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"Power ultrasound, the use of
high-frequency sound waves, has great potential among these new
technologies," said Feng, whose lab contains a specially designed
multi-frequency, multi-mode, modulated sono-reactor, "the first of
its kind in the world." Feng
is investigating ultrasound's proficiency in killing food-borne
pathogens on the surface of fresh produce. He's also combining
ultrasound with electrolyzed water and other sanitizers to penetrate
and destroy such pathogens as Listeria monocytogenes and Escherichia
coli in the narrow and deep crevices of certain fruits and
vegetables.
"Electrolyzed water is created when
electrolysis is used to split salt water into two streams: one
acidic, the other alkaline," he said. "Acidic water is very powerful
in killing micro-organisms on food surfaces, on everything from
fruits and vegetables to eggs, poultry, beef and seafood."
Feng achieves the best results by
combining methods to achieve a synergistic effect. "We have combined
ultrasound with a mild heat treatment, such as a hot-water wash, for
added benefit, and we've introduced elevated pressure into the mix
to kill an even greater number of microbes," he continued.
According to the researcher, U of I
food microbiologist Scott Martin and graduate student Adam Baumann
combined ultrasound with ozonated water to eliminate all Listeria
biofilm on a stainless steel chip in 60 seconds -- "an exceptional
result," Feng said. The Listeria and Shigella pathogens produce
sticky biofilms that adhere so tightly to food and kitchen surfaces
it's difficult to remove them by scrubbing during food preparation.
Feng has also treated apple cider
with ultrasound and mild heat to achieve the 99.999 percent
reduction in E. coli 0157:H7 required by the Food and Drug
Administration. Traditional methods of eliminating this very
dangerous and acid-tolerant pathogen have involved using high
temperatures alone, which compromised quality, Feng said.
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column in this article] |
And that's where the other promising
uses of ultrasound come in. In addition to killing microbes,
ultrasound holds promise as a tool for extending the shelf life of
juices and enhancing the quality of other food products.
Feng has used ultrasound to
deactivate two tomato enzymes that were causing a loss of body in
tomato pastes and sauces, and he has reduced the activity of an
enzyme in orange juice that causes pulp to separate, reducing the
juice's cloudiness and making it more appealing to consumers.
The scientist also uses ultrasound
for peeling. "Right now, industry uses a 15 percent lye solution to
peel tomatoes," he said. "Using ultrasound reduces the amount of lye
needed to 2 percent, and better peeling results in a higher-quality
food product."
Feng and his colleagues also hope to
investigate the use of irradiation to eliminate viruses, such as
hepatitis B. The food science and human nutrition department has
purchased a new irradiator and an electron beam machine, and a
high-dose X-ray machine is on order. When the X-ray equipment
arrives, the U of I labs will be among the best in the country in
terms of research capacity on irradiation of foods, he said.
Feng's work has been published in a
number of academic journals, including the Journal of Food
Engineering and Food Research International. Funding has been
provided by ConAgra Foods, the Illinois Council on Food and
Agricultural Research, and the Center for Advanced Processing and
Packing Studies.
[University of Illinois news
release]
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