80 Produce Degradation: Reaction Pathways and their Prevention
dropping, and shearing of produce will decrease postharvest losses, improve quality,
and enhance growers’ returns. This chapter is a review of some factors that influence
susceptibility of produce to mechanical damage and the biochemical effects of such
injury on produce quality.
During the preharvest stage of development, fruits and vegetables may be sub-
jected to mechanical stresses from a variety of sources (e.g., wind, rain, hail, and
compression of developing fruit due to adjacent fruit or limbs), and these stresses
can have a pronounced effect on the eventual appearance of the product. Mechanical
stress can be separated into two general types: mechanical perturbment and physical
wounding.^4 The former, while not resulting in a direct wound to the product, can
result in distinct alterations in its growth and development, altering the eventual size
and shape of the product. Physical wounding is perhaps the more readily recognized
form of mechanical damage in that it causes a physical injury (a mechanical failure)
to the tissue. Types of mechanical stress include friction, impact, and compression,
and these lead to one or more types of tissue failure (cleavage, slip, bruising, and
buckling), which result in subtle to pronounced alterations in the appearance of the
product.^4
Injury may also be related to harvesting, hauling, and packing, resulting in cuts
and bruises of differing severity. Minor wounds provide entry points for postharvest
pathogens, which invariably leads to decay. Postharvest, mechanically induced dam-
age may be caused by loading compression, impact, and vibration as in normal
packing lines where damage results from forces such as pressure between fruit and
machinery, surface abrasion, and handling.^5 Other factors that determine the differ-
ences in bruising susceptibility to a given force include packaging, transportation
and harvesting methods, storage conditions, and produce characteristics.^6
Fresh-cut processing involves the deliberate wounding of fruit and vegetable
tissues to provide a product that requires less handling by the consumer. Fresh-cut
products are usually washed, packaged, and maintained with refrigeration. The
demand for convenience and freshlike produce has resulted in the rapid growth of
this industry. Fresh-cut produce is the fastest growing food category in the super-
market, with an estimated retail market of $14 billion in the year 2003. Cutting
removes the natural protection of the epidermis and destroys the internal compart-
mentation that keeps cells separate. The disruption of tissue and cell integrity that
results from fresh-cut processing decreases produce’s shelf life through physiological
and biochemical changes similar to those seen in tissues of fruits and vegetables
that are not fresh-cut.
4.2 WOUND RESPONSE
Responses to mechanical damage involve the generation, translocation, perception,
and transduction of wound signals to activate the expression of wound-inducible
genes.
There is clear evidence that plant tissues have evolved a highly sensitive and
efficient system for monitoring changes in their environment. Surviving cells in a
wounded plant must perceive a “death message” from killed cells in order to start
the signal processing that results in defense responses. Many structurally different