Antioxidant activity of commonly consumed vegetables in yemen.

Of late, more attention has been paid to the role of natural antioxidants, especially phenolic compounds, which may act both by reducing the content of toxic compounds in foods and by supplying the human body with exogenous antioxidants. The total phenolic contents and the total antioxidant activities (% AA) of 17 commonly consumed vegetables in Yemen were determined. Total phenolics was measured colorimetrically using the Folin-Ciocalteu reagent with D-catechin as the standard. The antioxidant activity (%AA) of vegetables using their juices at different levels (50μl, 100μl, 200μl) was assayed in vitro by the inhibition of liver homogenate oxidation mediated by FeSO4 / ascorbate system. The % AA was measured by the TBAR method. The results showed that for all vegetable juices, increased antioxidant activity or decreased prooxidant activity increased with volume of juice. With the addition of 50μl from each sample, most vegetable juices showed antioxidant activity and it appears that coriander had exceptionally high antioxidant activity (60%). However, garlic, yellow onion, parsley, red onion and Cissus rotundifolia showed considerably high antioxidant activities (54-41 %). Other vegetables with low antioxidant activities (27 to 3 %) showed an order of increase in %AA as follows: tomato > spinach > horseradish-leaves > carrot > cabbage > chilli > leek > horseradish-roots. At the same, time some vegetable juices such as that of green pepper, cucumber and lettuce showed initial prooxidant activities (-11 to -40 %). The complete inhibition of oxidation was noticed when the highest level of juices (200μl) was used in the cases of coriander, onions, garlic and parsley. The correlation between total phenolics and the antioxidant activities of vegetables with different levels of juices (50μl, 100μl and 200μl) showed positive but not significant correlations (R = 0.41 - 0.55). Some vegetables such as carrots and tomatoes show the highest relative antioxidant efficiencies despite the small content of total phenolics compared to other vegetables tested in this study.