Sterigmatocystin is a toxic metabolite structurally closely related to the aflatoxins, and consists of a xanthone nucleus attached to a bifuran structure. Sterigmatocystin is mainly produced by the fungi Aspergillus nidulans and A. versicolor. It has been reported in mouldy grain, green coffee beans and cheese although information on its occurrence in foods is limited. It appears to occur much less frequently than the aflatoxins, although analytical methods for its determination have not been as sensitive until recently, and so it is possible that small concentrations in food commodities may not always have been detected. Although it is a potent liver carcinogen similar to aflatoxin B1, current knowledge suggests that it is nowhere near as widespread in its occurrence. If this is the true situation it would be justified to consider sterigmatocystin as no more than a risk to consumers in special or unusual circumstances.
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