The Inhibitory Activity of Salicylaldehyde Compounds on Aspergillus Species and Their Effects on Aflatoxin Production and Crop Seed Germination

Crops such as tree nuts, corn and peanut are highly susceptible to infestation by the aspergilli Aspergillus flavus or Aspergillus parasiticus and subsequent aflatoxin (AF) contamination, a serious threat to public food safety. Conventional control of the aspergilli has been through the application of fungicides; however, certain fungicides at sub-optimal doses have been correlated with increased production of mycotoxins including AF. Natural products (NP) have been a potential source of antifungal agents. In this study, we performed risk assessment testing, for which thirteen NP/derivatives (generally recognized as safe) were examined at sub-inhibitory concentrations to determine the enhancement of AF production in aspergilli. We found that benzaldehyde derivatives or thymol (THY) enhanced AF production in aspergilli, while 4-isopropyl-3-methylphenol (4I3M), a synthetic analog of the NP THY and carvacrol, or salicylaldehyde (SLD) exerted a potent antifungal or mycotoxin-inhibitory effect. In seed testing (corn, pistachio kernels), SLD effectively prevented fungal growth as a fumigant, while 4I3M completely inhibited AF production at ≥1.0 mM. Therefore, we concluded that NP/derivatives that do not have any significant environmental impact can be a potent source of antifungal or anti-mycotoxigenic agents, either in their nascent form or as leads for more effective derivatives; however, NP should be applied at optimum concentrations to prevent the abnormal enhancement of mycotoxin production by fungi.