toxin A contamination from any source other than the cocoa (Table 2). The ochratoxin A levels are low in chocolate and in cocoa drink powder, with an average between 0.16 and 0.26 ng/g. More than 40% (44 to 76%) of the samples were below 0.1 ng/g. Similar results have been reported from Germany and Spain (Burdaspal and Legarda, 2003; Engel, 2000). The levels are higher in cocoa powder with an average of 1.0 ng/g. This result is expected since cocoa powder is a concentrated cocoa solids fraction. Cocoa powder is used as a flavoring ingredient, usually at levels < 5%, in products such as biscuits, cakes, desserts, ice cream, etc.
Our results imply that interventions to reduce contamination with ochratoxin A need to occur at the farm level if the toxin levels are to be significantly reduced. These preliminary studies show that ochratoxin A contamination starts between the on-tree/harvesting to pre-fermentation stages, and that damaged pods are a major part of the problem. Further research is needed at the smallholder level to determine the contribution made by each class of damaged pod and to identify farm level interventions that can reduce ochratoxin A contamination. Developing an appropriate, simple method for the farmers to use will be difficult. In a smallholder crop, e.g. cocoa, farmers and farm laborers harvest the crop and process it for sale. Thus, these practitioners are the ones who will require training and must be convinced to change their practices. Communicating with and training hundreds of thousands of smallholder cocoa farmers, often in remote areas, is a daunting task. The national agricultural research centers in the cocoa producing countries must be involved, and could work through one of the several farmer organization strengthening projects currently underway in West Africa. Even with the help of these organizations, however, the education process will take time due to the unorganized nature of the cocoa smallholder producer base.
Fresh wet cocoa beans from undamaged cocoa pods do not contain measurable ochratoxin A, but this toxin is found in fermented, dried cocoa beans delivered to the end users. Fungi that produce ochratoxin A are present in the on-farm environment and on the equipment used in the post-harvest treatment of cocoa beans, which enables contamination very early in the supply chain. At the smallholder level, ochratoxin A can be detected in beans that have just been fermented, an indication that the initial inoculation occurred before or during the fermentation. The drying procedure for cocoa beans may play a role in ochratoxin A development, but does not seem to be the main source of contamination. Instead, poor drying appears to allow further increase in toxin levels in already-contaminated beans.
Ochratoxin A contamination levels in smallholder bean samples vary within the cropping season, probably due to post-harvest practices that enable better survival and proliferation of the toxin-producing fungi, e.g., longer pod storage times and lower fermentation heap temperatures. Undamaged pods do not appear to be significantly contaminated with ochratoxin A even if they are stored. Any type of damage to the integrity of the pod wall can result in the growth of fungi that produce ochratoxin A, but mechanical or rodent damages appears to be the most significant. The type of fermentation procedure does not appear to have a major effect. Instead the presence of beans from damaged pods in the fermentation heap appears to be the primary determinant of ochratoxin A contamination.
Consistent with this conclusion are data showing that further increases in ochratoxin A levels are not found in samples of cocoa beans taken at stages later in the supply chain. The processing of cocoa beans into the raw materials for chocolate, either roasting or other heat treatments, do not destroy ochratoxin A, but ~50% of the contaminating toxin is physically removed when the shells are removed from the beans. The resulting cocoa raw materials are rarely consumed in a concentrated form and are almost always mixed with other ingredients, e.g., milk and sugar, which dilutes any remaining toxin even further. This dilution helps explain the low levels of ochratoxin A found in cocoa and chocolate products (44-76% samples below 0.1 ng/g), and underlines the relatively minor contributions that cocoa and chocolate products make to human dietary ochratoxin A exposure.
We thank the CAOBISCO, ECA, and FCC Ochratoxin A Working Group for their active participation in this study, and CIRAD, CABI Bioscience and the University of Aberyst-wyth for carrying out the research.
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