Pulsed Electric Field Processing
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Pulsed electric field (PEF) processing is a method for processing cells by means of brief pulses of a strong electric field. PEF holds potential as a type of low temperature alternative pasteurization process for sterilizing food products. In PEF processing a substance is placed between two electrodes then the pulsed electric field is applied. The electric field enlarges the pores of the cell membranes which kills the cells and releases their contents. PEF for food processing is a developing technology still being researched. There have been limited industrial applications of PEF processing for the pasteurization of fruit juices.
Nearly all cells have pores which control the flow of nutrients and wastes into and out of the cell. Once the pores are sufficiently enlarged the contents of the cell are released into the surrounding medium and foreign matter may enter the cell membrane.
PEF produces products with slightly different properties than conventional pasteurization treatments. Most enzymes are not affected by PEF. The fact that the maximum temperature reached is lower than in thermal pasteurization means that some of the flavors associated with the raw material are not destroyed. The lack of heat treatment makes PEF somewhat comparable to irradiation as a treatment. Spores, with their tough protective coats and dehydrated cells are often able to survive PEF processing. The survival of spores and enzymes means that products should be refrigerated after passing through PEF processing in order to slow the action of the enzymes and keep pathogens from growing.
The PEF process holds promise as a more efficient way of getting useful products out of cell membranes. PEF is particularly well suited to processing fruit and vegetable juices because the enlargement of the cell pores makes juice extraction easier. PEF may be useful in extracting sugar from sugar beets and oils from oil bearing plants. PEF may have a use in the developing field of extraction of oil and other products from microorganisms such as algae.
Part of the potential utility of PEF is that the properties of the electric field can be modified to have differing effects on cells. Most plant cells can survive weak electric fields, but over around 15,000 volts per centimeter most plant cells are killed. At over 30,000 volts per centimeter most other cells such as bacteria and fungi are also killed.
Issues with PEF include the potential for electrical arcs and a temperature increase on the order of 30 degrees Celsius (54 °F). In liquid PEF processing gas bubbles tend to allow for electric arcing between the electrodes which will burn the substance being processed and potentially generate unwanted materials, such as carcinogens, in the processed material. One solution to gas bubble formation is to pressurize the liquid. In static PEF for non-liquids there is a greater limitation on the maximum voltage possible without electric arcing through the air. This necessitates transferring the solid to an oil filled chamber before a high voltage PEF is applied.
