466 N. Terrier et al.
Double linkages, with C2-O-C7 or C2-O-C5 bond in addition to the C4-C6 or C4-
C8 bond, give rise to A-type proanthocyanidins. Depending on the nature of the
anthocyanidin released (see Chapter 9A), several groups of proanthocyanidins can
be distinguished. Grape and wine proanthocyanidins belong to two of these groups,
namely procyanidins and prodelphinidinsthat release cyanidin and delphinidin,
respectively (Fig. 9B.3). Besides, mass signals that may correspond to methoxylated
flavanol dimers have been detected in wine (Cooper and Marshall 2001) but their
identification has not been confirmed. Finally, some of the constitutive units can be
substituted (e.g. galloylated).
Flavanols are present in various vine plant tissues, including wood (Boukharta
et al. 1988), leaves (Bogs et al. 2005; Tesni`ere et al. 2006), stems (Souquet et al.
2000), and fruit. Within the grape berry, they are particularly abundant in seeds and
skins.
Table 9B.1 lists the flavanol dimers and trimers found in grape berries and the
methods used for identification. Procyanidin dimers and trimers were first identified
in seeds but they are also present in skins and stems with different distributions
(Ricardo da Silva et al. 1991a) and trace amounts of B1 through B4 have been
detected in pulp (Bourzeix et al. 1986). However, analysis of grape extracts by acid
degradation and^13 C NMR established the presence of prodelphinidins along with
the expected procyanidins (Czochanska et al. 1980). In agreement with this finding,
R = H : procyanidin
R = OH : prodelphinidin
R1, R2 as in Figure 9B.2
Rí= H, OHO
R2HOOHR
OHOH
R1
O
R2HOOHR’
OHOH
R1+ H+O
R2HOOHR
OHOH
R1
O
R2HOOHR’
OHOH
R1H
++O
R2HOOHR
OHOH
R1O
R2HOOHR’
OHOH
R1+
HO OOHR
OHOH
OH
R = H : cyanidin
R = OH : delphinidin+intermediate carbocation+ NuO
R2HOOHR
OHOH
R1NuoxidationFig. 9B.3Acid-catalysed cleavage of proanthocyanidin interflavanic linkages and subsequent
reactions, namely oxidation to anthocyanidin and nucleophilic (Nu) addition