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Sequential application of solvent extraction, gel permeation chromatography, and RP-HPLC in combination with taste dilution analyses, followed by LC-MS and 1D/2D-NMR experiments and thiolytic degradation, revealed that, besides theobromine and caffeine, the flavan-3-ols epicatechin, catechin, procyanidin B-2, procyanidin B-5, procyanidin C-1, epicatechin-(4beta-->8)(3)-epicatechin, and epicatechin-(4beta-->8)(4)-epicatechin were among the key compounds contributing to the bitter taste as well as the astringent mouthfeel imparted upon consumption of roasted cocoa. In addition, a series of quercetin, naringenin, luteolin, and apigenin glycopyranosides as well as a family of not previously identified amino acid amides, namely, (+)-N-4'-hydroxy-(E)-cinnamoyl-L-aspartic acid, (+)-N-3',4'-dihydroxy-(E)-cinnamoyl-L-aspartic acid, (-)-N-3',4'-dihydroxy-(E)-cinnamoyl-L-glutamic acid, (-)-N-4'-hydroxy-(E)-cinnamoyl-L-glutamic acid, (-)-N-4'-hydroxy-(E)-cinnamoyl-3-hydroxy-L-tyrosine, (+)-N-4'-hydroxy-3'-methoxy-(E)-cinnamoyl-L-aspartic acid, and (+)-N-(E)-cinnamoyl-L-aspartic acid, have been identified as key astringent compounds of roasted cocoa. Furthermore, (-)-N-3',4'-dihydroxy-(E)-cinnamoyl-3-hydroxy-l-tyrosine (clovamide), (-)-N-4'-hydroxy-(E)-cinnamoyl-L-tyrosine (deoxyclovamide), and (-)-N-3',4'-dihydroxy-(E)-cinnamoyl-L-tyrosine, reported previously as antioxidants, have been found as contributors of cocoa's astringent taste. By means of the half-tongue test, the taste thresholds of flavan-3-ols and glycosides have been determined.
Stark et al. (Wed,) studied this question.