Technological and Economic Hurdles
Food and Water’s anti-irradiation campaign may be the most public obstacle to wider use of food irradiation, but it isn’t the only one. “The real barrier is economics and the bottom line” says Martin Stein, president of GrayStar, which is designing a food irradiator that can be installed in existing food-processing plants. In fact, a quick review of the methods the food industry could employ to generate ionizing radiation-using gamma rays from radioactive cobalt-60 or cesium-137, and electron beams or x-rays from linear accelerators-shows that the options have shortcomings that diminish their cost effectiveness, while improved models are still on the drawing board.
Gamma rays: Anyone interested in irradiating food today would probably turn to a cobalt-60-based system like the one in Mulberry, Fla., the first commercial facility dedicated to irradiating food. The heart of the plant, established in 1991, is a shiny rack of 400 gamma-ray-emitting cobalt-60 “pencils,” each 18 inches long and the diameter of a fat crayon, housed in a chamber surrounded by a concrete wall 6 feet thick. When not in use, the rack is submerged in a 15-foot-deep pool of cooled water that absorbs and neutralizes the gamma rays. At the push of a button, hydraulic arms lift the cobalt rack out of its protective pool and tall metal boxes packed with food slide into the irradiation chamber on an overhead monorail. The boxes follow a zig-zag pattern around the radioactive rack so gamma rays can reach all sides. Treatment times vary-fresh strawberries pass through in 5 to 8 minutes, frozen chicken takes as long as 20 minutes.
Gamma rays from cobalt-60 can penetrate full boxes of fresh or frozen food. But food must be removed from standard shipping pallets, stacked into metal irradiation boxes, and then returned to the pallets when they emerge from the chamber-all extra labor that increases costs.
A new irradiator now under development by GrayStar promises to address this concern by accepting food loaded onto standard pallets, something “everyone in the food industry says is an absolute must,” says Stein. The unit will generate gamma rays using cesium-137, which GrayStar would chemically separate from high-level nuclear waste now stored at several power plants around the country.
The prototype machine-which measures 10 feet wide, 8 feet long, and 28 feet high, 12 of which are underground-is de-signed to be in-stalled along a meat-packing or food-processing line. After a standard
pallet of packaged food rolls into the irradiation chamber, which is constructed from 16-inch steel walls, the operator will seal the doors and in-struct a computer to raise the rectangular array of cesium-containing rods from underground for a programmed length of time. Stein is optimistic that the unit will prove attractive to food processors and packers who may be more willing to invest in small, in-house irradiators than build, or contract with, a large central plant to which it must ship food. A working prototype of the compact unit, he says, is still a year away.
Electron beams and x-rays: Linear accelerators can generate ionizing radiation for food processing in the form of electron beams. Like a television set, these devices produce electrons from a heated filament sitting inside a vacuum tube. Magnetic fields accelerate the electrons through the tube until they reach energies as high as 10 million electron volts. At the end of the tube, meat or other food is irradiated as it slides by on a conveyor belt. Turn off the juice and the radiation disappears. A linear accelerator delivers more radiation per second than gamma rays, so it may work more quickly than a cobalt- or cesium-based machine.
“The downside is that electrons don’t penetrate more than an inch and a half. Thus electron beams would not be able to handle such items as boxes of fruit or sides of beef. However, says Dennis Olson, a professor of food science at Iowa State University who has been testing this method, “you could handle a product up to about three inches thick, something like hamburger or chicken breasts, if you irradiate from both sides.” Electron-beam units for such thin food products could move from the lab to the factory within a year or two at today’s pace of development, according to Spencer Stevens, president of Omaha-based APA, Inc., an engineering and consulting firm for the food and meat industry.
Olson and others are also exploring the use of x-rays for irradiating food. While it takes even more energy to make x-rays than it does to generate electron beams, thus lowering the efficiency of the process, x-rays have dramatically better penetrating power and could be used on stacked boxes of fresh or frozen food or on slabs of meat.