PROPOSAL

Proposal

Proposal for Comparison of Effect of Different Temperatures, Voltages and Multiple Electric Pulses

Lay summary

The proposed research is based on examining the effect of different temperatures, voltages and multiple electric pulses. It has been studied that pulsed electric field technology are the generation of high electric field intensities, the design of chambers that impart uniform treatment to foods with minimum increase in temperature, and the design of electrodes that minimize the effect of electrolysis. The large field intensities are achieved through storing a large amount of energy in a capacitor bank (a series of capacitors) from a DC power supply, which is then discharged in the form of high voltage pulses. Studies on energy requirements have concluded that PEF is an energy-efficient process compared to thermal pasteurization, particularly when a continuous system is used.

Context of proposed research

High intensity pulsed electric field (PEF) processing involves the application of pulses of high voltage (typically 20 - 80 kV/cm) to foods placed between 2 electrodes. PEF treatment is conducted at ambient, sub-ambient, or slightly above ambient temperature for less than 1 s, and energy loss due to heating of foods is minimized. For food quality attributes, PEF technology is considered superior to traditional heat treatment of foods because it avoids or greatly reduces the detrimental changes of the sensory and physical properties of foods (Quass 1997). Although some studies have concluded that PEF preserves the nutritional components of the food, effects of PEF on the chemical and nutritional aspects of foods must be better understood before it is used in food processing (Qin and others 1995b).

 PEF may be applied in the form of exponentially decaying, square wave, bipolar, or oscillatory pulses. An exponential decay voltage wave is a unidirectional voltage that rises rapidly to a maximum value and decays slowly to zero. The circuit in Fig. 1 may be used to generate an exponential decay waveform. A DC power supply charges a capacitor bank connected in series with a charging resistor (Rs). When a trigger signal is applied, the charge stored in the capacitor flows though the food in the treatment chamber.

 

Figure 1. Electrical circuit for the production of exponential decay waveforms

 

Figure 2. Square pulse generator using a pulse-forming network of 3 capacitors inductor units and a voltage trace across the treatment chamber

Square pulse waveforms are more lethal and more energy efficient than exponential decaying pulses. A square waveform can be obtained by using a pulse-forming network (PFN) consisting of an array of capacitors and inductors and solid state switching devices (Fig. 2).

The instant-charge-reversal pulses are characterized by a +ve part and -ve part (Fig. 3) with various widths and peak field strengths. An instant-charge-reversal pulse width with charge-reversal at the end of the pulse is considerably different from a standard bipolar pulse. In the latter, the polarity of the pulses is reversed alternately with relaxation time between pulses. Even with a high frequency pulser (for example, 1000 Hz), the dielectric relaxation time at zero voltage between 4 µs square wave pulses is ...