Effects of Huanglongbing on orange juice quality

Citrus greening, or Huanglongbing (HLB), is a devastating disease of citrus trees caused by Candidatus Liberibacter spp., generally transmitted by an insect vector, and with no easy means of control. HLB infection affects tree development, yield and fruit quality. Fruits from infected trees can be symptomless (asymptomatic) or can show clear HLB symptoms (symptomatic). Key to the difference between healthy, asymptomatic and symptomatic fruits is the quality of juice produced by each. The juice from symptomatic fruits is of a lower quality than the juice from healthy or asymptomatic fruits and this has caused huge losses to the citrus industry. In a paper published in a recent issue of Frontiers in Plant Science, researchers from Brazil, where HLB has been a long standing problem, have reviewed the effects of HLB on orange juice quality and recommended sustainable measures which can be adopted by growers and citrus juice processors to mitigate the economic effects of this widespread disease. Juice made from symptomatic fruits from HLBaffected trees is generally described as bitter, sour, salty/umami, harsh, metallic, musty and lacking in sweetness and fruity/orange flavour. Chemical analyses have shown that symptomatic oranges have higher titratable acidity and lower soluble solids, solids/acids ratio, total sugars, and malic acid levels than asymptomatic fruits. Some flavour volatiles are lower but many monoterpenes are higher in symptomatic fruits than in healthy or asymptomatic fruits, and the disease also causes an increase in secondary metabolites such as limonin and hesperidin in orange peel and pulp. The juice quality of asymptomatic fruits, however, is similar to the juice quality of healthy fruits. Despite the typically bitter taste of juice from symptomatic fruits, sensory panel tests have shown that adding small amounts of the lower quality juice from HLB-symptomatic fruits to juice from healthy or asymptomatic fruits does not compromise taste quality. Symptomatic fruits may be suitable for orange juice production as long as the proportion of juice from these fruits does not exceed a maximum percentage which ranges from 10% to 25% in different studies. Photo creditElizabeth Chin, University of California, Davis