Screening and identification of bitter compounds in roasted coffee brew by taste dilution analysis

Intense bitter taste compounds were identified in roasted coffee brew using sensory-guided fractionation, LC-MS/MS and 1D/2D-NMR spectroscopy, syntheses, and model roasting experiments with potential precursors. The intense bitter tastants of coffee were 3-O-caffeoyl-γ-quinide (1), 4-O-caffeoyl-γ-quinide (2), 4-O-caffeoyl-muco-γ-quinide (3), 5-O-caffeoyl-muco-γ-quinide (4), 5-O-caffeoyl-epi-δ-quinide (5), 3-O-feruloyl-γ-quinide (6), 4-O-feruloyl-γ-quinide (7) 3,4-O-dicaffeoyl-γ-quinide (8), 4,5-O-dicaffeoyl-muco-γ-quinide (9) and 3,5-O-dicaffeoyl-epi-δ-quinide (10). Determination of the bitter taste recognition thresholds showed that, depending on their chemical structure, the bitter threshold concentrations ranged between 9.8 and 180 μmol/l (water). Quantification and determination of the dose over threshold factors for the individual bitter compounds revealed that approximately 80% of the bitterness of the decaffeinated coffee beverage could be related to these 10 quinides.