(Jan. 19, 3:30 p.m.) A new irradiation process could give producers a way to fit irradiation machines directly into their packing lines.

The patented process, from Rayfresh Foods Inc., Ann Arbor, Mich., has been in the works for more than 10 years. It has been tested at Michigan State University, East Lansing, for the last three, resulting in data that supports the process’ ability to kill foodborne pathogens and extend the shelf life of produce.

Rayfresh’s process is a low radiation X-ray that has shown it can kill 99.9% of foodborne pathogens, including E. coli 0157: H7, on both meat and produce items. The company was contracted by Omaha Steaks, Omaha, Neb., to build its first full-scale X-ray irradiation machine in 2008, and should be finished with the machine by August, said Pete Schoch, president. The machine will also be able to handle foodservice-size bags of lettuce, he said, although that will not be its purpose for Omaha Steaks.

“We built the first machine, but it didn’t run as fast as we were told it would, so we had to rebuild parts of it,” Schoch said.

Schoch is especially optimistic about Rayfresh’s process for foodservice lettuce and spinach, he said, in response to the U.S. Food and Drug Administration’s August decision to allow food processors to use irradiation on fresh spinach and iceberg lettuce to kill E. coli and other pathogens.

“There’s significant interest in the technology and how it might be used on leafy greens,” Schoch said. “And we’re interested in the leafy green market.”

The company custom builds the machines, so it has yet to build a full-scale irradiation machine specifically for produce.

“They’re a couple million bucks, so we’re not keeping them in our pockets,” Schoch said.

The two irradiation methods currently in the market use gamma radiation or electron beam radiation. Both of those methods require products to be shipped to a separate building specifically for radiation. A big benefit of X-ray radiation is that it would be able to be built directly into a packer’s line, not requiring the produce to be shipped to another building.

“The shielding requirements aren’t as much, so they can build a machine that goes into a processing plant,” said Bradley Marks, a professor at Michigan State who is heading up research and testing with the Rayfresh technology.

Schoch said the machine is meant to fit between the carton and the bagging machine.

“Hopefully, we’ll be able to make it run fast enough to keep up with the bagging machine,” he said.

In terms of results, the system has proven at least as effective as the other methods of food irradiation, Marks said, and has not shown any signs of damage to the food items tested.

Marks said the university has not quantified the quality results yet, though, and has not done any shelf life studies. Based on previous experiments of irradiation’s effects on shelf life, it has been shown to add several weeks for cherries, blueberries, asparagus and mixed greens, among other items. It is expected that X-ray irradiation would have similar effects.

Rayfresh’s system can’t do everything gamma rays and e-beams can do, though. At a dose that wouldn’t cause any cellular damage to produce, the X-ray beams can’t penetrate too thick. This drawback makes the machine work well for the processing line, but does not give it the ability to irradiate entire pallets of food.

Cost is another setback with the Rayfresh system. In addition to the capital cost of purchasing a machine and installing it into an existing processing line, the X-ray radiation requires quite a bit of electricity to operate.

“One issue is converting electrical energy into X-ray radiation, and finding a way to do that energy efficiently,” Marks said.

Marks said he and his colleagues are looking into the possibility of a low-energy X-ray, which has not been studied extensively before.

“People in the business don’t want anything that’s going to add cost. Unfortunately, this process does add cost,” Schoch said.

Because Rayfresh is currently working on its first full-scale machine, extensive testing has not been done on exactly how much energy the system will require.

Marks said the biggest issues facing this new irradiation process are making sure it’s technically feasible, making sure it’s accepted from a regulatory point of view and making sure it’s accepted from the companies’ and consumers’ points of view.

“Irradiation is not new, but we know it’s effective, so why isn’t it used on all food?” Marks said. The answer is consumer acceptance. “We need public education and consumer awareness.”

Schoch said he is not too worried about regulatory approvals related to irradiation.

“The FDA is more afraid of E. coli than of irradiation,” he said.

Schoch likened the public’s perception of irradiation to the perception of pasteurization when it was new. Now, that method of killing pathogens in dairy products is highly accepted.

Plus, the market is in need of a method that guarantees the kill of pathogens, Schoch said.

“Whether you triple-wash or quadruple-wash, it doesn’t work. There is no kill step for greens,” Schoch said.

X-ray technology could be used for leafy greens
Sanghyup Jeong, a visiting assistant professor in biosystems engineering at Michigan State University, loads samples of lettuce into a prototype x-ray machine to kill bacterial pathogens.