ABSTRACT
Survival curves of L. innocua and P. fluorescens exposed to pulsed electric fields (PEF) have exponential decaying form when plotted in linear coordinates, and follow linearity when plotted in semi-logarithmic coordinates. These survival curves were described by application of the model represented by Equation (2) of this chapter. This model worked best at electric fields ranging from 40–50 kV/cm, 40–100 pulses, and treatment times from 100–200 μs. The kinetic constants determined for L. innocua and P. fluorescens ranged from 2.467 μs−1 at 30 kV/cm to 0.131 μs−1 at 50 kV/cm for L. innocua, and from 4.470 μs−1 to 0.396 μs−1 for P. fluorescens at the same electric field intensities.
The viability of Listeria innocua and Pseudomonas fluorescens before and after treatment were assayed by counting colony-forming units (cfu). Logarithmic reduction of 2.7 and 2.6 cycles in L. innocua and P. fluorescens in raw skim milk were achieved when treated at electric field intensities of 30, 40–50 kV/cm with 30–100 pulses, 2 μs at a frequency of 4.0 Hz. A coaxial continuous treatment chamber, with electrode gaps of 0.63 cm, was selected for high intensity pulsed electric field (PEF) treatment. Effective lethality of PEF treatment was achieved at electric field intensities greater than 30 kV/cm and 40 pulses, treatment time 50–200 for both microorganisms. Raw skim milk was maintained at temperatures of 7, 25, or 28°C during PEF treatment.
