- HUANGLONGBING: DEVASTATING DISEASE OF CITRUS 349
panel. In addition, these juices and their blends were analyzed using
an electronic tongue, an instrument that can distinguish liquids, such
as juices, based on their solutes. A preliminary study had demonstrated
that the electronic tongue could distinguish orange juices with differ-
ent chemical compositions (levels of sucrose, citric acid, and potas-
sium chloride) or with different types of citrus juices (grapefruit and
tangerine) mixed with orange juice (Raithore et al. 2013). The results
of the blending study showed that the HLB-symptomatic fruit juice
was generally lower in sugars, soluble solids, and solids/acid ratio, and
higher in the bitter limonoids than was the healthy juice for both vari-
eties, with the blends being intermediate. In fact the “Hamlin” HLB
juice had a significant difference in levels of bitter limonoids compared
to healthy juice but not in solids/acids ratio, while the “Valencia” juice
had a significant difference in the solids/acid ratio and only a small
difference in levels of bitter limonoids. At a 25% blend of HLB juice
in a balance of healthy juice, 42–48% of the panelists for “Hamlin” and
“Valencia,” respectively, could detect a difference (detection threshold),
but only 26–27% could describe it (recognition threshold). At a 50%
blend, 74–90% could detect a difference and 49–73% could describe
the difference. The electronic tongue separated the 100% HLB juice and
50% juice blends from the healthy juices and from the 6.25%, 12.5%,
and 25% blends for both varieties, in agreement with the sensory data
(Raithore et al. 2015). This research demonstrated that HLB-induced off-
flavor could be managed by blending with healthy juice and that quality
screening could be accomplished using the electronic tongue. Unfortu-
nately, as the infection spreads, there is less healthy juice with which
to blend.
Another way to screen orange juice for off-flavor due to HLB disease
is to use qPCR to detect CLas titer in processed orange juice, since it
would relate to the amount of infected fruit used to make the juice.
To this end, a method was developed to detect CLas DNA by qPCR in
processed orange juice (Bai et al. 2013a), which was shown to corre-
late to HLB-related off-flavor (Zhao et al. 2013). This allows processors
to determine the amount of CLas-infected fruit that went into a batch
of juice, and to use this information to predict flavor as an HLB flavor
impact management tool (Zhao et al. 2013).
During the course of this research, CLas was found to be associated
with another citrus pathogen,Diplodia natalensis(Diplodia), in orange
juice and later also found in fruit abscission zones, which may induce
early fruit drop in the field and fruit stem-end rot in storage (Brown
and Lee 1993; Brown and Burns 1998; Zhao et al. 2015). It is of inter-
est to determine if the decrease in fruit yield associated with HLB is