Chemistry and Occurrence

The aflatoxins (AFs) were discovered as the causative agent of turkey X disease, which resulted in the death of thousands of turkey poults, ducklings, and chicks fed a contaminated peanut meal. Chemically, the AFs are a highly substituted coumarin moiety containing a fused dihydrofurofuran moiety. Four major AFs designated Bi, B2, Gi, and G2 are produced by A. flavus and A. parasiticus. AFB1 and AFB2 were named because of their strong blue fluorescence under ultraviolet light, whereas AFGi and AFG2 fluoresced greenish-yellow.

Commodities most often shown to contain AFs are peanuts, various other nuts, cotton seed, corn, and rice. Human exposure can occur from consumption of AFs from these sources and the products derived from them, as well as from tissues, eggs, and milk (AFM1) from animals that have consumed contaminated feeds. When contamination occurs, AFB1 generally predominates. Although contamination by the molds may be universal within a given geographical area, the levels or final concentrations of AFs in the grain product can vary from less than 1 ppb to greater than 12,000 ppb. It is important to note that obvious contamination of a commodity with A. flavus or A. parasiticus does not necessarily indicate the presence of AFs, and the appearance of a sound, unin-fected sample of commodity does not preclude the existence of significant quantities of AFs.

Widespread concern regarding the toxic effects of AFs in humans and animals and possible transfer of residues from animal tissues and milk to humans has led to regulatory actions governing the interstate as well as global transport and consumption of AF-contaminated food and feed commodities. The US Food and Drug Administration has set the action levels of AF in commodities. For feeding mature nonlactating animals, the action level is 100 ppb; for commodities destined for human consumption and interstate commerce, it is 20 ppb; and for milk it is 0.5 ppb.

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