Mycotoxin Levels in Conventional, GM, and Organic Foods
Mention the words 'food safety' and you're guaranteed to stir up some emotions around organic and genetically modified (GM) foods. But people are less knowledgeable about mycotoxins - and this can shed a different light on the food safety debate. Mycotoxins are naturally produced food- borne metabolites of fungi that are natural contaminants of agricultural crops. Their toxic
effects in animals have been known for a long time, and therefore health authorities worldwide have regulated mycotoxin levels in human food and animal feed. One such example is the mycotoxin aflatoxin B1 (AFB1), which is produced by the fungus Aspergillus flavus that grows on peanuts before or after harvesting and under poor storage conditions. In 1993 the International Agency for Research on Cancer classified AFB1 as a carcinogen - a substance that can cause cancer in humans. The tolerance levels of aflatoxins in human foodstuffs are regulated nationally and globally. Another example is patulin - which is a toxic secondary metabolite that is produced by a number of fungi, most important of which is Penicillium expansum. This fungus is a well-known post-harvest pathogen that causes 'blue mold rot' or 'soft rot' in apples. Patulin has been shown to possess mutagenic properties (can cause damage to the genetic material of cells), to have adverse effects on developing rat fetuses, and to cause immunotoxic, neurotoxic and gastro-intestinal effects in rodents. Recommended specifications are that patulin levels should not exceed 50 parts per billion (μg/L) in products intended for human consumption. Additionally, infestation by insects can in many cases lead to fungal infections that produce mycotoxins - and therefore the food is concomitantly contaminated with higher levels of mycotoxins. Consequently, the question has been posed as to whether there are differences between levels of these toxins in organic food versus conventional or GM food. For comparison, research has indicated that patulin levels in apple juice made from conventionally grown apples ranged from 250 to 4000 μg/L. But in organically produced apple cider, a study done by a second group of researchers has found patulin levels of up to 45,000 μg/L.
Another comparison has been made with transgenic corn. These hybrids are genetically modified with genetic material from a naturally-occurring soil-borne bacterium, Bacillus thuringiensis, that produces a protein that is toxic to certain insect pests such as stalk borers. Stalk borers cause damage to corn ears or kernels and this damage is often associated with Fusarium ear rot. The fungus Fusarium verticillioides is one of the most prevalent seed-borne fungi associated with corn intended for human and animal consumption throughout the world. The fumonisins, a family of food-borne carcinogenic mycotoxins, were first isolated in 1988 from cultures of F. verticillioides. Fumonisin B1 (FB1) was shown by researchers to cause equine leuko-encephalomalacia, pulmonary edema syndrome in pigs, and primary hepatocellular carcinoma in rats. The Bt corn strains, which are lethal to insects such as stalk borers, have been shown to significantly reduce the levels of insect damage - therefore yielding corn crops with significantly lower fumonisin concentrations compared to their non-Bt counterparts. Another plus is that the maize yields of the Bt-strains are larger than their non-Bt counterparts. So despite the current discussions surrounding GM foods, it appears that Bt hybrids could play a major role in lowering mycotoxin levels in food products, which should ultimately enhance the quality and safety of animal and human food. (Science in Africa, December, 2002).
