FACTORS THAT INFLUENCE VOLATILE ESTER BIOSYNTHESIS IN ‘DELICIOUS’ APPLES

Abstract

We studied the influence of the intensity of light reaching fruit surfaces, cultivar, and maturity on amounts of the principal aroma and flavor volatiles (acetate esters) emitted from 'Delicious' apple fruits, and the relationship between anthocyanin accumulation and acetate ester emission. Light treatments of full sun (FS), 53% FS, 19% FS, and <1% FS were created by season-long bagging of 'Starkrimson' and 'Topred' fruit with shade cloth. Anthocyanin levels decreased with decreased light exposure, with 'Topred' fruits generally accumulating more anthocyanin than 'Starkrimson'. Contents of all flavonoid classes were also reduced as light level decreased. Volatile ester emissions were strongly affected by light exposure, with maxima occurring below 100% FS. Ester emission from 'Starkrimson' fruit at 179 days after full bloom (DAFB) was roughly twice that from 'Topred' in both years. The primary ester of both strains at all light exposures was 2-methyl butyl acetate, accounting for 50 to 75% of total ester content, with butyl and hexyl acetates as secondary components. Fruit position on the canopy also affected color and aroma/flavor of fruit. Western and southern aspect fruit generally emitted more esters than northern and eastern aspect fruit; anthocyanin accumulation was maximal in fruit from northern and eastern aspects. Differences in ester, anthocyanin, and flavonoid content due to light exposure were as seen in the main study. These data suggest that anthocyanin accumulation and volatile ester formation increase together with increasing light exposure, but at higher light exposures, continued increases in anthocyanin production come at the expense of acetate ester biosynthesis. For these strains, this happened between 53% FS and FS. Results suggest that 'Delicious' apples managed for maximum color have less volatile content and less potential for volatile development.