Effects of temperature, water activity, and incubation time on production of aflatoxins and cyclopiazonic acid by an isolate of Aspergillus flavus in surface agar culture

An experiment with a full factorial design was used to study the elects of and interactions among temperature, water activity (a(w)), incubation period, and substrate on coproduction of aflatoxins (AF) and cyclopiazonic acid (CPA) by an isolate of Aspergillus flavus. Analysis of variance showed that there was a complex interaction among all of these factors and that this influenced the relative concentrations of the mycotoxins produced. The optimum temperatures for the production of AF and CPA were 30°C and 25°C, respectively. Both mycotoxins were maximally produced (0.306 to 0.330 μg of AF · ml of medium-1, 4.040 to 6.256 μg of CPA · ml of medium-1) at an a(w) of 0.996 and after 15 days of incubation. No AF were produced in either yeast extract agar or Czapek yeast autolysate agar medium at an a(w) of 0.90 at 20 or 37°C after 15 days (minimum conditions), while 0.077 to 0.439 μg of CPA · ml of medium-1 was produced under the same conditions. Yeast extract agar favored maximum AF production, and Czapek yeast autolysate agar favored maximum CPA production.