title: Structure determination of 3-O-caffeoyl-epi-gamma-quinide, an orphan bitter lactone in roasted coffee.
abstract: Recent investigations on the bitterness of coffee as well as 5- O-caffeoyl quinic acid roasting mixtures indicated the existence of another, yet unknown, bitter lactone besides the previously identified bitter compounds 5- O-caffeoyl- muco-gamma-quinide, 3- O-caffeoyl-gamma-quinide, 4- O-caffeoyl- muco-gamma-quinide, 5- O-caffeoyl- epi-delta-quinide, and 4- O-caffeoyl-gamma-quinide. In the present study, this orphan bitter lactone was isolated from the reaction products generated by dry heating of 5- O-caffeoylquinic acid model, and its structure was determined as the previously unreported 3- O-caffeoyl- epi-gamma-quinide by means of liquid chromatography-mass spectrometry (LC-MS) and one-/two-dimensional NMR experiments. The occurrence of this bitter lactone, exhibiting a low bitter recognition threshold of 58 micromol/L, in coffee beverages could be confirmed by LC-MS/MS (negative electrospray ionization) operating in the multiple reaction monitoring mode.
authors.affiliation: Lehrstuhl für Lebensmittelchemie and Molekulare Sensorik, Technische Universität München, Lise-Meitner-Strasse 34, D-85350 Freising-Weihenstephan, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Frank
authors.forename: Simone
authors.initials: S
authors.lastname: Blumberg
authors.forename: Gudrun
authors.initials: G
authors.lastname: Krümpel
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofmann
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003069:Coffee / Q000737:chemistry*; D006801:Humans; D007783:Lactones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D011801:Quinic Acid / Q000737:chemistry; D013649:Taste; D013652:Taste Threshold
chemical_list: D003069:Coffee; D007783:Lactones; D011801:Quinic Acid