This fact sheet describes how pulsed electric field (PEF) processing is used to inactivate food microbes or modify the foods’ structures.
What Is Pulsed Electric Field (PEF) Processing?
Pulsed electric field (PEF) processing is a new food pasteurization method that uses short bursts of high voltage electric fields on foods to achieve desired microbial inactivation or modification of food structure.
How Does PEF Work?
PEF processing applies high voltage pulses (20–80 kV/cm) with a duration of milliseconds to microseconds to treat liquid foods placed between two electrodes (Zhang et al. 2010; Toepfl, Heinz, and Knorr 2006). For solid foods, 1–8 kV/cm is used due to the large gap in the treatment chamber and the power limit of the pulse generator. The electric field may be applied as exponentially decaying, square wave, bipolar, or oscillatory pulses at ambient, sub-ambient, or slightly above-ambient temperatures. The pulses are applied at high repetition rates (up to 3,000 pulses per second) so that the entire volume of the food sample can be treated.
How Does PEF Inactivate Microorganisms?
PEF processing applies a series of short, high-voltage pulses. These pulses rupture the cell membranes of vegetative microorganisms by creating pores or by expanding existing pores (electroporation). The ruptures cause leak of intracellular contents, resulting in the concomitant loss of cellular metabolic activity such as growth and division, thus causing microbial inactivation (Buckow, Ng, and Toepfl 2013).
The inactivation of microbial populations by PEF depends on a variety of PEF equipment process parameters and treatment chamber geometry (Jin, Guo, and Zhang 2015):
- electric field strength
- treatment time
- pulse frequency
- pulse width
- treatment temperature
Microbial efficacy of PEF treatment is also influenced by various product parameters:
- presence of antimicrobial and ionic compounds
- medium ionic strength
PEF treatment has limited effect on bacterial and mold spores, enzymes, and viruses.
Can PEF Be Used to Pasteurize and Sterilize Foods?
To date, PEF is primarily used as a pasteurization technique. The technology does not inactivate bacterial spores. Ongoing research suggests that PEF in combination with heat may inactivate bacterial spores, but more comprehensive research is needed before PEF can be used as a sterilization method. To increase the degree of microbial inactivation and extend the shelf life of food, PEF processing can be combined with mild heating or other nonthermal processing and antimicrobial packaging (Jin 2017).
What Are Current Applications of PEF in the Food Industry?
PEF processing is used for food pasteurization. In 2005, PEF-processed organic fruit juice products were sold in the commercial market in Oregon, United States. PEF-pasteurized foods include liquid food (fruit juice, beverage, milk, liquid egg, etc.) and semi-solid food (yogurt, applesauce, salsa, pudding, etc.).
In recent years, PEF technology has been used for extraction and dehydration of foods where lower field strength (<10 kV/cm) is employed (Yu, Jin, Fan, and Wu 2018). PEF pretreatment facilitates the release of nutrients from fruits, vegetables, and herbs, thus increasing the extract yields. PEF pretreatment also promotes liquid diffusion inside food. The pretreatment significantly reduces food dehydration time and enhances the quality of dry or semi-dry food products (Yu, Jin, Fan, and Xu 2017).
Potato processors from the United States, Canada, Europe, and Australia use PEF pretreatment to improve cut quality and reduce French fry breakage as an alternative to preheaters.
PEF pretreatment of potatoes has many advantages:
- reduces water and energy consumption
- shortens drying and pre-frying times
- reduces frying oil absorption and fat content up to 50%
- enhances extraction of juice yields from fruits
- reduces the solid volume (sludge) of wastewater
Are Commercial PEF Processing Systems Available?
Commercial-scale PEF systems that process between 400–6,000 L/h (105.6 – 1585 gal/h) as well as scalable capacities are manufactured. Several equipment providers supply PEF systems for processing foods and beverages:
- CoolWave Processing B.V. (Wageningen, Netherlands)
- Diversified Technologies, Inc. (Bedford, MA, United States)
- Elea GmbH (Quakenbrück, Germany)
- Energy Pulse Systems, Lda. (Lisbon, Portugal)
Diversity Technology Inc. (DTI) can scale up the PEF system to 50,000 L/h (13209 gal/h) or more. Pulsemaster, a Dutch company, introduced a PEF system with capacities from 1 kg/h to 50,000 kg/h (110,000 lb/h) to process potato, sweet potato, and cassava to produce French fries, crisps, and other products.
Can PEF Systems Be Readily Incorporated Into Existing Manufacturing Lines?
PEF systems can be integrated with existing production lines. For solid food, cell disintegration applications, a typical PEF processing line includes a treatment chamber unit and a pulse generator unit. For liquid pasteurization application, a PEF system includes a supply tank, a fluid pump, a pulse generator unit, a treatment chamber unit, a packaging unit, an optional heater/cooler, and a storage tank (Figures 1 and 2). The processing lines can be sanitized using clean-in-place (CIP) or steam-in-place (SIP) systems.
What Are the Key Components of a PEF System?
A typical PEF processing system is composed of four major components:
- pulse generator (Figure 2a)
- PEF treatment chamber (Figure 2b)
- fluid handling system (Figure 2c)
- control and monitoring device (Figure 2d)
What Precautions Do Food Processors Need to Consider during PEF Treatment of Foods?
Care must be taken during the treatment of liquid or solid foods containing air bubbles. Air is a poor conductor of electricity. As a result, the application of PEF through air results in dielectric breakdown which can cause catastrophic equipment failure and fire hazard. It is important to remove air from liquid or solid foods using a deaerator prior to PEF treatment. For the same reason, PEF treatment may not be a good choice for sparkling liquids, or liquids containing foams.
Improperly designed electrodes may undergo electro-corrosion resulting in the migration of electrode material (e.g., Fe, Cr, Ni, and Mn) into liquid foods. Food processors should ensure that electrodes have a special coating or are comprised of a material that minimizes electro-corrosion.
The degree of microbial inactivation by PEF depends on a number of factors:
- the various relationships between different PEF treatment parameters (electric field strength, treatment time, pulse frequency, pulse width, and treatment temperature)
- the PEF treatment system (batch/static or continuous chamber; coaxial or co-field; and square wave, exponential decay, or oscillatory pulses)
- the food product’s parameters (electrical conductivity, density, viscosity, pH, and temperature)
- the microbial characteristics (bacteria or mold/yeast, gram-positive or negative, vegetable cell, or spores)
Food processors should pay attention to a specific PEF system and decide which parameters to apply for target food products.
How Does This Technology Benefit Consumers?
Consumers are interested in minimally processed foods with fresh-like quality. PEF technology enables the food processors to manufacture liquid foods with consumers’ desired attributes or pre-treat solids prior to other unit operations.
How Economical Is PEF Processing?
According to industry estimates, the overall cost for pasteurizing one liter of juice is about $0.04, and $0.056 per pound for cell disintegration applications. The cost varies depending on the product being processed and the process applied (Sampedro, McAloon, Yee, Fan, Zhang, and Geveke 2013).
What Regulatory Approval Is Required for Commercializing a PEF-processed Product?
In compliance with the FDA’s juice HACCP regulations (21 CFR 120), PEF can be used for the commercial pasteurization of juices. The juice processors must implement sanitation and good manufacturing practices (GMP) during the production of PEF-treated juice products. The treatment should meet a performance standard that results in a 5-log reduction of the most resistant pathogen likely to be present in the juice. The 5-log reduction can be achieved solely by PEF, or by a combination of other interventions if they are performed at the same facility.
The authors acknowledge the contribution of The Ohio State University Food Safety Engineering Laboratory, Center for Clean Food Process Technology Development (u.osu.edu/foodsafetyeng/). The authors also thank Dr. John Fulton, Dr. Erdal Ozkan, technical editor Tim Vargo, project manager Annie Steel, Ohio State University Extension for their constructive review comments. The authors gratefully acknowledge financial support from the USDA NIFA, HATCH program, the food industry, and the Ohio Ag Experiment Station. References to commercial products or trade names are made with the understanding that no endorsement or discrimination by The Ohio State University is implied.
Buckow, R., Ng, S., & Toepfl, S. (2013). Pulsed Electric Field Processing of Orange Juice: A review on microbial, enzymatic, nutritional, and sensory quality and stability. Comprehensive Reviews in Food Science and Food Safety, 12, 455–467.
Jin, T., Guo, M., & Zhang, H. Q. (2015). Upscaling from benchtop processing to industrial scale production: More factors to be considered for pulsed electric field food processing. Journal of Food Engineering, 146, 72–80.
Jin, T. (2017). Antimicrobial Packaging in Combination with Nonthermal Processing. In Packaging for Nonthermal Processing of Food, Second Edition (IFT Press Series). Melvin Pascall and Jung H. Han (Editors). Wiley Publisher.
Sampedro, F., McAloon, A., Yee, W., Fan, X., Zhang, H.Q., & Geveke, D. J. (2013). Cost analysis of commercial pasteurization of orange juice by pulsed electric fields. Innovative Food Science and Emerging Technologies, 17, 72–78.
Toepfl S., Heinz V., & Knorr D. (2006). Applications of pulsed electric fields technology for the food industry. In: Raso J, & Heinz V (eds.). Pulsed Electric Fields Technology for the Food Industry. Food Engineering Series. Springer, Boston, MA., 197–221.
Yu, Y., Jin, T. Z., Fan, X., & Wu, J. (2018). Biochemical degradation and physical migration of polyphenolic compounds in osmotic dehydrated blueberries with pulsed electric field and thermal pretreatments. Journal of Food Chemistry, 239(15), 1219–1225.
Yu, Y., Jin, T. Z., Fan, X., & Xu, Y. (2017). Osmotic dehydration of blueberries pretreated with pulsed electric fields: Effects on dehydration kinetics, and microbiological and nutritional qualities. Drying Technology, 35(13), 1543–1551.
Zhang, H. Q., Barbosa-Canovas, G., Balasubramaniam, V. M., Dunne, P., Farkas, D., & Yuan, J. (eds.). (2011). Nonthermal Processing Technologies for Food. Chicago: IFT Press, Wiley-Blackwell Publishing.
Jerish Joyner Janahar, Graduate research associate and doctoral student, Department of Food Science and Technology, The Ohio State University
Z. T. Jin, Food Safety and Intervention Technologies Research Unit, Eastern Regional Research Center, USDA, Wyndmoor, PA
V. M. Balasubramaniam, Professor of Food Engineering, Center for Clean Food Process Technology/Food Safety Engineering Laboratory, Department of Food Science and Technology and Department of Food, Agricultural and Biological Engineering, The Ohio State University.