448 M. Monagas and B. Bartolom ́e
(Bakker et al. 1993; Garc ́ıa-Viguera et al. 1994; Escribano-Bail ́on et al. 1996; Es-
Safi et al. 1999). Studies in model solutions using HPLC/ESI-MS have revealed
the detection of trimeric and tetrameric pigments linked by an ethyl bridge being
composed of various flavanol units but no more than two anthocyanin moeties, since
only one of the A-ring positions of the latter (C-8) was believed to be involved in
the polymerization process, while two positions (C-6 and C-8) could be used in the
case of the flavanol (Es-Safi et al. 1999). Contrarily to these findings, Atanasova
et al. (2002b) demonstrated that the C-6 position of anthocyanins was also reac-
tive, although to a lesser extent than the C-8 position since the polymerization of
anthocyanins in the absence of flavanols was also induced by acetaldehyde, giving
rise to dimers, trimers and tetramers composed of ethyl-linked anthocyanins units
in different structural forms (flavylium, hemiketal and quinoidal) (Fig. 9A.3e). Both
C-6 and C-8 positions seemed reactive in the hemiketal form whereas in the case
of the flavylium form only C-8 position was reactive and therefore ceased the poly-
merization process.
Model solutions containing malvidin-3-glucoside and flavanols (monomers and
dimers) in the presence of other aldehydes, such as isovaleraldehyde, benzalde-
hyde, propionaldehyde, isobutyraldehyde, formaldehyde, 2-methylbutyraldehyde,
vanillin, furfural and hydroxymethylfurfural also resulted in anthocyanin-aryl/alkyl-
flavanol pigments through the same mechanism described above for acetaldehyde
(Pissarra et al. 2003; Sousa et al. 2007). The NMR characterization of malvidin-
3-glucoside-catechin aryl/alkyl-linked pigments have recently been described (Pis-
sarra et al. 2004, 2005a; Sousa et al. 2007). Similar pigments have also been reported
in model solutions containing furfural and hydroxymethylfurfural as aldehydes
(Es-Safi et al. 2000).
Colored adducts in which the anthocyanin and the flavanol are linked by a
carboxy-methine bridge, have also been identified, in addition to colorless carboxy-
methine-linked catechin dimers (Chapter 9B), in model solutions containing (+)-
catechin, malvidin-3-glucoside and glyoxylic acid (Es-Safi et al. 2003).
Evidence in wine. The occurrence of ethyl-linked condensation products in
wine is well documented. The adducts malvidin-3-glucoside-(CH-CH 3 )-catechin
(Revilla et al. 1999; Vivar-Quintana et al. 1999, 2002; Atanasova et al. 2002a;
Heier et al. 2002; Mateus et al. 2002a; Alcalde-Eon et al. 2004, 2006; Mon-
agas et al. 2003; Wang et al. 2003a; Salas et al. 2005a; Boido et al. 2006),
malvidin-3-(6-p-coumaroyl)-glucoside-(CH-CH 3 )-catechin (Mateus et al. 2003a;
Alcalde-Eon et al. 2004, 2006; Monagas et al. 2003; Boido et al. 2006) and
malvidin-3-glucoside[AOH]-(CH-CH 3 )-malvidin-3-glucoside[A+] (Atanasova et al.
2002b; Salas et al. 2005a) were first confirmed both in wine and in wine fractions
by ESI-MS. Ethyl-(epi)catechin adducts of the glucosides and acylated-glucosides
of the entire series of anthocyanidin-3-glucosides (cyanidin, delphinidin, peoni-
din, petunidin and malvidin) as well as a ethyl-procyanidin dimer of malvidin-3-
glucoside have been later described in red wines (Atanasova et al. 2002a; Heier
et al. 2002; Alcalde-Eon et al. 2004, 2006; Salas et al. 2005a). The occurrence of
ethyl-linked adducts of (epi)gallocatechinwith the acetyl-glucoside of malvidin as
well as with the different anthocyanidin-glucosides has also been reported in wine