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Title: Effect of Liberibacter infection (Huanglongbing disease) of citrus on orange fruit physiology and fruit/fruit juice quality: chemical and physical analyses

Author
item Baldwin, Elizabeth - Liz
item Plotto, Anne
item Manthey, John
item McCollum, Thomas
item Bai, Jinhe
item IREY, MIKE - Us Sugar Corporation
item Cameron, Randall - Randy
item Luzio, Gary

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2009
Publication Date: 1/21/2010
Citation: Baldwin, E., Plotto, A., Manthey, J., Mccollum, G., Bai, J., Irey, M., Cameron, R., Luzio, G. 2010. Effect of Liberibacter infection (Huanglongbing disease) of citrus on orange fruit physiology and fruit/fruit juice quality: chemical and physical analyses. Journal of Agricultural and Food Chemistry. 58:1247-1262.

Interpretive Summary: Huanglongbing (HLB) or greening disease was discovered in Florida several years ago and has since spread throughout the state. This is a serious disease that can kill a citrus tree in 5-10 years. This disease is not feasible to eradicate, thus, the industry is forced to live with it for both fruit production and subsequent processing into orange juice. Since more than 90 percent of the fruit in Florida are processed into juice, and the disease is rumored to affect fruit and fruit juice flavor, chemical and physical analyses were conducted on fruit and juice from healthy and diseased trees on three processing varieties (Hamlin, Midsweet and Valencia) over two seasons (2007 and 2008) and in some cases, several harvests to determine disease effects. Many fruit and juice characteristics were measured that impact quality of fruit and/or juice including color, size, solids, acids, sugars, aroma volatiles, vitamin C, secondary metabolites (including bitter compounds), pectin and juice cloud. Results showed that normal-looking fruit from diseased trees were not very distinguishable from fruit from healthy trees for many of the quality factors measured, but that fruit symptomatic for the disease (small, green and lopsided) were higher in the bitter compounds limonin and nomilin, and thus, likely to cause flavor problems. If symptomatic fruit, which often drop off the tree, make it to the processing plant, they should be graded out to avoid flavor problems.

Technical Abstract: Huanglongbing (HLB) or greening disease was discovered in Florida several years ago and has since spread throughout the state. The disease is correlated to the presence of a gram-negative bacteria, Candididatus Liberibacter asiaticus (Las). This disease is not feasible to eradicate, thus, the industry is forced to live with it for both fruit production and subsequent processing. Since more than 90 percent of the fruit in Florida are processed, and the disease is rumored to affect fruit flavor, chemical and physical analyses were conducted on fruit and juice from healthy (- Las) and diseased (+ Las) trees on three processing varieties (Hamlin, Midsweet and Valencia) over two seasons (2007 and 2008) and in some cases, several harvests to determine disease effects. Both non-symptomatic fruit and fruit symptomatic for the disease were used, and fresh squeezed and processed/pasteurized juice were evaluated. Many fruit and juice characteristics were measured that impact quality of fruit and/or juice including color, size, solids, acids, sugars, aroma volatiles, ascorbic acid, secondary metabolites (including bitter compounds), pectin (galacturonic acid), pectin-demethylating enzymes and juice cloud. Results showed that non-symptomatic fruit were not very distinguishable from healthy fruit for many of the quality factors measured, but that symptomatic fruit were higher in the bitter compounds limonin and nomilin, and thus, likely to cause flavor problems. There was variation due to harvest date, which resulted in differences greater than those due to disease for non-symptomatic fruit, especially for Valencia juice. If symptomatic fruit, which often abscise from the tree, make it to the processing plant, they should be graded out to avoid flavor problems.