A rapid identification method for aflatoxin-producing strains of Aspergillus flavus and A. parasiticus by ammonia vapor

The colony reverse of aflatoxin (AF)-producing strains of Aspergillus flavus and A. parasiticus turned pink when their cultures were exposed to ammonia vapor. The color change was visible for colonies grown on media suitable for AF production such as potato dextrose, coconut, and yeast extract sucrose agars after 2 d incubation at 25°C. Of the 120 strains of A. flavus, A. parasiticus, and two related species in A. flavus group: A. oryzae and A. sojae tested in this study, only the AF-producing strains of A. flavus and A. parasiticus showed the pink pigmentation. The color change occurred immediately after the colony was contacted with ammonia vapor. This method was useful for rapid screening the AF-producing strains of A. flavus and A. parasiticus.