Flavonoid and chlorogenic acid changes in skin of ‘Elstar’ and ‘Jonagold’ apples during development and ripening

Abstract

Apple fruits are important dietary sources of potentially healthy phenolics. In two successive seasons, changes in the concentration and amount of individual flavonoids and chlorogenic acid during development and ripening were investigated by reversed-phase high performance liquid chromatography (RP-HPLC), in ‘Elstar’ and ‘Jonagold’ apples from the outside and the inside of the tree canopy. ‘Jonagold’ had a higher concentration and amount of flavonoids and chlorogenic acid than ‘Elstar’ during fruit development and ripening. In both cultivars, the concentration on a dry weight basis of quercetin glycosides, phloridzin and chlorogenic acid was highest early in the season, but decreased at different rates during fruit development to reach a steady level during maturation and ripening. Catechins (catechin plus epicatechin) concentration showed a similar pattern, but a temporary increase was observed in an early stage of development. The concentration of cyanidin 3-galactoside (anthocyanin) was relatively high early in the season, gradually decreased to a very low steady level during growth, but started to increase near maturation, especially in the outer fruit. On a fruit basis the amount of quercetin glycosides increased during development and was about two times higher in ‘Jonagold’ compared to ‘Elstar’, both in outer and inner fruit. These compounds were the most abundant flavonoids in the skin of both cultivars and their accumulation showed a strong dependency on fruit position on tree. In contrast, the amount of the second most abundant flavonoid type, catechins, increased during development to a maximum and then showed some decrease by mid season which was independent of fruit position on tree. The amount of phloridzin increased only early in the season reaching a steady level during development and ripening, and was independent of fruit position on tree. The amount of chlorogenic acid in both cultivars initially increased, but subsequently decreased to reach a low, steady level and was slightly higher in outer than in inner fruit. Although anthocyanin concentration was relatively high at early stages of development, significant accumulation on a fruit basis only occurred during maturation and ripening. The accumulation of anthocyanin, similar to that of quercetin glycosides, showed a strong dependency on fruit position on tree. Remarkably, the difference in accumulation of anthocyanin and quercetin glycosides in outer and in inner fruits had no effect on the accumulation of catechins, phloridzin and chlorogenic acid in these fruits. The results indicate that, in general, the overall production of total flavonoids and chlorogenic acid in apple skin is completed during fruit development before the onset of maturation.