Antifungal and antiaflatoxigenic properties of naphthoquinones toward Aspergillus flavus and their mode of inhibitory action on aflatoxin biosynthesis

Aflatoxins, currently thought to be the strongest natural carcinogens widely found in a variety of foods and feedstuffs, cause significant health problems to humans and animals alike. Prevention strategies for aflatoxin contamination are important for food safety issues, and control methods are continuously being developed and improved. In this study, the antifungal effects of six 1,4-naphthoquinones (1,4-NQ) on Aspergillus flavus growth were measured and it was confirmed whether similar structural moieties produced similar level of antifungal effects and whether these antifungal activities would be related to the presence of aflatoxin-producing ability in Aspergillus spp. Among the treated 1,4-NQs, only 5-hydroxy-2-methyl-1,4-NQ showed potent inhibitory effect on aflatoxin production with strong antifungal effects. Regarding 2-methyl-1,4-NQ, antifungal effects were observed, but aflatoxin production increased when the treated concentration of 2-methyl-1,4-NQ increased. The inhibitory effect of 5-hydroxy-2-methyl-1,4-NQ on aflatoxin production was primarily resulted in inhibiting the expression of aflC, which is codes for the enzyme polyketide synthase involved in the early stages of the aflatoxin biosynthesis pathway. Furthermore, 5-hydroxy-2-methyl-1,4-NQ inhibits erg28 expression, which codes for 14-α-demethylase, a precursor for ergosterol synthesis in fungal membrane components. For future practical uses, it is essential to study the efficacy of 5-hydroxy-2-methyl-1,4-NQ in storage containers on food systems and safety profile on mammalian system.