Deciphering the color of rosé wines using polyphenol targeted metabolomics

Abstract

The color of rosés wines is extremely diverse  and a key element in their marketing. It is  due to the presence of red anthocyanins extracted from grape skins and pigments formed from them and other wine constituents during wine-making. To explore the link between composition and color, 268 commercial rosé wines were analyzed by ultra-high performance liquid chromatography coupled to triple quadrupole mass spectrometry analysis in the MRM (multiple reaction monitoring) mode [1] and their color characterized using spectrophotometry. The concentration of 125 phenolic compounds was thus determined and related to color parameters using chemometrics [2]. Color intensity is primarily determined by the extent of polyphenol extraction from the grapes. However, different compositions characterize the different color styles. Dark rosé wines contain high concentrations of anthocyanins and flavanols and their color, like that of red wines, is attributable to these molecules and their reaction products. In contrast, major phenolic compounds in light rosé wines are hydroxycinnamic acids and their salmon shade is mostly due to phenylpyranoanthocyanins and carboxypyranoanthocyanin pigments, resulting from reactions of anthocyanins, respectively with these phenolic acids and with pyruvic acid, a yeast metabolite. Redness of intermediate color wines is associated to anthocyanins and carboxypyranoanthocyanins while yellowness seems related to oxidation.The same approach was applied to monitor color and composition changes during fermentation of six rosé musts made from Grenache, Cinsault and Syrah grapes. Hydroxycinnamic acids were the major phenolic compounds in Grenache and Cinsault musts while the Syrah musts showed higher concentrations of anthocyanins and flavanols, indicating that polyphenol extraction is not only related to maceration conditions but also depends on varietal characteristics. These differences resulted in different proportions of derived pigments as observed on the rosé wine collection [2]. Comparison of the spectrophotometric and MRM data indicated that the majority of phenolic compounds in the Cinsault musts were not among the compounds targeted by MRM. Size exclusion chromatography (SEC) analysis of the musts showed different profiles for the three varieties, Cinsault musts containing large proportions of oligomeric compounds likely derived from hydroxycinnamates. These larger molecular weight compounds were no longer detected after fermentation and were partly recovered from the yeast lees. Comparison of the SEC profiles obtained at different wavelengths also suggest that pigments of Cinsault and Grenache are hydroxycinnamic acid derivatives, likely resulting from enzymatic oxidation. Non targeted metabolomics approaches provided further information on these pigments.