Phenolic compounds in juices of apple cultivars and their relation to antioxidant activity

Apples and their juices are important sources of phenolic compounds in human diet. Using the same juice processing method, we compared phenolic composition as well as antioxidant activity of juices from various table apple cultivars, grown at the same location. Antioxidant activity of apple juices was estimated by application of two assays, ABTS cation radical decolorization and by scavenging of reactive oxygen species (ROS) generated by xanthine/xanthine oxidase (O2·-, H2O2, OH·; superoxide assisted Fenton reaction), as measured by inhibition of ethylene release from KMB (α-Keto-γ-(methylthio)-butyric acid). The apple juices differed in phenolic content and antioxidant activity, where cultivar differences were more relevant than environmental factors. Furthermore, to improve antioxidant performance in the XOD-test, a juice low in phenol content was supplemented with the appropriate amounts of phenols to the level of the best juice indicating that these phenolics contribute to the antioxidant activity of the apple juice. In accordance to literature, the phenolic compounds representing the main antioxidant activity in the apple juices comprise flavan-3-ols and chlorogenic acid.