Antioxidant activity and oxygen-scavenging system in orange pulp during fruit ripening and maturation

The antioxidant activity (ferric reducing/antioxidant power, FRAP) and oxygen-scavenging system of pulps during the fruit ripening and maturation were investigated in three cultivars of sweet orange (Citrus sinensis (L.) Osbeck). The highest FRAP values and activities of antioxidant enzymes and contents of nonenzymes were detected in ‘Red Flesh’ navel orange. The activities of oxygen-scavenging enzymes, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POD), decreased with ripening and maturation of fruit. Ascorbate peroxidase (AsA-POD) and dehydroascorbate reductase (DHAR) activities were also stably declined, whereas glutathione reductase (GR) activity and nonenzymes in the ascorbate–glutathione cycle displayed a single-peak pattern which paralleled the significant changes in FRAP values. In addition, the ratios of ascorbate/dehydroascorbate (AsA/DHAsA), reduced glutathione/oxidized glutathione (GSH/GSSG) were also decreased. Changes in the activities of antioxidant enzymes and the contents of nonenzymes during ripening indicated that the antioxidant system plays a fundamental role in the ripening of orange fruits.