About mycotoxins

The modern age of mycotoxicology has started in the early of the 60’ from the XX. century with the discovery of aflatoxins. Until today many new fungal toxins has been discovered, some of them remaining in the laboratory field, others were proved to be toxic as the time goes on. In the process of solving the food safety problems an important activity is the study of mycotoxins, including the improvement of the assay methods, knowing their biosinthesis, toxycology, epidemyology and prevention methods.

Today we can only approximate the total number of mycotoxins, they are with thousends. Those mycotoxins, which can be harmfull are less, but according to their diverse effects their number can be hardly evaluated as well. Mycotoxins are harmfull for man and animals, and can produce huge economic loses in plants. The economic loses of the grain crops in the food and feed industry are the most significant.

Major mycotoxins

The most harmful mycotoxins are the aflatoxins, trichothecenes, fumonisins, zearalenon,

ochratoxins and ergot-alkaloids.

·  the aflatoxins are produced mainly by the Aspergillus flavus and A. paraziticus fungs, they are important disease agents. Their effect a range from acute death to chronic diesease such as tumors.

·  the trichothecens are a large class of mycotoxins produced by several fungs like the Fusarium and Stachybotritis species. Likely the most common occuring trichothecen is deoxynivalenol (vomitoxin or DON), which contaminate maily the wheat, barley and maiz. T 2 is an other thichothecen found more frequently in the European grains

·  the fumonisins occur primarily in maiz and is produced by the Fusarium verticillioides. These toxins can produce diseases in horses and swine and have been shown their carcinogenic effect in rats and mice.

·  the zearalenon is produced primarily by the a Fusarium gramineanum, in swine can produce vulvovaginitis and estrogenic responses. It may also occur with DON in wheat, barley, oats and maiz.

·  the ochratoxins are produced primarily by Penicillium verrucosum and can cause significant disease in animals, in special swines and may be the causal agent for endemic kidney disease.

·  the ergot alkaloids are produced by several species of Claviceps that are plant pathogens and elaborate their toxins in spcialised fungal tissues called sclerotia. Ergotism is one of the oldest recognised mycotoxiscoses.

To the minor class of mycotoxins belong those which occur occasionally with human or animal mycotoxicoses, or that are frequently in selected substrates, but do not associate with human or animal diseases.

The mycotoxins formation

Mycotoxins in many cases are formed in the field during the growing season, but they are formed as well during harvest, drying and storage. One of the most important requirement ot the mycotoxin production is the water availability and right temperature. When the fungi are infecting the plant, temparature and water highly influence the growth and health of the plant, and the competiviness of fungs. During the storage some factors like the grain water activity,aeration, tempaarature,the competiviness of fungs, mechanical demages, the present of rodents, the innoculum concentration play a role in the contamination process.

The control of mycotoxigenic fungi

Mycotoxins are produced by a wide range of fungi that generaly are not aggressive pathogens. They are capable to growth on substrates with a wide range of umidity and nutrional content. From the point of wiev of the contamination three genera of fungi should be mentioned, the Aspergillus, Penicillium and Fusarium. Other generas with less importance are the Claviceps and Stachybotritys.

·  in the genus Aspergillus the major class of mycotoxins are the aflatoxins. The Aspergillus can damage the corn, cotton, ground nut and other crops. The Aspergillus flavus is the cause of the ear rot for corn, when the conidia from the soil inhabiting organsm are carried to the silk and the infection occur. The production of the aflatoxins can occur until the kernels moisture reach15%. Not conclusive an all crops that the high temperature play a role in aflatoxin contamination. Many control strategies has been developed to the prevention of the contamination like the controlling of the preharvest stress, breeding programes for resistance and application of potencial biocontrol agents.

·  within the genus Fusarium are a number of important mycotoxin producing species, some of them are pathogenic fungi which can cause plants wilt, scab or blight diseases. At corn the ear rot can be produced by Fusarium graminearum, F.verticillioides, F. proliferatum, F. subglutinans. The latest one can produce fumonisin during the pathogenic state of corn. The F. graminearum is a significant pathogen on wheat, barley and oats and is the major producer of DON. The fungus can produce zearalanon as well. The fungi are surviving on the crop residues, which is a source of innoculum in the next year. Therefore in the control and prevention methods the crop residues has to be tilled deep, in the dry perioud should apply irrigation and to breed for plant resistance.

·  the Penicillium species usually occur during the storage periods, they produce the ochratoxin which is formed in storage or during drying commodities for processing.

·  the Claviceps species are in general parasites, because they replace the plant structures (the grains) with fungal tissue called ergots. Ergotism is one of the oldest know mycotoxicosis in humans. The less cleaned, sived grains can content sclerotium which can enter under processing. Some Epichloe and Neotiphodium species which can occur in grasses like Festuca and Lolium spp. can produce alkaloids. The control of ergot alkaloids is attempted by a right pasture management practice.

·  the Stachybotritys is a cellulolytic saprophyte that can be found in many commodities, they produce trichothecens which effect is similar to those produced by Fusarium fungi. Human disease can be produced as well.

The mycotoxins occuring in food and feed can be controled by timely harvest, cleaning and drying, controlling the temperatures and moisture during the storage and using antifungal agents. To be able to control the contamination there is a need for research and dvelopment effort to undertand the genetic and biosynthetic aspects of mycotoxin development. Why are fungi producing toxins, we do not know, some mycotoxins seem to function as potencial virulence factors in plants and animal diseases.

The mycotoxin studies in food and feed are quate different, we know much better the mycotoxins in the feed sector and less in the food sector:

·  recently quite a huge attention was given to some Fusarium toxins and ochartoxin A. The admited levels for mycotoxins have benn settled in many countries for processed and unprocessed food and animal products, like meat, egg and milk. The ochratoxin A was surveiled from swine and poultry meat.

·  in processed food there are limited information available, most of which concern aflatoxins. Aflatoxin can occur in milk and in dairy products if the feeding is it done with contaminataed feed. The aflatoxin seems to be rapidly metabolised in most animal species, therefore little concern for human health from this exposure.

·  the deoxinivalenol (DON) contamination has been suirvaled from wheat flour, bread and baby foods. Although the commodities can be processed by dry or wet milling, the mycotoxins can occur in different concentrations. They can occur even in the fermented food.

·  in the beer brewing industry has been surveiled ochratoxin, fumonisin, aflatoxin, zearalenon and deoxinivalenol. Wine can content chratoxin A. Variable results has been obtained regarding the decrease of mycotoxins during food preparation such as roasting, flaking and cooking.

Mycotoxins harmfull for humans and animals

Mycotoxin / Contaminated commodities / Effect of mycotoxins
Affected species / Pathological effects
Aflatoxin (B1,B,2, G,1, G2, M1, M2) / Corn, wheat, rice, cottonseed, figs, nuts, milk, egg, cheese, / Birds: duck, turkey, poult, pheasan, quail
Mammals: young pigs, pregnant sows, dogs, calf, cattle, sheep, cat, monkey, human, fish, laboratory animals / Hepatotoxicity, bile duct hyperplasia, intestinal tracts and kidneys hemorrhage, liver tumors
Citrinin / Cereal grains / Swine, dogs, laboratory animals / Nephrotoxicity
porcin nephropathy
Cyclopiazonic acid / Corn, peanuts, cheese, kodo millet / Chicken, turkey, swine, rat, human / Muscle necrosis, intestinal hemorrhage
Ochratoxin A / Cereal grains, dry beans, moldy peanuts, cheese, coffe, grapes, dried fruits, wine / Swine, dog, duck, rat, human / Nephrotoxicity
porcin nephropathy,
mild liver demage, enteritis, teratogenesis, carcinogenezis, urinary tract tumors
Patulin / Moldy feed, rotted apples, apple juice, wheat straw, / Birds: chicken, quail
Mamals: rabbit, rat, cattle, mouse, cat, humans / Brain and lunge edema, hemorrhage, liver- spleen-kidney capillary damage, nerves paralysis, convulsions, carcinogenesis,
Penicillic acid / Stored corn, cereal grains, dried beans, moldy tobacco / Mouse, rat, quail, shrimp / Liver- kidney damage, dilated blood vesels, carcinogenesis, antibiotic, edema in rabbit skin, antidiuretic
Penitrem / Moldy cream cheese, hamburger, beer / Dog, mouse, human / Tremors death, inccordination, diarrhea
Sterigmatocystin / Green coffe, moldy wheat, hard cheese, peas, cottonsees / Mouse, rat / Hepatotoxin, carcinogenesis
Trichothecenes (T 2, nivalenol, DON, HT 2, fusarenon X etc.) / Corn, wheat, commercial cattle feed, mixed feed, barley, oats, / Swine, cattle, chicken, turkey, horse, rat, dog, mouse, human, cat / Digestive disorders hemorrhage, edema, oral lesions, dermatitis, blood disorders
Zearalenone / Corn, mouldy hay, pelleted feed / Swine, dairy cattle, chicken, turkey, lamb, rat, mouse, / Estrogen effects, atrophy of testicles- ovary, abortion

Source: CAST report, 2003

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