Anti- and prooxidant activity of water soluble components of some common diet vegetables and the effect of thermal treatment

The pro-antioxidant activity of carrot, cauliflower, celery, eggplant, garlic, mushroom, onion, white cabbage, white potato, tomato, yellow bell pepper, and zucchini was investigated. Juices obtained by centrifugation of vegetables were treated at different temperatures (2, 25, 102 degrees C) and assessed for antioxidant activity (AA) using a model system beta-carotene-linoleic acid. Antioxidant activity of all vegetable juices showed a linear correlation with time. The equations of all straight lines obtained showed positive slope values indicating either an increase in antioxidant activity or a decrease in prooxidant activity during the reaction. Negative intercept values were found when the juices showed prooxidant activity at least during the first phase of the reaction. Mushroom and white cabbage always showed more than 80% AA, while cauliflower, celery, and eggplant showed such high AA only after boiling. Tomato and yellow bell pepper were always prooxidant. Cluster analysis allowed the vegetables to be divided into five groups according to their anti- and prooxidant behavior as a function of thermal treatment and reaction time. Vegetable juice components were separated on a Bakerbond C-18 solid-phase extraction cartridge according to their polarity, and the AA of the bound and unbound fractions of each vegetable was also tested.