Effect of the sequence of nisin and pulsed electric fields treatments and mechanisms involved in the inactivation of Listeria innocua in whey

The combination of nisin and pulsed electric fields (PEF) on Listeria innocua in liquid whey protein concentrate (LWPC) were studied with the purpose of enhancing nisin antibacterial action.The efficiency of the combined treatment of nisin and PEF was strongly dependent on the sequence of application. The exposure to nisin after PEF produced an antagonistic effect on L. innocua inactivation. This behaviour could be mainly attributed to changes in the cell envelope and to modifications of the medium caused by PEF application. Consequently, the posterior action of nisin was reduced, showing an increase in the resistance of L. innocua to nisin. In opposite, the addition of nisin prior to PEF treatment exhibited an additive and slightly synergistic effect, suggesting that the binding of nisin to the cell membrane would increase the susceptibility of the microorganism to PEF treatment.