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  • Title: Application of a molecular sensory science approach to alkalized cocoa (Theobroma cacao): structure determination and sensory activity of nonenzymatically C-glycosylated flavan-3-ols.
    Author: Stark T, Hofmann T.
    Journal: J Agric Food Chem; 2006 Dec 13; 54(25):9510-21. PubMed ID: 17147440.
    Abstract:
    Application of comparative taste dilution analyses on nonalkalized and alkalized cocoa powder revealed the detection of a velvety, smoothly astringent tasting fraction, which was predominantly present in the alkalized sample. LC-MS/MS analysis, 1D- and 2D-NMR, and CD spectroscopy as well as model alkalization reactions led to the unequivocal identification of the velvety, smoothly astringent molecules as a series of catechin- and epicatechin-C-glycopyranosides. Besides the previously reported (-)-epicatechin-8-C-beta-D-galactopyranoside, additional flavan-3-ol-C-glycosides, namely, (-)-epicatechin-8-C-beta-D-glucopyranoside, (-)-catechin-8-C-beta-D-glucopyranoside, (-)-catechin-6-C-beta-D-glucopyranoside, (-)-epicatechin-6-C-beta-D-glucopyranoside, (-)-catechin-8-C-beta-D-galactopyranoside, (-)-catechin-6-C-beta-D-galactopyranoside, (-)-catechin-6-C,8-C-beta-D-diglucopyranoside, (-)-epicatechin-6-C,8-C-beta-D-digalactopyranoside, (-)-catechin-6-C,8-C-beta-D-digalactopyranoside, and epicatechin-6-C,8-C-beta-D-diglucopyranoside, were identified for the first time in cocoa. Most surprisingly, these phenol glycoconjugates were demonstrated by model experiments to be formed via a novel nonenzymatic C-glycosylation of flavan-3-ols. Using the recently developed half-tongue test, human recognition thresholds for the astringent and mouth-drying oral sensation were determined to be between 1.1 and 99.5 micro mol/L (water) depending on the sugar and the intramolecular binding position as well as the aglycone.
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