Evaluation of aflatoxin B^sub 1^ and ochratoxin A in interacting mixed cultures of Aspergillus sections Flavi and Nigri on peanut grains

The influence of inoculum size on the colony-forming units, production of aflatoxin B^sub 1^ (AFB^sub 1^) and ochratoxin A (OTA) was determined when Aspergillus flavus and A. niger aggregate strains were cultured alone and in pairs on irradiated peanut grains at 28°C and 0.97 water activity (a^sub W^). The results showed a marked influence of inoculum factor on fungal counts, AFB^sub 1^ and OTA production in single and paired cultures. Fungal counts of the A. niger aggregate strain in interacting cultures at 7, 14 and 21 days of incubation were significantly higher than those observed in the A. flavus strain, except in the mixed culture with 10^sup 2^ spores/ml of both strains. In all mixed culture assays, the AFB^sub 1^ production was significantly reduced in comparison with the accumulation of mycotoxin in single cultures. A total inhibition in AFB^sub 1^ production was observed in some interactions as 10^sup 2^ spores/ml of A. flavus and 10^sup 3^ spores/ml of A. niger aggregate strain at 7 and 14 days, among others. With regard to OTA production, a stimulation in the interacting cultures was observed at all inoculum sizes and incubation period. The highest levels of OTA accumulation were observed at 14 days for all interacting cultures. The maximum level was reach in the culture 10^sup 3^ spores/ml of A. niger aggregate and 10^sup 4^ spores/ml of A. flavus (p