548 C. Santos-Buelga and V. de Freitas
alcoholic fermentation, in which the formation of ethyl-linked polymers can be
expected to contribute to the anthocyanin losses by precipitation. In further stages of
wine life some amounts of acetaldehyde canalso be produced during malolactic fer-
mentation as well as from ethanol by coupled oxidation of polyphenols (Wildenradt
and Singleton 1974). In these stages lessacetaldehyde is available and the condi-
tions are less favorable for the formation of condensed pigments, so that no great
amounts of them are expected to be formed. Nevertheless, although these pigments
are not expected to contribute directly to the color of red wines, they could play an
important indirect role on the color changes due to their contribution to anthocyanin
losses by precipitation in early stages of winemaking and further involvement in the
formation of flavan-pyranoanthocyanins.
In addition to acetaldehyde, other aldehydes can also exist in wines (e.g., pro-
pionaldehyde, isovaleraldehyde, isobutyraldehyde, benzaldehyde or vanillinalde-
hyde), released from the wood of the barrels used in the aging process or as a result
of the addition of wine spirit in the case of fortified wines like Port wine. These
compounds can also be involved in the formation of alkyl/aryl adducts between
anthocyanins and flavanols similar to those induced by acetaldehyde
(Pissarra et al. 2003, 2004, 2005; Sousa et al. 2007). The UV-visible spectra of
all these pigments display a bathochromic shift in theirmaxin relation to that of the
parent anthocyanins, resulting in a “blueing” effect of different magnitude depend-
ing on the aldehyde. Thus, the bathochromic shift seems to be higher for branched
aldehydes, like benzaldehyde or isobutyraldehyde, than for non-branched ones (e.g.,
acetaldehyde, isovaleraldehyde or propionaldehyde). The steric hindrance promoted
by the more branched substituents probably favors a more -electron conjugated
conformation leading to a greater displacement of themaxin the visible region
(Pissarra et al. 2003). This pigment family could play a significant role in the color
of Port wines, especially during the initial stages of aging. The content and profile
of aldehydes in the wine spirit added would determine the type of aryl/alkyl adducts
formed, with different chromatic characteristics, thus having an influence on color
definition (Pissarra et al. 2004). The possibility of some aldehydes extracted during
oak aging being involved in the formation of pigments cannot be discarded either.
Quite recently a pigment from the condensation between malvidin 3-glucoside and
catechin mediated by vanillin aldehyde has been characterised (Sousa et al. 2007).
This aldehyde is reported to occur in oak aged wines as released from wood
(Escalona et al. 2002).
9D.2.3.4 Anthocyanin-flavanol Condensed Pigments
The formation in red wines of anthocyanin-flavanol adducts had been early hypothe-
sised by Jurd (1967, 1969). Two types of adducts seem possible, (1) F-A derivatives
resulting from the nucleophilic addition of the hemiketal form of an anthocyanin
through their C-8 or C-6 positions at C-4 of a carbocation resulting from the cleav-
age of a procyanidin, and (2) A-F derivatives from the electrophilic substitution
of the anthocyanin flavylium form (C-4) by a flavanol (C-8 or C-6). The former