Development of Gentle Intervention Processes to Enhance the Safety of Heat Sensitive Foods





	Dr. Howard Q. Zhang Research Leader, Lead Scientist Voice: 215-233-6583 Fax: 215-233-6406 e-mail: hzhang@errc.ars.usda.gov	Development of Gentle Intervention Processes to Enhance the Safety of Heat Sensitive Foods

Objectives:

Develop a VSV surface pasteurization processor suitable for field-testing at poultry processing plants. Develop the surface pasteurization process for other fresh, unprocessed solid foods such as fish, fruits and vegetables especially cantaloupes, grapefruits, and mangoes. Develop the process for processed meat products, particularly hot dogs. Model and simulate the bacterial destruction in the processes developed.
Develop a novel, mild, electromagnetic pasteurization treatment for liquids. Model and simulate the bacterial destruction in the process developed.

Method and Apparatus for the Treating and Packaging of Raw Meat

Processing such as blanching, cooking, canning, and pasteurizing can destroy harmful bacteria on foods. However, raw foods harbor bacteria, sometimes pathogenic bacteria and ready-to-eat foods can get cross contaminated before packaging.

Photo of VSV surface pasteurization process

Contacting bacteria with steam can kill bacteria but will thermally damage the food surface. Applying steam to the surface of solid foods can be accomplished with virtually no thermal damage if the process can be made sufficiently rapid. The chief deterrent to rapid treatment is the presence of a thin layer of air and moisture on the surface. We developed a concept in which the interfering layers of air and moisture are first removed by vacuum. This is followed by application of saturated steam. A reapplication of vacuum cools the surface stopping any thermal damage. We call the process the VSV (Vacuum/Steam/Vacuum) Surface Pasteurization Process. The novel effect depends on the lower activation energy of bacterial enzyme inactivation, contrasted to the higher activation energy of meat protein denaturation.

The process is capable of evacuating the surface, applying steam, and evacuating the surface again in less than 1 s. Even multiple cycles take less than 2 s. total process time. The speed of the treatment is necessary not only to prevent thermal damage but also to equal the speed of many process lines.

The pilot plant VSV process has been successfully applied to various foods, for example poultry, catfish, fruits and vegetables, and hot dogs. Results vary depending on the food treated. The most difficult is chicken. Bacteria kill, both in the pilot plant and in field trials, ranged from 90 – 97%. Kills on fruits and vegetables ranged from 99 to over 99.99%. Eviscerated catfish achieved 99% kills. The easiest to treat was hot dogs with kills of Listeria innocua of 99.999%

We have entered into a cooperative research and development agreement to commercialize the VSV surface pasteurization process for the ready-to-eat product industry, especially hot dogs.

Patents:

U.S. Patent 5,281428 issued January 25, 1994
U.S. Patent 6,245,294 issued June 12, 2001

Responsible Engineer:

Mr. Michael Kozempel, 215-233-6588
mkozempel@errc.ars.usda.gov

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Electromagnetic Pasteurization of Liquid Foods

Nonthermal or low temperature pasteurization of liquids, such as egg, with low power microwave or radio frequency (RF) energy is controversial. We developed a continuous 2.45 GHz microwave process to test the theory. The unique, patented process removes the microwave energy as soon as it passes through the flowing liquid. It separates the effects of thermal energy from nonthermal energy. Microwave energy alone did not destroy microorganisms at low temperatures.

Photo of system that exposes low conductivity liquids We made similar modifications to a 27 MHz RF oven to repeat the previous microwave experiments at the lower frequency. At the electric field strength, 0.5 kV/cm, and frequency used, neither nonthermal effects nor synergistic effects of RF energy with thermal energy were observed.

We then developed a treatment chamber that exposed microorganisms in liquids to an electric field strength of about 14 kV/cm. Even at the higher power, microorganisms were unaffected at low temperatures at 27 MHz.

Recently, we designed, purchased and developed an experimental system that exposes low conductivity liquids to RF energy at a frequency range of 20-100 kHz and a field strength of 45 kV/cm. Preliminary results of the new system indicate that liquids can be pasteurized using nonthermal electromagnetic energy. Due to power limitations of the energy supply, only low conductivity liquids may be treated. The populations of some bacteria and yeasts in water at 45°C were reduced by nearly 99%.

A more powerful RF supply has been designed and purchased that should enable higher conductivity liquids such as liquid egg and fruit juices to be treated.

Responsible Engineers:

Dr. David Geveke, 215-233-6507
dgeveke@errc.ars.usda.gov

Mr. Michael Kozempel, 215-233-6588
mkozempel@errc.ars.usda.gov

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Annual Reports

Updated: September 12, 2005