Isolation and quantification of oligomeric pyranoanthocyanin-flavanol pigments from red wines by combination of column chromatographic techniques

Effects of Phenolic Evolution on Color Characteristics of Single-Cultivar Vitis vinifera L. Marselan and Merlot Wines during Vinification and Aging

The loss of red hue in dry red wine has been a persistent issue for wine enterprises in western China. We investigated the changes in anthocyanins and non-anthocyanin phenols during the industrial-scale fermentation and one-year bottle aging of Vitis vinifera L. Merlot and Vitis vinifera L. Marselan, respectively, using the grapes in the Ningxia region. We also examined their correlation with color characterization. The study found that both anthocyanins and non-anthocyanin phenolics were rapidly extracted from grapes during alcohol fermentation. However, their concentrations decreased rapidly during malolactic fermentation. On the other hand, Vitisin A and Vitisin B were formed during alcoholic fermentation and decreased slowly from malolactic fermentation to storage period. Directly polymerized pigments (F-A and A-F), bridged polymerized pigments (A-e-F), and flavanyl-pyranoanthocyanins (A-v-F) from the reactions of anthocyanins (A) and flavan-3-ols (F), as well as pinotins were generated during the later stages of alcoholic fermentation, and remained at a high level throughout malolactic fermentation and bottle storage. Partial least squares regression and Pearson correlation analyses revealed that the red hue (a* value) of 'Merlot' and 'Marselan' wines was closely associated with monomeric anthocyanins and F-A type pigments. Furthermore, four pinotin components were positively correlated with the red hue (a* value) of 'Merlot' wine. These primary red components of the two varieties had a positive correlation with the level of flavan-3-ols. The data suggest that elevating the flavan-3-ol concentration during fermentation aids in improving the color stability of red wine.

The structure of anthocyanins and the copigmentation by common micromolecular copigments: A review

Under natural physiological conditions, anthocyanins can keep bright and stable color for a long time due to the relatively stable acid-base environment of plant vacuoles and the copigmentation from various copigment substances, such as polyphenols, nucleotides, metallic ions and other substances. Therefore, the copigmentation caused by copigments is considered an effective way to stabilize anthocyanins against adverse environmental conditions. This is attributed to the covalent and noncovalent interactions between colored forms of anthocyanins (flavylium ions and quinoidal bases) and colorless or pale yellow organic molecules (copigments). These interactions are usually manifested in both hyperchromic effect and bathochromic shifts. In addition to making anthocyanins more stable, the copigmentation also could make an important contribution to the diversification of their tone. Based on the molecular structure of anthocyanins, this review focuses on the interaction mode of auxochrome groups or copigments with anthocyanins and their effects on the chemical and color stability of anthocyanins.

Grape Pomace Valorization by Extraction of Phenolic Polymeric Pigments: A Review

In recent years there has been a growing concern about environmental pollution linked to the generation of agroindustrial waste. The wine industry generates approximately 8.49 million tons of grape pomace per year worldwide; this residue can be used to obtain compounds with biological activity. Grape pomace is a source of anthocyanins, pigments that have antioxidant properties and help prevent cardiovascular disease. The development of sustainable extraction, purification and identification techniques constitutes an important step in adding value to this waste. Therefore, the present research has focused on presenting a review of works carried out in the last years.

Relevance of the Concentrations and Sizes of Oligomeric Red Wine Pigments to the Color Intensity of Commercial Red Wines

Color is a major sensorial characteristic of red wines. Numerous monomeric and some small oligomeric pigments have been characterized from red wines but the contribution of larger oligomeric pigments to the color intensity has not been established by direct measurements. We measured the color intensity of 317 commercial red wines and semiquantified the malvidin glycosides and eight different adduct groups derived from the malvidin glycosides by ultra-performance liquid chromatography-tandem mass spectrometry. Two of these groups were oligomeric pigments consisting of proanthocyanidins and malvidin glycosides with either direct or methylmethine linkages. The carboxypyranomalvidins and the oligomeric pigments were found to be major contributors to the color intensity. Besides the concentrations, the sizes of the oligomeric pigments had a positive and significant connection to the color intensity. The 1-year-old wines were studied separately and, even in the youngest of wines, the adducts of the malvidin glycosides were the major contributors to the color intensity.

Reversed-phase liquid chromatographic analysis of hydrophobic interaction between proanthocyanidins and a C8-alkyl compound in aqueous solution

Structural and physicochemical properties of oligomeric flavan-3-ols (proanthocyanidins) in aqueous solution were investigated by spectrometric and reversed-phase (RP) HPLC analyses. Circular dichroism and fluorescence spectra of (–)-epicatechin (EC) oligomers linked through C-4 to C-8 interflavan bonds showed that EC oligomers larger than dimers formed a stable secondary structure in water. These EC oligomers are water-soluble hydrophilic compounds, whereas the oligomers were strongly retained by a C8-alkyl stationary phase under conventional RP-HPLC conditions. In a further C8-HPLC study, the hydrophobic interaction between EC oligomers and 1-octanesulfonic acid sodium salt (OSA Na) added to the mobile phase was quantitatively evaluated based on the relationship between the logarithm of the retention factor of the solute and the OSA Na concentration in the mobile phase. The strength values of the hydrophobic interaction of EC oligomers larger than dimers were the highest of 22 tested polyphenolic standards.

A polyamide resin based method for adsorption of anthocyanins from blackberries

A polyamide resin was successfully employed for the purification of blackberry anthocyanins and this proved to be an efficient and low-cost method.

Red-fleshed Apples: Old Autochthonous Fruits as a Novel Source of Anthocyanin Antioxidants

In order to promote breeding programs and a full reintroduction into production of two local red-fleshed apple varieties grown in Bekran and Bastam (Iran), the evaluation of their antioxidant properties was of interest. LC-MS(n) based metabolic fingerprinting analyses were applied to investigate the anthocyanin content of both peel and flesh components of the fruits. Cyanidin-3-O-hexoside isomers were present in both 'Bekran' and 'Bastam' apples, whereas 'Bekran' apple was a valuable source of anthocyanin rutinose derivatives. Employing DPPH(•), ABTS(•+), and ORAC methods, the antiradical efficacy was evaluated. The ability of the investigated fruit components to scavenge OH(•), and O(2) (•-) reactive species was also assessed. ID(50) values highlighted the massive antioxidant response of 'Bekran' peel component, able to counteract by 50 % OH(•), and O(2) (•-) at 130.3 and 91.6 μg/mL, respectively. The cytoprotective screening towards HeLa, HepG2, A549, SH-5YSY, and SK-N-BE(2)-C cell lines evidenced that the investigated Iranian red-fleshed apple fruits were able to exert a significant antioxidant response in hydrogen peroxide oxidized cell systems. Data collected suggested that the revaluation of 'Bekran' and 'Bastam' apple cultivars could represent a precious source of antioxidant compounds whose dietary intake could improve the human well-being reducing risks of free radical related chronic and degenerative diseases.

Highly selective separation and purification of anthocyanins from bilberry based on a macroporous polymeric adsorbent

Powdered bilberry extract (United States Pharmacopoeia, USP35-NF30), which is prepared from ripe bilberry fruits (Vaccinium myrtillus L.), is the main ingredient of drugs alleviating visual fatigue and diabetic retinopathy because of the rich anthocyanins (purity of 36%). In this study, a method based on a macroporous polymeric adsorbent was established to obtain anthocyanin compounds from bilberry, in which the purity of the anthocyanins was improved to 96%, conducive to further pharmacological research and improvement of the efficiency of the drug. On the basis of the structure of anthocyanins, we designed a series of macroporous polymeric adsorbents based on the copolymerization of divinylbenzene (DVB) and ethylene glycol dimethyl acrylate (EGDMA). In this situation, EGDMA not only regulated the polarity of the adsorbent but also acted as the cross-linking agent to ensure the matrix structure of the adsorbent, which had a high specific surface area and could provide more interaction sites during adsorption with anthocyanins. Among the synthesized polymeric adsorbents with different contents of EGDMA, the one with 20% EGDMA content (DE-20) was demonstrated to exhibit optimal adsorption capacity and selectivity to anthocyanins compared to various commercial adsorbents through static adsorption and desorption experiments. In addition, the optimum condition of the dynamic adsorption-desorption experiment was further explored. The results indicated that the purity of anthocyanins after rinsing with 20% ethanol was determined to be approximately 96% at a desorption ratio of 83%, which was clearly higher than that in powdered bilberry extract. The established separation and purification method of anthocyanins with high purity is expected to be applied in industrial production.

Studies on the preparative isolation and stability of seven main anthocyanins from Yan 73 grape

BACKGROUND

[corrected] Seven anthocyanin monomers of Yan 73 grape were separated using preparative HPLC and identified by UPLC-ESI-MS/MS. The stabilities of the seven isolated anthocyanins to light, temperature and pH were also investigated.

RESULTS

Seven anthocyanin monomers were successfully isolated with an Xbridge Prep C18 column on a preparative scale. The pigments delphinidin-3-O-glucoside, malvidin-3-O-acetylglucoside and malvidin-3-O-coumarylglucoside were yielded in a one-step separation by preparative HPLC, with purities up to 99.9%, 91.7% and 95.5%, respectively. The pigments cyanidin-3-O-glucoside, petunidin-3-O-glucoside, peonidin-3-O-glucoside, and malvidin-3-O-glucoside were further purified with another elution method and their purities were all improved up to 99.9%. Monomeric anthocyanin degradation fitted a first-order reaction model. The seven isolated anthocyanins were significantly more stable in the dark than under light. High temperature was also unfavourable for the stability of anthocyanins. The anthocyanins were more stable at lower pH than at higher pH. In addition, among these anthocyanins, delphinidin-3-O-glucoside, malvidin-3-O-acetylglucoside and malvidin-3-O-coumarylglucoside were more susceptible to light, heat, and pH than the others.

CONCLUSION

A simple and clean isolation method of seven anthocyanin monomers from Yan 73 grape was established. The stabilities of the seven anthocyanin monomers to light, temperature and pH were different, but the trends in changes were similar.

Identification, content and distribution of anthocyanins and low molecular weight anthocyanin-derived pigments in Spanish commercial red wines

The content and distribution of low molecular weight red wine pigments (anthocyanins, flavanol-anthocyanins adducts and pyranoanthocyanins) has been analysed in 283 wine samples. A total of 90 red wine pigments were identified and up to 68 of them quantified in most of the wine samples. The content of the different pigments classes accounted for wide ranges of values, because of the diversity of the commercial wines regarding grape cultivar and age. Garnacha young wines were prone to contain higher hydroxyphenyl-pyranoanthocyanin concentrations. The aging had an effect of making uniform the concentrations and molar percentages of every type of pigments, and only slight differences among wine groups were found for B-type vitisins (highest values for Syrah wines) and 10-hydroxyphenyl-pyranoanthocyanins (highest values for Merlot wines). Among Tempranillo wines, the ethylidene-bridged flavanol-anthocyanin adducts were the most affected by disappearance during aging, whereas hydroxyphenyl-pyranoanthocyanins increased their contribution in most of those aged wines.

Occurrence and formation kinetics of pyranomalvidin-procyanidin dimer pigment in Merlot red wine: impact of acidity and oxygen concentrations

Once released from red grape skins, anthocyanins undergo various chemical reactions leading to the formation of more stable pigments such as pyranoanthocyanin, as well as other derivatives. Among these pigments, pyranoanthocyanins linked directly to flavanol dimers have been detected and identified in aged Port wine but not in dry red wine. These pigments are very important with regard to the wine color evolution since they are involved in wine color evolution and stabilization. During this investigation, the occurrence in dry red wine of two pyranomalvidin-procyanidin dimer has been established by low and high resolution HPLC-UV-MS analysis. Moreover, the impact of acidity and oxygen levels on their formation in red wine has been estimated. After four months of evolution, the results showed that, for the same pH, the quantity of this pigment was correlated with oxygen concentrations. Moreover, for the same quantity of oxygen, the concentration of this pigment was related to the acidity level.

Anthocyanins and their variation in red wines. II. Anthocyanin derived pigments and their color evolution

Originating in the grapes, anthocyanins and their derivatives are the crucial pigments responsible for the red wine color. During wine maturation and aging, the concentration of monomeric anthocyanins declines constantly, while numerous more complex and stable anthocyanin derived pigments are formed, mainly including pyranoanthocyanins, polymeric anthocyanins produced from condensation between anthocyanin and/or flavan-3-ols directly or mediated by aldehydes. Correspondingly, their structural modifications result in a characteristic variation of color, from purple-red color in young red wines to brick-red hue of the aged. Because of the extreme complexity of chemical compounds involved, many investigations have been made using model solutions of know composition rather than wine. Thus, there is a large amount of research still required to obtain an overall perspective of the anthocyanin composition and its change with time in red wines. Future findings may well greatly revise our current interpretation of the color in red wines. This paper summarizes the most recent advances in the studies of the anthocyanins derived pigments in red wines, as well as their color evolution.

Formation of pyranoanthocyanins in red wines: a new and diverse class of anthocyanin derivatives

Pyranoanthocyanins constitute one of the most important classes of anthocyanin-derived pigments occurring naturally in red wine. Nonetheless, correct assignment of their structures and pathways of formation in red wine has been relatively recent--less than two decades. Study of these newly discovered pigments is progressively unfolding the chemical pathways that drive the evolution of red wine colour during ageing. The objective of this paper is to review current knowledge regarding the pathway of formation in red wine of a great variety of pyranoanthocyanin structures, namely carboxypyranoanthocyanins, methylpyranoanthocyanins, pyranoanthocyanin-flavanols, pyranoanthocyanin-phenols, portisins, oxovitisins, and pyranoanthocyanin dimers. The chromatic features of some of the compounds, for example their colour expression and acid-base equilibria in aqueous media, are also discussed.

Spectral features and stability of oligomeric pyranoanthocyanin-flavanol pigments isolated from red wines

The spectral characteristics and stability of three red wine pigments (pyranoMv-catechin, pyranoMv-epicatechin, and pyranoMv-dimer B3) toward pH variation and bisulfite bleaching, as well as their color stability and degradation during storage, have been studied. Unlike the absorbance spectra of most wine pigments, the intensity of which is more increased in more acidic conditions, oligomeric pyranoMv-flavanols have maximum absorbance at wine pH around 3.6, up to 30-50% higher than that in pH 1.0. This particular hyperchromic effect shown in mildly acidic solutions suggests the presence of intramolecular copigmentation in the molecule of pyranoanthocyanin-flavanols, giving rise to higher molar extinction coefficients around wine pH and contributing to the overall wine color. The most probable conformations were determined by computer-assisted model building and molecular mechanics. Besides exceptional stability toward pH variations, pyranoanthocyanin-flavanols were also shown to be entirely resistant to bleaching by sulfur dioxide. During a 6 month storage period, pyranoanthocyanin-flavanols were much more stable against degradation than the anthocyanin with the following order: pyranoMv-catechin > pyranoMv-dimer B3 > pyranoMv-epicatechin > carboxy-pyranoMv ≫ Mv. Kinetic decomposition monitored by high-performance liquid chromatography-diode array detection-mass spectrometry revealed the formation of a new pigment (pyranone-Mv structure) and the cleavage of the interflavanic linkage of procyanidin dimer in the solutions containing carboxy-pyranoMv and pyranoMv-dimer B3, respectively. Despite some degree of decline of these oligomeric pyranoanthocyanins, their color intensity was surprisingly enhanced, and their color stability greatly improved throughout the entire storage period, thus contributing significantly as long-lived orange-red pigments to the maintenance of aged wine color.

Oxovitisins: a new class of neutral pyranone-anthocyanin derivatives in red wines

A new class of stable yellowish pigments with similar unique spectral features, displaying only a pronounced broad band around 370 nm in the UV-vis spectrum, was detected in an aged Port wine fraction obtained by a combination of chromatography on TSK Toyopearl HW-40(s) and Polyamide resins. These compounds were identified by liquid chromatography-diode array detector/electrospray ionization mass spectrometry (LC-DAD/ESI/MS) and shown to be direct oxidative derivatives of carboxy-pyranoanthocyanins (vitisins A) by synthesis experiments performed in a wine model solution. Their structures were fully characterized by MS and NMR spectroscopy ((1)H, gCOSY, gHSQC, and gHMBC) and found to correspond to alpha-pyranone-anthocyanins (lactone or pyran-2-one-anthocyanins). Their formation involves first the nucleophilic attack of water into the positively charged C-10 position of vitisins, followed by decarboxylation, oxidation, and dehydration steps, yielding a new and neutral pyranone structure. The occurrence of these novel pigments in aged wines points to a new pathway involving anthocyanin secondary products (vitisins A) as precursors of new pigments in subsequent stages of wine aging that may contribute to its color evolution.

Photochemistry of flavonoids

Flavonoids and their photochemical transformations play an important role in biological processes in nature. Synthetic photochemistry allows access to molecules that cannot be obtained via more conventional methods. This review covers all published synthetic photochemical transformations of the different classes of flavonoids. It is first comprehensive review on the photochemistry of flavonoids.

Pyranoanthocyanin dimers: a new family of turquoise blue anthocyanin-derived pigments found in Port wine

In the present work, several compounds bearing similar spectroscopic features were found to occur in aged Port wines and respective sediments (lees). The data obtained revealed two new families of compounds with unique spectroscopic characteristics, displaying a wavelength of the maximum absorption at high wavelength in the visible spectrum at approximately 730 and approximately 680 nm. The structure of these pigments was elucidated by liquid chromatography/diode array detector-mass spectrometry (LC/DAD-MS) and nuclear magnetic resonance (NMR), and their formation pathway in wines was established. Their structure is constituted by two pyranoanthocyanin moieties linked together through a methyne bridge. This new family of compounds displays an attractive and rare turquoise blue color at acidic conditions and has never been reported in the literature.

Equilibrium forms of vitisin B pigments in an aqueous system studied by NMR and visible spectroscopy

The main species in the acid-base equilibria of two pyranoanthocyanins (vitisins B), pyranomalvidin-3-glucoside I and pyranomalvidin-3-O-coumaroylglucoside II, and the respective pK(a) were determined using NMR, visible spectroscopy, and mass spectrometry techniques. The three equilibria involve protonation of the pyranoflavylium cation of vitisin B (pK(a1)) and two deprotonations (pK(a2) and pK(a3)). For pigment I, the values obtained through the titration curves of the chemical shift of some protons versus pH were (pK(a1) < 0.68; pK(a2) = 4.40 +/- 0.08; pK(a3) = 7.45 +/- 0.09) very close to the values obtained by visible spectroscopy (pK(a1) < 0.63; pK(a2) = 4.43 +/- 0.02; pK(a3) = 7.34 +/- 0.03). For pigment II, it was only possible to calculate the pK(a) by visible spectroscopy (pK(a1) < 0.75; pK(a2) = 4.66 +/- 0.10; pK(a3) = 6.76 +/- 0.10). NMR studies have shown that pigment I does not undergo hydration, and the hypothesis of the occurrence of hemiacetal forms in equilibrium was discarded.

High performance liquid chromatography analysis of wine anthocyanins revisited: effect of particle size and temperature

The complex anthocyanin fraction of red wines poses a demanding analytical challenge. We have found that anthocyanins are characterised by extremely low optimal chromatographic velocities, and as a consequence generic HPLC methods suffer from limited resolving power. Slow on-column inter-conversion reactions, particularly between carbinol and flavylium species, are shown to occur on the same time scale as chromatographic separation, leading to increased plate heights at normal chromatographic velocities. In order to improve current routine HPLC separations, the use of small (1.7 microm) particles and high temperature liquid chromatography (HTLC) were investigated. 1.7 microm particles provide better efficiency and higher optimal linear velocities, although column lengths of approximately 20 cm should be used to avoid the detrimental effects of conversion reactions. More importantly, operation at temperatures up to 50 degrees C increases the kinetics of inter-conversion reactions, and implies significantly improved efficiency under relatively mild analysis conditions. It is further demonstrated using relevant kinetic data that no on-column thermal degradation of these thermally labile compounds is observed at 50 degrees C and analysis times of <2h.

Optimization of a solid-phase extraction method using copolymer sorbents for isolation of phenolic compounds in red wines and quantification by HPLC

Different solid-phase extraction (SPE) cartridges for the isolation of most of the phenolic compounds present in wines in low concentration were assayed and compared with the C18 SPE sorbent, which is the most common sorbent used for the isolation of these compounds. The use of C18 cartridges has several disadvantages; therefore, a SPE method using copolymer cartridges was developed, optimized, and validated. The method proposed seems to be a good alternative to replace C18 cartridges for the isolation of wine phenolic compounds. The advantages of the proposed SPE method with the HLB cartridge are that interferences can be eliminated with water without losing the compounds of great interest; the method has very good repeatability, reproducibility, and high percentages of recovery; it has a higher sensitivity and loading capacity than silica-based C18 cartridges due to the larger surface area of this type of sorbent, and the method is not adversely affected by drying, being more reproducible than C18 cartridge.

Role of vinylcatechin in the formation of pyranomalvidin-3-glucoside-+-catechin

Reactions between malvidin-3-glucoside (mv3glc) and 8-vinylcatechin were carried out to synthesize pyranomv3glc-(+)-catechin pigment and to study the formation of intermediates. A rapid decrease of mv3glc content concomitant with the formation of more complex structures such as mv3glc-vinylcatechin [precursor of pyranomv3glc-(+)-catechin pigment] and mv3glc-divinylcatechin was observed. On the other hand, 8-vinylcatechin undergoes acid-catalyzed dimerization in model wine solution, giving rise to 8-vinylcatechin dimers. These compounds were also found in the reaction between mv3glc and (+)-catechin mediated by acetaldehyde, which provides evidence for the formation of 8-vinylcatechin and its involvement in the formation of pyranoanthocyanins in aged red wines.

Rapid isolation of red wine polymeric polyphenols by solid-phase extraction

A rapid technique for the isolation of polymeric polyphenols from red wine has been developed and validated. A copolymer reversed-phase SPE cartridge was utilized in conjunction with predominantly organic eluents to provide three phenolic fractions from red wine without the need for sample pretreatment. The first fraction contained the bulk of the monomeric and oligomeric phenolic material, while the second and third fractions contained the polymeric polyphenolic compounds, as determined by HPLC analysis. The two polymeric polyphenolic fractions differed in their solubility and extent of pigmentation, and the differences appeared to be related to wine age. This method contrasted with other available fractionation techniques because the interfering, nonpolymeric material can be removed in a single wash fraction, while the polymeric material is separated into two distinct fractions based on their diverse physicochemical properties. It is anticipated that the rapid access to discrete polymeric fractions afforded by this method will be of benefit in furthering the understanding of red wine polymeric polyphenols.

Influence of alternative liquid chromatography techniques on the chemical complexity and bioactivity of isolated proanthocyanidin mixtures

Extracts rich in proanthocyanidins, which are implicated in multiple human health benefits, were comparatively separated using alternative separation methods [vacuum or open column liquid chromatography], separation matrices [Toyopearl, Sephadex, or silica gel], and degrees of subfractionation [8 or 12 subfraction series], to evaluate the influence of separation technique on the resolution of the chemical composition and the biological activity of separated proanthocyanidin mixtures in individual subfractions. Bioactivity was assessed using a DNA human topoisomerase II bioassay and structural composition by acid thiolysis (average degree of polymerization, DP) and HPLC-ESI/MS. The amount of parent fraction needed to inhibit 50% of topoisomerase II was 3.38 ng/mL with an average DP of 25.5. A 2(3) factorial analysis revealed that the vacuum and open column strategies for separation, when individually considered, did not yield significantly different results in terms of mass recovery, DP, or bioactivity; however, interactions with other factors such as matrix or subfraction series resulted in distinctive shifts in fraction profiles and biological activity. In general, Sephadex as a matrix permitted elution and separation of discrete, polymerized subfractions with potent inhibition against human topoisomerase II. Sephadex vacuum chromatography, Toyopearl open column chromatography, and Toyopearl vacuum chromatography separation techniques eluted highly polymerized proanthocyanidin mixtures, but the inhibitory bioactivity was attenuated as compared to the parent fraction, whereas Sephadex open column chromatography eluted highly polymerized subfraction mixtures that retained bioactive potential.