Mycotoxin: Ochratoxin A (OTA) in coffee | IncaFé Organic Coffee

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Mycotoxin: Ochratoxin A (OTA) in coffee

Posted by Joseph Verbeek on
Mycotoxin: Ochratoxin A (OTA) in coffee

At IncaFé Organic Coffee we have been aware of the presence of Ochratoxin A (OTA), a mycotoxin, in coffee for a long time. We decided that we don't know how much of an issue it is until we measure. Since 2013 we routinely take various samples each year from our green bean containers for OTA testing. Below some further explanation on what it is, why it occurs and why it is not a concern.

The following contains an excerpt of an older FAO article on OTA. More research is available online.

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.

OTA is deemed a carcinogenic but the link, as usual, between the cause of certain cancers and OTA is hard to prove. There is no reason why OTA levels in coffee should be high and hence certain countries take the position of being rather safe than sorry by setting a legal limit.

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. In 1996  the Finnish Customs Laboratory published data on 625 samples from the major coffee producing countries. 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 - this test level is lower nowadays). 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. Please note this data is now quite dated and probably no longer valid as the knowledge of processing in Africa has improved a lot, like in most countries.

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.

 A number of countries have set limits for the presence of OTA in roasted coffee and the EU has recently changed their settings and it has the most stringent limit with 3 ppb. New Zealand, Australia and the USA have no limits. 

Commercially available testing through recognised labs like Asurequality has a minimum detectable level of 1.25 ppb . During the roasting OTA is reduced by 50-97% which would make testing in roasted coffee most of the time quite meaningless with the low levels we see in green coffee. Hence we only test our green coffee.

Since coffee is mostly drunk as an extraction and relatively small amounts of coffee are used in the preparation (as opposed to ingested products like grains) the overall exposure from coffee is deemed extremely low and much lower than from other food groups. Hence, most countries have not set a limit on levels.

When it cannot be detected, there is no reason to assume that there is none, it just cannot be detected with the best commercially available tests.

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