Photo Mariana Jooste
Figure 5. Harvested fruit in bin covered with a wet blanket to increase the relative humidity around the fruit
ceptible plum cultivars. Regarding
the period between arrival of the
fruit at the pack house and the end
of forced air cooling, we found that
fruit should be packed and be under forced air cooling within 6 h
after harvest, or must be precooled
to 0 °C or just above the dew point
of the pack house to have the least
moisture loss. Remember that if
fruit is precooled using room cooling, more space is required compared to forced cooling, since produce must be spaced such to allow
adequate cooling. It must also be
kept in mind that condensation will
form on fruit precooled to 0 °C during packing. Such fruit may become dirty on the pack line and
there is a risk of decay development
during cold-storage.
We also found that, if fruit is precooled to 0 °C under room cooling
conditions (and not forced air cooling), it is better to keep the fruit at
0 °C for 72 h and not for a shorter
duration. If fruit is precooled for a
shorter period than 72 h at 0 °C
under room cooling conditions, we
found that a relatively large vapour
pressure deficit is created at the
onset of forced air cooling between
the then still warm fruit and the
cold delivery air, which will drive
moisture loss.
Our results also showed that less
shrivel will develop if fruit are precooled prior to forced air cooling
compared to not receiving precooling – even when fruit is packed as
soon as possible after harvest and
force air cooled. However, it should
be kept in mind that mass loss will
increase with an increase in precooling time of the fruit at 0 °C or
just above the dew point of the
pack house. Keeping fruit at ambient temperatures, especially for
longer than 24 h, is not recommended as it will lead to high moisture loss, generating a bigger risk
for shrivel development. Although
we found that precooling fruit can
redu ce moisture loss and shrivel, we
found that there is a tendency for
fruit that was precooled to 0 °C or
just above the dew point of the
pack house, to be softer after coldstorage compared to fruit packed
and put under forced air cooling
within 6 h after harvest. We also
found that, regardless of treatment
and although fruit was packed in
perforated bags, fruit lost approx.
1% in mass during cold-storage.
Since our results showed that only a
2% mass loss causes shrivel development in plums it is of critical importance that optimal packaging
solutions must still be found for
plums and that breaks in the handling chain after forced air cooling
must be eliminated to minimize
mass loss during cold-storage.
For the complete list of stone fruit
handling protocols, from farm to
ripening of produce overseas,
please visit http://
www.hortgro.co.za/production technical-information/technicalinformation/handling-protocols/
stone-fruit/
Reference
HORTGRO, 2014. Key deciduous
fruit statistics. www.hortgro.co.za
Theron, J.A., 2015. Moisture loss
studies in Japanese plums (Prunus
salicina Lindl.). MScAgric thesis,
Dept. of Horticultural Science, Stellenbosch University.