Inactivation of vegetative microorganisms by ohmic heating in the kilohertz range – Evaluation of experimental setups and non-thermal effects

Felix Schottroff, Dominik Biebl, Manuel Gruber, Nicole Burghardt, Joane Schelling, Maximilian Gratz, Christoph Schoenher, Henry Jaeger
2020 Innovative Food Science & Emerging Technologies  
Please cite this article as: F. Schottroff, D. Biebl, M. Gruber, et al., Inactivation of vegetative microorganisms by ohmic heating in the kilohertz range -Evaluation of experimental setups and non-thermal effects, Innovative Food Science and Emerging Technologies (2020), https://doi.Journal Pre-proof J o u r n a l P r e -p r o o f 2 Abstract The present study highlighted the importance of equipment design for the experimental differentiation of thermal and electric field effects during ohmic
more » ... ects during ohmic heating. Based on these findings, a specifically designed setup was capable of reducing temperature inhomogeneities of conventional and ohmic heating, thus allowing for a maximum comparability of the processes. The effects of the treatments were evaluated by determination of inactivation kinetics, using different microorganisms, i.e. Microbacterium lacticum, Escherichia coli, Listeria innocua, Staphylococcus carnosus, Saccharomyces cerevisiae, and Rhodotorula glutinis in neutral as well as acidic (pH 3.8) solutions. Selected kinetics were further analyzed by flow cytometry, using SYBR green and propidium iodide staining. Based on comparable T,t-profiles and plate counts, conventional and ohmic heating were shown to be capable of effectively inactivating all tested microorganisms (max. 2.5-6.5 log), depending on treatment intensity (2.5 kW, up to 140 s) and pH level. No additional, non-thermal inactivation effects were determined for ohmic heating treatments, independent of the used matrix, pulse repetition rate / frequency, or waveform. Industrial relevance text Ohmic heating is an alternative thermal preservation treatment increasingly used in the food and biotechnological industries for sensitive matrices, which are otherwise difficult to thermally process. It is able to overcome heat transfer limitations usually present in conventional thermal treatments, by application of an electric current flow through the product. The present paper contributes to better understand preservation by electrotechnologies and to the elucidation of inactivation mechanisms by ohmic heating. Thus, the understanding of the effects of ohmic heating on microorganisms is increased, which is crucial for industrial implementation of the technology and the corresponding process design. Therefore, it was the aim of this investigation to demonstrate the influence of different experimental setups on the inactivation results of conventional and ohmic heating. Consequently, an improved setup was deployed to study the electric field effects of ohmic Journal Pre-proof J o u r n a l P r e -p r o o f Highlights  Study on additional non-thermal effects during 12 and 300 kHz ohmic heating  Batch and co-linear flow-through chamber shown to not be suitable  Capillary setup enabled experimental differentiation of thermal and electric field effects  No additional inactivation of six different microorganisms (Gram+, Gram-, yeasts)  Electroporation was not induced by kHz ohmic heating Journal Pre-proof
doi:10.1016/j.ifset.2020.102372 fatcat:d4ebrzvny5e2vkhrqrisih4v6m