Georgia researcher perfecting fresh-sliced peaches

Fresh-cut sliced peaches, packaged in a clear plastic inverted cup, are about two years away from the convenience food market, if things come together as Kathryn Taylor hopes they will.

A horticultural specialist in stone fruits at the University of Georgia, Taylor has been working to develop the protocol for making this new product, which would put Georgia peaches alongside sliced apples and melons in the fresh, healthy, ready-to-eat fruit snack category.

She hopes to patent both the processing protocol and the solution needed to treat the cut peaches so they won’t brown, ferment, rot or lose their texture during two weeks or more of storage at 33˚ F.

She apologized to her audience during the Southeastern Peach Convention, which was part of the Southeast Regional Fruit and Vegetable Conference in Savannah in early January. She said she was “being very obtuse right now” about both the procedure and the formulation, saying she wanted to patent both, benefiting her research program, the University of Georgia and the USDA-ARS Citrus and Subtropical Products Research Laboratory.

Two years ago, Taylor developed a process called “cable girdling” for peaches, in which peach tree trunks are constricted with plastic cable ties – without damaging trees as knife girdling does. The girdling process keeps plant carbohydrates up in the tree leaves and produces peaches that are larger and sweeter and mature four or five days earlier. The freeze last Easter demonstrated another benefit: Trees girdled the previous October gained some protection from freezes and produced more sound fruit compared to non-treated trees.

The girdling process is so simple – requiring only plastic ties and pliers – that there’s nothing to patent.

Fresh-cut peaches are more complicated.

Taylor described the procedure developed by her and her collaborators at the USDA-ARS Citrus and Subtropical Products Research Laboratory in Winter Haven, Fla. Freshly picked peaches were cooled to 33˚ F overnight and the chilled fruit were rinsed and placed into a boiling lye solution. After a minute, the skins were slipped off by hand rubbing.

The fruit was then rinsed in a food-grade acid solution, dipped in a 0.5 percent bleach solution, dried with a sterile towel, sliced and treated with one of 13 different coatings.

The coatings contained various sterile mixtures of materials that included neutralizing agents, an ascorbate anti-browning agent, a calcium salt stabilizing agent and a sticking agent.

The treated slices were allowed to drain for five minutes on sterile towels before being packed in Fresh-R-Pax storage containers made by Maxwell-Chase Technologies in Atlanta.

A slice of fruit from each treatment was tested at intervals from one hour after treatment up to 26 days, being evaluated for color (change in Delta-E value calculated from the L a b color data) and texture (firmness measured in pounds of pressure).

Sterile water was used as a control,

In the early tests, promising coatings were tweaked to give even better results.

Several peach varieties were tested. Some were found to respond poorly to all coatings and others gave good results with three coatings – all of which gave acceptable results. The variety Flordacrest gave poor results; GaLa, Redglobe, Sunprince and Augustprince gave very good results, Taylor said.

The solution identified as best kept fruit texture “palatable” for at least 12 days after treatment.

“In our early season assessment of the variety GaLa, we began to realize that the degree of ripeness and degree of fruit injury impacted the appearance of the fruit substantially more than the election among our three coating finalists,” Taylor said. “If a fruit slice had been bruised during preparation, the bruise appeared brown in the finished product almost immediately and was beginning to be unattractive even two hours after slice preparation.

“As fruit ripened to a greater extent, they were less responsive to browning prevention by the edible coatings we tested. If fruit were sliced and coated immediately after picking, they produced better results than fruit prepared after further ripening by sitting at room temperature for 48 hours after picking.

“If we selected fruit that were stored at 33˚ F over a two-week period, the fruit prepared immediately after picking produced better results than fruit prepared two weeks after picking.”

Other observations were made during the study:

- Knife quality and quality of the slice impacts appearance greatly.

- Any bruising – handling or slicing – will be noticed as a dark, unattractive mark on the peach.

- Freestone peaches, which release from the pit easily, are better candidates for the process.

- Lye could be used to aid release of slices or peach halves from the pit, but lye promoted darkening of red pigmentation of the flesh.

- Some red pigmentation in the final product may be a plus for the health-conscious.

- Ripeness of the fruit impacts the effectiveness of the coatings. A fruit ripeness of No. 4 to No. 5 on the Clemson Color Chip – the same as the level of ripeness growers prefer for shipping fruit – provided better results than riper fruit.

- Some peach varieties do not respond well to coatings and are poor candidates for slicing.

- Smaller fruit than what consumers want for fresh eating appear acceptable as peach slices.

- The product needs to be treated in a manner similar to melon slices, with an absorbent layer of paper at the bottom to absorb juices.

Taylor said it would take about another year to further evaluate varieties suitable for slicing, including having a closer look at both yellow and white varieties and melting and non-melting varieties.

Taste panel tests also need to be conducted.

She said it would take perhaps another year to get the patents in order before the product could be licensed.