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Extending storage and shipping duration of cherries in British Columbia, Canada, can be achieved with minor modifications to the production, picking and packing operations, a research project has shown.

The first year of a two-year study, conducted by Drs. Peter Toivonen and Frank Kappel at the Pacific Agri-Food Research Centre in Summerland, British Columbia, established that Sweetheart cherries could be stored or shipped for up to three weeks and, in some cases, up to six weeks with no concern over market acceptability.

"Peter’s very preliminary data is very exciting and it appears we will get some tangible results as data continues to be processed," said Greg Norton, president of the Okanagan-Kootenay Cherry Growers’ Association, that funded the project.

Six cooperators were selected in 2008 for the study, and each included a combination of a grower and packinghouse facility; in some cases, the grower was also the packer.

To assess which phase of the production-packing continuum caused or contributed to defects in stored Sweetheart cherries, fruit was sampled at the tree, after commercial harvest but before delivery to packing facilities, and after fruit was run across the packing line. In addition, fruit temperature was monitored from picking to cooling. Points of impact were assessed on each line to evaluate whether specific points in the line contributed to pitting injury of fruit.

The researchers identified improvements in picking practices and packing line modifications at some of the locations that would likely reduce pitting.

"In regard to storage decay and pebbling, there needs to be some attention to improving the fruit on the tree, which may involve nutrition management of the crop," Toivonen said.

The cherries from all cooperators were free from decay at harvest and did not show any decay for up to three weeks of storage at 1ºC (34°F), underlining the effectiveness of preharvest disease control programs for all the cooperators, the researchers reported.

However, after six weeks of storage, significant decay had developed in fruit at half of the test sites.

"The decay developing late in storage can be attributed to deterioration in cherry tissues, which would make them susceptible to fungal growth," Toivonen said. "The fact that half of the cooperators did not have this problem and that harvesting and packing operations had no influence suggests that the intrinsic quality of the fruit at harvest is responsible for these differences. It is possible that the cherry calcium content may explain the variation in storage decay; however, more work is needed to confirm."

Pebbling was noted to be a significant issue in Sweetheart cherries for the first time in 2008. This defect can be differentiated from pitting in that pebbling is expressed as a shallow, uniform surface roughness that can cover varying extents of the fruit surface.

Pebbling

"Very little is known about the causes of pebbling," Toivonen said. "In this work, pebbling of the fruit was attributed wholly as an on-the-tree problem since levels of pebbling in storage were similar for fruit sampled from the tree, after commercial harvest, and after running across the line. Three of the cooperators had lower severity of pebbling and this may provide clues as to the factors affecting pebbling. More analysis is required to determine if there are overriding factors associated with pebbling development."

The severity of pitting associated with harvesting and packing varied, depending on the cooperator.

"For two cooperators, the packing-line operation did not significantly contribute to pitting severity and therefore they must concentrate on avoiding picking-induced injury that leads to pitting," Toivonen said. "In the case of one cooperator, the pick operation generated very little pitting injury and therefore they must concentrate on modifications in the packing line. The remaining three cooperators had significant pitting associated with both the picking and packing line operations."

The study found that fruit firmness was not affected by commercial picking or packing operations at all six test sites. Firmness generally increased with time in cold storage, a pattern that has been observed over many years in research at PARC. In all cases in the study, fruit firmness was above the minimum threshold for good marketing quality and hence firmness is interpreted as not being a significant issue for the B.C. Sweetheart cherry industry, the researchers said.

Stems

Stem browning was generally not a problem in this study, Toivonen said. "Previous work at PARC led to the general implementation of reflective tarp technology and this has resulted in tremendous improvements in stem quality and fruit quality. None of the six packing-line operations contributed significantly to stem browning."

Reflective tarps can help maintain fruit quality when used to cover cherries immediately after harvest in the orchard, and during transit to the packinghouse. The laminated tarp consists of a woven polyester core that is double coated with bright white on the outer surface and a silvered Mylar on the undersurface. The tarps are used with the white side facing the sun and the shiny metallic silver surface facing the fruit.

Stem pull force, the strength of the attachment of the stem to the cherry, is considered important, since buyers want a green stem attached to the fruit. Stem pull force tended to be similar for fruit sampled on the tree, after commercial harvest, and after running across the line.

Temperature

The researchers noted that no significant fruit quality issues could be attributed to a wide range in temperature profiles from time of harvest to packing in the box. The conclusion was that there is some flexibility in temperature control as long as fruit is properly handled (protected by reflective tarps) and the packing operation ensures the fruit is cold.

Manual

Results of the project will be used to produce a manual for growers and packers. The OKCGA will then provide training on use of the manual for industry stakeholders, said Brian Mennell, chairman of the association’s research committee.

With the volume of fruit production volumes expected to increase as more acreage is devoted to cherry production, growers want longer storage options in order to ship fruit further distances using ground and sea transport, he said.

About 60 percent of British Columbia’s sweet cherry crop goes to Western Canada by land, while most overseas shipping is by air.

"The flexibility to be able to use these shipping options is essential for them to access greater markets that will be needed to take the much larger volumes of fruit," Mennell said.

The introduction of late-season varieties such as Lapins, Skeena, Sweetheart, and Staccato from the Pacific Agri-Food Research Centre’s breeding program has allowed B.C. growers to harvest cherries into late July, helping to reverse a decline in the industry due to poor returns from early-season varieties and problems with fruit quality.