Resistance of Enterobacter sakazakii to pulsed electric fields

The influence of various environmental factors on Enterobacter sakazakii inactivation by pulsed electric fields was studied and the mechanisms underlying the changes in resistance were also explored. E. sakazakii PEF resistance was higher upon entering the stationary growth phase, but it did not significantly change with growth temperature. E. sakazakii cells were also more resistant to PEF in both acidified and low water activity media. Thus, for stationary-phase cells grown at 30 °C a treatment of 50 pulses at 31 kV/cm led to 5.1 log10 cycles of inactivation in media of pH 7.0 (aw > 0.99), 1.4 log10 cycles in media of pH 4.0 (aw > 0.99) and 0.3 log10 cycles in media of aw = 0.98 (pH 7.0). However, whereas the higher PEF tolerance in acid media was coincident with an increased number of cells capable of repairing their sublethally-injured cytoplasmic membranes, the higher resistance in media of lower water activity was not. To the best of our knowledge, this is the first time that sublethal injuries in outer membrane after PEF treatments have been found.Industrial relevanceThis work provides data about PEF inactivation kinetics and PEF resistance of E. sakazakii under several conditions that might be useful for designing food pasteurization processes by PEF technology. The occurrence of sublethal injuries in cytoplasmic and outer membranes under the most protective treatment conditions, gives the chance to develop combined processes that might increase the effectiveness of the PEF process.