Synergistic effect of temperature and pulsed electric field on inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in liquid egg yolk

The effects of temperature, treatment time and electric field strength on inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in liquid egg yolk by pulsed electric field (PEF) processing were examined using the reaction kinetics approach. Egg yolk, inoculated with ∼108 CFU mL−1 of E. coli O157:H7 or S. enteritidis, was treated in a continuous flow process at 20, 30 and 40 °C in combination with pulsed electric field intensities of 20 and 30 kV cm−1. A biphasic instant reversal PEF waveform with a 2 μs pulse width was used and a maximum of 105 pulses were applied. Increasing the applied electric field intensity, treatment time and process temperature resulted in increased bacterial inactivation. At 30 kV cm−1 and 40 °C, the populations of E. coli O157:H7 and S. enteritidis were reduced by ∼5  logs. The inactivation rate constants increased from 0.004 to 0.098 μ s−1 for S. enteritidis whereas for E. coli O157:H7 the constants increased from 0.009 to 0.039 μs−1 as processing temperature increased from 20 to 40 °C. S. enteritidis was more resistant to PEF inactivation than E. coli O157:H7 at lower processing temperatures.