Phenolic composition of Nebbiolo grape (Vitis vinifera L.) from Piedmont: characterization during ripening of grapes selected in different geographic areas and comparison with Uva Rara and Vespolina cv.

Grapes (Vitis vinifera L.) are rich in polyphenols; the phenolic composition of grape is very complex and depends on several factors, including grape varieties, ripening stage and pedoclimatic conditions. In this work the amount of total polyphenols, anthocyanins and tannins, the antioxidant activity and the chromatic characteristics of Nebbiolo grapes from Piedmont were determined. Four different cultivation areas and three different ripening stages (starting of veraison, veraison completion and physiological ripeness) were considered. The quantification of individual polyphenols and hydroxycinnamates was performed by RP-HPLC/DAD. In a general way, anthocyanins and flavonols increased during ripening, while antioxidant activity and tannin content remained constant. Differences in specific phenolic composition were observed depending on the sample origin. Nebbiolo samples at different maturity stages were compared among them and with Uva Rara and Vespolina cv.: overall Nebbiolo showed the lowest anthocyanin content, evidencing a different profile with respect to the other cultivars (major relative content of peonidin-3-O-glucoside). Multivariate statistical methods (principal components analysis and hierarchical clustering) further permitted recognition of Nebbiolo samples of different geographic origin, particularly those dedicated to Barolo winemaking.