4.0. Ochratoxin A in Coffee (OTA)
Ochratoxin A (OTA) is a form of mycotoxin produced as a metabolic product of certain fungi, mainly of the genera Aspergillus and penicillium. Its occurrence has been shown in a variety of unprocessed and processed foods. The main foodstuffs infested by OTA are cereals and cereal products. Other products that may contain OTA are coffee, beer, pork, blood plasma, etc.
The growth of mould on coffee beans is possible if the moisture content of the beans exceeds the accepted standard for an extended time. Beans containing OTA cannot be detected directly in all cases by visual and organoleptic control, because either not all mouldy beans are infected by OTA, or non-mouldy dried beans may still contain the toxin.
Since 1980, several studies have reported OTA presence in raw coffee. More recently, data from the Finnish Customs Laboratory for 1996 became available. In total, data on 625 samples from the major coffee producing countries are now available. The overall mean OTA content for the 625 samples of raw coffee was 1.6 ppb; whereas over 85% of the samples were in the lowest category (undetectable up to 2 ppb). 1-2% of the samples were highly contaminated and had a large effect on the overall mean value.
Another study was carried out in Italy (Santina, R. et al), in order to determine the level of OTA contamination in green coffee samples of different origins. A total of 162 samples of green coffee beans from various countries (84 from Africa, 60 from America, and 18 from Asia) were analysed for OTA. The results showed that 106 of the overall samples were positive for OTA, with concentration ranging from 0 to 48 ppb. In particular, it was possible to verify that, samples from African countries were more contaminated as compared to samples from other origins in terms of frequency and level of OTA. The highest concentrations observed were 18 and 48 ppb in two samples from The Congo D.R.
Some European Commission (EC) member states already have statutory legal OTA limits for coffee; Italy, (8ppb for green coffee and 4ppb for final product), Finland (10ppb) and Greece (20ppb). Currently, EC authorities in Brussels are discussing the introduction of a maximum limit for OTA on several agricultural products, including coffee. Such a limit, if and when established, would necessary result in the rejection of certain percentage of traded coffee for non-conformity with this safety limit. As there is no alternative use for raw coffee, rejected lots would most probably find their way to the consumers in the producing countries.
If such a limit were fixed at 5 ppb as currently discussed by EC authorities, some 7% of the samples included in the Finnish Customs Laboratory review would exceed this amount. Incidental values over 10 ppb were found in coffee lots originating from almost all producing countries, which would be hit by an EC OTA limit, most African producing countries would be in the top of the list. From the West African samples, about 18% exceeded this limit and from the East African samples 9%.
Surveillance of green coffee imported into the UK, Finland and Hungary shows that OTA can occur in coffee from most origins and of all major types of washed and unwashed Arabicas and Robustas, although there seems to be greater occurrence in unwashed coffees.
Further research in Thailand (Peter Bucheli et al., 2000) on drying of Robusta coffee has shown that OTA is formed during sun drying in the coffee cherry pericarp (pulp and parchment), the part of the cherry which is removed as husks in the dehulling process. Broken and infested beans, together with husks were the most important source of OTA contamination found in green coffee. The occurrence of 319ppb of OTA in an aggregate husk sample of a public coffee dehuller demonstrated that husks are the richest source of OTA in green coffee.
All the above mentioned factors call for increased attention to prevention as the method of choice for eliminating mould mediated loss and for improving the quality of coffee.
Very stringent measures must be taken to improve on post harvest handling and processing of coffee in the coffee exporting countries and particularly African countries which have shown higher percentages of OTA in their samples. The most critical stages for both wet and dry methods are the drying and storage stages. Drying must be done according to the recommended practice upto the required moisture content of 12%. Rewetting of the beans or reabsorption of moisture should be avoided at all times during or after drying. Storage should be in well-ventilated stores, which do not allow any form of moisture to get to the coffee.