Oranges - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 395

(12 ◦ Brix) packaged in half-gallon or one gallon contain-
ers, as 40 ◦ Brix distributed to food service businesses, or
as 40 ◦ Brix in 8 oz cans to be sold at grocery stores and
reconstituted by the consumer.

method using the correlation between SSC and juice
density. Prior to determining density, the juice is exposed
to vacuum to eliminate microscopic air bubbles that can
affect density readings. The conversion to SSC is compen-
sated for temperature effects. This process is automated in
Florida.
Titratable acidity is determined by titration with nor-
malized (0.1562 N) sodium hydroxide solution to pH 8.2.
These determinations are performed automatically. In the
quality assurance laboratory, these determinations are also
performed in samples of entire batches of extracted juice.
In most cases SSC is then determined by temperature-
compensated refractometry, and TA is determined by man-
ual or automatic titration.
Oil content is also critical. During the process of ex-
traction oil is incorporated into the juice, and a high con-
centration of oil, typically above 0.04% v/v, can produce
a burning sensation in the mouth of many consumers. Oil
is extracted with iso-propanol (1:1 juice:iso-propanol), dis-
tilled, and titrated with bromine-bromate using methyl or-
ange as an end point indicator. Recoverable oil is expressed
as percentage volume of d-limonene, which is brominated
preferentially over methyl orange.
Because different levels of pulp are preferred by differ-
ent groups of consumers, it is important to quantify and
adjust pulp content in orange juice. Owing to its size dis-
tribution, pulp content is characterized as sinking pulp and
floating pulp. Sinking pulp is determined by centrifugation
for 10 min in 50 mL tubes at 1500 rpm in a centrifuge with
a diameter of 29.2 cm (between the bottoms of opposed
tubes under centrifugation conditions). The volume of set-
tled pulp is recorded and the content is reported as percent-
age volume. Commercial orange juice typically contains
8-12% pulp.
As described in the “Pasteurization” section, orange juice
is pasteurized to inactivate PE. Although not assayed all the
time, PE activity determinations are not uncommon either.
Pectinesterase cleaves the methoxy groups of pectin re-
leasing methanol and hydrogen ions (protons) that cause
a decrease in pH. Because the pH of the juice is already
very low and below the optimal, and the change in pH in
the juice is extremely small, PE activity cannot be deter-
mined directly in the juice. Activity of PE is determined
by titration using 50 ml of a 1:4 juice:1% high methoxy
pectin at 30 ◦ C. The pH is first adjusted between 7.6 and 7.8
with a sodium hydroxide solution, then 0.10 ml of 0.05 N
sodium hydroxide solution is added. Then the time required
for the solution to return to the initial pH (7.6 to 7.8) is
recorded, and the pectin esterase units (PEU) are reported
in equivalents of sodium hydroxide per minute per milliliter
of juice.

Not from concentrate
Prior to pasteurization, NFC is deaerated to remove oxygen
and minimize oxidation reactions. Deoxygenating is done
by heating the juice to 50 ◦ -60 ◦ C and spraying it into a vac-
uum tank. Oxygen and volatile compounds flash out of the
juice. For juice with very low oil content vapors removed
are recondensed by cooling and mixed back with the juice.
For juice with very high oil content such as in the case of
late season 'Valencia' juice, oil is partially removed and not
recondensed. The juice is then pasteurized, and depending
on the quality of the juice, it can be either pumped to the
packaging line or stored in refrigerated tank farms. With
the increased demand for NFC, large processors have built
3.7 to 7.5 million liter storage tanks (Braddock, 1999b).
As with concentrate storage, aseptic tanks' headspace is
blanketed with nitrogen. Because of the value of such a
large volume of juice and because of the elevated cost of
sanitizing, these enormous storage tanks are kept aseptic
for over a year. To ensure continuous smooth filling opera-
tion, aseptic buffer tanks are used between the pasteurizers
or storage tanks and fillers. Buffer tanks are also used for
blending. Juice blending is common especially to compen-
sate for low SSC, high TA, and/or typically pale color of
juice from early season fruit.

Shelf-stable orange juice
Despite its convenience, shelf-stable orange juice is not
popular in the United States because of cooked off-flavors
developed during extended high-temperature pasteuriza-
tion. It is often used mixed with alcoholic beverages, hence
also called “cocktail juice.” However, in other countries
where the market for refrigerated NFC has not developed,
shelf-stable juice is more commonly consumed (Brown and
Lee, 2008).

QUALITY ASSURANCE METHODS OF ANALYSIS

Single-strength juice
The quality of orange juice is dictated by the composition
of the freshly extracted juice as well as by processing
and storage conditions. As mentioned earlier, the first
two quality parameters to be measured are SSC and TA
expressed as citric acid. By law in Florida, soluble solids
content is determined in the “test house” by the hydrometer