Flavonoid and chlorogenic acid levels in apple fruit: characterisation of variation

Abstract

Variations in flavonoid and chlorogenic acid levels within fruit, within tree, between orchards, between cultivars and among mutants were characterised and quantified in ‘Elstar’ and ‘Jonagold’ apples by reversed-phase high performance liquid chromatography (RP-HPLC). The sun-exposed skin of individual fruit had much higher cyanidin 3-galactoside (anthocyanin) and quercetin 3-glycoside levels than the shaded skin, while phloridzin, catechins and chlorogenic acid were similar in the skin of both sides. Individual flavonoid and chlorogenic acid levels were not equally distributed within the fruit. Quercetin 3-glycosides and anthocyanin were almost exclusively found in the skin. Catechins were mostly found in the skin but some were present in the flesh. Phloridzin was most abundant in the seeds, with intermediate levels in both the core area and the skin, and the lowest level in the flesh. Chlorogenic acid was mainly present in the core area and the seeds with an intermediate level in the flesh and a low level in the skin. The levels of anthocyanin, quercetin 3-glycosides and total flavonoids were highest in fruit borne in the top of the tree followed by fruit from the outer tree parts, whereas the lowest levels were found in fruit from the inner tree. Terminal fruit contained the highest levels of these compounds, including catechins, compared to lateral and spur fruit. Phloridzin and chlorogenic acid were not affected by the position of the fruit in the tree nor by the bearing wood type. There were large differences in flavonoid and chlorogenic acid levels in ‘Elstar’ fruit between two normally productive orchards differing mainly in growth vigour. ‘Jonagold’ and its mutants had considerably higher levels of flavonoid and chlorogenic acid than ‘Elstar’ and its mutants. The most blushed mutants of both cultivars had higher levels of anthocyanin but not of flavonoids or chlorogenic acid compared to the standard cultivar and to the less blushed mutants. The most blushed mutants had a higher number of red cells per cell layer and more cell layers containing red cells than the standard cultivar and the less blushed mutants.