Salmonella and E. coli 0157:H7—involved in many of the recent outbreaks—are two of the pathogens targeted by the new technology at MSU.
The x-ray machine uses a higher dose of irradiation than medical x-ray imaging, yet less than competing irradiation methods such as gamma ray and electron beam. So far, the researchers have proved that x-rays can kill bacterial pathogens on ground beef, leafy greens and nuts.
“Our work to date has shown that x-ray technology is very effective in killing the bacterial pathogens without causing undesirable changes in product quality,” says Bradley Marks, a professor in the MSU Department of Biosystems and Agricultural Engineering.
The MSU researchers are concentrating on x-ray irradiation because most research to date has been almost exclusively conducted with gamma ray or e-beam. According to the Centers for Disease Control and Prevention, only four commercial x-ray irradiation units have been built in the world since 1996.
“Our overall goal is not to promote a particular technology, but to give food processors the best information available so that they can decide which irradiation technology is best for their process,” Marks says.
Currently, the MSU researchers are testing their technology’s ability to kill pathogens in nuts such as walnuts or almonds, with a possibility for future work on peanuts.
Nuts, because of their high fat and oil content, tend to become rancid after irradiation. “High fat/oil products naturally become rancid over time. Irradiation could speed up that process,” Marks says, adding, “I’m not saying that it will happen, but we just need to test for that.”
Patrick Archer, President of the American Peanut Council, says irradiation has been tested on peanuts in the past, but was “found unacceptable because it degraded the taste of the nut.”
However, MSU’s preliminary tests show no major quality problems such as rancidity, possibly due to the different nature of x-ray irradiation, which is lower energy than other methods.
To determine the proper dosage, the researchers first inject food with bacteria. The contaminated food is then put in a prototype machine that’s about the size of three home refrigerators hooked together. After the food is irradiated, the researchers count any surviving bacteria and look for physical changes in the food product.
“Our preliminary results have shown that x-ray technology is at least as effective at killing bacteria as e-beam or gamma ray, and in some cases it might be more effective,” Marks says.
A major advantage is that its low energy requires less protective shielding which means the equipment is more compact and can be installed right in the processing plants. Other irradiation methods have to be located in specialty facilities.
One downside, however, is that the x-ray can only process small quantities of food at a time, such as five-pound bags of lettuce. “You have to treat the product in single servings,” Marks says. Other technologies can irradiate food by the pallet.
Rayfresh Foods Inc., a technology start-up company that provided MSU with an x-ray prototype machine, is looking to ramp it up to a commercial scale. Recently, the company landed its first contract to build an x-ray machine to treat ground beef for Omaha Steaks.