Apr. 4, 2005 URBANA -- Power ultrasound and electrolyzed water are promising new food-processing technologies that could make the American food supply safer, said University of Illinois food scientist Hao Feng.
"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 foodborne 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 microorganisms 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'll be introducing 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.
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, Inc., the Illinois Council on Food and Agricultural Research (C-FAR), and the Center for Advanced Processing and Packaging Studies (CAPPS).
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