Sensory-Guided Decomposition of Roasted Cocoa Nibs (Theobroma cacao) and Structure Determination of Taste-Active Polyphenols

Abstract

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-(4β→8)]₃-epicatechin, and [epicatechin-(4β→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. Keywords: Cocoa beans; astringency; bitter taste; taste dilution analysis; half-tongue test; (+)-N-[4‘-hydroxy-(E)-cinnamoyl]-l-aspartic acid; (+)-N-[3‘,4‘-dihydroxy-(E)-cinnamoyl]-l-aspartic acid