Inactivation of Bacillus subtilis spores by pulsed electric fields (PEF) in combination with thermal energy - I. Influence of process- and product parameters

- Inactivation of Bacillus subtilis spores can be realized by PEF in combination with thermal energy.
- At lower conductivity values higher electric field strengths can be achieved and less energy for the inactivation is required.
- At higher inlet temperatures, less energy is required for a successful inactivation.
- Medium containing sugar allows a higher inactivation at lower energy values.

In addition to inactivation of vegetative microorganisms, PEF can be used to inactivate bacterial endospores when combined with thermal energy. In the first part of this study, the impact of the product parameters pH value (4 and 7), sugar level (5 and 10%) and conductivity (4 and 15 mS/cm) as well as the process parameters specific energy (up to 350 kJ/kg), electric field strength (6-11 kV/cm) and inlet temperature (56, 70 and 80 °C) on the inactivation of Bacillus subtilis spores were analyzed.The results of spore inactivation by PEF at different inlet temperatures indicated less energy requirements for sufficient inactivation at higher inlet temperatures. Comparing the inactivation at different pH values, the inactivation at acid pH value required less energy than at neutral pH value. A 1.6 log reduction using 167 kJ/kg was detected in Ringer solution at pH 4 compared to 0.6 log in neutral medium at an energy of 165 kJ/kg (inlet temperature of 80 °C and 9 kV/cm as electric field strength). Under the same process conditions (9 kV/cm and 80 °C inlet temperature), the addition of 10% sugar permitted to reduce the energy from 178 to 146 kJ/kg, require to reach a 3 log cycles inactivation of B. subtilis spores. The results showed a successful inactivation of B. subtilis spores by PEF in combination with thermal energy and represent therefore a promising process for spore inactivation with reduced heat load.