Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 27, 1996
Publication Date: N/A
Interpretive Summary: INTERPRETIVE SUMMARY Superficial scald is a serious storage disorder that affects many varieties of apples and pears. It occurs after long-term cold storage and results in browning or blackening of the peel, making the fruit unsalable. An accurate and sensitive method was developed which has confirmed the connection between superficial scald and levels of farnesene, an oily compound found in apple peel. Farnesene combines with oxygen to make trienols, which are toxic to the fruit. Stored Granny Smith apples easily succumb to scald, whereas Gala apples are highly resistant. Using the new method on fruit stored for up to 6 months, it was found that farnesene and trienol levels were 20-fold higher in Granny Smith than in Gala. Production of both farnesene and trienols increased at higher oxygen levels in the three apple varieties studied. Granny Smith fruit stored in air (20 percent oxygen) developed severe scald after removal from storage, whereas fruit stored under 1.5 percent oxygen remained unblemished. This work has practical applications in terms of prevention of scald by low oxygen storage. It also provides information useful to other scientists that will help determine the chemical basis of scald development and ultimately lead to a strategy to genetically eliminate the disorder.
TECHNICAL ABSTRACT Conjugated triene oxidation products of alpha-farnesene are thought to induce the storage disorder superficial scald. A C18-HPLC method was devised which allows simultaneous quantification of farnesene and its oxidation products, conjugated trienols, in hexane extracts of apple peel using UV detection at 232 and 269 nm. Identification of the compounds was confirmed by UV spectrometry, HPLC with diode array detection, and GC-MS. Apples of high (Granny Smith; GS), moderate (Red Delicious; RD), and low (Gala; GA) susceptibility to scald were stored for up to 6 months at 0C under high or low oxygen or in air. Farnesene and conjugated trienol content in the peel correlated well with scald susceptibility and occurrence. Levels of both compounds were at least 20-fold higher in GS than in GA. Farnesene and trienols decreased at low oxygen levels in each cultivar. Two lots of RD fruit harvested 1 week apart differed markedly in farnesene and trienol production; first harvest fruit had higher levels of both and developed scald, whereas second harvest fruit did not scald. These results support the proposal that scald susceptibility in a given cultivar is a function of farnesene production and its oxidation to conjugated trienols.