Nonthermal inactivation of microorganisms using combination of shear and electric fields

A method to inactivate microorganisms in a fluid without degrading certain properties, by using both mechanical shearing and electric fields.

The Need

The US FDA requires all manufactures to subject juice products to a 5-log reduction in the number of the most resistant pathogens. Currently, the most widely used method to inactivate pathogenic bacteria from foods and biological fluids involves the application of heat. However, the food industry is searching for alternative methods to inactivate pathogenic bacteria, as antioxidants and bioactive compounds commonly found in fruit and vegetable juices become degraded and lose their potency with heat treatment. In addition, consumer demand is rising for minimally processed foods, with consumers demanding reductions in synthetic food preservatives.

While there are several bacterial inactivation methods that do not require heat, including high pressure and pulsed electric fields, these methods are relatively expensive and have very limited throughput. Therefore, novel methods of nonthermal bacteria inactivation are necessary to improve the availability of bioactive compounds, as well as, the overall quality of food.

The Technology

Researchers at The Ohio State University, led by Dr. Sudhir Sastry, have developed a new method for nonthermal bacterial inactivation. This methodology utilizes a combination of both mechanical shearing (SS) and moderate electric fields (MEF) with simultaneous cooling to maintain a constant temperature. Shear stress results in strong localized forces to the cell surface, potentially imparting physical damage to bacterial cells, and in conjunction with a moderate electric field, a greater rate of microbial inactivation than conventional pasteurization may be expected. This process is accomplished with the incorporation of a shearing assembly comprised of a rotor and stator, along with electrodes and a cooling jacket. The device becomes more efficient with a higher voltage per centimeter, a higher rotation speed, and a lower temperature.

In experiments with apple juice and a combination approach of the aforementioned methods along with nisin, inactivation of bacterial was increased relative to conventional methods. The nisin, SS, and MEF reduced microorganisms to a level low enough to satisfy FDA requirements. Furthermore, quality of the juice was preserved, both in terms of taste and nutritional content. Overall, this method has the potential to shorten processing time and improve the inactivation of microorganisms in juice products ensuing food safety and retaining food quality.

Commercial Applications

  • Beverage production industry
  • Food production


  • Inactivates bacteria in fluids, without degrading antioxidants and bioactive compounds
  • The device is easily scalable
  • Less expensive than other methods
  • Greater throughput than other methods

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