Mycotoxins are the toxic substances produced by the fungi on food materials. These are 'secondary metabolites'. Some of these cause very severe effects on animal, plant and microbial systems. These include aflatoxins, ochratoxins, sterigmatocystin, citrinin, patulin, rubratoxin, zearalenone and trichothecens and are produced by the different species of Aspergillus, Penicillium, and Fusarium.
Aflatoxins are highly oxygenated heterocyclic compounds. They contain a nucleus fused to a bifuran and in case of aflatoxin B, a pentanone structure which is substituted in aflatoxin G by a six membered lactone is present. In some animals, aflatoxin B1 and B2 are partially metabolized to give hydroxylated derivatives, which have been called aflatoxins M1 and m2 or milk toxins. Other aflatoxins isolated from the cultures of Aspergillus flavus are aflatoxins B2a, G2a, aflatoxicol, aflatoxin H, aflatoxins P and aflatoxins Q1.
During metabolism the fungi not only produce mycotoxins in the substrates but they also cause considerable loss to the food substrates by changing the levels of some of their vital chemical components. Toxigenic strains of A.flavus, A. parasiticus cause significant change during their infestations in the levels of sugar, protein, ascorbic acid and phenols of some fleshy fruits.
There are the well known diseases like ergotism, alimentary toxic aluki (ATA) and the liver cancer or Reya's syndrome caused by aflatoxins. Because of the carcinogenicity of the aflatoxins in various laboratory and farm animals, the possible ability of these toxins to produce liver tumours in human is an area of great interest.
Toxin producing potentials vary with the nature of the fungal organism and it may remain confined to specific or even at strain level. More than 150 species of fungi are known to produce different types of mycotoxins in laboratory as well as under natural conditions.
The concern about mycotoxins producing potentials of moulds has increased since 1960 ie. After the discovery of 'Turkey-K-disease' which was attributed to aflatoxin elaborated by Aspergillus flavus, since then several hundred strains belonging to this group have been isolated from various food and feed materials.
All the strains of A.flavus, do not possess the capacity of elaborating aflatoxins. Screening of A.flavus isolated for aflatoxin production also received considerable importance in India. Aflatoxins elaboration by A.flavus on various food substrates and the environmental conditions. Moisture and temperature are the two most important factors which exert decisive influence on mycotoxin elaboration.
Besides environmental factors, aflatoxin elaboration also varies with the nature. A particular danger from consumption of aflatoxin contaminated food and feed lies in the possibility that some may damage the hereditary material of man.The potential hazards of such mycotoxin- induced mutations for two more reasons i.e. the genetic impairments, and somatic hazards. Genetic hazards enhance burden of disease and premature death. Somatichazards include the impact of mycotoxin on DNA and other cellular constituents.
Among all the mycotoxins, aflatoxins occupy key position with regards to carcinogenic effects on animals and human systems.
A large number of chemical fungicides and fumigants like propionic acid, acetic acid, ethylene bromide, sulfur dioxide, luprosil etc. have been found to be very effective in preventing mould growth and aflatoxin elaboration. Propionic acid and crystal violet were found to exhibit greatest antifungal activity in liquid medium against toxigenic strains of A. parasiticus. These compounds also significantly prevented the aflatoxin elaboration by A. parasiticus. Prevention of aflatoxin production by the use of plant product have achieved alfatoxin inhibition.
Physical separation procedures have been found to be most successful. X-Rays and UV rays are used alternatively in minimizing alfatoxin level in food stuffs. Detoxification of alfatoxin have been achieved through heat treatment. Destruction of alfatoxin in food materials has also been suggested through roasting, frying in oils, spray drying, baking and autoclaving. Sunlight reduces alfatoxin level in peanut oil.
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