Influence of Temperature and Water Activity on Aflatoxin Production by Aspergillus flavus in Cowpea ( Vigna unguiculata ) Seeds and Meal.

Experiments were done to determine the influence of temperature (21, 30 and 37°C) and a (0.76 to 0.98) on aflatoxin production by Aspergillus flavus on cowpea ( Vigna unguiculata ) seeds, meal and meal supplemented with onion. Larger quantities of aflatoxin were produced at 21 and 30°C than at 37°C. The highest amount of aflatoxin (2777 μg/20 g, dry weight basis) was observed in meal containing onion at a 0.98 after 20 d of incubation at 21°C. A level of 870 |μg/20 g was detected in seeds at a 0.95 after 14 d of incubation at 30°C. Meal at a 0.96 supported production of 551 μg of aflatoxin per 20 g after 20 d at 30° C. Temperature had little influence on the optimal a for aflatoxin production in cowpea meal. However, an increase in temperature resulted in a decreased optimal a for aflatoxin production on whole cowpeas. When known quantities of aflatoxin were added to cowpea meal which was subsequently steamed for 5 min, only 29% was extractable using a variety of procedures, indicating that the toxin may be bound in some manner to cowpea constituents as a result of heat treatment.