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mycotoxins

Monday 7 March 2005

Mycotoxin (from Gk. μύκης (mykes) "fungus") is a toxin produced by a fungus under special conditions of moisture and temperature. These fungi are aerobic (use oxygen) and microscopic and, moreover, may colonise many kinds of food from the field to the table. Mycotoxins can appear in food and animal feed as a result of fungal infection of the crop, for example Fusarium ear diseases in cereals, or the infection of stored products. Not all fungi can produce mycotoxins. In addition some fungi are able to produce mycotoxins only in special conditions such as at specific levels of moisture, stress and the correct temperature. Even those with the ability to produce mycotoxins may not produce them all the time. The absence of mycotoxins doesn’t ensure the absence of fungal spores, so it’s possible for fungi to ’appear’ when the temperature and humidity are right. In addition, the mycotoxins are very resistant to temperature treatments and to conventional food processes such as cooking, freezing etc.

Public concern over mycotoxins increased following some of the multi-million dollar "toxic mould" settlements of the late 1990s. The negative health effects of mycotoxins are a function of the concentration, duration of exposure and the subject’s sensitivities. The concentrations experienced in a normal home, office or school are typically too low to trigger a health response in occupants. The mycotoxins are not gaseous (non-volatile), but rather they are associated with the spores and hyphae. Exposure typically occurs when contaminated food is eaten, as for aflatoxins. In some cases this may include meat from animals that have themselves been fed contaminated feed.

Types

Major groups of toxins include:

- aflatoxins

  • Aflatoxins produced by Aspergillus species, they are largely associated with commodities produced in the tropics and sub-tropics, such as groundnuts, other edible nuts, figs, spices and maize. aflatoxin-B1, the most toxic, is a potent carcinogen and has been associated with liver cancer.

- ochratoxin-A

  • ochratoxin-A is produced by Penicillium verrucosum, which is generally associated with temperate climates, and Aspergillus ochraceus which grows in warm humid conditions. It is found as a contaminant of a wide range of commodities including cereals and their products, dried vine fruit and a wide range of beverages and spices. It causes kidney damage in humans and is a potential carcinogen.

- patulin

  • Patulin is associated with a range of fungal species and is found in mouldy fruits, vegetables, cereals and other foods. It is destroyed by fermentation and so is not found in alcoholic drinks. It may be carcinogenic and is reported to damage the immune system and nervous systems in animals.

- Fusarium toxins

  • Fusarium toxins are produced by several species of the genus Fusarium which infect the grain of developing cereals such as wheat and maize. They include a range of mycotoxins including the Fumonisins, which affect the nervous systems of horses and cause cancer in rodents, the Trichothecenes, including deoxynivalenol, and Zearalenone, the last two of which are very stable and can survive cooking. The trichothecenes are acutely toxic to humans, causing sickness and diarrhoea and potentially death.

References

- Pitt JI. Toxigenic fungi and mycotoxins. Br Med Bull. 2000;56(1):184-92. PMID: #10885115#