Agriculture Reference
In-Depth Information
Table 10.8
Proposed Harvest Maturity Indexes
Based on Firmness (8.0 mm Tip) and Minimum
SSC for Different Plum Cultivars.
Harvesting and packaging handling
Japanese plums and the closely related interspecific plum-
type fruits including Pluots
®
and plumcots, are harvested
entirely by hand. Maturity is determined by fruit colour,
fruit pressure or a combination of both, and is cultivar
dependent. Soluble solids concentration, while important
from a consumer satisfaction standpoint, is not com-
monly used as a measurement of field or harvest maturity.
As most plum cultivars are well adapted to a late-
harvesting system, increase of SSC can be achieved
without jeopardizing the crop (Table 10.6). We suggest the
use of firmness as an indicator of how late to harvest ('Tree
Ripe') without inducing bruising, thereby maximizing
orchard quality. But the decision of when to harvest should
also take into account other factors such as fruit drop, envi-
ronmental conditions, hand labour availability, market
prices, distance to market, potential transportation damage
and temperature management at the receiving location.
As with other fruit trees, plum fruits ripen from top of
the tree to the bottom, a consequence of light environment.
Lower fruit can be delayed in maturity by as much as
10-14 days compared to well-exposed fruit at the top of
the tree. Consequently, harvests are multiple - generally
two to four in number - and frequently complex in logisti-
cal determination. Unlike for peaches and nectarines, the
first harvest in plums is commonly the largest pick. Since
many plum cultivars develop full colour up to several
weeks before commercial harvest and usually soften rela-
tively slowly, it is important to develop a method by which
field labourers can easily determine fruit maturity. In such
full colour cultivars this is commonly done by limiting
harvest to only a portion of the tree - usually segregated by
light exposure, such as the top third of the tree in the first
harvest, the middle third in the second and so on - so that
labourers can proceed more quickly.
The logistics of harvesting are very similar to that described
for peaches and nectarines. Fruits are harvested into picking
bags that can hold up to ∼20 kg of fruit. The pickers dump the
fruit into bulk bins that contain about 400-450 kg of fruit.
The bulk bins are transported in the orchard on tractor-pulled
trailers that hold four or five bins. Usually two tractors and
bin-trailers are required for each harvest crew. When full, the
bins are taken to a centralized area and unloaded from the
bin-trailers to await loading by forklift onto flatbed trailers
for delivery to the packing facility.
Sorting is done to eliminate fruit with visual defects
and sometimes to divert fruit of high surface colour to a
high-quality pack. Sizing segregates fruit by either weight
or dimension. In general, plums and fresh prunes are
packed into 12.6 kg volume-filled containers.
Minimum SSC
(%)
Cultivar
Firmness (Kg-force)
Blackamber
3.2-4.0
10-12
z
Fortune
3.2-4.07-9
11
Friar
3.2-4.0
11
Royal Diamond
3.2-4.0
11
Angeleno
2.7-4.0
12
Betty Anne
3.2-4.0
12
Blackamber plums with TA ≤0.60% after ripening
have a high consumer acceptance. If plums have ≥ 12.0%
SSC, TA does not play a role.
a
be harvested without suffering bruising damage during
postharvest handling. Plums are less susceptible to bruising
than most peach and nectarine cultivars at comparable firm-
ness. Fresh prunes are picked on the basis of colour, at least
50% of the fruit surface is red or purple and SSC is at least
16% in 'Moyer' and 19% in 'French' prunes.
Quality characteristics and criteria
High consumer acceptance is attained for most fruit with
high SSC. Fruit TA, SSC:TA and phenolic content (astrin-
gency) are also important factors in consumer acceptance.
However, there is no established minimum quality standard
based on these factors. Consumer acceptance of most tradi-
tional plums is related to SSC except for plums with high
titratable acidity (TA) at consumption as in some
'Blackamber' lots (> 0.7% TA). In 'Blackamber' plums
consumer acceptance and market life were highly depend-
ent on harvest date (Crisosto
et al
. 2004b). For plums within
the most common industry ripe soluble solids concentration
(RSSC) range (10.0-11.9%), ripe titratable acidity (RTA)
played a significant role in consumer acceptance. Plums
within this RSSC range combined with low RTA (
0.60%)
were disliked by 18% of consumers, while plums with RTA
≤
≥
1.00% were disliked by 60% of consumers. Plums with
RSSC
75% consumer acceptance, regardless
of RTA. This work also pointed out that ripening before
consumption decreased TA by approximately 30-40%
from the TA measured at harvest (HTA). In some cases, this
decrease in TA during ripening may increase the acceptabil-
ity of plums that would otherwise be unacceptable. Using
'in-store' consumer tests, we have proposed harvest matu-
rity indexes based on firmness and minimum SSC for
selected plum cultivars (Table 10.8).
≥
12.0% had
∼
