Combined effect of nisin and pulsed electric fields on the inactivation ofEscherichia coli

The Doehlert design was applied in order to investigate the combined effect of nisin and high voltage pulsed electric fields (PEF) on the inactivation of Escherichia coli in simulated milk ultrafiltrate media. Nisin alone was totally inactivated by PEF, but in the presence of bacterial cells a prote ctive effect was observed. However, the effectiveness of nisin was still de creased when bacterial cells were subjected to the combined treatment. In s pite of this phenomenon, an almost additive response emerged as a consequen ce of the combined treatment. A 4-log cycle reduction may be accomplished w ith around 1,000 IU/ml (7.15 mu M) of nisin and three pulses of 11.25 kV/cm or 500 IU/ml for five pulses of the same intensity. The observed efficacy arising from the combination of both treatments suggests the possibility of using PEF for improving the action spectrum of natural antimicrobials.