9A Anthocyanins and Anthocyanin-Derived Compounds 449
(Alcalde-Eon et al. 2004, 2006; Boido et al. 2006). Finally, evidence of (epi)catn-
ethyl-anthocyanins adducts (n≥2) has been recently obtained by thiolysis of HSCC
wine fractions (Salas et al. 2005a). However, to date the occurrence of condensation
products between anthocyanins and aldehydes other than acetaldehyde has not been
confirmed in wines.
Factors affecting the reaction.The anthocyanin-flavanolacetaldehyde-mediated
condensation reaction follows a first-order kinetic in relation to the disappearance of
the anthocyanin but does not follow any simple reaction order regarding the appear-
ance of polymers, probable due to their eventual precipitation (Baranowski and
Nagel 1983). The reaction rate is higher in the presence of oxygen and at acidic pH,
since the formation of acetaldehyde and itsprotonated form are favoured under these
conditions, respectively (Garc ́ıa-Viguera et al. 1994; Rivas-Gonzalo et al. 1995;
Atanasova et al. 2002a). Temperature also affects the evolution and accumulation
of the new formed pigments. At low temperatures (15◦C), the polymers are slowly
accumulated and are more stable in relation to their degradation and precipitation
(Baranowski and Nagel 1983; Rivas-Gonzalo et al. 1995).
The rate of the reaction between procyanidin B2 and different antocyanidin-
3-glucosides in the presence of acetaldehyde, increases in the following order:
malvidin-3-glucoside<cyanidin-3-glucoside<peonidin-3-glucoside (Dallas et al.
1996b). On the other hand, the degree of polymerization of the flavanol is also
important for the reaction rate. In the presence of acetaldehyde, the reaction with
malvidin-3-glucoside increases in the following order: (+)-catechin<(–)-epicatechin
<procyanidin B3<procyanidin B2-3’-O-gallate<procyanidin B2<procyanidin B1
<procyanidin C1 (Dallas et al. 1996a).
9A.2.4 Reactions Leading to Pyranoanthocyanin Formation
9A.2.4.1 Anthocyanin-Vinylphenol/Anthocyanin-Hydroxycinnamic Acid
Condensation Reactions: Hydroxyphenyl-Pyranoanthocyanins
Precursors.Both hydroxycinnamic acids and 4-vinylphenols can lead to the for-
mation of hydroxyphenyl-pyranoanthocyanins. The main hydroxycinnamic acids
present in wines arep-coumaric, caffeic, ferulic and sinapic acids. 4-Vinylphenol
and 4-vinylguaiacol are volatile phenols associated with off flavors in wine (Eti ́evant
- and arise from the decarboxylation ofp-coumaric and ferulic acid, respec-
tively, via the yeast cinnamate decarboxylase (CD) (Chatonnet et al. 1993).
Mechanism of reaction.The mechanism of the reaction between anthocyanins
and 4-vinylphenols was first proposed by Fulcrand et al. (1996). Hydroxyphenyl-
pyranoanthocyanins result from the cycloaddition of the ethylenic bond of the 4-
vinylphenol molecule at positions C-4 and C-5 of the anthocyanin followed by
an oxidation process, resulting in a pyrane ring (Fulcrand et al. 1996) for which
this type of compound receives the name ofpyranoanthocyanins (Fig. 9A.3f). The
vinylphenol addition at C-4 protects the anthocyanin of being hydrated.
Schwarz et al. (2003b) proposed a different mechanism for the form-
ation of hydroxyphenyl-pyranoanthocyanins in red wines, including the free