9D Influence of Phenolics on Wine Organoleptic Properties 535
carried out in our laboratory with anthocyanins in a wine concentration range (50–
600 mg/L) concluded that self-association could be responsible between 8% and
up to 60% of the absorbance increase at 520 nm observed in wine-like solutions,
depending on the type and concentration of the anthocyanins involved (Gonz ́alez-
Manzano et al. 2008b). Support to the existence of self-association in wines was
also be provided by the observations of di Stefano et al. (2005) that found that
young red wines deprived of the classical cofactors continued to deviate from the
Beer’s law. This situation should change in the presence of copigments. In model
assays carried out with wine anthocyanins in the presence of different mixtures of
flavanols, it was observed that self-association still contributes in some extent to the
increase the absorbance in the solutions (Gonzalez-Manzano 2007). Nevertheless,
it is necessary to take into account that flavanols are poor anthocyanin copigments
and that in wines more efficient cofactors also exist, such as flavonols or hydrox-
ycinnamic acids, which could favour intermolecular copigmentation with regard to
self-association. Further studies would be thus necessary to assess the actual effect
of self-association in the color of red wines.
Another process that influences the color of the anthocyanins and that is some-
times included as copigmentation is metal complexation. Metal cations like iron,
aluminium or magnesium can form complexes with anthocyanins that have free
o-hydroxyl groups in ring B. The metal selectively links with the quinonoidal forms
of the anthocyanin, modifying anthocyanin equilibria towards these structures and
provoking a change of the color to more violet hues (Dangles et al. 1994). Nev-
ertheless, metal complexation should not play a relevant role in wine color since
malvidin 3-glucoside, the majority anthocyanin in red wines, cannot form this type
of complex; in addition, low levels in metals should exist in wine to avoidcasses
(Riber ́eau-Gay ́on et al. 2000). At present, there is no evidence that the levels of
metal cations in wine are at all correlated with color expression (Boulton 2001).
9D.2.2.2 Type of Copigments
Different types of compounds have been evaluated as potential anthocyanin copig-
ments, including alkaloids, amino acids, nucleotides, carbohydrates or phenolic
compounds (Asen et al. 1972; Brouillard et al. 1991; Mistry et al. 1991). Many
of these compounds can be found in wine, although some of them should not be
expected to have a relevant contribution to the copigmentation phenomenon in red
wine, due to their low levels or their comparatively poor ability to act as antho-
cyanin copigments. Thus, sugars (i.e., fructose and glucose) have been found to
produce no change or slightly increase the absorbance of anthocyanin solutions
even at high concentrations (50% in water) (Lewis et al. 1995). Similar observations
were made for polysaccharides like pectins (Lewis et al. 1995) or mannoproteins.
Guadalupe et al. (2007) observed that wines elaborated with addition of commercial
mannoproteins or inoculation of must with yeast over-expressing mannoproteins
had lower values of color intensity than controls at the end of fermentation and that
these differences increased during malolactic fermentation and aging; this observa-
tion would question the usual belief thatpolysaccharides may protect wine color.