Inactivation of selected microorganisms and properties of pulsed electric field processed milk

Raw skim milk and ultra-high-temperature (UHT) skim milk inoculated with Pseudomonas fluorescens, Lactococcus lactis and Bacillus cereus were processed by pulsed electric field (PEF) treatment. A continuous PEF bench scale system was set to deliver 35 kV/cm field strength with 64 pulses of bipolar square wave for 188 us. The flow rate of milk was 1 mL/s. Milk temperature was raised to 52C and cooled to 22C during PEF treatment. Pasteurization at 73C for 30 s was used for comparison. Microbial inactivation and cell morphology were investigated. Analyses for protein, total solids, color, pH, particle size, density and electrical conductivity showed no significant effects (P > 0.05) in the PEF processed milk. PEF treatment accomplished a 0.3 to 3.0 log reduction of P. fluorescens, L. lactis and B. cereus in UHT milk and of total microorganisms in raw milk.