The relative contributions of ascorbic acid and phenolic antioxidants to the total antioxidant activity of orange and apple fruit juices and blackcurrant drink

The total antioxidant activity (TAA) and antioxidant composition of orange juice, apple juice and blackcurrant drink have been studied. Phenolic antioxidants in these juices have been identified and values derived for their relative molar antioxidant activities or Trolox Equivalent Antioxidant Activity (TEAC). The bulk of the TAA of apple juice could be accounted for by chlorogenic acid and the phloretins, while that of orange juice was accounted for by hesperidin and narirutin. In contrast, the anthocyanins in blackcurrant drink contributed only a fraction of its non-vitamin C antioxidant activity and it is suggested that there is a significant unidentified antioxidant present in this beverage. After equalisation of the vitamin C content, juices were subjected to mild oxidation; the decline in ascorbate was of the order of apple > orange > blackcurrant drink. The results suggest that the phenolic antioxidants protect vitamin C against oxidative decomposition, with those in blackcurrant having the greatest vitamin C-sparing activity. (C) 1997 Elsevier Science Ltd.