Pulsed Electric Field (PEF)
From Top Wiki
Pulsed Electric Field (PEF) is a so-called mild preservation technique for liquids (pumpable products). Characteristic for the technology is that the pasteurization effect takes place at a low temperature, resulting in a better preservation of the natural nutritional value and sensory qualities of the product than is normally obtained with conventional thermal pasteurization. The company Cool Wave Processing has developed a second generation PEF technology. They released this technology to the market under the alias “ PurePulse”. Pure Pulse’s unique PEF setup allows the heat load on the product to be greatly reduced.
PEF is a technology which causes biological cells to be ripped open and perforated. During the process, the biological cells are subjected to an electric field with high field strength, allowing plant and animal cells to be opened up (because of this opening effect, the technology can also be used to support or accelerate certain extraction or drying processes due to facilitated escape of water from the cell matrix). At higher power settings microbial inactivation will follow. The high electric field perforates the cell membranes of bacteria and thereby causes their inactivation. By making use of intense, but short high frequency pulses, there is only slight heating of the product itself while the bacterial inactivation effect remains. This lack of heating will benefit the sensory quality of the product. In order to generate the pulsed electric field, both a source and a treatment chamber are required. The treatment chamber consists of at least two electrodes, with an insulating region in between, where the treatment of the product takes place (see Figure 1).
The PEF treatment has the following relevant parameters:
- Flow rate: with industrial pulse generators, up to 2000 liters per hour can be treated.
- Pulse frequency: as all the product flows through the treatment chamber, and the entire volume of product needs to be treated in that treatment chamber to be treated, it is very important to set the pulse frequency (and the power) accordingly, in order to ensure even the fastest particle in the product stream is exposed to at least one pulse in the treatment chamber
- Electric field strength: the electric field strength determines whether the cell membrane of the bacteria will be punctured. In the PEF process, field strengths are used between 20 and 40 kV / cm
- Preheating: the process is more efficient at higher temperatures. Therefore, the treated product needs to be pre-heated to a temperature between 30 ° C and 60 ° C.
The PEF treatment is a continuous process. It is not a batch process. PEF can be applied to liquid products which do not contain air bubbles or sizeable particles. The maximum allowable size of particles in the product is approximately 2mm x 2mm x 2mm. In Figure 2, the PEF process is shown schematically. The product is pre-heated to about 30-60 ° C (1). This is conducive to the microbial inactivation. Subsequently, the product is treated with electrical pulses (2). The product is then cooled back (3), and aseptically filled to prevent post-process re-contamination (4). During and due to the PEF treatment, the product increases about 10 ° C in temperature. The geometry (shape) of the treatment chamber determines the retention time of the product. Expert-panellists have evaluated the quality of fresh juices compared to the quality of PEF-treated juices. This study showed that there was no significant difference in organoleptic properties between fresh juice and PEF-treated juice (Cserhalmi, 2006, Rahman, 1999). Also, no changes in pH (acidity) and vitamin C content were observed (Rahman, 1999). In the United States, fruit juices pasteurized with PEF existed in the market shortly around 2005. Due to financial problems, the brand (Genesis) was sold, but without the PEF technology, to another company (see). At the moment cold pasteurized juice is still sold under the brand name of Genesis juice, only now High Pressure Technology is used to that effect.
As the PEF process consists of short electric pulses, there is only little heating of the product of interest. This preserves the fresh original character of the product. In 2011, TOP extensively studied the effects of PEF on raw milk, on fruit juices, on vegetable juices and smoothies. A nice overview article can be found here.
Pros and Cons
- Low impact of heat
- Fresh character of product preserved
- Little energy compared with traditional thermal treatments
- Only for pumpable products
- Viscosity and size of particles in product pose a restriction
- Purchase price is higher than traditional thermal processing equipment
PEF equipment in which the product undergoes only a minimal temperature rise is available at:
The cost for a PEF treatment is around € 0.04 per liter. The investment cost for a PEF machine (30 kW, 1000 liters per hour) is approximately € 250,000.