Antioxidant activities of New Zealand-grown tomatoes

The objective of this study was to compare the antioxidant activities, total phenolics, lycopene and ascorbic acid content of four commercial tomato cultivars (Excell, Tradiro, Flavourine and Campari) of New Zealand, grown under similar hydroponic conditions. The mean antioxidant activity of the four cultivars, as measured with the ABTS radical decolourization assay, ranged from 2329 to 3268 µmole TEAC/100 g dry matter (DM) in the hydrophilic extracts and from 178 to 303 µmole TEAC/100 g DM in the lipophilic extracts. The major antioxidant components per 100 g DM were phenolics (343-451 mg gallic acid equivalents in hydrophilic extract and 53-74 mg gallic acid equivalents in lipophilic extract), flavonoids (175-204 mg rutin equivalents), ascorbic acid (153-195 mg) and lycopene (33-54 mg). Ascorbic acid and flavonoids were found to contribute 28-38% and 29-34%, respectively, to the antioxidant activity of the hydrophilic extract of tomatoes. The results showed that the smallest cultivar (Campari) had significantly (P < 0.05) higher antioxidant activities, total phenolics and flavonoids than the larger sized cultivars (Excell, Tradiro and Flavourine). This could be attributed to the significantly (P < 0.05) higher surface area/volume ratio of the small cultivar (0.15) when compared with the large-sized cultivars (0.10-0.12). The tomato cultivar (Flavourine) with a brighter red colour (higher a*/b* value), had a higher lycopene content as well, which suggests that the a*/b* value of tomatoes can be used as an indicator of their lycopene content. The phenolics (r=0.84**) and flavonoids (r=0.88**) were significantly related to the antioxidant activity of the hydrophilic extract, which suggests that measurement of total phenolics or flavonoids can be used as indicators of the antioxidant activity of tomatoes.