Anti- and Prooxidant Activity of Water Soluble Components of Some Common Diet Vegetables and the Effect of Thermal Treatment Gabriella Gazzani,* Adele Papetti, Gabriella Massolini, and Maria Daglia Department of Pharmaceutical Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy 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 °C) and assessed for antioxidant activity (AA) using a model system -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. Keywords: Vegetables; lipid peroxidation; antioxidants; prooxidant INTRODUCTION Lipid peroxidation is a major cause of the decrease in the flavor and nutritive value of fat and oil products. This reaction generates very reactive oxygen compounds which in humans are responsible for causing or ac- celerating chronic disease states such as cardiovascular, neoplastic, inflammatory, and amyloidosis pathologies and aging (Havesteen, 1983; Caragay, 1992; McCord, 1994). Since lipid peroxidation is a chemical reaction with low activation energy, the rate of this reaction is not significantly diminished by lowering the storage tem- perature of bulk diet lipids. As a consequence synthetic antioxidants are often incorporated to prevent peroxi- dation. In recent years the use of these compounds has been restricted because of the possibility of their toxic and carcinogenic effects (Imida et al., 1983; Maeura et al., 1984; Haigh, 1986; Van der Heijden et al., 1986; Van Esch, 1986). On the other hand, during the past two decades interest in lipid peroxidation has surpassed food technology. It has been realized that compounds deriv- ing from lipid peroxidation and their degradation prod- ucts have harmful effects on biological systems. Fur- thermore, a number of plant constituents have been recognized to have positive effects against the oxygen reactive compounds in biological systems (Hemeda and Klein, 1984). It is thus possible that a more in-depth knowledge about plant food properties can help to discover natural components that can act as antioxi- dants in vitro and in vivo. A number of reports studied the antioxidant proper- ties of either isolated plant constituents such as fla- vonoids (Hertog et al., 1992a,b; Lee et al., 1995), flavonols (Bilyk et al., 1984), essential oils (Farag et al., 1989), and tannins (Laughton et al., 1991) or plant extracts obtained from vegetables, fruits, spices, and wine (Onyeneho and Hettiarachchy, 1992; Kinsella et al., 1993). The effects of processing on food antioxidant properties (Gazzani, 1994; Al-Saikan et al., 1995; Nicoli et al., 1997) were also extensively studied. The aim of this paper was to assess the antioxidant activity (AA) of 12 common edible vegetables widely consumed in the mediterranean diet. Such activity is determined on vegetable juices obtained by simple centrifugation and filtration at 2 °C, to minimize the effects of handling. It is well known that many factors (i.e., the antioxidant concentrations, temperature and pH of the medium, the occurrence of chemicals with either positive or negative synergism) can strongly influence antioxidant activity. To evaluate the effects of storage and thermal treatment to which vegetables are commonly subjected, juices were also analyzed after storage at room temperature (25 °C) and boiling (102 °C). The antioxidant activity was determined using a model system containing -carotene-linoleic acid which is widely used to assess antioxidant activity of vegetable extracts (Tsushida et al., 1994; Lee et al., 1995; Al- Saikhan et al., 1995; Nicoli et al., 1997). Furthermore, total phenolic content, reducing substances, and per- oxidase activity were determined to verify any relation with antioxidant activity. MATERIALS AND METHODS Vegetable Samples. The vegetables purchased in Sep- tember from a local supermarket were carrot (Daucus carota L.), cauliflower (Brassica oleracea L. var. botrytis), celery (Apium graveolens L.), eggplant (Solanum melongena L.), * Corresponding author [telephone +39 0382 507373; fax +39 0382 422975; e-mail gazzani@chifar.unipv.it]. 4118 J. Agric. Food Chem. 1998, 46, 4118-4122 10.1021/jf980300o CCC: $15.00 © 1998 American Chemical Society Published on Web 09/19/1998