Identification, content and distribution of anthocyanins and low molecular weight anthocyanin-derived pigments in Spanish commercial red wines.

The content and distribution of low molecular weight red wine pigments (anthocyanins, flavanol-anthocyanins adducts and pyranoanthocyanins) has been analysed in 283 wine samples. A total of 90 red wine pigments were identified and up to 68 of them quantified in most of the wine samples. The content of the different pigments classes accounted for wide ranges of values, because of the diversity of the commercial wines regarding grape cultivar and age. Garnacha young wines were prone to contain higher hydroxyphenyl-pyranoanthocyanin concentrations. The aging had an effect of making uniform the concentrations and molar percentages of every type of pigments, and only slight differences among wine groups were found for B-type vitisins (highest values for Syrah wines) and 10-hydroxyphenyl-pyranoanthocyanins (highest values for Merlot wines). Among Tempranillo wines, the ethylidene-bridged flavanol-anthocyanin adducts were the most affected by disappearance during aging, whereas hydroxyphenyl-pyranoanthocyanins increased their contribution in most of those aged wines.

Synthesis, isolation, structure elucidation, and color properties of 10-acetyl-pyranoanthocyanins.

Grape anthocyanins reacted with diacetyl, a secondary metabolite of microorganisms involved in winemaking, to form 10-acetyl-pyranoanthocyanins, a type of anthocyanin-derived pigment similar to other vitisin-type pyranoanthocyanins found in red wines. The structures of 10-acetyl-pyranomalvidin-3-ß-O-glucoside and 10-acetyl-pyranopeonidin-3-ß-O-glucoside were confirmed by spectroscopic methods (UV-vis, MS/MS, and NMR) after their synthesis and isolation. In contrast to other vitisin-type pyranoanthocyanins, the newly described 10-acetyl-pyranoanthocyanins exhibited differentiated color-related properties. They showed an important tendency to occur as colorless hemiacetals at C-10 under wine pH conditions, while co-occurrence of flavylium cation and quinoidal base yielded a broad visible absorbance band around 510-520 nm. Moreover, they easily reacted with bisulfite in acidic aqueous solution (pH 2.0), but the expected bleaching was not observed. Bisulfite bonded to the carbonyl of 10-acetyl substituent instead of the expected C-10 position of the pyranoanthocyanin core, thus giving rise to a red pigment hypsochromically shifted toward orangish nuances (maximum absorbances at 487-491 nm).

HPLC-DAD-ESI-MS/MS characterization of pyranoanthocyanins pigments formed in model wine.

Formation of wine pyranoanthocyanins in model wine was monitored by HPLC-DAD-ESI-MS/MS, using red grape skin extracts and wine fermentation metabolites (acetaldehyde, pyruvic and acetoacetic acids, and diacetyl) and also hydroxycinnamic acids (p-coumaric, caffeic, ferulic, and sinapic acids). Pyruvic acid and acetaldehyde reacted fast, the first reaching high product yield and the second inducing mainly pigment polymerization. In contrast, acetoacetic acid and diacetyl reacted slowly with poor product yields. Hydroxycinnamic acids progressively reacted without apparent formation of polymeric pigments, the reaction rate and yield increasing as the number of hydroxy/methoxy groups did. Substituent at C-10 strongly affected the visible maximum absorbance wavelength, whereas B-ring substitution pattern or sugar acylation exerted little effect. The 10-methylpyranoanthocyanins formed from acetoacetic acid were also found as side products in the formation of 10-carboxypyranoanthocyanins. Finally, we report for the first time on UV-vis and MS spectral data of 10-acetylpyranoanthocyanins formed from diacetyl, and their occurrence in commercial red wines is suggested.