Mycotoxins

by Lakshmikantha “Kantha” Channaiah
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Mycotoxin contamination of grain is a complex and frustrating situation affecting producers, grain elevators, food and feed processors, and consumers. Although efforts are under way to find reliable, cost-effective and safe treatment techniques to control mycotoxins entering the food chain, many challenges remain.

Most mycotoxin-contaminated grain detoxification methods are either expensive or leave residues in the commodities that would affect its end use. Additionally, diagnosis can be quite difficult and challenging as many mycotoxins exhibit similar symptoms in the affected animals, and symptoms are non-specific and wide ranging.

Sanitation, screening, aeration and monitoring of stored grain are important good management practices during grain storage. Effective implementation of good manufacturing practices in grain elevators and hazard analysis at critical control points (HAACP) in feed mills will reduce levels of mycotoxins and pesticides in the food supply chain.

Mycotoxin impact
Mycotoxins are poisonous compounds produced by certain species of fungi found in contaminated grain and feed products. Mycotoxins have the potential to cause serious implications for human and animal health.

Mold infection and subsequent synthesis of mycotoxin starts during crop growth and continues during storage. Worldwide, approximately 25% of food crops are affected by mycotoxins causing a loss of nearly 1 billion tonnes of foodstuff per year.

U.S. farmers on average produce $100 billion worth of crops and about $100 billion worth of livestock each year. The presence of mycotoxins at the levels higher than the U.S. Food and Drug Administration (FDA) tolerance limits can have serious impact on the U.S. economy. U.S. grain producers and grain handlers suffer the consequences of reduced marketability of their products domestically and internationally.

Mycotoxin poisoning is called mycotoxicosis. The higher levels of mycotoxin contamination can affect the central nervous system, cardiovascular system, kidney, gastrointestinal system and immune system depending upon the type and stage of the animal. The mycotoxins that are a significant concern to both humans as well as animals are aflatoxins, fumonisin, vomitoxin, zearalenone and T-2 toxins.

Aflatoxins
Aflatoxin is the most naturally occurring mycotoxin produced mainly by Aspergillus flavus and A. parasiticus. Favorable conditions for growth of aflatoxins include high moisture content and high temperature.

Although there are at least 13 different aflatoxins present in nature, aflatoxin B1, B2, G1, G2, M1 and M2 are important. Crops that are frequently affected by Aspergillus spp. include cereals (corn, sorghum, wheat, rice), oilseeds (soybean, peanut, sunflower, cotton seeds), spices (chili peppers, black pepper, coriander, turmeric, ginger) and tree nuts (pistachio, almond, walnut, coconut, Brazil nut).

Aflatoxins are confirmed as potential human carcinogens. Aflatoxin B1 is the major toxin in the group found in corn, corn silage, most of the cereal grains, sorghum, peanuts and other oilseeds. Aflatoxin-contaminated feed may cause serious health risks in young animals.

The FDA has established action levels for aflatoxin content in food and feed products to protect human and animal health; 20 parts per billion (ppb) for corn, peanut products, cottonseed meal and other animal feeds and feed ingredients intended for dairy animals and when the intended use is not known.

For corn, peanut products and other animal feeds and feed ingredients, but excluding cottonseed meal, intended for immature animals, the level is 20 ppb. Corn and peanut products intended for breeding beef cattle, breeding swine or mature poultry have a limit of 100 ppb.

DON/Vomitoxin
Deoxynivalenol (DON) is a type B trichothecene that occurs predominantly in grains such as wheat, barley, oats, rye and corn, and less often in rice, sorghum and triticale. They are produced by molds of the Fusarium genus, i.e. F. culmorum and F. graminearum, which are abundant in various cereal crops and processed grains.

DON is responsible for economic losses of billions of dollars worldwide each year, causing plant infection and contaminating grain, particularly wheat and barley. In wheat F. graminearum (Gibberella zeae) infection is known as “head blight of wheat.”

DON has been implicated in incidents of mycotoxicoses in both humans and farm animals. The FDA has established advisory levels for DON content in various commodities: 1 part per million (ppm) on finished wheat products, e.g. flour, bran and germ that may potentially be consumed by humans; 10 ppm on grains and grain byproducts for cattle and chicken, not exceeding 50% of their diet; 5 ppm on grains and grain byproducts for swine, not exceeding 20% of their diet; and 5 ppm on grains and grain byproducts for all other animals not exceeding 40% of their diet.

Fumonisin
Fumonisins are carcinogenic mycotoxins produced by species of Fusarium, particularly F. verticillioides (G. moniliformis). Fumonisins are among the most important toxins regarding food and feed safety. Of the identified fumonisins produced by the fungus F. verticillioides (B1, B2, and B3), fumonisin B1 is the most prevalent toxin comprising approximately 75% of infections.

In addition to their adverse effect on the brain, liver and lungs in livestock animals, fumonisins can also affect the kidneys, pancreas, testes, thymus, gastrointestinal tract and blood cells. The FDA has established guidance for fumonisin levels in human and animal feeds: 2 ppm for degermed dry milled corn products for humans; 4 ppm for whole or partially degermed dry milled corn products and cleaned corn intended for mass production; 5 ppm for equids and rabbits and no more than 20% of diet; 20 ppm for swine and catfish and no more than 50% of diet; 100 ppm for poultry being raised for slaughter and no more than 50% of diet; and 10 ppm for all other species or classes of livestock and pet animals and no more than 50% of diet.

Zearalenone
Zearalenone, also known as F-2 mycotoxin, is produced by some Fusarium (Giberella) species. Zearalenone is heat-stable and is found worldwide in a number of crops such as corn, barley, oats, wheat, rice and sorghum.

It is produced by the fungus Fusarium roseum and F. moniliforme and is most commonly reported in the north central Corn Belt of the U.S. The fungus responsible for zearalenone toxin production (Fusarium spp.) has also been shown to produce deoxynivalenol and T-2 under suitable weather conditions.

Alternating low and moderate temperatures during storage is favorable for zearalenone production with optimum at 81 degrees F. Pigs are very sensitive to zearalenone, hence rations exceeding 0.5 ppm of zearalenone should not be fed to swine. Decreased fertility, abnormal estrus cycles, swollen vulvas, vaginitis, abortion, reduced milk production and mammary gland enlargement are the most common side effects reported in cattle and swine due to zearalenone toxicity.

Ochratoxin
Ochratoxins are mycotoxins produced mainly by species of Aspergillus and Penicillium, particularly A. ochraceus and P. viridicatum, with ochratoxin A as the most prevalent mycotoxin of this group.

Ochratoxin A is known to occur in commodities like cereals, coffee and dried fruit. Ochratoxin affects animals mainly by disrupting the protein synthesis, affecting lipid peroxidation, causing DNA damage and oxidoreductive stress.

It is of special interest as it can be accumulated in the meat of animals. Ochratoxin A can affect mammalian kidneys and may be carcinogenic. Although FDA has listed it as a potentially hazardous contaminant in food and feed products, so far the agency has not set advisory limits or action levels for ochratoxin.

Preventing pre- and post-harvest natural contamination of feed products is crucial for minimizing the ochratoxin levels in the feed and food chain. The infection of Aspergillus and Penicillium spp. occurs mainly during the post-harvest storage phase.

Prevention
The temperature and moisture content of the grain or commodity are the most critical factors favoring fungal growth and mycotoxin production. Relative humidity is another factor influencing the moisture content of stored grain resulting in more or less water available for mold growth and subsequent mycotoxin production. In general, molds grow at a temperature range of 50 degrees F to 105 degrees F, above 70% relative humidity and a pH range of 4 to 8.

For farmers and elevator managers, it is very important to monitor grain quality whenever there is a sudden change in the weather.

Farmers need to avoid factors that cause crop stress such as insect damage, bird damage, drought stress, and early harvest, and avoid kernel damage during harvesting, transporting, drying and storage. Mycotoxin content increases with delayed harvest coupled with rain and cool periods.

Proper cleaning of harvested grain is a must to reduce mycotoxin content as the concentration is greatest in broken kernels and fine material. Drying should be done soon after harvest. Controlling stored grain insects during storage will also reduce mold infection. In order to arrest fungal growth and avoid subsequent mycotoxin synthesis, grain needs to be dried to safe storage moisture contents. Grain dried below 14% moisture content can arrest further mold growth and mycotoxin production. However, it will not eliminate molds and mycotoxins that are already present. The following moisture contents are considered safe during storage: 14% to 14.5% for wheat, barley and oats; 14% for corn; 13% to 14% for rice and 7% to 8% for rapeseed.

Treatment
Several methods have been developed to treat mycotoxin contaminated grain and feed products. However, there are several limitations associated with each method. Application of ammonia (ammonification) to contaminated corn, peanuts, cotton seeds and meals is one potential treatment option that has been used around the world. It was found effective in reducing the fumonisin B1 levels in cultured and naturally contaminated corn by 30% and about 45%, respectively.

The use of chlorine dioxide (ClO2) gas at higher concentrations (500 or 1,000 ppm) with longer exposure time (24 hours) has been found effective to a degree (as a structural fumigant) in arresting certain species of mold. The alternative methods are the use of ozone (O3) and gamma-irradiation.

The addition of binders to contaminated diets has been considered as one potential option to reduce mycotoxin toxicity. Binders attach to mycotoxins, thus preventing them from being absorbed by livestock animals. Some of the potential absorbents include clay, bentonite, montmorillonite, zeolite, phyllosilicates, activated carbon and synthetic polymers such as cholestryamine and polyvinylpyrrolidone.

Mold inhibitors, such as propionic acid, food grade phosphates, sulfur dioxide and sodium bicarbonate, sorbic acid and potassium sorbate, dillapiol and apiol and dioctatin-A, can be used to inhibit mycotoxin synthesis in various commodities. Inhibitors, dioctatin-A, aflastatin-A, dillapiol and apiol have shown good results when tested for A. paraciticus and other aflatoxins.

Avoiding mold infection is the best preventive practice rather than trying to treat moldy grain. It is extremely difficult to destroy mycotoxins in grain and grain-based products.

Although pelletizing feeds may kill fungi, it will not reduce or eliminate the mycotoxins already present in the feed ingredients.
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