Pyranoanthocyanins Research Articles

Improvement of Naturally Derived Food Colorant Performance with Efficient Pyranoanthocyanin Formation from Sambucus nigra Anthocyanins Using Caffeic Acid and Heat.

Consumers and regulations encourage the use of naturally derived food colorants. Anthocyanins (ACN), plant pigments, are unstable in foods. In aged red wines, ACN with a free hydroxyl group at C-5 condenses to form pyranoanthocyanins (PACN), which are more stable but form inefficiently. This study attempted to produce PACN efficiently using high cofactor concentration and heat. Elderberry anthocyanins were semi-purified and caffeic acid (CA) was dissolved in 15% ethanol and diluted with a buffer to achieve ACN:CA molar ratios of 1:50, 1:100, 1:150, and 1:200, then incubated at 65 °C for 5 days. The effect of temperature was tested using ACN samples incubated with or without CA at 25 °C, 50 °C, and 75 °C for 7 days. Compositional changes were monitored using uHPLC-PDA-MS/MS. Higher CA levels seemed to protect pigment integrity, with ACN:CA 1:150 ratio showing the highest tinctorial strength after 48 h. PACN content growth was fastest between 24 and 48 h for all ACN:CA ratios and after 120 h, all ACN had degraded or converted to PACN. PACN formed faster at higher temperatures, reaching ~90% PACN in 24 h and ~100% PACN in 48 h at 75 °C. These results suggest that PACN can form efficiently from elderberry ACN and CA if heated to produce more stable pigments.

Pyranoanthocyanin formation rates and yields as affected by cyanidin-3-substitutions and pyruvic or caffeic acids

Anthocyanin-derived pyranoanthocyanins (PACNs) offer potential as food colorants as they may exhibit higher stability than anthocyanins (ACNs). Our objective was to compare PACN formation rate and efficiency from different cyanidin-3-derivatives and cofactors, in order to facilitate PACN production. Four cyanidin-3-derivatives (cyanidin-3-glucoside, cyanidin-3-xylosylglucosylgalactoside, cyanidin-3-malonylglucoside and cyanidin-3-xylosyl(sinapoylglucosyl)galactoside) were incubated with pyruvic or caffeic acids (PA, CA) at 25 °C in the dark for two months. PACN formation was monitored by uHPLC-PDA-MS/MS over time. ACNs incubated with PA produced PACNs with yields increasing steadily over time, reaching 15% after 2 months. PACN formation with CA increased exponentially from the start, reaching 85% during storage. PACNs were efficiently produced from 3 of the 4 ACNs in the presence of CA, with minimal pigment loss. Copigmentation between CA and ACNs may facilitate PACN formation by keeping reactants in close proximity. Anthocyanin glycosylation and acylation affected PACN formation to a lower degree than cofactors.

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.