Physical and chemical modifications of high-voltage pulse sterilization

Abstract

Pulse sterilization, which is a method of inactivation of cells by high-voltage pulsed electric field, can cause the destruction of cell membrane and cell death. Because the generated heat is relatively low, this method has the advantage of sterilizing contaminants in liquid foods without denaturation of some physiological compounds such as proteins, vitamins, etc. In this research, the effects of the shape of treatment chamber and the addition of bactericides on pulse sterilization were studied. Three types of electrode systems (a needle-plate electrode system, and a plate-plate electrode with and without edge systems) were used in this research. At an applied voltage of 12 kV, the most efficient sterilization was achieved when the needle-plate system was used. Pulse sterilization of Saccharomyces cerevisiae was carried out in treatment chambers with and without insulating plates between the electrodes. These insulating plates were Plexiglas plates with some holes. When an applied voltage was 10 kV, an insulating plate with nine holes which is 1.5 mm in diameter (the minimum size in our experiments) had better sterilization efficiency because the holes between the electrodes concentrated the electric field. Sterilization of Salmonella typhimurium was carried out under controlled temperature with and without pulsed electric field. The survival ratios at 50 °C with and without pulsed electric field were 10 −4 and 10 −1, respectively. Temperature dependence of pulse sterilization was also observed when S. cerevisiae and Escherichia coli were used as the subjects. Pulse sterilization of E. coli was carried out with and without ozone and H2O2 as bactericides. Although a lower concentration of these bactericides could not cause cell death, pulse sterilization with bactericides was more effective than pulse sterilization alone. The bactericides caused cell membrane wounding that resulted in easier pulse sterilization. Because no residual bactericides were detected in the sample liquid after treatment, pulse sterilization with bactericides appears to be possible in the food industry.