Inactivation of Bacillus subtilis spores by pulsed electric fields (PEF) in combination with thermal energy II. Modeling thermal inactivation of B. subtilis spores during PEF processing in combination with thermal energy

• Published in: Food control Vol. 39; pp. 244 - 250
• Main Authors: Siemer, Claudia, Toepfl, Stefan, Heinz, Volker
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2014; Elsevier
• Subjects: Bacillus subtilis; Bacterial endospore; Biological and medical sciences; cold treatment; cooling; endospores; energy; fiber optics; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; glass; heat; heat inactivation; Hygiene and safety; Modeling; PEF; Pulsed electric fields; specific energy; temperature; Thermal sensitivity; PEF; Pulsed electric fields; Bacterial endospore; Thermal sensitivity; Bacillus subtilis; Modeling
• ISSN: 0956-7135; 1873-7129
• DOI: 10.1016/j.foodcont.2013.09.067

The application of pulsed electric fields (PEF) can be used to inactivate bacterial endospores if combined with thermal energy. A model was developed in the second part of the study aiming to separate thermal and PEF induced spore inactivation. Therefore thermal inactivation data of B. subtilis spores was obtained by glass capillary method and combined with temperature time profile of the PEF process. The PEF process can be separated in pre heating, PEF treatment and cooling phase. The temperature development in pre heating and cooling phase was simulated based on a theoretical numerical approach, the temperatures in the PEF unit were measured by fiber optic sensors. To evaluate the effect of pH on the inactivation the PEF treatment was performed in Ringer solution (4 mS/cm) at pH 4 and 7. The results of the developed model indicate a thermal and a PEF induced inactivation, where the temperature induced inactivation is slightly higher in acid Ringer solution. The impact of specific energy inputs up to 195 kJ/kg was evaluated, showing an increasing total inactivation of the spores, but also shift towards PEF induced inactivation. Applying an energy input of 195 kJ/kg an inactivation of 4.4 log was obtained in Ringer solution at pH 7, which could be separated in 1.15 log of thermal and 3.25 log of PEF related inactivation. The F-value, typically used to describe thermal spore inactivation processes was calculated for the combined PEF process based on the temperature time profile. The highest F-value determined for the maximum applied energy was 2.43 s, which confirms the low product heat load. •Spore inactivation by the developed process can be divided in thermal and PEF induced inactivation.•Bacillus subtilis spores are more heat sensitive in acid environments.•No germination of B. subtilis is induced by PEF or pre heating temperature of 80 °C.•Small F-values indicate that PEF process is a temperature assisted process.