Aflatoxins: Mechanisms of Inhibition by Antagonistic Plants and Microorganisms

Aspergillus flavus and some other closely-related members of Aspergillus section Flavi especially A. parasiticus and A. nomius are common fungi that normally inhabit as saprobes in soils and on a wide variety of decaying organic matters (Samson, et al., 2000; Varga et al., 2010). Besides being an etiological agent of systemic aspergillosis and allergic reactions, A. flavus has received major attention due to its ability to produce the carcinogenic aflatoxins (AFs) (Hedayati et al., 2007). AFs are a group of structurally related compounds found worldwide in a wide array of food and feed crops including maize, peanuts, tree nuts and oilseeds. AF contamination of agricultural crops is a major concern due to economical losses resulting from inferior crop quality, reduced animal productivity and impacts on trade and public health. It has been estimated that about one-fourth of global food supply is contaminated annually with AFB1, the most toxigenic among AFs. Hence, an action level of 20 ppb for total AFs in foods for human consumption has been imposed by Food and Drug Administration (FDA) in the United States and by regulatory agencies in many other countries. The biosynthetic pathway of AF is one of the best known pathways of secondary metabolism in microorganisms (Trail et al., 1995). Our current understanding about chemistry and molecular biology of AF biosynthesis is a direct consequence of bioconversion experiments using several blocked mutants as well as successful cloning and characterization of the majority of the AF biosynthetic pathway genes (Georgianna and Payne, 2009). About 30 genes and related intermediates are involved in the production of AFs. To ensure global safety on food and feed supplies, extensive researches have been carried out to effectively control and manage AF contamination of crops. Conventional procedures have been used to prevent contamination process in crops before and after harvest, the majority of which are expensive, time consuming and with limited success. These technologies include crop rotation, use of fungicides, and alteration in planting time. The rapid expansion in our knowledge about inhibition of AF biosynthesis by plants and