Inactivation Of Escherichia Coli, Saccharomyces Cerevislae, And Lactobacillus Brevis In Low-Fat Milk By Pulsed Electric Field Treatment: A Pilot-Scale Study

We investigated the effects of a pulsed electric field (PEP) treatment on microbial inactivation and the physical properties of low-fat milk. Milk inoculated with Escherichia colt, Saccharomyces cerevisiae, or Lactobacillus brevis was supplied to a pilot-scale PEF treatment system at a flow rate of 30 L/h. Pulses with an electric field strength of 10 kV/cm and a pulse width of 30 mu s were applied to the milk with total pulse energies of 50-250 kJ/L achieved by varying the pulse frequency. The inactivation curves of the test microorganisms were biphasic with an initial lag phase (or shoulder) followed by a phase of rapid inactivation. PEP treatments with a total pulse energy of 200 kJ/L resulted in a 4.5-log reduction in E. coli, a 4.4-log reduction in L. brevis, and a 6.0-log reduction in S. cerevisiae. Total pulse energies of 200 and 250 kJ/L resulted in greater than 5-log reductions in microbial counts in stored PEP-treated milk, and the growth of surviving microorganisms was slow during storage for 15 d at 4 degrees C. PEP treatment did not change milk physical properties such as pH, color, or particle-size distribution (p<0.05). These results indicate that a relatively low electric-field strength of 10 kV/cm can be used to pasteurize low-fat milk.