Mechanical Injury of Fresh Produce 103
autumn-grown ones. Activity of wound-induced PAL activity in lettuce browning
increases with an increase in storage temperature from 0 to 25°C. PAL stimulates
phenolic metabolism and consequent tissue browning. A heat shock at 50°C for 90
sec protected fresh-cut lettuce tissue against browning, helped retain greenness, and
decreased subsequent production of phenolics when applied either after or before
wounding.^149
4.12 SUMMARY
The most important key to quality maintenance of fresh fruits and vegetables is
careful handling before and after they are harvested. Careless handling may cause
damage to produce that could be either internal or external. The effects of the injury
are immediate in that wound signals are rapidly propagated to adjacent and distant
tissues. Subsequent effects involve abnormal physiological breakdown during han-
dling and storage. Bruises and other mechanical damage not only detract from the
appearance of the product but are good avenues of entrance for decay organisms.
Variety, preharvest crop management, temperature, water content, and physiological
maturity are some of the factors that influence susceptibility to mechanical damage.
Appropriate harvesting implements and conditions are also essential for maintaining
product quality.
Postharvest mechanically induced damage may be caused by overfilling of
crates, excess movement of harvested product during in-field transport, loading
compression, impact and vibration from forces such as pressure between fruit and
machinery, and surface abrasion and handling. Symptoms of injuries, particularly
minor cuts and bruises incurred during harvesting, handling, grading, and packaging,
may be difficult to detect at the early stages. Subsequent physical and physiological
changes, the severity of which is influenced by factors such as the commodity,
severity of injury, maturity, storage temperature, and relative humidity during stor-
age, handling, and transportation, could lead to considerable product deterioration
that is quite visible by the time the products reach retail or consumer levels. Pro-
tective measures throughout pre- and postharvest handling can reduce damage.
Knowledge of the types of injuries and their response mechanisms will help us to
devise methods to limit the undesirable physical and physiological effects of mechan-
ical damage. Advances in detecting mechanical injury-related disorders and future
research in this area should improve screening and sorting methods and reduce the
percentage of product lost due to mechanical damage.
REFERENCES
- Baugher, T.A., Hogmire, H.W., Jr., and Lightner, G.W., Determining apple packout
losses and impact on profitability, Appl. Agric. Res., 5, 343–349, 1990. - FAO, Prevention of postharvest food losses: Fruits, vegetables and root crops, Food
and Agriculture Organisation of the United Nations, Rome, Italy, 1989. - Wright, W.R. and Billeter, B.A., Marketing loss of selected fruits and vegetables at
wholesale, retail and consumer levels in the Chicago area, U.S. Dep. Agric. Res. Rep.,
1017, 1975.