Mycotoxin research sponsored by the Sorghum Millet CRSP

Aflatoxin and fumonisin hazards are associated with cancer, liver disease, immune suppression, retarded growth and development, nutritional interference, acute toxicity, neural tube defects, and death depending on the amount of toxin exposure and its duration. The symptoms depend upon the level of the toxin in the grain and the length of the exposure. The general perception is that sorghum is a safer grain to consume than is maize because the fungi that produce these toxins are rarer on sorghum and more common on maize (Leslie and Marasas, 2002; Leslie et al., 2005). INTSORMIL has worked with the International Institute of Tropical Agriculture (IITA) and the PROMEC unit of the Medical Research Council (MRC) in South Africa to test the hypothesis that the relative mycotoxigenicity of maize and sorghum grain differ.

INTSORMIL CRSP/IITA/Kansas State University (KSU) collaborative research has shown that locally grown maize is significantly more heavily colonized by aflatoxin-producing Aspergillus spp. than is either locally grown sorghum or millet, and that the average level of aflatoxin contamination is higher in maize than it is in the other two crops. The average aflatoxin contamination level in maize (36 ng/g) was four to eight fold higher than the contamination level in either sorghum (8.8 ng/g) or pearl millet (4.6 ng/g). The median amount of aflatoxin per sample, however, was similar for all three grains (4.2 ng/g, 5.0 ng/g and 4.4 ng/g respectively) suggesting that the major problem is with the more heavily contaminated samples. Of the 23 maize samples in the test, four exceeded the 20 ng/g internationally accepted guideline (FAO, 2004) recommended by CodexAlimentarius, as did two of the 40 sorghum samples but none of the pearl millet samples. In addition to having a higher proportion of samples that exceeded the guidelines, the maize samples that exceeded the guidelines also contained higher levels of aflatoxin than did the non-conforming sorghum samples.

The most effective way to reduce aflatoxin contamination is to prevent it from ever forming on foodstuffs. Maize planted in marginal regions usually encounters both heat and drought stress, two factors that predispose the grain to higher levels of aflatoxin. Cultivating indigenous sorghum or pearl millet crops, which are well adapted to both drought and heat stresses, in marginal environments would disproportionately reduce aflatoxin exposure, since maize with extreme levels of contamination should be encountered less frequently and since sorghum and pearl millet both have a much smaller risk of being contaminated with aflatoxin. The Fusarium spp. that colonize maize, sorghum and pearl millet also are known to differ now that the former "Fusarium moniliforme" is being broken down into biologically meaningful species (Seifert et al., 2003). Species common on maize, e.g., F. verticillioides and F. proliferatum, typically produce fumonisins (Leslie et al., 1992a,b), while species from sorghum and pearl millet, e.g., F. thapsinum, F. andiyazi and F. pseu-donygamai, are more likely to produce moniliformin (Leslie et al., 1996; Fotso et al., 2002), a toxin that has not been well-studied and has not been associated with any disease outbreaks in humans or domesticated animals (Desjardins, 2006).

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