Figure 1. A long processing procedure for the preparation of kuli-kuli, a peanut-based food in West Africa.

The efficacy of sorting depends on the extent of grain contamination (Martin et al, 1999), and the ability of the people who do it (Fandohan et al, 2005). People trained to easily recognize diseased grains execute this process more efficiently (Desjardins et al, 2000). Sorting also depends on the goodwill of the people in charge and their willingness to spend enough time on this operation for it to be worthwhile. As a large segment of the African population is unaware of the human health problem posed by mycotoxins, they have no incentive to sort out poor quality grains or seeds (Bankole et al, 2004). Even if they do sort their grain, they are likely to feed the discarded grain to their animals reducing their health and productivity (Williams et al, 2004). Sorting is unlikely to be a practical solution in Africa as long as poverty, hunger and food insecurity are major issues. In such situations, having something to eat today is more important than the usually long-term effects that accompany mycotoxin toxicoses.

Following sorting, simply washing or steeping the grains or seeds in water also can contribute significantly to mycotoxin decontamination. Due to their relative water solubility, aflatox-ins and fumonisins often are leached into washing or steeping water during food processing. For example, Se (2002) recorded a 48% reduction in aflatoxin levels due to loss in steeping water during an experiment on maize wet-milling in Egypt. Similar losses of aflatoxins (37%) and fumonisins (51%) to wash water have been reported when maize was processed into derived products in Benin (Fandohan et al, 2005). The leaching of mycotoxins into the wash water may be even more substantial in the presence of additives, e.g., salt, in the wash water (Shetty and Bhat, 1999). Njapau et al. (1998) recovered 31% of the aflatoxin Bj in the steeping water that resulted from the preparation of nshima, the main edible maize-based food in Zambia.

Removing the floating grain fraction when washing also can reduce substantially the amount of mycotoxin present, as contaminated grains usually are less dense than the healthy grains (Shetty and Bhat, 1999). The high mycotoxin content of steeping water or supernatant of fermented foods is a cause for concern in many parts of Africa. These liquids often are not discarded, but instead are used to prepare porridges, beverages and traditional herbal medicines consumed by both adults and children (Njapau et al, 1998; Fandohan et al, 2005).

Dehulling and crushing

Dehulling is one of the oldest processing operations in Africa. This process removes the outer parts of grains or seeds, either mechanically or chemically, and often is followed by crushing or milling. In maize, mechanical dehulling often is accompanied by degerming of the grains, i.e., removal of the embryo.

Dehulling or crushing the grains can reduce mycotoxin contamination significantly as mycotoxins are concentrated in the outer layers of the contaminated grains (Sydenham et al, 1995). Dehulling maize grain can reduce aflatoxin contamination by 92% (Siwela et al, 2005). Crushing or grinding peanut seeds generally results in oil free of aflatoxin with the toxin remaining in the cake (Mbaye, 2004), which is used to prepare foods such as kuli-kuli, which is consumed by adults and children in West Africa as a snack or as a food supplement.

The efficacy of the dehulling process depends on the degree of fungal penetration of the grain, the degree of contamination and the distribution of the toxin in the grain as myco-toxins are unevenly distributed in the contaminated unprocessed commodity (Charmley and Prelusky, 1995; Bolger et al, 2001).


In many African countries, traditional food preparation is based on fermentation. These fermented foods have numerous advantages including: reduced spoilage, longer shelf-life, increased nutritional value, enhanced flavor and acceptability, and reduction in the toxic and antinutritive compounds present (Holzapfel et al, 1998).

Fermentation can increase the safety of some food products contaminated with myco-toxins (Westby et al, 1997). However, the available reports are contradictory, with some showing very efficient reductions in mycotoxins associated with fermentation, whereas others find lesser or no effects. Lactic acid fermentation can reduce the amount of aflatoxin present in some soybean-based foods (Ogunsanwo et al, 1989) and by up to 70% when contaminated maize and sorghum were processed into ogi, a popular West African food (Adegoke et al, 1994). Nout (1994) explained the significant effect of lactic fermentation on aflatoxin B1 reduction as the result of complete degradation of the molecule following the opening of the lactone ring. Significant decreases, 68-75%, in the levels of fumonisin and zearalenone in fermented maize meal also occur after four days of lactic fermentation (Mokoena et al, 2005). However, these authors suggest that this reduction may not suffice to significantly alter the toxic effects of the two toxins.

In contrast to these rather positive reports, Dada and Muller (1983) found that lactic fermentation during the preparation of ogi reduce aflatoxin levels by only 12-16% and the lactic fermentation involved in the preparation of kenkey from maize does not reduce aflatoxin levels at all (Jespersen et al., 1994; Kpodo et al, 1996). Indeed Kpodo et al. (1996) observed that aflatoxin levels increased initially and then persisted during the fermentation. The authors argue that a reduction of aflatoxin levels is unlikely under acid conditions, and that chemical transformation of the toxin is more likely, since reduction in aflatoxin content usually is accompanied by opening the lactone ring in the presence of alkali. Small reductions in mycotoxin levels (18% for aflatoxins and 13% for fumonisins) also have been observed following lactic fermentation when preparing ogi (Fandohan et al, 2005). The ability of etha-nol fermentations to reduce mycotoxin content during preparation of beer at traditional and industrial levels also has been evaluated, but no significant reduction of aflatoxin or fumo-nisin contamination was observed (Desjardins et al, 2000; Shephard et al, 2005).

The mixed results with lactic acid fermentations reported to date suggest that further in-depth studies are needed to clarify the effects of fermentation on mycotoxin, primarily aflatoxins and fumonisins, contamination in foods. Some researchers who collect survey data evaluate the mycotoxin content of the surveyed foods at fermentation stage. These surveys do not always take into account the other production steps in preparing fermented foods, e.g., cleaning, steeping, dehulling, milling and cooking, that also can contribute to the overall reduction in mycotoxin levels observed in the final fermented products and should not be ignored (Westby et al, 1997).

Thermal processing

Cooking and roasting are the most common thermal food-processing treatments at the household level in Africa. Mycotoxins such as aflatoxins and fumonisins are relatively heat-stable and cannot be easily destroyed by ordinary cooking. Significant reductions in toxin levels are more likely at higher cooking temperatures. Temperatures > 150°C are required for a reduction in fumonisins, and >195°C for a reduction in aflatoxins (Bolger et al, 2001). Such temperatures are difficult to reach during ordinary household cooking.

Cooking of food at the household level generally lasts no more than 30 min and is unlikely to result in a significant reduction of the mycotoxins present. After 20 min of cooking of a South African stiff porridge the fumonisin content was reduced by 23% (Shephard et al, 2002). A three hour cooking time could reduce aflatoxin levels by up to 80% in kenkey, a Ghanaian maize-based food (Kpodo et al, 1996). If nshima was cooked for 15 min, then aflatoxin Bi was reduced by 13% and no further reduction occurred if the cooking time was extended to 2 hours (Njapau et al, 1998). Conversely, Adegoke et al. (1994) observed a 68% reduction in aflatoxin B1 content after 30 min of cooking tuwo, a Nigerian maize-based product, and this reduction increased to 81% after 60 min. In general, moist conditions are more favorable for degradation of mycotoxins during cooking (Rehana and Basappa, 1990; Kpodo et al, 1996).

Relative to ordinary cooking or boiling, roasting is more likely to result in a substantial reduction of mycotoxin content in food. Roasting peanuts gives a highly significant reduction (85%) in the level of aflatoxin B1 whereas boiling results in a mean reduction in toxin of only 19% (Njapau et al, 1998). A complete loss of fumonisin B1 was observed when artificially contaminated maize meal was roasted at 218°C for 15 min (Castelo et al, 1998).

Further studies are needed on the effects of cooking on mycotoxin contamination, especially with respect to moisture conditions during cooking and pH, as many food products in Africa initially are fermented before being cooked. Of particular importance is the need to determine if the mycotoxin apparently lost during cooking and roasting has been degraded or if it is instead simply bound to a food matrix or is transformed into another prod-uct(s) toxic to humans during the cooking process.


Specific processing techniques in Africa clearly can be used to reduce human exposure to mycotoxins. Of these techniques, cleaning by removing poor quality products, washing the product before processing, and mechanically dehulling the grain are by far the most important and can be accomplished with simple tools. Cleaning and mechanical dehulling also are the least likely to produce other toxic residues in the food. Processes such as fermentation and cooking also need further investigations to determine their influence on mycotoxin decontamination in food. Interestingly, in Africa several unit operations, e.g., cleaning, de-hulling, milling, fermentation and cooking, all take place during the processing of food products and provide multiple opportunities for high reductions of mycotoxin levels. However, there is no single method that is likely to result in considerable food decontamination.


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