CORVALLIS - What started as an effort by Oregon State University researchers to improve the processing of surimi seafood has become a patented concept that may have a wide variety of applications in the food products industry.
The initial research into "capacitive dielectric heating," a way of tuning radio frequencies to precisely heat specific parts or materials in food, began in 1993 as a research project, funded by Oregon Sea Grant and aimed specifically at the specialty fish product, surimi.
But the far greater potential of the technique is reflected in the number of people who share in the patent awarded last fall by the U.S. Patent Office.
Sharing in the patent are Ed Kolbe, a mechanical engineer associated with both Extension Sea Grant and OSU's Coastal Oregon Marine Experiment Station; Jae Park, a COMES food scientist at OSU's Seafood Laboratory in Astoria; John Henry Wells, a packaging engineer and superintendent of OSU's Food Innovation Center in Portland; electrical engineer Benjamin Flugstad, owner of Flugstad Engineering in Port Townsend, Wash.; and Yanyun Zhao, a food process engineer at OSU's Department of Food Science and Technology in Corvallis.
OSU and Flugstad Engineering jointly own the patent.
Surimi is a washed paste made from fish that are typically underutilized as a food source. By mincing the fish, then washing it repeatedly, producers create a concentrate of fish protein, "surimi," that is then heated to form the crab- or other-flavored surimi seafood products commonly found in grocery stores and restaurants.
Surimi seafood is conventionally heated by gas burners and steam. The original Sea Grant project, begun by Kolbe and Park in 1993, applied a process called "ohmic heating" which sends regular household alternating current directly through the fish paste, generating heat as a result of electrical resistance, and rapidly firming it into a gel.
Once the seafood paste is heated, processed and packaged, a second heating step is required for pasteurization. Park reasoned that if the seafood could be heated internally, as in the ohmic heating process, it would reach pasteurization temperatures much sooner, increase energy efficiency and minimize loss of texture, flavor, color and nutrients.
However, ohmic heating requires direct contact between the electrodes and product. Because the surimi seafood is wrapped in plastic packaging by this point, ohmic heating won't work. Microwave heating is also not an option because of problems with non-uniform heating.
According to Kolbe, Flugstad suggested a third range of frequencies that could do the job. Radio frequencies (RF) in the range of 10 to 80 megahertz, or millions of cycles a second, will make food molecules vibrate and react. Based on this idea, the research team extended the original Sea Grant ohmic research, and preliminary RF experiments got under way.
The researchers discovered that certain characteristics could be varied to maximize the energy absorbed by the product. They also found that narrow ranges of frequency could resonate with individual ingredients or packaging materials, heating specific components of the food product very precisely. As the components heat up their resonance changes, and the RF can be tuned to match those changes, allowing rapid and uniform heating
As expected, the best combination of these RF characteristics changed as the food properties changed with increasing temperature. To achieve the rapid heating and maximum energy efficiency the system is capable of, a sophisticated and rapid control system was developed and a patent application on it is pending.
As preliminary experimental design proceeded, the technology's potential for food and packaging systems far beyond surimi seafoods attracted the interest of researchers in other areas.
Zhao, from OSU's department of food science and technology, began looking at its application to sprouting seeds, such foods as alfalfa, radish or other seeds which form sprouts for consumption, such as at salad bars and as sandwich garnishes. She was joined by Wells, from the Food Innovation Center. Researchers explored the application of RF heating to improve food safety with sprouting seeds, and a second program sought to demonstrate the rapid and uniform heating of packaged "muscle foods," such as packaged meat, poultry and fish.
Work continues to look at the temperature- and frequency-dependent property data for surimi seafoods, meats, plastic and edible packaging, and sprouting seeds. A series of tests showed initial success, producing rapid heating rates and uniform temperatures in both surimi gels and seeds. Results from these and other research projects have been extremely promising.
While pasteurization of surimi seafoods is still an important commercial goal, the potential for this technology reaches far beyond seafood and the Sea Grant funding that got it all started.
Sprouting seeds, packaged lunch meats, frankfurters, ready-to-eat meals, food service thawing, and other applications represent a vast potential that may be realized as work progresses.
Click photos to see a full-size version. Right click and save image to download.
Ed Kolbe, 503-872-6676