Active taste compounds in juice from oranges symptomatic for Huanglongbing (HLB) citrus greening disease

Citrus greening disease, also known as Huanglongbing (HLB), compromises the quality of citrus fruit and juice, causing increased bitterness, metallic taste, astringency and a burning mouthfeel. The chemical basis responsible for these changes remains largely unknown other than the roles of the bitter limonoids, limonin and nomilin, and of flavonoids that may cause astringency. A combination of chemical and sensory analyses was used to identify bitter components in HBL-affected orange juice (HLBOJ), and compared with juice from healthy fruit. DNA analysis of the juice revealed that HLBOJ was well infected with the bacteria, with Ct value of 27 compared with 33 for the healthy juice. There were differences (at least P < 0.05) in pH, titratable acidity (TA), soluble solids content (SSC), SSC/TA, total sugars, citric acid, secondary metabolites and sensory characteristics between healthy and HBLOJ, with, limonin and nomilin being 7.8 and 21.6 fold higher in HLBOJ than in healthy juice, respectively. Nonvolatile juice compounds were fractionated using fast centrifugal partition chromatography and semi preparative HPLC. Some fractions (7 out of 10) were described as bitter, but did not contain limonoids, polymethoxylated flavones or hesperidin, and, instead, were composed of hydroxycinnamates, suggesting these compounds might be involved with this sensory attribute.