Demonstration of the occurrence of flavanol–anthocyanin adducts in wine and in model solutions

doi:10.1016/j.aca.2003.11.084

Analytica Chimica Acta

Volume 513, Issue 1, 18 June 2004, Pages 325-332

https://doi.org/10.1016/j.aca.2003.11.084 Get rights and content

Abstract

Flavanol–anthocyanin (F–A⁺) adducts were detected in red wine. A mechanism involving acid-catalysed cleavage of flavanol oligomers followed by nucleophilic addition of the anthocyanin moiety (in its hemiketal form) to the resulting carbocation (F⁺) was postulated. To confirm this mechanism, reactions between malvidin 3-O-glucoside (Mv3glc) and procyanidin dimer epicatechin-(4-8)-epicatechin 3-O-gallate (B2-3′OG) were studied in a model solution system at pH 2. A new pigment with a UV-Vis spectrum similar to that of Mv3glc and a signal at m/z=781 in the positive ion mode was detected and was attributed to Ec–Mv3glc, in agreement with the proposed reaction pathway.

A protocol adapted from the synthesis of procyanidin dimers, in which the terminal flavanol units was replaced with Mv3glc, was tested. Two new pigments were formed with a signal at m/z=781, in the positive ion mode. These ions were attributed to catechin–Mv3glc.

Both adducts obtained by hemisynthesis showed exactly the same fragmentation pattern as that present in wine. In particular, the loss of a 126 amu fragment corresponding to the unsubstituted A-ring of the flavanol unit indicated that all of them were (epi)catechin–Mv3glc adducts.

These results prove that reactions between the carbocations resulting from cleavage of tannin interflavanic bonds and anthocyanins occur in wine.

Section snippets

Materials

Organic solvents (methanol, acetonitrile and ethanol) and phenylmethanethiol were purchased form Merck (Darmstadt, Germany) and Fluka (Buchs, Switzerland), respectively. Taxifolin was purchased from Extrasynthèse (France).

Wine

Two flavanol–anthocyanin (F–A⁺) adducts (retention time 23.8 and 26.9 min), showing a mass signal at m/z=781, were detected in wine (Fig. 2). One of these adducts showed a UV-Vis spectrum similar to that of Mv3glc. Its concentration, expressed in Mv3glc equivalents, was estimated at 2 and 3 mg l⁻¹, respectively, after 4 and 11 months of ageing. The other adduct (TR=26.9 min) was coeluted with Cy3glc; therefore it was not possible to obtain its UV-Vis spectrum.

Their MS/MS fragmentation (Fig. 3) gave

Conclusions

Hemisynthesis of F–A⁺ adducts was achieved by two different processes, yielding respectively cat–Mv3glc and Ec–Mv3glc. Their retention time in LC, their UV-Vis spectrum, and their mass fragmentation patterns are identical to those of pigments detected in wine, indicating that the latter are also F–A⁺ adducts. All of these products (in wine and those obtained by hemisynthesis) are resistant to thiolysis. Besides, we were able to confirm that the formation of these products in wine proceeds

Acknowledgements

The authors thank the Consejo Nacional de Ciencia y Tecnologia (CONACYT, Mexico) for providing a doctoral financement in a cooperation programme with the Société Française d’Exportation des Ressources Educatives (SFERE, France).

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Demonstration of the occurrence of flavanol–anthocyanin adducts in wine and in model solutions

Abstract

Section snippets

Materials

Wine

Conclusions

Acknowledgements

Phytochemistry

Anal. Chim. Acta

Am. J. Enol. Vitic.

J. Sci. Food Agric.

Phytochemistry