The free and bound phenols have been measured in 20 fruits commonly consumed in the American diet. Phenols were measured colorimetrically using the Folin-Ciocalteu reagent with catechin as the standard after correction for ascorbic acid contribution. On a fresh weight basis, cranberry had the highest total phenols, and was distantly followed by red grape. Free and total phenol quality in the fruits was analyzed by using the inhibition of lower density lipoprotein oxidation promoted by cupric ion. Ascorbate had only a minor contribution to the antioxidants in fruits with the exception of melon, nectarine, orange, white grape, and strawberry. The fruit extracts' antioxidant quality was better than the vitamin antioxidants and most pure phenols, suggesting synergism among the antioxidants in the mixture. Using our assay, fruits had significantly better quantity and quality of phenol antioxidants than vegetables. Fruits, specifically apples and cranberries, have phenol antioxidants that can enrich lower density lipoproteins and protect them from oxidation. The average per capita consumption of fruit phenols in the U.S. is estimated to be 255 mg/day of catechin equivalents.

Fruits and vegetables in the diet have been found in epidemiology studies to be protective against several chronic diseases. Epidemiological evidence suggests that flavonoid consumption in the diet is protective against heart disease. Phenols in 23 vegetables have been measured by extraction with and without acid hydrolysis to determine the percent of conjugated and free phenols. Phenols were measured colorimetrically using the Folin−Ciocalteu reagent with catechin as the standard. The extracts' antioxidant quality was assayed by the inhibition of lower density lipoprotein oxidation mediated by cupric ions. Vegetables had antioxidant quality comparable to that of pure flavonols and were superior to vitamin antioxidants. The phenol antioxidant index, measuring both the quantity and the quality of antioxidants present, was used to evaluate 23 vegetables. Isolated lower density lipoproteins from plasma spiked with two vegetable extracts were enriched with phenol antioxidants and showed decreased oxidizability. The average per capita consumption of vegetable phenols in the United States was estimated to be 218 mg/day of catechin equivalents. This is 3 times higher than the recommended intake of vitamin antioxidants. Keywords: Phenols; antioxidants; vegetables; lipoprotein oxidation

The apparent bioavailability of genistein and daidzein is not different when consumed as either aglycone or glucoside by American women.