Malvidin-3- glucoside pyruvic

Mechanism of reaction. The adduct of malvidin-3-glucoside with pyruvic acid, also known as vitisin A(Fig. 9A.3h), was firstly detected in fortified red wines (Bakker et al. 1997) and in a grape marc (Fulcrand et al. 1998) and further isolated and characterized by NMR (Bakker et al. 1997 Fulcrand et al. 1998). According to Fulcrand et al. (1998), the reaction between pyruvic acid and grape anthocyanins occurs through a series of steps similar to those previously described for the hydroxyphenyl-pyranoanthocyanins (Sect. 9A.2.4.1 Fig. 9A.3f). Later studies performed by NMR (Mateus et al. 2001b) and mass spectrometry (Asenstorfer et al. 2001 Hayasaka and Asenstorfer 2002) have confirmed the structure proposed by Fulcrand et al. (1998). This mechanism is extended to the condensation reaction between anthocyanins and other enolizable precursors found in wine (Benabdeljalil et al. 2000). 

The anthocyanins adsorbed onto the yeast cell walls were recovered from the lees of each wine in preparation. These were washed with distilled water and then extracted with formic acid methanol, as well as samples of the finished wines were analysed spectrophotometrically to determine colour, and by HPLC-ESI-MS/HPLC-DAD to confirm and evaluate their anthocyanin content. The following anthocyanins were identified in both wines and cell wall adsorbates delphinidin (D), cyanidin (Cy), petunidin (Pt), peonidin (Pn) and malvidin (M), as their 3-glucoside (3G), pyruvic (Py), acetyl glucoside (6Ac), cinnamoyl p-coumaryl (6Cm) and caffeyl (6CaQ) glucoside derivates. 

Reactions taking place in a model solution containing malvidin 3-0-glucoside, (-)-epicatechin and acetaldehyde was explored by HPLC/DAD and HPLC/ESI-MS analysis 29). Acetaldehyde is a product of yeast metabolism but may also result from ethanol oxidation or from decarboxylation of pyruvic acid during fermentation of grapes (43). 

Fraction A obtained from the elution of a two-year-old Port wine through Toyopearl gel column with 20% aqueous ethanol was found to be mainly comprised of eight pigments which structural identities were ascertained by LC-MS (Table 1). The number attributed to each compoimd in Table 1 corresponds to the elution order by HPLC in the condition described herein. The three major pigments detected were isolated by semi-preparative HPLC and their structures were fully elucidated by mass spectrometry and NMR. Based on their UV-visible characteristics and structural analysis, these pigments were found to correspond to the pyruvic acid adducts of malvidin 3-glucoside (3A), malvidin... 

Mv = malvidin Pt = petunidin Pn = paeonidin py = pyruvic acid glue = glucoside... 

Figure 7. Evolution of the level of malvidin 3-glucoside, malvidin 3-(acetyl)glucoside and malvidin 3-(coumaroyl)glucoside, and their pyruvic acid derivatives in fermented must during the first 200 days after fortification with wine spirit (13). (Reproduced with permission from reference 13. Copyright 2001American Chemical Society.)...

Fig. 6.29. Structure of three pigments produced by adding (a) vinyl-phenol, pyruvic acid (b, R = COOH) and ethanol (b, R = H) to malvidin-3-glucoside (R = glncose) or malvidin-3-p-conmarylglncoside (R = glncose + p-coumaric acid) (Cameria do Santos et al., 1996)...

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