Agriculture Reference
In-Depth Information
(TA), and pH were not affected by the MAP liners. Fruit skin
colour changes were repressed on plums packed in box liners
that modified gas levels and weight loss was reduced by the
use of any of the box liners. Plums packed without box liners
(bulk packed) had approximately 6% weight loss. High CO
2
and low O
2
levels were measured in boxes with MAP box
liners. Percentage of healthy fruit was not affected by any of
the treatments during the ripening period (shelf life) follow-
ing 45 days of cold storage. After 60 days of cold storage,
fruit from the MAP box liners with higher CO
2
and low O
2
levels had a higher incidence of flesh translucency, gel break-
down and 'off flavour' than fruit from the other treatments.
harvest, but most often is expressed during post-harvest
handling (Wells
et al
. 1994). Pre-harvest fungicide applica-
tion, prompt pre-cooling after harvest, and orchard sanitation
to minimize infection sources are control strategies.
Post-harvest fungicide treatments are used to limit decay.
Grey mould is caused by
Botrytis cinerea
. This rot can
be serious during years with wet spring weather. It can
occur during storage if fruit have been contaminated during
harvest and if wounding has occurred. Avoiding mechanical
injuries, effective temperature management and post-harvest
fungicide treatments are effective control measures.
Rhizopus rot is caused by
Rhizopus stolonifer
. This rot
can occur in ripe or near-ripe plums kept at 20°C to 25°C.
Pre-cooling and storing fruit below 5°C is effective in
controlling this fungus.
Physical damage
Our previous work on impact bruising damage during har-
vesting and packaging (Crisosto
et al
. 2001) demonstrated
that most plum cultivars with flesh firmness greater than
1.4 Kg-force tolerated very well impact forces up to 245 G
(simulating impacts occurring during rough packingline
operations) (Table 10.7). During transportation, our experi-
ence with plums suggested that plums will be even less
susceptible to bruising damage during transportation than
yellow flesh peach and nectarine. At retail, bruising poten-
tial was measured by placing an IS-100 recording acceler-
ometer in the centre of the top layer of a two-layer tray
packed box. Accelerations (G) ranging from 19.1 G to
44.9 G were measured during box handling - removal from
the pallet and boxes and dropped from different heights.
Thus, accelerations measured were lower than critical
bruising thresholds for many plums with firmness equal to
or higher than 1.4 Kg-force.
Temperature management and optimum
storage conditions
Plums and fresh prunes can be cooled in field bins using
forced-air cooling, hydro-cooling, or room-cooling prior to
packing. Packed plums and fresh prunes should be cooled
by forced-air cooling to near 0°C. A storage temperature of
-1.1°C to 0°C with 90 to 95% RH should be used. The
freezing point varies from -2°C to -1°C depending on
SSC. In late season plums and in fresh 'French' and
'Moyer' prunes, delays in flesh breakdown (IB) develop-
ment have been attained by storing IB-susceptible cultivars
at -1.1°C. However, to store plums at this low a temperature,
high SSC and excellent thermostatic control are essential
to avoid freeze damage.
Horticultural maturity indices
In most of the plum cultivars grown in California, harvest
date is determined by skin colour changes that are described
for each cultivar. A colour chip guide is used to determine
maturity for some cultivars. Firmness, measured by squeezing
Post-harvest fruit diseases
Brown rot is caused by
Monilinia fructicola
and is the most
important post-harvest disease of plums in California. Infec-
tion begins during flowering. Fruit rot may occur before
Table 10.6
Market Life of 'Blackamber' Plums Harvested on Four Different Dates, Then Stored
at 0°C or 5°C.
Maximum market life
b
(weeks at 0°C)
Minimum market life
(weeks at 5°C)
Harvest date
Firmness (Kg-force)
SSC
TA
a
SSC/TA
6/20/02
7.0
10.3
0.78
13.2
2
2,3
<2
3,4
6/26/02
5.1
10.8
0.47
22.9
5
3
2
3,4
7/2/02
4.8
11.7
0.43
27.2
5
3
3
1,3,4
7/8/02
2.8
12.3
0.33
37.3
5
3
2
1,3,4
a
Titratable acidity measured after ripening (0.4-0.7 Kg-force).
b
25% of the fruit became mealy
1
or leathery
2
, or
had flesh bleeding/browning
3
or gel breakdown/translucency
4
. Superscript indicates limiting condition.
End of market life based on chilling injury (CI) determined when
≥
