Mechanical and Temperature Effects on Shelf Life Stability of Fruits and Vegetables - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 46

Larsson 14 studied the incidence of mechanical injury of potatoes in Sweden and
reported that tuber damage in the packing line was equivalent to or even greater
than the damage sustained in the harvesting process. Misener and co-workers 15
conducted a study to identify the incidence and magnitude of mechanical injury
sustained by potatoes during commercial handling and packing operations in Eastern
Canada. Injury increased incrementally as the tubers traveled through the packing
line. The number of drops and cumulative drop heights were significant contributors
to the increased damage index. Shatter bruise (cracking) appears as a break in the
surface of potato that may penetrate deeply into the tuber. Mechanical injury in
potatoes refers to cutting, breaking, or any other damage mechanically inflicted on
the tuber. 16 Shatter bruise is an external damage that can be detected upon close
inspection. It occurs more frequently as tuber turgidity increases, but generally
decreases with maturity. Loading and unloading during storage and transportation
were singled out by Meyer and co-workers 16 as the likely causes of shatter bruise
in potatoes. Hand loading is less injurious to tubers than dump loading. Shatter
bruises of potatoes may also occur in the bottom of a rail car due to the combined
effects of compression and vibration. Grant and co-workers 17 reported that the
relatively high frequency of shatter bruise in potatoes occurs during transport, while
the amount of severely damaged tubers due to transport shock and vibration is
relatively low. Bruising is aggravated by low temperatures during handling.
In root and bulb crops, which are manually harvested, mechanical injury will
likely result from digging tools or lifting of the root. Mechanical injury to carrots
is inflicted during harvesting. Apeland 18 reported that as much as 30% of carrots
may be broken during mechanical harvesting and about 13% could be split. Tucker 19
observed that roots damaged before storage are predisposed to rotting and weight
loss during storage. Losses of carrots during refrigerated storage in Taiwan were
mainly due to bacterial infections that enter through cracks and broken taproots. 20
Physical damage of lettuce transported in mechanically refrigerated trucks was
a major problem in the produce market, 21 where as much as 63% of the heads showed
damage. In Thailand, Ketsa 22 investigated the effect of prepackaging on the physical
damage to fresh lettuce heads, namely, by (a) wrapping untrimmed heads in news-
paper and packing in bamboo baskets; (b) wrapping trimmed heads in newspaper
and packing in collapsible plastic crates with lids; or (c) wrapping trimmed heads
in stretch film and packing in collapsible plastic crates. After refrigerated transport
for 12 h, damage was 28.1, 23.1, and 19.5%, respectively, with the heads wrapped
in plastic retaining the greatest degree of freshness.
Since apples have an abundance of air-filled interstitial spaces in their flesh, they
are not prone to cracks during handling. Only about 1 to 4% of the apples are cut
and 3% are punctured in a study of commercial packing lines conducted by Brown
and co-workers. 6 On the other hand, produce with less air-filled interstitial spaces
incur injury appearing as cracks, breaks, or splits as in the case of potatoes. In
papayas, physical damage is in the form of cuts and punctures, arising from the
improper use of harvesting equipment, and contact of harvested fruits with rough
surfaces, fingernails, and adjacent fruit stems. 23 Crushing of fruits such as papayas
and bananas during rough handling is common because of increased softening of
the fruits during ripening.