Phenolic content and antioxidant activities of white and purple juices manufactured with organically- or conventionally-produced grapes.

Although the beneficial effects of moderate wine intake are well-known, data on antioxidant capacity of grape juices are scarce and controversial. The purpose of this study was to quantify total polyphenols, anthocyanins, resveratrol, catechin, epicatechin, procyanidins, and ascorbic acid contents in grape juices, and to assess their possible antioxidant activity. Eight Vitis labrusca juices--white or purple, from organically- or conventionally-grown grapes, and obtained in pilot or commercial scale--were used. Organic grape juices showed statistically different (p<0.05) higher values of total polyphenols and resveratrol as compared conventional grape juices. Purple juices presented higher total polyphenol content and in vitro antioxidant activity as compared to white juices, and this activity was positively correlated (r=0.680; p<0.01) with total polyphenol content. These results indicate that white and purple grape juices can be used as antioxidants and nutritional sources.