9A Anthocyanins and Anthocyanin-Derived Compounds 441
varietal characterization (Roggero et al. 1986b; Ortega Meder et al. 1994; Baldi
et al. 1993; Roggero et al. 1988; Mattivi et al. 2006). These relationships are related
to the enzymatic activities of flavonoid-3’-hydroxylase ando-dihydroxyphenol-
O-methyltransferase (Ortega Meder et al. 1994; Roggero et al. 1986b). Another
widely used variety classification is based on the presence and relative abundance of
anthocyanins acylated with acetic andp-coumaric acids (Ortega Meder et al. 1994;
Marx et al. 2000; N ́u ̃nez et al. 2004), which is related to the grape’s acetyl and
cinnamoyl transferase activities (Roggero et al. 1988). The grape variety deter-
mines the production of each of these enzymes since they are direct expressions
of the genome.
The wine anthocyanin composition depends on the original grape profile but also
on the extraction and winemaking techniques employed. Maceration, which allows
the diffusion of anthocyanins and other phenolic compounds from the solid part of
the grape to the must, can occur before fermentation, as in the case of thermovinifi-
cation, or during the alcoholic fermentation using crushed (traditional vinification)
or whole (carbonic maceration) grapes. After reaching a maximum level after a
few days of fermentation, the concentration of anthocyanins decreases as a con-
sequence of their adsorption on yeast cell walls (Sect. 9A.4), precipitation in the
form of colloidal material together with tartaric salts and elimination during filtra-
tion and fining. Hydrolysis reactions (i.e., enzymatic deglycosilation; Sect. 9A.3), as
well as condensation reactions with otherphenols (Sect. 9A.2) during winemaking
also modify the anthocyanin composition of wines. Despite all these changes, the
wine anthocyanin profile has also been used as chemotaxonomy criteria to establish
differences between grape varieties, vineyard localization and yield, vintages and
winemaking techniques (Eti ́evant and Schilich 1988; Gonz ́alez-San Jos ́e et al. 1990;
Almela, et al. 1996; Arozarena et al. 2000).
Anthocyanin reactivity. Four different anthocyanin structures exist in equilibrium
in acidic or neutral medium: the flavylium cation (red), the quinoidal base (blue), the
hemiketal or carbinol pseudo-base (colorless) and the chalcone (colorless) (Brouil-
lard 1982) (Fig. 9A.2). At wine pH (3.5), the equilibrium is largely displaced
towards to the colorless hemiketal form. Depending on pH, anthocyanins can act as
electrophiles in the flavylium form throughtheir C-2 and C-4 positions (C-ring), or
as nucleophiles in the hemiketal form through their C-6 and C-8 positions (A-ring).
However, the low content of flavylium cations present at wine pH does not seem to
limit the progress of chemical reactions requiring this specie, as it will be discussed
later (Sect. 9A.2).
Anthocyanin bleaching in wine can occur by the nucleophilic addition of either
water at C-2 (Cheminat and Brouillard 1986)or bisulfite (an antifungal and antiox-
idant normally used during winemaking) at the C-4 position of the flavylium cation
(Berke et al. 1998) (Fig. 9A.2). However, wine anthocyanins and thus color, can
be stabilized either by copigmentation or through their conversion into more sta-
ble pigments by different condensation reactions that occur during the winemaking
process. Copigmentation consists of the hydrophobic interaction of the polarizable
planar nuclei of the colored form of anthocyanins (flavylium cation and quinoidal
base) with another molecule or copigment (intermolecular copigmentation) or with