Aflatoxinas

AFLATOXIN
JC Ritchie

Beneath those rugged elms, that yew-tree’s shade, Where heaves the turf in many a mouldering heap, Each in his narrow cell for ever laid, The rude forefathers of the hamlet sleep. Elegy Written in a Country Churchyard. Thomas Gray 1716–71.

In this famous poem Thomas Gray describes a hamlet’s dead forefathers quietly mouldering under ‘heaves’ of turf in a countrychurchyard. This represents a traditional view whereby moulds were principally associated with decay and disintegration of living matter following death. However, in recent years scientific investigations have revealed the wider economic, toxicological and public health importance of certain mould species. For example, it is now known that in some circumstances mould-infected foods can be associatedwith serious toxicity, and sometimes death. In this Chapter the toxicity of a group of compounds called aflatoxins are described in order to illustrate the importance of the toxins produced by moulds. Description, Occurrence, Uses Description Moulds are organisms belonging to the fungal kingdom. They are either saprophytic, growing on dead organic matter, or more rarely parasitic, existing on otherliving organisms. They are capable of growing on many substances of importance to man (eg foodstuffs,

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JC Ritchie

wood, clothing), their growth often being highly dependent on the presence of appropriate conditions of humidity and temperature. Some moulds are beneficial and economicallyimportant. These include the cultivated varieties used in cheese making which provide the distinctive aroma, taste and veining which makes these cheeses so attractive and delicious (eg Roquefort, Blue Vinney, Stilton). Penicillium is an example of another well-known mould made famous by Sir Alexander Fleming when he discovered the potential of penicillin, produced by the mould, as an antibacterialmedicine. However, many moulds are far from beneficial to man. They may damage stored food, clothing, leather, wood and other materials of economic importance. They may also cause extensive crop losses in the form of blights and rusts. Finally, they may pose health hazards by producing toxic substances called mycotoxins (from the Greek: mukes~mushroom, toxikon~toxic). The enormous public health andeconomic implications of mycotoxin contamination are illustrated by the fact that the Food and Agricultural Organisation of the United Nations estimates that up to 25% of the worlds food crops are affected by mycotoxins. Examples of mycotoxins include the ergot alkaloids produced when the ergot fungus grows on rye (responsible for outbreaks of a disease called ergotism, or St Anthony’s Fire),trichothecanes produced by Fusarium species (associated with alimentary toxic aleukia fatalities in the Second World War) and the aflatoxins. Aflatoxins are a group of chemically related mycotoxins which are produced by particular species of moulds. Their name derives from the fungus Aspergillus flavus on which much of the early work with these substances was performed (i.e. the genus Aspergillus, thespecies flavus and the suffix toxin). Subsequent research revealed that aflatoxins are produced by strains of A. flavus and strains of the related species A. parasiticus, A. nominus and A. niger. Furthermore, it was discovered that there are a number of distinct, but structurally related aflatoxin compounds — the four most commonly seen being designated B1, B2, G1 and G2. The B designation ofaflatoxins B1 and B2 resulted from the exhibition

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by these compounds of Blue fluorescence under the ultraviolet (UV)-light, whereas the G designation refers to yellow-Green fluorescence under UV-light. Aflatoxins M1 and M2, are hydroxylated derivatives of aflatoxin B1 and B2 that may be...