The relationship between fungi growth and aflatoxin production with ergosterol content of corn grains

Abstract

The relationships between fungal growth and ergosterol content and between aflatoxins B1 and B2 production and ergosterol content were verified in corn grains. In the first experiment, fungal growth and ergosterol content were monitored during incubation of corn grains presenting water activities of 0.85aw and 0.92aw at 25oC over a period of 18 days. For the Taiuba variety, the fungi growth and ergosterol content increased more rapidly for 0.92aw than 0.85aw. Maximum ergosterol levels were 2.8 and 4.6 µg/g, respectively, for 0.85aw and 0.92aw. For the Cargill hybrid 606, a more pronounced increase in fungal growth was verified just at the end of the incubation period, mainly for 0.92aw when an acentuated increase in ergosterol content was also observed. Maximum ergosterol levels detected were 1.6 µg/g and 5.8 µg/g, respectively, for 0.85aw and 0.92aw. There was a significant correlation between ergosterol content and log of CFU g-1 for 0.92aw but not for 0.85 aw. In the second experiment, samples of corn grains of the Taiuba variety at 0.87aw and 0.95aw were inoculated with a toxigenic Aspergillus flavus strain and incubated at 25oC. Ergosterol levels reached maximum values of 12.1 and 73.4 µg/g, respectively, for 0.87aw and 0.95aw. In both water activities, content aflatoxin B1 followed the same trend as ergosterol. For the aflatoxin B2 this trend was not observed. Ergosterol assay appears to be a useful test to measure fungal growth and to indicate the possibility of aflatoxin production in corn grains.