|Collin, Sue - UC KEARNEY AG|
|Sievert, Jim - UC KEARNEY AG|
|Fjeld, Kent - UC KEARNEY AG|
|Arpaia, Mary Lu - UC KEARNEY AG|
|Thompson, James - UC DAVIS|
|Slaughter, David - UC DAVIS|
Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2009
Publication Date: April 1, 2009
Citation: Obenland, D.M., Margosan, D.A., Collin, S., Sievert, J., Fjeld, K., Arpaia, M., Thompson, J., Slaughter, D. 2009. Peel fluorescence as a means to identify freeze-damaged oranges. HortTechnology. 19:379-384. Interpretive Summary: Navel oranges that have been damaged by freezing conditions in the field are sometimes difficult to identify which allows poor quality fruit to reach the marketplace. Following the 2007 freeze in California, ultraviolet (UV) fluorescence of the peel was evaluated as a means to determine which fruit were internally damaged. Using fruit harvested from fifteen different sites, it was found that the accuracy of UV fluorescence in classifying fruit as damaged ranged from 6 to 72%, with the sites having the greatest amount of freeze damage having the highest classification percentages. The peel fluorescence remained easily visible for at least 9 weeks. Taste panel evaluation of potentially freeze-damaged fruit from packing houses indicated that neither the currently-used method of freeze damage detection nor the UV method was very effective in predicting eating quality of the fruit. Ultraviolet fluorescence may be a means to more accurately and quickly identify moderately-to severely-frozen oranges than the methods currently available.
Technical Abstract: The use of ultraviolet (UV) fluorescence to identify navel oranges (Citrus sinensis L. Osbeck) that were internally freeze-damaged was evaluated using fruit harvested following a natural freeze that occurred in California in January 2007. In the first part of the test, oranges were harvested after the freeze from fifteen sites that were previously determined to have a slight to moderate amount of freeze damage. Some of the sites were harvested periodically over time to determine the persistence of the fluorescence. The fruit were initially evaluated for the presence of small yellow spots characteristic of freeze damage that fluoresce when viewed under UV light and then cut and rated using a method currently used by the California Department of Food and Agriculture (CDFA) to determine the presence of internal freeze damage. The percentage of freeze-damaged fruit in each lot as determined by the CDFA method ranged from 0 to 88%. The accuracy of classifying fruit as freeze-damaged in each lot by UV fluorescence ranged from 6 to 72%, with the fruit lots containing the greatest amount of freeze damage having the highest classification percentages. False positives generally occurred at a low rate among the lots. Although some fading was evident, the fluorescence persisted and was readily visible for at least 9 weeks after the freeze event. In the second part of the test, eighteen lots of potentially freeze-damaged fruit were obtained from a packing house, a portion of each lot evaluated for freeze damage under UV light and by the CDFA method, and the rest evaluated for various aspects of taste using a sensory panel following four weeks of storage. Neither the CDFA method nor the UV method was very effective in predicting sensory preference. Ultraviolet fluorescence was ineffective in identifying oranges with light freeze damage but may be useful for the identification of moderately- to severely-frozen oranges.