Abstract
A new group of blue anthocyanin-derived pigments was recently found to occur in ageing Port wines and were named as portisins. The UV–vis spectrum of these pigments was found to have a λ max around 570 nm that is bathochromically shifted from that of original anthocyanins, exhibiting a more bluish hue in acidic solution. Three portisins were synthesised through the reaction between malvidin 3- O-glucoside, malvidin 3- O-coumaroylglucoside and cyanidin 3 -O-glucoside-pyruvic acid adducts and catechin in presence of acetaldehyde. These portisins were structurally and chromatically characterized (pH, SO 2 stability assays and determination of the molar extinction coefficient) and showed to have high resistance to the attack of water or bisulfite, specially when compared to malvidin-3-glucoside. This portisin resistance to discoloration may be explained by a higher protection of the chromophore group against the water or bisulfite nucleophilic attack that gives rise to the hemiacetal form, which is usually colourless. Portisins also showed to have a very high colorant capacity as they displayed a higher molar extinction coefficient than anthocyanins and the respective pyruvic acid adducts. These chromatic characteristics may help better understand the contribution of these anthocyanin-derived pigments to the overall wine colour.
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