Inactivation of vegetative microorganisms by ohmic heating in the kilohertz range – Evaluation of experimental setups and non-thermal effects. (July 2020)

• Record Type: Journal Article
• Authors: Schottroff, Felix; Biebl, Dominik; Gruber, Manuel; Burghardt, Nicole; Schelling, Joane; Gratz, Maximilian; Schoenher, Christoph; Jaeger, Henry
• Is Part Of: Innovative food science & emerging technologies. Volume 63(2020)
• Publication Date: 2020-07
• Subjects: Electrotechnologies -- Ohmic heating -- Inactivation -- Pasteurization -- Differentiation of effects -- Non-thermal effects; Food -- Biotechnology -- Periodicals; Food industry and trade -- Technological innovations -- Periodicals; Aliments -- Biotechnologie -- Périodiques; Food -- Biotechnology; Periodicals; Electronic journals; 664.005
• DOI: 10.1016/j.ifset.2020.102372
• Languages: English
• ISSNs: 1466-8564

Abstract

Abstract: The present study highlighted the importance of equipment design for the experimental differentiation of thermal and electric field effects 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: 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. 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.