Identification and Quantitation of Reaction Products from Chlorogenic Acid, Caffeic Acid, and Their Thermal Degradation Products with Odor-Active Thiols in Coffee Beverages

A holistic ultraperformance liquid chromatography (UPLC)-time of flight (TOF)-mass spectrometry-based approach was used to screen for storage-induced reaction products consisting of the volatile key coffee thiols methanethiol, 2-furfurylthiol, 2-methyl-3-furanthiol, 3-mercapto-3-methylbutanol, and 3-mercapto-2-butanone and low-molecular weight phenolic constituents of coffee beverages including chlorogenic acid, caffeic acid, and their thermal degradation products hydroxyhydroquinone, catechol, and 4-ethylcatechol. Multiple marker compounds could be detected in thiol-enriched coffee brews after UPLC-TOF-MS profiling and statistical data analysis. Subsequently, marker compounds were synthesized and structurally characterized via high-resolution mass spectrometry and 1D- and 2D-NMR experiments. Quantification of these reaction products in fresh and stored coffee beverages was realized in native coffee and after stir bar sorptive extraction with liquid desorption by means of UHPLC-MS/MS. The quantitative data revealed the biggest influence of storage time on the formation of reaction products between hydroxyhydroquinone and methanethiol and 2-furfurylthiol, while other reaction products were only slightly affected by storage and thus most likely formed during the roasting process.