Effects of temperature, water activity and incubation time on fungal growth and aflatoxin B1 production by toxinogenic Aspergillus flavusisolates on sorghum seeds

Sorghum, which is consumed in Tunisia as human food, suffers from severe colonization by several toxigenic fungi and contamination by mycotoxins. The Tunisian climate is characterized by high temperature and humidity that stimulates mold proliferation and mycotoxin accumulation in foodstuffs. This study investigated the effects of temperature (15, 25 and 37°C), water activity (aw, between 0.85 and 0.99) and incubation time (7, 14, 21 and 28d) on fungal growth and aflatoxin B1 (AFB1) production by three Aspergillus flavusisolates (8, 10 and 14) inoculated on sorghum grains. The Baranyi model was applied to identify the limits of growth and mycotoxin production. Maximum diameter growth rates were observed at 0.99awat 37°C for two of the isolates. The minimum awneeded for mycelial growth was 0.91 at 25 and 37°C. At 15°C, only isolate 8 grew at 0.99aw. Aflatoxin B1 accumulation could be avoided by storing sorghum at low water activity levels (≤0.91aw). Aflatoxin production was not observed at 15°C. This is the first work on the effects of water activity and temperature on A. flavusgrowth and AFB1 production by A. flavusisolates on sorghum grains.