Physical Methods of Food Preservation.pdf

Methods of food preservation

1. Physical Methods of
Food Preservation
Presented by JASNA S,
I MSc MICROBIOLOGY

2. Food Preservation
Food preservation is the
process of treating and
handling food to slow down
spoilage, prevent
contamination and extend its
shelf life while mentioning its
nutritional value, lecture and
flavour.
This is achieved though
various physical chemical
and biological methods.
Physical
Chemical
Biological

4. Physical methods of food preservation
Physical method of food preservation are those that utilize physical treatments to inhibit, destroy or remove
undesirable microorganism
Heat treatment
Radiation
Light
High Pressure Processing(HPP)
Pulsed Electric Field (PEF)
Modified Atmosphere

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”
The are three sources of radiation approved for the use on foods.
1, Gamma rays
2, X rays
3, Electron beam

6. Use of ionizing radiation
Applications of food radiation
Application Commodity
Inhibition of sprouting
Potatoes, onions, garlic
Decontamination of food Spices
Insect disinfection Grains
Delay in fruit maturation Mangoes, papayas, strawberries
Inactivation of MO (Salmonella) Poultry, eggs

7. Use of ionizing radiation
Mode of action:
Affects on bacteria, yeasts and moulds.
Main sites of damages: nuclei acid and the lipids of the cell
membrane.
Membrane lipid degradation
Change the permeability of the cell membrane
Leach out of sell components and inhibition of the DNA
replication
Indirect effect: inhibitory effects of free radicals produced
by the radiolysis of water

8. Use of non-ionizing 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

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 wavelength: 260 nm.

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

11. High pressure processing
Nonthermal method and covalent bonds are not broken, flavour is unaffected.
The process has three parameters;
Pressure
Temperature of pressurization
Time 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 temperature

12. 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).

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

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 food such as
vitamins
Major disadvantage: high initial investment
Antimicrobial effects of PEF are functions of:
Electric field strength
Treatment time
Treatment temperature

15. Pulsed electric fields
General features of PEF:
G- bacterial cells are 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 pores requires a higher voltage and longer
period of time
Temperature can be increased to 60’C or higher to obtain a greater microbial
destruction

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 of cell death

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 for gaseous environment during the
entire storage period
The composition of the gas atmosphere changes during storage
as a result of product and microbial respiration

18. Modified atmosphere
2) Controlled Atmospheric Packaging (CAP)
Atmosphere in a storage facility is altered, levels of the gas
are continually monitored
The product environment is maintained constant throughout
storage
Used for long term storage of fruits and vegetables to
maintain their freshness

19. Modified atmosphere
3) Vacuum packing
involves removal of air
from the package and
then sealing the
package hermetically

20. Modified atmosphere
Mode of action
The growth of aerobes (mold, yeast, aerobic bacteria) is prevented in
products
However, anaerobic and facultative anaerobic 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

21. Methods of food preservation - Pradeep Shrivastava
Food processing and preservation - G subbulakshmi
Online source - Articles, Chat GPT, Wikipedia
Image source - Google , Meta AI
REFERENCE

22. THANKYOU