OREGON STATE UNIVERSITY

OSU RESEARCHERS PUT PRESSURE ON CHEESE TO KILL BAD BACTERIA

08/02/1996

CORVALLIS - Scientists at Oregon State University are pressure-treating cheese slurry to study the application of high pressure in accelerated cheese ripening.

"We're cooperating with food technology researchers at Ohio State University to develop a method of accelerating flavor ripening in cheese," said Dan Farkas, head of the OSU Department of Food Science and Technology. "An accelerated process will allow increased production of cheese at less cost, which will give marketers more flexibility in serving the growing consumer demand for various cheese products."

Researchers also hope accelerated processing will allow a high degree of flavor control in cheese, which would enable processors to develop a broad range of new products.

The average ripening period for cheese is six to 12 months. This can be shortened to around five days by raising the temperature of the cheese slurry, a liquid concentrate including curds and whey.

"Increasing the temperature of the slurry from eight to 30 degrees C dramatically reduces the ripening time, but it also increases the growth of undesirable microorganisms such as 'Staphylococcus' bacteria," said Tony Jin, a post-doctoral research fellow in the Ohio State University Department of Food Science and Technology.

That's where the pressure comes in.

Researchers have known for many years that exposing food samples to high pressure destroys many of the microorganisms in the food. Farkas is a nationally known leader in this research and has conducted several studies on the use of pressure in food preservation since joining the Oregon State University food science faculty several years ago.

According to Farkas, exposure to high pressure is extremely effective in killing undesirable bacteria in foods, while leaving desirable qualities of the product unchanged.

Among other projects, Farkas led a team of researchers who successfully used pressure technology to develop better-tasting field rations for the U.S. military.

"We're using an experimental pressure unit to expose cheese slurry samples to various levels of pressure ranging from 50,000 to 80,000 pounds per square inch," said Farkas. "We're looking for combinations of temperature and pressure to eliminate the microorganisms that cause health problems."

To make this accelerated process work, a way has to be found to kill harmful bacteria without eliminating the starter enzymes that give the cheese its flavor, Farkas said.

It may be possible, he added, to apply just the right amount of pressure to selectively control the harmful microorganisms, leaving the desirable microorganisms intact.

"If that isn't possible, we can apply enough pressure to kill all the microorganisms in the cheese slurry and starter enzymes can be added back into the product following the treatment," he said.

Pressure treatment of other kinds of foods has given those items longer shelf-life while maintaining their natural taste and flavor. Farkas expects the same result with pressure treatment of cheese products.