Mycotoxins have both economic and health impacts because they contaminate human food and animal feeds. A central question is whether there are food processing strategies that reduce mycotoxin levels in food products. In this chapter we critically review food processing methods tested in Africa for their efficacy in reducing mycotoxin contamination in maize and peanut. These methods include cleaning, separation of screenings, washing, steeping, aqueous extraction, dehulling, milling, fermentation, cooking and roasting. Some methods reduced mycotoxin levels significantly while others were less effective. Encouraging the widespread use of the toxin-reducing processing techniques would lower consumption of contaminated food products in Africa, and improve food quality and human health.
Mycotoxins are noxious secondary metabolites produced by fungi that are found in food products worldwide. In Africa, mycotoxins, particularly aflatoxins and fumonisins, are receiving increasing attention because of their impact on human health and international trade. Contamination of food commodities by these toxins results in reduction in quality and market value, with significant economic losses for farmers and food processors, and serious health implications for consumers (Cardwell and Miller, 1996). As much as 40% of the human productivity lost to diseases in developing countries may be due to diseases exacerbated by aflatoxin contamination (Miller, 1996). Aflatoxicosis outbreaks occurred in Kenya in 2004 causing 125 deaths (Azziz-Baumgartner et al, 2005; Okioma, Chapter 11), and reoccurred in 2005. Fumonisins have been associated with esophageal cancer in South Africa (Rheeder et al, 1992) and in China (Chu and Li, 1994). An outbreak of abdominal pain and diarrhea has been reported in India due to consumption of products contaminated with fumonisins (Bhat et al, 1997).
Food products that are particularly susceptible to mycotoxin contamination in Africa include maize and peanuts. These products are widely cultivated and consumed across the continent and are very susceptible to contamination with mycotoxins. For example, 5-56% of maize collected in a nationwide survey in Benin were contaminated with aflatoxin (Hell et al, 2003). Various interventions to minimize human exposure to mycotoxins and thereby prevent economic loss have been proposed or are being tested with appropriate integrated management from field to fork. In this respect, recent research has focused on the development of food processing methods as a strategy to lower mycotoxin content in foods. The use of methods such as cleaning, separation of screenings, washing, aqueous extraction, de-hulling and milling, and alkaline cooking all are effective, at least to some extent, in reducing mycotoxins in food commodities (Charmley and Prelusky, 1995; Shetty and Bhat, 1999; Voss et al, 2001). In Africa, diverse traditional processing procedures for food products are used, some of which reduce consumers' exposure to mycotoxins. The present chapter critically reviews these methods and analyzes their efficacy in reducing mycotoxin contamination, with a focus on maize- and peanut-based foods.
Processing procedures for maize and peanut in Africa
In Africa, maize and peanut may undergo short or long processing protocols that lead to various derived fermented and non-fermented food products. For instance, owo, a non-fermented food product, is obtained from maize in Benin by a short processing procedure involving sorting/winnowing of raw maize, followed by milling and cooking of maize meal (Fandohan et al., 2005). Makume, a fermented food product, is prepared by a long processing protocol comprising several steps including sorting, winnowing, washing, crushing, dehulling, dry screening, milling, fermentation and cooking (Fandohan et al., 2005). Another example of a long processing procedure is that of the peanut-based kuli-kuli found in West Africa (Fig. 1). In Benin, ~ 40 different derived products are obtained from maize (Nago, 1997). Most of the processing procedures involve simple but critical operations, e.g., cleaning, dehulling, milling, fermentation, cooking, etc. Some of these operations are very effective in reducing mycotoxin content in foods while others are less so.
Cleaning is generally the first step when processing maize and peanuts. Initially the grains/seeds are sorted, winnowed and/or washed. Cleaning can be done manually at the household level or by using specific machines at an industrial level. During this process, visibly moldy and damaged grains as well as chaff and other undesirable particles are systematically discarded. The remaining apparently healthy grains may undergo a washing process during which grains that float are collected and removed from the bulk.
Sorting out the moldy, damaged and shriveled grains and impurities is a very useful decontamination operation. In South Africa, Sydenham et al. (1994) reduced fumonisin levels 29-69% by removing screenings from maize bulk. Sorting followed by winnowing of naturally contaminated maize grains resulted in a mean reduction of 59% and 69% in afla-toxin and fumonisin levels, respectively (Fandohan et al, 2005). Aflatoxins generally are associated with the smaller, shriveled peanut seeds (Davidson et al., 1982), and with seeds or grains that often are different in color (IPCS, 1979). Martin et al. (1999) recommend sorting as the only remedial technique available for reducing aflatoxin contamination of peanut in Senegal. Sorting may begin by subsistence farmers in the field at harvest, before storage and processing, with the removal of damaged cobs, pods and grains, and cobs with poor husk cover (Hell et al, 2000).
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