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PHYSICAL METHODS OF FOOD PRESERVATION:
Radiation, High Pressure, Pulsed Electrical Field, Light and Modified Atmosphere
Basura J. Jayasundara
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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 2
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.
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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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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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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
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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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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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
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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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.
11 High Pressure Processing
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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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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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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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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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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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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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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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
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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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
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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THANK YOU
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