Development of a Continuous Pulsed Electric Field (PEF) Vortex-Flow Chamber for Improved Treatment Homogeneity Based on Hydrodynamic Optimization

Felix Schottroff; Justus Knappert; Pauline Eppmann; Anna Krottenthaler; Tobias Horneber; Christopher McHardy; Cornelia Rauh; Henry Jaeger

doi:10.3389/fbioe.2020.00340

Development of a Continuous Pulsed Electric Field (PEF) Vortex-Flow Chamber for Improved Treatment Homogeneity Based on Hydrodynamic Optimization

Front Bioeng Biotechnol. 2020 Apr 30:8:340. doi: 10.3389/fbioe.2020.00340. eCollection 2020.

Authors

Felix Schottroff¹, Justus Knappert², Pauline Eppmann², Anna Krottenthaler¹, Tobias Horneber², Christopher McHardy², Cornelia Rauh², Henry Jaeger¹

Affiliations

¹ Institute of Food Technology, Department of Food Science and Technology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria.
² Institute of Food Technology and Food Chemistry, Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin, Germany.

Abstract

Pulsed electric fields (PEF) treatment is an effective process for preservation of liquid products in food and biotechnology at reduced temperatures, by causing electroporation. It may contribute to increase retention of heat-labile constituents with similar or enhanced levels of microbial inactivation, compared to thermal processes. However, especially continuous PEF treatments suffer from inhomogeneous treatment conditions. Typically, electric field intensities are highest at the inner wall of the chamber, where the flow velocity of the treated product is lowest. Therefore, inhomogeneities of the electric field within the treatment chamber and associated inhomogeneous temperature fields emerge. For this reason, a specific treatment chamber was designed to obtain more homogeneous flow properties inside the treatment chamber and to reduce local temperature peaks, therefore increasing treatment homogeneity. This was accomplished by a divided inlet into the chamber, consequently generating a swirling flow (vortex). The influence of inlet angles on treatment homogeneity was studied (final values: radial angle α = 61°; axial angle β = 98°), using computational fluid dynamics (CFD). For the final design, the vorticity, i.e., the intensity of the fluid rotation, was the lowest of the investigated values in the first treatment zone (1002.55 1/s), but could be maintained for the longest distance, therefore providing an increased mixing and most homogeneous treatment conditions. The new design was experimentally compared to a conventional co-linear setup, taking into account inactivation efficacy of Microbacterium lacticum as well as retention of heat-sensitive alkaline phosphatase (ALP). Results showed an increase in M. lacticum inactivation (maximum Δlog of 1.8 at pH 7 and 1.1 at pH 4) by the vortex configuration and more homogeneous treatment conditions, as visible by the simulated temperature fields. Therefore, the new setup can contribute to optimize PEF treatment conditions and to further extend PEF applications to currently challenging products.

Keywords: differentiation of thermal and electric field effects; effects of PEF on alkaline phosphatase; non-thermal inactivation of microorganisms; numerical simulation; process optimization; proof of concept; pulsed electric fields (PEF); treatment chamber design.