Electric field applications to food at moderate voltages can inactivate bacteria, thereby ensuring food safety. Recent findings demonstrate that by combining electric fields and agitation, harmful food bacteria can be inactivated at a temperature of only 80 F after 10 minutes, while retaining the food’s nutrients. Electric fields also facilitate some food processing operations, such as tomato peeling, by making vegetable and fruit cells permeable. In addition, electric fields inactivate some food enzymes that can cause undesirable effects such as browning. This fact sheet describes the application of moderate electric fields for food preservation.
What is Moderate Electric Field (MEF)?
Moderate electric field uses less than 1,000 volts per centimeter to inactivate bacteria. This process increases the permeability of cell membranes while keeping the product temperature lower than conventional pasteurization.
How Does MEF Differ from the Conventional Heating Process?
The conventional heating process uses at least 170 F (like a slow cooker) for liquid foods. MEF heats food more uniformly by using lower temperatures controlled through the use of external cooling jackets.
How Does MEF Differ from Other Electric Field Applications such as Pulsed Electrical Field (PEF)?
Electric fields can be applied at varying levels. While MEF applies less than 1,000 volts per centimeter, pulsed electric field (PEF) applies strong electric fields that are greater than 1,000 volts per centimeter. PEF results in extreme heating, but the fields are “pulsed” (applied briefly), to allow for cooling. PEFs are effective for destroying and opening the cell structure within vegetables or fruits. However, they are mostly used for fluid foods and are not applicable for use on food with particulates, such as yogurt with pieces of fruit and soup with vegetables or meat.
How Does Agitation During MEF Application Improve Effectiveness?
When liquid foods (e.g., fruit or vegetable juices) are agitated by using a mixer during MEF treatment (shear-MEF), the product may be pasteurized within minutes at temperatures between 75 F and 100 F. Agitation disrupts and mixes the cells while MEF is applied. The higher the field strength (up to peak voltage of 170 V) and the greater the agitation (up to 9,500 revolutions per minute), the faster the bacteria are inactivated (Mok et al. 2020; Mok et al. 2019).
How Does Shear-MEF Work?
MEF passes an electrical current through a food and builds electrical charges across cell membranes. As a result, bacteria develop holes (pores) in their cell membranes, cannot maintain integrity, and die (Figure 1). The electric current may be direct or alternating at main frequency; however, it is possible to use other frequencies in various waveforms.
The basic components of shear-MEF systems are a power supply, a cell (treatment chamber with one static and one rotating electrode, Figure 2), and a data logger along with temperature and electrical sensors. The system may also be equipped with a variable transformer and a function generator to adjust the voltage and other parameters (i.e., frequency, waveform, or rotational speed).
How Does Shear-MEF Technology Benefit Customers?
Today’s consumers are conscious about the nutritional value and freshness of food. Shear-MEF technology provides many customer benefits:
- the nutritional losses of liquid foods are minimized
- “fresh-like” sensory attributes (appearance, taste, and flavor) are maintained by the low-heat process
- microbiologically safe food with increased shelf life under refrigerated conditions can be made widely available
Color loss in juices commonly occurs in all thermal and nonthermal process technologies. During shear-MEF technology processing, colors of juices such as kale-apple juice blends are maintained (Mok et al., 2021). In addition, MEF can accelerate the enzymatic reaction of biomass (i.e., cellulose). This reaction improves the efficiency and stability of enzymes leading to the development of green technologies for diverse applications (Durham and Sastry 2020).
What are the Advantages of Shear-MEF Technology?
During shear-MEF processing, foods are mixed as electric current is passed through them. This method of processing is completed rapidly and uniformly. Shear-MEF ensures nutrient retention and maintains fresh-like sensory attributes due to mild temperatures even after extended treatment time. The technology also has other advantages:
- relatively low capital investment—no boiler and heat transfer surface is required as with conventional pasteurizers
- low operational cost because no steam or hot water generation is required
- the system can be instantly shut down if needed
Is Shear-MEF Equipment Safe to Operate?
With proper training, food plant personnel can learn to safely operate the equipment. It is of the utmost importance for processors to ensure that the electrical parts are properly insulated, and other components are manufactured, installed, tested, and operated according to regulations and codes. This technology is in the early stage of development, and approval has not yet been sought from regulatory agencies.
Is Shear-MEF Technology Environmentally Friendly?
The technology uses commercially available electricity. Greenhouse gases are not produced during processing. One emerging application of MEF processing is fruit peeling, which may greatly reduce the use of peeling processes that use lye or steam. Both lye and steam peeling processes have negative impacts on the environment and high waste disposal costs for processors.
What are the Current Activities Related to MEF Technology?
At The Ohio State University, work continues on inactivating microorganisms with shear-MEF technology to produce pasteurized juices. We are exploring its use for environmental bacterial control, peeling of tomatoes (Wongsa-Ngasri and Sastry 2016; Wongsa-Ngasri and Sastry 2015), and targeted enzyme inactivation for food quality improvement (Samaranayake and Sastry 2018; Samaranayake and Sastry 2016a; Samaranayake and Sastry 2016b; Samaranayake et al. 2022). Work is also underway on scalability of the technology from a small-scale pilot to industrial scale.
Support from the National Institute for Food and Agriculture (NIFA) via AFRI Award No. 2019-68015-29229 is gratefully acknowledged.
Durham, Emily K., and Sudhir K. Sastry. 2020. “Moderate Electric Field Treatment Enhances Enzymatic Hydrolysis of Cellulose at Below-Optimal Temperatures.” Enzyme and Microbial Technology, Volume 142: 109678.
Mok, Jin Hong, Taras Pyatkovsky, Ahmed Yousef, and Sudhir K. Sastry. 2020. “Synergistic Effects of Shear Stress, Moderate Electric Field, and Nisin for the Inactivation of Escherichia coli K12 and Listeria innocua in Clear Apple Juice.” Food Control, Volume 113: 107209.
Mok, Jin Hong, T. Pyatkovskyy, A. Yousef, and S.K. Sastry. 2019. “Combined Effect of Shear Stress and Moderate Electric Field on the Inactivation of Escherichia coli K12 in Apple Juice.” Journal of Food Engineering, Volume 262: 121–130.
Mok, Jin Hong, Taras Pyatkovskyy, Ahmed Yousef, and Sudhir K. Sastry. 2021. “Effects of Combination Shear Stress, Moderate Electric Field (MEF), and Nisin on Kinetics and Mechanisms of Inactivation of Escherichia coli K12 and Listeria innocua in Fresh Apple-Kale Blend Juice.” Journal of Food Engineering, Volume 292: 110262.
Samaranayake, Chaminda P., Jin Hong Mok, Brian F. Heskitt, and Sudhir K. Sastry. 2022. “Nonthermal Inactivation of Polyphenol Oxidase in Apple Juice Influenced by Moderate Electric Fields: Effects of Periodic On-Off and Constant Exposure Electrical Treatments.” Innovative Food Science & Emerging Technologies, Volume 77: 102955.
Samaranayake, Chaminda P., and Sudhir K. Sastry. 2018. “In-Situ Activity of α-Amylase in the Presence of Controlled-Frequency Moderate Electric Fields.” LWT, Volume 90: 448–454.
Samaranayake, Chaminda P., and Sudhir K. Sastry. 2016a. “Effect of Moderate Electric Fields on Inactivation Kinetics of Pectin Methylesterase in Tomatoes: The Roles of Electric Field Strength and Temperatures.” Journal of Food Engineering, Volume 186: 17–26.
Samaranayake, Chaminda P., and Sudhir K. Sastry. 2016b. “Effects of Controlled-Frequency Moderate Electric Fields on Pectin Methylesterase and Polygalacturonase Activities in Tomato Homogenate.” Food Chemistry, Volume 199: 265–272.
Wongsa-Ngasri, Pisit, and Sudhir K. Sastry. 2015. “Effect of Ohmic Heating on Tomato Peeling.” LWT-Food Science and Technology, Volume 61, Issue 2: 269–274.
Wongsa-Ngasri, Pisit, and Sudhir K. Sastry. 2016. “Tomato Peeling by Ohmic Heating: Effects of Lye-Salt Combinations and Post-Treatments on Weight Loss, Peeling Quality and Firmness.” Innovative Food Science & Emerging Technologies, Volume 34, 148–153.