A good, hot meal can be a rare commodity for U.S. soldiers fighting abroad, but work by Washington State University researchers in developing a better food processing technique for military rations may eventually mean tastier army meals.

In collaboration with researchers from WSU Food Science department, U.S. Army Natick Soldier Center and industrial partners, Juming Tang, associate professor of biological systems engineering, and his associates have worked to develop a processing technology that uses radio frequency or microwave energy to shorten food processing time, allowing food to be heated evenly throughout without ruining its quality.

In preparing low acid, shelf-stable military rations, the conventional processing method uses hot water or steam to kill the C. Botulinum spore, which can cause deadly botulism in the anaerobic environment of hermetically sealed packages. In order to kill the bacteria spores, the core temperature of the product must reach temperatures beyond that of boiling water (100°C) and be maintained for a sufficient time. In general, the process times used for military meal-ready-to-eat (MRE) rations and humanitarian daily rations (HDR), like those that were recently air dropped in Afghanistan, are much longer than for meals sold in grocery stores. Otherwise, heat resistant no-pathogenic thermopiles that survive normal canning processes may cause spoilage in warm environments. Depending upon the package size and type of food, the steaming process can take anywhere from one to two hours. By the time the core is adequately heated, the outside of the meal can overcook, resulting in poor consistency in some meals.

“If you were to produce a ready-to-eat meal of Kraft’s macaroni and cheese made from the family size boxes in grocery stores, for instance, the conventional canning process would degrade the texture of pasta into the consistency of cheesecake, and the cheese would taste burnt,’’ says Tang, a leading expert in the area of microwave and radio frequency sterilization.

The foods cooked in such a manner also have a compromised nutritional content.

The pilot-scale 915 MHz microwave sterilization system developed in Tang’s laboratory cuts down processing time to approximately five minutes. In microwave sterilization, polymeric (plastic) trays are used, so the microwaves can propagate through the plastic and turn into heat inside the package. The researchers are using a variety of frequencies to process the food, depending on the size and shape of their meal, ranging from 27 to 2,450 megahertz (MHz). The long wavelength radio frequency waves at 27 MHz was used to process large trays of foods as group rations and the same processes may be used for schools and institutional uses. The short wavelength microwaves at 2,450 and 915 MHz are used to process single meals. The processed meals are shelf-stable and don’t need to be frozen. And, they taste good. In addition, the new process can be easily automated and may improve energy efficiency, according to Tang.

In the past, such microwave or radio frequency processing was difficult because the systems did not provide uniform and consistent heating, and the safety of the product could not be assured. To solve this problem, the researchers used computer simulation to design appropriate microwave or radio frequency application cavities and a chemical marker method developed recently at the U.S. Army Natick Soldier Center to determine heating uniformity in foods. Fiber-optic temperature sensors were used to monitor temperature-time history of the least heated spot to determine the process parameters. Dr. Tang’s laboratory, housed in WSU Food Processing Pilot Plant, has a range (1.5 to 15 kW) of pilot-scale systems to conduct experiments at three FCC allocated frequencies (27, 915 and 2,450 MHz) — and the capacity to measure properties that govern the interaction between electromagnetic energy and foods over a large range of frequencies (3 to 3,000 MHz) and temperature (10° to 120oC), as well as computational tools to guide experimentation.

Tang has received more than $350,000 in grants from the U.S. Army to further his research in the past three years. Last fall, the Department of Defense and U.S. Army approved a Dual Use Science and Technology proposal for $460,000 for a two-year project. Several U.S. food processing (Kraft Foods, IL; Hormel, MN; and Truitt Brothers, OR), packaging and equipment companies (Rexam Containers, MO; Graphic Packaging, CO; Ferrite Components; NH) also have committed resources to support the research and development activities. A consortium with those companies hopes to translate the pilot-scale results into commercial processes within the next four to five years. The new processing technique will also require approval by the Food and Drug Administration.