Submitted to: Journal Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 9/1/1998
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 unmarketable. A new, 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 times higher in Granny Smith than in Gala. Production of both farnesene and trienols increased at higher oxygen levels in the 3 apple varieties studied. Granny Smith fruit stored under 100 percent oxygen or 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 biochemical basis of scald development and ultimately lead to a strategy to genetically eliminate the disorder.
Technical Abstract: TECHNICAL 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 0C under high (100 percent) or low (1.5 or 3.0 percent) oxygen or in air. Hexane extracts of peel samples were analyzed for farnesene and its major oxidation product, a conjugated trienol, using an HPLC method which allows simultaneous detection at 232 and 269 nm, respectively. Their identity was confirmed by UV spectrometry, HPLC with diode array detection, and GC-MS. In general, farnesene and trienol content correlated with susceptibility to scald. 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 percent oxygen were completely "bronzed" after 3 months and had a high level of ethanol. Lots of RD fruit harvested 1 week apart differed markedly in their rate and extent of farnesene and trienol production. Fruit from the earlier harvest had higher levels of both compounds at all times. Overall 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.