High pressure processing (HPP) is a non-thermal method of food preservation that involves pressurizing food between 100-1000 MPa for a short period of time to inactivate microorganisms. It is effective for both liquid and solid foods. HPP works by compressing food volumes and increasing temperatures, which primarily damages non-covalent bonds in microbes. Gram-negative bacteria are generally more susceptible than Gram-positive bacteria and spores. The degree of inactivation depends on pressure level, temperature, and duration of pressurization. HPP damages cell membranes and structures, altering permeability and causing cell death.

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Basura J Jayasundara
PHYSICAL METHODS OF FOOD PRESERVATION
Use of High Pressure Processing in Food Preservation
High Pressure Processing (HPP) is a nonthermal method and it involves pressurization (100 to
1000 MPa or more) of a packed food in a water filled closed chamber for a short duration to
inactivate microorganisms. The use of high pressure processing or Pascalization to reduce or
destroy microorganisms in foods dates back to 1884. This method is effective for both liquid
and solid foods. Liquid food can be pressurized directly and solid food can be pressurized
placing food in suitable containers and sealed.
The pressurization causes the volume of the pressurized material to be compressed, depending
on the applied pressure it may be 10 to 15 percentages and rise of the temperature also happen.
These changes are not permanent and during the depressurization return back to the original state
of the material. Following are the important points of HPP method in food preservation.
 High pressure acts primarily on non-covalent linkages, such as ionic bonds, hydrogen bonds
and hydrophobic interactions.
 Gram negative bacteria are relatively more susceptible than the Gram positive bacteria.
Vegetative cells are inactivated by pressures between 400 and 600 MPa.
 Bacterial spores are fairly resistant to pressure below 700 MPa at ambient temperature.
Spores may resist pressures higher than 1000 MPa at ambient temperatures.
 Spores inactivation is proportional to the level of pressurization, Temperature of
pressurization and time of Pressurization.
 At low pressure range (< 300 MPa) some spores are germinate and outgrow, once germinated
spores are susceptible to the pressurization.
Figure: Diagram of High Pressure Processing method

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Basura J Jayasundara
Mode of action
Many vital structure and components adversely affected, causing viability loss and sub lethal
injury. Damage to the cell membrane is the major cause of cell death. Adverse effects on protein
structure and activity also contribute to the antimicrobial effect of high pressures. Membrane
lipid bilayers are compress under pressure and this alters permeability of membrane. Damages to
the cell wall, damages to DNA & RNA, inactivation of enzymes also may be happen during the
process.
REFERENCES
 Adams, M.R., and Moss, M, O., 2008. Food Microbiology, third edition. RSC publishing,
UK.
 Ray, B., Fundamental Food Microbiology, third edition, 2004. CRC press.
 Jay, J.M., Loessner, M.J., and Golden, D.A., Modern Food Microbiology, seventh edition,
2005. Springer.
 Rahman, M.S., Handbook of Food Preservation, second edition, 2007. CRC press.
 www.fda.gov/Food/ResourcesForYou/Consumers/ucm261680.htm