Effect of Temperature, Water Activity, and Incubation Time on Growth and Aflatoxin Production by Aspergillus flavus and A. parasiticus on Niger seeds

Indianapolis, IN

Mycotoxins are toxic secondary metabolites produced by some fungi. Mycotoxin contamination posts high health risk for human and livestock. Aflatoxin B1 (AFB1), a highly toxic metabolite produced by some strains of Aspergillus flavus and Aspergillus paraciticus, represents one of the most widespread mycotoxins in agricultural commodities in the world. It is well known that mold growth and mycotoxin production are influenced by temperature, water activity, and incubation time. However, the environmental conditions that support AFB1 production on Niger seeds have not yet been extensively studied. In this project, the growth rates of the two fungi on Niger seeds with 0.86, 0.90, 0.94, and 0.98 water activities at 27 and 35oC were determined. Mycotoxin production on seeds was quantified using enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC). The results showed that at 35°C both fungi grew most rapidly on seeds with 0.94 water activity and the lowest growth rates were found on seeds with 0.86 water activity. At 27°C, the two fungi had similar growth rates on seeds with 0.90, 0.94, and 0.98 water activities, and lower growth rates were observed on seeds with 0.86 water activity. Highest AFB1 production was observed on seeds with 0.90 water activity at 27 or 35°C. This result will be useful for establishing guidelines for storing Niger seeds to minimize mycotoxin production.