Oranges - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 398

Essential oils
On a per weight basis, the most valuable components of
citrus are essential oils. In contrast to grapefruit and tan-
gerine priced at tens of US dollars, orange essential oil is
rather inexpensive and is priced at $0.65 to $1.25 US per
pound. They are used as flavor and aroma ingredients in
foods, cosmetics, household detergents, furniture polish,
and so on. The largest component (95%) of orange essen-
tial oil is d-limonene. The rest is a mixture of terpenes and
terpene derivatives, aldehydes, ketones, esters, alcohols,
and acids that impart its characteristic aroma (see “Flavor
Chemistry and Aroma Active Compounds” section). Oil
from 'Valencia' is more desirable and valuable than early
and midseason varieties in Florida. Most orange essential
oils are recovered as cold-pressed oils. In the JBT system,
as the upper cup in the extractor lowers during juice extrac-
tion, the peel is shredded and the citrus glands are burst and
exposed. A mist of water is sprayed through a manifold of
nozzles mounted on the upper cups, forming an emulsion
that flows into a finisher that removes small peel particles.
Brown oil extractors (BOEs) are separate from juice extrac-
tors. Oranges are conveyed into rollers with over three mil-
lion small, sharp blades that puncture the fruit peel. The
puncturing rollers are immersed in a shallow vat with water
where the oil emulsion is formed. For both JBT and Brown
systems, the oil emulsion is separated using two centrifu-
gal separators in series. The first centrifuge separates the
0.5-3.0% emulsion into a 50-70% concentrated emulsion
and an aqueous discharge that is recycled back to the ex-
tractor. The second centrifuge or polisher produces 100%
oil and a sludge stream. The oil is then stored in a cold
room to solidify and separate waxes from the oil in a pro-
cess called “winterization.” The overall yield of recovery of
cold-pressed oil ranges from 55% to 70%. A small fraction
of the recovered oil (about 5%) is lost in the aqueous and
sludge streams.

800 to 900 g/liter in an aseptic finisher, packaged, and in
most cases frozen. Recently, high-density pulp pasteurizers
have been developed where 800-900 g/liter pulp recovered
from the second finisher setup for a “tight finish” is pas-
teurized. To ensure uniform pasteurization, on-line static
mixers are used. The advantage of pasteurizing high den-
sity pulp is the ability to aseptically package without any
risk of contamination during the third finishing step of the
conventional system. Approximately 50 kg of pulp per ton
of oranges can be obtained.

Dry pulp pellets
In total weight, the largest by-product of orange juice pro-
cessing is dry pulp pellets. About 55% of the wet mass of
oranges is peel and rag (also referred as “pulp” and not to
confuse with pulp from burst juice sacs). Although peel can
be fed to cattle without drying, it quickly ferments and is
impractical to ship long distances. The energy value for dry
citrus pulp for beef cattle is 1.5 kcal/kg pulp. It is high in
digestible energy and fiber while low in digestible protein.
Dry pulp pellets contain approximately 10% moisture, 6%
protein, 3% fat, 10% fiber, 63% nitrogen-free extract, and
7% ash (Kesterson and Braddock, 1976). Citrus pulp can
constitute up to 40% of a healthy cattle diet. Adequate dry-
ing and addition of molasses make citrus pulp very palat-
able to cattle. During juice extraction, peel is conveyed and
stored for a short period of time in peel bins. Then the peel
is conveyed to a hammer mill where it is shredded. Size
reduction is necessary to maximize water removal during
pressing and drying. Lime (calcium oxide or, more com-
monly, calcium hydroxide) is added (0.2-0.5%) before, af-
ter, or before and after the hammer mill as a processing
aid to neutralize the acidic peel and deesterify pectin. Peel
and lime are allowed to react in a reaction conveyor where
deesterified pectic acid reacts with divalent calcium to pro-
duce calcium pectate, liberating methanol and water. Then,
reacted peel is pressed. Press cake with 65-75% moisture
content and 9 ◦ Brix press liquor are recovered. The press
cake is then conveyed to a steam tube or direct fire ro-
tary drier. Press liquor (typically 8 ◦ -15 ◦ Brix) is typically
concentrated into molasses in a multiple-effect “waste heat
evaporator” that uses residual heat from steam produced
at the peel dryer to heat the first effect of the evaporator.
Molasses are concentrated to approximately 45 ◦ Brix and
then fed back to the peel at the beginning of the reaction
conveyor to reduce overall moisture content and facilitate
drying. The set of unit operations and equipment used to dry
citrus pulp is commonly referred as the “feed mill.” Despite
the integration of the feed mill with the waste heat evapo-
rator, and the energy efficiency associated with the use of a

Pulp and pulp wash
Among orange by-products, pulp has perhaps the fastest
growing market in recent years due to growing beverage
markets in Asia that use it as a base. To produce pulp,
extracted juice is first finished through a finisher with a
20 mesh screen. Then the pulpy juice is pumped to a hy-
drocyclone, where defects such as embryonic seeds and
small peel particles are removed by difference in specific
gravity. In a conventional system the pulpy juice passes
through a second finisher where approximately 500 g/liter
pulp (see “Quality Assurance” section) is recovered and
pasteurized. Finally, pasteurized pulp is concentrated to