Impact of air bubbles in a dielectric liquid when subjected to high field strengths

Processing temperature, alcohol and carbonation levels and their impact on pulsed electric fields (PEF) mitigation of selected characteristic microorganisms in beer

“…Stainless steel flow-through cells were connected to the tubing to allow temperature measurement before and after the pre-treatment cooling coil, the treatment chamber inlet and outlet, and the subsequent post-treatment tubing coil submerged in a cooling bath (NESLAB RTE 7, Thermo Fisher Scientific Inc., Newlington, NH, USA) to decrease the product to 10°C prior to sampling. Possible occurrence of arcing during PEF processing of carbonated beer without back pressure (Góngora-Nieto et al, 2003) was not observed in the present study. T-type thermocouples (TMTSS-040G-6, Omega, Stamford, CT, USA) connected to the flow-through cells on the one end and a portable WLAN datalogger (OM-SQ2020-2F8, Omega, Stamford, CT, USA) on the other end were used to transmit the processing temperature of the beer to the logger for monitoring and recording.…”

“…The antimicrobial effectiveness of an applied processing technology for the preservation of beer depends on the treatment conditions, such as product temperature and residence time but, in addition, it may also be affected by product parameters such as carbonation and alcohol levels of beer. Many studies have investigated the combined effects of heat treatment and PEF (El-Hag, Jayaram, & Griffiths, 2006;Iu, Mittal, & Griffiths, 2001;Li, Zhang, Jin, Turek, & Lau, 2005;Walkling-Ribeiro, Noci, Cronin, Lyng, & Morgan, 2009) or temperature-assisted PEF (Amiali, Ngadi, Smith, & Raghavan, 2005;Grahl & Märkl, 1996;Jaeger, Meneses, Moritz, & Knorr, 2010;Walkling-Ribeiro et al, 2008) on the reduction of microbial populations in liquid foods, while few research groups (Góngora-Nieto, Pedrow, Swanson, & Barbosa-Cánovas, 2003;Mañas, Barsotti, & Cheftel, 2001) have looked into possible effects of gas bubble saturation in PEF-treated liquids and, to our knowledge, no research on a PEF-treated product at different alcohol contents is available in the literature at the present time.…”

Review: Potential of High-Intensity Pulsed Electric Field Technology for Milk Processing

“…The optimization of the treatment chamber should also include measures to control the residence time distribution and variations in temperature on account of their indirect effect. Attending the chamber design, turbulent flow through the treatment chamber may be desirable since residence time distribution in turbulent flow is more homogeneous than in laminar flow [28]. Temperature can modify the electrical conductivity, density, viscosity and thermal conductivity of the milk media and, as a consequence, electric field distribution and product flow are inherently coupled to variations in temperature.…”

“…These two models agree on the need to eliminate recirculation regions in order to reduce the time during which the fluid product remains in the system, since product remaining trapped in the treatment chamber may dissipate less energy in a given volume of product and, consequently, increasing its temperature. However, thermal equilibration by heat removal across the electrodes may be complicated and even insufficient, despite suitable dimension of electrode area and gap, due to inhomogeneities in the electric field and the boundary layer of the flow [28]. The possibility of two or more chambers in series may facilitate heat dissipation by inserting a cooling system after a determined number of chambers, as well as multiple pulses can be applied [25].…”

Moderate and high intensity pulsed electric fields : Effect on microbial inactivation, shelf life and quality of fruit juices

“…Products where foam formation cannot be avoided are not suitable to be subjected to high intensity PEF . Furthermore, Góngora-Nieto et al (2003) have shown that presence of air bubbles in the treatment chamber led to a drop in electric field strength and inhomogeneity in the treatment chamber, resulting in less microbial inactivation. Formation of air bubbles may be suppressed by application of static backpressure (Mastwijk, 2006).…”