Anthocyanins with flavanols

Francia-Aricha, E.M. et al.. New anthocyanin pigments formed after condensation with flavanols, J. Agric. Food Chem., 45, 2262, 1997. 

Fig. 2.103. Structures of all the compounds found in fraction B (a) anthocyanins and acylated anthocyanins direct condensation products between flavanols and anthocyanins (c) dimers resulting from the condensation mediated by acetaldehyde between anthocyanins and flavanols. Reprinted with permission from C. Alcalde-Eon el al. [236].

In a further trial involving a high O2 dosage rate (76 mg/L/month in a pilot trial with 141-L tanks), binding of acetaldehyde with anthocyanins and flavanols was suggested as a reason for low concentrations of... 

Studies in model solution containing an anthocyanin and flavanol oligomers (up to tetramers) at pH 3 carried out at 50 °C demonstrated that temperature is another factor that affects the progress of direct condensation reactions (Malien-Aubert et al. 2002). At acidic pH and high temperature, the anthocyanin is in equilibrium with the colorless chalcone. Although breakage of the flavanol C-C bond occurred under these conditions, the formation of the chalcone impeded the synthesis of F-A products and only A-F adducts were formed (Malien-Aubert et al. 2002). 

Among polyphenolic compounds, two types of flavonoids, the anthocyanins and flavanols (i.e., catechins, proanthocyanidins, condensed tannins), are particularly relevant to the quality of red wines, as they are key compounds for color definition and astringency. Other flavonoids such as flavonols may have some influence on color and bitterness, although they are present in red wines in much lower amounts. Phenolic acids and hydrolysable tannins, released from barrel wood, may also have an influence on wine taste and color, and hydroxycinnamoyl derivatives from grape must are involved in the oxidative browning of white wines together with flavanols. Besides, some of these perceptions may be modified by other sensory characteristics (e.g. sourness, sweetness) related to other wine components (Preys et al. 2006). 

Finally, the relative amounts of anthocyanin-flavanol pigments and anthocyanin-anthocyanin pigments obviously depend on the anthocyanin to flavanol ratio. However, the kinetics of anthocyanin polymerization and flavanol-anthocyanin reactions as well as the quantities of the resulting pigments in wine remain to be established. Consequently, the importance of these processes with respect to other anthocyanin reactions (hydration and subsequent degradation, cycloadditon with yeast metabolites) and the impact of resulting polymeric anthocyanins on wine quality are speculative. 

The reaction mechanism proposed by Timberlake and Bridle (1976), suggests that acetaldehyde, in the form of a carbo-cation, reacts with flavanol (tarmin) at position C-6 or C-8 (Figure 1 (1)). This, via several condensation reactions, gives rise to tannin-ethyl-anthocyanin derivatives (Figure 1 (2)) such as malvidin-3-glucoside-ethyl-(epi)catechin and malvidin-3-(6-/7-coumaroyl)-glucoside-ethyl-(epi)catechin. 

Adducts of malvidin-3-glucoside with vinylcatechin, vinylepicatechin or vinyidiepicatechin (procyanidin B2), reported in model solutions containing malvidin-3-glucoside, acetaldehyde and the respective flavan-3-ol (Francia-Aricha et al., 1997) (Fig. 3, (b)), have also been detected in wine fractions (Mateus et al., 2002a, b Atanasova et al., 2002). In the latter work, the authors showed, via thiolysis, diat both proanthocyanidins and monomeric flavanols are involved in the formation of anthocyanin-vinylflavanol and anthocyanin-ediyl-flavanol pigments induced by acetaldehyde. 

The first phenomenon that should be mentioned is the direct reaction of red anthocyanins, in the form of positive flavylium cations, with flavanol molecules (catechins, procyanidins, etc.). This results in the formation of a colorless complex (flavene) that produces a red pigment when oxidized (Section 6.3.10). This reaction is stimulated by an acid pH (<3.5) and aT/A molar ratio <5. This mechanism causes wine to deepen in color following running-off. 

More recently, a new family of anthocyanin-derived compounds (named portisins) has been detected in Port wine and found to display unusual spectroscopic features, presenting a bluish color at acidic conditions [290] (Fig. 57.18). Studies performed in wine model solution revealed that these pigments are formed from the reaction of carboxypyranoanthocyanins with flavanols mediated by acetaldehyde [290, 291]. 

Three major classes of secondary metabolites are involved in these phytochemicals, which are alkaloids, terpenes, and phenoUcs [16]. There are many phytochemicals recognized with health benefits such as sulfur-containing compounds of garlic family, various terpenoids, and polyphenols (anthocyanins, flavones, flavanols, isoflavones, stilbenes, ellagic acid, etc.). 

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