Flavanol-anthocyanin adducts

Salas, E. et ah. Demonstration of the occurrence of flavanol-anthocyanin adducts in wine and in model solutions. Anal. Chim. Acta, 513, 325, 2004. 

Salas, E. et al.. Isolation of flavanol-anthocyanin adducts by countercurrent chromatography, J. Chrom. ScL, 43, 488, 2005. 

The separation and identification of flavanol-anthocyanin adducts in wine and in model solutions were performed with RP-HPLC coupled to DAD or ESI-MS. The investigation was motivated by the assumption that the formation of flavanol-anthocyanin complexes may influence the organoleptic characteristics of wine during ageing. Measurements were carried out in an ODS column (250 X 2 mm i.d. particle size 5 pm) at 30°C. The flow rate was 0.25 ml/min. Solvent A was water-formic acid (95 5), solvent B consisted of ACN— solvent A (80 20, v/v). The Gradient elution began with 3 per cent B for 7min to 20 per... 

FIGURE 5.7 Structures of anthocyanin-flavanol and flavanol-anthocyanin adducts. 

Finally, reactions of flavonoid and nonflavonoid precursors are affected by other parameters like pH, temperature, presence of metal catalysts, etc. In particular, pH values determine the relative nucleophilic and electrophilic characters of both anthocyanins and flavanols. Studies performed in model solutions showed that acetaldehyde-mediated condensation is faster at pH 2.2 than at pH 4 and limited by the rate of aldehyde protonation. The formation of flavanol-anthocyanin adducts was also limited by the rate of proanthocyanidin cleavage, which was shown to take place at pH 3.2, but not at pH 3.8. Nucleophilic addition of anthocyanins was faster at pH 3.4 than at pH 1.7, but still took place at pH values much lower than those encountered in wine, as evidenced by the formation of anthocyanin-caffeoyltartaric acid adducts, methylmethine anthocyanin-flavanol adducts,and flavanol-anthocyanin adducts. The formation of pyranoanthocyanins requiring the flavylium cation was faster under more acidic conditions, as expected, but took place in the whole wine pH range. Thus, the availability of either the flavylium or the hemiketal form does not seem to limit any of the anthocyanin reactions. 

The flavylium ions of direct flavanol-anthocyanin adducts (i.e., A" -F and F-A" ") and anthocyanin dimers (A+-AOH) have the same UV-visible spectra as anthocyanins. Species in which the anthocyanin is substituted in the 4-position (A" -F, A" -AOH) are expected to be resistant to sulfite bleaching and hydration whereas F-A is as susceptible to water addition as their anthocyanin precursor. ... 

Salas, E., Eulcrand, H., Poncet-LeGrand, C., Meudec, E., Kohler, N., Winterhalter, R, Cheynier, V. (2005b). Isolation of flavanol-anthocyanin adducts by countercurrent chromatography. J. Chromatog. Sci. 43, 488-493. 

Monitoring of the reaction also indicated that ethyl-linked flavanol-anthocyanin adducts are more stable than ethyl-linked flavanol oligomers. 

In red wines, flavanols may also react directly with anthocyanins, leading to the formation of anthocyanin-flavanol and flavanol-anthocyanin adducts [283-285], The condensation may also occur mediated by aldehydes, such as acetaldehyde, furfural, HMF, benzaldehyde, and others, leading to the formation of alkyl-methine bridged adducts. These latter display the same /Lav in the visible region at around 540 nm, which is bathochromically shifted when compared with the original anthocyanin (/Lax 525 nm) [279, 280, 286-289], thereby contributing to the color change in red wine. 

Salas E, Poncet-Legrand C, Fulcrand H, Meudec E, Cheynier V (2004) Structure and properties of a flavanol-anthocyanin adduct. In 228th National meeting of the American-Chemical-Society, Philadelphia, 22-26 Aug 2004. American-Chemical-Society, Philadelphia, pp 112-CELL... 

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