MDS Nordion has developed a revolutionary new method of using x-rays for the processing of pallet loads of pre-packaged food or other materials. Conventional wisdom would say this is impossible, because you cannot give the right dose to the center of a pallet without overdosing the outside.
"Dose uniformity is critical to maintaining product flavor," said Dr. Joseph Borsa who partnered with Jiri Kotler in developing the system. "Most meat processors are looking for a ratio of maximum to minimum dose that is less than 1.5. Our new system gives a ratio of 1.3 or better for typical densities encountered in commercial shipments - on a full pallet."
The process takes advantage of the powerful penetrating ability of x-rays, together with the ability to control the direction, shape and power of the beam. It is completely compatible with existing product packaging. This greatly simplifies the incorporation of radiation processing into existing manufacturing operations. Each individual pallet is processed independently of other pallets, making the system extremely versatile in accommodating a variety of mixed products, such as would be encountered in commercial cold storage warehouses or distribution centers. Thus, the system is ideal for the provision of contract irradiation services. However, it would work equally well at a dedicated site, such as a manufacturer's warehouse, where handling product on pallets is routine.
A typical layout for this new system consists of a shielded chamber with thick concrete walls, not unlike that required for conventional systems, except for its considerably smaller size. Product pallets are transported into the shielded chamber, one pallet at a time, by means of a standard conveyor system. Inside the chamber, each individual pallet is loaded onto a computer-controlled turntable where the x-ray energy is applied as the pallet rotates. According to Dr. Borsa, it is this rotation, combined with the beam control mechanism that allows this system to beat the specifications of other existing devices. On completion of the irradiation step the pallet is conveyed out of the chamber and replaced with the next pallet. Energy utilization efficiency is comparable to, or even exceeds, that for conventional x-ray systems. The fact that product is handled on pallets greatly reduces labor requirements for moving product through the irradiator. The capital cost of this new system is lower than for conventional x-ray designs, because of the smaller footprint and the relative simplicity of the product conveyors.
X-rays for this system are produced in the standard manner, using a powerful electron beam accelerator and x-ray converter. Throughput capacity is determined by the power of the accelerator. Annual throughputs of 175 million pounds per year are possible with a 300 kW, 5 MeV accelerator, assuming a minimum dose of 1.75 kGy. Depending on the product characteristics and process requirements, a pallet load can be processed in about 3 to 15 minutes.
"This represents a true breakthrough in food irradiation technology," said Dr. Borsa. "Operations people love the simplicity of irradiating the product right on its pallet. At the same time, the technical people know that the uniform dose will safeguard the flavor of their product."
When asked about cost, Dr. Borsa did not give any details. "It will be more cost effective than a conventional x-ray system, but still not as economical as gamma." MDS Nordion is the world's leading supplier of gamma technology.
The company reports an enthusiastic response from major processors of beef, poultry and ready-to-eat products. They point out that it would be ideal for seafood, could be designed to irradiate bulk meat products in combos or agricultural commodities such as fruits and vegetables requiring quarantine security treatment for entering into international trade. MDS Nordion has a patent pending on this system.