Mechanical and Temperature Effects on Shelf Life Stability of Fruits and Vegetables - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 42

P UNCTURE
The produce may be punctured because of the presence of stem or pedicel, which
has not been detached at harvest. Punctures can also be inflicted by fingernails,
protruding sharp objects, and surfaces of containers.
T EARS
Tearing is common to leafy vegetables resulting in excessive water loss and increased
respiration leading to desiccation, discoloration or decay of the affected leaf.
T EMPERATURE E FFECTS
Fresh produce may not only suffer mechanical damage caused by physical handling,
but disorders may result from undesirable storage temperatures. Certain fruits and
vegetables are sensitive to temperature variations during handling and storage. Low
temperature results in chilling or freezing injury, which may be manifested by a
water-soaked appearance, pitting, discoloration or failure to develop the proper
ripening pigments, and the development of strong off-odors. On the other hand,
heat injury is sustained by a produce due to exposure to the sun after harvest, or
with any warm surface like the soil or a wall heated by the sun. Weight loss,
softening, discoloration, and eventual desiccation of the affected tissue are common.
The causes and effects of injuries sustained by fruits and vegetables are summarized
in Table 2.1 .
MECHANICAL INJURY
During the postharvest life of a produce, handling events contribute to cumulative
damage decreasing its quality and storage life. In a baseline study for tangerines, it
was reported that “non-handled” fruits (those that were carefully picked and packed)
incurred only 1% loss due to decay compared with the normally “handled” fruits,
which had 20% loss due to decay after 2 weeks at 21°C. 8 A third of the damage was
inflicted during manual picking and the majority was inflicted by the polisher brushes
in the packinghouse.
Mechanical causes of failure in fruits and vegetables can be classified as cracking
or splitting, slip, and bruising. 9 In the case of potatoes, cracking may occur either
at the center of the tuber due to tensile and shear stresses, or around the outside of
the tuber due to tensile hoop stresses. Tensile hoop stress on tomatoes can cause
splitting. Failure by slip is due to compression, but actual failure takes place by
shearing with two parts of the produce sliding past each other, along a plane 45° to
the compressive load. Crushing has been observed in products subjected to impact
and compression such as potatoes, unripe plantains, pineapples, unripe papayas, and
unripe pears. Bruising results when the cells below the skin or rind are ruptured and
the cellular contents are subjected to enzymatic oxidation. This is observed in
potatoes, apples, and pears. The incidence and cause of mechanical injury on selected
fruits and vegetables is shown in Table 2.2 .