Inhibitory effects of essential oils on the growth of grain storage molds and the formation of aflatoxin in stored organic corn grains

Background: Mold contamination in post-harvest grain storage degrades grain quality and produces mycotoxins, causing economic losses and health issues. This study evaluated the inhibitory effects of six essential oils (cinnamon, clove, eugenol, orange terpenes, oregano, and thyme oil) on total and specific mold genera growth using potato dextrose agar (PDA) and selective media plates, respectively, at different concentrations of EOs (0–0.8 mg/mL). The antifungal index (AI) of each treatment were measured after 7 days incubation at 22°C. The fungicidal activity of EOs in stored organic corn grains was tested using a simulated fumigation method, and the aflatoxin contents in the corn grains were determined biweekly for 6 weeks. Results: Results indicate that the tested EOs, except orange terpenes, significantly inhibited mold growth. Overall, eugenol demonstrated the highest effectiveness against total mold growth with cinnamon oil following closely behind. The cinnamon oil also consistently showed highest AI and lowest IC50 (0.065 mg/mL) against the growth of Aspergillus and Penicillium followed by clove oil with IC50 being 0.12 mg/mL. The Fusarium spp. was more sensitive to EOs, particularly cinnamon oil (IC50 = 0.006 mg/mL), and eugenol and oregano oil (IC50 = 0.01 mg/mL). In the simulated fumigation tests, cinnamon, oregano, and thyme oils at 0.05 mL/25 g corn significantly inhibited the mold growth and aflatoxin production at water activity 0.85, and temperature 25 and 35°C over a period of 42 days storage. Conclusion: The EOs tested in this study except orange terpenes can potentially serve as alternatives to toxic synthetic fungicides/fumigants for organic corn grain protection during storage.