Phenol antioxidant quantity and quality in foods: Vegetables

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.