RF energy and thermal energy might optimize product safety, quality.

It's been known for years that radio frequency (RF)-based energy has a nonthermal effect on microorganisms. If we could use RF to nonthermally inactivate microbes, a product would retain its fresh-like qualities and many nutrients. For instance, you could use the technique to pasteurize liquid foods such as whole eggs, fruit and vegetable juices, as well as beer. The product would experience little degradation.

In addition to the pure nonthermal effect of RF energy, researchers also have found that a combination of RF and thermal energy might have a synergistic effect on products. In the past, scientists treated slices of bread that were inoculated with fungi, A. niger and Penicillium sp., with 2450 MHz of microwave energy. Excellent results were achieved by raising the temperature of the bread to about 66 C for 5 minutes to 10 minutes. Inactivating microbes using conventional approaches requires temperatures of 68 C to 71 C for approximately 20 minutes.

USDA-ARS scientists investigated using radio frequency (RF) energy as a nonthermal alternative to thermal pasteurization. Two RF power supply systems were assembled and provided frequencies in the range of 20 kHz to 27 MHz. Electric field strengths of 14 kV/cm to 30 kV/cm were applied to suspensions of S. cerevisiae in water over a temperature range of 28 C to 55 C. The flow rate was 1.2 l per minute, and the number of exposures to the fields ranged up to 30.

The population of S. cerevisiae was reduced by more than 5 logs following 30 exposures to a 100 kHz, 25 kV/cm field at 28 C. Increasing the field strength and temperature--as well as decreasing the frequency--enhanced inactivation. These preliminary results of radio pasteurization, RAP, are encouraging and will be used in an effort to extend this technique to bacteria in vegetable and fruit juices. At present, the RAP equipment is only capable of treating yeasts in low conductivity fluids.

Further information. David Geveke, USDA-ARS, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].