Investigation in antioxidant activities of various tomatoes at different drying processes

• Main Authors: Ching-Hui Chang, 張景煇
• Other Authors: 劉永銓
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/90699558768701163791

博士 === 國立中興大學 === 化學工程學系所 === 95 === Tomato, rich in antioxidants is an important vegetable and fruit in daily dietary. Consumption of tomato products has been associated with decreased risk of cancers. Many studies have shown the close relation between the intake of vegetables and cancer prevention. Due to tomato can’t long time store in room temperature, therefore, tomatoes have to be processed, dried, and used as a component for various vegetable dishes and food additives. However, during the heating processing, tomato products might show some oxidative damage due to the exposure to heat and oxygen. It is important how to remain the antioxidant content of tomato products. This study contains three parts. The first part is investigating two extraction approaches using tetrahydrofuran/petroleum ether (TPE) solvent and phosphate buffer (pH 7.4) respectively were carried out to process tomatoes. Four tomato cultivars were used as the testing models and the antioxidant contents and antioxidative properties of the extracts were measured. To evaluate the multiple antioxidative performances, an antioxidative performance index (API) was defined as the average of four antioxidative assays, i.e. relative reducing power, ferrous ion chelating ability, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity, and superoxide radical-scavenging activity. It showed that a linear correlation (r2 = 0.9174) could be obtained between the total antioxidant contents and the API. The concept of representing the antioxidative capacities by an index is helpful to the evaluation of the antioxidative values of the complex compounds in all respects. In the second part, two varieties of tomatoes were used to study the effects of different drying processes, freeze-dried (FD) and hot-air-dried (AD), on the antioxidant properties of tomatoes. In the quantitative analysis of antioxidative components, fresh tomato had the highest amount of total ascorbic acid, total flavonoids, and total phenolics, meanwhile, fresh TTL tomato contained the highest amount of lycopene. In the analysis of antioxidative activity, fresh tomato reveals the highest antioxidant ability. However, comparison of FD and AD processing, the FD products have higher antioxidative activity. The third part was study the effects of varieties of tomatoe processing temperature (40℃, 80℃, and 120℃), and drying timing (0-240 min) during air-drying process on lycopene content for tomatoes were investigated. Meanwhile, the total antioxidant contents (TACs), including amount of total phenolics, total flavonoids, total ascorbic acid, and lycopene, were also measured. The result showed that lycopene content increased under air-drying process during the first 60 min. However, after drying for 75 min at 120 ℃, the red tomato cultivars, i.e. HR, SN, and TTL, exhibited a significant decrease in lycopene content. Referring to the TACs of all cultivars in the drying process, a threshold level of TAC (500 mg/100 g dry matter of tomato) could be defined. It was observed that while the level of TACs was lower than this value, lycopene content would drop dramatically under air-drying processing.