Effect of different conditions on bacterial inactivation of Pulsed Electric Field (PEF) treatment

The aim of this study was to evaluate Pulsed Electric Fields (PEF) bacterial inactivation ability in relation to different conditions (initial bacterial concentration and mixing). The experiments were performed on E. coli, E. coli O157:H7 and S. aureus. A laboratory scale PEF batch unit with a rectangular electric pulse was used. Measures of inactivation were carried out at 25 Kv/cm (E. coli, E. coli O157:H7) and at 30 kV/cm (S. aureus), 1 µs, pulse repetition rate of 1 Hz, at different pulse number (range 20-350). The initial bacterial concentration tested ranged between 10^5-10^10, 10^5-10^12, 10^3-10^11 CFU/mL for E. coli, E. coli O157:H7 and S. aureus respectively. The trials with and without bacterial suspension mixing were performed at 300 pulses. A similar behaviour was observed for all bacteria studied. Results indicated that microbial inactivation statistically depends on the bacterial concentration at high pulse number (>200). A higher inactivation rate was observed at the greatest bacterial concentrations. Considering the experiments with and without mixing a higher bacterial inactivation was observed with mixing. Since PEF inactivation activity seems to be influenced by the different conditions investigated further studies are needed to improve and optimise PEF treatment as a non-thermal process of food preservation.