Application of a Molecular Sensory Science Approach to Alkalized Cocoa (Theobroma cacao):  Structure Determination and Sensory Activity of Nonenzymatically C-Glycosylated Flavan-3-ols

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.

The Occurrence, Fate and Biological Activities ofC-glycosyl Flavonoids in the Human Diet

“…These are the corresponding (-)-catechin epimers of the cocoa (-)-epicatechin C-glycosides alongside (-)-catechin-6-C--D-galactopyranoside (Stark and Hofmann, 2006;Stark et al, 2007). Table 4 outlines these structures.…”

“…The principal reaction is catalysed in these plants by the C-glycosyltransferase (CGT) family of enzymes, the best characterised of which is OsCGT: a 49 kDa enzyme related strongly in amino acid sequence to the known O-glycosyltransferases (Brazier-Hicks et al, 2009). More recently, aglycone flavan-3-ol structures such as epicatechin have been shown to be non-enzymically mono-or di-C-glycosylated with glucose or galactose during post-harvest processing, although as with OsCGT-catalysed glycoconjugation, positions of substitution are limited to the hydroxyl groups at 6 and 8 positions (Stark and Hofmann, 2006).…”

Phytochemical investigation of the rhizomes of Dryopteris crassirhizoma

“…1), 1 was elucidated as trisflavaspidic acid ABB which differ from the known trisflavaspidic acid BBB by having an acetyl group at C-3 instead of a butyryl group. Known compounds were characterized as filixic acid ABA (Widen et al, 1994), dryocrassin (Noro et al, 1973), albaspidin AA (Widen et al, 1994), flavaspidic acid AB (Hisada et al, 1973), (À)epicatechin, (À)epicatechin-8-C-b-D-glucopyranoside (Stark and Hofmann, 2006), hydroxyhopane (Nakano et al, 2004), nerolidol, caffeic acid, hexacosanoic acid, pentacosanol, and 3-hydroxyheptacosanol.…”

Taste Modulating N-(1-Methyl-4-oxoimidazolidin-2-ylidene) α-Amino Acids Formed from Creatinine and Reducing Carbohydrates

“…15,16 Besides Maillard-type glycation of amino acids and organic acids, the nonenzymatic C-glycosylation of flavan-3-ols was reported to give rise to taste modulators during the manufacturing of roasted, alkalized cocoa powder. 17 By means of the sensomics approach, (epi)catechin-6-C-β-D-glucosides, (epi)-catechin-8-C-β-D-glucosides, and (epi)catechin-6,8-C-β-D-glucosides were identified as velvety astringent taste molecules and demonstrated to significantly decrease the perceived bitterness of theobromine. 17 Very recently, application of the sensomics approach on commercial yeast extracts revealed (S)-N 2 -(1-carboxyethyl)-guanosine 5 0 -monophosphate as a previously unreported umami-enhancing nucleotide.…”

“…17 By means of the sensomics approach, (epi)catechin-6-C-β-D-glucosides, (epi)-catechin-8-C-β-D-glucosides, and (epi)catechin-6,8-C-β-D-glucosides were identified as velvety astringent taste molecules and demonstrated to significantly decrease the perceived bitterness of theobromine. 17 Very recently, application of the sensomics approach on commercial yeast extracts revealed (S)-N 2 -(1-carboxyethyl)-guanosine 5 0 -monophosphate as a previously unreported umami-enhancing nucleotide. 18,19 Supported by systematic model experiments, this taste modulator, besides a series of structurally related (S)-N 2 -(1-carboxyalkyl)guanosine 5 0 -monophosphates and (S)-N 2 -(1-alkylamino)carbonylalkyl) guanosine 5 0 -monophosphates, could be confirmed to be generated by Maillard-type reactions between 5 0 -GMP and reducing monosaccharides.…”