Evaluation of radical scavenging activity of fresh and air-dried tomatoes by three model reactions

The radical scavenging activity and the antioxidant content of fresh and air-dried tomatoes were investigated. Tomato halves were dried in a pilot-scale dryer under the following conditions: air temperature, 80 degrees C; air flow rate, 1.5 m/s; drying time, 400 min; final moisture, 25%. Carotenoid (lycopene, beta-carotene, lutein) and ascorbic acid were analyzed by HPLC with a spectrophotometric and an electrochemical detector, respectively. Total phenolics were determined by using the Folin-Ciocalteu reagent. The radical scavenging activity was studied in three model systems: (a) the xanthine oxidase and xanthine system, which generates superoxide radical and hydrogen peroxide; (b) the 3-morpholinosydnonimine system, which releases spontaneously superoxide radical and nitrogen monoxide, forming peroxynitrite; (c) the linoleic acid and CuSO(4) system, which promotes lipid peroxidation. These model systems allow the simulation of key reactions involved in the pathogenesis of certain chronic diseases and may be related to the in vivo activity of tomato antioxidants. Hence, these measurements can be used for optimizing tomato processing and storage. The drying process resulted in a decrease of ascorbic acid content, whereas phenol reagent reducing compounds increased. Carotenoid levels were substantially unchanged upon drying. Fresh and air-dried tomato extracts could act as radical scavengers both in the reactive oxygen species-mediated reactions and in lipid peroxidation. Drying affected the antioxidant effectiveness as measured in the xanthine/xanthine oxidase system, which was found to be the most sensitive method for the measurement of tomato antioxidant activity (lower I(50)) but retained the antioxidant effectiveness in the other two systems.