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Pulsed electric fields and spore inactivation (PEF-P)

Identification

Key words pulsed electric fields, microbiological inactivation, PEF, pre-treatment, sterilisation, preservation, spore inactivation
Latest version 2012/07/17
Completed by DIL

How does it work?

Primary objective Inactivation of spores and pathogen microorganisms
Working principle The application of pulsed electric fields offers the possibility to inactivate various vegetative microorganisms (e.g. E.coli , S.cerevisiae, moulds)( inactivation microorganisms) (and also to disintegrate cellular material (Cell disintegration by Pulsed electric fields). For a sterilisation not only an inactivation of vegetative cells is required, also an inactivation of spores.

Spores are very resistant against extreme conditions of pH and temperature, radiation, and chemical disinfectants. Not only the structural changes are responsible for the resistance, also dehydration of the spore core, mineralisation and thermal adaption [1, 2]. The operating principle of PEF is the action on the cell membrane. The application of pulsed electric fields induces pore formation in the cell membrane as a result of polarisation of the membrane due to an external electric field [3, 4]. Because of the additional protection of the spores through their membranes (cortex, coat, exosporium), an inactivation of spore only with PEF cannot be easily realized. For an inactivation of spores high electric field strengths (> 30 kV/cm) and long treatment times are required [5]. But it has to be considered that a complete inactivation of spores is not possible applying pulsed electric fields [6]. A complete inactivation of spores can be reached by combining the PEF process with another process (e.g. high pressure processing, thermal treatment, chemicals). The first process induces the germination of the spores and the second process inactivates the germinated spores. During the germination the cortex of the spore disappears and the spore coat layer dissolves. The second process inactivates the germinated spores [7, 8]. Preliminary tests [9] showed an inactivation of spores (B.subtilis spores) in combination with heat (75 °C). But in comparison to thermal methods the temperature for PEF treatment is much lower. Consequently, a combined process of the application of pulsed electric fields and another process can achieve an inactivation of spores.

Images
Additional effects Ohmic heating

Enzyme inactivation Textural changes More flavor retention in comparison to thermal methods

Important process parameters electric field strength, specific energy, treatment time

Other process parameters are the pulse shape (square wave pulses are most effective) and configuration of the treatment chamber (co-linear configuration is the most common design of the treatment chamber)

Important product parameters
  • pH
  • protein
  • lipid
  • salt
  • sugar content
  • water activity

What can it be used for?

Products Liquid and semi-liquid, pumpable products, emulsions, suspensions, soups and sauces
Operations Stabilizing
Solutions for short comings Sterilization of heat sensitive products; through combining with other processes (e.g. high pressure processing or temperature) other positive effects can be induced (e.g. less thermal energy is required in comparison to thermal methods leading to less heat load of the product)

What can it NOT be used for?

Products Not for solid material, conductivity limitations below 0,1 or above 30 mS/cm, maximum particle size of 20 mm, carbonated products require back-pressure
Operations A total inactivation of spores cannot be achieved by a PEF process only, but with combining it with a high temperature an inactivation is possible
Other limitations Considerable investment cost and maintenance costs
Risks or hazards Electrochemical reactions and electrode erosion

An inactivation of spores by only using pulsed electric fields only is not possible; treatment homogeneity and consistency need to be guaranteed by process control

Implementation

Maturity Continuous system is commercially available, continuous system is available up to capacities of 5.000 l/h at a voltage of up to 30 kV and an average power of up to 240 kW.

A new control system for a continuous online measurement of temperature in the food during PEF treatment has been developed within the frame of i3Food eu-project, which can modulate the process for each batch and assure the process impact [10].

Modularity /Implementation Continuous system can be easily implemented into existing lines.

Feasible for commercial use for pasteurization and extended shelf life

Consumer aspects Consumers perceive the technique as environmental friendly and are positive to the naturalness of the product
Legal aspects EU: According to available scientific papers: no novel food approval required

No declaration or labeling required US: FDA letter of no objection (1996)

Environmental aspects Energy efficient, waste free technique

Further Information

Institutes DIL, TU Berlin, Karlsruhe Institute of Technology, University of Zaragoza, University College Dublin, University of Technology of Compiègne, Lund University, University of Salerno, Washington State University, McGill Uni DFSAC, Jilin University, Wageningen UR - FBR
Companies DIL Technologie GmbH, Diversified Technologies, ScandiNova, KEA-Tec
References 1. Beaman, T.C. and P. Gerhardt, Heat Resistance of Bacterial Spores Correlated with Protoplast Dehydration, Mineralization, and Thermal Adaption. Appl. Environ. Microbiol., 1986. 52(6): p. 1242-1246.

2. Errington, J., Bacillus subtilis sporulation: regulation of gene expression and control of morphogenesis. Microbiol. Mol. Biol. Rev., 1993. 57(1): p. 1-33.

3. Grahl, T. and H. Maerkl, Killing of microorganisms by pulsed electric fields. Applied Microbiology and Biotechnology, 1996. 45(1/2).

4. Barbosa-Cánovas, G.V., et al., Fundamentals of High-Intensity Pulsed Electric Fields (PEF), in Preservation of Foods with Pulsed Electric Fields. 1999, Academic Press: San Diego. p. 1-19.

5. Hamilton, W.A. and A.J.H. Sale, Effects of high electric fields on microorganisms: 2. Mechanism of action of the lethal effect. Biochimica et Biophysica Acta (BBA) - General Subjects, 1967. 148(3): p. 789-800.

6. Barbosa-Cánovas, G.V., et al., PEF Inactivation of Vegetative Cells, Spores, and Enzymes in Foods, in Preservation of Foods with Pulsed Electric Fields. 1999, Academic Press: San Diego. p. 108-155.

7. Spilimbergo, S., et al., Inactivation of bacteria and Spores by Pulse Electric Field and High Pressure CO2 at Low Temperature. Biotechnology and Bioengineering, 2002. 82(1): p. 118-125.

8. Pagán, R., et al., Inactivation of Bacillus subtilis spores using high intensity pulsed electric fields in combination with other food conservation technologies. Food Science and Technology International, 1998. 4: p. 33-44.

9. Toepfl, S., C. Siemer, and M. Kiessling, Inaktivierung bakterieller Endosporen durch kombinierte Anwendung gepulster elektrischer Felder und thermischer Energie, in Jahrestagung Processnet 2011. 2011: Vlaardingen, NL.

10. Toepfl, S. (2017) PEF treatment of fruit and vegetable products – process design and validation. Institute for Thermal Process Specialists 37th Annual Meeting, San Antiono, March 7-10.

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  • protein
  • lipid
  • salt
  • sugar content
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  • lipid
  • salt
  • sugar content
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Created by Hamoen on 17 January 2012, at 11:19