Red Wine Color Research Articles

Anthocyanin Copigmentation - Evaluation, Mechanisms and Implications for the Colour of Red Wines

Anthocyanin Copigmentation - Evaluation, Mechanisms and Implications for the Colour of Red Wines

Advanced ultra high pressure liquid chromatography–tandem mass spectrometric methods for the screening of red wine anthocyanins and derived pigments

Anthocyanins are responsible for the colour of red grapes and wine. In addition to their contribution to the sensory properties of wine, these compounds are also of interest due to their beneficial biological properties. Wine anthocyanins exhibit a large structural diversity due to variations in glycosylation and acylation patterns, which is further exacerbated by the diverse reactions involving grape-derived anthocyanins during wine ageing. Chromatographic as well as mass spectrometric resolution of wine anthocyanins is often precluded due to the complexity of these compounds. In this paper we report a rapid, high-efficiency ultra high pressure liquid chromatography (UHPLC) procedure with tandem mass spectrometric (MS/MS) detection for the in-depth screening of wine pigments. Selective detection of wine anthocyanins and derived pigments was achieved utilizing MS/MS in neutral loss scanning mode to observe the loss of dehydrated sugar moieties. This facilitated tentative compound identification based on molar mass information as well as the structured elution order of these compounds. In a second experiment, product ion spectra were recorded to allow identification of the anthocyanidin base using characteristic fragmentation patterns. The proposed methodology therefore involves two analyses for the sensitive and accurate identification of anthocyanins and their derived products in red wines. Mass spectra of wine anthocyanins under high energy collision induced dissociation (CID) conditions are reported, some for the first time. Significantly, chemical alteration of anthocyanins during wine ageing results in an off-set of the predominant fragments for each anthocyanidin base, whilst maintaining similar relative intensities. This allows unambiguous assignment of the derived products of anthocyanidin-glycosides. Using this approach, a total of 121 anthocyanins and derived compounds were identified in wines based on their relative reversed phase elution order as well as mass spectral information.

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.

Ripeness estimation of grape berries and seeds by image analysis

Digital imaging has become a powerful tool for the characterization and quality control of foodstuff. Because of the need to automate processes, faster tools are needed and Computer Vision is a good alternative to chemical analysis of many products in quality control. Appearance of grape seeds and grape berries change during the ripeness. These changes are closely related to the chemical composition, especially phenolics, which are very important compounds due to their implications on the intensity and stability of red wine colour. In this study, a complete characterization of grape seeds and grape berries by digital image analysis is described. The size of grapes and the veraison has been determined by image analysis and it has been also established an objective Browning Index of seeds. Morphological differences between varieties were studied by applying discriminant analysis models which allowed us to classify the grape seeds with high accuracy.

Effects of fining on phenolic compounds and colour of red wine obtained with addition of increased amounts of grape solid phase in pomace

The purpose of this work is to study the effect of grape pomace enrichment in solid phase (stems and seeds) on phenolic compounds and colour stability of obtained red wines, before and after use of different fining agents. Results have shown increase in total phenols and flavan-3-ols content after grape solid phase addition. On the other hand, decrease in anthocyanins content has generally been recorded in all wine samples except in wines obtained with addition of 40 g/l of seeds during maceration. Stems addition caused decrease in colour intensity while addition of seeds has increased this colour parameter. The use of four fining agents (albumin, gelatine, bentonite and PVPP) has been investigated and compared, especially in terms of their influence on potential stabilization effect of grape solid phase on wine colour. Fined wines tended to have considerably lower anthocyanin and flavan-3-ol levels, especially in the case of gelatine and PVPP treatment (decrease up to 60 and 70%, respectively). In the case of chromatic parameters, used fining agents caused colour intensity decrease but it is important to emphasize that their values, after fining, are still as high as expected from red wine. This can be explained by the stabilization effect of increased flavan-3-ols content.

Copigmentation and anti-copigmentation in grape extracts studied by spectrophotometry and post-column-reaction HPLC

Copigmentation is a very important contributor to colour in young red wines. Further understanding of the copigmentation effect has been elucidated by investigating the contribution of various fractions of grapes – skin, pulp, and seed – in varieties Shiraz, Sangiovese and Pinot Noir. A series of spectrophotometric and HPLC experiments elucidated the effect of this interaction in grape extracts simulating wine conditions. A post-column reaction method was developed to permit the evaluation of the reactivity of each grape anthocyanin with different reagents: pure compounds (quercetin and caffeic acid) and extracts of grape sections (seed, Semillon skin, Semillon pulp). Certain extracts produced a decrease in colour, suggesting that competing equilibria are important in the copigmentation effect and that an “anti-copigmentation” effect is possible. Flavonols appear to be the best copigmentation cofactors, and the concentration of quercetin 3-O-glucoside was found to correlate with the strength of copigmentation. Flavonols appear capable of displacing cofactors derived from seed extracts.

Prediction of red wine colour and phenolic parameters from the analysis of its grape extract

Summary Herein, the phenolic composition and colour attributes of red grapes extracts (obtained with a fast methodology) were correlated with those of their corresponding wines to predict the final quality properties of wines. The phenolic parameters were evaluated as total phenolic compounds (TPC), total anthocyanins (TA) and total condensed tannins (TCT), whereas the chromatic parameters were evaluated as colour intensity (CI), tonality (To), and the percentages of yellow, red and blue tones. All of them were determined by usual UV–Vis spectrophotometric methods. To get robust models, grapes of five red varieties were collected at three different ripening stages throughout the 2009 vintage. Good correlations between the results from grapes and wines were obtained, showing high regression coefficients and low prediction errors for TPC (R2 = 0.929, RMSE = 5.99%), TA (R2 = 0.953, RMSE = 7.23%) and CI (R2 = 0.954, RMSE = 7.58), concluding that these wine phenolic properties can be predicted reliably from the extracts obtained with an optimised fast extraction method from grapes on the ripening controls along the maturity process.

Colour and phenolic compounds in sweet red wines from Merlot and Tempranillo grapes chamber-dried under controlled conditions

Chamber drying under controlled temperature and humidity conditions of the red grape varieties Merlot and Tempranillo grown in Andalusia (Spain), and the fortification and maceration of the musts in the presence of skin from both types of grapes, to obtain sweet red wines, has been studied. Changes in colour and in monomeric and polymeric phenols during the vinification process were examined. Chamber drying increased the sugar content to about 31.4 °Brix within 48h in Merlot grapes and 72h in Tempranillo grapes. This drying process also causes skin rupture, facilitating the access of phenolic compounds to the pulp. The resulting musts exhibited slight browning and increased red hues, due to a high concentration of anthocyanins; maceration in the presence of grape skins for 24h provided the best results. The end-product contained highly acceptable tannin, colour and phenolic compounds for marketing as a high quality sweet red wine, in comparison with other commercial sweet red wines.

Adulteration of the anthocyanin content of red wines: Perspectives for authentication by Fourier Transform-Near InfraRed and 1H NMR spectroscopies

In the Italian oenological industry, the regular practice used to naturally increase the colour of red wines consists in blending them with a wine very rich in anthocyanins, namely Rossissimo. In the Asian market, on the other hand, anthocyanins extracted by black rice are frequently used as correctors for wine colour. This practice does not produce negative effects on health; however, in many countries, it is considered as a food adulteration. The present study is therefore aimed to discriminate wines containing anthocyanins originated from black rice and grapevine by using reliable spectroscopic techniques requiring minimum sample preparation. Two series of samples have been prepared from five original wines, that were added with different amounts of Rossissimo or of black rice anthocyanins solution, until the desired Colour Index was reached. The samples have been analysed by FT-NIR and 1H NMR spectroscopies and the resulting spectra matrices were subjected to multivariate classification. Initially, PLS-DA was used as classification method, then also variable selection/classification methods were applied, i.e. iPLS-DA and WILMA-D. The classification with variable selection of NIR spectra permitted to classify the test set samples with an efficiency of about 70%. Probably these not excellent performances are due to the matrix effect, together with the lack of sensitivity of NIR with respect to minor compounds. On the contrary, very satisfactory results were obtained on NMR spectra in the aromatic region between 6.5 and 9.5 ppm. The classification method based on wavelet-based variables selection, permitted to reach an efficiency in validation greater than 95%. Finally, 2D correlation analysis was applied to FT-NIR and 1H NMR matrices, in order to recognise the spectral zones bringing the same chemical information.

Polymorphism of Crystalline 4-Amino-2-Nitroacetanilide

This paper reports the preparation and structural characterization of 4-amino-2-nitroacetanilide (ANA). Comprehensive analysis of the conformational, hydrogen bonding, and crystal packing preferences of ANA has been performed using X-ray crystallography, verified using high-resolution solid-state 13C, 15N, and 1H MAS NMR, and rationalized using ab initio calculations. The compound crystallizes in two different polymorphic forms, red (P21/n space group) and orange (P21/c space group), and as a monohydrate (C2/c space group). The latter pseudopolymorph has a deep, red wine color. All three forms crystallize in the monoclinic space group with comparable molecular volumes (V/Z) for the polymorphs and a significantly larger molecular volume for the monohydrate. Significant structural relationships have been identified for the crystal forms of ANA. The crystal color is dependent on the conformation of the molecule and its ability to form an intramolecular hydrogen bond (HB) involving the nitro group. In the orange polymorph, both nitro and acetanilide groups are twisted relative to the plane of the phenyl ring. This arrangement precludes formation of the intramolecular HB between these groups. In contrast, the groups in the red polymorph and in the monohydrate are favorably disposed, and thereby, such HBs are formed. Our work demonstrates the utility of integrating crystallography, spectroscopy, and ab initio calculations in detailed structural studies of polymorphism and hydrate formation. The most significant result is that the experimental molecular geometries of ANA in the studied crystal forms correspond well to the minimum values of the theoretical DFT energy curve for the amide group rotation.

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.

Electronic Nose Analysis of Cabernet Sauvignon (Vitis viniferaL.) Grape and Wine Volatile Differences during Cold Soak and Postfermentation

Cold soak is a prefermentation maceration process at cold temperatures, traditionally used to enhance red wine color. This study monitored changes in Vitis vinifera L. cv. Cabernet Sauvignon volatiles using a commercial conducting polymer electronic nose (ENose) during a five-day cold soak and postfermentation. Principal component analysis (PCA) of juice volatiles detected by the ENose during cold soak showed PC1 accounted for 95.7% of the variation. Various volatile associations were made with specific ENose sensors. In comparison, PCA of must chemistries had 52.4% of the variation accounted for by PC1. The PCA of wine volatiles detected by GC-MS showed PC1 accounted for 97.1% of the variation between control and cold soak treatment, where control wine volatiles were associated with several ethyl esters, while cold soak wine volatiles were associated with diethyl succinate, isovaleric acid, benzyl alcohol, 3-methyl butanol, cis -3-hexenol, γ-nonalactone, benzaldehyde, 2-methyl propanol, phenethyl acetate, 1-octanol, β-damascenone, terpinene-4-ol, γ-butyrolactone, ethyl acetate, hexanoic acid, citronellol, phenethyl alcohol, and n -butanol. Comparatively, PC1 accounted for 100% of the total variance when using the ENose to measure volatile composition. Sensory evaluation did not demonstrate significant differences in aroma between control and cold soak wines. This study demonstrates differences in volatile chemistry between control and cold soak wines, as well as the ability to use a conducting polymer ENose as a simple tool for analysis of volatiles.

Effect of the presence of lysated lees on polysaccharides, color and main phenolic compounds of red wine during barrel ageing

A practice in wineries is to age wine in the presence of lysated lees instead of fresh lees, in order to reduce the time wine is conserved on lees and avoid possible microbiological and organoleptic risks caused by lees. Two treatments were used to induce lees lysis: acidification and acidification in combination with a mixture of β-glucanases and pectinases. Acidification treatment in combination with enzymes induced significantly greater mannoprotein and glucan release. The presence of lysated lees during wine storage in barrels produced wines with significantly different tannin contents. The ageing technique on lysated lees by acidification in combination with enzymes produced wines with more intense colors, lower luminosity and saturation, and a slight tendency towards red tones, and an increase in sweetness, fullness and mouth length. On the contrary, ageing technique on lysated lees by acidification increased wine acid and fresh sensations.

Effect of wine micro-oxygenation treatment and storage period on colour-related phenolics, volatile composition and sensory characteristics

In this paper, we have evaluated the effects of micro-oxygenation before malolactic fermentation and after five months of storage on Cencibel red wines. In particular, we have considered the colour characteristics, the phenolic compounds related to red wine colour, the individual volatile composition, and the complete descriptive sensory analysis of the wines. The fact that the concentration of the malvidin-3-glucoside-ethyl-flavan-3-ol adducts and pyranoanthocyanins (B-type vitisins) increased is closely related to the red wine colour stabilization. Red wine aroma quality was slightly improved as a consequence of oxygen addition after five months of storage. New attributes appeared (plum/currant) and others were increased (spicy and liquorice) in micro-oxygenated red wines, whereas herbaceous values were significantly decreased. The results suggest the joint use of both treatments (micro-oxygenation and storage) give rise to an enhancement of the colour stability and the aroma and sensorial quality of red wines.

Mass-spectrometry evidence confirming the presence of pelargonidin-3-O-glucoside in the berry skins of Cabernet Sauvignon and Pinot Noir (Vitis vinifera L.)

Background and Aims: Anthocyanins are a group of important phenolic compounds which are responsible for the colour of red grape and wine. This study aimed to confirm the existence of pelargonidin-3-O-glucoside in Vitis vinifera grape berry skins. Methods and Results: The anthocyanin profiles in the berry skins of Cabernet Sauvignon and Pinot Noir were analysed by high performance liquid chromatography – electronic spray ionization – tandem mass spectrometry. Besides 17 anthocyanins that are commonly determined in the berries of these two varieties, pelargonidin-3-O-glucoside was also detected at trace levels. Conclusions: The mass-spectrometry evidence confirmed the existence of pelargonidin-3-O-glucoside in non-teinturier V. vinifera grapes. Significance of the Study: This finding will be beneficial for the further understanding of anthocyanin profile and its biosynthesis in grape berries.

Original article: Prediction of the colour and polyphenolic composition of the young red wines from the phenolic potential of the grapes

SummaryThe phenolic potential of the grapes of Tannat, Cabernet Sauvignon and Merlot produced in the south region of Uruguay was analysed in four years. The grapes of Tannat had the highest total phenolic richness (A280 = 80.0), total anthocyanin potential (ApH1 = 2540 mg L−1) and extractable anthocyanin potential (ApH3.2 = 1269 mg L−1), although there were important differences between the years. Representative winemaking of each vineyard was carried out. The differences verified in the grapes phenolic indexes were related to the colour and polyphenolic composition of the wines. The correlations between the phenolic indexes of the grapes and the colour and polyphenolic composition of the wines were very high. The estimation of the polyphenolic richness and the extractability of the anthocyanins of the grapes allow to improve the management of the winemaking and the prediction of the chromatic characteristics and the global polyphenolic composition of the wines.

Short- and long-term effects of micro-oxygenation treatments on the colour and phenolic composition of a Cabernet Sauvignon wine aged in barrels and/or bottles

Micro-oxygenation is the controlled and continuous addition of small doses of oxygen to the wine in order to achieve a rational management of the evolution of the colour and mouthfeel properties of red wines. The short and, especially, the long-term effects of this technology on the colour characteristics of wines are still little known. In this study, a Cabernet Sauvignon wine was subjected to oxygenation treatments before (15 mg O2/L in 3 weeks) and after (6 mg O2/L in 3 months) malolactic fermentation and then aged for 20 months in barrels and/or bottles. Analysis was carried out of the dissolved oxygen concentration, the acetaldehyde content, and the evolution of several parameters related to the anthocyanic composition and the chromatic characteristics of wines for 113 weeks. The supplying oxygen significantly accelerated the kinetics of the degradation and transformation reactions of anthocyanins providing wines with a more intense bisulphite non-bleachable colour, with little or not impact on the normal evolution of their tonality. These beneficial effects produced during the treatments were kept over time, in such a way that the differences between the micro-oxygenated wines and the control wines remained after 20 months of ageing.

Micro-oxygenation and oak chip treatments of red wines: Effects on colour-related phenolics, volatile composition and sensory characteristics. Part I: Petit Verdot wines

In this paper, the effects of micro-oxygenation before malolactic fermentation and oak chip treatments on Petit Verdot red wines have been evaluated. Our attention was focused on the colour characteristics, the phenolic compounds related to the colour of red wine, the volatile compounds, and the sensory characteristics of the wines. The micro-oxygenation treatment promoted the stabilisation of red wine colour by increasing the formation of colour-related phenolic compounds (higher concentrations of pyranoanthocyanins and anthocyanin-ethyl-flavan-3-ol adducts). Red wine aroma quality was improved with the addition of oak chips (eugenol and 4-vinyl-guaiacol concentration increased). Micro-oxygenation treatment resulted in higher scores for the plum/currant and spicy attributes, as well as the appearance of tobacco and nutty notes which were absent in the non-treated wines. Nevertheless, the typical oak chip aromas (vanilla and woody) were observed to a lesser extent in wines obtained by micro-oxygenation.

Influence of Prefermentative Cold Maceration on the Color and Anthocyanic Copigmentation of Organic Tempranillo Wines Elaborated in a Warm Climate

The stabilization of red wine color by the copigmentation phenomenon is a crucial process that does not always proceed favorably under natural conditions during the first stages of vinification. The impact of the prefermentative cold maceration technique on the phenolic composition and magnitude of the copigmentation level of organic Tempranillo wines elaborated in a warm climate have been studied as an enological alternative to the traditional maceration for obtaining highly colored wines. Tristimulus colorimetry was applied to study the color of wines during vinification, and a high-performance liquid chromatography (HPLC) procedure was used for the analysis of phenolic compounds. Spectrophotometric and colorimetric analyses were also performed to evaluate the copigmentation level of the wines. Significant chemical and color differences were found depending on the maceration technique applied. Prefermentative cold macerated wines were richer in those compounds accounting directly for the color of red wine (anthocyanins) and those involved in anthocyanin stabilization through copigmentation reactions (phenols), which was in accordance with the higher copigmentation degree and darker, more saturated and vivid bluish colors. The evaluation of the copigmentation based on colorimetric parameters in the CIELAB color space showed that prefermentative cold maceration caused greater effectiveness of copigmentation than traditional maceration since it induces more important and hence more easily perceptible color changes.

Influence of sustained deficit irrigation on colour parameters of Cabernet Sauvignon and Shiraz microscale wine fermentations

Background and Aims: This study aimed to explore the influence of sustained deficit irrigation (SDI) on the grape and wine colour parameters of two premium red wine grape varieties grown in the Sunraysia region of South Eastern Australia. Methods and Results: The SDI experiments were conducted during three vintages from 2003 to 2004, 2004 to 2005 and 2005 to 2006 on the Vitis vinfera cultivars Cabernet Sauvignon and Shiraz grafted to 140 Ruggeri (V. berlandieri × V. rupestris) rootstock. The grapevines were drip irrigated providing 100% of estimated ETc (control) and three graded sustained water deficits (Cabernet Sauvignon 70, 52 and 43% of the control; Shiraz 65, 45 and 34% of the control). Microscale wine fermentations were conducted on grapes from the 2006 harvest to assess wine colour density, wine hue, red pigments, anthocyanins, phenolics and copigmentation products in the wine. Wine anthocyanin and phenolic concentrations for both varieties showed significant increases with increasing intensity of SDI. Conclusion: Increases in wine colour with SDI may result from changes in flavonoid biosynthesis as a result of grapevine responses to water deficit. Alternatively, increases in red wine colour could be caused by changes in chemical properties of the anthocyanins to copigmented or polymeric forms during the winemaking or ageing process. Significance of the Study: The Australian wine industry is currently affected by drought and reduced water allocations resulting in production of wine from grapes exposed to water deficit. Findings from this study provide knowledge to the wine industry as to how sustained deficit irrigation may modify wine colour.