UI researchers working to make food sound

Hey kids (and you rockin' adults, too), you might turn down the volume on your iPod if you saw what Hao Feng is doing to bacteria with sound waves.

OK, the University of Illinois food engineering professor is using ultrasound, which is in reality above the range of human hearing.

But the high energy brand of sound Feng and colleagues generate can actually poke holes in and kill bacteria threatening to human health, like E. coli, by causing their cell membranes to fracture or leak.

It's the same technology as the ultrasound used in medical imaging, notably to make images of babies in the womb, although that flavor has high frequency and low energy so it does no damage to the body. Feng uses a lower-frequency, higher-energy version.

In particular, he's looking at the method for use in food processing, perhaps in combination with other methods, to make our food safer and in some cases more tasty as well.

Feng has used ultrasound and mild heat to treat apple juice and yielded the 99.9 percent reduction in E. Coli demanded by the Food and Drug Administration. That's without the high heating the product usually goes through, which lowers its quality.

"Traditionally, we use high temperature to kill bugs, but quality is not good," Feng said recently. "We want to produce minimally processed food which is safe, tasty."

In addition, he's demonstrated that ultrasound can be employed to, in effect, turn off two tomato enzymes – proteins that act as biochemical catalysts in the body – that cause tomato paste and sauce to lose body.

He's also used ultrasound to curtail the activity of an enzyme in orange juice that causes pulp to separate and make the juice cloudy.

The ultrasound treatment not only affects the enzymes but kills foodborne pathogens in the bargain.

The UI scientist has applied the technology to the process of peeling tomatoes, too, reducing the amount of lye, which the food industry typically uses in the process, and resulting in a better quality product.

Besides E. Coli, Feng and colleagues Scott Martin, a UI food microbiologist, and graduate student Adam Baumann have used ultrasound on Listeria and Shigella, two pathogens that produce sticky biofilms that allow them to adhere to food and kitchen surfaces, making them difficult to wash away.

In that case, they used ultrasound in combination with a spray of electrolyzed water – salt water split into two streams, one acidic and one alkaline – to flush bacteria out of the hard-to-reach nooks and crannies of vegetables and fruits.

Ultrasound may negatively impact pathogens for a number of reasons, but Feng showed electron microscope images that illustrate what is likely a big one: the E. coli in the images look a bit like holey lumps of Swiss cheese after treatment.

In a process called "cavitation," the ultrasound waves make tiny bubbles in any liquid medium around the bacteria – whether it's apple juice or a water spray – until a critical mass is reached and those bubbles implode, or collapse. The resulting shock wave, so to speak, is what pokes holes in the bacteria.

"There are several mechanisms," Feng said. "But obviously the implosion is the most powerful of them."

Feng and colleagues have outlined their techniques in the Journal of Food Engineering and the journal Food Research International, among other places.

The research has been supported by ConAgra Foods, the Illinois Council on Food and Agricultural Research and the Center for Advanced Processing and Packing Studies.

The UI researchers also are studying irradiation in combination with other processing methods as a way of killing foodborne viruses, which are difficult to kill without damaging the food, Feng said.

You can reach News-Gazette staff writer Greg Kline at (217) 351-5215 or via e-mail at kline@news-gazette.com.

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