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