Fresh-cut fruit moves into the fast lane

August 1, 2005, ARS News Service: When it comes to eating, many Americans value convenience—a mentality that can get our waistlines into trouble. Fortunately, the term “fast food” is starting to include colorful, fiber-rich fruits and veggies—already peeled, sliced, and ready to eat.

According to the International Fresh-cut Produce Association, fresh-cut fruits and vegetables make up one of the fastest growing food categories in U.S. supermarkets. U.S. sales of fresh-cut produce sprang from $3.3 billion in 1994 to $11 billion in 2000 and are projected to reach $15 billion in 2005. Fresh-cut veggies, including ready-to-eat salads, account for most of these sales.

But Olusola Lamikanra, a chemist with ARS’s Food Processing and Sensory Quality Research Unit in New Orleans, Louisiana, is working to get fresh-cut fruits a much larger share of this market—and make them more available to consumers.

“What’s holding fresh-cut fruits back,” says Lamikanra, “are the physiological and biochemical changes that occur when they’re processed and stored. Compared to vegetables, fruits commonly used for the fresh-cut market generally have a higher pH and water content, making them more vulnerable to microorganisms and enzymatic changes.”

Mixing the Signals

Most of us don’t think very much about the act of slicing an apple. But the moment a knife pierces the skin of a piece of fruit, a series of physiological signals is set off. These signals, which can be transmitted within seconds, initiate defense responses that promote wound healing, guard against bacterial attack, and generally protect plant cells from further stress.

Lamikanra has devised ways to use this plant biology to his advantage. “The critical moment is when the plant tissues are cut,” he says. “It’s at this point that I’m trying to alter plant signals and change how they would normally respond.”

Plant cells will communicate stress signals if something changes the turgor (fluid) pressure within their tissues. Slicing through a piece of fruit—like popping a balloon—will certainly cause a change in pressure. So to keep the signals from firing, Lamikanra has tried cutting fruit while it’s submerged in water.

“By slicing the melon under water,” says Lamikanra, “we can control turgor pressure, because water forms a barrier that prevents movement of fruit fluids while the melon’s being cut.”

Lamikanra is still working to improve the engineering designs surrounding his submerged-processing technology. He says this approach also works well for vegetables, since they don’t require as much peeling and separating—tasks more difficult to do under water.

Heat and ultraviolet light

Lamikanra is using another cue from the outside environment to trick plant tissues: heat. By submitting cantaloupes to temperatures 50°F above their normal growing temperature for a period of time, he causes the fruit’s tissues to produce a unique set of proteins.

“This response is ubiquitous across microorganisms, plants, and even animals,” says Lamikanra. “The plant produces heat-shock proteins, which prevent wound proteins from forming and protect the shocked tissue from later stress.”

For instance, a heat shock of about 115°F for about 3 minutes keeps lettuce leaf tissue from producing certain enzymes that would eventually cause it to turn brown. This mild heat treatment is enough to produce heat-shock proteins without harming quality.

Hoping to provide as many options as possible to food processors, Lamikanra has tested another technology to extend the shelf life of cut fruits. While it’s traditionally been used to sterilize foods, ultraviolet (UV) light can also be used to trip up a plant’s classic stress response.

Testing Our Senses—and Sensibility

What sets his work apart from others in his field is that Lamikanra is working alongside a food sensory expert—Karen Bett-Garber—to see whether fruits cut with his novel processing methods actually taste fresh longer. Bett-Garber oversees activities at the sensory lab at the Southern Regional Research Center (SRRC) in New Orleans. She conducts studies with trained panelists to see whether food-processing technologies being developed by SRRC scientists are truly improving quality from a human sensory standpoint.

And Lamikanra’s technologies are doing just that.

“We’ve seen an improved duration of the fruity flavors in melons processed with his methods,” says Bett-Garber. “And that’s our goal—to keep those desirable flavors lasting longer.”

 

"Fresh-Cut Fruit Moves Into the Fast Lane" was published in the August 2005 issue of Agricultural Research magazine.
http://www.ars.usda.gov/is/AR/archive/aug05/fruit0805.htm

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