This document discusses various physical methods for food preservation, including ionizing radiation, nonionizing radiation, light, high pressure processing, pulsed electric fields, and modified atmosphere packaging. Ionizing radiation works by affecting nucleic acids and cell membranes, while nonionizing microwave radiation causes protein and nucleic acid denaturation. High pressure processing and pulsed electric fields disrupt cell membranes. Modified atmosphere packaging and vacuum packaging inhibit aerobic microorganisms by reducing oxygen levels.

1. PHYSICAL METHODS OF FOOD
PRESERVATION:
Radiation, High Pressure, Pulsed Electrical
Field, Light and Modified Atmosphere
Basura J. Jayasundara
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2. CONTENTS
 Introduction
 Use of ionizing radiation
 Use of nonionizing radiation
 Light energy in food preservation
 High pressure processing
 Pulsed electric fields
 Modified atmosphere
 Summary
 References
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3. INTRODUCTION
 Food begins to deteriorate from the time it is
harvested or slaughtered.
 Each foodstuff has a specific period after which it
begins to spoil.
 Preservation is needed to slow down the spoilage
process, extend the shelf life and ensure the safety
and quality of food.
 Food preservation methods can be divided into
physical, chemical and biological. 3

4. INTRODUCTION
 Physical methods of food preservation are those
that utilize physical treatments to inhibit, destroy
or remove undesirable microorganisms .
 Heat treatment
 Radiation
 Light
 High Pressure Processing (HPP)
 Pulsed Electric Fields (PEFs)
 Modified Atmosphere
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5. USE OF IONIZING RADIATION
 “Food irradiation (the application of ionizing radiation
to food) is a technology that improves the safety and
extends the shelf life of foods by reducing or
eliminating microorganisms and insects”(FDA, 2014)
 There are three sources of radiation approved for
use on foods.
 Gamma rays
 X rays
 Electron beam
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6. USE OF IONIZING RADIATION
 Applications of food irradiation
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Application Commodity
Inhibition of sprouting Potatoes, onions, garlic
Decontamination of food Spices
Insect disinfestation Grains
Delay in fruit maturation Mangoes, papayas, strawberries
Inactivation of MO
(Salmonella)
Poultry, eggs
Logo for irradiated foods

7. USE OF IONIZING RADIATION
Mode of action:
 Affects on bacteria, yeasts and moulds.
 Main sites of damages: nucleic acid and the lipids
of the cell membrane
 Membrane lipid degradation
 Change the permeability of the cell membrane
 Leach out of cell components and
 Inhibition of the DNA replication
 Indirect effect: inhibitory effects of free radicals
produced by the radiolysis of water.
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8. USE OF NONIONIZING RADIATION
Microwave Radiation
 Two frequencies used in food processing are 2450
MHz and 915 MHz.
 Domestic microwave ovens use 2450 MHz
which is less penetrating than the lower frequency.
Mode of action :
 Microwaves act indirectly on micro-organisms
through the generation of heat.
 Destruction of MO is accomplished through the
denaturation of protein and nucleic acids.
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9. LIGHT ENERGY IN FOOD PRESERVATION
UV Radiation
 Use to inactivate MOs on the surface of foods and
thin films of liquid.
 Use extensively in disinfection of equipment,
glassware, and air.
 The optimum wavelengths: 260 nm.
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Use of UV light UV light conveyer

10. LIGHT ENERGY IN FOOD PRESERVATION
Mode of action:
 UV light is absorbed by proteins and nucleic acid, in
which photochemical changes are produced.
 It disrupt DNA molecules, produce lethal mutations
and thereby prevent cell replication.
 Degradation of the bacterial cell walls also cause
the germicidal effect
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11. HIGH PRESSURE PROCESSING
 Involving pressurization of a packed food in a water
filled closed chamber for a short duration to
inactivate microorganisms.
 Effective for both liquid and solid foods (liquid food
can be pressurized directly.
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High Pressure Processing

12. HIGH PRESSURE PROCESSING
 Nonthermal method and covalent bonds are not
broken, flavor is unaffected.
 The process has 3 parameters;
 Pressure
 Temperature of pressurization
 Time of pressurization
 Gram (+) bacteria are more resistant than Gram(-).
 Vegetative cells are inactivated by pressures
between 400 and 600 MPa.
 Spores may resist pressures higher than 1000 MPa
at ambient temperatures.
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13. HIGH PRESSURE PROCESSING
Mode of action:
 Many vital structure and components adversely
affected, causing viability loss and sub lethal injury.
 Damages to cell membrane
 Alter the permeability of membrane
 Damages in cell wall
 Inactivation of enzymes
 Cell lysis
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14. PULSED ELECTRIC FIELDS
 Consists of the application of short pulses of high
electric fields to foods placed between two
electrodes.
 No significant detrimental effect on heat-labile
components present in foods such as vitamins.
 Major disadvantage: high initial investment.
 Antimicrobial effects of PEF are functions of:
 Electric field strength
 Treatment time
 Treatment temperature
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15. PULSED ELECTRIC FIELDS
General features of PEF:
 G- bacterial cells more sensitive than G+ or yeasts.
 By increasing electric field intensity and number of
pulses greater microbial destruction can be
achieved.
 Destruction of bacterial and fungal spores requires
a higher voltage and longer period of time.
 Temperature can be increased to 60 0C or higher to
obtain a greater microbial destruction.
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16. PULSED ELECTRIC FIELDS
Mode of action:
 Cell death by PEF is due to disruption of cell
membrane function.
 When microbial cells in a suspension are exposed
to PEP, a potential differences occurs between
outside and inside cell membrane.
 Because of this difference , pore formation in the
membrane, cause destruction of membrane
function and cell death.
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17. MODIFIED ATMOSPHERE
 Three different procedures are used.
1) Modified Atmosphere Packaging (MAP)
 Bulk or retail pack is flushed with a gas mixture
usually containing combination of CO2, O2 and N2.
 Does not require a control of gaseous environment
during the entire storage period.
 The composition of the gas atmosphere changes
during storage as a result of product and microbial
respiration.
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18. MODIFIED ATMOSPHERE
2) Controlled Atmosphere Packaging (CAP)
 Atmosphere in a storage facility is altered, levels of
the gases are continually monitored
 The product environment is maintained constant
throughout storage.
 Used for long term storage of fruits and vegetables
to maintain their freshness.
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19. MODIFIED ATMOSPHERE
3) Vacuum Packaging
 Involves removal of air from the package and then
sealing the package hermetically.
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Vacuum packed food products

20. MODIFIED ATMOSPHERE
Mode of action
 The growth of aerobes (mold, yeast, aerobic
bacteria) is prevented in products .
 However, anaerobic and facultative anaerobic
bacteria can grow unless other techniques are
used to control their growth.
 The inhibitory effect of CO2 on microbial growth
occurs at the 10% level and increase with the
increase in concentration.
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21. SUMMARY
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Preservation method Mode of action
Ionizing radiation Affect on nucleic acid & membrane lipids
Microwave radiation Denaturation of protein and nucleic acids
UV Light Disrupt DNA molecules, produce lethal
mutations
High Pressure Damages to cell membrane
Pulsed Electric Fields Disruption of cell membrane function
Modified Atmosphere
(Vacuum packaging)
Low oxygen level inhibit aerobes
Modified Atmosphere
(MAP or CAP)
Inhibition of MO by CO2

22. 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.
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23. THANK YOU
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