|Food Chain No. 17 - March 1996 (ITDG, 1996, 16 p.)|
With the recent attention given to the incidence of food poisoning organisms such as salmonella and listeria in the UK food industry, what of the problems of food poisoning in the context of developing countries? One of the chief areas of concern in this regard is the problem of aflatoxin poisoning, particularly as it can occur in a wide range of unprocessed food crops such as cereals and legumes, which constitute the staple diet of the rural poor in many developing countries. Aflatoxins are compounds highly toxic to both animals and man, and are known to cause severe liver damage and carcinomas Due to their chemical nature, aflatoxins are not destroyed by heating, boiling, or other simple means, and therefore, once present in a food crops, can be carried intact through subsequent processing and cooking stages.
The danger of aflatoxins was first noted in the 1960s following the death of 100,000 young turkeys in the UK after having been given feed containing imported peanut meal. The deaths were subsequently found to be due to a toxin produced by the moulds Aspergillus flavus and Aspergillus parasiticus. The toxic compounds produced by these moulds in peanut meal have subsequently been identified in a wide range of products including wheat, maize, millet, rice, cottonseed, sweet potato, cassava, coconut, soybean and sunflower. Subsequent stringent import regulations, including regular aflatoxin testing at ports of entry, has minimized the incidence of aflatoxin in these crops in the developed world. However, the people most at risk from aflatoxins are those who live in the developing world, and whose diet is heavily dependent on those crops most likely to carry the toxins. It should be pointed out however, that unlike the majority of food poisoning cases, aflatoxicosis occurs as a result of prolonged exposure to aflatoxic food rather than as a result of eating a single contaminated meal.
While techniques to remove aflatoxins are known and are under development, the processes involved are frequently too complex and costly to undertake in the context of a developing country; and in any case the resulting aflatoxin-free product is only suitable for animal consumption. Research has shown that the growth of Aspergillus moulds and subsequent formation of aflatoxin in food crops occurs primarily after harvesting during drying and storage, and that the most important factors affecting aflatoxin formation are moisture and temperature.
Moulds require moisture to grow, and products with moisture levels above 16 per cent are capable of supporting the growth of A. flavus. The optimum temperature for the formation of aflatoxin producing moulds is about 24-28°C Therefore aflatoxin poisoning can most effectively be controlled by taking measures to control the growth of aspergillus moulds; by ensuring the food crops are properly dried to below a moisture content of 16 per cent and through the introduction of adequate and improved storage techniques to prevent moisture pick up. Detection of aflatoxin can be problematic. In a consignment of peanuts for example only a relatively few kernels may contain toxin, and substantial differences in toxin levels can occur in individual kernels from the same toxic consignment. Care in sampling procedures and in taking a sufficiently large sample are therefore essential for an accurate determination of aflatoxin to be made.
The production of relatively inexpensive test kits based on imuno-assay techniques has enabled an easier detection of aflatoxin, particularly under field conditions However, the costs per individual test are too high to allow for frequent and routine monitoring of aflatoxin incidence, and therefore it is likely that agricultural marketing boards or corporations in developing countries, who act as bulk purchasers will continue to accept or reject food crops based simply on their moisture content. While crops whose moisture content is above specification (e.g. 9.5 per cent for groundouts), are rejected on the grounds that they are likely to contain aflatoxic material, in reality infected crops can be expected to be found in local markets, and it is to be hoped that the consumers, natural rejection of produce that is obviously shrivelled or mouldy will minimize the incidence of aflatoxin.