Flavanol Units Research Articles

Taste and Mouthfeel Properties of Red Wines Proanthocyanidins and Their Relation to the Chemical Composition

The aim of this work is to assess the relationship between the in-mouth sensory properties of proanthocyanidins (PAs) and its chemical composition. To achieve such a goal, the proanthocyanidin fraction from six different young commercial red wines was obtained by gel permeation chromatography. A sensory panel, selected on the basis of their PROP status and trained in taste and mouthfeel sensations, described both the wines and fractions. MALDI-TOF-MS and UPLC-MS were used to identify thoroughly the polyphenolic composition of each proanthocyanidin fraction. The results showed that the PAs fractions were exclusively described as astringent and persistent. The astringent subqualities studied (velvety and puckering/drying) were mainly related to the quantity of proanthocyanidins and the proportion of the extension flavanol units linked to proanthocyanidins. A significant negative correlation was found between both of the astringencies (velvety and puckering/drying). Furthermore, both subqualities appeared to contribute to the persistence. A significant correlation was observed between the astringency and the persistence data of the wines and fractions. Significant multiple linear regressions were found between the sensory astringency data and the chemical compounds analyzed. The concentration of proanthocyanidins present in young red wines is the major determinant of the differences perceived in the astringency. Additionally, the extension flavanol units linked to the proanthocyanidins seem to have a different impact on the astringent subqualities.

Structural Elucidation of Condensed Tannin from <i>Picea mariana</i> Bark

The aim of this work was to determine the structural characteristics of the condensed tannins isolated from the aqueous extract of black spruce (Picea mariana Mill) bark. This is the first report on the structural characterization of condensed tannins from black spruce bark. The condensed tannins from the hot water extract prepared from Picea mariana bark were isolated by column chromatography on Sephadex LH-20 media. In this study, UV-visible and 13C-NMR spectroscopic techniques, along with pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and liquid chromatogramphy analyses were applied to determine the structural characteristics of black spruce bark tannins. We have confirmed for the first time the presence of methoxylated B-rings in the flavanol units of condensed tannins from black spruce bark, which could be regarded as further contribution to the chemotaxonomy of the genus Picea. The methoxylation of Norway spruce bark condensed tannins have been demonstrated previously.

Analysis of catechins and condensed tannins by thermally assisted hydrolysis/methylation-GC/MS and by a novel two step methylation

The objective of this study is to observe high molecular weight markers of catechins and condensed tannins by thermally assisted hydrolysis/methylation (THM)-GC/MS. Techniques for formation of intact methylated flavanols of catechins using THM in the presence of trimethylsulfonium hydroxide (TMSH), and, of a dimer marker of condensed tannins using a novel two step methylation technique, are presented. The two step methylation procedure involves pre-methylation of the sample with trimethylsilyl diazomethane (TMS-diazomethane) followed by THM. The dimer marker, a methylated product containing the C–C linkage between adjacent flavanol units, has a molecular weight of 540. Intact methylated flavanols of catechins were also successfully observed as high molecular weight compounds including partially methylated catechin and epicatechin (3-flavanol, 3′,4′,5,7-tetramethoxy, cis/trans; m/ z = 346), epigallocatechin and gallocatechin (3-flavanol, 3′,4′,5,5′,7-pentamethoxy, cis/trans; m/ z = 376). These techniques were successfully applied to the analysis of series of condensed tannins isolated from plants, and catechins and other phenolics present in (hot water) extracts of tea leaves. In green tea the major catechins were identified as epicatechin and epigallocatechin along with flavonols and tannin dimers.

Influence of an 8-trifluoroacetyl group on flavanol couplings

The effect of an electron attracting substituent in the Lewis acid catalyzed oligomerization of flavanols was investigated. The results showed that the presence of a COCF 3, at the 8 position of a (+)-catechin unit strongly influenced the attack of the 6 free nucleophile flavanol position by the electrophile generated from a 4- O-alkyloxy protected catechin unit. This was observed either with TiCl 4 or TMSOTf as Lewis acids in which the carbon–carbon bond formation was inhibited and the corresponding dimer was detected in small amount. On the contrary, the formation of a carbon–oxygen bond was observed and the corresponding C-4→ O→C-3 ether linked procyanidin dimer was isolated in a good yield. In order to avoid the participation of the C-3 hydroxyl group in the dimerization reaction, the two flavanol units were forced into C-4→C-8 coupling by use of an internal link. The structural elucidation of the isolated compounds was achieved through MS and NMR spectroscopy.

Inhibition of Angiotensin Converting Enzyme Activity by Flavanol-Rich Foods

Angiotensin converting enzyme (ACE) activity was evaluated in the presence of flavanol-rich foods, i.e., wines, chocolates, and teas, and of purified flavonoids. All foods assayed inhibited ACE activity, red wines being more effective than white wine, and green tea more effective than black tea. The inhibition of ACE activity was associated with both phenolic and flavanol content in the foods. When isolated polyphenols were assayed, procyanidins (dimer and hexamer) and epigallocatechin significantly inhibited enzyme activity; similar concentrations of (+)-catechin, (-)-epicatechin, gallic acid, chlorogenic acid, caffeic acid, quercetin, kaempferol, and resveratrol were ineffective. When ACE activity was assayed in rat kidney membranes in the presence of chocolate extracts or purified procyanidins, it was observed that the inhibition depended on the chocolate content of flavanols and the number of flavanol units constituting the procyanidin. These experiments demonstrate that flavanols either isolated or present in foods could inhibit ACE activity. The occurrence of such inhibition in vivo needs to be determined, although is supported by the association between the consumption of flavanol-rich foods and reductions in blood pressure observed in several experimental models.

Demonstration of the occurrence of flavanol?anthocyanin adducts in wine and in model solutions

Flavanol–anthocyanin (F–A + ) adducts were detected in red wine. A mechanism involving acid-catalysed cleavage of flavanol oligomers followed by nucleophilic addition of the anthocyanin moiety (in its hemiketal form) to the resulting carbocation (F + ) was postulated. To confirm this mechanism, reactions between malvidin 3- O -glucoside (Mv3glc) and procyanidin dimer epicatechin-(4-8)-epicatechin 3- O -gallate (B2-3′OG) were studied in a model solution system at pH 2. A new pigment with a UV-Vis spectrum similar to that of Mv3glc and a signal at m / z =781 in the positive ion mode was detected and was attributed to Ec–Mv3glc, in agreement with the proposed reaction pathway. A protocol adapted from the synthesis of procyanidin dimers, in which the terminal flavanol units was replaced with Mv3glc, was tested. Two new pigments were formed with a signal at m / z =781, in the positive ion mode. These ions were attributed to catechin–Mv3glc. Both adducts obtained by hemisynthesis showed exactly the same fragmentation pattern as that present in wine. In particular, the loss of a 126 amu fragment corresponding to the unsubstituted A-ring of the flavanol unit indicated that all of them were (epi)catechin–Mv3glc adducts. These results prove that reactions between the carbocations resulting from cleavage of tannin interflavanic bonds and anthocyanins occur in wine.

Demonstration of the occurrence of flavanol–anthocyanin adducts in wine and in model solutions

Flavanol–anthocyanin (F–A +) adducts were detected in red wine. A mechanism involving acid-catalysed cleavage of flavanol oligomers followed by nucleophilic addition of the anthocyanin moiety (in its hemiketal form) to the resulting carbocation (F +) was postulated. To confirm this mechanism, reactions between malvidin 3- O-glucoside (Mv3glc) and procyanidin dimer epicatechin-(4-8)-epicatechin 3- O-gallate (B2-3′OG) were studied in a model solution system at pH 2. A new pigment with a UV-Vis spectrum similar to that of Mv3glc and a signal at m/ z=781 in the positive ion mode was detected and was attributed to Ec–Mv3glc, in agreement with the proposed reaction pathway. A protocol adapted from the synthesis of procyanidin dimers, in which the terminal flavanol units was replaced with Mv3glc, was tested. Two new pigments were formed with a signal at m/ z=781, in the positive ion mode. These ions were attributed to catechin–Mv3glc. Both adducts obtained by hemisynthesis showed exactly the same fragmentation pattern as that present in wine. In particular, the loss of a 126 amu fragment corresponding to the unsubstituted A-ring of the flavanol unit indicated that all of them were (epi)catechin–Mv3glc adducts. These results prove that reactions between the carbocations resulting from cleavage of tannin interflavanic bonds and anthocyanins occur in wine.

Effect of the number of flavanol units on the antioxidant activity of procyanidin fractions isolated from chocolate.

Of three different solvents (acetone, ethanol, and methanol) mixed with water and acetic acid, the acetone/water/acetic acid mixture (70:28:2, v/v) proved to be best for extracting dark-chocolate procyanidins. High-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-MS-ESI) was further used to identify oligomers found in the extract. After HPLC fraction collection, the reduction power of flavanoid fractions was measured in the AAPH [2,2'-azobis(2-amidinopropane)dihydrochloride] assay, where oxidation of linoleic acid is induced in an aqueous dispersion. Even expressed in relative monomeric efficiency units, the oxidation-inhibiting power of polymerized oligomers is much stronger than that of monomers. A comparison with 10 usual antioxidants indicated that oligomers with three or more (epi)catechin units are by far the most efficient.

Reaction Between Malvidin 3‐Glucoside and (+)‐Catechin in Model Solutions Containing Different Aldehydes

ABSTRACT: The contribution of the aldehyde composition of wine spirit to the color changes in Port red wine was studied in model solutions. Malvidin 3‐glucoside was shown to be very reactive towards catechin in the presence of different aldehydes: acetaldehyde, isovaleraldehyde, benzaldehyde, propionaldehyde, isobutyraldehyde, formaldehyde, and 2‐methylbutyraldehyde. LC/MS data confirmed the formation of oligomeric pigments resulting from the reaction between the anthocyanin and the flavanol (colored products) and between 2 flavanol units (colorless products) mediated by each aldehyde assayed. The UV‐visible spectra of the colored pigments showed a λmax bathochromically shifted relatively to the λmax of original anthocyanins. All samples revealed a “blueing” and “darkening” color effects using the CIELAB system.

Study of the reactions between (+)-catechin and furfural derivatives in the presence or absence of anthocyanins and their implication in food color change.

(+)-catechin was separately incubated with furfural or with 5-(hydroxymethyl)furfural, and the formation of new oligomeric bridged compounds having flavanol units linked by furfuryl or 5-hydroxymethylfurfuryl groups was observed. LC/ESI-MS analyses detected four dimeric adducts along with intermediate adducts in each solution, and reaction was faster with furfural than with hydroxymethylfurfural. In addition, new compounds exhibiting the same UV--visible spectra as xanthylium salts with absorption maxima around 440 nm were also detected. When malvidin 3-O-glucoside or cyanidin 3-O-glucoside was added to the mixtures, new oligomeric colorless and colored pigments involving both (+)-catechin and anthocyanin moieties were detected, showing thus that the two polyphenols competed in the condensation process. Among the obtained colored pigment adducts, two dimeric compounds in which the flavanol was bridged to the anthocyanin were observed. Their UV-visible spectra were similar to the spectrum of malvidin 3-O-glucoside, but their maximum in the visible region was bathochromically shifted.

The phenols and prodelphinidins of white clover flowers

White clover flowers ( Trifolium repens L.) contain an abundance of phenolics, namely cis- and trans-p-coumaric acid 4- O-β- D-glucopyranoside, the 3- O-β- D-galactopyranosides of myricetin, quercetin and kaempferol together with two new derivatives namely myricetin 3-O-(6″-acetyl)-β- D-galactopyranoside and kaempferol 3- O-(6″-acetyl)-β- D-galactopyranoside. Gallocatechin, epigallocatechin, gallocatechin-(4α-8)-epigallocatechin and their corresponding prodelphinidin polymers were also present. The 13C-NMR spectra showed that the polymers consisted of only gallocatechin and epigallocatechin monomeric units with the latter being about twice as abundant in the extenders but only slightly more than that in the terminating units. The average degree of polymerization was estimated by 13C-NMR and ES–MS, which gave a remarkably consistent result of about 5.8 flavanol units.

Xanthylium salts formation involved in wine colour changes

Summary The reaction of (+)‐catechin in wine‐like model solution was investigated. First appearance of colourless dimeric compounds consisting of two flavanol units linked by carboxy‐methine bridge was observed. Their isolation and further incubation was found to yield two types of yellowish pigments showing visible absorption maxima at 440 and 460 nm, respectively. Mass spectroscopy (MS) spectral analysis showed that the first type were xanthylium salt pigments formed by dehydration of the colourless compounds followed by an oxidation process. The loss of a water molecule was shown to take place between two A ring hydroxyl groups of the colourless dimers. The second type were shown to be ester derivatives of the first ones. Thus ethylester of xanthylium salt was obtained and fully characterized by mass and nuclear magnetic resonance (NMR) spectroscopy. Esterification was found to involve the colourless compound before dehydration and thus a general scheme for xanthylium salt formation was postulated. The proposed scheme constitutes a new xanthylium formation pathway as up to now only anthocyanin‐flavanol reactions were supposed to form xanthylium salt derivatives during wine ageing. This work also provides new support to the contribution of xanthylium salt in colour evolution observed during wine ageing which is generally expressed in an increase of absorption in the 400–500 nm, region of xanthylium salt absorption maxima.

Studies on the acetaldehyde-induced condensation of (-)-epicatechin and malvidin 3-O-glucoside in a model solution system.

The reaction between (-)-epicatechin, malvidin 3-O-glucoside, and acetaldehyde was studied in a model solution system. Ethyl-linked flavanol oligomers and anthocyanin-flavanol derivatives were observed, showing that the two polyphenols competed in the condensation process. Among the anthocyanin-ethyl-flavanol adducts, dimeric compounds in which the flavanol was linked to the anthocyanin with CH(3)-CH bridges were observed. In addition, trimeric and tetrameric products containing one anthocyanin and one, two, or three flavanols units were detected. A tetrameric product containing two anthocyanin and two flavanol units was also found as a doubly charged ion. No compound containing more than two malvidin 3-O-glucosides was detected, suggesting that only one anthocyanin A ring summit can be included in the polymerization process, which thus stops when both ends are occupied by an anthocyanin moiety. Thioacidolysis of the two isolated anthocyanin-ethyl-flavanol dimeric derivatives showed that anthocyanin-ethyl linkage was not sensitive to such reactants, whereas the flavanol-ethyl one was. In addition, flavanol-ethyl linkages involved in anthocyanin-ethyl-flavanol adducts were found to be less sensitive to those involved in flavan-ethyl dimers.

Study of wine tannin oligomers by on-line liquid chromatography electrospray ionization mass spectrometry.

Thiolysis of a wine tannin fraction yielded trihydroxylated flavanol units (as previously observed in grape skins) in addition to the well-known procyanidins (dihydroxylated units), usually described in the literature for grape condensed tannins. To determine how they occur in condensed tannins, the wine fraction was analyzed by liquid chromatography coupled to electrospray ionization mass spectrometry. Thus, various series of ion peaks containing a variable number of trihydroxylated units were detected as monocharged ions from dimers up to pentamers. From pentamers, oligomers were found as doubly charged ions. Heptamer species corresponded to the highest mass detected. These results showed that wine condensed tannins consist of, besides procyanidins, mixed tri- and dihydroxylated flavanol units and also of pure trihydroxylated flavanol units. These new data should be taken into account to interpret organoleptic properties of wines.

An oxidized tartaric acid residue as a new bridge potentially competing with acetaldehyde in flavan-3-OL condensation

Iron-induced oxidation of (+)-catechin in a wine-like solution yielded typical products, including colourless and yellow compounds. Structural characterization of the major colourless one indicated that it is a dimer, in which flavanol units are linked through a carboxy-methine bridge. Unlike what might be expected, the structure showed that oxidation does not affect catechin directly, but tartaric acid, to give glyoxylic acid, which then reacts with two flavanol units. From a mechanistic point of view, the reaction resembles, once glyoxylic acid is formed, that of acetaldehyde-induced condensation well documented in enology. Thus, an ion series (up to trimer) was detected by mass spectrometry in the model solution. On the other hand, yellow products formed from colourless ones, especially from that isolated, suggests that a second pathway contributing to browning competes with polycondensation reactions.

Proanthocyanidin polymers with antisecretory activity and proanthocyanidin oligomers from Guazuma ulmifolia bark

Bioassay-guided fractionation of a crude extract of Guazuma ulmifolia bark led to the isolation of polymeric proanthocyanidins which inactivated cholera toxin (CT). The average degree of polymerization (DP) of the active compounds ranged from 14.4 to 32.0. The polymers consisted mainly of (−)-epicatechin units. In polymers of a representative fraction, the flavanol units were connected by [4 → 8] bonds and, less frequently, by [4 → 6] bonds. Inhibition of CT by tannins increased with M r and conformation flexibility of the tannin molecule. Several known procyanidin oligomers were also isolated. 1H NMR shift rules to distinguish between [4 → 8] and [4 → 6] linked proanthocyanidin peracetates, that have been proposed for dimers, were extended to trimers and a tetramer. A further diagnostic shift parameter to determine the interflavanoid bonding position is presented and the conformation of oligomeric proanthocyanidin peracetates is discussed.

Induction of sister-chromatid exchanges (SCE), polyploidy, and micronuclei by plant flavonoids in human lymphocyte cultures. A comparative study of 19 flavonoids

Nineteen naturally occurring flavonoids were studied with regard to their SCE-inducing potency and their capability of inducing polyploidy and micronuclei in human lymphocyte cultures. The cells were treated for a period of 48 h. The flavone C-glycosides, vitexin and orientin, exhibited a moderate SCE-inducing activity, whereas the other compounds displayed only weak effects or were inactive. Polyploidy was induced by procyanidins consisting of 3 or 4 flavanol units and to a lesser extent by flavone, flavonol, and anthocyanidin aglycones. The aglycones as well as the C-glycosides and the O-glycosides, spiraeoside and luteolin-7-glucoside, were more or less active in inducing micronuclei in the lymphocytes. The flavonol O-glycosides, rutin and hyperoside, and the monomeric and dimeric flavanols failed to produce any genotoxic effects. The results are discussed with respect to a possible structure-activity relationship.

A hypotensive procyanidin-glycoside from Rhamnus lycioides ssp. lycioides

A lyophilized hot water extract of the aerial parts of Rhamnus lycioides L. (Rhamnaceae) produced a lowering of systemic arterial blood pressure in normotensive anaesthetized Wistar rats. An activity-guided fractionation of the methanolic extract led to the isolation of a tetrameric procyanidin-glycoside which produced a clear dose-dependent hypotensive response (1.5–6 mg/kg i.v.). This principle was characterized using acid hydrolysis, thiolytic degradation and spectroscopic methods. It consisted of four flavanol units with a 2,3- cis configuration and with a O-ß- D - glucosylpyranoside function on the epicatechin terminal unit. The interflavan linkage was (4–8).

Proanthocyanidins from Krameria triandra root.

Oligomeric proanthocyanidins were isolated from rhatany root (Krameria triandra) and characterised by acid hydrolysis, thiolytic degradation, and spectroscopic methods. They consisted of 2-14 flavanol units with mainly 2,3-cis configuration and with a propelagonidin:procyanidin ratio of 65:35. The predominant interflavan linkage was [4,8]. [4,6]-Bonds were present in the higher oligomers, presumably forming branched chain units. The astringency of the drug was mainly due to proanthocyanidins with degrees of polymerization from 5-10, and these were also the astringent compounds of rhatany tea and tincture. A pharmacological screening of the extract revealed a significant antimicrobial effect.

Tannins fromHamamelis virginiana: Identification of Proanthocyanidins and Hamamelitannin Quantification in Leaf, Bark, and Stem Extracts

The tannins in leaf, bark, and stem extracts of HAMAMELIS VIRGINIANA were analyzed. Four proanthocyanidins were isolated by HPLC. One was a procyanidin polymer containing only one type of flavanol unit; the other three were polymers of procyanidin and prodelphinidin containing two types of flavanol units. A method of assay of hamamelitannin showed the bark extract to be 31 times richer in hamamelitannin than the leaf extract and 87 times richer than the stem extract.