Effect of aw and CO 2 level on Aspergillus flavus growth and aflatoxin production in high moisture maize post-harvest

Abstract

The potential for using modified atmospheres of 25–75% CO 2 (balanced with N 2) and water activity ( a w, 0.95, 0.92) to control Aspergillus flavus development and aflatoxin B 1 production has been evaluated (a) on synthetic medium and (b) on maize grain during storage for up to 21 days at 25 °C. On agar medium up to 75% CO 2 at both 0.95 and 0.92 a w significant inhibition of growth was obtained ( P < 0.05). In stored grain inoculated with spores of A. flavus there was significantly higher populations of the species at 0.95 a w than 0.92 a w. Up to 75% CO 2 resulted in an inhibition of the populations of A. flavus isolated from the grain. Contrasting aflatoxin B 1 production was obtained on agar and in stored maize grain. On agar, greatest amounts were produced at 0.92 a w, while more was produced at 0.95 a w on maize grain. Overall, the efficacy of controlled atmospheres × a w showed that treatment with 25% CO 2 could be sufficient to efficiently reduce A. flavus development but at least 50% CO 2 was required to obtain a significant reduction of aflatoxin synthesis.