PpHYH is responsible for light-induced anthocyanin accumulation in fruit peel of Prunus persica

Peach Prunus persica is an economically important fruit tree crop worldwide. Although the external color of fruit is an important aspect of fruit quality, the mechanisms underlying its formation remain elusive in peach. Here, we report an elongated hypocotyl 5-homolog gene PpHYH involved in the regulation of anthocyanin pigmentation in peach fruit peel. Anthocyanin accumulation in fruit peel is light-dependent in peach. PpHYH had no auto-activation activity and its transcription was induced by sunlight. PpHYH activated transcription of a cluster of three PpMYB10 genes in the present of a cofactor PpBBX4 encoding a B-BOX protein, leading to anthocyanin accumulation in the sun-exposed peel. However, the PpHYH activity was repressed by a negative regulator of PpCOP1 encoding constitutive photomorphogenesis protein 1 which accumulated in the nucleus under dark condition, resulting in failure of anthocyanin accumulation in the shaded peel. PpCOP1 was re-localized into the cytosol under light condition, in accordance with fruit peel pigmentation. Additionally, transport of anthocyanins from the cytoplasm to the vacuole was a rate-limiting step for anthocyanin accumulation in peach fruit peel. Our results reveal for the first time the HYH gene involved in the regulation of anthocyanin accumulation in fruits, and provide target genes for genetic manipulation of fruit coloration.

Comparing the thermal stability of 10-carboxy-, 10-methyl-, and 10-catechyl-pyranocyanidin-3-glucosides and their precursor, cyanidin-3-glucoside

Pyranoanthocyanins are vibrant, naturally derived pigments formed by the reaction of an anthocyanin with a cofactor containing a partially negatively charged carbon. This study compared the thermal stability and degradation products of 10-carboxy-pyranocyanidin-3-glucoside (pyruvic acid cofactor), 10-methyl-pyranocyanidin-3-glucoside (acetone cofactor), and 10-catechyl-pyranocyanidin-3-glucoside (caffeic acid cofactor) with their anthocyanin precursor to evaluate the role of the pyranoanthocyanin C10 substitution on stability. Pyranoanthocyanins exhibited absorbance half-lives ~2.1-8.6 times greater than cyanidin-3-glucoside, with ~15-52% of their original pigment remaining after 12 h of 90 °C heating at pH 3.0. 10-Methyl-pyranocyanidin-3-glucoside was the most stable (p < 0.01) based on UHPLC-PDA analysis, while 10-catechyl-pyranocyanidin-3-glucoside had the most stable color in part due to contribution from a colored degradation compound. Protocatechuic acid formed in all heated samples, which suggested a similar degradation mechanism among pigments. In conclusion, the C10 substitution impacted the extent of pyranoanthocyanin stability and the degradation compounds formed.

Natural and Synthetic Flavylium-Based Dyes: The Chemistry Behind the Color

Flavylium compounds are a well-known family of pigments because they are prevalent in the plant kingdom, contributing to colors over a wide range from shades of yellow-red to blue in fruits, flowers, leaves, and other plant parts. Flavylium compounds include a large variety of natural compound classes, namely, anthocyanins, 3-deoxyanthocyanidins, auronidins, and their respective aglycones as well as anthocyanin-derived pigments (e.g., pyranoanthocyanins, anthocyanin-flavan-3-ol dimers). During the past few decades, there has been increasing interest among chemists in synthesizing different flavylium compounds that mimic natural structures but with different substitution patterns that present a variety of spectroscopic characteristics in view of their applications in different industrial fields. This Review provides an overview of the chemistry of flavylium-based compounds, in particular, the synthetic and enzymatic approaches and mechanisms reported in the literature for obtaining different classes of pigments, their physical-chemical properties in relation to their pH-dependent equilibria network, and their chemical and enzymatic degradation. The development of flavylium-based systems is also described throughout this Review for emergent applications to explore some of the physical-chemical properties of the multistate of species generated by these compounds.

Evolution of Flavylium-Based Color Systems in Plants: What Physical Chemistry Can Tell Us

Anthocyanins are the basis of the color of angiosperms, 3-deoxyanthocyanins and sphagnorubin play the same role in mosses and ferns, and auronidins are responsible for the color in liverworts. In this study, the color system of cyanidin-3-O-glucoside (kuromanin) as a representative compound of simpler anthocyanins was fully characterized by stopped flow. This type of anthocyanin cannot confer significant color to plants without intra- or intermolecular interactions, complexation with metals or supramolecular structures as in Commelina communis. The anthocyanin's color system was compared with those of 3-deoxyanthocyanins and riccionidin A, the aglycone of auronidins. The three systems follow the same sequence of chemical reactions, but the respective thermodynamics and kinetics are dramatically different.

Chemical, Microbiological and Sensory Stability of Steam Extracted Jaboticaba (Myrciaria jaboticaba) Juice

Jaboticaba (Myrciaria jaboticaba) is a Brazilian berry rich in phenolic compounds, much appreciated for its sweet and slightly acid taste, and highly perishable. Thus, we aimed at producing jaboticaba juice by steam extraction and at investigating its microbiological, sensorial and chemical qualities during storage for up to 168 days. Juice was microbiologically safe and even though unsweetened juice was well accepted, sucrose addition further improved flavor (21%), overall impression (11%) and purchase intent (21%) scores. Cyanidin-3-O-glucoside (C3G) was the major phenolic (40%), followed by gallic (28%) and ellagic acids (21%). Total phenolics contents decreased from 27% (50 °C) to 50% (25 °C), mainly driven by C3G degradation. At 60 °C, total phenolics contents did not change after 42 days since C3G degradation was counterbalanced by gallic acid formation (129%), which followed zero-order reaction kinetics. Anthocyanins degradation followed first-order reaction kinetics (C3G half-life at 25 °C = 21.7 days) and was associated with color changes during storage. In conclusion, steam extraction followed by hot-filling technique ensured a juice with at least six months of shelf life.

Adiabatic-Molecular Dynamics Generalized Vertical Hessian Approach: A Mixed Quantum Classical Method To Compute Electronic Spectra of Flexible Molecules in the Condensed Phase

We present a general mixed quantum classical method that couples classical molecular dynamics (MD) and vibronic models to compute the shape of electronic spectra of flexible molecules in the condensed phase without, in principle, any phenomenological broadening. It is based on a partition of the nuclear motions of the solute + solvent system in "soft" and "stiff" vibrational modes and an adiabatic hypothesis that assumes that stiff modes are much faster than soft ones. In this framework, the spectrum is rigorously expressed as a conformational integral of quantum vibronic spectra along the stiff coordinates only. Soft modes enter at the classical level through the conformational distribution that is sampled with classical MD runs. In each configuration, reduced-dimensionality quadratic Hamiltonians are built in the space of the stiff coordinates only, thanks to a generalization of the Vertical Hessian harmonic model and an iterative application of projectors in internal coordinates to remove soft modes. Quantum vibronic spectra, specific for each sampled configuration of the soft coordinates, are then computed at the desired temperature with efficient time-dependent techniques, and the global spectrum simply arises from their average. For consistency of the whole procedure, classical MD runs are performed with quantum-mechanically derived force fields, parameterized at the same level of theory selected for generating the quadratic Hamiltonians along the stiff coordinates. Application to N-methyl-6-oxyquinolinium betaine in water, dithiophene in ethanol, and cyanidine in water is presented to show the performance of the method.

Effect of certain treatments to prevent or partially reverse the pinking phenomenon in susceptible white wines

Pinking is a phenomenon occurring in certain white wines produced under highly reductive conditions which occasionally develop a pink colouration when suddenly exposed to air. The pink colouration gives the impression of wine being stained with red grape pigments, but in fact the phenomenon is a transformation in the presence of oxygen of some specific phenolic compounds found in the susceptible varieties. In our experiments two white wines based on Sauvignon blanc and Chardonnay, respectively, were found to have a high potential toward pinking. This study evaluates the potential of certain treatments to prevent the development of pinking or to partially reverse it after occurrence. Treatments tested involved the addition of 20 to 40 mg/l ascorbic acid or 5 to 30 mg/l of catechinic tannin prior to bottling. Both types of treatments had the potential to prevent pinking, irrespective of dosage used, as long as a normal concentration of free SO2 (above 0.8 mg/l molecular SO2) was maintained in the wines. Other treatments tested for bottled wines already developing a pink shade were the exposure of the bottle to UV light or the keeping in complete darkness, respectively. In the absence of any other pinking preventive measure both treatments proved to have a certain effect upon reversing the phenomenon. The UV light treatment shows more potential to reverse pinking than darkness and it may work even better on bottles with lower UV light filtering power (in this experiment Antique green glass bottles, with 70–80% UV reduction effect, were used). Differences among the responses of varieties are also present, with Chardonnay being less responsive to antioxidants than Sauvignon blanc. The parameters determined for the evaluation of pinking level are: Pinking potential index (PPI), proanthocyanidins (PAC), co-pigmented anthocyanins (Cp), polymeric pigmented anthocyanins (P) and total pigments (TP), as well as the absorbtion at 420 nm (for browning), 500 and 520 nm (for pinking), 620 nm (for blue shades).

The Influence of Chemical Structure and the Presence of Ascorbic Acid on Anthocyanins Stability and Spectral Properties in Purified Model Systems

The loss of color pigment is an important quality factor of food products. This work aimed to systematically study, in purified model systems, the influence of anthocyanins' structure (by increasing the size of the conjugated sugar) and the presence of ascorbic acid on their stability and spectral properties during storage at two pH levels relevant to medium and high acid foods (6.5 and 4.5, respectively). Anthocyanins (cyanidin (Cy), cyanidin 3-O-β-glucoside (Cy3G) and cyanidin 3-O-β-rutinoside (Cy3R)) displayed first-order degradation rates, presenting higher stability in acidic medium and enhanced stability with increasing size of conjugated sugar. The addition of ascorbic acid resulted in significantly enhanced degradation. Changes in ultra violet visible (UV-VIS) spectral properties presented a decrease in typical color intensity and pointed towards formation of degradation products. Identification and kinetics of formation for cyanidin degradation products were obtained by high performance liquid chromatography system-mass spectrometry (HPLC-MS).

Thermal and Photochemical Stability of Anthocyanins from Black Carrot, Grape Juice, and Purple Sweet Potato in Model Beverages in the Presence of Ascorbic Acid

Anthocyanins are natural dyes widely used in the food industry, but their chemical stability in beverages can be affected by the presence of additives. In the present paper, the interaction between anthocyanins and ascorbic acid (AA) is more particularly investigated. Ascorbic acid is an ubiquitous component in food products. In this study, the thermal stability at 43 °C and the photolysis stability in air and in an inert atmosphere (N₂) of anthocyanins extracted from black carrot (BC), grape juice (GJ), and purple sweet potato (SP) were studied in the presence and absence of ascorbic acid (in citrate buffer at pH 3). Discriminating the main environmental factors (i.e., heat and light) affecting anthocyanin stability is a key point for better understanding the degradation pathways. The stability of the anthocyanins was followed by UV-vis spectrometry. Moreover, to understand the degradation mechanisms in both the presence and absence of ascorbic acid, various techniques such as fluorescence quenching, cyclic voltammetry, and electron-spin-resonance (ESR) spectroscopy were also used to furnish a full coherent picture of the chemical mechanisms associated with the anthocyanin degradation. In addition, molecular orbitals and bond-dissociation energies (BDE) were calculated to extend the investigation. Moreover, the effects of some supplementary stabilizers (chlorogenic acid, sinapic acid, tannic acid, fumaric acid, β-carotene, isoquercitrin, myricitrin, green coffee bean extract, and rosemary extract) and sugars (sucrose, fructose, and glucose) on anthocyanins stability in the presence of ascorbic acid were examined.

pH-Dependent Multistate System Generated by a Synthetic Furanoflavylium Compound: An Ancestor of the Anthocyanin Multistate of Chemical Species

The multistate of chemical species generated by 4'-hydroxy-3,2'-furanoflavylium is similar to that of anthocyanins and related compounds. This furanoflavylium multistate system was fully characterized by UV-visible and NMR spectroscopy, allowing determination of the respective equilibrium and rate constants. In contrast to the multistate generated by flavylium cations derived from anthocyanins and related compounds, the furanoflavylium multistate is characterized by much slower hydration and tautomerization (pyran ring opening-closing). In addition, the cis-trans isomerization of the chalcones of this system (2'-hydroxyaurones) is extremely slow when compared with anthocyanins. The observed similar order of magnitude for tautomerization and isomerization rate constants leads to peculiar kinetics from the flavylium cation (pH = 1) to the stable trans-chalcone (higher pH values). The hemiketal appears and disappears during the first stages of the kinetics, which gives the intermediate cis-chalcone (pseudo-equilibrium). This last species disappears in a much slower process, as fully characterized by ¹H NMR, to give the final trans-chalcone.

A model compound for pyridinechalcone-based multistate systems. Ring opening-closure as the slowest kinetic step of the multistate

Amino-substituted pyridinechalcones configure multistate systems where a new type of flavylium derivative with potential biological activity are present.

Stereochemistry and glycosidic linkages of C3-glycosylations affected the reactivity of cyanidin derivatives

The impact of glycosylation on anthocyanin stability has largely been associated with sugar type, site, and size, with glycosyl stereochemistry being under-explored. Seven cyanidin-3-glycosides were isolated by HPLC, diluted in pH 1-9, mixed with bisulfite or ascorbic acid at pH 3, and stored for 8 weeks (25 °C, dark). Spectral changes, half-lives, and bleaching rates were determined. Cyanidin-3-galactoside was more reactive (susceptible to hydration and bleaching) than cyanidin-3-glucoside. The 1 → 2 disaccharides exhibited greater λ_vis-max (≤16 nm), resistance to hydration, and bleaching compared to 1 → 6 disaccharides.The 1 → 6 disaccharides had similar λ_vis-max (∼2 nm) to the monosaccharides but slightly improved resistance to hydration and bleaching. The tri-glycosylated anthocyanin had the greatest stability and its spectral and bleaching characteristics was intermediate to 1 → 2 and 1 → 6 disaccharides. The 1 → 2 disaccharides generally exhibited lower half-lives compared to monosaccharides; whereas, 1 → 6 disaccharides exhibited higher stability. These findings highlight the role of glycosyl assembly on anthocyanin reactivity and stability.

Anthocyanin Tissue Bioavailability in Animals: Possible Implications for Human Health. A Systematic Review

Anthocyanins (ACNs) are promising health-enhancing phenolic compounds. We focus on ACN animal tissue bioavailability to provide an evidentiary link between tissue ACNs and their associated health properties. We performed a systematic review of electronic libraries; 279 results were retrieved, and 13 publications met inclusion criteria. Extracted information included animal model employed, administration route, doses, analysis method, and ACN concentration values in tissues. Total ACN concentrations were detected in mice kidney (2.17 × 10⁵ pmol/g), liver (1.73 × 10⁵ pmol/g), heart (3.6 × 10³ pmol/g), and lung (1.16 × 10⁵ pmol/g); and in pig brain (6.08 × 10³ pmol/g). ACNs showed a predominance of parent ACNs in long-term experiments versus an ACN metabolite predominance in short-term experiments. ACNs detected in animal tissues, such as cyanidin-3-glucoside, suggest it may have an important role in human health. This information could be useful to determine proper ACN-intake biomarkers in biological samples in futures studies.

The Chemical Reactivity of Anthocyanins and Its Consequences in Food Science and Nutrition

Owing to their specific pyrylium nucleus (C-ring), anthocyanins express a much richer chemical reactivity than the other flavonoid classes. For instance, anthocyanins are weak diacids, hard and soft electrophiles, nucleophiles, prone to developing π-stacking interactions, and bind hard metal ions. They also display the usual chemical properties of polyphenols, such as electron donation and affinity for proteins. In this review, these properties are revisited through a variety of examples and discussed in relation to their consequences in food and in nutrition with an emphasis on the transformations occurring upon storage or thermal treatment and on the catabolism of anthocyanins in humans, which is of critical importance for interpreting their effects on health.

Stabilizing and Modulating Color by Copigmentation: Insights from Theory and Experiment

Natural anthocyanin pigments/dyes and phenolic copigments/co-dyes form noncovalent complexes, which stabilize and modulate (in particular blue, violet, and red) colors in flowers, berries, and food products derived from them (including wines, jams, purees, and syrups). This noncovalent association and their electronic and optical implications constitute the copigmentation phenomenon. Over the past decade, experimental and theoretical studies have enabled a molecular understanding of copigmentation. This review revisits this phenomenon to provide a comprehensive description of the nature of binding (the dispersion and electrostatic components of π-π stacking, the hydrophobic effect, and possible hydrogen-bonding between pigment and copigment) and of spectral modifications occurring in copigmentation complexes, in which charge transfer plays an important role. Particular attention is paid to applications of copigmentation in food chemistry.

Fe3O4@PEG-SO3H rod-like morphology along with the spherical nanoparticles: novel green nanocomposite design, preparation, characterization and catalytic application

A new heterogeneous nanocatalyst was successfully synthesized, completely characterized and efficiently applied in the synthesis of dihydropyrimidines.

Mimicking Positive and Negative Copigmentation Effects in Anthocyanin Analogues by Host-Guest Interaction with Cucurbit[7]uril and β-Cyclodextrins

Copigmentation and the anti-copigmentation effects can be mimicked by the interaction of anthocyanin's model compounds respectively with cucurbit[7]uril (CB7) and β-cyclodextrin (β-CD). The complex network of chemical reactions displayed by this family of compounds includes the colored flavylium cation, AH(+), and quinoidal base, A, along with the colorless hemiketal, B, cis-chalcone, Cc, and trans-chalcone, Ct. Whereas AH(+) is stable only at very acidic pH values, the remaining species are formed at slightly acidic and neutral conditions. However, under these conditions, for most of the natural and synthetic flavylium salts, the colorless species predominate (B, Cc, and Ct) at the expense of A. The host CB7 was found to improve the color of solutions in two different ways: first, it stabilizes AH(+) at higher pH values by decreasing its acidity and, second, it enhances the mole fraction of A due to selective complexation of this species in the pH range where the flavylium cation is no longer stable. In contrast, β-CD increases the acidity of AH(+), favoring the formation of Ct at the expense of all the other multistate species (Bası́lio et al. New J. Chem. 2013, 37, 3166-3173; Petrov et al. J. Phys. Chem. A 2013, 117, 10692-10701; Gago et al. Dyes Pigments 2014, 110, 106-112; and Lopes-Costa et al. Photochem. Photobiol. Sci. 2014, 13, 1420-1426). Although both hosts have a large effect on the hydration rate and pH domain of the flavylium cation, the effect on the degradation kinetics of anthocyanidins is modest. CB7 decreases the hydration rate and decreases the acid-base (AH(+)/A) equilibrium constant (Ka), leading respectively to a slowing and a speeding of the anthocyanin degradation rate. On the other hand, β-CD increases the hydration rate but increases Ka, both effects acting in opposite directions.