Aflatoxins hurt farmers’ earnings

The ideal time to harvest your maize crop is when the whole plant dry matter is between 32- 40 per cent. File photo

What you need to know:

  • Both commercial and small-scale grain farmers risk losing out on the export market due to contamination of grain by aflatoxin.
  • Aflatoxins are poisonous and cancer-causing moulds that can lead to stunting in children and severe health problems in adults, writes Beatrice Nakibuuka.

A report released last year by the Partnership for Aflatoxin Control in Africa (PACA), indicated that 45 per cent of grains produced in Uganda are contaminated with Aflatoxins, a dead chemical that causes cancer.
This is the reason Uganda does not export as much agricultural produce in the international markets.
Fungi are microorganisms that can contaminate food that is in the garden because it has high moisture content. These in turn cause plant diseases.
Another type of fungi affect drying food produce with low moisture content. As the food dries, these fungi find themselves suitable water content and, together with suitable temperatures, they grow and multiply.

According to Prof Achilleo Kaaya, head of department of food technology and nutrition, Makerere University, this type of fungi if present can grow onto the food, feed on it then produce waste products (chemicals) so that when people eat this food, they may suffer food poisoning.
“Aflatoxins are therefore a type of toxins that are produced by moulds. They are a highly toxic and carcinogenic compounds produced by the fungus, Aspergillus flavus,” hence the name, Aspergillus flavus toxins (Aflatoxins), he says.

Not even cooking or roasting of the produce can destroy the toxins.
This is because the roasting usually happens at 120 - 150 degrees Celsius yet aflatoxins can only be destroyed at temperatures above 400 degrees Celsius. Besides, these toxins are not visible and, they do not have any smell, making it difficult to detect their presence in food.

What causes aflatoxins?
Prof Kaaya says soil is the best medium for microorganisms. When farmers dry their food produce on the bare ground, it increases the risk of moulds developing in the produce.
Drought conditions also stress the plants and they dry before they actually mature thereby creating favourable conditions for the growth of moulds.

“Some farmers leave the produce especially maize in the garden. Since there is heat during day and dew in the night, moulds grow on the maize to produce aflatoxins,” says Kaaya.
Sometimes the foods are not dried to the right moisture content before storage; and poor storage for example heaping produce such as maize inside the house or in a granary, creates an environment for the growth of moulds.

Meats and poultry products become contaminated because they are fed with feeds whose raw materials are contaminated.
“Farmers get rotten maize and maize bran and feed it to animals. Besides, some farmers get spent grains from breweries and feed them to animals. Usually, these are contaminated with a wide range of moulds including those that produce toxins. Thus, some farmers especially those practicing zero grazing, have had their animals die after feeding on spent grains,” he says.
Rabbits, dogs, cats, pigs and cows are very sensitive to aflatoxins and can die once they consume high quantities of these toxins.

Why worry?
There are several reasons why we should worry about aflatoxins but most importantly because they have both economic and health impacts.
Prof Kaaya says Uganda has the potential to export plant produce to many countries in and out of Africa but if it is contaminated with aflatoxins, it cannot be traded.
“It is hard to completely eliminate aflatoxins given the high temperature and humidity as in Uganda and the surrounding countries. For this reason, there is a standardised limit of aflatoxins in grains which is 10 parts per billion (ppb) set for East Africa and while that of Europe is 4ppb,” he says.

This means Europe has stricter aflatoxin regulations. Once a produce is above 10 ppb, it is not supposed to be traded in East Africa.
The products from Uganda, however, can have high levels. For example, maize and sorghum samples containing between 100 to 700ppb have been found. As a country we lose a lot of money because such food cannot be traded in any market.

When the produce is rejected at the export market, it is supposed to be destroyed because it is not safe for consumption but traders do not want to make losses so they sell it locally to the people in their own countries since majority are not aware of the presence of these toxins.
If one consumes food that has very high levels of aflatoxins, they can suffer from acute toxicity, according to Amanda Tumwebaze, a nutritionist.

The cases of toxicity present with jaundice, abdominal pain, vomiting, diarrhoea and ascites.
Tumwebaze says, “Consuming foods containing aflatoxins exposes an individual to chronic toxicity which is likely to cause cancer especially of the liver which is the commonest that is caused by aflatoxins. Liver cancer in Uganda is on increase.”

Prof Kaaya warns farmers to ensure effective drying of all farm produce to the required moisture content which is 14 per cent and below, measured using a moisture metre.
The produce should be dried off the ground using tarpaulins, cemented floors or racks.

“There are traditional methods of telling that the produce has dried, such as biting and shaking. These do not tell whether the produce has dried to safe storage moisture content. Farmers can use the salt method to ensure their foods are dried to the right moisture,” he says.
“Get a clear dry bottle (plastic or glass bottle); put a reasonable amount of salt and a sample of dried seeds. Shake vigorously and let it settle for some time. If all the salt settles down, your sample is dry to the right moisture content,” he says.

Foods with aflatoxins

The foods and crops most likely to be contaminated with aflatoxin include:
• Foods that are dried at home can be contaminated by aflatoxins. These include maize, cassava, sorghum, ground nuts, soybeans, millet, and rice. In general, majority of cereals and legumes can be contaminated.
• Milk (including milk from lactating mothers), meat (beef and chicken), and eggs.
• Animal feeds because they are usually made from contaminated ingredients such as maize, silver fish and soya bean.
• Dried fish, especially silver fish (Mukene) may grow aflatoxin moulds if not well dried.
• Dried spices such as chili, basil and coriander.
• Local brews made from malted sorghum, millet and maize and to some extent, beer made from barley. The fermentation process does not eliminate aflatoxins.


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