Biomedical Engineering Reference
In-Depth Information
damage was intermediate in bagmaster cartons where apples were packed in poly-
ethylene bags.
When packaging perishable produce, two important principles should be
observed: individual specimens should not move with respect to one another or the
walls of the package to avoid damage due to vibration, and the package should be
full without overfilling or tight packing, which increases compression and impact
bruising.
2
To cushion the specimen from damage, liners, tray cups of paper or
polystyrene foam, and nets have been employed. If packed in woven jute sacks or
nets, commodities like root crops and onions should be stacked in unit loads on
pallets or pallet boxes. The packaging material chosen should provide adequate
ventilation and protection to the packaged produce.
C
URING OF
R
OOT
C
ROPS AND
T
UBERS
Curing is an important postharvest operation among root crops like Irish potatoes,
sweet potatoes, and onions. It is carried out in order to heal harvest-inflicted injuries
and also to close the neck of onions and garlic. Breaks in the periderm in injured
root crops can serve as an entrance for pathogens, induce water loss, and increase
metabolic activity. Following wounding of the tuber tissue, suberization of the cells
on the surface of the wound takes place, which involves the deposition of suberin
along the cell walls.
80
Suberin, which serves as a barrier to water loss and microor-
ganisms, is an insoluble polymeric material attached to the cell walls of periderms,
including wound periderm among aerial plants.
81
Van Es and Hartmans
80
outlined
the following event of wound healing:
The wound periderm is formed at the onset of primary suberization. A few cell layers
away from the wound surface, new cell walls are formed parallel to the wound surface.
This gives rise to a phellogen (cork cambium), which serves as the basis for wound
periderm formation: the phellogen cells form a number of phellem cells parallel to
the wound surface. These phellem cells subsequently become suberized and this is
known as secondary suberization.
For conditions in the Netherlands, Meijers
82
recommended a curing temperature
of 12 to 18°C and a relative humidity of 80 to 95% for 10 to 14 days. Wound healing
is faster when temperatures are high. No wound tissue appears to be formed at a
relative humidity of 30%. While in saturated atmospheres, curing is delayed due to
the proliferation of the cells on the surface of the wound.
82
Wound healing for sweet
potatoes occurs in two stages.
83
The first stage is the deposition of suberin on the
cell walls adjacent to the lesion, followed by the formation of the wound periderm.
Temperatures around 30°C and relative humidities of 85 to 95% are optimal for
wound healing. The curing period used to be 14 days, but the present recommenda-
tion for sweet potatoes is 4 to 7 days.
84
The range of 4 to 7 days is allowed for
different responses to the curing process dependent on environmental conditions and
germplasm variability. Studies carried out by Walter and Schadel
85
showed that the
initial response to wounding was the deposition of lignin-like materials rather than
suberin. Walter and co-workers
83
confirmed the lignification phase of wound healing,
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