Effect of processing parameters on inactivation of Bacillus cereus spores in milk using pulsed electric fields

The inactivation of Bacillus cereus spores in milk by treatment using pulsed electric fields (PEF) was studied. The effects of the electric field, temperature, number of pulses, pulse width, frequency and nisin concentration were tested in skim and whole milk. Results showed high resistance of spores to PEF alone; mild thermal treatment (40 °C) applied together with PEF had an antagonistic effect, and treatment at 50 °C enhanced spore death. Skim milk was a better medium than whole milk for inactivation; stronger thermal treatment (65 °C) together with PEF achieved a slight increase in spore reduction. The effect of pulse width was not consistent. Addition of nisin (50 IU mL−1) was synergistically effective (40 kV cm−1, 144 pulses, 65 °C), reducing spore count (by 3.6 log) in skim milk. Regardless of the severity of the treatment, spores showed resistance to the different processing variables.