Evolution of antioxidant activity and bioactive compounds in tomato (Lycopersicon esculentum Mill.) fruits during growth and ripening

The interest in the consumption of tomato (Lycopersicon esculentum Mill.) is, to a large extent, due to its content of bioactive compounds and their importance as dietary antioxidants. During the growth and ripening process, there are quantitative and qualitative changes in the fruit composition which determine the nutritional quality and antioxidant potential at each stage. Two half determinate early hybrids cultivars (Prekos and Balkan) and one indeterminate mid-early hybrid cultivar (Reyana) were considered for this study. Fruits from plants grown on sandy soil in an unheated greenhouse were collected at three growth and six maturity stages. Antioxidant activity, dry matter, soluble solids, titratable acidity, ascorbic acid, lycopene, beta-carotene, chlorophylls and total phenolic contents were monitored. During fruit growth, dry matter, soluble solids and titratable acidity recorded a slight decrease, polyphenols and b-carotene contents remained almost the same while ascorbic acid content and antioxidant activity increased continuously. The stage of ripening significantly influenced the content of all bioactive compounds as well as the antioxidant activity of tomato fruits. The first stages of ripening were characterized by a slight decrease of the dry matter content and by an increase of the titratable acidity, while in the last two stages of ripening these variations reversed. Ascorbic acid and total phenolics content increased as maturity progressed from mature green to pink or light red stage and decreased afterward. Lycopene started to accumulate since turning and sharply increased in the last three stages, on average 36 % of the lycopene content being accumulated in the last stage of ripening. In terms of hydrophilic antioxidant activity, depending on the cultivar, the pink or light red stages were the ones with the greatest potential. Although there were significant differences among the contents of bioactive compounds and antioxidant activity of the three cultivars studied, their patterns of variation during the nine stages were quite similar.