Malvidin-3-glucoside-8-ethyl-catechin

The presence of the dimers malvidin-3-glucoside-ethyl-catechin (m/z 809, [M]" and malvidin-3-(6-p-coumaroyl)-glucoside-ethyl-catechin (m/z 955, [M] ) has been confirmed in wine and wine fractions with the help of ESI-MS. Other pigments (see below), in which the anthocyanin is joined to a flavanol via a vinyl fragment, can also be produced in the presence of acetaldehyde. 

The reaction mechanism proposed by Timberlake and Bridle (1976), suggests that acetaldehyde, in the form of a carbo-cation, reacts with flavanol (tarmin) at position C-6 or C-8 (Figure 1 (1)). This, via several condensation reactions, gives rise to tannin-ethyl-anthocyanin derivatives (Figure 1 (2)) such as malvidin-3-glucoside-ethyl-(epi)catechin and malvidin-3-(6-/7-coumaroyl)-glucoside-ethyl-(epi)catechin. 

Figure 4 examples of products obtained by aldehyde-induced reactions ethyl-linked catechin dimer (1), ethyl-linked catechin-malvidin-3-glucoside adduct (2), ethanoic acid-linked catechin-dimer (3)... 

Petunidin-3-(6-0-p-coumaroylglucoside) Malvidin-3-0-glucoside-4-vinyl-catechin Malvidin-3-(6-0-p-coumaroylglucoside)-8-ethyl-(epi )catechin... 

The red-violet color of malvidin-3-glucoside - (+)-catechin condensation products (via acetaldehyde), which some authors have suggested is an intramolecular copigmentation effect (Escribano-Baildn et al., 1996), is more pH-stable and SO2 discoloration-stable than are free anthocyanins (Escribano-Bail6n et al., 2001). However, these adducts are also less stable in aqueous solution because of the breakage of the ethyl bridge that joins the anthocyanin to the catechin (Escribano-Bail6n et al., 2001). 

---