PHYSICAL AND CHEMICAL MODIFICATIONS OF HIGH-VOLTAGE PULSE STERILIZATION

Pulse sterilization, which is a method of inactivation of cells by hig h-voltage pulsed electric field, can cause the destruction of cell mem brane and cell death. Because the generated heat is relatively low, th is method has the advantage of sterilizing contaminants in liquid food s without denaturation of some physiological compounds such as protein s, vitamins, etc. In this research, the effects of the shape of treatm ent chamber and the addition of bactericides on pulse sterilization we re studied. Three types of electrode systems (a needle-plate electrode system, and a plate-plate, electrode with and without edge systems) w ere used in this research. At an applied voltage of 12 kV, the most ef ficient sterilization was achieved when the needle-plate system was us ed. Pulse sterilization of Saccharomyces cerevisiae was carried out in treatment chambers with and without insulating plates between the ele ctrodes. These insulating plates were Plexiglas plates with some holes . When an applied voltage was 10 kV, an insulating plate with nine. ho les which is 1.5 mm in diameter (the minimum size in our experiments) had better sterilization efficiency because the holes between the elec trodes concentrated the electric field. Sterilization of Salmonella ty phimurium was carried out under controlled temperature with and withou t pulsed electric field. The survival ratios at 50 degrees C with and without pulsed electric field were 10(-4) and 10(-1), respectively. Te mperature dependence of pulse sterilization was also observed when S. cerevisiae and Escherichia coli were used as the subjects. Pulse steri lization of E. call was carried,out with and without ozone and H2O2 as bactericides. Although a lower concentration of these bactericides co uld not cause cell death, pulse sterilization with bactericides was mo re effective than pulse The bactericides caused cell membrane wounding that resulted in easier Because no residual bactericides were detecte d in the sample liquid after treatment, pulse sterilization with bacte ricides appears to be possible in the food industry.