Mycotoxins

 Fungal toxins

Mycotoxins are fungal metabolites which may contaminate foods, animal feeds, and are toxic to humans or their domestic animals. They are proposed to have carcinogenic properties. As common adulterants of foods or animal feeds, they are important food contaminants. Mycotoxicosis results from the ingestion of toxin in a mold-contaminated food.

            The fungi include the molds, yeasts, mildews, blights, rusts, and mushrooms. Many fungi are useful. Some are edible, e.g., mushrooms and single-cell protein from yeast. Others are widely used in industrial and food fermentations; e.g., Aspergillus oryzae is used in the production of soy sauce, miso, and sake, and molds take part in the ripening of certain cheese. The metabolite of Penicillium chrysogenum, penicillin, has contributed immensely to human well-being. Some mushrooms are harmful or poisonous to humans, but in contrast, molds have generally been regarded as harmless.

The two predominant genera of fungi in stored products are probably Penicillium and Aspergillus, members of which produce mycotoxins.

 Ergot

The first documented case of mycotoxicosis was that of rye ergot. Claviceps purpurea parasitizes rye and other grains and produces many lysergic acid derivatives which are responsible for the syndrome. Consumption of the infested grain or flour made from it over a period of time can result in gangrenous ergotism.

Outbreaks of ergotism were quite common during the Middle Ages. More recent outbreaks of ergotism have been reported in the Soviet Union (1926-1927), England (1928), and France (1951).

Claviceps purpurea is a parasite of grasses including cereals. As part of its life cycle, the tissues of infected grains are replaced by sclerotium which is fungal mycelium. The sclerotium helps to survive the adverse conditions of the winter and germinate later. It is also known as an ergot.

Ergotism is the name for severe pathological syndromes affecting humans or other animals that have ingested plant material containing ergot alkaloid, such as ergot-contaminated grains. The common name for ergotism is "St. Anthony's fire", in reference to the severe burning sensations in the limbs.

Ergotism, is due to ergot alkaloids which is toxic and cause a constriction of the peripheral blood capillaries leading, to fingers and toes becoming gangrenous and necrotic.Ergots contain alkaloid metabolites which may be incorporated into the flour, and the bread, made from the harvested grain. The ergot sclerotium contains high concentrations (up to 2% of dry mass) of the alkaloid ergotamine, and ergoline group. Ergot alkaloids have a wide range of biological activities including effects on circulation and neurotransmission. Ergot contains lysergic acid which is a precursor for the synthesis of LSD which is a potent synthetic hallucinogenic drug.

There are two types of ergotism. The first is characterized by muscle spasms, fever and hallucinations and the victims may appear dazed, be unable to speak, or have other forms of paralysis or tremors, and suffer from hallucinations. This is caused by stimulation of the central nervous system by some of the alkaloids. The second type of ergotism is marked by violent burning, and shooting pain of the poorly vascularized distal organs, such as the fingers and toes. It is caused by effects of ergot alkaloids on the vascular system due to vasoconstriction, sometimes leading to gangrene and loss of limbs due to severely restricted blood circulation.

Ergot metabolites also have profound effects on the central nervous system stimulating smooth muscle activity. The neurotropic activities of the ergot alkaloids may also cause hallucinations, convulsions, and even death. Other symptoms include strong uterine contractions, nausea, seizures, high fever, vomiting, loss of muscle strength and unconsciousness.

Ergot alkaloids has been used in pharmaceutical preparations, to treat migraine headaches, and to induce uterine contractions and control bleeding after childbirth.  Since the Middle Ages, controlled doses of ergot were used to induce abortions and to stop maternal bleeding after childbirth.

The causative agents of most ergot poisonings are the ergot alkaloid class of fungal metabolites. The fungi of the genera Penicillium and Aspergillus also produce ergot alkaloids, particularly some isolates of the human pathogen Aspergillus fumigatus.

Aflatoxin

Aflatoxicosis is a fungal toxicosis that may affect all species of animals. Aflatoxins are produced by certain strains of Aspergillus flavus and A. parasiticus. These fungi grow on carbohydrate-rich feeds such as peanuts, cottonseed, corn, sorghum and cereal grains when they are stored in hot conditions without adequate drying and aeration. Optimal conditions for the production of aflatoxin would be an aw of 0.85 and a temperature of 25 to 40^oC.

The number and types of aflatoxins produced vary with the strain. For example, A. flavus strains produce B1 and its related metabolities, while A. parasiticus produces both B1 and G1 and the related metabolites.

In 1959 there was the deaths of several thousand turkey poults and other poultry on farms in East Anglia due to poisoning of the groundnut meal used as a protein supplement in the pelleted feed. The contaminant, which was called aflatoxin, fluoresces intensely under ultra-violet light and was shown to be produced by the mould Aspergillus flavus growing on the groundnuts.

Acute aflatoxicosis can be caused by ingestion of high doses of aflatoxin over a short period of time. Aflatoxin toxicity may result in nausea, vomiting, abdominal pain, convulsions, and other signs of acute liver injury. Long-term exposure also leads to various complications like growth retardation, cirrhosis, and hepatocellular carcinoma.

The two major aflatoxins have been designated B1 and G1 because they fluoresce blue (B1) and green (G1) when exposed to long-wave ultraviolet light. Aflatoxins B2 and G2 are the dihydroderivatives of B1 and G1. Aflatoxins M1, M2, and P1 are the hydroxylated derivatives of B1 and B2 which are excreted in the urine, faeces, and milk as metabolic products of B1 and B2 following their consumption by mammals.  

Aflatoxin B1, the most toxic of the aflatoxins, is toxic to various animals. Many of the other aflatoxins have been shown to be toxic or carcinogenic to different species of fish, mammals, and poultry. When cows eat feed containing aflatoxin, aflatoxin M1 and M2 is excreted in the milk. Although M1 and M2 are less toxic than the parent compounds B1 and B2, M1 retains its toxic and carcinogenic ability in many animals. M1 has also been detected in the urine of Philippine women who had consumed peanut butter containing aflatoxin.

Many commodities will support the growth of toxigenic strains, including various dairy products, bakery products, fruit juices, cereals, and forage crops.  Aflatoxins have been reported from a wide range of foods and animal feeds. Initially, it was considered that aflatoxin contamination was a problem of poor storage of commodities after harvest allowing the growth of storage fungi such as Aspergilli with consequent formation of mycotoxins. High humidity and warm temperatures can give rise to the highest levels of aflatoxin in food.

Aflatoxins can be produced in the growing crop before harvest also. Aflatoxigenic species of Aspergillus can establish an endophytic relationship with the healthy plant and produce low, but significant, amounts of aflatoxin when the plant is stressed, such as occurs during a drought.

It is assumed that a correlation is there between aflatoxin and liver cancer and liver damage in different parts of the world. Very young children may be exposed to aflatoxins even before they are weaned because mothers, consuming aflatoxin in their food, may secrete aflatoxin M1 in their milk.

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