Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Estimation of the parameters of the Smoluchowski equation describing the occurrence of pores in a bilayer lipid membrane under soft poration

The conductive lipid pores occurring in planar bilayer membranes are known to manifest themselves experimentally as current fluctuations. Reliable recording of such fluctuations during phase transitions, as well as in membranes with various additives (for example, SDS), allows one to determine the characteristics of hypothetical hydrophilic pores, namely, their number, sizes, lifetimes, and duration of time intervals between pores. Because, in contrast with electroporation, the emergence of pores in a membrane does not require high voltages, this process is called soft poration. Studying the characteristics of pores under soft poration allows us to estimate the parameters of the Smoluchowski equation and compare them with the corresponding parameters used to describe electroporation. In this work, the experimental characteristics of current fluctuations in the membrane with the addition of SDS to the bulk solution were used to estimate the parameters of the Smoluchowski equation: the pore edge tension, the energy of the hydrophobic pore/hydrophilic pore barrier, the coefficient of pore diffusion in the radius space, the initial distribution density of the number of pores, and the attempt rate density of the lipids in a membrane. The obtained estimates are close to the parameter values used in studies of electroporation.

Increase in the current variance in bilayer lipid membranes near phase transition as a result of the occurrence of hydrophobic defects

Most researchers associate the increase in the permeability of lipid bilayers of artificial and biological membranes observed in various experiments with the formation of hypothetical hydrophobic and hydrophilic pores. Although the existence of hydrophobic defects, as the first stage of the formation of a hydrophilic pore, was hypothesized decades ago from electroporation experiments, the difficulty of describing this stage is determined by the lack of experimental data confirming the existence or at least associated with hydrophobic pores. We explored the increase in the current variance through the lipid membrane, observed when approaching the phase transition from the side of high temperatures, and have associated it with capacitive currents arising in response to the formation of hydrophobic pores. Assuming that the number of hydrophobic pores in a membrane follows a Poisson distribution, and thus, the mean number of hydrophobic pores is equal to the variance of that number, we used the measurements of the membrane current variance to evaluate the number of hydrophobic pores. Analysis of experimental data within this model allows us to estimate the number of hydrophobic pores at or above the phase transition and shows that the number of hydrophobic pores in a membrane close to the phase transition increased 20 times compared to the number of hydrophobic pores existing in the membrane far from the melting transition.