DEVELOPMENTAL-CHANGES IN THE CONCENTRATION AND COMPOSITION OF FLAVONOIDS IN SKIN OF A RED AND A GREEN APPLE CULTIVAR

Flavonoids from the skin of Granny Smith, a green apple cultivar, and Splendour, a red apple cultivar, were quantified by high-performance liquid chromatography for two seasons (1989-1990 and 1990-1991). Both cultivars contained a similar composition and concentration of quercetin glycosides and proanthocyanidins. Splendour also synthesised cyanidin glycosides during ripening. Quercetin glycosides and proanthocyanidins were highest in the skin of very young fruit of Granny Smith and decreased by 50% during fruit development. In Splendour, concentrations of quercetin glycosides and proanthocyanidins in the skin decreased by 50% from early to mid-season but then increased during ripening. Cyanidin glycosides in Splendour increased to about 1 mg g(-1) fresh weight during ripening. There were significant differences between the two cultivars but not between years. Total amount of flavonoids increased throughout the season as fruit surface area increased. For Granny Smith there was an estimated net synthesis per apple of 0.16 mg day(-1) quercetin glycosides, 0.1 mg day(-1) proanthocyanidins and for Splendour a net synthesis per apple of 0.28 mg day(-1) quercetin glycosides, 0.21 mg day(-1) proanthocyanidins and during ripening 0.21 mg day(-1) cyanidin glycosides. Relative proportions of major quercetin glycosides and proanthocyanidins were stable during fruit development. For Splendour, however, cyanidin glycoside synthesis was accompanied by a corresponding increase in quercetin glycoside and proanthocyanidin synthesis. The data suggest a coordinate regulation of enzymes in the flavonoid biosynthetic pathway during fruit development.