Researchers make progress on fresh-cut tree fruits

Researchers are able to stop apple slices
from turning brown for up to five weeks.

By Melissa Hansen

Pacific Northwest tree fruit industry representatives who visited East Coast research centers are excited about progress made in developing techniques to prevent browning and lengthen the shelf life of fresh-cut apples, pears, and other tree fruit.

Several eastern U.S. laboratories are working on fresh-cut research, including Cornell University, New York, and U.S. Department of Agriculture (USDA) research centers in Beltsville, Maryland, and Wyndmoor, Pennsylvania. The University of California, Davis, is working on value-added products for pears.

Beltsville discovery

Agricultural scientists at USDA's Horticultural Crops Quality Laboratory in Beltsville have discovered a way of keeping fresh, sliced apples from browning for up to five weeks. The technique--which uses a combination of natural compounds or their derivatives, without using special packaging--could eventually have a major impact in developing value-added products from fresh fruit.

Lead researcher Dr. George Buta explained how they looked at a variety of compounds working together in coming up with their special mixture. Apple slices have been dipped in ascorbic acid (vitamin C) to prevent browning, but the sliced fruit can only be kept for a short period at low temperatures or in modified atmosphere packaging.

"We decided to try other natural compounds in combination with each other instead of individually to see if we could improve shelf life," said Buta. "All we've really done is to take things one step farther. There is nothing patentable here--none of the compounds are proprietary or secretive."

The compounds are 4-hexylresorcinol (found in Sucrets lozenges), isoascorbic acid, a sulfur-containing amino acid called N-acetylcysteine, and calcium propionate. The additives are a combination of enzymatic inhibitors, reducing agents, and calcium-enriched antimicrobials.

Red Delicious apple slices were used in Buta's research and stored at temperatures of 5 and 10°C (41 and 50°F) under normal atmospheric conditions. The appearance of apple slices treated with a mixture of the four compounds remained unchanged for up to five weeks at 5°C. Apple slices stored at 10°C showed similar measurements after three weeks of storage.

Buta said analyses of organic acids and the major sugars revealed that treated apple slices retained higher levels of malic acid and had no deterioration in sugar levels at 5 and 10°C.

"This indicates that higher quality was maintained during storage," he said.

Taste tests of the sliced apples showed vitamin C was the only component that could be detected. Buta believes technology will be able to eliminate most of the vitamin C flavors.

"We are encouraged by the compound's success with apples," said Buta, adding they will be using the same concept to prevent browning in other fruits and doing research on Bartlett, Bosc, and d'Anjou pear varieties.

"There may be some possibilities to extend the shelf life of fresh-cut peaches," he added.

The Beltsville lab specializes in postharvest research to improve crop quality. Natural compounds, like methyl jasmonate, are studied for their effect on improving shelf life and preventing storage molds.

Wyndmoor progress

Not far from Beltsville is the Eastern Regional Research Center of USDA's Agricultural Research Service (ARS) in Wyndmoor, Pennsylvania. This lab specializes in developing value-added products from existing commodities, as well as putting effort in food safety, microbial issues.

Dr. Gerald Sapers and his colleagues have been active in fresh-cut and enzymatic browning problem research for many years, looking for a substitute to sulfites.

The Wyndmoor lab is collaborating with a private company, EPL Technology, Inc., in developing compounds that will keep fresh, sliced apples, pears, and other fruit from browning.

Sapers said they are studying neutral-based formulations as an alternative to Buta's compound, which is acid. They are also working on the microbiological safety issue that can develop from greatly extending the shelf life of certain fruits.

"We are concerned about what happens to the fruit during that five-week period," he said. "That's an awfully long time."

Sapers would not comment on specific progress of the fresh-cut project because of its proprietary nature.

Industry views

The objective of the East Coast tour, organized by the Washington Tree Fruit Research Commission, was to exchange information between researchers and the Northwest tree fruit industry, learn what type of research is under way, and stimulate ideas for new research and relationships.

Jim Johnson, a research commissioner from Tonasket, Washington, said they saw a lot of good things happening in the USDA research labs. "The research is going in the right direction needed by our industry. Researchers are touching on the right issues, from phytonutrients and nutritional aspects to postharvest quality."

Buta's research looks very promising, said pear grower Mike McCarthy from Parkdale, Oregon.

McCarthy, as chair of the marketing committee of the Hood River Grower-Shipper Association, is keenly interested in research on fresh-cut pears.

"But there remains a lot of work to be done on refining the technique and understanding how fruit maturity and storage regimes affect shelf life and quality of the product," he said.

Pear texture has been a particularly difficult fresh-cut issue for researchers. Products have been developed to prevent browning, but the fruit loses juiciness during the extended shelf life. Researchers have found it difficult to maintain quality in sliced pears that have reached a certain pressure. Any formulation to extend fresh-cut fruit shelf life must maximize customer satisfaction without any detectable off flavors.

He sees the need for further "finessing" of any fresh-cut technology that is developed to make sure the consumer will accept the product 99% of the time.

"In general, all the research on fresh-cut fruit looks promising," said McCarthy, who majored in biochemistry in college and received a doctorate in animal physiology.

He took a side trip while on the East Coast to visit a private lab in Westport, Connecticut, also working on an antibrowning product for sliced apples and pears.

Denny Hayden, research commissioner from Pasco, Washington, is impressed with the potential of solving the fresh-cut problem in the near future. "We left with the notion there are real possibilities."

Another commissioner, Jim Doornink of Wapato, Washington, was impressed with the sincerity of the researchers working on fruit projects.

"The product of Buta's from Beltsville looked good, and the scientist appeared confident with his results," Doornink said, adding he was impressed that realistic storage temperatures were used in the research.

Some caution should be exercised when reviewing the fresh-cut research. Although the compounds are natural products, the U.S. Food and Drug Administration has not approved their use specifically on fresh-cut fruit, food which could be consumed in high quantities by children.

Any product or formulation must be affordable to the industry, be acceptable in terms of food safety, and be able to draw repeat customers.

"It's one thing to see apple slices on a Petri dish," said Jim McFerson, in charge of internal programs for the Research Commission. "It's another to see the product reach commercialization and be available on a commercial basis."

The East Coast trip was important for industry representatives, as it showed both the quality and quantity of research being done on a national level in areas of entomology, postharvest quality, pathology, and others.

"The distance of the laboratories from the West Coast makes it difficult to know what's going on," explained McFerson. Research projects from the East Coast have been funded by the Research Commission, though it's difficult to be informed without personally visiting research staff and facilities.

"These researchers are a great resource for our industry," said Doornink. "Because we're a large chunk of the fruit industry, we need to be supporting these scientists and become their constituency."

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Researchers make progress on fresh-cut tree fruits

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