Evaluation of strain variability of food microorganisms in response to decontamination by pulsed electric fields and thermal treatments

The effect of pulsed electric fields (PEF) and thermal treatments on the inactivation of the population of 40 strains of 4 model microorganisms (Escherichia coli, Listeria monocytogenes, Lactiplantibacillus plantarum, Saccharomyces cerevisiae) were investigated. Microbial samples of McIlvaine buffer pH 7.0 were subjected to pulses with electric field strength 20 kV/cm and total specific energies (88, 136, and 184 kJ/kg). Depending on the species and strain, microorganisms exhibited various resistances. PEF microbial resistance and strain variability data were correlated to the total specific energy used. E. coli strains showed statistical log₁₀ inactivation differences under the 88 and 136 kJ/kg but not under the 184 kJ/kg PEF treatment. In contrast, L. monocytogenes strains showed statistical log₁₀ inactivation differences only under the 184 kJ/kg treatment. L. monocytogenes L6 strain was identified as the most resistant strain at PEF treatment (184 kJ/kg). This result was in accordance with the resistance under thermal treatment (62.8 °C, 30 min).

Industrial relevance

The identification of target microorganisms related to their resistance in one or more technologies can help at establishing treatment conditions that reassure food safety. Data obtained in this research show that species and strain behaviours vary and are dependent on the technology and the applied treatment conditions. Thus, the resistance exhibited by microorganisms of public health importance may be dependent on the used technology and the applied treatment.