Progressive Crop Consultant May/June 2021

Continued from Page 6
inches in the case of hard plastic fruit
catching surfaces or by modifying the
fruit catching surfaces to create a softer
fruit landing surface. Ideally, the fruit
catching surface should not exceed
120 g impact even when the BIRD II is
dropped from a height of 48 in (equivalent
to the distance between the top of a
large mature blueberry bush and catch
plates on the harvester).
The design of soft surfaces can be
achieved by either incorporating netted
material or a soft “rubber” sheet with no
hard surfaces beneath for catching the
fruit (Takeda and Wolford, U.S. Patent
No. 9,750,188 and the Oxbo SoftSurface
kit). For example, even with a soft
surface insert in a hollowed-out plexiglass
catch plate, the margins of the plate
contributed to more than 20% of the
exposed surface area. In addition, catch
plates on the harvester overlapped with
adjacent plates and rested on top of another
plate. The outline of the plate below
another created about 10% additional
hard surfaces.
When blueberries are HH, the packout
is about 95% or better and fruit usually
have little or no internal bruise damage
(Table 1). The packout of MH blueberries
is lower and typically ranges from 70% to
slightly more than 80%. The remaining
20% consists of soft, overripe and immature
green- and red-colored berries.
Commercial packing operations, for
the most part, do not check for internal
bruise damage in their MH blueberries.
However, close inspections of MH
blueberries packed into clamshells after
sorting on commercial packing lines
revealed berries were bruised (Figure 3,
see page 4). Our studies evaluated different
catch surface designs by inserting
soft, flexible material to reduce internal
bruise damage. We did record improvements
in packout. However, neither
the improvement in packout nor berry
firmness approached that of HH fruit
in the case of varieties Duke, Draper
or southern highbush blueberry (SHB)
Optimus even when they were harvested
with OTR machines equipped with soft,
flexible catch surfaces. The only exception
to date has been the variety Last
Day of bruise assessment
Surface Drop height (ft) Day of drop After 14 days
2 11 .4 1 6.2
Hard
3 14.4 1 9.7
4 20.3 25.6
2 3.1 4.9
Soft
3 3.7 2.0
4 2.9 6.6
Not dropped 0 0.6 2.0
Table 1. Effect of catch surface (hard or soft) and drop height on internal bruise damage
within one day of drop and after 14 days in cold storage (32 degrees F to 37 degrees F).
Bruise damage is expressed as the percentage of cut surface area indicated by dark color
(see Figure 4, see page 5).
Call, where MH produced the quality
approaching that of HH berries. MH of
SHB Optimus produced higher-quality
packout than other SHB varieties, such
as Jewel, Star and Farthing, but even
Optimus should not be cold-stored for
more than one week. Our studies have
shown that fresh market pack-out can
be increased by installing a soft catch
surface on the harvester, but the quality
of HH blueberries has been better.
Cultivar Susceptibility
In a study conducted in Oregon, the
susceptibility of 11 blueberry cultivars
to impact damage was determined by
dropping the fruit from 2-, 3-, and 4-foot
heights onto a hard, plastic catch plate.
Bruises developed more rapidly in rabbiteye
cultivars (Ochlocknee, Powderblue
and Overtime) than in northern highbush
(NHB) and SHB cultivars. NHB
cultivars Aurora, Cargo, Draper and Last
Call had the least amount of bruising
after two weeks in cold storage. Blue Ribbon,
Legacy and Liberty had a moderate
amount of bruising.
These studies showed that simulated
drop tests are useful in determining the
potential of varieties for long-term cold
storage and, more importantly, their
potential to MH for fresh market. In a
study in 2020 in Oregon, Draper and
Legacy were MH with two OTR Oxbo
harvesters, one fitted with and the other
without the SOFTSurface kit. To date,
the challenge for Oxbo Corporation and
other machine manufacturers has been
to procure soft materials that meet food
safety standards and are durable for
harvesting blueberries.
The preliminary findings of this study
were: 1) Machine harvesting with the
SOFTSurface kit reduced fruit internal
bruise damage in both Draper and Legacy
fruits compared to those harvested
with the unmodified OTR harvester as
shown with a laboratory test (Table 1); 2)
Draper and Legacy fruit harvested with
the machine fitted with the SOFTSurface
kit and sampled before sorting in the
packing house were firmer compared
to fruit harvested by the unmodified
harvester; and 3) After one and two
weeks in cold storage, there was no difference
in firmness of berries harvested
by machines fitted with and without the
SOFTSurface kit.
We found that fruit firmness-based sorting
by itself may not be a good predictor
of berry quality when MH blueberries
are cold-stored for two weeks or more,
but both Draper and Legacy blueberries
picked by the OTR machine fitted with
the SOFTSurface kit maintained better
fruit firmness (>160 g/mm) values and
lower internal bruise ratings in cold
storage (Table 1). The improvements in
fruit quality may well have been from a
70% reduction in hard catch surface area
in the SOFTSurface kit compared to the
hard polycarbonate fruit catching surfaces
in the regular harvesters. A laboratory
test determined the effects of dropping
blueberries from different heights onto
either a hard (e.g., polycarbonate catch
plate on conventional harvesters) or soft
catch surface (e.g., prototype SOFTSurface
kit) on internal bruise development
(Table 1). Blueberries were sliced to
visually assess bruise damage on the day
of the drop test and after cold storage for
two weeks.
Young (~3-ft-tall) and mature (6-ft-tall)
trellised Last Call blueberry plants were
either HH or picked with a modified
OTR machine. Fruit samples from both
methods were manually sorted and
evaluated for internal bruise damage
on the day of harvest and the remaining
samples were placed in cold storage.
Cold-stored samples were taken out after
8 Progressive Crop Consultant May / June 2021