Effect of Huanglongbing or Greening Disease on Orange Juice Quality, a Review

Abstract

Huanglongbing (HLB) or citrus greening is the most severe citrus disease, currently devastating the citrus industry worldwide. The presumed causal bacterial agent Candidatus Liberibacter spp. affects tree health as well as fruit development, ripening and quality of citrus fruits and juice. Fruit from infected orange trees can be either symptomatic or asymptomatic. Symptomatic oranges are small, asymmetrical and greener than healthy fruit. Furthermore, symptomatic oranges show higher titratable acidity and lower soluble solids, solids/acids ratio, total sugars, and malic acid levels. Among flavor volatiles, ethyl butanoate, valencene, decanal and other ethyl esters are lower, but many monoterpenes are higher in symptomatic fruit compared to healthy and asymptomatic fruit. The disease also causes an increase in secondary metabolites in the orange peel and pulp, including hydroxycinnamic acids, limonin, nomilin, narirutin, and hesperidin. Resulting from these chemical changes, juice made from symptomatic fruit is described as distinctly bitter, sour, salty/umami, metallic, musty, and lacking in sweetness and fruity/orange flavor. Those effects are reported in both Valencia and Hamlin oranges, two cultivars that are commercially processed for juice in Florida. The changes in the juice are reflective of a decrease in quality of the fresh fruit, although not all fresh fruit varieties have been tested. Earlier research showed that HLB-induced off-flavor was not detectable in juice made with up to 25% symptomatic fruit in healthy juice, by chemical or sensory analysis. However, a blend with a higher proportion of symptomatic juice would present a detectable and recognizable off flavor. In some production regions, such as Florida in the United States, it is increasingly difficult to find fruit not showing HLB symptoms. This review analyzes and discusses the effects of HLB on orange juice quality in order to help the citrus industry manage the quality of orange juice, and guide future research needs.

Keywords: Candidatus Liberibacter asiaticus; Hamlin; Valencia; bitter compounds; flavor.

Figure 1

Countries currently affected by Huanglongbing (HLB) disease (adapted from CABI, ; EPPO, 2017).

Figure 2

Size and color differences between fruit affected by Huanglongbing (HLB). (A) Hamlin healthy; (B) Hamlin HLB-asymptomatic; (C) Hamlin HLB-symptomatic; (D) Valencia healthy; (E) Valencia HLB-symptomatic (Photography by the authors).

Figure 3

Side-by-side chromatograms of headspace volatiles of juice samples extracted from healthy (top) and HLB (bottom) Valencia oranges. Ethyl butanoate (ester) and sesquiterpenes are in greater amount in healthy than in HLB juice.