Aflatoxins

Aflatoxins are naturally occurring mycotoxins that are produced by many species of Aspergillus, a fungus, most notably Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are toxic and among the most carcinogenic substances known (Hudler, 1998). After entering the body, aflatoxins may be metabolized by the liver to a reactive epoxide intermediate or be hydroxylated and become the less harmful aflatoxin M1. At least 13 aflatoxins have been identified including B1, B2, G1, G2, M1 and M2. The B aflatoxins fluoresce blue and the G aflatoxins fluoresce green in the presence of ultraviolet light. The M aflatoxins are present in milk products. Aflatoxin B1 is the most ubiquitous, most toxic and most well studied of the aflatoxins. Aspergillus spp. contamination occurs as a result of environmental stresses on plants such as heat, dryness, humidity or insect infestation. It can also occur if plants are harvested and stored in hot, humid environments. As a result, people who live in the regions of the world most prone to these conditions, sub-Saharan Africa and south-east Asia are at highest risk for aflatoxin poisoning. Aflatoxins were first discovered in England in 1960 when more than 10,000 turkeys and ducks died within a few months. Today, it is agreed that only four species of fungi produce aflatoxins. They are namely, Aspergillus flavus, Aspergillus paraticus, Aspergillus nomius, Aspergillus pseudotamarii (Ito et al., 2001). However, only Aspergillus flavus and Aspergillus parasiticus are economically important. Aflatoxins are produced when adequate substrate and favourable environmental conditions are present (tropical and subtropical climates, humid storage conditions). They usually appear on cereals (barley, corn, millet, oats, rice, sorghum, wheat), cottonseeds, peanuts, tree nuts and soybeans. Aflatoxins can be formed before harvest, but also during storage if the grain is improperly stored (Tangendjaja, 2002).