Oranges - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 396

Color of orange juice used to be determined by visual
comparison to standards provided by the USDA in assay
tubes using a specific background angle of view and light-
ing. A score was given based on the closeness to increas-
ingly orange (decreasingly yellow) standards. Electronic
colorimeters using the Hunter scale are now used. Equa-
tions to calculate a color number (CN) and correlate it to
USDA color score have been developed.
From a nutrition perspective, the most important
parameter to determine is vitamin C content. Vitamin C
is determined by titration with indophenol or high per-
formance liquid chromatography (HPLC). Folic acid is
another nutrient in orange juice, and women of childbearing
years are encourage to include orange juice in their diets to
protect against specific birth defects that result from folate
deficiency.
Finally, juice bitterness is critical to orange juice ac-
ceptability. Bitterness in orange juice is due mainly to the
presence of limonin. With the exception of 'Navel' vari-
eties, limonin and its precursors are normally in low con-
centration in the juice and accumulate in the seeds. When
the limonin precursor limoninoate A-ring lactone (which
is tasteless) is exposed to the acidic environment of the
juice, it converts to limonin. In the case of seedless Navel
oranges, the limoninoate A-ring lactone accumulates in the
cytoplasm and the membrane of the juice cell. Therefore,
when juice is extracted, limonin is present as a constituent
of the pulp and cloudy matter. The rate of limonin for-
mation is affected by several factors beyond the scope of
this chapter. Hence accurate determination of limonin is
somewhat difficult and laboratory results may vary depend-
ing on sample preparation and storage time. A very small
portion of Navel oranges, typically rejects from packing-
houses, are processed into juice, but such processes always
require either blending, debittering, or both. This process
is more common in California. Debittering is typically ac-
complished using ion exchange resins or other method of
separation (Norman and Kimball, 1990). The most com-
mon method of determination of limonin is HPLC with
ultraviolet detector. Details for vitamin C and limonin de-
terminations as well as other quality methods are described
elsewhere (Praschan, 1975; Kimball, 1999a).

using a Brookfield viscometer with a cylindrical spindle
#4 rotating at 60 rpm. Because orange juice concentrate is
non-Newtonian, apparent viscosity is shear rate dependent.
Above about 20 ◦ Brix, orange juice displays pseudo-plastic
behavior, that is, the apparent viscosity decreases with shear
rate. Orange juice is also thixotropic, that is, the apparent
viscosity decreases with time from the moment the fluid
is set in motion and reaches a constant shear rate until it
reaches a steady value. Therefore conditions under which
the determination was done need to be carefully reported.
At 25 ◦ C, single-strength juice, 42 ◦ Brix, and 65 ◦ Brix have
apparent viscosities of about 20 cP, 2500 cP, and 8000 cP,
respectively. Apparent viscosities of up to approximately
17,000 cP at 30 ◦ C and up to 40,000 cP at 8 ◦ C are not

uncommon for 65 ◦ Brix juice (Crandall et al., 1982).
Several other quality parameters are analyzed in partic-
ular determination of pesticide and fungicide residues as
well as processing contamination and product adulteration
are common but beyond the scope of this chapter. Read-
ers interested in those topics may consult other references
(Praschan, 1975; Kimball, 1999a).

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Food safety of processed products
As previously discussed, most microbial issues for both
whole and processed oranges involve controlling spoilage
organisms that limit shelf life of product and cause eco-
nomic loss. Oranges, especially for the fresh market, are
ideally produced using good agricultural practices (GAPs)
which are a set of guiding principles used to help minimize
the risk of microbial food-borne illness associated with
fresh produce (FDA, 2008; AFDO, 2009). These principles
include control of factors such as the quality of the water
used for irrigation and at the packing house, the sanitation
of field and shipping containers, and the hygiene practices
of workers.
The FDA is the government agency responsible for the
safety of juice products, including orange juice. Juice pro-
cessing plants are subject to inspection by the FDA, who
ensure that plants are producing and packaging juice ac-
cording to federal food safety standards. All plants are
required to produce orange juice following good manufac-
turing practices (sometimes known as current good man-
ufacturing practices [cGMPs]). This set of rules covering
important general principles such as sanitary design, con-
trol of pests, hygiene of personnel, and others must be
addressed and followed by all food manufacturing plants
and can be found in 21 CFR Title 110.
Owing to food-borne outbreaks associated with fresh
fruits, vegetables, and juices, mandatory HACCP was
instituted in all juice processing and packaging facilities

Concentrate
Frozen concentrate is characterized in a similar way as
single strength juice regarding SSC and TA, color, and so
on. Rheological properties of orange juice are critical for
handling, that is, pumping and blending or reconstituting.
Viscosity of juice concentrate is determined using a rotating
viscometer. Determinations are commonly done at 30 ◦ C