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Auto-Control Of Ochratoxin-A Levels
In Green Coffee


By Dr. Liberty Sibanda

Dr. Liberty Sibanda looks at the methods of eliminating OTA contamination in coffee products.

Coffee is one of the most important commodities in the world’s economy. It was the second most valuable traded commodity after oil, with a traded value of $5.6 billion in 2000/2001. The total world coffee consumption is estimated to be over 6 million tonnes per annum, with Europe being the largest market, followed by the U.S., and Japan in third position. Producing countries consumed 28 million 60-kg bags in the 2003/2004-crop year, which is approximately 27% of world output as estimated by the International Coffee Organization (ICO). Recent projections for the 2005/2006 global production are in the region of 110 million bags.

Contamination of Ochratoxin A
Coffee is a woody, perennial evergreen dicotyledon belonging to the botanical family Rubiaceae. Coffea is the most important member of this family economically, of which two species are traded widely. Coffee Arabica (Arabica), accounts for 60-70% of the world’s production. Coffea Canephora (Robusta) comprises 30-40% of world’s production. Ochratoxin A (OTA) contamination is commonly associated with cereals, fresh grapes, dried vine fruit, wine, beer, cocoa and specifically coffee. OTA is a mycotoxin produced mainly by the fungal genera Penicillium (P. verrucosum and P. nordicum) and Aspergillus, especially Aspergillus Ochraceus.

Generally, coffee is harvested annually, when the coffee cherries are ripe. OTA contamination of coffee occurs in the field, during processing and drying. Overripe coffee cherries are a source of fungus and subsequently the production of OTA. Harvesting cherries from the soil may result in highly contaminated coffee cherries in the harvest, hence increasing the OTA risk. Strip harvest, which is widely used, requires a certain level of uniformity of cherry maturation (ca. 75%). This may result in some of the cherries being overripe, thus also presenting a high OTA risk.

The lack of visible mold is not a guarantee that the foodstuff is free from toxins, as the fungi may have already died, leaving the toxin intact. The HACCP-based approach to food safety throughout the coffee production and processing chain, helped in the prevention and control of OTA- contamination of coffee.

Coffee Processing
Coffee passes through various stages of primary processing in the country of origin. Primary processing separates the coffee beans from the skin and the pulp of the coffee cherry. Beneath the red skin (exocarp) lies the pulp (mesocarp), containing two beans, each surrounded by a parchment-like coating (endocarp). Underneath the parchment the beans are covered in an additional membrane, the seed cover. There are two methods for removing these outer layers, known as the ‘wet’ method and the ‘dry’ method. Essentially, in wet processing, ripe cherries are harvested, pulped, fermented and washed, dried, peeled and then polished. This is known as ‘washed’ or ‘Mild’ coffee. In dry processing, cherries are harvested, dried whole and then mechanically decorticated (hulled) in order to extract the green coffee bean.

De-pulping is the key difference between the wet and dry methods, as in the wet method the pulp of the fruit is separated from the beans before the drying stage. Should the pulping operation be delayed after harvesting, deterioration of the fruit occurs leading to fungal growth and OTA production. The pulped beans are separated through flotation, and finally fermented to remove the mucilage. At this stage, the wet parchment coffee has a Moisture Content (M.C.) of approximately 60%. To reduce it to 12-12.5% M.C., the parchment coffee is dried either in the sun or in a mechanical dryer, or a combination of the two.

In the dry processing method, the whole cherry is dried to allow the separation of the bean from the exocarp and mesocarp. This occurs in three basic steps: cleaning, drying and hulling. The coffee cherries are sun-dried on drying terraces or on raised drying tables. The drying process can take up to four weeks to reach the optimum 12.5% M.C. Coffee that is not dried quickly and sufficiently will be too wet, therefore, prone to fungal infection and risk OTA contamination. Wet parchment coffee has a M.C. of approximately 60%, and the optimum amount for processed coffee beans must be 12.5%, which is the maximum level recommended by the International Coffee Organization.

Both dry and wet processing steps are one of the most critical for OTA contamination, as this requires about two-three days, after which the bacteria enters into a toxin production phase. Once the coffee bean is contaminated with a fungal propagule this can start producing mycotoxins during this drying period without external indications of contamination. It is, therefore, clear that ten days (parchment drying) and four weeks (dry process) is certainly long enough for mold growth and OTA production during this process. In addition to OTA produced in the ripening cherries, during storage and shipment, the drying process can also significantly increase the OTA levels in green coffee.

Coffee Storage
During storage, the production of OTA is mainly due to high levels of humidity, which may encourage mold growth, and resulting in mycotoxin production. After processing, dried green beans are usually stored in bags or in silos, before final milling or hulling and prior to export. When the coffee is not covered during transportation, OTA contamination might occur. The loading or unloading of coffee under wet conditions may cause re-wetting, resulting in fungal and OTA contamination. Mixing of different coffees (i.e. parchment coffee, dry cherries and/or beans) during storage is also a risk factor.

Bagged green coffee should be stored in well-ventilated and leak-proof warehouses, and away from walls on pallets raised off the floor to facilitate ventilation. Once beans are dried to maximum 12.5% M.C., all efforts to prevent re-wetting and airborne moisture absorption must be prevented (be it from rain, fog, or condensation). After processing for export, coffee is either transported bagged or shipped in bulk containers. In both cases, the critical issue is to avoid rewetting through condensation, as this leads to further fungal and OTA contamination.

European Union & OTA Regulations for Coffee
The European Union has set union-wide regulations on OTA in food service. Given the significant contribution of roasted coffee together with soluble coffee, to the OTA human exposure, maximum OTA limits were set (Regulation [EC] No 466/2001). The limits are for roasted coffee and soluble coffee, and these are five ppb and 10 ppb, respectively. This protects public health by preventing the distribution of highly contaminated foodstuffs. The Commission shall review the provisions of the regulation by June 30, 2006, at the latest. This review will concern, in particular, the consideration of setting a maximum level for OTA in green coffee.

Importance of Ochratoxin A Auto-Control
In order to eliminate product rejection costs, it has become imperative to control incoming green coffee for OTA content. The testing of green coffee batches or lots is irregular. The most frequent claim by coffee importers and roasters is that their coffee is delivered with a Quality Certificate. The certificate mainly serves to legally protect the receiver. However, once OTA contaminated coffee is mixed with non-contaminated coffee this will result in high costs due to waste, and product recall. Deliveries of mycotoxin contaminated foodstuffs whose quality guaranteed by a certificate still continues. Therefore, the testing of roasted coffee and its products is already too late to avert these problems. This also damages the supplier’s name in the market when contaminated products are supplied to consumers. The quality certificate has a limited function in protecting the coffee roaster or distributor in this case. However, there is an easy way of ensuring that the quality of the consignment you receive, at any given time, conforms to your set standards. This is achieved through auto-control by means of portable, easy and inexpensive screening tools.

A screening tool for this purpose contains everything the screener needs for the test and the total time of the test is only a couple of minutes. Results of such a screening test are evaluated visually in which case the tester is able to make a quick decision as to whether or not the delivery conforms to internal quality specifications and or EU regulations. Euro-Diagnostica BV, (www.eurodiagnostica.nl) markets a rapid test for OTA detection in green coffee. This test does not require a laboratory environment or the equipment. The test is fairly simple, so much so that an untrained person can perform it. The results are evaluated visually and the test takes 10 minutes to complete (sample preparation included). A number of coffee importers and roasters are already using this test for auto-control within their receiving and processing environments.

OTA testing should be used as part of the HACCP system within the coffee processing company. Coffee reception is a critical control point where OTA screening should take place.

About the Author: Dr. Liberty Sibanda is the product manager at: Toxi-Test N.V., Harelbekestraat 72, B-9000 Gent, Belgium.


Tea & Coffee - January/February, 2006
Modern Process Equipment

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