Inhibitory Effect Of Essential Oil On Aspergillus Flavus Growth And Aflatoxin Production In Stored Maize

Aspergillus flavus and Aspergillus parasiticusare can able to produce toxic secondary metabolites : aflatoxins in food and feed stuffs. Aflatoxins are potent carcinogenic, teratogenic, mutagenic and immunosuppressive mycotoxins that have received world wide attention. Besides, A. flavus can cause the food to spoil leading to enormous economic loss in international food trade. Plant extract components have been shown to inhibit aflatoxin production by inhibiting the growth of the fungi. The research methods and specific results are as following: 1. Contact assays method was used to compare three kinds of essential oils: cinnamaldehyde, citral and eugenol on A. flavus growth and aflatoxin production in YES media. Cinnamaldehyde has more inhibitory effect than the other two essential oils: eugenol and citral. The inhibitory effect of the oil is proportional to its concentration. It completely inhibited the A. flavus at 100 μg/m L, while eugenol and citral had the same effect at 500 μg/m L. 2. To further elucidate the mechanism of action, their inhibitory effects on the expression of aflatoxin biosynthetic genes: afl R、nor-1、ver-1、omt A and afl T were evaluated by real-time PCR. Down regulation of five aflatoxin biosynthetic genes were significant in cinnamaldehyde treatment, followed by eugenol and citral, which in turn reduced the AFB1 production. For 50 μg/m L of cinnamaldehyde, ver-1 was highly down-regulated(average of 5963 folds), followed by omt A and afl R. For 100 μg/m L of eugenol, omt A was highly down-regulated(average of 2061 folds), followed by ver-1 and afl R. For 125 μg/m L of citral, afl T was completely inhibited, followed by ver-1 and omt A. 3. When the moisture content was 14%,the growth of A. flavus was effectively inhibited by cinnamaldehyde in a dose-dependent manner at 150-600 μg/m L. The mycelial growth of the A. flavus was totally inhibited at 600 μg/m L, while volatilization concentration of cinnamaldehyde was 96μL/L. And the inhibition rate of AFB1 was 97.98%. 4. The inhibitory effect of cinnamaldehyde was affected by moisture content of maize. At low moisture content, the growth of A. flavus was significantly inhibited, while the inhibition of AFB1 production was no significant. 5. Storage temperature had an impact on the inhibition effect of cinnamicaldehyde at 20-37 oC. The inhibition rate of cinnamaldehyde on A. flavus growth increased firstly and then decreased with the temperature increases, and the suitable temperature was 28 oC. While at 20 oC, the inhibition rate of cinnamaldehyde on AFB1 production was highest, with 91.00% of reduction. These results suggested that cinnamaldehyde may be a new practical fungistatic agent to control A. flavus growth and AFB1 production in stored grains and feeds.