Growth and aflatoxin production by Aspergillus parasiticus in a medium at different pH values and with or without pimaricin.

A glucose-yeast extract-salt medium containing 0, 5, 7.5, 10, 15 or 20 micrograms pimaricin/ml with an initial pH of 3.5 or 5.5 was inoculated with Aspergillus parasiticus WB 108 and incubated at 15 degrees or 28 degrees C. The pH, weight of mycelium and amount of aflatoxin produced were determined after 3, 7, and 10 days and after 14, 21, and 30 days when incubation was at 28 degrees or 15 degrees C, respectively. Increasing the concentration of pimaricin in the medium with an initial pH of 5.5 decreased the amounts of aflatoxin B1 and G1 produced after 3 days of incubation. When the initial pH of the medium was 3.5, no growth or toxin production occurred after 3 days of incubation in the medium containing 7.5 micrograms or more of pimaricin/ml. The presence of 20 micrograms of pimaricin/ml inhibited growth and toxin production after 7 days of incubation. When cultures were incubated at 15 degrees C, there was a lag phase which extended from 9 to 16 days, and the amounts of aflatoxin produced decreased with an increasing concentration of pimaricin. Pimaricin did not completely inhibit the growth and aflatoxin production by A. parasiticus. Pimaricin, in combination with a low pH, low temperature or 4% or 6% NaCl, initially caused slow mycelial growth and low toxin production, but the mold overcame the inhibitory effects and produced substantial amounts of mycelium and toxin.