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
“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
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
“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
"Fresh-Cut Fruit Moves Into the Fast Lane" was published
in the August 2005 issue of Agricultural Research magazine.