Effect of Huanglongbing or greening disease on orange juice quality, a review

Authors: DALA PAULA, BRUNO - Federal University Of Minas Gerais; Plotto, Anne; Bai, Jinhe; Manthey, John; Baldwin, Elizabeth - Liz; FERRAREZI, RHUANITO - University Of Florida; GLORIA, MARIA BEATRIZ - University Of Minas Gerais

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2018
Publication Date: 1/22/2019
Citation: Dala Paula, B., Plotto, A., Bai, J., Manthey, J.A., Baldwin, E.A., Ferrarezi, R., Gloria, M. 2019. Effect of Huanglongbing or greening disease on orange juice quality, a review. Frontiers in Plant Science. 9:1976. https://doi.org/10.3389/fpls.2018.01976.
DOI: https://doi.org/10.3389/fpls.2018.01976

Interpretive Summary: Huanglongbing (HLB) has affected the citrus industry worldwide. Most research focuses on understanding this complex bacterial disease which changes tree physiology and is vectored by an insect. This review paper focuses on the effect of the disease on fruit quality and the implications for commercial orange juice. In general, because the bacteria block nutrient uptake by the roots and transport to the leaves and fruit, most of the metabolites result from a stress response. Fruits have less sugars, more acids, more flavonoids, and more of some amino acids. As a result, fruit that show the symptoms of the disease (small, green and misshapen) taste less sweet, more sour and bitter than fruit that are infected but do not show HLB symptoms, or fruit from healthy trees. A few suggestions for future research are given.

Technical Abstract: Huanglongbing (HLB) or citrus greening disease is the most severe citrus disease, devastating the industry worldwide. The presumed causal bacterial agent Candidatus Liberibacter spp. affects tree health as well as fruit development, ripening and quality of citrus fruit and juice. Fruit from infected trees can be either symptomatic or asymptomatic. Symptomatic fruit are small, asymmetrical and greener than healthy fruit. Furthermore, symptomatic fruit show higher titratable acidity and lower soluble solids, solids/acids ratio, total sugars and malic acid levels, lower ethyl butanoate, valencene, decanal and other ethyl esters, straight-chain aldehydes and sesquiterpenes, but higher in many monoterpenes 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. The presumed HLB pathogen remains unconfirmed and its management is challenging due to the unpredictable latency times for symptoms after the tree has become infected, and the lack of effective curative treatment methods. When present, disease management depends on incidence rate, and relies on vector control, tree eradication, nutritional programs and use of plant varieties with increased tolerance. Earlier research showed that HLB-induced off-flavor was not detectable in juice made with up to 25% symptomatic fruit. In some production regions, it is increasingly difficult to find fruit not showing HLB symptoms. This review focuses on the effects of HLB on orange juice quality regarding chemical, physicochemical and biochemical characteristics, including levels of sugars, organic acids, secondary metabolites, levels and profiles of amino acids, bioactive amines, volatile compounds and sensory characteristics, as well as future research needs.