Evolution of antioxidant capacity in seeds and skins during grape maturation and their association with proanthocyanidin and anthocyanin content

In order to investigate the antioxidant activity in seeds and skins during grape maturation and their relation with anthocyanin and proanthocyanidin content, two Portuguese red grape varieties, 'Touriga Nacional' and 'Tinta Roriz' were studied. For antioxidant activity analysis, one analytical method was used (ABTS method). Different proanthocyanidins fractions according to their degree of polymerization were analyzed, while 13 different individual anthocyanins were evaluate by HPLC as well. During the maturation period the antioxidant activity content quantified from the different grape berry fractions was characterized by a general decrease with a slight oscillation in the early stages of maturation, followed by a stabilization and slight increase of the values in the last weeks of ripening. Similar evolution was observed for the different proanthocyanidins fractions quantified. For the individual anthocyanins, in general the evolution was characterized by a slowly increase in the first 3 weeks of ripening process, followed by a marked increase and finally a slight decrease or stabilization in the last weeks of ripening. Finally, high linear positive correlations between proanthocyanidin fractions and the antioxidant activity evolution during the grape maturation were obtained while for the individual anthocyanins a high negative correlation values was quantified.