Abstract

Sensory-guided fractionation of a roasted coffee brew by means of sequential solvent extraction, ultrafiltration, and RP-HPLC demonstrated a group of ethyl acetate soluble compounds formed from O-hydroxycinnamoyl quinic acid derivatives upon coffee roasting as the key compounds contributing to the bitter taste of roasted coffee beverages. LC-MS/MS studies, 1D- and 2D-NMR spectroscopy, syntheses, and model roast experiments with 5-O-caffeoyl- and 5-O-feruloylquinic acid led to the unequivocal identification of 3-O-caffeoyl-γ-quinide (2a), 4-O-caffeoyl-γ-quinide (3a), 5-O-caffeoyl-epi-δ-quinide (4a), 4-O-caffeoyl-muco-γ-quinide (5a), 5-O-caffeoyl-muco-γ-quinide (6a), 3-O-feruloyl-γ-quinide (2b), and 4-O-feruloyl-γ-quinide (3b) as intense coffee bitter tastants. Besides these individual bitter compounds, a highly complex and intensely bitter HPLC fraction was isolated from the ethyl acetate extractables of coffee brew. Application of COSY spectroscopy and alkaline hydrolytic degradation gave strong evidence that the bitter taste of that fraction is due to a multiplicity of rather complex quinic acid lactone isomers multiply esterified with p-coumaric acid, caffeic acid, ferulic acid, 3,4-dimethoxycinnamic acid, and quinic acid, respectively. As representatives of this fraction, 3,4-O-dicaffeoyl-γ-quinide (10), 3,5-O-dicaffeoyl-epi-δ-quinide (11), and 4,5-O-dicaffeoyl-muco-γ-quinide (12) have been isolated, purified, and identified as strongly bitter-tasting compounds in roasted coffee. For the first time, bitter taste recognition thresholds were determined for the individual compounds showing that, strongly depending on their chemical structure, the bitter threshold levels ranged between 9.8 and 180 μmol/l (water).

Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.