2.5.2. Experiments with recirculation/refrigeration cycles
Electric fields of 30 and 40 kV cm1 were used in combination with up to 240 exponentially decaying pulses of around 2.5 ms pulse width. Inlet and outlet temperatures of the treatment chamber were monitored with digital in-line k-type thermocouples and a recirculation and refrigeration system was used with a coiled
tubing (VWR Refrigerated Recirculator 1174, Arlington Heights, IL, USA) between each set of pulses to cool the milk. Two groups of experiments were conducted. The first group consisted of maintaining the temperature at 55 C and applying PEF at the same time; the second group of experiments kept the temperature at 65 C
while also using PEF treatment.
For experiments using nisin in milk as an anti-microbial, electric peaks at 40 kV cm1, 144 pulses (2.5 ms) in combination with an inlet temperature of 65 C were used as processing conditions to evaluate high (50 IU mL1) and low (10 IU mL1) concentrations of nisin in spore inactivation.