Dried and Tested - India
Some crops, such as peanut (also known as groundnut), can be severely affected by fungus. Warm, moist conditions are perfect for the growth of fungi, during which they produce harmful poisons. One of the most common is aflatoxin, which can be lethal to humans and animals. If aflatoxin is detected in the crops they are rejected for sale, but if they are consumed the damage could be far greater. A cheap and convenient test to check for contamination has now been introduced, safeguarding farmers’ livelihoods and consumers’ health.
Alfatoxins
Aflatoxins are naturally occurring toxic substances that are produced by the fungi Aspergillus flavus and Aspergillus parasiticus. These two fungi grow on the debris of many crop plants left on and in the soil as well in air.
The fungi are found worldwide, with a tendency to be more common in countries with tropical climates that have extreme ranges of rainfall, temperature and humidity.
Aflatoxicosis is a disease which occurs in humans and livestock if contaminated food or animal feed is eaten. The incidence of aflatoxin contamination in food and feed is high, and it can occur in cereals, spices and tree nuts as well as oilseeds such as the peanut. |
Aflatoxins are naturally occurring toxic substances that are produced by the fungi Aspergillus flavus and A. parasiticus. These two fungi grow on the debris of many crop plants left on and in the soil as well in air.
The fungi are found worldwide, with a tendency to be more common in countries with tropical climates that have extreme ranges of rainfall, temperature and humidity.
Aflatoxicosis is a disease which occurs in humans and livestock if contaminated food or animal feed is eaten. The incidence of aflatoxin contamination in food and feed is high, and it can occur in cereals, spices and tree nuts as well as oilseeds such as the peanut.
The fungus that produces aflatoxins infests economically important crops in countries all over the world. Often farmers are not aware of the problem, and unfortunately there are many cases of deaths when infected crops have been eaten. The toxin is invisible, but there are many technologies available that can detect it. Most of these are very expensive, so the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has developed its own cost-effective system.
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| A wide range of crops can be affected by Aflatoxins, such as this maize |
Health Risk
The peanut plays an important role in the diets of rural populations, particularly children, because of its high content of protein, fat, and carbohydrate. It is also rich in calcium, potassium, phosphorus, magnesium and vitamin E.
Peanut stalks are nutritious and widely used for feeding livestock; and protein meal, a by-product of oil extraction, is an important ingredient in livestock feed.
As peanuts are used in a variety of food and feed products, the risk of contamination is widened. Contamination at high levels can cause death, and at lower levels it is considered to be an important cause of liver cancer. Small-scale farmers are particularly vulnerable as they often consume poor quality kennels, more prone to infection, which would not be accepted in the market. When livestock eat contaminated feed their productivity declines and their milk is also contaminated with toxin.
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| If the pods are damaged by insects, peanuts become more susceptible to virus attack. |
Aflatoxin contamination of peanuts is a major hazard to human and animal health and is one of the most important constraints to peanut trade. As a result of these concerns, the European Union has banned the import of peanuts with aflatoxin content above 4 µg/kg. The FAO (Food and Agriculture Organisation) categorises samples with over 30 µg/kg as unfit for human consumption. However, peanuts and peanut products available in Africa can have much higher levels; for instance, in Nigeria, scientists have found as much as 120-510 µg/kg of aflatoxin B1, B2, G1 and G2 in peanuts sold in the market. Due to the imposition of strict quality regulations, international peanut trade has declined; exports have fallen sharply in many developing countries, with severe impacts on their economic development. Much attention has been given to aflatoxin contamination and other quality issues relating to export peanuts, but very little on produce that is consumed within the country.
ICRISAT Research
At present ICRISAT's research on aflatoxins is focused on the peanut crop. Worldwide, approximately 25.7 million tonnes of peanuts are produced annually. Asia produces 17.9 million tonnes, about 70 per cent of global production, while Africa produces another 20 per cent. The fungi can infect peanuts during the crop season and even after harvest. Pre-harvest infection by A. flavus is more important in the semi-arid tropics, especially when drought occurs just before harvest. Drought-stressed plants lose moisture from pods and seeds, and growth is greatly reduced. This increases susceptibility to fungal invasion. Damage caused by soils pests may also increase aflatoxin contamination.
Post-harvest conditions are important. Poor harvesting and storage conditions can lead to rapid development of the fungi, which in turn leads to production of the toxin. Peanuts are often stored in the pod, but insects can easily damage the pods, so leading to penetration by the fungi. Shelled peanuts are also stored in poorly ventilated areas, which can promote fungal development.
The ELISA Test
Conventional tests for aflatoxins are time-consuming and expensive. ICRISAT has developed a simple, adaptable and cost-effective technique called ELISA (Enzyme Linked ImmunoSorbant Assay) to diagnose and estimate aflatoxin contamination.
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| The ELISA Test is simple and cost-effective |
The ELISA test uses the action of an enzyme on a sample to recognise specific aflatoxins. Methanol is used to extract toxins from the ground-up grain sample. The basic principle of the test is then to immobilise the aflatoxin on a solid surface, capturing it with a specific antibody that reacts to aflatoxins, and finally test it with a specific enzyme. When a suitable reactor is added, a colour change occurs which indicates the level of aflatoxin within the sample. More specific details of the test can be found at http://www.aflatoxin.info
This ELISA test is not only useful for research, but also helps farmers, traders and exporters. The test is cheap, only Rs133 (£1.70) per sample as compared to the previous cost of Rs800-1000 (£10), so its uptake has been considerable. For example, now that feed manufacturers can check supplies are safe, their turnover has improved dramatically.
The ELISA test can be used for detection of aflatoxins in many other crops.
Toxin Management
Farmers have been developing methods of reducing contamination. This may mean more resistant crops, control agents, altering the soil type, or using new ways of harvesting.
Several national and international institutes, including ICRISAT, have carried out research on pre-harvest aflatoxin contamination, and control through genetic resistance as well as biological and cultural methods. Recent studies at ICRISAT have shown that changes in farming practices can reduce contamination.
In collaboration with a local radio station, FM India, ICRISAT has been working with farmers to look at this problem. The ICRISAT team goes into villages and discusses the situation with farmers. Right from the planting farmers are instructed in measures to be followed to avoid contamination. For example, harvested crops used to be heaped in piles, but now pods/cobs are immediately removed and dried. Farmers are seeing the benefits as the percentage of rejected crops has dropped considerably.
ICRISAT’s motto, ‘Science with a human face’, is about promoting research that directly benefits the rural poor. With this test and other research into aflatoxins they are helping raise farm productivity, while making sure their products are safer for humans and animals.
Acknowledgements
Hands On would like to thank Dr Farid Waliyar for his help in putting together this case study.
Further Information
To contact Dr Farid Waliyar, email: f.waliyar@cgiar.org
Participating Organisations
International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)
ICRISAT-Patancheru (Headquarters)
Patancheru 502324
Andhra Pradesh
India
Tel: +91 40 30713071
Fax: +91 40 30713074/30713075
E-mail: ICRISAT@CGIAR.ORG
Website: http://www.icrisat.org/
Aflatoxin Website
This is an initiative of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) to disseminate information about aflatoxin research worldwide. This was made possible with financial support from DFID, UK.
http://www.aflatoxin.info/
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