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Research continues into the use of pulsed electric fields for preservation.

Nonthermal processes still attract attention when it comes to making foods safe. Scientists at Ohio State University (Department of Food Science and Technology, Food, Agricultural and Environmental Sciences, 122 Vivian Hall, 2121 Fyffe Rd., Columbus, Oh 43210) are developing continuous pulsed electric field (PEF) technology and pilot plant equipment for processing foods in the form of liquids, slurries, purees and pastes.

Their goal is to enhance the lethal effect of PEF to spores and vegetative microorganisms by using a high-pulse repetition rate (up to 2 kHz). Researchers are studying the mechanisms involved in cell injury and recovery and want to combine the PEF process with other treatments. They are optimizing PEF operation parameters to maximize microbial inactivation and minimize energy consumption.

A pilot scale, continuous flow, pulsed electric field PEF processing system has been integrated with an aseptic packaging machine to test and demonstrate the efficacy of this technology. Liquid foods are being processed at ambient temperature and packed in 200 ml plastic cup containers. A laboratory scale PEF unit provides microbiologists with the needed tool to investigate the efficacy of PEF against health-hazardous pathogens. Investigators are using a microscopic high-speed imaging system to visually study the changes that PEF treatment causes to the microorganisms.

At Washington State University (Biological Systems Engineering, 213 Smith, Pullman, WA 99164), scientists also are assessing processing conditions using PEF technology, either alone or in combination with other technologies. Their goal is to extend the shelf life of foods. An integrated pilot plant processing system for PEF technology has been assembled. The system has the capability of processing 240 l of pumpable food each hour. Its operation is controlled by a computer, which can easily be interfaced with a commercial production line. Basic processing parameters, such as processing temperature, applied electric field intensity, treatment time, flow rate and pulse repetition rate, are monitored with a computer-controlled process and diagnostic system.

Investigators have optimized a pilot plant PEF processing system to produce food products with extended shelf life. A significant number of studies have already been conducted at Washington State University to process several foods using the PEF technology. For apple juice, researchers have identified some processing conditions that will offer quality produce at a low cost. Preliminary sensory evaluation indicated that the processed apple juice was of excellent quality, even though it tasted somewhat different than commercially available brands.

The apple juice processed by PEF shows good stability after storage, and the preliminary sensory evaluation studies clearly indicate that the PEF process offers excellent quality juice. The representative microorganism S. Cerevisiae in apple juice was successfully inactivated: a 6 log reduction using PEF technology at 50 kV/cm at only 29.6 C, a treatment temperature significantly lower than the 80 C required for heat pasteurization. The PEF-treated apple juice, at 4 C storage temperature, had a shelf life of more than three weeks.

Meanwhile, for liquid whole eggs, researchers have achieved more than four weeks of storage at refrigeration temperature. They combined the PEF process with a very mild heat treatment. The quality of the PEF-processed eggs, in terms of functionality and sensory properties, is much higher than commercial heat-pasteurized liquid eggs, we're told. Microbial challenge tests with some key microorganisms indicate PEF technology can process liquid whole eggs, a product with significant quality problems when it is pasteurized using heat exclusively.

Scientists also have pasteurized skim milk using PEF, and the shelf life of the processed product reached more than 28 days. By combining PEF and a mild heat treatment, it was possible to pasteurize whole milk with a shelf life of 28 days at refrigeration temperature. PEF extended the shelf life of commercial heat-pasteurized milk for more than seven days. The sensory properties were not altered by the PEF treatment.

Further information. Further information. At Ohio State University: Qinghua Zhang; phone: 614-688-3644; fax: 614-292-0218; email: At Washington State University: Gustavo Barbosa-Canovas; phone: 509-335-6188; fax: 509-335-2722; email:
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Publication:Microbial Update International
Date:Apr 1, 2001
Previous Article:High pressure imparts sterility; has little impact on flavor, color, texture.
Next Article:PEF research extends apple juice shelf life.

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