Pulsed Electric Field Processing (PEF)

Pulsed electric field processing (PEF) is a non-thermal food preservation method in which liquid or pumpable food is exposed to brief, intense bursts of electrical energy between two electrodes. The electric field disrupts microbial cell membranes through a process called electroporation, inactivating vegetative bacteria, yeasts, and moulds at temperatures well below conventional pasteurisation. Because PEF does not involve sustained heat, it preserves heat-sensitive vitamins, flavour compounds, and fresh sensory characteristics more effectively than thermal alternatives.

PEF is one of several non-thermal preservation technologies that have moved from laboratory research to commercial deployment since the 1990s, alongside high pressure processing (HPP) and UV treatment. Both PEF and HPP occupy a similar niche in food preservation: pasteurisation-equivalent microbial safety with superior retention of fresh food quality. Their technical domains are complementary — PEF is well suited to liquid foods and continuous processing; HPP handles solid and semi-solid products in batch mode.

Mechanism: electroporation

At the core of PEF is the phenomenon of electroporation. When a sufficiently strong electric field is applied across a biological cell, it induces a transmembrane voltage. Once this voltage exceeds a critical threshold — typically 0.5–1 V across the membrane — the electric field reorganises the phospholipid bilayer, forming nanoscale water-filled pores.

Whether the cell recovers depends on field intensity and pulse energy:

• Reversible electroporation occurs at moderate field strengths and short pulse durations. The membrane reseals after the pulse is removed and the cell survives. This is exploited in biotechnology and medicine to temporarily permeabilise cells for drug delivery or gene insertion.
• Irreversible electroporation occurs when the field strength and total energy input are sufficient to cause pore expansion beyond the membrane’s repair capacity. The cell loses homeostasis, leaks intracellular contents, and dies. This is the mode used for microbial inactivation in food processing.

The transmembrane voltage is proportional to cell size: larger cells are affected at lower field strengths. This means yeasts and moulds (larger cells) are more sensitive than bacteria, which are more sensitive than bacterial spores (which have no conventional plasma membrane in the vegetative sense and are not inactivated at food-relevant PEF conditions).

Process parameters

Electric field strength

Food-grade PEF systems operate at field strengths of 15–80 kV/cm. For liquid food pasteurisation, the effective range is typically 20–40 kV/cm — sufficient to achieve irreversible electroporation in vegetative bacteria and yeasts without generating excessive heat. Higher field strengths increase lethality but also increase energy input and heat generation.

Pulse duration and frequency

Individual pulses last 1–300 microseconds (µs), most commonly 1–20 µs. Shorter pulses reduce heat generation per pulse; longer pulses at the same field strength deliver more energy and are more lethal. Pulse frequency ranges from 1 Hz to 2,500 Hz depending on system design and target throughput. Total number of pulses per product volume is a key process parameter, typically 5–100 pulses.

Treatment temperature

The product temperature rise during PEF is a function of total energy input. Well-designed continuous-flow systems maintain product temperatures at 35–45°C — well below pasteurisation temperatures — by controlling pulse energy and system geometry. The process is considered “cold pasteurisation” because no sustained heating is applied, although the brief energy deposition does raise temperature slightly. Product temperature is monitored and controlled to remain below the threshold for significant thermal damage.

Pulse shape

Pulses are typically monopolar square waves or exponentially decaying waves. Square wave pulses at constant voltage are more energy-efficient; exponentially decaying pulses are simpler to generate. Bipolar pulses (alternating polarity) are more lethal at equivalent energy and produce less electrolysis at the electrode surfaces.

Equipment

Treatment chambers

The treatment chamber is the central component, where the food flows between two electrodes connected to a high-voltage pulse generator. Designs include:

• Co-field (parallel-plate) chambers: food flows parallel to the electric field between flat plate electrodes; simple geometry, uneven field distribution
• Co-axial chambers: an inner cylindrical electrode surrounded by an outer tubular electrode; more uniform field distribution and better suited to continuous flow
• Co-linear chambers: multiple electrode pairs in series; allows multiple sequential pulses with intermediate cooling

Chamber materials must resist corrosion from food acids and the electrochemical effects of high-voltage pulses. Stainless steel electrodes with food-grade surface finishes are standard.

Pulse generators

Solid-state pulse generators using thyristors, insulated-gate bipolar transistors (IGBTs), or spark gaps produce the high-voltage pulses. Modern systems are fully programmable and monitor pulse shape, field strength, and temperature continuously. Pulse generators account for the largest share of capital cost in a PEF installation.

Energy consumption

PEF energy consumption for liquid food pasteurisation is typically 40–150 kJ/kg, comparable to or lower than equivalent thermal pasteurisation when total system energy (including heating and cooling) is included. At commercial scale, PEF installations in the juice industry consume approximately 20–40 kJ per litre of product.

Commercial system suppliers

Commercial PEF systems are manufactured by companies including Elea (Germany), Pulsemaster (Netherlands), and Diversified Technologies (USA). Industrial installations range from pilot-scale units (200–1,000 litres/hour) to full production lines (up to 20,000 litres/hour).

Microbial inactivation

Vegetative bacteria

PEF at 20–40 kV/cm achieves 4–6 log reductions (99.99–99.9999% inactivation) in vegetative foodborne pathogens including Escherichia coli O157:H7, Salmonella enteritidis, Listeria monocytogenes, and Staphylococcus aureus under optimised conditions in liquid media. Inactivation efficacy depends on field strength, pulse number, treatment temperature, product conductivity, pH, and the target organism.

Listeria and Gram-positive bacteria in general are somewhat less sensitive to PEF than Gram-negative bacteria, due to differences in cell wall structure. The presence of fat globules in dairy products or pulp particles in juices can provide physical protection to some cells.

Yeasts and moulds

Yeasts — including Saccharomyces cerevisiae and spoilage yeasts — are more sensitive to PEF than bacteria due to their larger cell size. 5–6 log reductions are achievable at lower field strengths and fewer pulses than required for bacterial inactivation. Mould vegetative cells are similarly sensitive; mould spores are more resistant.

Bacterial spores

Bacterial endospores (Clostridium botulinum, Bacillus cereus) are not inactivated by PEF at food-relevant conditions. Like HPP at ambient temperature, PEF can achieve pasteurisation-equivalent effects but cannot produce shelf-stable low-acid products without additional hurdles. For products with pH < 4.6, spore germination is inhibited by acidity and PEF alone is sufficient for safety.

Synergistic effects

PEF efficacy is enhanced in combination with mild heat (thermoelectric processing), antimicrobials, or acidification. The combination of 55–60°C and PEF achieves greater inactivation than either treatment alone, at shorter times and lower temperatures than conventional pasteurisation. These synergies are studied under the framework of hurdle technology.

Effects on food quality

Vitamins and bioactive compounds

Because PEF does not apply sustained heat, heat-labile vitamins are substantially better preserved than in thermally pasteurised equivalents. Studies on orange juice show:

• Vitamin C (ascorbic acid): 95–98% retention after PEF versus 60–80% after thermal pasteurisation
• Folate: >90% retention after PEF
• Carotenoids (in carrot and tomato juices): >95% retention

Phenolic compounds and flavonoids — which contribute both to flavour and to the antioxidant capacity marketed in premium juices — are similarly preserved.

Flavour and colour

Volatile aroma compounds responsible for fresh flavour are not broken down at PEF process temperatures. Sensory panel studies consistently rate PEF-treated orange, apple, and tomato juices as closer to fresh-squeezed than thermally pasteurised equivalents in flavour, colour, and overall acceptability. Colour degradation (e.g., chlorophyll in green juices) is minimal.

Enzymes

PEF does not uniformly inactivate food enzymes. Polyphenol oxidase (PPO) — responsible for browning in apple and grape juice — requires field strengths above 40 kV/cm and multiple pulses for significant inactivation and may not be fully controlled at commercially practical parameters. Pectin methylesterase (PME) in citrus juice, which causes cloud loss, is partially inactivated by PEF but often not to the degree achieved by thermal pasteurisation. Residual enzyme activity means PEF products require continuous cold chain storage.

Alkaline phosphatase, the marker enzyme for pasteurisation adequacy in milk, is partially inactivated by PEF, though achieving the same degree of inactivation as thermal HTST pasteurisation requires careful process optimisation. Regulatory acceptance of PEF-treated milk as equivalent to thermally pasteurised milk differs between jurisdictions.

Texture and viscosity

In liquid foods, PEF treatment at typical pasteurisation conditions has negligible effect on viscosity or texture. This is a significant advantage over thermal treatment, which can alter protein structure in dairy, reduce pectin-bound viscosity in tomato products, and cause starch gelatinisation.

Commercial applications

Juice and beverage pasteurisation

Fruit and vegetable juices — particularly orange, apple, carrot, and cold-pressed blends — are the most established commercial application of PEF. PEF treatment allows marketing as “cold-pressed” or “minimally processed” while meeting food safety standards for pathogen reduction. Commercial PEF juice production operates in the United States, the Netherlands, Germany, Spain, and Australia.

Extended shelf life under refrigeration is typically 14–45 days for PEF-treated juices, compared with 7–14 days for thermally pasteurised equivalents (at the same microbial starting level). This extended window facilitates retail distribution without sacrificing the fresh flavour proposition.

Potato and vegetable processing

PEF permeabilises plant cell membranes in solid foods when applied before cutting, blanching, or extraction. In potato processing, pre-treatment with PEF at 0.5–1.5 kV/cm (low-field, reversible electroporation conditions) before frying:

• Reduces acrylamide formation by 40–60%, because permeabilised cells leach asparagine (the acrylamide precursor) before the high-temperature frying step
• Reduces oil uptake during frying by 5–15%, as the cell structure is better maintained during heating
• Reduces cutting energy and improves strip uniformity

This application is commercially established at large scale in potato processing in the United States, Canada, the Netherlands, and Australia, and is arguably the largest-volume industrial application of PEF globally by weight of product treated.

Liquid egg products

PEF pasteurisation of liquid whole egg and yolk — products that are particularly sensitive to thermal denaturation — allows reduction of Salmonella to regulatory requirements while preserving functional properties (foaming, emulsification, viscosity) better than thermal pasteurisation. This application is commercially operated in several European countries.

Dairy

PEF treatment of milk has been studied extensively and achieves pasteurisation-equivalent microbial inactivation. Commercial adoption has been slower than in the juice sector due to regulatory requirements around alkaline phosphatase inactivation and the fact that thermal HTST pasteurisation already has an excellent safety and quality record for milk. Premium fresh milk and raw-milk-like dairy products represent the most likely near-term market.

Plant extraction and biorefinery

Reversible PEF electroporation is used to increase extraction yields from plant cells — sugar beet (sucrose extraction), grape skins (anthocyanins and tannins in winemaking), microalgae (lipids and pigments), and chicory (inulin). In these applications, PEF is used not for microbial inactivation but as a cell disruption tool to improve mass transfer, replacing or supplementing blanching, mechanical pressing, or solvent extraction.

Sugar beet PEF pre-treatment before diffusion extraction is commercially deployed at industrial scale in European sugar production, reducing energy requirements for the diffusion step.

Advantages and limitations

Advantages

• Preservation of vitamins, aroma, flavour, and colour significantly better than thermal pasteurisation
• Continuous-flow processing with short treatment times (seconds to minutes total)
• Lower energy consumption per litre than equivalent thermal pasteurisation in many applications
• Compatible with existing HTST plant infrastructure in some configurations
• No chemical additives required
• Effective at reducing acrylamide precursors in potato processing
• Increases extraction yields from plant material

Limitations

• Effective only against vegetative microorganisms; bacterial spores are not inactivated at food-relevant conditions
• Requires liquid or pumpable products; not applicable to solid foods in pasteurisation mode
• Residual enzyme activity (PPO, PME) necessitates cold chain storage
• Products with high electrical conductivity (e.g. high-salt foods) or low conductivity (oils) are difficult to process
• Products containing particulates require careful chamber design to ensure uniform field exposure
• Higher capital cost than conventional HTST pasteurisation equipment
• Regulatory frameworks for PEF-treated milk differ between countries; market access depends on local approval

Regulatory status

In the United States, PEF is generally accepted under existing food safety regulations when validated to achieve the required log reductions for target pathogens. The FDA has accepted PEF as a valid pasteurisation technology for juices under the Juice HACCP rule (21 CFR Part 120). Liquid egg PEF pasteurisation has USDA acceptance.

In the European Union, PEF-treated food products may in some interpretations fall under the Novel Food Regulation (EU 2015/2283) if the processing substantially changes the product’s composition or nutritional value. In practice, the regulatory treatment of PEF-treated juices and similar products has been managed under existing pasteurisation frameworks in most EU member states, without formal novel food assessment. The European Food Safety Authority (EFSA) has reviewed PEF in the context of processed food safety.

Relation to other non-thermal technologies

PEF complements rather than competes with other non-thermal preservation approaches:

• High pressure processing (HPP) — handles solid and semi-solid foods in batch mode; achieves the same microbial targets as PEF in liquids, but with no continuous flow option and higher capital cost per unit of throughput for liquid products
• Ultraviolet (UV) treatment — effective for surface decontamination and clear liquids; limited penetration depth; no heating
• Ohmic heating — uses electrical resistance of food to generate heat uniformly; a thermal method, not non-thermal, but shares electrode-based infrastructure with PEF systems
• Ultrasound — used in combination with mild heat (thermosonication); physical cavitation disrupts cells; limited commercial deployment for microbial inactivation

All these technologies, along with conventional thermal methods, fall within the framework of food preservation and are increasingly combined as hurdles — overlapping safety margins that together achieve targets no single method can reach alone.