Abstract
Xanthylium derivatives are yellow to orange pigments with a glyoxylic acid bridge formed by dimerization of flavanols, which are built by oxidative cleavage of tartaric acid. Although their structure and formation under wine-like conditions are well established, knowledge about their color properties and their occurrence and importance in wine is deficient. Xanthylium cations and their corresponding esters were synthesized in a model wine solution and isolated via high-performance countercurrent chromatography (HPCCC) and solid phase extraction (SPE). A Three-Alternative-Forced-Choice (3-AFC) test was applied to reveal the color perception threshold of the isolated compounds in white wine. Their presence and color impact was assessed in 70 different wines (58 white and 12 rosé wines) by UHPLC-DAD-ESI-MSn and the storage stability in wine was determined. The thresholds in young Riesling wine were 0.57 mg/L (cations), 1.04 mg/L (esters) and 0.67 mg/L (1:1 (w/w) mixture), respectively. The low thresholds suggest a possible impact on white wine color, but concentrations in wines were below the threshold. The stability study showed the degradation of the compounds during storage under several conditions. Despite the low perception threshold, xanthylium derivatives might have no direct impact on white wine color, but might play a role in color formation as intermediate products in polymerization and browning.
Highlights
White wine might develop various defects during storage and aging, including the loss of characteristic aromas and undesirable color changes
The study revealed new aspects regarding the impact of xanthylium derivatives on the color of white wine
The sensory evaluation demonstrated the extraordinarily low perception thresholds of the compounds in young Riesling wine. Due to their low concentration in wine, which might be a result of their low stability and high reactivity, non-esterified xanthylium cations and their ethyl esters do not seem to have a direct impact on white wine color
Summary
White wine might develop various defects during storage and aging, including the loss of characteristic aromas and undesirable color changes. The oxidation of polyphenols involving either enzymatic or non-enzymatic reactions is generally considered to be the major browning process. The oxidation leads to the formation of quinones, which take part in polymerization processes. Flavanols like (+)-catechin and (−)-epicatechin are related to color alterations in wines [6,7,8,9]. These alterations are mostly based on the reactions of flavanols with non-phenolic compounds like aldehydes [5,10,11,12]. An oxidized tartaric acid residue, contains an aldehyde group and is formed under oxidative wine storage conditions [13,14]. The presence of metal ions promotes the oxidative reactions [15,16,17]
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