Antioxidative capacity of wine on human LDL oxidation in vitro: Effect of skin contact in winemaking of white wine

To assess the antioxidative effect of the non-alcoholic components of wine, human low-density lipoprotein (LDL) was oxidized in vitro by copper ions in the presence of polyphenolic extracts from three wines: standard red wine (R), standard white wine (W1), and white wine the must of which had been in contact with grape solids during 8 h before fermentation (W2). Lipoprotein peroxidation was monitored as the formation of conjugated dienes, of thiobarbituric acid reactive substances (TEARS), and fluorescent substances. At equal volume-of-extract additions to LDL, the lag phase of diene production increased proportionally with the polyphenol concentration of each extract. By the addition of equal phenolic substance concentration (8 mu mol of gallic acid equiv/L) the timing of lag phase was 410 +/- 8, 442 +/- 11, and 516 +/- 57 min for W1, R, and W2 respectively compared to 78 +/- 6 min for control LDL without added extract. At 9 h of incubation, TEARS and fluorescence production were drastically inhibited by W1 but completely inhibited by R and W2. At 24 h of oxidation only fluorescence was still inhibited. The results indicate that the polyphenols contained in wines could inhibit protein derivatization but only delay lipid peroxidation and that the type, as well as the concentrations, of polyphenols of the different wines have varying protective effects. The wine-making process that includes the pre-incubation of the must with the grape skin prior to and during fermentation (red and certain white wines) was the most effective in preventing LDL oxidation in vitro.