Direct reaction between anthocyanins

Both flavanol-anthocyanin pigments and colorless A(-0-)F have been detected in wines 11). Mass signals do not allow to distinguish between F-A+ and A+-F derivatives. However, dimeric anthocyanins consisting of one unit under flavylium cation and the other one under hydrated hemiketal form (A+-AOH) were characterized by mass spectrometry in wine like solutions (72). The existence of such structures arising from direct reactions between anthocyanin molecules confirms that they react both as nucleophiles and as electrophiles in wine. 

Similarly, direct reactions between anthocyanins and a flavanol dimer (namely epicatechin-epicatechin 3-gallate) were investigated in model solutions at pH 2 and pH 3.8 (31). Compounds with mass values corresponding to epicatechin-anthocyanin adducts and to anthocyanin-epicatechin-epicatechin 3-gallate, were detected at pH 2 and pH 3.8, respectively. Given the structure of the flavanol precursor, the former can be interpreted as F-A+ arising from cleavage of the flavanol dimer followed by addition of the anthocyanin AOH form onto the epicatechin carbocation whereas the latter is presumably an A+-F species formed by nucleophilic addition of the flavanol dimer onto the flavylium cation. Anthocyanin dimers (A+-AOH) were detected in model solutions at pH... 

The direct reaction between anthocyanins and hydroxycinnamic acids readily explains the formation of anthocyanin-vinylphenol-type adducts in red wines. At the time of writing, this is the only experimentally verified mechanism leading to the development of 4-vinylcatechol and 4-vinylsyringol pigments, as the free vinylphenols have neither been detected in wines nor was it possible to generate these compounds via enzymatic decarboxylation using yeasts commonly applied to red wine fermentation... 

Vitisin B pigments are another minor group of pyranoanthocyanins that show no substituent on the pyranic D-ring (Bakker Timberlake, 1997). These pigments were described to result from the direct reaction between anthocyanins and acetaldehyde. However, there is no consensus on this matter because that reaction is very difficult to occur in model wine conditions and the mechanism involved is not fully understood. Morata et al. (2007) have observed that the addition of acetaldehyde (200 mg L ) to a young red wine (cv. Tempranillo) led to the production of fivefold amounts of vitisin B after 4 weeks with control wines (Morata et al, 2007). 

The probable involvement of xanthylium salts in red wine color change is supported by the fact that their absorption maxima match well with the increase in yellow color around 420 nm observed during ageing of red wine. Thus, Liao et al. (22) demonstrated in model systems that reactions between anthocyanins and flavan-3-ols give rise to orange-yellow (440 nm) pigmented products. Based on the earlier observations of Jurd Somers (24) and Hrazdina Borzell (48 such products have been postulated to be xanthylium salts proceeding from direct anthocyanin-flavanol adducts. 

Direct reactions Reactions between anthocyanins (-h) and tannins (-) (A+ T ). The molecules formed are colorless and turn red when the medium oxidates. They also evolve towards orange due to the appearance of xan-thylium structures. 

The overall organoleptic impression is based on a harmonious balance between these two types of sensations, directly related to the type and concentration of the various molecules, such as anthocyanins, and especially tannins. One of their properties is to react with glycoproteins in saliva (mucine) and proteins in the mouth wall, modifying their condition and lubricant properties. A study of the reaction of the B3 procyanidins with synthetic, proline-rich proteins showed that three dimers were strongly bonded to the protein chains (Simon et al., 2003). According to the type and concentration of tannins, they may produce a soft, balanced impression or, on the contrary, a certain aggressiveness that is either perceptible as... 

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