Occurrence of the Ochratoxin A Degradation Product 2′R-Ochratoxin A in Coffee and Other Food: An Update

Food raw materials can contain the mycotoxin ochratoxin A (OTA). Thermal processing of these materials may result in decreased OTA levels but also in the formation of the thermal isomerization product 2'R-ochratoxin A (2'R-OTA). So far, only 2'R-OTA levels reported from 15 coffee samples in 2008 are known, which is little when compared to the importance of coffee as a food and trading good. Herein, we present results from a set of model experiments studying the effect of temperatures between 120 °C and 270 °C on the isomerization of OTA to 2'R-OTA. It is shown that isomerization of OTA starts at temperatures as low as 120 °C. At 210 °C and above, the formation of 25% 2'R-OTA is observed in less than one minute. Furthermore, 51 coffee samples from France, Germany, and Guatemala were analyzed by HPLC-MS/MS for the presence of OTA and 2'R-OTA. OTA was quantified in 96% of the samples, while 2'R-OTA was quantifiable in 35% of the samples. The highest OTA and 2'R-OTA levels of 28.4 µg/kg and 3.9 µg/kg, respectively, were detected in coffee from Guatemala. The OTA:2'R-OTA ratio in the samples ranged between 2.5:1 and 10:1 and was on average 5.5:1. Besides coffee, 2'R-OTA was also for the first time detected in a bread sample and malt coffee powder.