Continuous processing of skim milk by a combination of pulsed electric fields and conventional heat treatments: does a synergetic effect on microbial inactivation exist?

The objective of this research was to evaluate the effect of the combination of PEF with conventional heat treatment on the microbial inactivation of Salmonella enteritidis in skim milk. The purpose was to identify possible synergies that would make it possible to design minimal treatment regimes. Heat-resistance parameters (D and z) were firstly determined using a temperaturecontrolled water bath. Then, the effect of the PEF treatment followed by a heat treatment on the inactivation of Salmonella enteritidis in skim milk was evaluated using a PEF of 47 kVcm -1 / 500 ns / 60 Hz, and a temperature of 62 C for 19 s, at a volumetric flow rate of 5 Lh -1 . The effect of PEF or heating only was also studied with the same equipment. From the heat-resistance parameters previously determined, continuous heat processing at 62 C for 19 s should give an inactivation ratio of 1.7 log. PEF processing of the milk resulted in a decimal reduction of 1.2 0.3 log and the combination of the two operations gave a reduction of Salmonella enteritidis equal to 2.3 0.4 log. The results suggested that the combination of PEF and heating was more effective than each on its own. However, the lethality of the two treatments was additive rather than synergistic. milk stabilization / Salmonella enteritidis / pulsed electric fields / heat treatment