Quantitative studies on the influence of the bean roasting parameters and hot water percolation on the concentrations of bitter compounds in coffee brew

To investigate the influence of roasting time and temperature on the degradation of the bitter precursors 3-O-caffeoyl quinic acid (1), 5-O-caffeoyl quinic acid (2), and 4-O-caffeoyl quinic acid (3) as well as the formation of bitter tastants during coffee roasting, we prepared coffee brews from beans roasted either at 260 ^°C for 60-600 s or for 240 s at 190-280 ^°C. By means of HPLC-UV/vis and HPLC-MS/MS, bitter-tasting monocaffeoyl quinides (4-8), dicaffeoyl quinides (9-11), and 4-vinylcatechol oligomers (12-20) as well as the parent bitter precursors 1-3 were quantitatively analyzed in these brews. Quinides 4-11, exhibiting a coffee-typical bitter taste profile, were found to be preferentially formed under slight to medium roasting degrees and were observed to be degraded again to generate harsh bitter-tasting 4-vinylcatechol oligomers under more severe roasting conditions, thus matching the change in bitter taste quality observed by means of sensory studies. In addition, quantitative studies of the release profile of bitter compounds from ground coffee upon water percolation revealed that compounds 1-8 were rapidly extracted, dicaffeoyl quinides 9-11 were released rather slowly, and, in particular, compounds 12-17 were found to show strong retention to the ground coffee material. These data imply that the knowledge-based control of the roasting and/or the extraction conditions might be helpful in tailoring the bitter taste signature of coffee beverages.