Aflatoxin Biosynthesis and sclerotial development in aspergillus flavus and aspergillus parasiticus

Abstract

Aflatoxins are a family of fungal secondary metabolites. They are produced by species in the genus Aspergillus. The commonly recognized producers of aflatoxins include A. flavus, A. parasiticus, A. nomius, A. tamarii, A. pseudotamarii, A. bombycis, and A. ochraceoroseus (Cary et al. 2005). Aflatoxin contamination of agricultural commodities can arise from field conditions conducive to fungal growth before harvest as well as from improper storage of foods and feeds. A. flavus and A. parasiticus are the most important aflatoxigenic species. While both can produce aflatoxins, the majority of A. flavus isolates produce aflatoxins B1 and B2 although some strains have been reported to also produce aflatoxins G1 and G 2. In contrast, A. parasiticus produces all four types of the aflatoxins. The toxic, carcinogenic, mutagenic, and teratogenic effects of aflatoxin B1 on humans and animals have been studied in great detail. Aflatoxin B1 has been linked to a specific G to T transversion in the codon 249 in the p53 tumor suppressor gene in primary human hepatocellular carcinoma. The International Agency for Research on Cancer (IARC) has designated aflatoxin as a human liver carcinogen (Wogan 2000). To minimize potential human exposure to aflatoxins, maximum levels of aflatoxins in many commodities have been set (Wu 2004). Forty-eight countries have specific regulations limiting total aflatoxins in foodstuffs, a further 21 having regulations for aflatoxins in feedstuffs (FAO 1995). Regulatory guidelines of the U.S. Food and Drug Administration (FDA) prevent the sale of commodities if contamination by aflatoxins exceeds allowed levels. The FDA has set limits of 20 ppb total aflatoxins for interstate commerce of food and feedstuff and 0.5 ppb aflatoxin M1 in milk. The European Commission has set the limits on groundnuts subject to further processing at 15 ppb for total aflatoxins and 8 ppb for aflatoxin B1, and for nuts and dried fruits subject to further processing at 10 ppb for total aflatoxins and 5 ppb for aflatoxin B1. The aflatoxin standards for cereals, dried fruits, and nuts intended for direct human consumption are even more stringent, and the limit for total aflatoxins is 4 ppb and 2 ppb for aflatoxin B1 (Otsuki et al. 2001). © 2010 Springer-Verlag Berlin Heidelberg.