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Postharvest Research and Extension at MCAREC

By YAN WANG

Oregon State University

Nationally, Oregon is second (after Washington) in fresh pear production and third (after Washington and California) in fresh sweet cherry production.

Oregon has about 19,000 acres of pear orchard land, with primary growing regions in the Hood River area and the Rogue River valley.

Today, Hood River County is the world’s leading producer of Anjou pears, a short-necked winter pear. Many Hood River Valley orchards are relatively small and operated by families, but together they account for about two-thirds of the state’s pears. The Oregon cherry industry has experienced a 14 percent increase in sweet cherry bearing acreage over the last decade, going from 11,000 acres to 12,500 acres.

The goal of the Postharvest Research and Extension at MCAREC is to increase growers’ economic return.

The major duties of the Postharvest Research and Extension at MCAREC are to identify, prioritize and conduct research on the postharvest biology of pears and cherries grown in the mid-Columbia region of Oregon and the Pacific Northwest.

The center’s overall objectives are to preserve fruit quality, reduce postharvest disorders and lengthen marketability of pears and sweet cherries through:

n Developing and improving postharvest chemical and non-chemical treatments

n Modifying temperature and atmospheric conditions

n Elucidating the effect of pre-harvest factors on fruit quality, disorders and storability

Six Postharvest research and extension programs are currently in progress; three examples are given as following.

Exporting continues to play a key part in keeping tree fruit production profitable in the Pacific Northwest. About one-third of the pear and sweet cherry production is exported to foreign markets. Therefore, extending Postharvest storage/shipping life and assuring good arrival quality is an essential requirement for the PNW tree fruit industry.

In addition to good temperature management practices, new pear and sweet cherry technologies are needed for long-term storage/shipping and subsequent marketing shelf life.

The major quality issues upon arrival at long-distance markets are over-ripening and physiological disorders of pears. The pear industry has tried using modified atmosphere packaging (MAP) to ensure arrival quality of Bartlett pears; however, numerous MAP-related complaints have presented problems for receivers and buyers.

[Editor’s note: MAP, according to Wikipedia, is the practice of modifying the internal atmosphere of common food packages in order to improve shelf life in food products. The modification process often tries to lower the amount of oxygen (O2), in order to slow down the growth of aerobic organisms and the speed of oxidation reactions. The removed oxygen may be replaced with nitrogen or carbon dioxide (CO2) that can lower the pH or inhibit the growth of bacteria.]

The pear industry has also been interested in using MAP for maintaining quality similar to the use of CA without the extensive investment in infrastructure and instrumentation.

However, there are significant data gaps on optimum MAP conditions for each pear cultivar, such as the most efficient O2 and CO2 ranges, low O2 and/or high CO2 injury thresholds, effect of ethylene accumulation with MAP on fruit quality, and safe storage life.

We collaborated with the major international MAP bag manufactures to identify the optimum O2, CO2, and ethylene ranges for MAP bags to extend storage/shipping life for Stark Crimson, Bartlett and Comice pears. We have also determined causes of the internal browning disorder (IBD) of Bartlett and Comice pears during long-term storage and long-distance transportations.

The commercial use of MAP on cherries has become more prevalent in the Northwest for delivering high-quality, late-season sweet cherries to distant markets. Optimum MAP conditions were developed for the standard cultivar.

Bing and commercial MAP bags were developed based on the physiological requirements of the mid-season cultivar Bing. The newly developed late-season cultivars may have distinctly different physiological activity. Therefore, existing commercial MAP bags may not fit the requirement needed for the late season cultivars.

Consumers often complain that MAP sweet cherries have good appearance but little flavor. We are determining the physiological requirements, the effects of O2 and CO2 on fruit quality, the optimum O2 and CO2 range for extending storage/shipping life of the late-season cultivars. We are also comparing the efficacy of commercially available MAP bags and evaluating the effects of new PGRs, edible coatings and food additives on fruit quality, in particular, flavor loss during storage.

SmartFresh, otherwise known as 1-MCP, a gaseous ethylene antagonist, delays ripening in many fruit by competing with ethylene at the ethylene receptor sites within the tissue. 1-MCP has been commercially successfully used by the apple industry to maintain firmness, improve acid retention, reduce postharvest disorders and prolong storage life.

The pear industry is highly interested in the potential for commercial use of 1-MCP for extending packing season, disorder control, and replacing CA to reduce storage cost. Existing impediments to commercialization are predicting the ripening ability of treated fruit and the consistency of the effect on a commercial scale.

Research is in progress on developing commercial protocols for extending the packing season and enhancing postharvest quality maintenance through the postharvest use of 1-MCP while allowing ripening to develop outstanding eating quality.

Pitting of sweet cherries continues to be the leading cause of product rejection and price modification by buyers and receivers on both domestic and international markets. Efforts have been directed toward identifying the basic cause(s) of susceptibility/resistance of cherry fruit to pitting; however, the results thus far have been contradictory.

Very limited research has been conducted on late-season cultivars that are becoming the leading cultivars for the export market. We are determining the effects of both pre- and postharvest factors on fruit quality, storability and pitting development.

Cultivars are known to be an important factor in pitting susceptibility. We are comparing the anatomy, cell wall chemistry and selected physiological characteristics of the cultivars with differing resistance to pitting.

The information from this research will allow developing horticultural practices and postharvest treatments to induce or increase resistance of sweet cherry fruit to postharvest pitting. The relationship of anatomy, cell wall structure and chemistry to pitting development may be useful for breeding new pit-resistant cultivars.

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