Quality of CA-Stored Anjou Pears Packed in Trays or Handwrapped-1996 Crop
The need to market larger crops of Anjou pears compels investigation of alternative methods of packing. Traditionally, Anjou pears are handwrapped and place packed into fiber cartons for shipment. In the Wenatchee district, the majority of fruit are stored in controlled atmosphere (CA) for up to 10 months after packing. In some years, decay or disorders develop within the cartons following long-term storage and repacking must be done to clean up the pack. This becomes very costly to packer and grower.
Markets may require packing into various types of containers including bulk and/or bags. In these cases, fruit which is handwrapped and packed at harvest may have to be repacked into different containers at time of shipment.
One type of container under exploration by the industry utilizes trays rather than handwrapping. The advantages of trays include the ability to automate the process, reducing packing material (paper), and can provide more rapid temperature reduction. Tray packing may also reduce bruising at retail, since the pears do not need to be individually unwrapped by store employees.
Tray packing of Anjou pears has been performed successfully in limited volumes by several shippers in Washington. However, industry concern about scald, decay, and shrivel appearing on fruit stored in trays has slowed adoption of the method.
An experiment was performed to determine the quality of tray packed Anjou pears following long-term CA storage as compared with handwrapped/place packed pears.
The following comparisons between tray packed and handwrapped pears were made:
- rate of temperature pull-down
- appearance of scald
- appearance of decay
- appearance of skin marking
- appearance of shrivel and weight loss
- Three pallets of pears of size 70 fruit were made up
from two grower lots (identified as Grower 70 and 361) on
October 29, 1996. The handwrapped fruit was commercially
wrapped. The trayed fruit were originally packed (that
day) on trays with foam pads above and below the fruit in
each tray. Half the trays were repacked so that some had
foam only between the fruit and tray above, and half had
foam both on top and bottom of the fruit. Thus, there were
three types of packing for each grower:
- Handwrap--Fruit were individually wrapped in paper and
packed tightly (not on trays) into pear boxes. This
treatment is designated "handwrap" in this
- Single Foam--Foam pads were placed on top
of each layer of fruit. No foam was between the fruit and
the tray below it. No paper was used. Fruit were packed
into apple boxes. This treatment is designated as
"SF" in this report.
- Double Foam--Foam
pads were placed both above and below the fruit on each
tray. No paper was used. Fruit were packed into apple
boxes. This treatment is designated as "DF" in
The foam used in this experiment was the thinner type of Richter pad (Astrofoam) cut 12" x 18 1/4". This foam was too small to cover the entire tray. I was informed that most of the industry uses the 3/32" thickness.
The sizes of the boxes were as follows:
BoxLengthWidthHeight Pear20-1/4"12-1/2"10" Apple20-1/4"12-3/4"12"
- Handwrap--Fruit were individually wrapped in paper and packed tightly (not on trays) into pear boxes. This treatment is designated "handwrap" in this report.
Thermocouples were placed in fruit in a box in every layer of each pallet. These fruit were located on the second layer from the bottom in each box. Equipment was set to record temperatures hourly. Temperature recording equipment was removed after 5 days; probes remained in the fruit for the entire storage season.
Pallets were placed in refrigerated storage the afternoon of October 29 and the thermocouples began monitoring the morning of October 30. CA was imposed on October 30.
One box of fruit from each grower lot and each treatment was brought back to the lab. on October 29 for evaluation. A box of fruit from each packing system was removed at regular intervals until the end of the long-term CA storage season in June.
Firmness, soluble solids, pH, decay, and visual quality were evaluated. As part of the visual inspection, each fruit in every box was examined for scuffing and shrivel. In the evaluations for January and February, no noticeable shrivel was found, so the visual score is the percent fruit per box with noticeable scuffing.
In March, in addition to the tests described above, the inspection for skin marking was intensified. Fruit marking was divided into three types: scuffing (Sc), Shrivel (Sh), and speckling (Sp). Each was evaluated at four levels with none = 0, small amount = 1, moderate = 2, and severe = 3.In April, in addition to the tests described above, fruit from each tray from each box was also weighed. An equal number of fruit from the handwrapped box was unwrapped and weighed.
Firmness (lbs.) was evaluated by taking 20 fruit from each box by using a drill press mounted penetrometer with a small diameter tip on two sides of each fruit. The results were averaged. Following warm room shelf life tests, this was done on 10 fruit per treatment.
Soluble Solids (%) was determined using a refractometer on juice obtained from the mid-section of 10 pears following juicing; pH was also determined on this juice.
An additional ten fruit from each treatment were held at 70°F for 96 hours and tested for firmness, SS, and pH.
Cooling Rate Study
All boxes were placed on pallets used by the commercial cooperator. Blocks of wood were used to separate boxes vertically on each layer. Handwrapped pears were in standard pear boxes separated by 2" x 4" blocks, giving 1.5" of air space between the boxes.
Fruit packed in either type of foam (DF or SF) were in standard apple boxes separated using 1" x 2" blocks which gave 0.75" of air spaces between the boxes, as the "footprint" of the apple boxes was larger than that of the pear boxes. Thus, it was possible to obtain more air flow along the sides of the pear boxes than the apple boxes.
The 7/8 and 1/2 cooling times can be found in Table 1. The handwrapped fruit in the pear boxes cooled slightly faster than those in SF boxes, but equal to that in the DF boxes.
Previous work by Faubion has shown that tray packed fruit cooled faster than handwrapped fruit under more strict experimental conditions in which the stacking pattern was equal. In this commercial situation, cooling rate of the three packages was influenced by the separation between the boxes on the pallet.
November initial test results. The November examination lacked the intensity of subsequent examinations. One box of each treatment was removed from the pallets on October 29, held at ambient temperature for 48 hours, then placed at 34°F until November 6. The fruit were tested for firmness and soluble solids.
Results from the tests in January, March, April, and June can be found in Tables 2 through 6.
- Cooling Rate Study
There was no significant difference in the rate of cooling of either handwrapped or tray packed pears in this experiment. This was not the case when Faubion compared cooling in a research cooler rather than in this commercial facility. He found that the fruit in the tray packed boxes cooled more rapidly. In this commercial experiment, boxes of tray packed pears (in apple boxes) were palletized closer together than were the boxes of handwrapped pears. Apparently, the configuration of the boxes on the pallet, air space between boxes, and the dimensions of the pallet play a very significant role in cooling-as much or more than the location of the fruit in the box. In all cases, polyliners were inside the cartons providing a significant barrier to cooling.
Fruit firmness directly out of storage slowly declined during the season from an average of 13.33 lb. in January to 12.23 lb. in June (Table 2). This slight decline is remarkably small in light of the length of time in storage. Over the entire season, firmness of the handwrapped fruit was slightly softer. The average firmness of the handwrapped fruit was 12.65 lb. as compared with 13.23 lb. for the double foam treated fruit and 13.07 lb. for the single foam fruit on trays.
One might conjecture that the higher firmness of the fruit on trays could be due to shrivel. However, the weight per fruit did not vary significantly by treatment. The visual analysis showed that the handwrapped fruit (5.4 fruit/70 fruit inspected) had shrivel intermediate to the double foam, which had the least shrivel (4.1) and the single foam which had the most shrivel (6.6) (Table 6).
Handwrapped fruit had significantly more bruises (8.25 fruit bruised/70 fruit sampled) than either those in single (5.75) or double (6.25) foam layer boxes.
There was no apparent difference in soluble solids or pH for any of the treatments or pull-out dates (Tables 4 and 5).
The appearance of dark skin discoloration (DSD) in fruit following storage until June has been a serious problem for a number of Wenatchee River Valley packers this season. We started noticing the appearance of DSD on a few fruits in April. In May and June, DSD became apparent on fruit from Grower 361 and not on fruit from Grower 70 and only on handwrapped pears. Grower 361's fruit had been wrapped in darkly printed non-copper treated paper, wrapped with the print facing the pear. Grower 70's fruit had been wrapped using lighter copper treated paper, wrapped with the print facing away from the pear. Grower 70's handwrapped box showed no signs of DSD. The DSD appearing on Grower 361's wrap box was spaced about a half inch apart. The DSD sites also had small indented bruising and often a layer of a blue substance that could be cleaned off. The bruising seemed to occur at sites were pears had settled against each other. The sides of pears against the cardboard box (with no other pear contact) had very little or no DSD.
Finally, it appears that tray packing of pears, although it does not appear to dramatically improve cooling rate under these commercial conditions, has significant benefit in fruit quality. Firmness was slightly improved over handwrapped fruit. DSD was lower, weight was equivalent, and bruising was less. Pears were slightly better when a double foam layer pack was used than when only a single layer was used.
Dr. Eugene Kupferman with cooperation from Ken Miller, Blue Star Growers, and Dr. Dana Faubion, WSU-Cooperative Extension, Yakima
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Tree Fruit Postharvest Journal 8(3):11-15