Copigmentation between malvidin-3- O -glucoside and hydroxycinnamic acids in red wine model solutions: Investigations with experimental and theoretical methods

Intermolecular interactions between malvidin-3-O-glucoside and caffeic acid: Structural and thermodynamic characterization and its effect on real wine color quality

The copigmentation effect between malvidin-3-O-glucoside and caffeic acid was comprehensive inquiry on the model wine solution, theoretical simulation and real wine. Thermodynamic parameters were determined by UV/Visible spectroscopy and Isothermal titration calorimetry (ITC). Theoretical data were obtained employing a dispersion-corrected density functional approach. The effects in real wines were investigated by adding the caffeic acid during different fermentation periods. Results shown that the copigmentation reaction between caffeic acid and malvidin-3-O-glucoside is a spontaneous exothermic reaction driven by hydrogen bonding and dispersions forces. Computations show that the polyhydroxyl sugar moiety and phenolic hydroxyl groups are the key active sites. The addition of caffeic acid in post-alcohol fermentation samples evidences an improving color characteristics in the wine.

Gallic acid improves color quality and stability of red wine via physico-chemical interaction and chemical transformation as revealed by thermodynamics, real wine dynamics and benchmark quantum mechanical calculations

The aim of this study was to explore the copigmentation effect of gallic acid on red wine color and to dissect its mechanism at the molecular level. Three-dimensional studies, e.g., in model wine, in real wine and in silico, and multiple indicators, e.g., color, spectrum, thermodynamics and phenolic dynamics, were employed. The results showed that gallic acid significantly enhanced the color quality and stability of red wine. Physico-chemical interactions and chemical transformations should be the most likely mechanism, and physico-chemical interactions are also a prerequisite for chemical transformations. QM calculations of the physico-chemical interactions proved that the binding between gallic acid and malvidin-3-O-glucoside is a spontaneous exothermic reaction driven by hydrogen bonding and dispersion forces. The sugar moiety of malvidin-3-O-glucoside and the phenolic hydroxyl groups of gallic acid affect the formation of hydrogen bonds, while the dispersion interaction was related to the stacking of the molecular skeleton.

RuBisCo can conjugate and stabilize peonidin-3-O-p-coumaroylrutinoside-5-O-glucoside in isotonic sport models: Mechanisms from kinetics, multispectral, and libDock assays

The co-pigmentation behaviour of RuBisCo proteins (with different concentrations) on peonidin-3-O-p-coumaroylrutinoside-5-O-glucoside (P3C5G, extracted from Rosetta potato's peels) conjugates in isotonic sport drinks (ISD) was examined using multispectral, thermal stability kinetics, and libDock-based molecular docking approaches. The colorant effects of RuBisCo on P3C5G were also studied in spray-dried microencapsulated ISD-models. RuBisCo, especially at a concentration of 10 mg/mL in ISD, showed a co-pigmentation effect on the color of P3C5G, mostly owing to its superior hyperchromicity, pKH-levels, and thermal stability. Results from multispectral approaches also revealed that RuBisCo could noncovalently interact with P3C5G as confirmed by libDock findings, where P3C5G strongly bound with RuBisCo via H-bonding and π-π forces, thereby altering its secondary structure. RuBisCo also preserved color of P3C5G in ISD-powdered models. These detailed results imply that RuBisCo could be utilized in ISD-liquid and powder models that might industrially be applied as potential food colorants in products under different conditions.

Artificial shading of teinturier grape Kolor clusters reveals light-responsive biomarkers: focus on flavonoid profiles and metabolism

Kolor is a teinturier grape cultivar, that accumulates flavonoids in the skin and pulp. However, the concentrations and proportions of flavonoids in Kolor skin and pulp differ, suggesting tissue specificity in teinturier grapes. Light conditions significantly influence the evolution of flavonoids. Moreover, studies on the mechanisms governing flavonoid accumulation in light response sensitivity of teinturier grapes are limited. In the three consecutive years of study, the exposure of Kolor clusters was altered by bagging from pre-veraison to harvest. QqQ/MS and RT‒qPCR wereused to determine the individual anthocyanin contents and the relative gene expression. There was a significant decrease in the total anthocyanins and flavonols in the Kolor berries, with flavonols showing greater sensitivity to bagging. Bagging did not exert a consistent impact on the flavan-3-ols in Kolor berries. The sensitivities of anthocyanins in Kolor skin and pulp differed under light exclusion conditions. The concentration of trihydroxy-substituted anthocyanins in the skin decreased, while the proportion of dihydroxy-substituted anthocyanins in the pulp significantly increased, but the anthocyanin concentration in the pulp did not change significantly after bagging. The contents of malvidins and quercetins in the skin, and myricetins and quercetins in the pulp, were significantly reduced after bagging. The expression of flavonoid synthesis genes in Kolor skin and pulp was tissue-specific. After bagging, UFGT expression increased in the pulp and decreased in the skin. In addition, LDOX, FLS-1, CHI-1, CHI-2, F3H-1, F3H-2, and MYB4a exhibited sensitive light responses in both the skin and pulp. This study offers new insights into the regulation of flavonoids in Kolor grapes under light exclusion conditions.

Artificial saliva precipitation index (ASPI): An efficient evaluation method of wine astringency

Astringency is one of the most important organoleptic characteristics of red wines, and its intensity evaluation method has been the focus of research in recent years. An artificial saliva system was developed to establish an accurate and reliable evaluation method for the astringency intensity of dry red wines based on saliva precipitation index (SPI). To achieve this, five key protein families, which presented high reactivities and sensitivities in protein-tannin binding reactions, were selected from human whole saliva. The concentrations of the five proteins (proline-rich protein, α-amylase, lactoferrin, lysozyme, and albumin) and pH were optimized using response surface methodology based on the human salivary conditions to simulate the real salivary environment. The artificial saliva precipitation index method was applied to 60 commercial dry red wines and it exhibited a high correlation (Coef_ASPI = 0.94) with the sensory scores, indicating better performance than the traditional SPI method and other analytical approaches.

Investigation of the difference in color enhancement effect on cyanidin-3-O-glucoside by phenolic acids and the interaction mechanism

Co-pigmentation effect of phenolic acids on cyanidin-3-O-glucoside (C3G) and the mechanisms were investigated. Sinapic acid (SIA), ferulic acid (FA), p-coumaric acid (p-CA) and syringic acid (SYA) significantly enhanced C3G stability (P < 0.05), whereas vanillic acid (VA) and gallic acid (GA) showed no influence (P > 0.05). Among these phenolic acids, SIA and FA had higher binding coefficient with C3G (48.83 and 43.38), reduced degradation rate constant by 40.0 ∼ 50.0 %, prolonged half-life by 74.6 ∼ 94.7 % at 323 K, and significantly inhibited C3G hydration reaction (pK_h = 2.87 and 2.80, P < 0.05). Molecular docking revealed that C3G and co-pigments were connected by hydrogen bond and π-π stacking interaction. Hydroxycinnamic acids of SIA, FA and p-CA bound with ring B and ring C of C3G, while hydroxybenzoic acids of SYA, VA and GA hardly interacted with ring C. Generally, the protection effect of hydroxycinnamic acids on C3G was better than that of hydroxybenzoic acids, exhibiting stronger hyperchromic effect.

Anthocyanins: Modified New Technologies and Challenges

Anthocyanins are bioactive compounds belonging to the flavonoid class which are commonly applied in foods due to their attractive color and health-promoting benefits. However, the instability of anthocyanins leads to their easy degradation, reduction in bioactivity, and color fading in food processing, which limits their application and causes economic losses. Therefore, the objective of this review is to provide a systematic evaluation of the published research on modified methods of anthocyanin use. Modification technology of anthocyanins mainly includes chemical modification (chemical acylation, enzymatic acylation, and formation of pyran anthocyanidin), co-pigmentation, and physical modification (microencapsulation and preparation of pickering emulsion). Modification technology of anthocyanins can not only increase bioavailability and stability of anthocyanin but also can improve effects of anthocyanin on disease prevention and treatment. We also propose potential challenges and perspectives for diversification of anthocyanin-rich products for food application. Overall, integrated strategies are warranted for improving anthocyanin stabilization and promoting their further application in the food industry, medicine, and other fields.

Red wine coloration: A review of pigmented molecules, reactions, and applications

Color is one of the most distinctive qualities of red wine. Despite new knowledge in the field of pigment identification, copigmentation, and oxidation being forthcoming, there is still a large gap between the fundamental research and practical winemaking outcomes. A state-of-art review from these two aspects is, therefore, necessary. This review first introduces updated knowledge about the primary pigments in wine, with emphasis on their physicochemical properties. Then, the mechanisms of copigmentation and oxidation are elucidated in detail, along with their relative contributions to wine color. Finally, the practical effects of copigmentation and micro-oxygenation (MOX) in winemaking are summarized and discussed. In general, wine coloration is ultimately determined by the anthocyanin flavylium cation, which is greatly influenced by wine pH. In young red wine, grape-derived anthocyanins and nonanthocyanin polyphenols (as copigments) are the foundation for wine coloration. During aging and storage, anthocyanin derivatives are formed via various chemical reactions, where moderate oxidation plays a vital role, whereas copigmentation constantly decreases. The essence of wine color evolution relates to the changes of physicochemical properties of primary pigments in wine, where the hydration equilibrium gradually diminishes. In practice, the effects of copigment addition and MOX during real vinification can be viewed as somewhat controversial, considering that many studies showed different effects on wine color and pigment concentration. Universal features can be summarized but some phenomena still remain unclear and deserve further exploration.

Effects of organic acids on color intensification, thermodynamics, and copigmentation interactions with anthocyanins

Anthocyanins are attractive alternatives to synthetic colorants, but their low stability impedes practical applications. Intermolecular copigmentation can enhance both color intensity and stability. Herein, the copigmentation interactions of Kyoho grape skin anthocyanins (KSA) or cyanidin-3-O-glucoside (Cy-G) with organic acids were investigated. Color enhancement was evaluated at different acid molar ratios and treatment temperatures. The optimal copigmentation effects were observed for KSA/tannic acid (1:150) and Cy-G/tannic acid (1:100). Based on enthalpy variation, KSA/ferulic acid and Cy-G/ferulic acid exhibited the highest stability. The distinct color differences observed in the presence of different acids were attributed to structural effects. The influence of ferulic acid on various anthocyanins was also evaluated using theoretical approaches. Owing to steric hindrance, the acyl groups in KSA affected the spatial conformation, hydrogen bonding, and van der Waals interactions of the complexes. Further, hydroxyl groups decreased complex stability. These findings contribute to furthering the understanding of copigmentation effects.

Influence of phenolic acids/aldehydes on color intensification of cyanidin-3-O-glucoside, the main anthocyanin in sugarcane (Saccharum officinarum L.)

Sugarcane contains various anthocyanins, which are responsible for the colors present in sugarcane. In this study, the color intensification of the major anthocyanin, cyanidin-3-O-glucoside, by phenolic acids/aldehydes (ferulic acid, vanillic acid, p-coumaric acid, syringic aldehyde and vanillic aldehyde) was investigated. The color enhancement of cyanidin-3-O-glucoside (hyperchromic effect and bathochromic shift) was affected by the temperature and concentration of phenolic acids/aldehydes present. Reactions were spontaneous and exothermic, as determined using different thermodynamic parameters (ΔG⁰, ΔH⁰, ΔS⁰). Quantum chemical calculations demonstrated their intermolecular interaction differences, and AIM analysis indicated that hydrogen bonds and van der Waals force interactions contributed to color. Pyranoanthocyanins derived from cyanidin-3-O-glucoside and ferulic/p-coumaric acids during storage were recognized as cyanidin-3-O-glucoside-vinylphenol and cyanidin-3-O-glucoside-vinylguaiacol, respectively, by UPLC-ESI-QTOF-MS/MS. The electron-donating substituents on the aromatic ring of ferulic/p-coumaric acids stabilized the intermediately formed carbenium ion. Decarboxylation and further oxidation of the pyran moieties to the aromatic heterocycles resulted in the final products.

The implication of phenolic acid matrix effect on the volatility of ethyl acetate in alcohol-free wine model: Investigations with experimental and theoretical methods

Hydroxycinnamic acids and ethyl acetate were assessed in simulated alcohol-free wine solutions to explore the effect of phenolic acids on the aroma volatility of esters. The results showed that the phenolic acids could inhibit the volatilization of ethyl acetate, and the extent of inhibition was influenced by the concentration and structure of the phenolic compounds. The ultraviolet absorption spectra of the phenolic acids and ethyl acetate confirmed the interaction between the two compounds. The thermodynamic parameters of the interaction implied a spontaneous exothermic interaction, driven primarily by hydrophobic effects. Meanwhile, the results of the fluorescence-quenching analysis indicated electron transfer between the reactants. The quantum chemical investigations revealed negative and positive charge density distributions in the structures of ethyl acetate and the phenolic acids, respectively. These results will provide some data reference and theoretical support for further research on the effects of phenolic acid matrix on other structural esters.

Identification of Tentative Traceability Markers with Direct Implications in Polyphenol Fingerprinting of Red Wines: Application of LC-MS and Chemometrics Methods

This study investigated the potential of using the changes in polyphenol composition of red wine to enable a more comprehensive chemometric differentiation and suitable identification of authentication markers. Based on high performance liquid chromatography-mass spectrometry (HPLC-MS) data collected from Feteasca Neagra, Merlot, and Cabernet Sauvignon finished wines, phenolic profiles of relevant classes were investigated immediately after vinification (Stage 1), after three months (Stage 2) and six months (Stage 3) of storage, respectively. The data were subjected to multivariate analysis, and resulted in an initial vintage differentiation by principal component analysis (PCA), and variety grouping by canonical discriminant analysis (CDA). Based on polyphenol common biosynthesis route and on the PCA correlation matrix, additional descriptors were investigated. We observed that the inclusion of specific compositional ratios into the data matrix allowed for improved sample differentiation. We obtained simultaneous discrimination according to the considered oenological factors (variety, vintage, and geographical origin) as well as the respective clustering applied during the storage period. Subsequently, further discriminatory investigations to assign wine samples to their corresponding classes relied on partial least squares-discriminant analysis (PLS-DA); the classification models confirmed the clustering initially obtained by PCA. The benefits of the presented fingerprinting approach might justify its selection and warrant its potential as an applicable tool with improved authentication capabilities in red wines.

Multiple co-pigments of quercetin and chlorogenic acid blends intensify the color of mulberry anthocyanins: insights from hyperchromicity, kinetics, and molecular modeling investigations

BACKGROUND

The effect of multiple co-pigments on the color intensification of mulberry anthocyanins (ACs) using spectroscopic techniques in combination with a molecular docking study was studied. The hyperchromicity of ACs co-pigmented with chlorogenic acid (CH) and quercetin (Q) blends was measured and their color stability in liquid and encapsulated particle models was evaluated.

RESULTS

Multiple co-pigments exhibited higher hyperchromicity, pK_H -values, and heat-stability than their individual counterparts. Surflex-docking findings confirmed that stronger binding occurred between multiple ligands and AC than single ones due to their extra -OH, -COOH groups, and delocalization systems. The binding was allowed by increased H-bonding, van der Waals forces, and π-π sites by the extra groups of the multiple co-pigments with AC in aqueous juice and whey particle-based models.

CONCLUSION

This is the first report of the ternary mixture of phenolic acid-flavonol-anthocyanin which could be used as promising food red-colorants. © 2020 Society of Chemical Industry.

On the Limits of Anthocyanins Co-Pigmentation Models and Respective Equations

Anthocyanins co-pigmentation models with application on 1:1 complexes were revisited, and their limitations were critically commented. The flavylium multistate of species is dramatically simplified to a single acid-base equilibrium between flavylium cation and its conjugated base CB, equal to the sum of quinoidal base, hemiketal, and cis and trans-chalcones. Bearing this, a new equation that simultaneously allows calculation of the co-pigmentation constant with flavylium cation (K_AH+_CP) and with its conjugated base CB (K_CBCP) was deduced. This equation can be used at a fixed co-pigment concentration with pH as a variable or at fixed pH and co-pigment concentration variable. A global fitting of all data allows us to calculate both association constants with good accuracy. The model was applied to the co-pigmentation of malvidin-3-glucoside with caffeine and pentagalloyl glucose (PGG). Caffeine gives rise to complexes not only with flavylium cation K_AH+_CP = 125 ± 7 M^-1 but also with CB with K_CBCP = 23 ± 3 M^-1. PGG complexes exclusively with flavylium cation, K_AH+_CP = 914 ± 10 M^-1, and the possible interaction with quinoidal base is lower than the detection limits that the inherent experimental error permits.

Copigmentation evidence of oenin with phenolic compounds: A comparative study of spectrographic, thermodynamic and theoretical data

The copigmentation effects of polyphenol with different structures vary greatly. Therefore, the aim of this study is to investigate possible interactions in red wine model solutions between oenin and three phenolic compounds: danshensu, caffeic acid and rosmarinic acid. Our results show that the copigmentation of rosmarinic acid is the strongest among the compounds tested. The colourimetric parameters indicate that colour intensity becomes enhanced with increasing concentration of these copigments, leading to darker and more vivid bluish colours. Thermodynamic and quantum chemical investigations are performed to interpret the absorption properties in the visible range. Fluorescence spectroscopy confirms the interaction between caffeic acid and oenin, while FTIR spectroscopic results further suggest a role for hydrogen bonds in the overall process. To our knowledge, this is the first experimentally corroborated direct evidence of hydrogen bonds in copigmentation.

Enhanced stability of red-fleshed apple anthocyanins by copigmentation and encapsulation

BACKGROUND

Red-fleshed apples are a great source of natural colorants and functional food ingredients because of their high anthocyanin content. Generally, anthocyanins are highly unstable after extraction, which limits their wide applications in the food and pharmaceutical industries. This study was aimed at investigating the effects of combining copigmentation with encapsulation on the stability of anthocyanins from red-fleshed apples. In this study, red-fleshed apple anthocyanins were copigmented with caffeic acid, and then the copigmented complexes were encapsulated using gum arabic and maltodextrin using spray drying and freeze drying.

RESULTS

All anthocyanin microcapsules had high encapsulation efficiencies ranging from 93.84 to 96.85% with mean hydrodynamic diameter smaller than 350 nm. After heating at 80 °C for 2 h, the dispersions of microencapsulated anthocyanins with copigments exhibited the highest absorbance values at λ_max (515 nm) (P < 0.05). Light stability experiments demonstrated that the half-life of the red-fleshed apple anthocyanins increased from 5 to 12 days after being treated with copigmentation and encapsulation. The drying methods (spray/freeze drying) did not significantly influence the stability of the microencapsulated anthocyanins.

CONCLUSIONS

Applying copigmentation and spray-drying encapsulation in tandem has great potential for enhancing the stability of red-fleshed apple anthocyanins. Thus, such anthocyanins with enhanced stability may be increasingly used in the food and pharmaceutical industries as value-added natural food pigments. © 2018 Society of Chemical Industry.

Understanding the shielding effects of whey protein on mulberry anthocyanins: Insights from multispectral and molecular modelling investigations

Assembling between polyphenols and proteins has been recently spotlighted and this binding is of specific importance in food chemistry since these complexes are typically used in different foodstuffs. A study on the copigmentation among three encapsulation wall-materials, including maltodextrin, gum Arabic, and whey proteins, with mulberry anthocyanins (AC) proved that whey protein (WP) is an outstanding wall-material due to its wrapping and hyperchromicity effects. Additionally, high binding ability of WP with AC was shown to be responsible for its superior copigmentation effects. Accordingly, the underlying shielding mechanism of WP on AC based on their non-covalent assembling was deeply studied using multispectral and computational assays. The fluorometric results demonstrated that a static and heat-stable binding between WP and AC occurred, leading to modification in size, hydrophobicity, and secondary structures of WP. The docking results explained that WP-AC complex was mainly molded via hydrophobic effects of WP surface and subsequently be stabilized by H-bonding and van der Waals forces. These results may contribute to a better understanding on the enhanced colouring proprieties of anthocyanins by using whey proteins.

The effect of prefermentative addition of gallic acid and ellagic acid on the red wine color, copigmentation and phenolic profiles during wine aging

Though non-anthocyanin phenolics normally do not have red color, they affect the red color expression in the copigmentation of red wines. In this study, the influence of prefermentative addition of 300mg/L gallic acid and ellagic acid, as cofactors, on aging dry red wines had been systematically evaluated at the industrial scales from the perspectives of color, phenolic profiles and copigmentation effects of anthocyanins. Red wines made with these two compounds exhibited better color properties than the control, having better CIELAB chromatic parameters. Additionally, significantly higher levels of detectable anthocyanins and copigmented anthocyanin ratio had been observed. Wines with ellagic acid showed better chromatic properties and phenolic profiles than wines with gallic acid, as shown in previous theoretical results. Anti-copigmentation phenomenon was noticed and elucidated. These practical results confirmed that ellagic acid was the better cofactor, and would give more additional guidance for the production of high quality wine.

CHEMICAL COMPOUNDS

Malvidin-3-O-glucoside (PubChem CID: 443,652); Petunidin-3-O-glucoside (PubChem CID: 443,651); Delphinidin-3-O-glucoside (PubChem CID: 443,650); Peonidin-3-O-glucoside (PubChem CID: 443,654); Ellagic acid (PubChem CID: 5,281,855); Gallic acid (PubChem CID: 370); Quercetin (PubChem CID: 443,654); Caffeic acid (PubChem CID: 689,043); (+)-catechin (PubChem CID: 9064); Vanillic acid (PubChem CID: 8468).

Colorimetric study of malvidin-3-O-glucoside copigmented by phenolic compounds: The effect of molar ratio, temperature, pH, and ethanol content on color expression of red wine model solutions

In the recent research, the copigmentations of malvidin-3-O-glucoside with eight types of phenolic copigments have been investigated. The influence of the pigment/copigment molar ratio, the reaction temperature, the pH and the ethanol content of solutions has been examined. The results showed that the copigmentation effect was dependent on not only the particular structures of the phenolic compounds but also the factors of the reaction systems. The increase of the copigment concentration can strengthen the copigmentation effect, improve the solution color, and enhance the red-purple features. Different temperatures had different influences on the copigmentation reactions. The destruction of the copigmentation complexes can result in the hypsochromic shift of the reaction solution when the temperature was higher than 20°C. The bathochromic shift of the solution gradually progressed with the increase of the pH value. A significant copigmentation feature was spotted when pH reached 3.0, which demonstrates obvious red-purple characterization. The addition of the ethanol weakened the copigmentation effect. According to measurement through color analysis, it was found that the color differences caused by ethanol in red wine were typically attributed to quantitative changes. Remarkably, all of the above delicate color deviations caused by the structural or environmental factors can be precisely and conveniently depicted via the CIELAB space analysis.