Fumigation alternative studied
Being able to treat fruit in a shipping container in transit to foreign markets would reduce costs and hassles for packers while preserving fruit quality.
Photo by Don Wilson, Port of Seattle
A Washington State University researcher is assessing a quarantine treatment that would have several advantages over methyl bromide fumigation for exported apples and cherries. It could be less expensive and more environmentally friendly, and should enhance fruit quality, rather than mar it.
Fumigation is required for U.S. cherries exported to Australia, New Zealand, and South Korea to prevent live pests from being introduced in the receiving country. Most Northwest cherries shipped to Japan are fumigated, rather than produced under a complicated systems approach, according to Northwest Fruit Exporters. Fumigation is also required for apples exported to Japan, but no apples are shipped there because of the difficulties of fumigating apples and the negative impacts on their shelf life.
Global production of methyl bromide is being phased out because of concerns that it is depleting the earth’s ozone layer. Its use for quarantine treatments is still allowed, but whether it will continue to be available at affordable prices is questionable.
Dr. Shaojin Wang, engineer in WSU’s Department of Biological Systems Engineering, is leading a research project looking at a low-pressure system that might in the future be used as a quarantine treatment for both conventional and organic fruit.
In a project description obtained by Good Fruit Grower through a public records request, Wang states that previous research with a low-pressure system on other crops suggests that it could be an effective, environmentally friendly, nonchemical alternative to fumigation.
It might even be possible to treat fruit in the shipping containers during transit to overseas markets, eliminating the need for fumigation, reducing operational costs, and saving space for fruit packers.
Low pressure is achieved by applying a vacuum to the treatment chamber, which reduces the pressures of the gases and lowers the oxygen concentration. In an extremely low oxygen atmosphere, any insects in the fruit suffer cell damage or death.
The low-pressure system Wang is using for the project maintains an atmosphere with an oxygen level of 0.02 to 0.10 percent (depending on temperature), no carbon dioxide, no ethylene, and nearly 100 percent relative humidity. These conditions, while killing the pest, help preserve fruit quality by inhibiting bacterial and fungal decay and preventing ripening and other causes of deterioration.
In previous tests conducted by Stanley Burg, who invented the low-pressure system, the maximum storage length for sweet cherries was extended to up to 70 days with the low-pressure system, compared with up to 35 days in controlled-atmosphere storage and 21 days with standard refrigeration. With apples, the maximum storage time with the low-pressure treatment was more than 300 days, compared with 300 days in CA and 200 in regular storage. Moisture loss was also lower in the low-pressure treatment than in regular-atmosphere or CA storage.
Wang believes that with optimum pressures and temperatures in the treatment chamber, the storability of the fruit could be further enhanced. Ultra-low pressures of 10 to 15 millimeters of mercury (mmHg) below atmospheric pressure inhibit fruit respiration by 90 percent compared with 50 percent under optimal CA conditions, Burg has reported. This means that fruit destined for distant markets would not need to be harvested immature in order to maintain its quality during shipping.
Dr. Tom Davenport, plant physiologist at the University of Florida, and Dr. Judy Johnson, entomologist with the U.S. Department of Agriculture in Parlier, California, are working with Wang on the project.
The scientists have already researched the effect of a low-pressure treatment on the codling moth and other quarantine pests, using a pressure level of 50 mmHg and a temperature of 25° to 30°C (77° to 86°F). In tests with codling moth, larvae were the most susceptible life stage, and eggs were the least susceptible.
Future research will focus on whether the same effects on codling moth can be achieved with lower pressures and lower temperatures. Since the treatment must kill the most tolerant life stage, the scientists will also look at how different lengths of exposure affect eggs in order to identify the optimal treatment. Atlas Technologies of Port Townsend, Washington, is leasing pilot-scale chambers to WSU for the tests.
The effect of the treatment on product quality must also be studied. Treated fruit will be assessed for weight loss, firmness, peel and pulp color, soluble solids and acidity.
Once a treatment protocol that controls the insects without harming the fruit is confirmed, the low-pressure treatment will be tested on a commercial scale. Trials will be done at Snokist Growers’s packing facilities in Grandview, Washington, to confirm the efficacy of the treatment, evaluate the effects on fruit quality, and assess the engineering and economic feasibility of commercial implementation.
The treatment would have to be approved as a quarantine protocol by governments of importing countries before it could be used commercially.
Mark Powers, vice president of the Northwest Horticultural Council, said the tree fruit industry would welcome an alternative to fumigation. The low-pressure treatment might help address the quarantine concerns of South Korea, which currently does not allow imports of U.S. apples and pears because of codling moth. It might also have potential as an alternative to the complicated systems approach that producers have to follow to ship apples to Taiwan.
Wang’s project is funded by a grant from the U.S. Department of Agriculture’s National Institute for Food and Agriculture. The total cost of the project is $190,374.
Low-pressure storage has the potential both to extend storage life and to reduce physiological disorders such as scald, tests at the U.S. Department of Agriculture’s laboratory in Wenatchee, Washington, indicate. Dr. Jim Mattheis, plant physiologist, conducted tests with apples and pears during the 2009–2010 season, and plans to do experiments with cherries as well in the coming season.
The low-pressure concept, which involves creating a vacuum in the storage container to reduce the oxygen and ethylene to very low levels, was invented by Stanley Burg about 50 years ago to reduce the rate of ripening of fruits and vegetables. It works in a similar way to controlled-atmosphere storage.
Mattheis said technological advances in recent years have solved some of the problems with the older low-pressure equipment, such as undetectable leaks. “It’s almost like starting over again because the equipment is so much better,” he said.
The research-scale equipment that Mattheis tested was developed by Atlas Technologies of Port Townsend, Washington, which also has a shipping-container-size model that is being tested by a flower importer in Florida for extending the life of cut roses.
Mattheis thinks the current technology is commercially feasible. It’s just a question of what benefits tree fruit packers would gain from using it. “It’s not a question of whether or not it can work, it’s how well it can work. Based on the economics of it, does it fit into the packer’s suite of postharvest tools?”
With climacteric fruits, such as apples and pears, the respiration rate rises rapidly during ripening, and the internal ethylene content increases dramatically. For these fruits, the low-pressure system reduces both the oxygen and ethylene levels. Mattheis said it remains to be seen with cherries, which are not a climacteric fruit, whether the ultra-low oxygen level would provide a significant benefit in terms of fruit quality and stem condition.