The antioxidant properties of lycopene, a carotenoid found primarily in tomatoes, have raised interest in the tomato as a food with potential anticancer properties. Natural antioxidants from tomato extract have been shown to reduce blood pressure in some people.

Scientists in New Zealand

and colleagues elsewhere wanted to determine which were the major antioxidants in different fractions--the skin, pulp and seeds--of three tomato cultivars: Excell, Tradiro and Flavourine. These were grown under hydroponic conditions in a commercial greenhouse in New Zealand. The researchers also wanted to determine the antioxidant activity of these fractions.

The skin fractions of all of the cultivars were found to be significantly high in major antioxidant components and antioxidant activity, as measured by ABTS assay, compared with the pulp and seed fractions. The researchers calculated that on a fresh weight basis, the skin and seed fractions of tomato, collectively, contributed 53% of the total phenolics, 52% of the total flavonoids, 48% of the total lycopene, 43% of the total ascorbic acid and 52% of the total antioxidant activity of whole tomatoes. The results indicate that discarding tomato skin and seeds during home cooking or commercial processing can result in a significant loss of antioxidants.

The scientists also semi-dried these tomato cultivars at 42 C to an average dry matter content of 19%. They compared the major antioxidant components and antioxidant activity of the fresh and semi-dried tomatoes. The semi-dried tomatoes contained very low levels of 5-hydroxymethyl-2-furfural and had a higher mean a*/b* value of 1.6 than did the fresh tomatoes, which had a value of 1.2.

The mean total phenolics, total flavonoids, lycopene and ascorbic acid content of the fresh tomatoes decreased by 26%, 13%, 14% and 21%, respectively, as a result of the semidrying process. However, the overall appearance of the semi-dried tomatoes was better compared to previous studies in which higher temperatures were used to dry tomatoes. The semidried product also retained more ascorbic acid.

Further information. Geoffrey Savage, Animal and Food Sciences Division, Hilgendorf 442, Lincoln University, Canterbury, New Zealand; phone: +64 3 325 2811; email: savage@lincoln.ac.nz.