Aflatoxins: Their Measure and Analysis

Abstract

Aflatoxins are natural secondary metabolites produced by some moulds (mainly Aspergillus flavus and Aspergillus parasiticus) and are contaminants of agricultural commodities in the field particularly in critical temperature and humidity conditions before or during harvest or because of inappropriate storage (Rustom, 1997; Sweeney & Dobson, 1998). Aflatoxins B1 (AFB1) and B2 (AFB2), producted by A. flavus, and aflatoxins G1 (AFG1) and G2 (AFG2), producted by A. flavus as well as A. parasiticus, can contaminate maize and other cereals such as wheat and rice, but also groundnuts, pistachios, cottonseed, copra and spices. Following the ingestion of contaminated feedstuffs by lactating dairy cows, AFB1 is biotransformed by hepatic microsomal cytochrome P450 into aflatoxin M1 (AFM1), which is then excreted into the milk (Frobish et al., 1986). Because of the binding of AFM1 to the milk protein fraction, in particular with casein (Brackett & Marth, 1982), it can be present also in dairy products manufactured with contaminated milk. The WHO-International Agency for Research on Cancer (IARC) has classified AFB1, AFB2, AFG1, AFG2 and since 2002 also AFM1 as carcinogenic agents to humans (group 1) (IARC, 2002). Considering their natural occurrence, it is impossible to fully eliminate their presence; so, coordinated inspection programmes aimed to check the presence and concentration of aflatoxins in feedingstuffs are recommended by the Commission of the European Communities. National and international institutions and organizations such as the European Commission (EC), the US Food and Drug Administration (FDA), the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) have recognized the potential health risks to animals and humans posed by consuming aflatoxin-contaminated food and feed. To protect consumers and farm animals regulatory limits have been adopted. The current maximum residue levels (MRL) for aflatoxins set by the EC (Commission European Communities, 2006a) are 2 μg/kg for AFB1 and 4 μg/kg for total aflatoxins in groundnuts, nuts, dried fruits and cereals for direct human consumption. These have been extended to cover some species of spices with limits of 5 μg/kg and 10 μg/kg for AFB1 and total aflatoxins, respectively. These levels are about five times lower than those adopted in the USA. Limits of 0.1 μg/kg are established by the EC for AFB1 in baby foods and dietary foods. The current regulatory limit for AFM1 in raw milk is 0.05 μg/kg, while in baby foods and dietary foods has been set at 0.025 μg/kg. Taking into account the developments in Codex Alimentarius, recently EC has introduced the maximum accepted levels for aflatoxins in other foodstuffs, like oilseeds (2 μg/kg for AFB1 and 4 μg/kg for total aflatoxins),