Inhibition of Human Low-Density Lipoprotein Oxidation in Relation to Composition of Phenolic Antioxidants in Grapes (<i>Vitis vinifera</i>)

Antioxidant activities of phenolic extracts from fourteen different types of fresh grapes were investigated by measuring the inhibition of human low-density lipoprotein (LDL) oxidation in vitro. The inhibition of LDL oxidation ranged from 22% to 60% at 10 μM gallic acid equivalents (GAE) of total phenols and from 62% to 91% at 20 μM GAE. The antioxidant activities were thus comparable to those previously found for wines. The relative LDL antioxidant activity correlated with the concentration of total phenols (r = 0.89, p < 0.01), with the level of anthocyanins (r = 0.56, p < 0.05) and flavonols (r = 0.54, p < 0.05) in the grape extracts as analyzed by high-performance liquid chromatography (HPLC). When seed crushing and longer extraction times were employed, high amounts of flavan-3-ols and hydroxybenzoates were extracted. With these extracts relative LDL antioxidant activity correlated highly with the levels of flavan-3-ols (r = 0.86, p < 0.01), total phenols (r = 0.79, p < 0.05), and hydroxybenzoates (r = 0.77, p < 0.05). Keywords: LDL oxidation; flavonoids; hydroxycinnamates; anthocyanins; flavan-3-ols; flavonols; HPLC