Effect of ferrous and ferric ions on copigmentation in model solutions

Iranian Qara Qat fruit (redcurrant) in Arasbaran forests as the resource of anthocyanin pigments in formation of [ACN-Mg2+/Al3+/Ga3+/ Sn2+/Cr3+/Fe3+] chelation clusters

Clusters of metallic cations (Mg2+, Al3+, Ga3+, Sn2+, Cr3+ and Fe3+) jointed to anthocyanins in water media were studied for unraveling the color shifting of different complexes of these structures in the low ranges of pH. Anthocyanin jointed to metallic cation progresses the color expression range of anthocyanin in more different range of pH. In this verdict, it has been studied the metallic cations diffusing of deprotonating for the anthocyanin (B)-ring of cyanidin (Cy), delphinidin (Dp) and petunidin (Pt) in two media of gas and water, transforming flavylium cations to the blue quinonoidal bases at lower range of pH applying the infrared method by approaching Beer Lambert law for getting the physico-chemical parameters of frequency, intensity, and absorbance of the compounds, respectively. In previous investigation, it has been indicated that the important factor for enhancing the absorbance in a positive non-linear fashion due to deviating from the Beer Lambert law is the self-association of anthocyanins of cyanidin, delphinidin and petunidin of anthocyanin structures. The difference of heat of formation (∆HR) among clusters of metallic cations jointed to anthocyanins has been illustrated toward the double bonds and carbonyl groups by the chelation of (B)-ring for cyanidin, delphinidin and petunidin anthocyanins in two media of gas and water that explains the stability and color of [anthocyanin-metallic cations] cluster chelation of cyanidin (Cy), delphinidin (Dp) and petunidin (Pt) colorful pigments in a weak acidic medium. By this work we exhibited that the color of the anthocyanin chelates is an important factor for estimating the efficiency of these types of food colorants.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.

Topical oral wound healing potential of anthocyanin complex: animal and clinical studies

Aim: An anthocyanin complex (AC), combined Zea mays and Clitoria ternatea extracts, was evaluated for topical oral wound healing in rats and a clinical trial in orthodontic patients. Methods/results: AC enhanced anthocyanin permeation in vitro. In rats, 10% w/w of AC in a mucoadhesive gel (AG) reduced erythema and sizes of oral wounds after topical applications at higher extent than its placebo gel. Acute orthodontic wounds in 68 volunteers were randomly assigned to topically receive either AG or placebo gel and double-blind assessed. Wound size reduction and wound closure enhancement were obvious in AG-treated group on day 3 (p < 0.05). Conclusion: At 10% w/w, AC promoted wound closure and possessed a potential in healing stimulation of acute oral wounds.

Topical Niosome Gel Containing an Anthocyanin Complex: a Potential Oral Wound Healing in Rats

Anthocyanins from dietary sources showing potential benefits as anti-inflammatory in oral lesions were developed as an anthocyanin complex (AC), comprised of extracts of Zea mays (CC) and Clitoria ternatea (CT), and formulated into a niosome gel to prove its topical oral wound healing in vitro and in vivo investigations. The AC formed nano-sized clusters of crystalline-like aggregates, occurring through both intra- and inter-molecular interactions, resulting in delivery depots of anthocyanins, following encapsulation in niosomes and incorporation into a mucoadhesive gel. In vitro permeation of anthocyanins was improved by complexation and further enhanced by encapsulation in niosomes. Collagen production in human gingival fibroblasts was promoted by AC and AC niosomes, but not CC or CT. The in vivo wound healing properties of AC gel (1 and 10%), AC niosome gel (1 and 10%), fluocinolone acetonide gel, and placebo gel were investigated for incisional wounds in the buccal cavities of Wistar rats. AC gel and AC niosome gel both reduced wound sizes after 3 days. AC niosome gel (10%) gave the highest reduction in wound sizes after day 3 (compared to fluocinolone acetonide gel, p < 0.05), and resulted in 100% wound healing by day 5. Histological observations of cross-sectioned wound tissues revealed the adverse effects of fluocinolone gel and wound healing potential of AC niosome gel. Topical application of AC niosome gel exhibited an anti-inflammatory effect and promoted oral wound closure in rats, possibly due to the improved mucosal permeability and presence of delivery depots of AC in the niosome gel.

Protection of color and chemical degradation of anthocyanin from purple corn (Zea mays L.) by zinc ions and alginate through chemical interaction in a beverage model

Anthocyanin-rich purple corn pericarp water extract (PCW) has the potential to be used as a natural pigment in beverages. However, it has a limited shelf-life in aqueous solutions. The aim was to evaluate the effect of zinc ion (Zn²⁺) and alginate on color and chemical stability of anthocyanins from colored corn (PCW) in a beverage model for 12weeks. PCW was incorporated to Kool-Aid® Invisible™ along with ZnCl₂ and/or alginate. Individual ANC were quantified through HPLC, and color stability was evaluated through the CIE-L*a*b* color system. Complexation between PCW and Zn/alginate was evaluated with fluorescence spectroscopy. The combination of Zn and alginate was the most effective treatment improving the half-life of total ANC concentration (10.4weeks), cyanidin-3-O-glucoside (7.5weeks) and chroma (18.4weeks), compared to only PCW (6.6, 4.5 and 12.7weeks, respectively). Zn and alginate had bimolecular quenching constants (Zn k_q: 3.4×10¹¹ M^-1S^-1 and AA k_q: 1.0×10¹² M^-1S^-1) suggesting that fluorescence quenching was binding rather than collisional. Results suggested that Zn/alginate interacted with ANC from purple corn slowing its chemical degradation.

Evaluating the role of metal ions in the bathochromic and hyperchromic responses of cyanidin derivatives in acidic and alkaline pH

In many food products, colorants derived from natural sources are increasingly popular due to consumer demand. Anthocyanins are one class of versatile and abundant naturally occurring chromophores that produce different hues in nature, especially with metal ions and other copigments assisting. The effects of chelation of metal ions (Mg(2+), Al(3+), Cr(3+), Fe(3+), and Ga(3+)) in factorial excesses to anthocyanin concentration (0-500×) on the spectral characteristics (380-700nm) of cyanidin and acylated cyanidin derivatives were evaluated to better understand the color evolution of anthocyanin-metal chelates in pH 3-8. In all pH, anthocyanins exhibited bathochromic and hyperchromic shifts. Largest bathochromic shifts most often occurred in pH 6; while largest hyperchromic shifts occurred in pH 5. Divalent Mg(2+) showed no observable effect on anthocyanin color while trivalent metal ions caused bathochromic shifts and hue changes. Generally, bathochromic shifts on anthocyanins were greatest with more electron rich metal ions (Fe(3+)≈Ga(3+)>Al(3+)>Cr(3+)).

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.

Anthocyanins and their variation in red wines I. Monomeric anthocyanins and their color expression

Originating in the grapes, monomeric anthocyanins in young red wines contribute the majority of color and the supposed beneficial health effects related to their consumption, and as such they are recognized as one of the most important groups of phenolic metabolites in red wines. In recent years, our increasing knowledge of the chemical complexity of the monomeric anthocyanins, their stability, together with the phenomena such as self-association and copigmentation that can stabilize and enhance their color has helped to explain their color representation in red wine making and aging. A series of new enological practices were developed to improve the anthocyanin extraction, as well as their color expression and maintenance. This paper summarizes the most recent advances in the studies of the monomeric anthocyanins in red wines, emphasizing their origin, occurrence, color enhancing effects, their degradation and the effect of various enological practices on them.

The chemical mechanism for Al3+ complexing with delphinidin: a model for the bluing of hydrangea sepals

The blooms of many hydrangea cultivars can be red or blue, with the color depending on the soil pH. This dependence reflects the availability of Al(3+) to the plant under acidic conditions, as Al(3+) changes the color of the anthocyanin pigment in hydrangea sepals from red to blue. A chemical model, Al(3+) and delphinidin in acidic ethanol, was developed to understand the spectral characteristics and bluing of the hydrangea sepals. Delphinidin as its flavylium cation leads to red solutions in the model system. In the presence of Al(3+), the Al(3+) removes H(+) ions from delphinidin, transforming delphinidin's flavylium cation to its blue quinoidal base anion which complexes with the Al(3+). To further stabilize this complex, a second flavylium cation stacks on top of the complexed quinoidal base anion, creating a bathochromic shift of the cation's spectral signature and accentuating the blue color. This Al(3+)-delphinidin entity forms in adequate concentration for bluing only if there is a sufficient excess of Al(3+), the exact excess being a function of pH and concentration. The role of Al(3+) in bluing is not just to form a primary complex with delphinidin, but also to create a template for the stacking of delphinidin (or possibily co-pigments).