To investigate antioxidant capacity in seeds and skins during grape maturation and its relationship with anthocyanin and proanthocyanidin content, two Portuguese red grape varieties, Touriga Nacional and Tinta Roriz (Vitis vinifera L.) were studied. Two analytical methods were used for antioxidant capacity analysis: the DPPH and ABTS methods. Proanthocyanidins from seeds and skins were separated into monomers, oligomers and polymers, while 13 individual anthocyanins from the skins were also evaluated by HPLC. For both grape varieties studied, antioxidant capacity from the skins and seeds was characterised during grape maturation by a general decrease, mainly in the first weeks after véraison, followed by stabilisation and a slight increase in the values in the last three weeks of ripening. A similar tendency was observed for the amount of all the different proanthocyanidin fractions quantified. Our results also showed that seeds are an important source of proanthocyanidins with respect to the grape berry skins. Seeds were also the grape berry fraction with the highest antioxidant capacity when compared to the antioxidant capacity content of the skins. For the 13 individual monomeric anthocyanins quantified during grape maturation, evolution was generally characterised by a continuous increase in the values. However, for some of the individual anthocyanins, the continuous increase was followed by stabilisation or a decrease in the values in the last weeks of ripening. Finally, there was a positive relationship between the different proanthocyanidin fractions and antioxidant capacity of both grape varieties studied; while a negative relationship during grape maturation was obtained for individual anthocyanins.
INTRODUCTIONGrapes have long been appreciated for their rich content of phenolic compounds such as gallic acid, catechin, anthocyanins and resveratrol, and a wide variety of procyanidins (Cheynier & Rigaud, 1986;Ricardo-da-Silva et al., 1992a;Jordão et al., 1998aJordão et al., , 1998bKennedy et al., 2000aKennedy et al., , 2001 Jordão et al., 2001a,b;Sun et al., 2001). Phenolic compounds can be classified into two groups: flavonoids and nonflavonoids. The main C 6 -C 3 -C 6 flavonoids in wine include conjugates of the flavonols, quercetin and myricetin; flavin-3-ols (+)-catechin and (-)-epicatechin; and anthocyanins. The nonflavonoids incorporate the C 6 -C 1 hydroxy-benzoic acids, and gallic and ellagic acids; the C 6 -C 3 hydroxycinnamates caffeic, caftaric and p-coumaric acids, and the C 6 -C 2 -C 6 stilbenes trans-resveratrol, cis-resveratrol, and trans-resveratrol glucoside.In the grape berry, flavonoids such as anthocyanins are located mainly in the skins (Jordão et al., 1998a), while the flavan-3-ols (catechins and proanthocyanidins) are present in the skins, seeds and stems (Ribéreau-Gayon, 1972; Ricardoda-Silva et al., 1992b;Fuleki & Ricardo-da-Silva, 1997;Kennedy et al., 2000aKennedy et al., , 2000b Jordão et al., 2001a,b;Sun et al., 2001).Anthocyanin accumulation in the vacuoles of the skin begins ...
