Aflatoxins and Toxicity

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Aflatoxins : Toxins produced by Fungi

The aflatoxins are a group of structurally related toxic compounds produced by certain strains of the fungi Aspergillus flavus and A. parasiticus.

Under favorable conditions of temperature and humidity, these fungi grow on certain foods and feeds, resulting in the production of aflatoxins. The most pronounced contamination has been encountered in tree nuts, peanuts, and other oilseeds, including corn and cottonseed.

Among various mycotoxins, aflatoxins have assumed significance due to their deleterious effects on human beings, poultry and livestock.

Aflatoxicosis is poisoning that results from ingestion of aflatoxins in contaminated food or feed.

Aflatoxins are potent toxic, carcinogenic, mutagenic, immunosuppressive agents, produced as secondary metabolites by the fungi.

Among 18 different types of aflatoxins identified, major members are aflatoxin B1, B2, G1 and G2.
Aflatoxin B1 (AFB1) is normally predominant in cultures as well as in food products.
Pure AFB1 is pale-white to yellow crystalline, odorless solid.
Aflatoxins are soluble in methanol, chloroform, actone, acetonitrile.

Aspergillus flavus typically produces AFB1 and AFB2, where as A. parasiticus produce AFG1 and AFG2 as well as AFB1 and AFB2.

Four other aflatoxins M1, M2, B2A, G2A which may be produced in minor amounts were subsequently isolated from cultures of A. flavus and A. parasiticus.

A number of closely related compounds namely aflatoxin GM1, parasiticol and aflatoxicol are also produced by A. flavus.

Aflatoxin M1 and M2 are major metabolites of aflatoxin B1 and B2 respectively, found in milk of animals that have consumed feed contaminated with aflatoxins.

Aflatoxins are found in contaminated Food products which include cereal (maize, sorghum, pearl millet, rice, wheat), oilseeds (groundnut, soybean, sunflower, cotton), spices (chillies, black pepper, coriander, turmeric, zinger), tree nuts (almonds, pistachio, walnuts, coconut) and milk.

Aflatoxins are normally refers to the group of difuranocoumarins and classified in two broad groups according to their chemical structure:

1. Difurocoumarocyclopentenone series : (AFB1, AFB2, AFB2A, AFM1, AFM2, AFM2A and aflatoxicol).
2. Difurocoumarolactone series (AFG1, AFG2, AFG2A, AFGM1, AFGM2, AFGM2A and AFB3).

The aflatoxins display potency of toxicity, carcinogenicity, mutagenicity in the order of AFB1 > AFG1 > AFB2 > AFG2.
The aflatoxins fluoresce strongly in ultraviolet light (ca. 365 nm):
B1 and B2 produce a blue fluorescence where as G1 and G2 produce green fluorescence.

Toxicity of Aflatoxins

Aflatoxins produce acute necrosis, cirrhosis, and carcinoma of the liver in a number of animal species; no animal species is resistant to the acute toxic effects of aflatoxins; hence it is logical to assume that humans may be similarly affected.

A wide variation in LD50 values has been obtained in animal species tested with single doses of aflatoxins. For most species, the LD50 value ranges from 0.5 to 10 mg/kg body weight.

Animal species respond differently in their susceptibility to the chronic and acute toxicity of aflatoxins. The toxicity can be influenced by environmental factors, exposure level, and duration of exposure, age, health, and nutritional status of diet.

Aflatoxin B1 is a very potent carcinogen in many species, including nonhuman primates, birds, fish, and rodents. In each species, the liver is the primary target organ of acute injury.

Although humans and animals are susceptible to the effects of acute aflatoxicosis, the chances of human exposure to acute levels of aflatoxin is remote in well-developed countries.



References:
1. PROPERTIES OF AFLATOXIN AND ITS PRODUCING FUNGI
Reddy,S.V. and Farid Waliyar, International Crops Research Institute
2. US FDA/CFSAN
Natural Toxins Handbook




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