Diversity of polyphenols in the peel of apple (Malus sp.) germplasm from different countries of origin

This study investigated ten polyphenolic compounds in the peel of 145 apple cultivars grown in the same location while originated from different countries over two successive years. Despite significant year effect of individual and total polyphenol concentrations on each cultivar, both concentrations showed similar distributions in the 2 years, and genotypic correlations among them were relatively stable. Genotypic variations were considerable, with total polyphenol concentration ranging from 363.9 to 2516.9 mu g g(-1) FW. Cyanidin-3-galactoside was found only in red apple peels, at levels of 67.8-371.6 mu g g(-1) FW. Flavanols (epicatechin and catechin) and dihydrochalcones (mainly phloridzin) accounted for 8.8-66.1% and 8.58-61.2% of total polyphenols, respectively. Six flavonols (quercetin-3-galactoside, quercetin-3-glucoside, quercetin-3-rhamnoside, quercetin-3-xyloside, quercetin-3-arabinoside, and quercetin-3-rhamnoglucoside) were identified. The proportion of flavonols was 9.3-70.6% of total polyphenols. This wide variation could help in selecting cultivars with different polyphenol patterns in the peel. Principal component analysis showed that cultivars originated from different countries could not be distinguished in terms of polyphenol profiles.