Inhibitory effects of three monoterpenes from ginger essential oil on growth and aflatoxin production of Aspergillus flavus and their gene regulation in aflatoxin biosynthesis

Ginger (Zingiber officinale) essential oil (ZOE) possesses strong antibacterial and antifungal activities. In this study, the antifungal activity of ZOE against Aspergillus flavus was investigated, and a chemical analysis was carried out to identify compounds that control fungal growth. A total of 37 compounds were identified by gas chromatographic analysis with a mass detector, and the antifungal and antiaflatoxigenic properties of three constituents, γ-terpinene, isoborneol, and citral, against A. flavus were tested. All compounds exhibited strong antifungal activity at 1000 μg/mL, and the antifungal activity of γ-terpinene and citral remained until treatment with tenfold diluted solution. The decrease in aflatoxin production by the three compounds was observed until treatment with 10 μg/mL. To evaluate their antiaflatoxigenic activity, RT-qPCR was used to compare the expression of 11 genes involved in aflatoxin biosynthesis by A. flavus. Among the three compounds, γ-terpinene and citral markedly reduced the expression of most of the tested genes but a different pattern of downregulation of the expression was observed. γ-Terpinene did not downregulate aflR, aflS, and yap, whereas citral did not alter the expression of aflC and aflG. Therefore, γ-terpinene and citral may have the potential to control A. flavus growth and aflatoxin production in agricultural products, including at the storage stage.