Mechanical and Temperature Effects on Shelf Life Stability of Fruits and Vegetables - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 48

and distribution. Miller and Delwiche 36 reported that bruising due to physical injury
during harvest is the most common problem among peaches, where as much as 10
to 30% of the fruit may suffer bruises. In Denmark, about 20% of peaches and
nectarines at retail are bruised. 32 Bruises cannot be identified immediately but appear
later as brown discolorations in the injured flesh due to enzymatic browning reaction.
Pears are also susceptible to bruising by impact. After sizing, 82% of “Bartlett”
pears have accumulated bruises due to impact. 37 Bruising in pears caused by impact
was recorded to be 14% at the pickers' bag, 26% at the field bin, and 38% after
dump. Mitchell 37 found that all fruits can be bruised if dropped from a height of 16
in., 78% can be bruised at a drop height of 12 in., 56% at 9 in., 44% at 6 in., and
40% at 4 in. Chen and co-workers 38 reported that different varieties of pears differ
infirmness, susceptibility to impact, compression damage, and response to storage
at 0°C and subsequent ripening at 20°C. Asian pears are bruised more easily than
European pears because they do not change texture after picking and storage at 0°C
for several months. Pears often show friction discoloration that appears as diffused
brown skin discoloration especially at high points on irregular fruit surfaces. 39
Excessive compressive forces from the adjacent potato tubers in a pile may cause
aflattened or sunken area known as a pressurebruise . A disorder that cannot be
detected on the surface also resulting from rough handling is blackspot , which is
characterized by the discoloration of potato tissue just beneath the skin. Bruising in
potatoes occurs when tubers are stored and stacked at heights of 3 to 4 m, 40 which
causes an excessive compressive load at the bottom of the pile. The tissue that is
bruised is more or less badly deformed and damaged depending on the severity of
the defect. The relationship of stack height and the incidence of bruising is shown
on Table 2.3 , where incidence of bruising appears to be less when air during storage
is humidified at 90 to 95% relative humidity. The unsuitability of potatoes for
industrial processing is caused mainly by bruise damage, i.e., blue discoloration and
hypodermic damage or blackspot .
Deterioration through mechanical injury is the most serious problem among
bananas. Thus, careful attention is required in handling during packaging, transport,
storage, and marketing. Impact damage on bananas is not discrete because it occurs
first to the latex vessels running longitudinally in the banana skin. 41 Consequently,
bananas are very prone to develop a dark brown surface coloration that has an effect
on perceived quality disproportionate to the volume of bruised flesh which more
truly reflects eating quality. Abrasion and bruising are also observed in papayas, and
is manifested as latex stain and dark green stains, respectively, which will rapidly
soften and decay. 23 Causes of these injuries are the incorrect use of harvest instru-
ments, contact with rough surfaces, dropping of fruits, and excessive movement of
fruits during transport.
Mature green tomatoes can be bruised significantly (5 to 45%) after dropping
the fruits on their opposite sides at a height of 20 cm. 42 Tomatoes in the breaker
stage were susceptible to bruise with 15 to 75% incidence of internal bruising.
“Spartan Banner” onions were subjected by Timm and co-workers 43 to drop tests.
It was observed that dropping the bulbs by only 5 mm onto a flat steel surface
resulted to a bruising incidence of 20%, while drops at 17 mm caused bruises in all
bulbs. In packing lines, several drops are experienced by the bulb. Onions are