In this article we will discuss about the classification of mycotoxins:- A. Food Toxins B. Ergot Toxins C. Mushroom Toxins.
A. Food Toxins:
These toxins are mainly responsible for poisoning of foods. The mycotoxin production occurs in many plant products, especially cereals and oilseeds. Others like peanuts, rice, corn and cotton seeds also get contaminated and store mycotoxins. The mycotoxins are produced by more than 100 mold species, mainly by Aspergillus, Penicillium and Fusarium.
According to World Health Organisation (WHO), 1969, the mycotoxins associated with human diseases are of four types. These are aflatoxins, ochratoxins, zearalenone, and trichothecenes.
Aflatoxins are potent toxic, carcinogenic, mutagenic, immuno-suppressive agents, produced as secondary metabolites by the fungi on variety of food products. The anatoxin problem was first recognised in 1960, when there was severe outbreak of a disease referred as “Turkey X’ Disease” in U.K., in which over 100,000 turkey birds died.
Aflatoxins are the most potent carcinogens, known as the suspected cause of liver cancer in human beings. The aflatoxins are produced in dried food and groundnut meal, infested with Aspergillus flavus, A. parasiticus, A. fumigatus or Penicillum islandicum.
Aflatoxins normally refers to the group of difuranocoumarins and are classified in two broad groups according to their chemical structure the difurocoumarocyclopentenone series and the difurocoumarolactone series. About 18 types of aflatoxins have been identified, the major members are aflatoxin B1, B2, G1, G2, while M1, and M2 are less significant.
Aflatoxins are soluble in methanol, chloroform, acetone, acetonitrile and fluoresce strongly in ultraviolet light (365 nm); B1 and B2 produce a blue fluorescence, while G1 and G2 produce green fluorescence.
Aflatoxins bind with DNA to prevent transcription, thereby protein synthesis is inhibited.
In addition to suspected carcinogenic nature, other clinical symptoms due to aflatoxin poisoning are jaundice, portal hypertension, rapidly developing ascites, etc.
Structure of Aflatoxins:
Molecular weight, 312; melting point 268-269°C and molecular formula C17H12O6.
It is dihydro derivative of B1, a minor toxin with lower Rf value than B1. Molecular weight, 314; melting point 286-289°C and molecular formula C17H14O6.
Molecular weight, 328; melting point 244-246°C and molecular formula C17H12O7.
It is the dihydro derivative of G,. Molecular weight, 330; melting point 237-240°C and molecular formula C17H,4O6.
It is the hydroxy aflatoxin B, with molecular weight 328; melting point 299°C and molecular formula C17H12O7.
It is dihydroaflatoxin M, with molecular eight 330; melting point 293°C and molecular formula C17H14O7.
(vii) Other Forms such as B2a Molecular Weight 330, Melting Point 240°C, Formula:
C17H14O7) and G2a (Molecular weight 346, melting point 190°C, formula: C17H14O8) are the hydroxyl derivatives of aflatoxin B2 and G2.
Ochratoxins are closely related derivatives of isocoumarin, linked to an amino acid, L-β-phenylalanine. Of the nine types of ochratoxins, ochratoxin A is the most effective one. Ochratoxins are produced in maize, peanuts, beans etc., infested mainly with Penicillium viridicatum or Aspergillus ochraceus.
Zearalenone is a phenolic resorcyclic acid lactone, produced in maize and also in other cereals, infested with different members of Fusarium such as F. moniliformae and F. graminearum. It shows esterogenic symptoms in swine.
Trichothecenes possess a tetracyclic 12, 13-epoxytrichothecoene skeleton. So far, more than 30 trichothecenes have been identified, of which T-2 toxin, nivalenol and deoxynivalenol, shows marked importance.
Trichothecenes are produced by different species belongs to the genera Fusarium, Myrothecium, Trichoderma, Stachybotrys and Cephalosporium. This group of toxins shows sub-epidermal haemorrhage, several local irritations and general necrosis.
B. Ergot Toxins:
These toxins are stored in the elongated sclerotia of Claviceps purpurea, the pathogen of ergot disease of rye. These are the poisonous alkaloids such as ergotamine, ergocrystinine, ergometrimine, ergonovin and ergocrystine.
Due to consumption of sclerotia along with rye straw, the domestic animals show the following symptoms:
(i) The hoofs, legs and tail become gangrenous,
(ii) Abortion in cows.
Due to consumption of powdered sclerotia along with rye flour, following symptoms become pronounced in human being:
(i) Diarrhoea, abdominal pain and vomiting.
(ii) Effects on nerves and cause psychiatric disturbances, and
(iii) Decrease the diametre of terminal blood vessels.
C. Mushroom Toxins:
Several mushrooms produce toxins and by consuming such mushrooms as food, different abnormalities become visible in human beings like diarrhoea and vomiting within 2-3 hrs of consumption. At a later stage they cause liver damage, kidney failure, complete unconsciousness and even death.
The following mushrooms are important in this respect:
(i) Amanita phalloides (the ‘death cup’). Out of 10 toxins so far reported, the phalloidin and α-amanitin are important. The phalloidin affects the cell membrane of liver cells and α-amanitin causes lesions in stomach and intestine cells.
(ii) Different species of Helvella such as H. infula, H. gigas, H. esculenta and H. underwoodii, produce gyromitrin, a fatal toxin.
(iii) Inocybe and Clitocybe produce toxin muscarine that causes several abnormalities.