Microbial synthesis of anthocyanins and pyranoanthocyanins: current bottlenecks and potential solutions.

Anthocyanins (ACNs) are secondary metabolites found in plants. Due to their impressive biological activities, ACNs have gained significant popularity and extensive application within the food, pharmaceutical, and nutraceutical industries. A derivative of ACNs: pyranoanthocyanins (PACNs) possesses more stable properties and interesting biological activities. However, conventional methods for the production of ACNs, including chemical synthesis and plant extraction, involve organic solvents. Microbial synthesis of ACNs from renewable biomass, such as amino acids or flavonoids, is considered a sustainable and environmentally friendly method for large-scale production of ACNs. Recently, the construction of microbial cell factories (MCFs) for the efficient biosynthesis of ACNs and PACNs has attracted much attention. In this review, we summarize the cases of microbial synthesis of ACNs, and analyze the bottlenecks in reconstructing the metabolic pathways for synthesizing PACNs in microorganisms. Consequently, there is an urgent need to investigate the mechanisms behind the development of MCFs for PACNs synthesis. Such research also holds significant promise for advancing the production of food pigments. Meanwhile, we propose potential solutions to the bottleneck problem based on metabolic engineering and enzyme engineering. Finally, the development prospects of natural food and biotechnology are discussed.

Cholesterol-Lowering Activity of Vitisin A Is Mediated by Inhibiting Cholesterol Biosynthesis and Enhancing LDL Uptake in HepG2 Cells.

Pyranoanthocyanins have been reported to possess better chemical stability and bioactivities than monomeric anthocyanins in some aspects. The hypocholesterolemic activity of pyranoanthocyanins is unclear. In view of this, this study was conducted to compare the cholesterol-lowering activities of Vitisin A with the anthocyanin counterpart Cyanidin-3-O-glucoside(C3G) in HepG2 cells and to investigate the interaction of Vitisin A with the expression of genes and proteins associated with cholesterol metabolism. HepG2 cells were incubated with 40 µM cholesterol and 4 µM 25-hydroxycholeterol with various concentrations of Vitisin A or C3G for 24 h. It was found that Vitisin A decreased the cholesterol levels at the concentrations of 100 µM and 200 µM with a dose-response relationship, while C3G exhibited no significant effect on cellular cholesterol. Furthermore, Vitisin A could down-regulate 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR) to inhibit cholesterol biosynthesis through a sterol regulatory element-binding protein 2 (SREBP2)-dependent mechanism, and up-regulate low-density lipoprotein receptor (LDLR) and blunt the secretion of proprotein convertase subtilisin/kexin type 9 (PCSK9) protein to promote intracellular LDL uptake without LDLR degradation. In conclusion, Vitisin A demonstrated hypocholesterolemic activity, by inhibiting cholesterol biosynthesis and enhancing LDL uptake in HepG2 cells.

A Comparative Study on the Photophysical Properties of Anthocyanins and Pyranoanthocyanins.

Anthocyanins and pyranoanthocyanins are flavonoids that are present in various food products (e.g., fruit, vegetables, wine, etc.). The large chemical diversity amongst these molecules leads to compound-specific properties such as color and stability towards external conditions. These properties are also attractive for food and non-food applications. The photophysical experimental characterization is not easy as this generally demands advanced analytical techniques along with optimized separation procedures. Molecular modeling can provide insights into the fundamental understanding of the photophysical properties of these compounds in a uniform way for a broad set of compounds. However, the current literature is quite fragmented on this topic. Herein, a large set of 140 naturally derived anthocyanins was evaluated in a systematic way with three functionals (B3LYP, PBE0, and CAM-B3LYP). The accuracy of these functionals was determined with experimental literature λmax,vis values. In addition to λmax,vis values, time-dependent (TD)-DFT calculations also provided oscillator strengths, molar absorption coefficients, and orbital energies, which define whether specific natural anthocyanin-based compounds can be deployed in food and non-food applications such as food additives/colorants, textile dyeing, analytical standards, and dye-sensitized solar cells (DSSCs).

Influence of the Anthocyanin and Cofactor Structure on the Formation Efficiency of Naturally Derived Pyranoanthocyanins.

Pyranoanthocyanins are anthocyanin-derived pigments with higher stability to pH and storage. However, their slow formation and scarcity in nature hinder their industrial application. Pyranoanthocyanin formation can be accelerated by selecting anthocyanin substitutions, cofactor concentrations, and temperature. Limited information is available on the impacts of the chemical structure of the cofactor and anthocyanin; therefore, we evaluated their impacts on pyranoanthocyanin formation efficiency under conditions reported as favorable for the reaction. Different cofactors were evaluated including pyruvic acid, acetone, and hydroxycinnamic acids (p-coumaric, caffeic, ferulic, and sinapic acid) by incubating them with anthocyanins in a molar ratio of 1:30 (anthocyanin:cofactor), pH 3.1, and 45 °C. The impact of the anthocyanin aglycone was evaluated by incubating delphinidin, cyanidin, petunidin, or malvidin derivatives with the most efficient cofactor (caffeic acid) under identical conditions. Pigments were identified using UHPLC-PDA and tandem mass spectrometry, and pyranoanthocyanin formation was monitored for up to 72 h. Pyranoanthocyanin yields were the highest with caffeic acid (~17% at 72 h, p < 0.05). When comparing anthocyanins, malvidin-3-O-glycosides yielded twice as many pyranoanthocyanins after 24 h (~20%, p < 0.01) as cyanidin-3-O-glycosides. Petunidin- and delphinidin-3-O-glycosides yielded <2% pyranoanthocyanins. This study demonstrated the importance of anthocyanin and cofactor selection in pyranoanthocyanin production.

The Role of Anthocyanins, Deoxyanthocyanins and Pyranoanthocyanins on the Modulation of Tyrosinase Activity: An In Vitro and In Silico Approach.

Tyrosinase is the central enzyme involved in the highly complex process of melanin formation, catalyzing the rate-limiting steps of this biosynthetic pathway. Due to such a preponderant role, it has become a major target in the treatment of undesired skin pigmentation conditions and also in the prevention of enzymatic food browning. Numerous phenolic-based structures from natural sources have been pointed out as potential tyrosinase inhibitors, including anthocyanins. The aim of the present study was to individually assess the tyrosinase inhibitory activity of eight purified compounds with a variable degree of structural complexity: native anthocyanins, deoxyanthocyanins, and pyranoanthocyanins. The latter two, the groups of anthocyanin-related compounds with enhanced stability, were tested for the first time. Compounds 1 to 4 (luteolinidin, deoxymalvidin, cyanidin-, and malvidin-3-O-glucoside) revealed to be the most effective inhibitors, and further kinetic studies suggested their inhibition mechanism to be of a competitive nature. Structure-activity relationships were proposed based on molecular docking studies conducted with mushroom tyrosinase (mTYR) and human tyrosinase-related protein 1 (hTYRP1) crystal structures, providing information about the binding affinity and the different types of interactions established with the enzyme's active center which corroborated the findings of the inhibition and kinetic studies. Overall, these results support the applicability of these compounds as pigmentation modulators.

Pyranoanthocyanins Interfering with the Quorum Sensing of Pseudomonas aeruginosa and Staphylococcus aureus.

Bacterial quorum sensing (QS) is a cell-cell communication system that regulates several bacterial mechanisms, including the production of virulence factors and biofilm formation. Thus, targeting microbial QS is seen as a plausible alternative strategy to antibiotics, with potentiality to combat multidrug-resistant pathogens. Many phytochemicals with QS interference activity are currently being explored. Herein, an extract and a compound of bioinspired origin were tested for their ability to inhibit biofilm formation and interfere with the expression of QS-related genes in Pseudomonas aeruginosa and Staphylococcus aureus. The extract, a carboxypyranoanthocyanins red wine extract (carboxypyrano-ant extract), and the pure compound, carboxypyranocyanidin-3-O-glucoside (carboxypyCy-3-glc), did not cause a visible effect on the biofilm formation of the P. aeruginosa biofilms; however, both significantly affected the formation of biofilms by the S. aureus strains, as attested by the crystal violet assay and fluorescence microscopy. Both the extract and the pure compound significantly interfered with the expression of several QS-related genes in the P. aeruginosa and S. aureus biofilms, as per reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results. Indeed, it was possible to conclude that these molecules interfere with QS at distinct stages and in a strain-specific manner. An extract with anti-QS properties could be advantageous because it is easily obtained and could have broad, antimicrobial therapeutic applications if included in topical formulations.

Non-Saccharomyces as Biotools to Control the Production of Off-Flavors in Wines.

Off-flavors produced by undesirable microbial spoilage are a major concern in wineries, as they affect wine quality. This situation is worse in warm areas affected by global warming because of the resulting higher pHs in wines. Natural biotechnologies can aid in effectively controlling these processes, while reducing the use of chemical preservatives such as SO2. Bioacidification reduces the development of spoilage yeasts and bacteria, but also increases the amount of molecular SO2, which allows for lower total levels. The use of non-Saccharomyces yeasts, such as Lachancea thermotolerans, results in effective acidification through the production of lactic acid from sugars. Furthermore, high lactic acid contents (>4 g/L) inhibit lactic acid bacteria and have some effect on Brettanomyces. Additionally, the use of yeasts with hydroxycinnamate decarboxylase (HCDC) activity can be useful to promote the fermentative formation of stable vinylphenolic pyranoanthocyanins, reducing the amount of ethylphenol precursors. This biotechnology increases the amount of stable pigments and simultaneously prevents the formation of high contents of ethylphenols, even when the wine is contaminated by Brettanomyces.

Production of pyranoanthocyanins using Escherichia coli co-cultures.

Hydroxyphenyl-pyranoanthocyanins are one of the pyranoanthocyanins found in red wines and some fruit juices. Since they have a fourth ring (pyran or ring D) which provides higher color intensity and exceptional stability toward pH variations in comparison to their anthocyanin precursors, these molecules are one of the most important candidates as natural colorants especially for low- and medium-acidic food and beverages. However, their isolation and characterization are difficult due to their very low concentration. In this study, we co-cultured recombinant E. coli strains to synthesize pyranoanthocyanins with improved titers and yields. To accomplish this task, firstly we engineered 4-vinylphenol and 4-vinylcatechol producer modules then we co-cultured each one of these strains with cyanidin-3-O-glucoside producer recombinant cells to obtain pyranocyanidin-3-O-glucoside-phenol (cyanidin-3-O-glucoside with vinylphenol adduct) and pyranocyanidin-3-O-glucoside-catechol (cyanidin-3-O-glucoside with vinylcatechol adduct). By optimizing the co-culture conditions, we were able to significantly increase final titers and yields, allowing our co-culture approach to easily outperform production of pyranoanthocyanins from red wine. Finally, we demonstrate that the produced pyranoanthocyanins are far more stable than the starting plant-produced cyanidin 3-O-glucoside.

Engineering Lactococcus lactis for the production of unusual anthocyanins using tea as substrate.

Plant material rich in anthocyanins has been historically used in traditional medicines, but only recently have the specific pharmacological properties of these compounds been the target of extensive studies. In addition to their potential to modulate the development of various diseases, coloured anthocyanins are valuable natural alternatives commonly used to replace synthetic colourants in food industry. Exploitation of microbial hosts as cell factories is an attractive alternative to extraction of anthocyanins and other flavonoids from plant sources or chemical synthesis. In this study, we present the lactic acid bacterium Lactococcus lactis as an ideal host for the production of high-value plant-derived bioactive anthocyanins using green tea as substrate. Besides the anticipated red-purple compounds cyanidin and delphinidin, orange and yellow pyranoanthocyanidins with unexpected methylation patterns were produced from green tea by engineered L. lactis strains. The pyranoanthocyanins are currently attracting significant interest as one of the most important classes of anthocyanin derivatives and are mainly formed during the aging of wine, contributing to both colour and sensory experience.

Influence of Saccharomyces and non-Saccharomyces Yeasts in the Formation of Pyranoanthocyanins and Polymeric Pigments during Red Wine Making.

Yeast are able to modulate many sensory parameters of wines during red must fermentation. The effect on color and on the formation of derived pigments during fermentation has been studied thoroughly since the 90s. Yeast can increase grape anthocyanin's color by acidification by hyperchromic effect (increase of flavylium molecules). Recent studies with non-Saccharomyces species, as Lachancea thermotolerans, described the intense effect of some strains on anthocyanin's color, and subsequent, stability, by strongly reducing wine's pH during fermentation. Moreover, selected yeast strains of Saccharomyces have been shown to release metabolites such as pyruvic acid or acetaldehyde that promote the formation of vitisin A and B pyranoanthocyanins during must fermentation. Schizosaccharomyces pombe, because of its specific metabolism, can produce higher concentrations of pyruvate, which enhances the formation of vitisin A-type derivatives. The hydroxycinnamate decarboxylase activity that some Saccharomyces strains express during fermentation also promotes the formation of vinylphenolic derivatives. Some non-Saccharomyces species, such as S. pombe or P. guilliermondii can also improve the production of these derivatives compared to selected strains of Saccharomyces cerevisiae. Lastly, some yeasts are also able to modulate the formations of polymeric pigments between grape anthocyanins and flavonoids, such as catechins and procyanidins.

Investigating the Interaction of Ascorbic Acid with Anthocyanins and Pyranoanthocyanins.

Juices colored by anthocyanins experience color loss related to fortification with ascorbic acid (AA), thought to be the result of condensation at Carbon-4 of anthocyanins. To further understand this mechanism, pyranoanthocyanins, having a fourth-ring covalently occupying Carbon-4, were synthesized to compare its reactivity with AA against that of anthocyanins. Pyranoanthocyanins were synthesized by combining chokeberry anthocyanins with pyruvic acid. AA (250-1000 mg/L) was added to either chokeberry extract, cyanidin-3-galactoside, or 5-Carboxypyranocyanidin-3-galactoside. Samples were stored in the dark for 5 days at 25 °C and spectra (380-700 nm), color (CIE-L*c*h*), and composition changes (HPLC-MS/MS) were monitored. Extensive bleaching occurred for cyanidin-3-galactoside and chokeberry colored solutions, with a decrease in half-lives from 22.8 to 0.3 days for Cyanidin-3-galactoside when 1000 mg/L AA was added. 5-Carboxypyranocyanidin-3-galactoside solution better maintained color with limited loss in absorbance, due to the formation of colored degradation products (λvis-max = 477 to 487 nm), and half-life decrease from 40.8 to 2.7 days, an 8-13-fold improvement compared to anthocyanins. This suggested alternative sites of reactivity with AA. Carbon-4 may be the preferred site for AA-pigment interactions, but it was not the only location. With Carbon-4 blocked, 5-Carboxypyranocyanidin-3-galactoside reacted with AA to form new pigments and reduce bleaching.

Comparison of Aquitaine and Rioja Red Wines: Characterization of Their Phenolic Composition and Evolution from 2000 to 2013.

Wine chemical analysis was carried out on 194 commercial blended red wines produced by two major wine-growing areas-the Aquitaine (France) and Rioja (Spain) regions-in order to compare the wines of both regions. Anthocyanins and derived pigments, tannins and derivatives were identified and quantified by HPLC-DAD-ESI-MS/MS (high pressure liquid chromatography coupled to diode array detector and mass spectrometry using the electrospray ionization interface). Mean degree of polymerization (mDP) was determined. The influence of the wine-growing region and the predominance of the properties of some grape varieties used are confirmed by the significant differences observed between both regions. Rioja and Bordeaux "generic" (Bordeaux and Bordeaux-Supérieur appellations) red wines showed the highest anthocyanic content and the highest mDP, as these wines are in a majority made from Merlot (Bordeaux "generic") and Tempranillo (Rioja). On the contrary, Bordeaux "specific" regions (Blayais, Médoc, Graves, and Libournais) showed the red wines with the highest total phenolic content and tannin concentration, as the predominant grape variety used is Cabernet Sauvignon. A principal component analysis (PCA) and a hierarchical ascendant classification (HAC) suggesting patterns between the chemical parameters and the distribution of the red wines in three groups were proposed. The comparison of the two wine-growing areas also reveals some similarities between the various grape varieties used. A general effect of a progressive decrease in anthocyanins, anthocyanin-derived pigment and tannins is observed for older wines.

Characterization of polymeric pigments and pyranoanthocyanins formed in microfermentations of non-Saccharomyces yeasts.

AIMS: To assess the influence of non-Saccharomyces yeasts on the pyranoanthocyanins and polymeric pigments formation after the addition of (+)-catechin and procyanidin B2 to fresh red grape must. METHODS AND RESULTS: The fermentation of red grape musts was done with non-Saccharomyces yeasts either alone or in sequential fermentations with the Saccharomyces cerevisiae species. The characterization of both pyranoanthocyanin and polymeric pigments has been carried out with liquid chromatography coupled to mass spectroscopy (HPLC-DAD-ESI/MS). Red wines were also characterized by infrared spectroscopy (FTIR), gas chromatography (GC-FID) and spectrophotometry (UV-Vis). It has been observed that fermentation with the species Schizosaccharomyces pombe led to higher concentrations of pigments of all types: anthocyanins, polymeric pigments and pyranoanthocyanins, particularly vitisin A. CONCLUSIONS: The use of non-Saccharomyces yeasts improve the formation of stable pigments in red wines thanks to the differences in the microbial metabolism from among the yeasts studied. SIGNIFICANCE AND IMPACT OF THE STUDY: Colour stability as one of the main organoleptic properties in red wines, may be improved by the controlled use of selected non-Saccharomyces yeasts during red must fermentation.

p-Hydroxyphenyl-pyranoanthocyanins: An Experimental and Theoretical Investigation of Their Acid-Base Properties and Molecular Interactions.

The physicochemical properties of the wine pigments catechyl-pyranomalvidin-3-O-glucoside (PA1) and guaiacyl-pyranomalvidin-3-O-glucoside (PA2) are extensively revisited using ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and quantum chemistry density functional theory (DFT) calculations. In mildly acidic aqueous solution, each cationic pigment undergoes regioselective deprotonation to form a single neutral quinonoid base and water addition appears negligible. Above pH = 4, both PA1 and PA2 become prone to aggregation, which is manifested by the slow build-up of broad absorption bands at longer wavelengths (λ ≥ 600 nm), followed in the case of PA2 by precipitation. Some phenolic copigments are able to inhibit aggregation of pyranoanthocyanins (PAs), although at large copigment/PA molar ratios. Thus, chlorogenic acid can dissociate PA1 aggregates while catechin is inactive. With PA2, both chlorogenic acid and catechin are able to prevent precipitation but not self-association. Calculations confirmed that the noncovalent dimerization of PAs is stronger with the neutral base than with the cation and also stronger than π-π stacking of PAs to chlorogenic acid (copigmentation). For each type of complex, the most stable conformation could be obtained. Finally, PA1 can also bind hard metal ions such as Al3+ and Fe3+ and the corresponding chelates are less prone to self-association.

Enhancement of pyranoanthocyanin formation in blueberry wine with non-Saccharomyces yeasts.

The development of blueberry wine provides an alternative method for maintaining the nutritional value and extending the shelf life of blueberries. However, anthocyanin loss and off-flavor compound generation during fermentation impair blueberry wine color and quality. Hydroxycinnamate decarboxylase from yeast can catalyze the conversion of hydroxycinnamic acids to vinylphenols, which later may condense with anthocyanins to form more stable vinylphenolic pyranoanthocyanins. In this study, 10 non-Saccharomyces yeasts from Daqu that showed hydroxycinnamate decarboxylase activity were screened. Among the 10 strains, Wickerhamomyces anomalus Y5 showed the highest consumption (34.59%) of the total tested phenolic acids and almost no H2S production. Furthermore, Y5 seemed to produce four vinylphenol pyranoanthocyanins (cyanidin-3-O-galactoside/glucoside-4-vinylcatechol, cyanidin-3-O-galactoside/glucoside-4-vinylsyringol, malvidin-4-vinylguaiacol, and malvidin-4-vinylcatechol) during blueberry wine fermentation, which may improve the color stability of blueberry wine. These findings provide new insights for improving the quality of blueberry wine using non-Saccharomyces yeasts.

Early versus late leaf removal strategies for Pinot Noir (Vitis vinifera L.): effect on colour-related phenolics in young wines following alcoholic fermentation.

BACKGROUND: The widely adopted viticultural practice of late (véraison) leaf removal is now losing many of its advantages as a result of today's warmer vineyard conditions. With the aim of seeking a good alternative, the influence of earlier leaf removals (at pre-flowering and berry-set) on colour-related phenolics in young Pinot Noir wines was investigated in the years 2009 and 2010. RESULTS: Total flavonols in 2009 wines were 71 and 52% higher in case of véraison and berry-set treatments respectively as compared with untreated controls, while in 2010 the average content of flavonols was highest with pre-flowering leaf removal (75% higher than controls). The anthocyanin content in 2009 wines was 18 and 11% higher in case of véraison and berry-set treatments respectively and was favoured by early leaf removals in 2010 (50 and 43% higher in case of berry-set and pre-flowering treatments respectively) as compared with controls. Changes in hydroxycinnamic acid profiles were shown to be greatest in 2010 wines resulting from early leaf removal treatments. Promoted formation of vitisin A-like pigments in 2010 leaf removal treatments was observed during fermentation. CONCLUSIONS: The phenolic profiles of grapes/wines were affected by leaf removal timing, although differently in two (extremely different) seasons. Earlier leaf removal strategies showed some promising results, with good proportions mainly of flavonols and anthocyanins, retained also in young wines. Vitisins A in wines were positively affected by all leaf removals.

Theoretical Study on the Multiple Free Radical Scavenging Reactions of Pyranoanthocyanins.

The free radical trapping capacities of multiple pyranoanthocyanins in wine storage and ageing were theoretically explored by density functional theory (DFT) methods. Intramolecular hydrogen bonds were detected in all pyranoanthocyanins, and the planarity of the compounds worsened with an increasing dielectric constant in the environment. Solvents significantly influenced the reaction enthalpies; thus, the preferred thermodynamic mechanisms of the free radical scavenging reactions were modified in different phases. This study incorporates hydrogen atom transfer (HAT), proton loss (PL), electron transfer (ET) reactions, and demethylation (De) of methoxy group mechanisms. The three pyranoanthocyanins have the capacity to capture n1+1 free radicals, where n1 represents the number of methoxy groups. In the gas phase, they prefer employing the n1-De-HAT mechanism on the guaiacyl moiety of the B ring, resulting in the formation of a stable quinone or a quinone radical to scavenge free radicals. In the benzene phase, pyranoanthocyanins trap free radicals via a PL-n1-De-HAT mechanism. In the water phase, the targeted pyranoanthocyanins may dissociate in the form of carboxylate and tend to utilize the n2-PL-n1-De-ET mechanism, where n2 and n1 represent the number of phenolic groups and methoxy groups, respectively, facilitating multiple H+/e- reactions.

High yield production of cyanidin-derived pyranoanthocyanins using 4-vinylphenol and 4-vinylguaiacol as cofactors.

Pyranoanthocyanins are anthocyanin-derived pigments with vivid colors and enhanced stability, making them promising food colorants. We evaluated two 4-vinylphenols, decarboxylated p-coumaric (pCA) and ferulic acid (FA), as cofactors for pyranoanthocyanin formation. Cyanidin-3-glycosides from saponified black carrot were incubated with 4-vinylphenol or 4-vinylguaiacol in different anthocyanin-to-cofactor molar ratios (1:1-1:30) to form pyranoanthocyanins. Formation efficiency (45 °C, ≤96 h) was compared to their respective precursors at a 1:30 ratio. Composition changes were monitored using uHPLC-PDA-ESI-MS/MS. Pyranoanthocyanin yields with 4-vinylphenol (13.8-33.4%) were ∼12× higher than with pCA and yields with 4-vinylguaiacol (8.1-31.0%) were ∼6.5× higher than with FA. Molar ratios of 1:5 and 1:10 yielded significantly more pyranoanthocyanins. Pyranoanthocyanin formation with 4-vinylphenols followed first-order kinetics, whereas formation with hydroxycinnamic acids followed zero-order kinetics. Detection of intermediate compounds was consistent with a nucleophilic addition and aromatization formation mechanism. Overall, pyranoanthocyanin formation with 4-vinylphenols was more efficient than with hydroxycinnamic acids.

Preparation of 10-(hexylcarbamoyl)pyranomalvidin-3-glucoside from 10-carboxypyranomalvidin-3-glucoside using carbodiimide chemistry.

Anthocyanins and pyranoanthocyanins are appealing natural pigments for replacement of synthetic ones. However, due to instability and solubility issues, lipophilization process of anthocyanins has raised as a valuable and efficient strategy to extend their stability and affinity into liposoluble formulations and enhance their unique physicochemical and biological properties. In this work, 10-carboxypyranomalvidin-3-glucoside was functionalized with hexylamine via carbodiimide chemistry compatible with the absence of hydroxyl protecting groups. A new amide conjugate attached to an alkyl chain with better hydrophobic features was obtained and isolated from its precursor. Mass spectrometry, FTIR, and NMR spectroscopy confirmed that the lipophilization site took place at the carboxyl group and the octanol-water partition coefficient determined by UV-Vis revealed its superior affinity for non-polar media. Overall, we reported a new pyranoanthocyanin lipophilic derivative for the first time which encourage further investigation for this novel class of compounds towards their incorporation into lipid-based foods and cosmetic formulations.

Photophysics and Electrochemistry of Biomimetic Pyranoflavyliums: What Can Bioinspiration from Red Wines Offer?

Natural dyes and pigments offer incomparable diversity of structures and functionalities, making them an excellent source of inspiration for the design and development of synthetic chromophores with a myriad of emerging properties. Formed during maturation of red wines, pyranoanthocyanins are electron-deficient cationic pyranoflavylium dyes with broad absorption in the visible spectral region and pronounced chemical and photostability. Herein, we survey the optical and electrochemical properties of synthetic pyranoflavylium dyes functionalized with different electron-donating and electron-withdrawing groups, which vary their reduction potentials over a range of about 400 mV. Despite their highly electron-deficient cores, the exploration of pyranoflavyliums as photosensitizers has been limited to the "classical" n-type dye-sensitized solar cells (DSSCs) where they act as electron donors. In light of their electrochemical and spectroscopic properties, however, these biomimetic synthetic dyes should prove to be immensely beneficial as chromophores in p-type DSSCs, where their ability to act as photooxidants, along with their pronounced photostability, can benefit key advances in solar-energy science and engineering.