Pulsed electric field (PEF) processing is based on the application of short pulses of high voltage (typically 20 to 80 kV/cm) to food placed between two electrodes. PEF is considered a nonthermal process, as foods are treated at room temperature or below for only a few microseconds, minimizing the energy loss caused by heating.

Principles

In PEF technology, the energy derived from a high-voltage power supply is stored in one or several capacitors and discharged through a food material to generate the necessary electric field. The energy stored in one capacitor (Q [J/m³]) is given by:
                                          Q = 0.5CV²

Where

C is the capacitance, and

V is the charging voltage

The energy stored in the capacitors can be discharged almost instantaneously at very high levels of power. The discharge occurs in a treatment chamber in which the food is placed or circulates through a small gap between two electrodes. When a trigger signal is activated, a high voltage switch is closed and the charge stored in the capacitor flows through the food in the treatment chamber. In order to avoid undesirable thermal effects, cold water is recirculated through the electrodes to dissipate the heat generated by the electric current passing through the food. Varying arrangements of capacitors, inductors, and resistors produce different types of pulses. Pulse polarity can be constant or alternating, and pulse waveform can be of exponential decay or square shape, among others.

Square pulses are more effective on microbial inactivation, as they maintain a peak voltage for a longer period than do exponential decay pulses. Exponential decay pulses have a long tail with a low electric field, during which excess heat is generated in the food without bactericidal effects. Treatment chambers are designed to hold the food between two electrodes during PEF application. The chambers can be designed to work in static or continuous modes. In the static mode, food is held between two parallel electrodes, whereas in the continuous mode food circulates between the electrodes during PEF treatment. Two designs more commonly used in a continuous mode are coaxial (cylindrical or conical) and co field.

Application

Pulsed electric field (PEF) technology is used in the areas of genetic engineering and biotechnology to promote cell membrane reversible electroporation and cell electrofusion, respectively. The same principle is applied to PEF technology for microbial inactivation during food processing. The duration and intensity of the treatment are increased to make the membrane disruption an irreversible phenomenon. Electroporation is the most widely accepted concept used to describe the phenomenon of cell membrane discharge (reversible electroporation) and cell membrane breakdown (irreversible electroporation) with the application of short pulses.