How does it preserve fruits & vegetables?
Consumer interests in healthier and fresher foods have driven much of the interest in ‘advanced’ preservation methods, such as pulsed electric field (PEF) processing, which are safe but at the same time capable of imparting fresh-like characteristics to processed food. Pulsed electric field (PEF) treatments of less than 100 kV/cm are applied to foods placed between 2 electrodes at ambient or slightly above ambient temperatures for less than 1 sec. As described in a Food and Drug Administration report , microbial inactivation is proposed to occur via one of several processes, the most studied of which are membrane electroporation and electrical breakdown. Detrimental changes in physical, sensory or nutritional properties are minimized due to the short heating treatments.
PEF has been utilized for juice pasteurization to a limited extent in the U.S., but in Europe there are several PEF treated juices in the commercial marketplace. Pulsed electrical fields enhance extraction of juices, resulting in higher yields. Potato processors in the U.S., Canada, Europe, India, China and Australia are currently using Elea GmbH PEF treatments for cell disintegration, in place of the preheater operation. In this application, pulsed electrical fields create pores in cell membranes, which enable the loss of primarily liquid contents, and more efficient heating with less use of water.
Pulsed electric fields research
The use of PEF for preservation of higher-quality foods was studied extensively in the 1980s and 1990s, in particular at Ohio State University (OSU) and the United States Department of Agriculture’s Agricultural Research Service. Researchers at OSU developed a fact sheet on pulsed electric field processing, which provides a useful overview: Raghupathy Ramaswamy, Tony Jin, V. M. Balasubramaniam, and Howard Zhang. 2005. Pulsed electric field processing. Fact sheet for food processors. FSE 2-05. Ohio State University Extension Fact Sheet (peer-reviewed), Columbus, OH.
Microbial inactivation, and cell rupture in plant and animal tissues, are affected by a number of PEF process factors which include: electric field intensity, treatment time and temperature, pulse width and wave shape. While there are a number of commercial systems in operation, the effects of PEF on pathogens of concern and the kinetics of their inactivation still need further study. In our laboratory at the University of California, Davis, two PEF related projects determined critical field strengths required to rupture membranes in a model onion system (see publications by Ersus or Asavasanti at http://www.fruitandvegetable.ucdavis.edu/publications/). For 100-us pulses, breakdown of the primary membrane occurred above Ec = 67 V/cm for 10 pulses. The minimum field strength required to cause a significant property change decreased with an increasing number of pulses. This suggests that PEF treatments may be more effective if a higher field strength is applied for fewer pulses.
Domestic institutions currently carrying out HPP research
- National Science Foundation – Center for Advanced Processing & Packaging Consortium between North Carolina State University, the Univ. of California-Davis and the Ohio State University
- US Dept. Of Agriculture – Food Safety and Intervention Technologies Research, Wyndmoor, PA
- Also, numerous individual researchers at domestic and international universities