Commercial grape juices inhibit the in vitro oxidation of human low-density lipoproteins

This study was aimed at determining the antioxidant activity of commercial grape juices in inhibiting the copper-catalyzed oxidation of human low-density lipoproteins (LDL) in vitro and at relating this activity to the phenolic composition of the juices. This work also evaluated the effect of vitamin C on this antioxidant activity. When standardized to a total phenolic concentration of 10 mu M gallic acid equivalents (GAE), samples of grape juices inhibited LDL oxidation from 62 to 75%. White grape juices inhibited LDL oxidation on the average by 72%, Concord purple grape juice by 67%, and grape juice blends (mixture of white and Concord grape juice) by 63%. Vitamin C had no significant effect on the antioxidant activity of the grape juices tested. The antioxidant activity of Concord juice samples was related to their anthocyanin levels, while that of the white grape juices was related to their levels of flavan-3-ols and hydroxycinnamates, as determined by HPLC. On the basis of the same total phenolic concentration, the antioxidant activity of grape juices toward LDL oxidation was comparable to that of several California red wine. However, based on their undiluted total phenolic concentration, the Concord and blends of grape juices had comparable activity to that of the red wines, while the white grape juices were less active.