Chemical Hazard : Mycotoxins

Chemical Hazard : Mycotoxins

 

Mycotoxins 

        Mycotoxins are a chemically diverse range of secondary metabolites and are produced by various fungal species (Aspergillus, Penicillium, Fusarium, and Claviceps). Several hundred different mycotoxins have been identified, but the most commonly observed mycotoxins that present a concern to human health and livestock include aflatoxins, ochratoxin A, patulin, fumonisins and zearalenone.

They are toxic to humans and most are chemically stable and survive prolonged heat processing.

 Aflatoxins are difuranocoumarin derivatives produced by a polyketide pathway

A.flavus and A. parasiticus, which produce aflatoxins in maize, groundnuts, tree nuts, and, less frequently, other commodities

A.ochraceus and A. carbonarius, which produce ochratoxin A commonly occur in grapes, dried vine fruits, wine, and coffee.

Penicillium verrucosum also produces ochratoxin A but occurs only in cool temperate climates, where it infects small grains. Ochratoxin A is a nephrotoxin to all animal species studied to date and is most likely toxic to humans. ochratoxin A is a liver toxin, an immune suppressant, a potent teratogen, and a carcinogen (2).

Aspergillus niger also produces fumonisins.

F. graminearum is the major producer of deoxynivalenol and zearalenone, is pathogenic on maize, wheat, and barley 

Claviceps purpurea produces sclerotia among the seeds in grasses, including wheat, barley, and triticale.

Fusarium fungi are common to the soil and produce a range of different toxins, including trichothecenes such as deoxynivalenol (DON), nivalenol (NIV) and T-2 and HT-2 toxins, as well as zearalenone (ZEN) and fumonisins.

Patulin is a toxic fungal metabolite produced by certain moulds of the Penicillium, Aspergillus and Byssochlamys.

 

Occurrence in Foods:

They commonly enter the food chain through contaminated food and feed crops, mainly cereals.

Other occurrence in foods include nuts, spices, dried fruits, apples and coffee beans, often under warm and humid conditions.

 Animals consuming mycotoxin-contaminated feeds can produce meat and milk that contain toxic residues and biotransformation products. Thus, aflatoxins in cattle feed can be metabolized by cows into aflatoxin M1, which is then secreted in milk (1).

Ochratoxin in pig feed can accumulate in porcine tissues (2)

 

Effects on Health: The toxic effects of mycotoxins can be significant and varied depending on the toxin, dose, host and food matrix involved.

These effects include: Carcinogenicity (cancer causing) especially in the liver, Hepatotoxicity (liver damage), Mutagenicity (changes to DNA), Other toxic effects include kidney disease, immuno-suppression and disturbance to the nervous and hormone systems.

Aflatoxin is associated with both toxicity and carcinogenicity in human and animal populations. The diseases caused by aflatoxin consumption are loosely called aflatoxicoses. Acute aflatoxicosis results in death; chronic aflatoxicosis results in cancer, immune suppression, and other “slow” pathological conditions (3, 4).

 Control and Preventive Measures:

 Good Agricultural Practice:

Proper preparation of the land, crop rotation, use of fungus and/or pest resistant cultivars, control of insect damage to the growing crop, control of fungal infection, prevention of stress to the growing crop, e.g. drought, weeds, harvesting at the appropriate time, and correct handling and storage after harvesting.

 Monitoring Programs:

Inspection and sampling of commodities intended for introduction into the food supply chain. Maximum levels are defined and often legally controlled in specific legislation. Rejection and removal of failed batches is a common control measure

 Pest Control Program:

Pest damage may result in heating and moisture generation, leading to fungal growth and mycotoxin production in localised “hot spots”. Therefore, it is important to have adequate pest control programs in place.

 Inactivation of Toxins:

This can be achieved through roasting of peanuts, heat and moisture control, chemical control, e.g. acids, H2O2, NH3, hypochlorites.

 Testing

Monitoring using analytical methods have been developed based on HPLC, TLC and ELISA.

Bioterrorism

Mycotoxins can be used as chemical warfare agents (5). There is considerable evidence that Iraqi scientists developed aflatoxins as part of their bioweapons program during the 1980s. Toxigenic strains of Aspergillus flavus and Aspergillus parasiticus were cultured, and aflatoxins were extracted to produce over 2,300 liters of concentrated toxin (5). The majority of this aflatoxin was used to fill warheads; the remainder was stockpiled. Aflatoxins seem a curious choice for chemical warfare because the induction of liver cancer is “hardly a knockout punch on the battlefield” (6).

 Reference

 1.       Van Egmond, H. P. 1989. Aflatoxin M1: occurrence, toxicity, regulation, p. 11-55. In H. P. Van Egmond (ed.), Mycotoxins in dairy products. Elsevier Applied Science, London.

2. Rutqvist, L., N.-E. Bjorklund, K. Hult, E. Hockby, and B. Carlsson. 1978. Ochratoxin A as the cause of spontaneous nephropathy in fattening pigs. Appl. Environ. Microbiol. 36:920-925.

3. Hsieh, D. 1988. Potential human health hazards of mycotoxins, p. 69-80. In S. Natori, K. Hashimoto, and Y. Ueno (ed.), Mycotoxins and phytotoxins. Third Joint Food and Agriculture Organization/W.H.O./United Nations E.  Program International Conference of Mycotoxins. Elsevier, Amsterdam, The Netherlands.

4. Beardall, J. M., and J. D. Miller. 1994. Disease in humans with mycotoxins as possible causes, p. 487-539. In J. D. Miller and H. L. Trenholm (ed.), Mycotoxins in grains. Compounds other than aflatoxin. Eagan Press, St. Paul, Minn.

5. Ciegler, A. 1986. Mycotoxins: a new class of chemical weapons. NBC Defense & Technol. Int., April 1986, p. 52-57.

6. Stone, R. 2002. Peering into the shadows: Iraq's bioweapons program. Science 297:1110-1112.