Aflatoxin production byAspergillus flavus and Aspergillus parasiticus on deoiled ground nyjer seeds

Nyjer seeds are oil rich (35-40% oil content) seeds of the plantGuizotia abyssinica, which is closely related to sunflower. They are pressed mechanically for cooking oil in Ethiopia and elsewhere. The remaining deoiled cake, which contains approximately 10% oil is commonly used as animal feed. This study investigated the effect of water activity and temperature on the growth and aflatoxin production of the four main forms of aflatoxin (B1, B2, G1 and G2) byAspergillus flavus andAspergillus parasiticus on ground nyjer seed with 10% oil. The ground nyjer seeds were adjusted to different water activity aw levels (0.82, 0.86, 0.90, 0.94 and 0.98 aw) and incubated at 20, 27 and 35 °C, up to 30 days. Our results show thatA. flavus andA. parasiticus had similar growth patterns in which the slowest fungal growth occurred on ground seeds with 0.86 aw at 20 °C. There was no fungal growth for eitherA. flavus orA. parasiticus at 0.82 aw. The most rapid growth conditions forA. flavus andA. parasiticus were 0.94 aw at 35 °C, and 0.94 aw at 20 °C, respectively.Aspergillus flavus produced aflatoxins (13 μg/kg aflatoxin B1) only on seeds with 0.94 aw at 27 °C, whileA. parasiticus produced high levels of aflatoxins under several conditions; the highest concentrations of aflatoxin B1 (175 μg/kg) and AFG1 (153 μg/kg) were produced on deoiled ground seeds with 0.94 aw at 27 °C. It is likely that storing ground deoiled nyjer seeds with a water activity up to 0.82 aw at 20 °C will reduce fungal growth aflatoxin production.