Oranges - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 387

the slowing economy that was followed by a recession at
the end of the decade.

Postharvest physiology
In the United States, California is the largest producer of or-
anges for the fresh market. China and Mexico also produce
fruit that is mostly consumed in the fresh market. Fruit
intended for the fresh market is cultivated and harvested
manually with additional precautions compared to fruit that
is processed into juice, mostly to preserve cosmetic appear-
ance. Like all citrus, orange is a nonclimacteric fruit and
does not ripen after harvest. After harvesting it shows very
little ethylene production and exhibits no respiratory peak.

HARVEST, POSTHARVEST PHYSIOLOGY,
PACKINGHOUSE OPERATIONS, AND STORAGE
TECHNOLOGIES

Harvesting
Harvesting can account for up to about 40% of the total
delivered-in costs of oranges. Oranges are harvested mostly
by hand. Typically, orange pickers first fill bags they carry
and then dump them in 400-kg pallet bins or tubs that are
dumped into 20-ton trucks. In the United States, where la-
bor is expensive and immigration laws threaten to shorten
the availability of low-cost immigrant worker labor, me-
chanical harvesting systems have been recently developed.
Mechanical harvesters are estimated to reduce harvesting
costs by up to 50%. Trunk shakers and canopy shakers are
the most commonly used. Trunk “shake and catch” systems,
as the name indicates, grabs the trunk of the tree and shakes
it at selected intensities and oscillation frequency that at-
tempt to maximize fruit detachment and minimize tree dam-
age. The catching system prevents the fruit from contacting
the ground, reducing the potential for fruit contamination
with soil micro-organisms. After detachment, the fruit is
conveyed automatically to the truck. These systems can
harvest about 90-140 trees per hour. Another system is the
canopy shake and catch that uses a stack of spokes or rods
radiating on from a common mast and arranged on parallel
planes. Two systems, one on each side of the tree, penetrate
the canopy at a selected angle and shake it with oscillatory
movements as they simultaneously advance along the row
of trees. Canopy shakers can harvest up to 400 trees per
hour. Tree spacing and pruning is critical to the selection
and effective use mechanical harvesters. Although mechan-
ical harvesting increases the amount of trash coming into
the processing plants (Spann and Danyluk, 2010) and in-
creases processing costs, there is no precise estimate of the
economic impact. There is no evidence of significant de-
crease in fruit yield due to mechanical harvesting. For late
'Valencia' varieties, where young fruit is already set before
mature fruit is harvested, mechanical harvesting requires
the application of abscission chemicals to facilitate mature
fruit drop with mild shaking to prevent young fruit from
falling. Abscission chemicals are currently undergoing the
approval process in the United States. The University of
Florida maintains a website that lists current research on
mechanical harvesting of citrus fruit (UFL, 2011).

Packinghouse operations
Packinghouse operations aim at extending the storage life
of the fruit while retaining its quality. Hence much effort
is directed at minimizing the likelihood of fungal contami-
nation of fruit (see “Microbiology of Fresh and Processed
Oranges” section). After dumping, trash (leaves and twigs)
is eliminated and fruit is presized. Fruit is then sprayed
with water and washed with soap as it is conveyed onto
rollers with spinning brushes that remove dirt. A set of hard
brushes followed by soft brushes are common. Fruit is then
conveyed onto dripping rollers and into a drying tunnel,
where hot air is blown with a fan to dry the fruit. A pregrade
stage eliminates off-color and blemished fruit. Fungicide is
then applied. There are three fungicides approved by the
US Food and Drug Administration, Canada, the European
Union, and Japan: Imazalil, sodium o-phenylphenate, and
thiabendazole. The Codex Alimentarius requires residue to
be under 5 ppm, 10 ppm, and 10 ppm for each fungicide, re-
spectively (Ritenour et al., 2003). These fungicides cannot
be applied to oranges marketed as “organic.” Proper pack-
inghouse sanitation accompanied by frequent monitoring
of fungal spores in the air is critical to the minimization of
fungal infections. Fruit is then waxed to minimize moisture
loss (Mukhopadhyay, 2004). Wax is sprayed on the surface
of the fruit and dried in hot air tunnels. Final grading and
sizing precedes final labeling and packaging. Final grading
is done with optical sorters that separate fruit by size and
color.

Storage
After the final grading, oranges then can be stored at
32 ◦ -34 ◦ C and 90-98% humidity in wooden crates or
85-90% in carton containers. Lower humidity is needed
to avoid carton deterioration, and wooden crates are grad-
ually being replaced by more sanitary plastic containers.
Cold storage can cause chilling injury but minimizes fruit
pitting, a physiological disorder caused by the decrease in
oxygen concentration that results from waxing the fruit.