All liquid foods (water, milk, fruit juice, beer, etc.) contain single cell organisms such as bacteria and fungi. Some of these organisms are pathogenic, posing a health risk if ingested. In developed countries, most liquid foods are pasteurized or chlorinated prior to human consumption as a means to reduce pathogenic organisms. Pasteurization is a thermal process whereby the temperature of a liquid food is rapidly increased for a short period, then rapidly reduced to a temperature suitable for storage and transport. Chlorination is a chemical process, primarily used for potable water. Both of these processes kill a large fraction of target organisms present in the liquid, typically 99.99%, although the cost of achieving this kill ration is rather high. The health and economic benefits of theses processes are enormous, as is the energy expended. World wide, costs associated with the thermal energy required to pasteurize milk in 2002 were approximately two billion dollars. An efficient non-thermal, non-chemical means to accomplish a similar effect would represent a great economic benefit, not only to developed societies, but also to underdeveloped countries where thermal or chemical pasteurization is an economic burden or otherwise technically infeasible.
Morphologically, all bacteria and fungi cells share a common structure comprised of a thin phospholipid membrane encapsulating organelles and other cellular machinery suspended in the fluid cytoplasm. These membranes are complex heterogeneous structures separating the living cytoplasm from the extra-cellular environment. Biological membranes are remarkably robust, serving as a structural, chemical, and electrical barrier, while conducting the transmembrane metabolic affairs of the cell. The integrity of this membrane and its barrier function is paramount to cell viability. If an electric field of sufficient intensity and duration is applied to a living cell, membrane integrity can be severely disturbed, causing mechanical perforation, lysis, and death. This process is known as electroporation. Thus, electroporation can be used as a means of killing microbial organisms.
Traditional electroporation devices have been used by microbiologists in clinical settings for decades. These small systems do not scale up for commercial pasteurization, however, due to excessive energy consumption, excessive fluid heating, deleterious electrochemical reactions, and electrolysis, notably hydrogen gas production, posing a hazard at large scales. Traditional electroporation devices in laboratory settings consist of a pair of electrically conductive bare metal electrodes positioned as opposing flat plates, separated by a few millimeters. The electrodes are immersed in a fluid suspension of bacteria, voltage is applied, and electric current conducts from one electrode to the other through the suspension fluid. The resulting electric field causes membrane perforation. The salient operational feature of standard electroporation devices is the use of conducting bare-metal electrodes in intimate contact with the fluid under treatment. We have termed treatment with this type of device ‘Low Impedance Electroporation’ (LIE), referring to the low impedance of the conductive electrodes.
By contrast, a method employing a dielectric barrier between the electrodes and the fluid under treatment, thus electrically insulating the metal plates, is termed ‘High Impedance Electroporation’ (HIE). HIE is the subject of the MRT invention. The HIE device is differentiated from a LIE device by the placement of a dielectric barrier separating the conductive metal electrodes from the fluid under treatment. Since the electrodes are electrically insulated, near zero conduction current occurs, thus curing the problem of electrochemical reactions, free radical production, electrolysis, electrode degradation, and excessive waste heat production. By overcoming these challenges, the HIE system can be applied to commercially scaled pasteurization of liquid foods such as milk, fruit juice, beer, wine, soups, and water.
HIE cold pasteurization is a much simpler operation than thermal pasteurization. Compared to large, complicated boilers, chillers, and heat recovery equipment currently in use, an HIE system only needs to provide liquid flow through the processing plant, and a power supply. The flow section of the HIE system resembles an open grid, which can be plumbed directly in process flow piping. The system will be fully instrumented, including a proprietary method used to monitor pasteurization efficacy in real time (similar to thermal pasteurization tracking time and temperature).
Because HIE is solid state with few parts, e.g. reaction flow grid, power supply, and instrumentation, its capital, installation, and maintenance costs are much lower than any thermal pasteurization system. Because HIE can work at storage, transport and processing temperatures, the vast amount of energy needed to heat liquid foods to pasteurization temperatures is no longer necessary, also resulting in huge energy and cost savings. HIE operational cost can be as much as 90% lower than thermal pasteurization depending upon the type of liquid food being processed and flow conditions. In addition, many of the nutrients, and the original taste and aroma of the liquid foods will be preserved by HIE, which are now degraded by the thermal pasteurization process, providing a ‘fresher’ healthier product to consumers. Since no conduction current flows through the fluid under treatment, HIE does not degenerate flavor, aroma, color, pH, or the nutrient content of liquid foods. Proteins, fats, and oils are not cooked in the HIE process. Inlet liquid temperatures can be as low as 4° C, and depending upon process variables, HIE will only raise fluid temperature by 3° to 7° C.
In 2002 a US law was passed that mandated effective alternatives to thermal pasteurization be allowed in the processing of foodstuffs, provided they could demonstrate equal effectiveness with regard to public health requirements. In response to this law, the National Advisory Committee on Microbiological Criteria for Foods (NACMCF) has identified electroporation as a promising alternate technology that warrants continued development. In 2005, the USFDA approved Low Impedance Electroporation (Pulsed Electrified Field or PEF) for commercial juice pasteurization, issuing an operating permit to Genesis Juice in Oregon. Since the mechanism for killing bacteria is exactly the same for HIE as for all types of LIE, including PEF, we expect regulatory approval and licensing for any liquid food or water.
In conversations with FDA agents we have been assured that if HIE performs as predicted, and shows effective food processing in laboratory and field trials, then government certification will not be an obstacle.
HIE can also be used before or after thermal pasteurization to prolong the shelf-life of milk by targeting spore forming and thermoduric psychrotrophic organisms. In this way HIE can add value to the pasteurization process without requiring government certification, as the thermal pasteurization process remains in place.
A proof-of-concept prototype has been successfully constructed and tested, and used as the basis to file a patent application. The goal of this device was to demonstrate that sufficiently intense field energy, absent a conducting current, could produce lethal electroporation. Patent is pending in the US and Canada, and in 40 other countries through the Patent Cooperative Treaty.
Over the course of approximately two years, MRT developed two analytical models for high impedance electroporation: 1) a mathematical model based on field behavior and boundary conditions, and 2) an equivalent circuit model based on network theory. Both models were completed in the time and frequency domain, including both analytical and numeric formulary. The behavior of the equivalent circuit model was emulated in a virtual computer environment using an analytical software program called SPICE. MRT engaged the services of Dr. Weldon Vlasak, PhD Electric Engineering & Network Theory, George Washington University, to aid in this effort. Although diverse in their approach, the two models predict dynamic response and numeric results with good agreement.
MRT has also had the HIE concept and analytical models reviewed by the National Institute of Nanotechnology in Edmonton, Alberta. The Institute analyzed the HIE model and assembled a 60 page report documenting their conclusions that HIE technology is technically feasible, and that the model is scientifically sound.
Over the last year MRT has entered into a contractual relationship with ACAMP (Alberta Center for Advanced Products) for the HIE Prototype development. To date Phase one has been completed successfully. We look forward to the completion of the bench top prototype by the spring of 2013.
If the reduced energy consumption of a commercially scaled HIE system is fully realized, its introduction to the liquid food industry would be revolutionary in terms of reducing operating costs and GHG emissions associated with thermal pasteurization. HIE will not only revolutionize the dairy and beverage industries, but also has potential applications in water and wastewater treatment, environmental air quality in HVAC systems, and irrigation and reverse-osmosis systems (to prevent biological fouling of piping or membranes). Aside from economic and environmental benefits, HIE technology may also benefit the health and welfare of populations in underdeveloped countries by treating drinking water.