Structural diversity of anthocyanin-derived pigments in port wines

One year-old Port wine made from grapes of the Douro Valley was analysed for its anthocyanin-like pigment composition. The samples were purified by low pressure Toyopearl gel column chromatography, yielding two fractions. Fraction A was eluted with water/methanol 20% (v/v) and fraction B was eluted with methanol 100% (v/v). Structural elucidation of the pigments detected was attempted using LC/DAD-MS. Several anthocyanin-derived pigments were detected. Fraction A was mainly comprised of malvidin 3-glucoside and its pyruvic acid adducts. Additionally, other minor anthocyanin-pyruvic acid derivatives were also detected. Fraction B was shown to contain three groups of anthocyanin-derived pigments: (1) pigments in which anthocyanins are linked to a catechin unit via an ethyl linkage; (2) pigments in which anthocyanins are linked to a catechin unit or a procyanidin dimer via a vinyl linkage; (3) pigments in which anthocyanins are linked to a 4-vinylphenol group. The UV-visible spectral characteristics of most of these pigments show that they are contributing to the changing colour of Port wine from purple-red to a more orange-red hue.