Submitted to: International Controlled Atmosphere Research Conference Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/1997
Publication Date: N/A
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. The occurrence of scald has been linked with high levels of farnesene, an oily compound found in apple peel. Farnesene combines with oxygen to make trienols, which are toxic to the fruit. Scald can often be controlled by storing apples in low oxygen atmosphere, and it was thought that this beneficial effect resulted from reduced oxidation of farnesene to trienols. However, this study showed that the primary effect of low oxygen is to greatly reduce farnesene production. Furthermore, it was found that delayed transfer of apples from air to low oxygen after 6 weeks of storage failed to inhibit accumulation of farnesene and trienols, and consequently failed to control scald. 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 physiological and biochemical bases of scald development and ultimately lead to a strategy to genetically eliminate the disorder.
Technical Abstract: We confirmed recently that the main products of alpha-farnesene oxidation in vivo are 2,7,9,11-tetraen-6-ols (conjugated trienols), with one isomer comprising over 90 percent of the total. We also showed that severe scald symptoms are associated with high levels of both farnesene & conjugated trienols. In the past year we further investigated the correlation between farnesene and trienol concentrations & scald development in 'Granny Smith' and 'Empire' apples. Fruit of both cultivars were stored at 1C in a flow-through system either in air or 1.5 percent oxygen. In addition, for one set of 'Granny Smith' transfer to 1.5 percent oxygen was delayed for 6 weeks. Imposition of low oxygen directly after harvest strongly inhibited synthesis of farnesene & production of trienol in fruit of both cvs, & prevented development of scald symptoms in 'Granny Smith' after 25 weeks at 1C plus 1 week at room temperature in air. Delayed transfer of 'Granny Smith' to low oxygen resulted in only a small decrease in farnesene & trienol production. In accord with this, the delayed low oxygen storage gave only a modest reduction in scald development during cold storage, & 1week after transfer to room temperature in air scald symptoms were almost as severe as those observed in air-stored fruit. These results indicate that scald development is closely associated with the concentration of farnesene & its oxidation product. We also conclude that farnesene oxidation in vivo is probably enzymatic, & that the beneficial effects of low oxygen are mainly the result of inhibition of farnesene synthesis.