Inactivation kinetics of pulsed electric field-resistant strains of Listeria monocytogenes and Staphylococcus aureus in media of different pH

A study of the effect of pulsed electric fields (PEF) on the inactivation of Listeria monocytogenes STCC 5672 and Staphylococcus aureus STCC 4459 in McIlvaine buffer covering a range from pH 3.5 to 7.0 was conducted. Mathematical models based on the Weibull distribution were developed to describe the influence of the electric field strength, treatment time and pH of the treatment medium on the lethality of both Gram positive pathogenic bacteria after PEF treatments. Both microorganisms were more sensitive to PEF in media of low pH, although the influence of the pH on the PEF resistance was more significant in S. aureus. In the best cases scenario, the highest inactivation levels achieved were 3.3 and 6.1 log10 cycles for L. monocytogenes and S. aureus respectively in pH 3.5 after 500 μs of 35 kV/cm. Based on these results and those observed in literature, L. monocytogenes STCC 5672 at any pH investigated has been shown as one of the most PEF resistant microorganism. Therefore, this microorganism should be considered as a possible target microorganism to define process criterion for PEF pasteurization.