Estimation of procyanidin chain length.
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Biflavonoids↗
Biomedical subjects
M Moutounet
Publications and source records attributed to M Moutounet.
New phenolic compounds formed by evolution of (+)-catechin and glyoxylic acid in hydroalcoholic solution and their implication in color changes of grape-derived foods.
The reaction between (+)-catechin and glyoxylic acid in model solution system was investigated by LC/DAD and LC/ESI-MS analyses. The formation of phenolic compounds exhibiting absorption maxima near 300 nm and presenting a shoulder around 350 nm was observed. Their structures consisted of a (+)-catechin unit with one or two aldehyde groups linked at positions 6, 8 or 6 and 8 of the A ring. In addition, new yellow pigments exhibiting UV-visible spectra similar to those of xanthylium salts with absorption maxima at 450 and 280 nm were also detected. The major yellow compound was isolated and identified by ESI-MS and 1D and 2D NMR spectroscopy. The implication of these compounds in color change and browning observed during aging of grape-derived beverages is also discussed.
Alcohols↗
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.
Anthocyanins↗
Phenolic composition of grape stems.
Grape stems contain significant amounts of polyphenolic compounds, especially phenolic acids, flavonols, and flavanonols such as astilbin. The tannin content was characterized after the depolymerization reaction thiolysis. Tannins consisted of polymeric proanthocyanidins (up to 27 units) mainly consisting of (-)-epicatechin units along with smaller amounts of (+)-catechin, (-)-epicatechin gallate, and (-)-epigallocatechin. Flavanonols (astilbin) have been identified for the first time in stem and characterized by LC/MS and NMR. All phenolic compounds in grape stems were quantified by HPLC: quercetin 3-glucuronide was the most important, followed by catechin, caffeoyltartaric acid, and dihydroquercetin 3-rhamnoside (astilbin). Comparison was made of proanthocyanidin characteristics in different white and red grape varieties and also among parts of the cluster (skin, seed, and stem). Stem-condensed tannins were qualitatively intermediate between seed and skin but could not be differentiated between red and white varieties.
Flavonoids↗
Interactions of grape seed tannins with salivary proteins.
To evaluate the amount and type of condensed tannins binding salivary proteins, which are supposed to be involved in astringent sensation, model systems allowing further analyses of proteins and condensed tannins were developed. The precipitates formed after addition of grape seed tannins to salivary proteins indicate that a binding interaction occurs. Dissociation of insoluble complexes was achieved by sodium dodecyl sulfate treatment. Thiolysis reaction allowed the quantification and characterization of proanthocyanidins on both the resulting pellet and the supernatant. Binding proteins were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The higher polymerized tannins predominantly precipitated together with the salivary proteins. The condensed tannins remaining in solution were low molecular weight polymers.
Electrophoresis, Polyacrylamide Gel↗
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.
Catechin↗
Competition between (+)-catechin and (-)-epicatechin in acetaldehyde-induced polymerization of flavanols.
The reactions of (+)-catechin and (-)-epicatechin in the presence of acetaldehyde were studied in model solution systems. When incubated separately with acetaldehyde and at pH values varying from 2.2 to 4. 0, reactions were faster with (-)-epicatechin than with (+)-catechin. In mixtures containing both (+)-catechin and (-)-epicatechin with acetaldehyde, new compounds besides the homogeneous bridged derivatives were detected. These compounds were concluded to be hetero-oligomers consisting of (+)-catechin and (-)-epicatechin linked with an ethyl bridge. In this case, the reaction of (-)-epicatechin was faster than that of (+)-catechin. This was also observed in solutions containing the two flavanols and the (+)-catechin-ethanol intermediate. Under these conditions, the homogeneous (+)-catechin bridged dimers and heterogeneous dimers were obtained by action of the intermediate on (+)-catechin and (-)-epicatechin, respectively. In addition, the homogeneous (-)-epicatechin ethyl-bridged dimers were also detected, showing that ethyl linkages underwent depolymerization and recombination reactions.
Acetaldehyde↗
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.
Acetaldehyde↗
Quantitative fractionation of grape proanthocyanidins according to their degree of polymerization.
A method was developed for the fractionation of grape (seed or skin) proanthocyanidins according to their degree of polymerization. After precipitation in chloroform/methanol (75:25, v/v), the grape proanthocyanidins were deposited onto an inert glass powder column and sequentially dissolved in several fractions by increasing proportions of methanol in the solvent. Each fraction from each proanthocyanidin source was quantified and characterized after acidic degradation with phenylmethanethiol (i.e., thiolysis). The comparison of data from total extract and successive fractions showed that a quantitative separation was achieved so that estimation of polymer size distribution in relation to other compositional characteristics (proportions of prodelphinidin units, galloylation rate) was thus possible. Mean degree of polymerization of separated proanthocyanidins ranged increasingly from 4.7 to 17.4 in seed (8.1 for total extract) and from 9.3 to 73.8 in skin (34.9 for total extract). The method proposed is very interesting for the study of grape proanthocyanidins according to their degree of polymerization because it gives both qualitative and quantitative information especially on the highly polymerized forms, which were not fractionated by previous techniques.
Anthocyanins↗
New polyphenolic compounds with xanthylium skeletons formed through reaction between (+)-catechin and glyoxylic acid.
The reaction between (+)-catechin and glyoxylic acid was studied in a model solution system. The major (+)-catechin carboxymethine-linked dimer was isolated and shown to proceed to new polyphenolic compounds exhibiting absorption maxima around 440 and 460 nm. Three yellow pigments were obtained by incubation of the 8-8 colorless isomer. One was the previously reported xanthylium compound NJ2 with a maximum at 440 nm. The other two, showing absorption maxima at 460 nm, were obtained separately by incubation of the colorless dimer in hydroethanolic or methanolic medium. Structural elucidation of these two new yellow pigments was achieved by means of MS and 1D and 2D NMR techniques and showed that they were, respectively, ethyl and methyl esters of NJ2. The fact that these compounds were not obtained when NJ2 was incubated in hydromethanolic or ethanolic medium showed that esterification took place before the formation of the xanthylium chromophores. The detection of the esterified colorless compounds and the corresponding xanthene intermediates confirmed the postulated mechanism. New pigments exhibiting a strong absorption at 560 nm were also observed.
Catechin↗
A new class of wine pigments generated by reaction between pyruvic acid and grape anthocyanins.
A new class of stable red pigments detected in grape pomace was analysed by electrospray ionisation mass spectrometry. They were shown to be pyruvic acid derivatives of genuine grape anthocyanins by synthesis experiments. The major product was identified by NMR (1H, NOE, HSQC, HMBC) experiments as the malvidin-3-monoglucoside pyruvic acid adduct. Its formation results from cyclisation between C-4 and the hydroxyl group at C-5 of the original flavylium moiety with the double bond of the enolic form of pyruvic acid, followed by dehydration and rearomatisation steps. This type of reaction leads to increased colour stability. Various yeast metabolites other than pyruvic acid were shown to react with grape anthocyanins following this mechanism, suggesting that it may be an important route of conversion into stable pigments during the maturation and ageing of wine.
Anthocyanins↗
New investigations of the structure of grape arabinogalactan-protein.
The structure of an arabinogalactan-protein (AGP) isolated from grape juice was studied by methylation analysis, n.m.r. spectroscopy, and interactions with peanut lectin, after specific degradation with purified enzymes and/or Smith degradation. AGP appeared to be homogeneous with a weight-average molecular weight of 110,000. Treatment of AGP with arabinofuranosidase released 88% of the arabinose and left GP1. Hydrolysis of GP1 with an endo-(1----6)-beta-D-galactanase removed 50% of the galactose and left GP2. Smith degradation of GP1 gave a 3-linked galactan that still contained 3,6-linked residues. Endogalactanase- and Smith-degraded GP1, but not AGP and GP1, reacted strongly with peanut lectin. Thus, AGP is a 3-linked galactan cross-linked at positions 6. The core also carries, at positions 6, 6-linked galactan chains heavily 3-substituted with arabinofuranose residues.
Carbohydrate Sequence↗
Determination of ellagitannins in extracts of oak wood and in distilled beverages matured in oak barrels.
A method is described for determination of ellagitannins in ethanol-water extracts of oak wood and in distilled alcoholic beverages matured in oak barrels. It is based on the combined ellagic acid content according to ellagitannin structure. Hydrolysis was carried out in the presence of hydrochloric acid under reflux in a 100 degrees C oil bath for 3 h. Total ellagic acid was thus determined by liquid chromatography (LC), and the free ellagic acid content present in the ethanol-water media was subtracted, the difference being the combined ellagic acid content corresponding to ellagitannins. A 5 micron C18 column was used with detection at 254 nm. The method is specific for ellagitannins, which is an advantage over other analytical techniques for overall evaluation of these substances extracted from wood. Results for spirits distilled from wine, grain, and sugarcane were highly variable.
Alcoholic Beverages↗
Liquid chromatographic determination of scopoletin in hydroalcoholic extract of oak wood and in matured distilled alcoholic beverages.
A liquid chromatographic (LC) method is described for determination of the coumarins esculin, umbelliferone, scopoletin, and 4-methyl umbelliferone in hydroalcoholic extracts of oak wood and in matured distilled alcoholic beverages. Samples were injected directly into the LC column (30 cm, 5 micron C18) and detected by fluorescence detector. Under these experimental conditions, only scopoletin (detection limit, 200 pg) was found in hydroalcoholic oak wood extracts and in spirits matured in oak wood. Applications of this method to spirits distilled from wine, grain, and sugar cane aged in oak barrels showed that amounts varied from 0.026 to 1.57 ppm.
Alcoholic Beverages↗