Quarantine treatment enhances fruit quality

Dr. Lisa Neven

Dr. Lisa Neven is shown here with insect supercooling point apparatus.

By Geraldine Warner

A new quarantine treatment for apples and pears might actually improve fruit quality, a Yakima, Washington, scientist says.

"This is the best news the industry has ever had and ever will have," declared Dr. Lisa Neven, entomologist with the U.S. Department of Agriculture.

Neven has been looking for alternatives to methyl bromide fumigation, which is required as a treatment for codling moth for apples exported to Japan. Pears have not been exported to Japan because they do not tolerate fumigation.

Neven has developed a controlled atmosphere and temperature treatment (CATTS) that looks promising for cherries, and even better for apples and pears.

"It's the first quarantine treatment ever that gives you better quality fruit after storage," she said.

More good news is that it perhaps could replace the lengthy cold treatment and complex monitoring required for apples exported to Mexico.

Neven has built on research done in Israel where scientists explored the use of heat treatments to reduce storage scald. There, the fruit was heated up slowly and held at high temperatures for days.

Neven has developed a model that predicts insect mortality at different rates of heating and a range of temperatures.

Fruit can be treated with hot, moist, forced air for two to six hours, depending on the temperature and heating rate used. Temperatures of 44°C or 46°C seem to work best.

For her experiments, which began two years ago, she has used several varieties of apples and pears. The fruit was heat-treated after harvest and stored in a regular CA (controlled atmosphere) storage for 90 days. Dr. Stephen Drake, horticulturist with the USDA in Wenatchee, Washington, then assessed fruit quality. Drake said heat treatment had more impact than fumigation on fruit quality. "You can't heat anything up and expect to get the same thing out of the oven," he commented.

However, in some cases, fruit quality was enhanced. Red Delicious apples treated at certain temperatures were redder than untreated fruit, while Granny Smith and Golden Delicious apples maintained their color. The balance of acids and soluble solids was better, indicating that treated fruit should have better flavor, although that would have to be determined by a taste panel, Neven said. The fruit was firmer, because ripening was delayed. Heat-treated pears ripened more uniformly.

There was a huge reduction in storage scald and a large reduction in decay organisms, even though the fruit was not treated with fungicides. Neven plans to do further studies on the effect of the heat treatment on decay, in collaboration with Dr. Peter Sanderson of the Washington Tree Fruit Research Commission. She suspects the heat treatment would be compatible with soft postharvest fungicides such as beneficial yeasts.

Meanwhile, she is refining the heat treatment and looking at combining it with a controlled atmosphere of 1% oxygen and 15% carbon dioxide to further stress the insect. By doing so, she believes the treatment time can be cut in half.

She is also figuring out how long treated fruit can be stored. "We were able to store Galas for 90 days and have good fruit, which was weird," she commented. "It's amazing there's a treatment where you get better quality fruit."

However, the treatment makes problem fruit worse. For example, Fuji with severe watercore exploded, bitter pit on Jonagold was accentuated, and Braeburn apples with browning disorder could easily be identified from the exterior after they had received the heat treatment. This, Neven points out, is not necessarily bad, as it would make the fruit easier to cull out before it goes into storage.

It might not be too difficult for the industry to make the switch from fumigation, as large heat treatment units are already available commercially. They are used to treat papaya in Hawaii and can hold 10 and 20 tons of fruit at a time.

Scientists with the USDA in Weslaco, Texas, are exploring the idea of converting methyl bromide fumigation chambers to heat treatment units.

"There might not be a lot of capital input for this," Neven said.

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Quarantine treatment enhances fruit quality

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