9D Influence of Phenolics on Wine Organoleptic Properties 543
not satisfactorily explained and even in the case of the identified pigment families
the actual contribution of each of them is not yet well established. Thus, further stud-
ies are required to elucidate the actual contribution of each of them to the definition
of the color of red wines.
9D.2.3.2 Pyranoanthocyanins
As previously revised in this same book, this type of pigments contains an addi-
tional pyran ring attached to positions 4 and 5 of the anthocyanin structure. Three
families of pyranoanthocyanins have been described according to the nature of the
substituents on that pyran ring as influenced by the type of precursors involved in
their formation, either products of the microbial metabolism (e.g., pyruvic acid,
acetaldehyde or vinylphenols), compounds extractedfrom grape or released by
the barrels (e.g., hydroxycinnamic acids) or products derived from chemical reac-
tions taking place in wine (e.g., vinyl-flavanols). Depending on the type of pre-
cursors, pyranoanthocyanins can be formed at different stages of the wine life.
Those resulting from products of the metabolism of yeasts, like the so-called
vitisins A and B, first described by Bakker and coworkers (Bakker et al. 1997;
Bakker and Timberlake, 1997), can be formed in early events of winemaking (Asen-
storfer et al. 2003). However, at that stagehigh anthocyanin concentrations still
exist in wine and, therefore, pyranoanthocyanins are not expected to have a rele-
vant impact in wine color. Hydroxyphenyl-pyranoanthocyanins, whose formation
involve hydroxycinnamic acids (Schwarz and Winterhalter 2004) or vinylphenols
(Fulcrand et al. 1996), and flavan-pyranoanthocyanins, derived from vinyl-flavanols
released from the cleavage of ethyl-linked oligomers (Francia-Aricha et al. 1997;
Mateus et al. 2002b), would appear in further stages of the wine life (Schwarz
and Winterhalter 2004) and could have a determining influence in the color of
aged red wines. The absorption spectra of all these pigments in the visible region
is characterised by a maximum wavelength hypsochromically shifted (20–40 nm)
with regard to that of the anthocyanins (Fig. 9D.5). Pyranoanthocyanins are more
resistant against sulfites and pH-induced color loss (Bakker et al. 1997). This is
explained by the substitution at position C4 of the anthocyanin that confer them
protection against the nucleophilic attack of SO 2 and water. Although pyranoan-
thocyanins could likely undergo similar reactions at C2, the presence of the addi-
tional aromatic pyran ring (as well as other conjugated aromatic rings in the case of
hydroxyphenyl and vinyl-flavanol derivatives) contribute to the delocalisation of
the positive charge and help to stabilize the colored flavylium cation (Hakans-
son et al. 2003). This is illustrated in Fig. 9D.6, where the influence of the pH value
and the addition of SO 2 on the spectra of cyanidin 3-glucoside and a pyranoantho-
cyanin is shown.
The color of pyranoanthocyanins is more orange than that of anthocyanins,
which leads one to suppose that they can contribute to the red tile and orange
hues characteristics of aged wines. Similar molar extinction coefficients values for
malvidin 3-glucoside (1.6× 104 L/mol/cm) and its corresponding carboxypyra-
noanthocyanin (i.e., vitisin A; 1.3× 104 L/mol/cm) were determined by Mateus and