Peel to Flesh Bioactive Compounds Ratio Affect Apple Antioxidant Potential and Cultivar Functional Properties

More than ten thousand apple cultivars with high variability in the quality traits and year-round availability place apples at the forefront of consumed fruits. Yet consumers and producers alike are still looking for new apple cultivars with specific quality attributes such as plant resistance to biotic and abiotic stresses as well as a high health-promoting potential. The model plants were three cultivars: a new 'Chopin' and an old 'Granny Smith', scab resistant cultivars with green peel, and a red-skinned cultivar 'Gala Schniga'. Apple peel and flesh were analyzed separately during two growing seasons: 2016 and 2017. The total ascorbate and phenolics as well as individual phenolic compounds, such as (+)-catechin, (-)-epicatechin, chlorogenic acid, phloridzin, and rutin concentrations, proved to be highly tissue-type and cultivar dependent. The apple of the 'Chopin' and 'Granny Smith' cultivars expressed much lower skin-to-flesh antioxidant potential differences as compared to 'Gala Schniga'. The lowest differences between tissue types were observed in the case of chlorogenic acid and flavan-3-ols, followed by total phenolics and ascorbate concentrations. Except for phloridzin, 'Gala Schniga' exhibited the highest differences in global and individual phenolic compound concentrations as well as total antioxidant capacity between the apple peel and flesh. 'Chopin' was definitely distinguished by the highest concentration of ascorbate in both the peel and the flesh and expressed a higher concentration of flavanols, especially compared to 'Granny Smith'. In contrast to 'Gala Schniga', 'Chopin' was richer in chlorogenic acid, (+)-catechin, and (-)-epicatechin in the flesh. The total antioxidant capacity of the green-peel apple cultivars was similar to that of the red-peel one. A narrower range of differences between the concentration of antioxidants in apple peel and flesh could mean better health-promoting properties and might be related to a greater resistance to environmental stress factors.