SYNTHESIS AND OXIDATION OF α-FARNESENE DURING HIGH AND LOW O2 STORAGE OF APPLE CULTIVARS DIFFERING IN SCALD SUSCEPTIBILITY

Abstract

Apples of high ('Granny Smith'; GS), moderate ('Red Delicious'; RD), and low ('Gala' ; GA) susceptibility to superficial scald were stored for up to 6 months at 0°C under high (100%) or low (1.5%) oxygen or in air. Hexane extracts of peel samples were analyzed for α-farnesene and its major oxidation product, a conjugated trienol, using an HPLC method which allows simultaneous detection at 232 and 269 nm, respectively. Identification of the compounds was confirmed by UV spectrometry, HPLC with diode array detection, and GC-MS. In general, α-farnesene and trienol content correlated with scald susceptibility. Levels of both isoprenoids were over 20-fold higher in GS compared with GA, the latter having only trace amounts. Farnesene content peaked in both GS and RD at 2 months, whereas trienol rose sharply from 1 to 4 months. Production of farnesene and trienol increased at higher oxygen levels in all three cultivars. The amount of trienol was more closely correlated with oxygen concentration. GS fruit stored under 100% oxygen were completely bronzed after 3 months and had a high level of ethanol. Two lots of RD fruit harvested 1 week apart differed markedly in their rate and amount of farnesene and trienol production. Fruit from the earlier harvest had higher levels of both compounds at all times. These results support the hypothesis that susceptibility to scald in a given cultivar is a function of farnesene production and its subsequent autoxidation to conjugated trienols.