Occurrence of ochratoxin A and its stereoisomeric degradation product in various types of coffee available in the Czech market

Ochratoxin A (OTA) belongs among the most frequently occurring mycotoxins in coffee. In order to investigate its contamination levels in products currently available in the market, a broad set of coffee samples (103 in total) collected between 2016 and 2018 in the Czech Republic was investigated. Aqueous-methanolic extracts purified by using immunoaffinity columns were analysed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (U-HPLC-MS/IVIS). The undertaken study revealed a relatively low OTA contamination of roasted coffee (in the range 0.2-2.5 mu g/kg with the mean concentration of 0.6 mu g/kg, and 71% of positive samples). The roasted coffee samples did not exceed the maximum limit of 5 mu g/kg set by 1881/2006/EC. With regard to instant coffee samples, OTA concentrations were considerably higher. All the samples were positive, with a mean concentration of 2.9 mu g/kg (ranging from 0.6 to 12.8 mu g/kg, with 100% of positive samples). One of the analysed samples of instant coffee even exceeded the maximum limit of 10 mu g/kg (1881/2006/EC). The study further revealed a relatively high incidence of 14-(R)-OTA, stereoisomer of OTA (14-(S)-OTA), originating as its main degradation product. Its identity was confirmed by high resolution mass spectrometry (HRMS/MS). Most of the samples positive for OTA were also positive for this diastereoisomer, with signal intensities of approx. one-third to one half of the signal of 14-(S)-OTA.