Evaluation of antioxidant capacity of blood orange juices as influenced by constituents, concentration process and storage

Total Antioxidant Activities (TAA) of freshly squeezed and processed blood and blond orange juices were measured using the ABTS radical-cation method. Blood juices have TAA values higher than blond juices, and freshly-squeezed juices are higher than processed. Levels of ascorbic acid, hydroxycinnamic acid and anthocyanins were determined in order to calculate relative contributions to TAA by Trolox Equivalent Antioxidant Capacity (TEAC) of such constituents. Ascorbic acid was the main contributor (∼70%), followed by hydroxycinnamic acids and anthocyanins. Calculated TAA accounted for 91% (mean) of that measured, reaching a maximum of 98% (mean) for the ‘not-from-concentrate’ blood juices (NFC). Reconstituted (from concentrate) blood juices (RFC) had higher TAA than NFC, and the difference could be ascribed to the increased amount of carotenoid pigments in the serum of RFC juices, as a consequence of the thermal concentration process. Despite the degradation of anthocyanins during storage, TAA of NFC and RFC juices remained unchanged up to 60 days at 2°C, whereas it decreased when RFC juice was stored at 20°C, in accordance with the observed decrease of ascorbic acid.