Use radio frequencies to pasteurize fish.

Radio waves may be invisible, but they enrich life in many ways. Without them, radios, televisions, cellular phones and global positioning systems wouldn't be possible. They've found medical uses, and now researchers are looking to use them to make fish safer.

The radio frequency (RF) electric fields technique inactivates bacteria in different products without heating them. Although RF has been studied in the laboratory for more than 50 years as a pasteurization method, it has not had much commercial use. Now European scientists are developing an RF-heating technique for the fast pasteurization of vacuum-packed fish products, such as cod or salmon fillets. The treatment is expected to help improve the quality of these foods, while maintaining their microbiological safety and an acceptable shelf life.

The new approach involves the fast RF-heating of vacuum-packed fish products that have been immersed in deionized water of very low electric conductivity. This is followed by fast cooling or freezing--cook-chill or cook-freeze. Heating times of 1 minute to 2 minutes, compared with 30 minutes in the conventional autoclave process, may increase the temperature to above 75 C.

At these temperatures, vegetative microorganisms will be inactivated, and a safe shelf life at 4 C can extend beyond 10 days. Additionally, eating quality appears to improve using this rapid heat transfer technique.

RF treatment is one of several minimal processing techniques that are still being optimized. The concept is based on the application of the lightest possible treatment that yields a fresh-like, convenient, safe and high-quality product.

Examples of different minimal processing treatments include:

* Modified atmosphere packaging;

* Aseptic processing;

* High-pressure treatment;

* High-temperature short-time heating (HTST);

* Sous-vide processing; and

* Very fast heat-transfer technologies.

RF heating at 27.12 MHz has been used to treat several types of foods, in particular for post-baking biscuits and cereals, drying foods and thawing frozen products. Heat is created inside the product mainly by means of its electric conductivity.

This European study brings together three research institutes and four companies from Germany, Iceland and Norway. The project will last three years. During the last year, the quality and safety of the products will be documented and the processing costs will be estimated.

Further information. Thomas Pfeiffer, Fraunhofer IVV, Giggenhauser Strasse 35, D-85354 Freising, Germany; phone: [phone]; fax: [phone]; email: [e-mail].