What makes coffee taste that bitter?

AGFD 104

Thomas Hofmann, thomas.hofmann@wzw.tum.de1, Oliver Frank2, Simone Blumberg2, Christoph Kunert2, and Gerhard Zehentbauer3. (1) Food Chemistry and Molecular Sensory Science, Technische Universität München, Germany, Lise-Meitner-Str. 34, Freising, 85350, Germany, (2) Institute for Food Chemistry, University of Muenster, Corrensstrasse 45, Münster, 48149, Germany, (3) Miami Valley Innovation Center, The Procter & Gamble Company, 11810 East Miami River Road, Ohio, Cincinnati, OH 45252
In addition to its stimulatory effect, the wide popularity of a freshly brewed roast coffee beverage is mainly based on its pleasant, attractive overall flavor including a balanced bitter taste. Compared to the aroma-active volatiles, the information available on these bitter tasting non-volatiles is yet very fragmentary. Although, caffeine, chlorogenic acid degradation products, and a series of heterocycles such as 2,5-diketopiperazines are known as bitter compounds in roasted coffee, it is still unclear as to which of these compounds are coffee key tastants or which additional yet unknown compounds are responsible for the typical coffee bitter taste. By application of a molecular sensory science approach to roasted coffee, combining analytical natural product chemistry and human psychophysical tools, multiple bitter tasting caffeoylquinides, feruloyl quinides, and dicaffeoylquinides have been identified in medium roasted coffee on the basis of LC-MS and 1D/2D-NMR spectroscopy as well as synthetic experiments. Quantitative analysis revealed that quinides are formed with increasing roasting time up to a medium roasting degree. Thereafter, the quinides were found to be degraded again and converted into previously not reported bitter tasting vinylcatechol oligomers. Differing from the pleasant bitter taste profile of the quinides, these compounds exhibited an intense harsh bitter taste quality with human threshold concentrations between 0.023 and 0.178 mmol/kg (water). Preliminary sensory experiments revealed that a synergisitic interplay between the bitter quinides and the harsh bitter vinylcatechol oligomers is contributing to the bitter taste of roasted coffee.