Antioxidant content and ascorbate metabolism in cherry tomato exocarp in relation to temperature and solar radiation

Considering the economic importance of the tomato and its nutritional benefits to human health, a study was made of how two different environmental factors (temperature and overall solar radiation) influence the nutritional quality of cherry tomatoes during the plant full production cycle. Solanum lycopersicum L. cv. Naomi plants were grown in an experimental greenhouse. Three fruit samples were taken over the full production period: first sampling at the beginning of harvest (7 January 2004), second at mid-harvest (22 March 2004) and third at harvest end (30 May 2004). Values for temperature and overall accumulated solar radiation peaked at a maximum in the third sampling, without lowering the yield with respect to previous samplings. Regarding the antioxidant activity in the exocarp fraction of the cherry tomato fruits, the results showed that the increase in temperature and solar radiation diminished the lycopene and β-carotene contents in the third sampling, inducing defective pigmentation (sunscald). This occurred simultaneously with an increase in lipid peroxidation during the third sampling, quantified as lipoxygenase activity and malondialdehyde content. Finally, in relation to ascorbate metabolism, the higher temperatures and stronger solar radiation at the third sampling increased the oxidation of reduced ascorbate (AsA) due to intensified ascorbate peroxidase (APX) and ascorbate oxidase (AO) activities and a depression of the enzyme dehydroascorbate reductase (DHAR). In conclusion, the results indicate that despite the oxidation of AsA by APX and AO, the minimal regeneration of the latter, together with the greater lipid peroxidation with increasing temperature and solar radiation in the greenhouse, explained the lower content of antioxidants in the exocarp and therefore the loss of nutritional quality of the cherry tomato fruits grown under these conditions.