Effects of Pulsed Electric Fields on Inactivation Kinetics of Listeria innocua

Abstract

The effects of pulsed electric field (PEF) treatment and processing factors on the inactivation kinetics of Listeria innocuaNCTC 11289 were investigated by using a pilot plant PEF unit with a flow rate of 200 liters/h. The electric field strength, pulse length, number of pulses, and inlet temperature were the most significant process factors influencing the inactivation kinetics. Product factors (pH and conductivity) also influenced the inactivation kinetics. In phosphate buffer at pH 4.0 and 0.5 S/m at 40°C, a 3.0-V/μm PEF treatment at an inlet temperature of 40°C resulted in ≥6.3 log inactivation of strain NCTC 11289 at 49.5°C. A synergistic effect between temperature and PEF inactivation was also observed. The inactivation obtained with PEF was compared to the inactivation obtained with heat. We found that heat inactivation was less effective than PEF inactivation under similar time and temperature conditions.L. innocua cells which were incubated for a prolonged time in the stationary phase were more resistant to the PEF treatment, indicating that the physiological state of the microorganism plays a role in inactivation by PEF. Sublethal injury of cells was observed after PEF treatment, and the injury was more severe when the level of treatment was increased. Overall, our results indicate that it may be possible to use PEF in future applications in order to produce safe products.

Occurrence of sublethal injury after pulsed electric fields depending on the micro-organism, the treatment medium ph and the intensity of the treatment investigated

“…Nevertheless, when the selective medium was used as a recovery medium, among bacterial species investigated there still exist differences in PEF resistance under the same experimental conditions. So, as suggested by other authors, the intrinsic microbial resistance might also be related to other factors, such as the type of micro-organism (Hülsheger et al 1981;Wouters et al 1999;MacGregor et al 2000), their cell size and shape (Kehez et al 1996;Qin et al 1998;Heinz et al 2002), etc.…”

“…Whereas according to several authors Hülsheger et al 1981;Heinz and Knorr 2000;Ravishankar et al 2002;Á lvarez et al 2003) the pH of treatment media did not affect microbial inactivation by PEF, some micro-organisms such as E. coli, Listeria innocua, L. monocytogenes or Lact. plantarum were more PEF sensitive at acidic than at neutral pH (Vega-Mercado et al 1996;Wouters et al 1999Wouters et al , 2001Aronsson and Rönner 2001;Á lvarez et al 2002;Aronsson et al 2004), and others, such as Salm. Enteritidis, Salm.…”

Modelling and optimization of inactivation of Lactobacillus plantarum by pulsed electric field treatment

“…Electric field strength, pulse length, number of pulses, pulse shape and starting temperature are the main processing parameters that affect microbial inactivation (Wouters and Smelt 1997;Barbosa-Cánovas et al 1999;Schoenbach et al 2000). An increase in the electric field intensity and in treatment time, defined as the product of the number of pulses and the pulse length, increases the microbial inactivation (Qin et al 1998;Wouters et al 1999). Application of pulses, quantified as energy input, results in thermal energy dissipation and consequently in an increase of the temperature of the product.…”

Effects of pulsed electric fields on inactivation and metabolic activity of Lactobacillus plantarum in model beer

“…DNA fragments, without loss of viability. Higher field strengths and energy inputs are thought to induce irreversible pore formation, leading to cell death (Wouters et al 1999;Heinz and Knorr 2000;Jayaram 2000). Based on literature data, a threshold value of field strength must be exceeded to induce the critical transmembrane potential (D u) of ) 1 V. To achieve this transmembrane potential a field strength above 30 kV cm )1 is required for most bacteria in liquid systems.…”