- HUANGLONGBING: DEVASTATING DISEASE OF CITRUS 347
the two main juice varieties and effects were greater early in the sea-
son (Baldwin et al. 2010; Dagulo et al. 2010; Massenti et al. 2015). As
indicated in Table 7.2, the bitterness in HLB-symptomatic “Hamlin”
juice was associated with the increase in bitter limonoids (limonin and
nomilin). For “Valencia” juice, the flavor problem was reduced sweet-
ness or increased sourness due to a lower sugar/acid ratio in HLB com-
pared to healthy juice. In the worst case scenario, you have lower sugars
and higher bitter limonoids (Raithore et al. 2015).
Perplexingly, the levels of the bitter limonoids, limonin and nomilin,
were below their reported taste thresholds (concentration of a com-
pound that is detectable by humans), and thus, should not have affected
flavor. Cloud loss in juice was greater for HLB-affected juice than
healthy juice if not pasteurized, and flavonoids were elevated in the
juice (Baldwin et al. 2010; Massenti et al. 2015), which would explain
the increased astringency, as well as in the peel (Massenti et al. 2015).
Nevertheless, there were large seasonal differences that sometimes were
greater for chemical flavor compounds than differences associated with
HLB (Baldwin et al. 2010; Dagulo et al. 2010). The effect of HLB dis-
ease on chemical flavor compounds was found to mimic the chemical
profile of immature fruit (Dagulo et al. 2010), and this would explain
why the greater off-flavor effects due to HLB tend to be more preva-
lent early in the harvest season. As the season progresses, fruit maturity
can somewhat compensate for the HLB off-flavor effects due to lower
sugars, higher acids, and higher bitter limonoids since sugars tend to
increase and acids and bitter limonoids decrease over the harvest sea-
son in oranges (Manners 2007).
- Impact of HLB on Orange Fruit/Juice Aroma.The orange juice
aroma volatile profile is altered in HLB-affected trees and contributes
to the reduction in overall flavor quality, although differences in the
aroma profile and aroma perception is less than that of the solute pro-
file and taste perception. The esters, aldehydes (giving top fresh notes),
and sesquiterpenes are lower and mono-terpenes (like훾-terpinene and
훼-terpinolene) reportedly higher in HLB-affected juice compared to
healthy controls (Dagulo et al. 2010), resulting in sensory trained panel
descriptors like “earthy,” “flat,” “more peel oil aroma,” and “sour-
fermented” (Plotto et al. 2010).
B. The Dilemma of Bitterness Perception in HLB-affected Juice
The fact that sensory panelists were picking up bitterness, when the
bitter limonoids were below their reported thresholds was puzzling.