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

Nyjer seeds are oil rich (35-40% oil content) seeds of the plant Guizotia 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 (B-1, B-2, G(1) and G(2)) by Aspergillus flavus and Aspergillus parasiticus on ground nyjer seed with 10% oil. The ground nyjer seeds were adjusted to different water activity a(w) levels (0.82, 0.86, 0.90, 0.94 and 0.98 a(w)) and incubated at 20, 27 and 35 degrees C, up to 30 days. Our results show that A. flavus and A. parasiticus had similar growth patterns in which the slowest fungal growth occurred on ground seeds with 0.86 aw at 20 degrees C. There was no fungal growth for either A. flavus or A. parasiticus at 0.82 a(w). The most rapid growth conditions for A. flavus and A. parasiticus were 0.94 aw at 35 degrees C, and 0.94 aw at 20 degrees C, respectively. Aspergillus flavus produced aflatoxins (13 mu g/kg aflatoxin B-1) only on seeds with 0.94 aw at 27 degrees C, while A. parasiticus produced high levels of aflatoxins under several conditions; the highest concentrations of aflatoxin B-1 (175 mu g/kg) and AFG(1) (153 mu g/kg) were produced on deoiled ground seeds with 0.94 aw at 27 degrees C. It is likely that storing ground deoiled nyjer seeds with a water activity up to 0.82 aw at 20 degrees C will reduce fungal growth aflatoxin production.