Mycotoxins in Food and Feed
Mycotoxins (mould toxins) are secondary metabolites produced by moulds, smallest amounts of which have a toxic effect on vertebrates. Mycotoxins can either be located in the mycelium of the mycotoxin-producing moulds or be secreted into the surrounding environment.
Aflatoxin B1, B2, G1, G2
Aflatoxin B2 and G2 are doubly hydrated derivatives of aflatoxin B1 and G1. The index number 1 indicates that these are aflatoxins of extremely high toxicity, while aflatoxins with the index number 2 show no effect with some animal species. Indexes B and G indicate blue or green fluorescence in ultraviolet light. Aflatoxins are not only found in the hyphae and conidia of the aflatoxin-producing fungi, but also diffuse into the surrounding substrate.
Aflatoxin B1 is one of the strongest orally ingestible natural compounds. The reason for this is that it is converted into a highly carcinogenic compound. This occurs as a result of oxygenase in the liver. Subsequently this compound is capable of binding to DNA, which leads to the inhibition of RNA polymerase. The fact that absorption of one molecule would suffice to start the development of cancer explains its extremely acute toxicity. This acute poisoning is referred to as aflatoxicosis. In the case of chronic toxicity after long-term ingestion, conditions such as liver cancer, deformities, stomach cancer as well as sporadic metastases in the lung and kidneys may occur.
All over the world, a large variety of plant and animal source foods are contaminated with aflatoxins. In Europe this is an imported problem. The toxin-forming fungi, which require temperatures of between 25 and 40 °C for mycotoxin development, originate chiefly from tropical and subtropical areas. Therefore especially maize, peanuts, Brazil nuts and pistachios from these producing areas have a high potential risk. Other frequently contaminated foodstuffs include millet, wheat, spices, rice, soy beans, figs, almonds, hazelnuts and nutmeg.
At high levels of humidity and corresponding temperatures, aflatoxin contamination may occur in any stored type of seeds. Occurrence is also promoted by insect attacks, rodents, leaking silos and the possibility of moisture transfer into the stored goods.
When feeding animals fodder containing aflatoxins, aflatoxins are carried over to animal products as well, especially to milk. The index M1 therefore stands for milk or metabolite.
Deoxynivalenol (also referred to as vomitoxin) is produced by various fungi of the genus Fusarium, especially by F. culmorum and F. graminearum, and it is found especially in wheat, barley, oats and maize. Excessive intake of strongly contaminated foods may cause nausea and vomiting and even kidney damage.
Fumonisin B1, B2
These mycotoxins too are formed by moulds of the genus Fusarium, among other things by F. verticillioides, F. proliferatum, F. moniliforme and F. anthophilum.
Like the other mycotoxins produced by Fusarium, fumonisins are also often found on corn, especially on maize.
Ochratoxin A is produced by many Penicillium and Aspergillus species. Those mentioned most frequently are Aspergillus ochraceus, Penicillium verrucosum and Penicillium viridicatum.
Ochratoxin A can be found in numerous foodstuffs and animal feed, notably in wheat, spices, coffee, cocoa, figs, hazelnuts, peanuts and products made from these foods. Contamination usually occurs in the field, while germination of the conidia takes place under favourable conditions in the warehouse. Ochratoxin A finds its way into pork and poultry through contaminated animal feed. In the stomachs of cattle, ochratoxin A is degraded, which is why there is no cross-over effect in the case of beef and milk.
Patulin is a secondary metabolite of various moulds of the genera Penicillium, Aspergillus, Byssochlamys and Paecilomyces variotii. Among the most important patulin-producing fungi is Penicillium expanasum.
It was isolated from Penicillium griseofulvum (previously Penicillium patulum) in 1941 for the first time. At the time, scientists were searching for new antibiotics, and due to its antibacterial and antifungal effect, patulin was believed to be this new kind. Because of its toxicological properties for mammals and plants, it was never used in medical treatment. After all, it has a cytotoxic and haemorrhagic effect on the respiratory chain, causing swelling, bleeding and suppurations.
T2 and HT2 toxin
T2 and HT2 toxin is also produced by fungi of the genus Fusarium. T2 toxin and its metabolite HT2 toxin are classified in the group of trichothecenes.
Zearalenone, which belongs to the group of Fusarium toxins, is found predominately on mouldy corn. This mycotoxin mostly appears in combination with deoxynivalenol.