Joan M. King, Terry Walker, Henry Njapau, Douglas L. Park and Kenneth E. Damann Jr.
Aflatoxin is a natural toxin produced by the fungus Aspergillus flavus. Aflatoxin in corn appears when high temperatures and drought stress occur, which favors infection of the ear by the fungus. Southern states are more likely to have this problem than are the cooler mid-western and northern Corn Belt areas. Louisiana experienced particularly severe aflatoxin contamination during the 1998 growing season. This resulted in a large financial loss to Louisiana farmers who had to either destroy their crops or sell them at a significantly reduced price. If a viable alternative had existed for treating the infected grain to eliminate the aflatoxin, the farmers could have received a larger return for their investment.
The possible contamination of food crops by aflatoxins and their potential toxicity to people and livestock have been known for almost 40 years. Aflatoxin is known to cause liver damage and cancer in animals and humans.
Worldwide, numerous studies aimed at understanding the biology of the fungi that produce aflatoxins and the elimination of the toxins have been carried out. Indeed, the understanding of events leading to the formation of aflatoxins in food crops and the effects on consumers has increased tremendously.
Preventing contamination is the best method for managing the risk associated with consuming aflatoxin-contaminated foods. If contamination occurs, however, the hazards associated with the toxin must be managed through post-harvest procedures. Research has focused on both pre-harvest prevention and post-harvest removal of aflatoxins from grains. The continuing challenge of aflatoxin prevention necessitates the need for improved post-harvest techniques to detoxify valuable grain supplies that would otherwise end up as hazardous waste material.
Aflatoxin decontamination can be done physically, biologically and chemically. Physical methods such as separation of contaminated grain by density in water, screening or milling result in loss of product and do not completely remove all contaminated portions. Other physical methods such as heating or irradiation are either cost-prohibitive or non-effective for dry samples. Biological methods, which include development of transgenic crops resistant to the mold or use of microorganisms that destroy the mold, are relatively harmless to the crop and show some potential, but they have yet to be completely effective in decontamination.
A number of chemical methods have been successfully implemented for deactivation of aflatoxins in grains. Treatment with chemicals such as ammonia, methylamine and sodium hydroxide in the presence of moisture and heat have shown potential, but reduced protein nutritional availability was observed in rat feeding tests. Chemical inactivation by ammoniation has wide-spread use and acceptance, but the cost is approximately $20 per ton.
Ozonation is a chemical method that shows potential for decontamination of grains containing aflatoxin. Ozone is becoming a widely used replacement for chlorine-based chemicals for sanitation purposes in food processing, especially in the meat industry and for water quality purposes, such as bacterial, odor, pesticide and hazardous compound degradation. Compared to ammoniation treatment, decontamination with ozonation is estimated to cost only about $4 per ton.
One area of research in the Food Science and Biological and Agricultural Engineering departments is focused on the suitability and safety of the ozonation procedure for decontaminating aflatoxin-contaminated corn. The ultimate goal is not only 100 percent detoxification of aflatoxin-contaminated corn, but ensuring the product is safe for consumption by animals.
Other research at the LSU Agricultural Center includes the following:
A breeding approach to production of resistant corn hybrids. This is a joint project in the Agronomy Department and with the Dean Lee Research Station.
In the Entomology Department, scientists are developing control practices to limit insect damage, thereby closing off a potential avenue of entry and spread into the ear by the fungus.
At the Northeast Research Station, scientists are assessing management practices, such as irrigation and fertilization, which minimize stress.
In a joint project between the Northeast Research Station and the Plant Pathology Department, researchers are evaluating about 75 commercial corn hybrids each year for aflatoxin contamination in an inoculated test. This provides information for growers on hybrids to select to minimize exposure to aflatoxin contamination.
LSU AgCenter scientists also are exploring novel approaches to the aflatoxin problem, including chemical treatment to turn on corn disease resistance genes leading to systemic acquired resistance. A second approach uses the herbicide Liberty on inoculated LibertyLink and non-LibertyLink corn to produce ammonia through its interaction with the fungus and the plant. Ammonia is toxic to the fungus and also directly degrades the aflatoxin molecule. Preliminary results appear promising. A third biological control approach applies a microorganism to the corn ear that is inhibitory to the fungus in culture.
No single method will ensure the complete removal of aflatoxin. A multidisplinary effort can significantly reduce the risk associated with aflatoxin contamination and yield products safe and acceptable to the consumer, yet costeffective for producers.
Joan M. King, Assistant Professor, Department of Food Science; Terry Walker, Assistant Professor, Department of Biological and Agricultural Engineering; Henry Njapau, Research Associate, Audubon Sugar Institute; Douglas L. Park, former Professor and Head, Department of Food Science; and Kenneth E. Damann Jr., Professor, Department of Plant Pathology and Crop Physiology, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the spring 2000 issue of Louisiana Agriculture.)