Biomedical Engineering Reference
In-Depth Information
80
b
Box position
70
Top Boxes
Middle Boxes
Bottom Boxes
60
b
50
40
30
20
a
a
a
a
a
a
10
a
a
a
a
a
a
a
aa
a a
a
a
a
a
a
0
25 - 30
2 - 5
5 - 7.5
5 - 10
7.5 - 10
10 - 15
16 - 20
20 - 25
Frequency Treatments (HZ)
FIGURE 2.1
Percent unsalable strawberries after vibration at different frequencies. Loca-
tion or frequency treatments with the same letter above the bar are not significantly different.
(From Fischer, D., Craig, W. L., Watada, A. E., Douglas, W. and Ashby, B. H.,
Appl. Eng.
Agric.
, 8, 366, 1992. With permission.)
Tomatoes in plastic containers were subjected to dynamic compression due to the
vibrations. The compressive stress on the bottom was 2 to 3 times that of the static
conditions at the resonance frequency. Damage of the vibrated ripe tomatoes in
corrugated cardboard boxes occurred under vertical acceleration of 10 m/s
2
in
30 min. A high percentage of unmarketable weight loss (more than 55% in top
boxes), after subjecting strawberries to vibration frequencies between 7.5 to 10 Hz,
of 5 to 10 Hz caused the most damage to strawberries and table grapes with the
fruits in top boxes sustaining the most damage.
EFFECTS OF MECHANICAL INJURY ON THE QUALITY
AND SHELF LIFE OF THE PRODUCE
Depending on the physical characteristics of the produce, mechanical damage may
cause severe deterioration of quality and shortened shelf life. Injured fruits and
vegetables increase their respiratory activity. Transpiration also increases because
the exposed surfaces of the produce caused by cuts, punctures, cracks, abrasion, and
tears serve as avenues of water loss. Through the exposed surfaces, microorganisms
can infect the product and accelerate its deterioration. Since the cell contents are
exposed, oxidation and a host of other reactions occur, impairing the sensory quality
and shortening the shelf life of the produce. Due to damaged tissues, ethylene
production also increases, and this triggers other deteriorative changes leading to
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