Investigation of the antioxidant properties of tomatoes after processing

A study was made of the antioxidant content, activity and colour of two New Zealand commercially grown tomatoes (Lycopersicon esculentum L. var. Excell and Aranca) cultivated in glasshouses using hydroponic techniques. Excell tomatoes were harvested and stored individually while cultivar Aranca was harvested by cutting the vine, which consisted of a group of eight tomatoes. Both cultivars of tomatoes were stored in the dark for 4 days at 15degreesC to simulate normal pre-purchase storing conditions. The antioxidant content of the raw tomatoes after 4 days of storage were markedly different while the CIE LAB colour values of the cut inner surfaces of the two cultivars were similar. After 4 days storage, subsamples of each cultivar were either boiled, baked or fried, and analysis of CIE colour, ascorbic acid, total phenolics, lycopene and antioxidant activity (using the ABTS assay) was undertaken. Boiling and baking had a relatively small effect on the ascorbic, total phenolic, lycopene and antioxidant activity of the two cultivars while frying significantly reduced (P<0.001) the ascorbic, total phenolic and lycopene contents of the two cultivars. Chromatic colour analysis showed that both cultivars became significantly (P < 0.001) darker and less red after cooking by all methods. In a following experiment, the two cultivars of tomatoes were sliced and allowed to soak for 20 min in a mixture of olive oil and white vinegar, or olive oil and white vinegar separately. CIE colour of the two cultivars showed no change after processing but the treatments of oil and vinegar separately and together reduced (P < 0.05) the red component of the colour. Treating the two cultivars of tomatoes with the oil and vinegar mixture resulted in a significant reduction (P < 0.001) in the ascorbic acid, total phenolic and antioxidant activity of the tomatoes. Treatment with oil significantly reduced the amount of lycopene that could be extracted from the tomatoes while treatment with vinegar had no effect. (C) 2003 Elsevier Inc. All rights reserved.