Science Snippets!

Coffee (Coffea arabica or canephora) is consumed world-wide in different forms: boiling, drip (gravity), espresso, instant, and French press for example. Coffee is produced in Central- and South-America, Africa, and Asia---climates with warm days and cool nights, and plenty of moisture. Ochratoxin A (OTA) is a mycotoxin that can be a problematic for the coffee industry when levels are too high.

In cereal crops, OTA is generally reduced when grain is exposed to heat and moisture. However, research on coffee roasting and OTA content showed varying results: some data show a large reduction, while others showed a moderate reduction of OTA content (Suárez-Quiroz et al., 2005). Thus Suárez-Quiroz et al. (2005) designed a study to test the effect of roasting and brewing on OTA content in coffee.

Roasting: Green Arabica coffee beans were purposefully contaminated with Aspergillus spores to produce OTA and then roasted at two different air temperatures: 200 or 250°C. Three different roasting types were achieved: light, medium, and dark. The greatest OTA reductions were found in the dark and medium roast (approx. 81.0 to 77.0% respectively). The light roast showed an average reduction of 55.6%. The authors suggest roasting time is more important in OTA reduction than air temperature.

Brewing: The authors used roasted coffee that was contaminated with 25.0-µg/kg (or 25.0 ppb) OTA for their brewing experiments. They prepared coffee by gravity (filter), espresso, and plunger (French press) methods. The coffee brews were then analyzed by HPLC for OTA. Suárez-Quiroz et al. (2005) surprisingly found that OTA content in the filter and plunger coffee was higher (30.1 ppb) than the original OTA contamination level. The espresso coffee showed a reduction of OTA by 25.0%. The authors hypothesize the OTA increase in the filter and plunger coffee could be due to: 1. ‘hot’ extraction of OTA—e.g. OTA was higher in coffee brews because it was extracted using high temperature used during coffee brewing; 2. the exposure time to water is longer in filter and plunger coffee compared to espresso coffee, and 3. the OTA content tested after the roasting process was actually higher due a partial ‘masking” of the OTA molecule by binding to proteins during roasting (Suárez-Quiroz et al., 2005).

The authors discuss the conflicting results in the OTA reduction found in the roasting and brewing experiments. The authors suggest that starting out with green un-roasted coffee beans low in OTA content is the best to ensure low exposure to OTA by coffee drinkers. Thus testing green coffee beans for OTA seems warranted.

Reference:

Suárez-Quiroz, M., B. De Louise, O. Gonzales-Rios, M. Barel, B. Guyot, S. Schorr-Galindo, and J-P. Guiraud. 2005. The impact of roasting on the ochratoxin A content of coffee. Int. Journal of Food Science and Technology. 40:605-611.