Effect of Liberibacter Infection (Huanglongbing or “Greening” Disease) of Citrus on Orange Juice Flavor Quality by Sensory Evaluation

Abstract

Some anecdotal reports suggest that infection of citrus trees with Candidatus Liberibacter asiaticus (Las), the suspected causal agent of huanglongbing (HLB) disease, imparts off flavor to orange juice. It is of interest to the industry to know how Las infection affects juice quality with respect to cultivar, maturity, or processing method. Hamlin, Midsweet, and Valencia oranges were harvested over 2 y from trees that tested negative (Las-) or positive (Las+) for Las from different groves and included normal looking (nonsymptomatic) and symptomatic fruit (small, green, and lopsided) from Las+ trees. In the 1st year, fruit were manually juiced, while in the 2nd year, a commercial process was used. Juice from Las+ trees was compared to juice from Las- trees in difference-from-control tests, and by descriptive analysis. Results showed large variability due to tree, harvest date, and cultivar. Juice from Hamlin Las+ trees tended to be more bitter and sour than its Las- counterpart. In contrast, hand processed Valencia juice from Las+ trees was perceived to have some off-flavor and bitterness compared to control, but the following year, commercially processed Valencia juice from Las+ trees was perceived to be only slightly more sour than juice from Las- trees for the April harvest, and to be sweeter for the June harvest. When juice from individual replicates was pooled to be more representative of a commercial situation, there was no difference between Las+ and Las- juice in Valencia. Trained panel differences were noted for juice from Hamlin Las+ fruit, especially for symptomatic fruit. Assumptions that juice made from oranges harvested from Huanglongbing (from infection with Liberibacter sp.) affected trees is off-flavored appeared to be generally more true for Hamlin juice than for Midsweet or Valencia, especially for Hamlin juice made from symptomatic fruit. For Midsweet and Valencia, flavor differences between juice made from fruit harvested from diseased or healthy trees varied greatly between trees, season, and even processing method. Under a commercial processing situation, where juice is blended from several varieties, seasons, and multiple locations, it is expected that off-flavor will not be a major problem.