Bacterial Inactivation Of Liquid Food With High Conductivity By High Voltage Pulsed Electric Field

Plulsed electric field for bacterial inactivation can maintain the nutrition and flavor of the food. Therefore, it attracts a wide spread attention. A large pulse current will occur if high voltage pulse is applied to liquid food with high conductivity because of its small equivalent impedance. The temperature increment of the liquid food is insignificant. The high conductivity can also influence parameters of high voltage pulse. And the effect of bacterial inactivation is lower by it. It is difficult to treat high conductivity liquid food by high voltage pulsed electric field. The paper provides technical basis for industrial application of high conductivity liquid food bacterial inactivation by pulsed electric field.In order to analysis the response of bacterial membrane in pulsed electric fields, a single spherical model of bacterium is built in this paper. The transmembrane voltage expression is derived by solving the Laplace’s equation. The transmembrane voltage is also analyzed in frequency domain and time domain. The result of frequency domain analysis shows that bacterial membrane represents low-pass filter characteristic in pulsed electric field. The result of time domain analysis shows that the transmembrane voltage amplitude in square wave, exponentially decaying wave, oscillation wave pulsed electric field are related to the pulse width, decaying time constant, oscillating frequency respectively.A high efficiency bipolar exponentially decaying pulse circuit is designed to overcome the shortcoming of the practical bipolar high voltage pulse circuit. The treatment chambers with different forms of electrode are designed. The electric fields in these chambers are slightly non-uniform electric field distribution, non-uniform electric field distribution and highly non-uniform electric field distribution respectively. By the bacterial inactivation experiment with different pulse amplitude and pulse width, the influences of different electric field distribution are compared. By the comparison of bacterial inactivation under the pressure of 0.02MPa、0.1MPa、0.2MPa and 0.3MPa, the influences of vaccum, normal pressure and high pressure on pulsed electric field bacterial inactivation is analyzed. Experimental result shows that the bacterial survival can be decreased by means of setting up highly non-uniform electric field, increasing local electric field intensity and pressure.In order to compare the bacterium suppression effects of square wave pulse and exponential decaying wave pulse at the same electric field intensity, a square wave pulse circuit is designed. The generation of square wave pulse is controlled by IGBT. The pulse is stepped up by pulse transformer. With the same electric field intensity, bacterial inactivation effects of lmm gap electrode applied square wave pulse and 3mm gap electrode applied exponentially decaying wave pulse are compared. Experimental result shows that the bacterial survival can be decreased by means of decreasing pulses amplitude, improving high voltage pulses waveform if electric field intensity is constant.By experimental data a new bacterial inactivatin model is presented in order to analyzing the rule of bacterial survival-electric field intensity in pulsed electric fields. In the new model, the bacterial survival changes exponentially if electric field intensity increases. By mathematic derivation, the relationship and their application range between the practical linear model and exponential model are analyzed. It is considered that the linear model is a local linear approximation of the exponential model.