86 Produce Degradation: Reaction Pathways and their Prevention
height of drops during onion harvest and handling appear to be best suited for
minimizing mechanical damage in onions. Mechanical damage also stimulates
sprouting of onions during storage.^55 An impact rate of 1.5 m/sec onto a firm surface
and a static load of 400 N are considered critical from the viewpoint of subsequent
keeping quality of watermelons.^56 A study of the damage caused to Bykovskii 22
watermelons by mechanical harvesting and transport during storage at 12°C (80%
relative humidity) for 1 month, followed by 1 month at –6°C (90% relative humidity),
indicated that the greatest losses occurred in abraded fruit (none acceptable after 1
month) and in bruised fruit (67% acceptable after 1 month, 17% after 2 months),
while controls showed 100% acceptability after 30 days, 97% after 40 days, and
87% after 60 days. Solo papaya (Carica papaya L.) fruit removed at different points
from a commercial packing house showed that skin injury due to mechanical damage
increased as fruit moved through the handling system.^57 The occurrence of green
islands — areas of skin that remain green and sunken when the fruit is fully ripe
— was apparently induced by mechanical injury. Skin injury was seen in fruit
samples in contact with the sides of field bins, but not in fruit taken from the center
of the bins. When bruise-free fruit at different stages of ripeness (5 to 50% yellow)
were dropped from heights of 0 to 100 cm onto a smooth steel plate to simulate
drops and injury incurred during commercial handling, no skin injury occurred,
although riper fruit showed internal injury when dropped from > 75 cm. Fruit (10
to 15% yellow) dropped onto sandpaper from a height of 10 cm had skin injury
symptoms similar to those seen on fruit from the commercial handling system. These
results suggest that abrasion and puncture injury were more important than impact
injury for papaya fruit.
4.3.3 FRESH-CUT PRODUCE
Wound severity in cut produce may also be affected by cultivar, preharvest crop
management, physiological maturity, and degree of cutting-induced injury.^58 The
extent of physical damage that results from cutting fruit tissue affects the intensity
of physiological stress, microbial growth, and product shelf life. Inner tissue expo-
sure facilitates contamination by the epithelial microflora. It also increases respira-
tion rates, decompatmentalization of enzymes and substrates, total moisture loss,
and overall sensory quality.59,60 Very sharp cutting tools limit the number of injured
cells, unlike blunt cutting instruments, which induce injury to cells many layers
below the actual cut.^15 Fruit pieces prepared with sharp cutting tools retained mar-
ketable visual qualities longer than the same fruit processed with dull cutters.^61 Pre-
and postharvest conditions, tissue anatomy, cell-to-cell adhesion, cell turgor, and
cell wall strength are factors contributing to the bruising response,^62 and the mag-
nitude of these factors seems to be affected by ripening and variety.^63
4.5 HARVESTING
Harvest methods and conditions influence mechanical stress. Kolodyaznaya and
Zakatova^64 indicated that mechanically harvesting carrots could considerably
increase the percentage of mechanically damaged tubers and that susceptibility may