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.
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