGO-CS-MCs, indicating the bioavailability of CNO-CS-MCs is higher than the LGO-CS-MCs. These slow-release formulations have a great potent as green pesticides against A. flavus on stored grains.