Bin cold storage.
During the storage period, ethylene levels were always
lower than 10 parts per billion
(ppb). For small fruit sampled from
the bottoms of the bins, fruit firmness
decreased from approximately 12.0 lbf
to 4.0 lbf after 10 weeks cold storage
(fig. 2). The greatest drop in fruit firmness
occurred within the first 4 weeks
of storage.
Using the regression equation (Pvalue
c 0.0001, r2 = 0.75) for the relationship
between changes in firmness
versus weeks in air storage for the
bins, we predicted that after 7 weeks
our kiwifruit reached the critical firmness
level for packaging (5.0 lbf). The
kiwifruit lost approximately 0.6 lbf per
week during bin storage in air at 32°F.
The difference in time to reach 5.0 lbf
can be explained by the different storage
conditions in the commercial situation.
Thus, this regression equation
can be used as a tool to predict the potential
storage time under optimum
conditions (ethylene-free air at 32°F).
Firmness measurements should be
done during the storage period to determine
the end of the bin storage period
and a safe packaging date.
Exposed kiwifruit in the tops of the
bins (the worst-case scenario for fruit
damage) lost weight at a constant rate
during the cold-storage period (fig. 2).
The use of canvas covers over the tops
of the bins reduced the rate of water
loss by nearly half. In previous work,
we have observed kiwifruit shriveling
only after fruit water-loss values exceeded
4.0% of the initial fruit fresh
weight. Bruising incidence after packaging
varied from 1.0% to 4.1%. More
bruising occurred on the last twopacking
dates
when kiwifruit
had
firmness values
equal to
or less than
4.0 lbf. Decay
was not observed
during
this cold-storage
trial.
We observed
a difference
in the
rates of fruit
softening under
laboratory
versus bin air
storage. Under
laboratory
conditions, it took 1 week longer to
reach 5.0 lbf than under commercial
bin storage conditions. This may be
due to better circulation of air around
the fruit under laboratory conditions,
or possibly the difference in the
weight of fruit upon fruit. It is important
to point out that the softening rate
of a given size of kiwifruit during ethylene-
free storage is also influenced by
orchard factors. For instance, Johnson
and others (1997) have reported the influence
of different nitrogen application
rates and the nitrogen/calcium ratios
on kiwifruit softening.