Growing concern over the safety of the US food supply could lead to more facilities that will irradiate meat to kill bacteria, larva, and other carriers of diseases. Fourteen Isomedix irradiation plants in the United States, Canada, and Puerto Rico currently sterilize disposable medical equipment and a broad range of consumer products, including baby-care products. If beef irradiation becomes an accepted practice, Isomedix hopes to build plants, which will serve a single beef-processing facility or to contract out for multiple processors. The article discusses that the most likely scenario for plant construction in the future is building dedicated food irradiation plants either at or as near as possible to the point of transportation and distribution, after the final packaging and labelling is complete, to prevent the possibility of recontamination after irradiation. Irradiation also delays the ripening of certain fruits and vegetables, including strawberries, tomatoes, and mushrooms, which are the main crops that are treated at Food Technology Service Inc, in Mulberry, Florida.


SIXTEEN COLORADO DINER.S became ill last year and 25 million pounds of ground beef were taken off the market-the largest such recall in U.S. history- all because of micro-organisms that made their way into the meat at one N ebraska processing facility. Such stories involving the E. coli bacteria, the culprit in Colorado, and other organic contaminants always raise fears among the public about food safety.

Several methods of destroying those organisms are available. One of the most effective and most controversial is irradiation, in which food is exposed to measured amounts of intense radiant energy to d estroy any pathogens. While the technology was first put into reg- ular use in the United States on bacon, wheat, wheat flour, and potatoes in the 1960s, the Food and Drug Administration (FDA) approved it for fresh and fro zen red meats such as beef, lamb, and porkjust last December. The agency's approval was made in response to a 1,300-page petition filed in 1994 by Isomedix Inc., an irradiation company in Whippany, N.J. According to John Masefield-founder, ch airman, and CEO of Isomedix, and principal au thor of the petitionharmful microbial pathogens in food are estim ated to ca use many as 9,000 dea ths and 200 million to 250 million illnesses each year in the United States.

Fourteen Isomedix irradiation plants in the United States, Canada, and Puerto Rico currently sterilize disposable medical equipment and a broad range of consumer products, including baby-care products. "We will be able to conduct test work for the beef companies at our existing plants, and will be able to design dedicated beef-irradiation plants in the future based on this work," said Grace Masefield, Isomedix's director of market strategy development. These plants either would be dedicated to a single, large beef producer or would treat beef from smaller producers on a contract basis.

Any new facilities resulting from the FDA approval would most likely be based on designs from Isomedix or from the only two commercial food-irradiation companies currently operating in the United States: SteriGenics International in Tustin, Calif.; or Food Technology Service Inc. (FTSI) in Mulberry, Fla. However, de spite the agency's sanction of the process for meat, which should help contain outbreaks of virulent micro-organisms such as E. coli 0157:H7 and species of Salmonella, the construction of new food-irradiation plants will hinge on public acceptance of the practice.

Some consumer groups have expressed strong reservations about the process. According to Daniel Engeljohn, a food technologist and chief of the Standards Development Branch of the U.S. Department of Agriculture's Food Safety and Inspection Service in Washington, D. e., the vocal opposition to food irradiation appears to be generated partly from people opposed to any aspect of the nuclear industry plus a lack of understanding of what irradiation actually is. "In fact," he said, "food irradiation is a well-studied technology that has been more researched than any food-processing technique."

Opposition to irradiation and the latest FDA approval also lies in concerns over food safety in general. "Consumers prefer to have no filth on meat than to have filth sterilized by irradiation;' said Michael Jacobson, executive director of the Center for Science in the Public Interest in Washington, D.e. And even though the FDA endorsed the process, the agency added that irradiation "is a complement to, not a replacement for, proper food-handling practices by producers, processors, and consum.ers."



Driving Out Contaminants

The push to improve food quality through irradiation began early this century, when researchers ain"led newly discovered X-rays at foodstuffs to preserve them. In the 1950s, the availability of manmade isotopes such as cobalt-60, used to sterilize medical equipment, changed the course of food irradiation. Gamma rays emitted by the isotope were able to destroy pathogens in food as effectively as luore-expensive technologies such as an electron accelerator. Since then, the technique has been applied to such items as poultry, fruits and vegetables, and spices.

In 1986, SteriGenics began irradiating dryfood ingredients such as pepper, onion powder, and dehydrated vegetable powder at facilities in Tustin; Schaumburg, Ill.; Rockaway, N.J.; and Salem, N.]. These plants irradiate approximately 50 million pounds of spices annually, according to Tom Mates, genera l manager of the Tustin facility. Founded in 1979 to sterilize single-use, disposable medical products such as syringes and gowns, the company now operates a total of 12 contract sterilization facilities in the United States and a joint venture in Taiwan.

The spices arrive at SteriGenics plant warehouses in bulk form in bags and drums, or sometimes in their final form in boxes. Workers affix dosimeters, such as those made by Far West Technology in Goleta, Calif., on the containers before loading them into metal containers or totes. The totes are loaded onto carriers that are suspended from an overhead monorail to move them into an irradiating treatment cell. The cell walls and ceiling are 6Y2-foot-thick concrete poured around steel rebar to ensure that no crack can penetrate the walls.

The totes are exposed to gamma rays with very short wavelengths, similar to ultraviolet light and microwaves, emitted from an array of cobalt-60 "pencils" installed on either side of an 8- by 16-foot stainless-steel rack. The pencils are actually tainless-steel tubes containing two zircon alloy tubes that encapsulate nickel-coated pellets of cobalt-60. When the pencils are not in useduring maintenance, for example-they are submerged. in a 26-foot-deep pool of deionized water, more than twice the depth needed to protect maintenance workers when the array is submerged, and raised when irradiation recommences.

A U-shaped overhead conveyor in the cell guide the totes until they are exposed for a timed interval for the desired absorbed dosage of gamma radiation, a maximum of 30 kilograys for spices. (A gray, measuring the absorbed dose of ionizing radiation, is equal to 1 joule per kilogram.) The treated totes are returned to the warehouse on the other side of the conveyor dividing the loading and unloading operations. T he spice containers are removed from the totes and shipped to their customers.

SteriGenics retrofit its Tustin plant in 1996 to treat low dose foo ds requ ir ing less than 1 kilogray of ra diatio n. "These are fresh vegetables, including avocado, onions, celery, belJ peppers, and broccoli, that are sold either for retail sale or as ingredients for other products such as a salsa," Mates said. T he shelf life of fresh produce ir radiated at Tustin is extended by up to two weeks.

Palletlzed Loads

The yea r before Ste riGe nics began irradiating food, FTSI, the other American food irradiator, was formed because the Florida Citrus COlIDllission sought an alternative to methyl bromide as a quarantine treatment for citrus. The agency was acting on an Environmental Protection Agency suggestion that methyl bromide, used to prevent the spread of fruit fli es, would be banned (which will take place in 2001).

The FTSI plant in Mulberry has been operating since the firs t quarter of 1992. The company trea ts several tru ckloads of packaged agricultural products per week fo r both local and natio nal b ro ker s and distr ibuto rs. T hese foods are sold to retail establishments and institutions. "We believe the food-irradiation industry will be based on public health concerns, such as food poisoning, ra ther than economic benefits," said FTSI executive vice president Harley Everett, although such economic benefits do accrue, specifically by extending shelf life and serving as a quarantine measure. T he process eliminates sprouting in tubers such as potatoes, garlic, and onions, for example. " Irra diation also delays the ripening of certain fruits and vegetables, including strawberries, tomatoes, and mushrooms, which are the main crops we treat here," he said.

As a quarantine measure, irradiation kills the larva of insect pests such as fruit fli es and seed weevils in mangoes, preve nting them from spreading between growing re- gions. " Irradiation can also be used to pasteurize seafood," Everett said.

FTSI's irradiator and safety control system were designed and built by MDS Nordion in Kanata, Ontario, a major supplier of cobalt-60 as well as a designer of medical-sterilization plants and research-irradiator equipment. "We became involved in FTSI to get a conU11.ercial food-irradiation facility going that would demonstrate not only the safety and efficacy of the technology but that consumers would buy clearly labeled irradiated foods," said Frank Fraser, a mechanical engineer and vice president of market development at MDS.

The MDS engineers used their own controls and interlocks for the FTSI safety system, which also included radiation monitors, restricted openings, and a procedure to replace cobalt-60 pencils underwater with magnifYing lenses and manip ulators. Several hundred different conditions will automatically shut down the system in case of component failure or system inconsistency.

Unlike the process loops at other facilities, FTSI's can irradiate large pallets of packaged foods. MDS engineers had to build a plant that would handle the heavier loads than their earlier systems could. According to Fraser, this involved scaling up the 48- by 24-inch conveyors used in facilities like the Canadian Irradiation Facility in Montreal to 48 by 42 inches to handle U.S. pallet sizes. "This involved testing monorails, bearings, wheels, and I-beams to build an overhead conveyor that could transport the 2-ton loads in a single carrier," he said. "We also used hydraulic cushions to gently stop the larger loads, and built forklift clearances so the pallets could be loaded and unloaded from the carriers."

These carriers are 18-foot-tall, 4-foot-wide, 4-foot-deep aluminum boxes holding a shelf at floor and midlevel. Forklift operators load a pallet on each shelf of the carrier. The carriers are transported from the warehouse into the 6Y2-foot-thick concrete treatment cell via a pneumatic overhead monorail. Once inside, hydraulics move the carriers, primarily because greater locational accuracy of movement is required; this also reduces the number of cylinders needed to carry the heavy loads.

As in the SeriGenics process, the FTSI carriers follow a U-shaped traj ectory in the treatment cell that exposes them to ganU11.a rays from cobalt-60 pencils. The exposure time in the concrete cell and other process parameters is directed by Omron logic controllers.

After being irradiated, the carriers return to the warehouse on the other side of an interior chainlink fence that separates the two halves of the irradiating process. The pallets are removed by forklift and placed on trucks for delivery. "Our intent is to expand irradiation to service other parts of the cOllntry," Everett said. "The approval of using the technique to treat beef can only help."

Accelerating Irradiation

ONLY TWO COMPANIES-SteriGenics International in Tustin, Calif.; and Food Technology Service Inc. in Mulberry, Fla.-irradiate food in the United States, and both use the same basic process involving cobalt-50 isotopes. Linear accelerators, however, may be the technology of future plants. These devices emit a beam of electrons that directly contact the product or convert the accelerated electrons into Xrays, which can penetrate deeper than an electron beam but are less efficient.

Most linear-acceleration opera tions opt for showering the product with electrons, according to Daniel Engeljohn, chief of the Standards Development Branch of the U.S. Department of Agriculture's Food Safety and Inspection Service in Washington, D.C. The Utilization Center for Agricultural Products at Iowa State University in Ames uses this technique. Dennis Olson, a meat scientist and director of the center, is conducting food-irradiation experiments on meat products with a Circe 3 irradiator built by Thomson CFE in Saint-Aubin, France. The center's work is sponsored by the U.S. Army, the Agriculture Department, and the Electric Power Research Institute in Palo Alto, Calif., with grants from meat producers' groups including the Cattlemen's Association and Pork Producers.

Olson and his colleagues are using the device to address two major concerns facing linear-accelerator irradiation. "The first is to determine which packaging materials can be used in irradiation without causing compounds to migrate into the food," Olson said. "Our second goal is to determine the optimum packaging environment for meat products being irradiated-specifically, vacuum packing, a modified atmosphere such as nitrogen blanket, or oxygen."

The Iowa researchers load meat products onto carts attached to conveyor chains that transport the carts through the 93/4-footthick concrete walls of the irradiation area. The floor-mounted Circe 3 contains an electron gun comprising a cathode and anode that generate electrons, which are pulsed into an accelerating tube. At the same time, radio-frequency power is pulsed into the accelerating tube by a klystron, forming waves for the electrons to follow.

A series of alternating magnets in the tube accelerate the electrons to the high energy levels required for irradiation. When they reach the end of the tube, the electrons pass through a Glaser lens that focuses them into a beam. The beam is bent by a magnet to a 107-degree angle, so only the particles of the selected energy level are emitted. Those filtered electrons pass through a scanning magnet and sweep across the meat's surface, changing the DNA of microbes in the food and killing these pathogens.

Three different energy levels can be selected: 5 million, 7.5 million, and 10 million electron volts, which can penetrate 3/4, 1, and 1.5 inches on one side, respectively, or 13/4, 2lf4 inches, and 3l.f.l inches if both sides are irradiated. "We pick up some electrons when irradiating both sides, which is why the penetration is more than double," Olson said.

A multilayered safety system is a hallmark of the Ames irradiation facility, starting with the maze through which the carts are conveyed-three gO-degree turns that serve as a biological shield, preventing electrons or X-rays from ricocheting to the product-handling area. This and other safety devices are wired to the control panel and to the Circe 3. "Thus, if one electric path fails, the other will trip the electron source and shut down the facility," Olson said.



Irradiatlon's Future

According to Everett, the most likely scenario for plant construction in the future "is building dedicated foodirradiation plants either at or as near as possible to the point of transportation and distribution, after the final packaging and labeling is complete, to prevent the possibility of recontamination after irradiation."

SteriGenics' Mates agreed with the importance oflocation, especially because rising freight costs could exceed irradiation costs. (An increase in gasoline prices could also affect the economics of irradiation.) He noted that relatively few plants, each of which he estimated at $10 million to $12 million, would suffice. "For example, a well-built, well-located spice plant could treat up to 150 million pounds of product a year."

"Food irradiation is a technology whose. time has come, because food inspection and testing are revealing more incidents of foodborne disease," MDS's Fraser added. "Also, based on trade shows we attend, studies we conduct, and the experience of the commercial irradiators like FTSI, we were able to show that consumers are willing to buy irradiated food. The next step is convincing corporate officers that irradiated foods will sell."