Nov. 9, 1999 COLUMBIA, Mo. -- In 1865, French chemist Louis Pasteur introduced the world to the process now known as pasteurization. By heating milk at 145 degrees for 30 minutes, rapidly cooling it and then storing it below 50 degrees, Pasteur discovered that harmful bacteria were destroyed without significantly changing the milk's composition, flavor or nutritional value.
In 2000, U.S. consumers will be introduced to a new kind of pasteurization being developed by an interdisciplinary team of researchers at the University of Missouri-Columbia, Iowa State University and Natick Army Laboratory. Like its 19th century forerunner, it destroys bacteria without significantly changing product composition, flavor or nutritional value. However, this 21st century process, termed cold pasteurization, is much different. Using electron beam technology, it is fast, does not require heat and is designed to destroy one of the most feared bacterium in recent history - E. coli O157:H7.
"Today, you wouldn't even think of drinking milk that wasn't pasteurized," said Nan Unklesbay, MU food science professor. "So we asked ourselves, 'Why aren't other foods, such as ground beef, pasteurized against dangerous bacteria like E. coli O157:H7?'"
Unklesbay has been the principal food scientist for the development of electron beam, or "E-beam," technology since 1995. That is when electrical engineering professor Randy Curry came to MU, bringing with him an accelerator. The high-powered accelerator is a type of cathode ray tube, similar to that found in a conventional television set.
In the 1980s, Curry developed similar devices for President Reagan's Strategic Defense Initiative, popularly known as "Star Wars." After "Star Wars" lost funding, he continued to develop accelerator technologies for national defense, but on a different level. Instead of defending against missile attacks, the accelerator defends against harmful microbes in food. Working together, Curry and engineering professors Kenneth Unklesbay and Tom Clevenger developed and refined the process. Their research was funded by a $250,000 grant from the Electrical Power Research Institute.
"We focused on E. coli O157:H7 contamination of ground beef for two reasons," Nan Unklesbay said. "First, meat is the most common source of E. coli O157:H7 poisoning. Second, E. coli O157:H7 is the nastiest bacteria we know about. It can survive temperatures and acidic conditions that others cannot. Because of its resilience, it is considered to be an indicator organism. We know that if we can kill E. coli O157:H7, we can kill everything else too."
In essence, the process of cold pasteurization is relatively simple. Once the linear accelerator is activated, electrons are accelerated down a tube. With a flip of a switch, the accelerator then propels the electrons at high speeds, creating an "E-beam." When this invisible beam hits the E. coli, it interacts with the microbe's DNA, deactivating it.
"The whole process takes only a few seconds," Unklesbay said. "Though a number of variables, including fat content, thickness and state (fresh or frozen) of the meat, affect the duration and intensity of the process, the cold pasteurization occurs in the same way."
Consumers will see evidence of cold pasteurization as early as February. Two U.S. meat processors plan to offer frozen hamburger patties treated with "E-beams" to grocers and fast food restaurants. Processing will be at a new, $6 million plant in Iowa City, Iowa, built by The Titan Corporation, a manufacturer of the accelerators. Patties will be frozen, processed, packaged and then treated. A cost increase of three to seven cents per pound is expected.
"At first, cold pasteurized products at the grocery store will be labeled as 'irradiated,' but the term should not worry consumers. It is simply the term that the USDA requires," Unklesbay said. "The process is non-nuclear, and we're working to have cold pasteurized products labeled as such to avoid confusion." Curry believes new accelerators will make the process less expensive to commercialize.
As a food scientist, Unklesbay's responsibility has been to monitor the affects of cold pasteurization on products. She said the process does not alter the proteins, fats and carbohydrates in the meat, and that nutrient losses are less than traditional methods of preservation. In addition, cold pasteurization does not significantly affect the color, texture or flavor of frozen ground beef, and only a minimal flavor change was evident in ground beef.
"The 'E-beams' do create minute levels of radiolytes, natural compounds created when meat tissue is heated," she said. "These same non-carcinogenic compounds are created when meat is grilled or broiled."
Unklesbay also said that while "E-beams" effectively destroy E. coli and other microbes, they have some limitations. Presently, the process is limited to liquid and homogenized products of uniform shape that ensure even distribution of electrons. In time, the MU team hopes to improve the technology so that it may be used on items of varied shapes.
Researchers also are investigating the uses of X-rays instead of electron beams. New accelerator technologies are being introduced commercially allowing electron beams to be converted to X-rays for greater penetration into foods.
"This technology has a lot of potential beyond ground meat," she said. "Drs. Curry and Clevenger are developing a method for destroying cryptosporidium in drinking water, and we're considering it for fruits and vegetables." In time, Unklesbay said cold pasteurization could be combined with sensitizers, a group of compounds that boost the efficiency of "E-beams."
"Right now, we're working with soluble polylactic acid, or SPLA," she said. "It reduces E. coli O157:H7 by creating intolerable acidic conditions, and we've seen significant results by combining the methods." Working with Unklesbay, Curry and Clevenger have developed other sensitizers that may be more effective than SPLA when combined with electron beam treatment.
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