Influence of treatment time and pulse frequency on Salmonella Enteritidis, Escherichia coli and Listeria monocytogenes populations inoculated in melon and watermelon juices treated by pulsed electric fields.

Consumption of unpasteurized melon and watermelon juices has caused several disease outbreaks by pathogenic microorganisms worldwide. Pulsed electric field (PEF) has been recognized as a technology that may inactivate those bacteria present in fluid food products at low temperatures. Hence, PEF treatment at 35 kV/cm, 4 mus pulse duration in bipolar mode and square shape were applied on Salmonella Enteritidis, E. coli and L. monocytogenes populations inoculated in melon and watermelon juices without exceeding 40 degrees C outlet temperatures. Different levels of treatment time and pulse frequency were applied to evaluate their effects on these microorganisms. Treatment time was more influential than pulse frequency (P</=0.05) on the PEF microbial reduction levels for both melon and watermelon juices. Populations of S. Enteritidis, E. coli and L. monocytogenes were experimentally reduced and validated in a single process up to 3.71+/-0.17, 3.7+/-0.3 and 3.56+/-0.26 log(10) units, respectively, in melon juice when 1440 micros and 217 Hz were used; whereas reductions up to 3.56+/-0.12, 3.6+/-0.4 and 3.41+/-0.13 log(10) units of those microorganisms, respectively, were reached in watermelon juice treated for 1727 micros at 188 Hz. Although PEF treatment reduced the populations of the three microorganisms, L. monocytogenes was more resistant to PEF than S. Enteritidis and E. coli in both juices when treated at the same processing conditions.