Citrus HLB is a destructive citrus disease in Florida and other citrus production regions around the world. A primary symptom of HLB is that fruit of affected trees will remain green, and postharvest degreening will not induce their peel to turn orange due to insufficient carotenoid levels (Chen et al., 2016; Zhao et al., 2015). Some fruits, if harvested late, will naturally degreen on the tree, but will remain yellow instead of completely turning orange (Chen et al., 2016; Zhao et al., 2015). The inability for HLB-affected fruit peel to turn orange even after degreening due to insufficient carotenoids is especially true of ‘Hamlins’ (Liao and Burns, 2012).
Before HLB was spread over the Florida citrus regions, only early oranges, temples, tangelos, and ‘K-Early’ citrus had color problems. The fruits were typically degreened and then treated with a dye, CR2, to adjust the color, which is the only dye allowed for this purpose (Hall, 2013). Previously, research in this laboratory searching for a CR2 alternative found that several oil-soluble natural colorants were comparable to CR2 as a color enhancer (Sun et al., 2015). However, postdye waxing was considered a necessity to reduce oxidation of carotenoid colorants (Sun et al., 2015).
Commercially, citrus fruits, regardless if degreening and dying were applied, are waxed to reduce water loss, lower the respiration rate, improve shine, and reduce spoilage (Lahlali et al., 2014; Mannheim and Soffer, 1996). Waxing also preserves higher levels of total phenolics during storage (Shen et al., 2013). Carnauba wax is a common coating used for such purposes in a variety of fruit, such as limes (Caron et al., 2015), apples (Jo et al., 2014), and orange (Sun et al., 2015).
The objective of the current research was to develop a natural colorant-containing carnauba wax so that the application of colorant and wax is a one-step process, instead of the current two-step (CR2 dye then waxing) process. The goal was to develop a coating that imparts improved peel color comparable to CR2, while imparting shine, retaining moisture, and modifying internal gases to extend storage life.
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