Differences Between Aspergillus flavus Strains in Growth and Aflatoxin B 1 Production in Relation to Water Activity and Temperature

The optimum and limiting conditions of water activity (a ) and temperature for growth of and aflatoxin B production by various Aspergillus flavus strains were determined. Agar media were used in which the a was adjusted by addition of sucrose or glycerine. Optimum temperatures for aflatoxin B production at high a varied with the strain tested being 13-16, 16-24, or 31 C. Strains with a low temperature optimum for aflatoxin B production showed fast growth at 37 C without aflatoxin B production. A reduced a (0.95 and less) together with a moderate or low temperature inhibited toxin production more than growth. However, at a high temperature one strain showed stimulation of aflatoxin B production on the glycerine medium at reduced a No differences were noted between aflatoxinpositive and aflatoxin-negative strains with respect to growth under various conditions.