Influence of ecophysiological factors on growth, lag phase and ochratoxin A production by Aspergillus niger aggregate strains in irradiated corn grains

Ochratoxin A (OTA) is one of the most important mycotoxins of worldwide concern for human health. The aims of this study were to evaluate the effects of water activity, temperature, incubation time and their interactions on growth, lag phase and OTA production by two strains belonging to A. niger aggregate in irradiated corn grains. This study shows that OTA production on corn grains occurs within a more restricted range of water activity and temperature than fungal growth. This point is important in order to maintain the appropriate conditions in stored corn that prevent toxigenic fungal growth and thus OTA production. Irradiated corn grains were re-hydrated to 0.910–0.995 of aW with sterile distillate water. The temperatures assayed were 15, 25 and 30 °C. Growth assessment was made every day during the incubation period (21 days) to calculate the growth rate, lag phase and the OTA production at 7, 14 and 21 days. Both strains showed optimum growth at 30 °C at 0.951 aW. Ochratoxin A production occurred over a range of temperatures (15–30 °C) with optimum production at 25 °C depending on aW assayed. Maximum OTA production was obtained for both strains at 0.973 aW. The results obtained suggest that the storage of corn grains at water activities lower than 0.951 and 15 °C should prevent these fungal species growth and OTA production during 21 days approximately.