Fatty acids as precursors for aroma volatile biosynthesis in pre-climacteric and climacteric apple fruit

Changes in the concentration of free fatty acids (FA) and FA as constituents of neutral and polar lipids were determined during the course of ripening in the peel of 'Golden Delicious' apple fruit. The concentration of these FA was then related to previously examined volatile aroma substances in order to evaluate a possible quantitative relationship between both variables. In particular, the concentrations of the C18:1 and C18:2 FA in the free FA fraction were low in pre-climacteric fruit but rapidly increased three- to fourfold during the climacteric rise. Changes in FA concentrations during maturation were less pronounced in the neutral lipid fraction and almost absent in the polar lipid fraction. Treatment of immature fruit (harvested almost 5 weeks before the climacteric rise) with 100 mul l(-1) ethylene increased the concentration of FA in the free and neutral lipid fraction but not in polar lipids. The increase in the free and 'neutral lipid' 18:2 FA after ethylene treatment in immature apples exceeded the concentration of this FA found in mature climacteric fruit. A hypothesis is discussed linking the examined dynamic changes of FA with previous results of ATP and aroma volatiles in an attempt to explain deficiencies in aroma volatile production in unripe and long-term stored apple fruit. (C) 2003 Elsevier B.V. All rights reserved.