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WSU-TFREC/Postharvest Information Network/Reducing Postharvest Losses in Anjou Pears:
A Report on the 1991 Crop



Reducing Postharvest Losses in Anjou Pears:
A Report on the 1991 Crop


Introduction

This report discusses a research project aimed at determining the reasons for postharvest generated cullage of Anjou pears. The project is funded by the Washington Tree Fruit Research Commission and the Winter Pear Control Committee.

The largest volume of winter pears for fresh consumption in the USA is grown and shipped from packinghouses in Washington and Oregon. During the period 1989-1991 the largest volume of Anjou pears was shipped from the Wenatchee district (43%), followed by the mid-Columbia district (39%), the Yakima district (14%) and the Medford district (4%).

Anjou pears are stored in regular or controlled atmosphere storage (CA) and marketed from September through June. They are sold throughout the USA and in an expanding number of export markets. For example, large volumes of the 1991 crop were sold in Sweden, Canada, Mexico, Saudi Arabia, and Taiwan.

Cullage due to postharvest problems can appear at the time of packing, after storage or in the marketplace. It reduces grower returns and can endanger the reputation of the industry when fruit of poor quality appears in the market.

A survey by Dave Burkhart at the request of the industry estimated postharvest losses in excess of $1.7 million in 1990 and $1.4 million in 1991. This amounts to about a 16-cent loss on every box shipped. The 1990 crop year losses were due to a combination of decay and skin discoloration while in 1991 losses were solely due to decay. Losses by each warehouse were different over the two years. Some warehouses that had appreciable problems in 1990 were virtually free of problems in 1991 and vice versa (Figure 1).


Study Methodology

Technicians repeatedly visited the major Anjou pear packinghouses in northcentral Washington and the mid-Columbia region of Oregon during the packing of the 1991 Anjou pear crop to obtain a picture of similarities and differences in fruit handling practices among packinghouses. The study investigated four areas:
  • Chemical use
  • Temperature management
  • Fruit quality at time of packing
  • Fruit quality after storage

The project began on October 21, 1991, with 15 warehouses in the mid-Columbia and Wenatchee districts cooperating. By this date the Anjou packing season was already in high gear, and some sheds had finished packing for the year. The technicians obtained samples of 96 different grower lots for the 1991 season.

Storage and packing practices vary between warehouses and districts. Most packinghouses pack fruit as soon after harvest as possible, store it in boxes and ship from this inventory. Other packers store fruit in bins either field run or presized and pack on demand.

Fruit was sampled on a weekly basis as it was being packed. During each visit temperature and chemical treatment information were obtained and a commercially packed box of fruit was purchased from every warehouse.

During the 1991 packing season technicians were able to sample 96 lots of fruit from the 15 packinghouses. Most of the packing was completed by mid-December. Packing continued at the few warehouses that store fruit in bins and pack on demand.

The pears were analyzed in the lab for quality, including firmness, soluble solids, starch content and acidity. To estimate shelf life, additional pears were allowed to remain at 70°F for seven days and then examined.

To estimate the latent diseases/disorders within the remaining pears from each lot each week, the fruit were placed in a commercial CA storage room and removed in March or April (depending on the date sampled) and again in June for complete analysis which included external and internal defects as well as quality.


Chemical Use Practices

This section summarizes current packinghouse practices encountered when technicians visited each packinghouse on a regular basis.

Chemical use was restricted to very few chemicals and was fairly uniform among those packers surveyed.

Drenching
Few pears were drenched and it was not standard operating procedure for any of the participating packinghouses.

Dump tank
In the dump tank only one of the packinghouses used chlorine, the rest used sodium orthophenylphenate (sold as SOPP, Stop-Mold, Dowcide, Deccosol or Steriseal).

To float the pears, 11 of the 15 packinglines used sodium or calcium lignin sulfonate (also known as "Lignosite" or "Orzan") (Figure 2). Three of the packinglines used sodium silicate (known as "pear float" or "waterglass"). Both of these compounds are liquids. One packinghouse reported the use of sodium sulfate which is a powder.

Line sprays
Nine packinglines did not apply wax. Two packinglines used Semperfresh on Anjous. All but one packingline applied thiabendazole (TBZ sold as "Mertect" or "Deccosalt 19" or "597 F"). Ethoxyquin was applied as a line spray in 4 of the 15 packinglines.

Paper wraps
All pears in the survey were hand-wrapped in paper. Two-thirds of the packinghouses used paper embedded with copper to prevent the spread of decay. Four of the 15 packinglines used oil wraps and another 5 used wrap with ethoxyquin to prevent storage scald.


Temperatures on the Packingline

Each time the technician visited the packinghouse, fruit, water and dryer temperatures were measured. At each location five fruit temperatures were tested. Fruit temperatures were taken with a needle-nose thermometer inserted about 0.5 inches into the fruit flesh.

The first fruit temperatures were taken as the bin waited to be dumped and the dump tank water was also measured. Fruit temperature averaged 39.5°F prior to being dumped and the water temperature measured 42.3°F. As the fruit rose from the dump tank onto the line temperatures averaged 42.1°F. Rinse water on the line ranged from a low of 38.0°F to a high of 122.4°F with an average temperature of 66.3°F. Immediately prior to running through the dryer the average fruit temperature averaged 44.7°F, thus an average increase of 5°F from the temperatures of the fruit in the bin. However, the average temperatures of the fruit treated to the hot water (122.4°F) rinse rose 10°F even though the dump tank water was average.

Three-quarters of all of the lines used forced air dryers to dry the fruit. The air in dryer ranged from a low of 32.8°F to a high of 135.0°F. The fruit temperature fell 2°F in the cold air dryer (32.8°F) while the fruit temperatures rose 6°F in the hottest dryer. Overall the fruit temperature rose 4°F in the dryer. This where the greatest fruit temperature rise occurred on most packinglines (Figure 3).

The rise in fruit temperature from prior to dumping to the time the fruit dropped into the tubs averaged 10°F (39.5 to 49.3°F). However the line with the highest rinse water temperature also had the highest dryer temperature and the fruit rose 15° to 55.1°F.

Boxed fruit was palletized in rooms where temperatures averaged 49°F. The time it took for the fruit to go across the line averaged 6:41 minutes.


Fruit Quality at Time of Packing

The averages for the industry during the packing season were as follows:

 At time of packingAfter 7 daysGain/loss
Firmness (lbs)15.27.6-7.6
Starch (score)6.0NANA
Soluble solids12.813.8+1.0
Acidity0.2970.316+0.019
% Extractable juiceNA60.3NA
Defects and diseases were not scored at time of packing but were carefully evaluated after both mid-term and long-term storage.

Fruit Quality After Storage

Fruit Quality at Mid-term Storage
The term mid-term storage is used to denote an examination date halfway between the time the fruit was packed and the last week in May. Fruit was in a commercial storage room at 1.5% oxygen, 0.5% carbon dioxide at 32°F. The cooperation of Blue Star Growers, Cashmere, in allowing us to store fruit in their CA rooms was greatly appreciated.

The averages for the industry following mid-term storage were as follows:

 At time of removalAfter 7 daysGain/loss
Firmness (lbs)14.03.6-10.4
Soluble solids12.813.7+0.9
Acidity (%)0.2400.248+0.008
% Extractable juiceNA46.5NA

Fruit Quality after Long-Term Storage
Fruit in long-term storage was held until the last week in May under CA conditions described above.

 At time of removalAfter 7 daysGain/loss
Firmness (lbs)12.73.6-9.1
Soluble solids12.413.4+1.0
Acidity (%)0.2290.260+0.031
% Extractable juiceNA63.2NA

Change in Fruit Quality Over Time in Storage
It is best to compare fruit quality after the warm room tests (7 days at 70°F) since this most closely resembles what the consumer would experience.

 At packingMid-TermLong-Term
Firmness (lbs)7.63.63.6
Soluble solids13.813.713.4
Acidity (%)0.3160.2480.260
% Extractable juice60.346.563.3


Fruit Quality Summary

The change in fruit quality over time was small with the exception of firmness at the time of packing. This demonstrates that pears have a longer shelf life at packing than they do after storage. The 1991 Anjou crop held up very well in storage

Defects and Diseases

Defects and Diseases at Mid-Term
As commercially packed fruit were removed from storage halfway through the storage period, certain defects emerged. Russetting and decay were the most serious defects. Limb rub, stem punctures and insect stings were also found on pears from a few packinglines. There was no scorable skin speckling, no external sign of cork, no chemical damage and no scald. Shrivel and scuffing were found on a number of lots. There was no scorable moldy core, pithy brown core or cork.

Defects and Diseases on Fruit in Late May
The most serious external problems found in late May were decay, shrivel and scuffing. To a lesser extent we found russetting, limb rub, scald and punctures. We did not find scorable amounts of chemical burn, cork, skin speckling or internal decay.

A significant amount of decay was found after storage from fruit on certain packinglines. The major types of fungal decay were blue mold (44%), gray mold (25%), mucor rot (19%), stem end rot (10%) and side rot (3%) (Figure 4). Packinglines whose pears had this decay were not sanitized carefully and had fruit debris in the equipment and on the floor. However, growers also should focus on methods of reducing the number of fungal spores entering the packinghouse.

The major diseases encountered in this study were blue mold, gray mold and mucor rot. Here is supplemental information about those diseases.


Blue Mold

Blue mold is also known by its scientific name, Penicillium. This is one of the most destructive diseases of all fruits in storage and in the marketplace. Blue mold is considered a wound parasite but can penetrate through lenticels, particularly those near bruises. Susceptibility increases in mature fruit or late in the storage season. Delays in cooling the fruit, bruising and late harvesting increase susceptibility.

Gray Mold

The scientific name for gray mold is Botrytis and it is a common decay of pears and apples. Gray mold enters through wounds and punctures in the skin. The source of gray mold spores is the orchard. It grows abundantly on dead and dying plant material found in most cover crops and grows especially rapidly during cool, moist weather. Infection can occur in the orchard or at any time the spores come in contact with unprotected wounds. These initially rotted fruits spread the disease to fruit in contact with others and produce nests. To reduce gray mold, avoid having pears grow on limbs that reach down into cover crops and supervise pickers to avoid bruising.

Mucor Rot

Mucor is a soilborne fungus that grows well even at cold temperatures in storage. There is no effective fungicide registered for control of this disease. It can be devastating because it moves from fruit to fruit and continues to grow in storage. This fungus grows in fruit that has fallen on the orchard floor, so any practice that reduces contact with this rotting fruit will help. Never allow harvest crews to put grounders into bins, and keep soil off bins and bin skids to reduce cullage from this rot. Make sure driveways are not dusty and staging areas are barked.

Tips For Decay

Here are some pointers for minimizing decay problems:

In the orchard:

  • Harvest at the right maturity for the intended length of storage.
  • Do not pick fruit off the ground.
  • Handle carefully to minimize bruising and stem punctures.
  • Do not allow tree limbs to bend down into the cover crop.
  • Deliver fruit to the warehouse for immediate cooling.
  • Control perennial canker and woolly aphids.
  • Use fungicides as needed to control preharvest infections.
  • Keep dust down on orchard roads and loading areas.
  • Use balanced horticultural approaches and calcium sprays as needed
  • Do not overirrigate, especially with overtree sprinklers.

In the warehouse:

  • Cool fruit immediately upon receipt.
  • Use the proper water treatments to keep down the spores.
  • Clean dump tanks and change water frequently or heat the tank to kill spores.
  • Keep the packingline and packing room clean.
  • Do not allow standing water on the packing room floor.
  • Keep a close eye on maturity and scuffing.
  • Put the right fruit in the right storage regime for the right length of time.
  • Let the fruit quality determine how long it can be stored, not the sales department or the grower.


Summary

The 1991 packing and marketing season was characterized by fruit of high quality with few problems outside of decay.

The pear industry is challenged by a decreasing number of registered chemicals to protect the fruit against scald and decay after harvest. Sanitation within the orchard and packinghouse is increasingly recognized as important. The few chemicals left must be used appropriately and should be supported while other methods of control are developed.

Temperature management is extremely important to fruit longevity after harvest. Fruit were cooled to an average of 40°F prior to packing, but the average flesh temperature rose to 49.3°F by the time it was boxed. There was a large range of temperatures in the rinse water and hot air dryers which increased fruit temperature. The industry needs to find ways to reduce the temperature of the fruit as it goes over the packingline. We must pull out the heat as rapidly as possible after packing since it affects the rate of fungal growth and softening.

The most serious problems emerging during the storage period were fruit skin scuffing and decay. These problems are not new and additional specific research is needed to determine how to reduce them. We plan to continue this project to develop recommendations about handling Anjou pears to minimize postharvest disorders and decay.

Dr. Eugene Kupferman, Ken Miller, Lori Kutch, and Dave Burkhart

WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Kupfer@wsu.edu

Tree Fruit Postharvest Journal 3(4):18-22
December 1992

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