Sterilization can be defined as any process that can effectively kill or eliminate transmissible agents (such as fungi, bacteria, viruses and prions) from a surface, equipment, foods, medication or biological culture medium.

1. COLD PLASMA
STERILIZATION
A NOVEL METHOD OF
FOOD PRESERVATION

2. FOOD PRESERVATION
– Food preservation is the process of treating and handling
food to stop or slow down food spoilage, loss of quality,
edibility, or nutritional value and thus allowing the food to
last for long term storage.
– Preservation usually involves preventing the growth of
bacteria, fungi and other microbes.
– It also involves inactivating chemical reactions that can
facilitate food spoilage.

3. STERILIZATION
– Sterilization can be defined as any process that can
effectively kill or eliminate transmissible agents (such
as fungi, bacteria, viruses and prions) from a surface,
equipment, foods, medication or biological culture
medium.
– There are various methods of sterilization:
1. Thermal sterilization
2. Chemical sterilization
3. Radiation sterilization
4. Plasma sterilization

4. STERILIZING AGENETS
•The media is subjected to high
temperatures causing the
microbial destruction.
•Cannot be applied to
thermophilic microbes, heat
sensitive products.
THERMAL
•Chemicals like formaldehyde,
ethylene oxide posses biocidal
activity.
•These can be potentially
mutagenic and carcinogenic so
addition to food is not advised.
CHEMICAL
•The main mechanism of this
sterilization is by ionizing the
nucleic acids.
•Undesirable changes in
irradiation products due to
radiolysis of water.
RADIATION

5. PLASMA STERILIZATION
– A plasma is a quasi-neutral collection of electrons,
positive ions, and neutrals capable of collective
behaviour.
– Positive ions = free radicals
– Plasma sterilization operates synergistically via three
mechanisms:
• Free radicals interactions
• UV/VUV radioactive effects
• Vitalization
– Dead microorganisms = sterilization

6. PLASMA STERILIZATION
PARAMETERS
– Factors affective plasma
– Choice of Gas
• Determine effectiveness of sterilization
• Type of active species present
• Types of free radicals formed are a direct result of the ionized constituent gas molecules.
• Dictates the intensity and wavelengths emitted radiation.
• Common gas: O2, CO2, O2/H2, O2/Ar, O2/CF4 and H2O2.
– Gas Flow Rate
• Increasing the gas flow rate, increases the flux of active species on the medium, which increases the effectiveness
of the treatment.

7. – Gas Pressure
• Influence the volatilization rate of the plasma.
• Increasing the pressure can introduce competing effects in the sterilization processes.
– Power
• Increase in electron density, which allows for a larger volume of active species to interact with the medium.
– Quantity of Material to be Sterilized
• Higher the quantity, reduced efficiency.
• Compensated by gas flow rate and pressure.
– Nature of Microorganism, Density and Surface Layer Formation
• Dependence of active species.
• Low permeability of plasma.

8. – Packaging
• The presence of packaging inhibits the efficiency of sterilization.
– Geometrical Factors
• Reactor design strongly influence the concentration of active species.
• Direct and after glow.

9. PLASMA SOURCES
– Corona Discharge
• In electricity, a corona discharge is an electrical discharge
brought on by the ionization of a fluid surrounding a
conductor that is electrically energized. The discharge will
occur when the strength of the electric field around the
conductor is high enough to form a conductive region, but
not high enough to cause electrical breakdown or arcing to
nearby objects. It is often seen as a bluish glow in the air
adjacent to pointed metal conductors carrying high voltages.
– Dielectric Barrier Discharge
• Dielectric barrier discharge (DBD) is the electrical discharge
barrier between two electrodes separated by an insulating
dielectric barrier

10. – Gliding Arc Plasma Generation
• In general, the gliding arc plasma generator consists of two divergent
electrodes, where the arc starts at the shortest distance between the
electrodes, then moves with the gas flow and the length of the arc column
increases together with the voltage.
– Microwave Induced Plasma
• A microwave-induced plasma consists of a quartz tube surrounded by a
microwave waveguide or cavity. Microwaves produced from a magnetron (a
microwave generator) fill the waveguide or cavity and cause the electrons in the
plasma support gas to oscillate. The oscillating electrons collide with other
atoms in the flowing gas to create and maintain a high-temperature plasma. As
in inductively coupled plasmas, a spark is needed to create some initial
electrons to create the plasma. Atomic emission is measured from excited
analyte atoms as they exit the microwave waveguide or cavity.

11. WORKING PRINCIPLE
– Cold plasma is generated at atmospheric pressure by passing
a process gas through an electric field.
– Electron arising from ionization processes, accelerated in this
field, trigger impact ionisation processes.
– Free electrons colliding with gas atoms transfer their energy,
thus generating highly reactive species that can interact with
the food surface.
– The electron energy is sufficient to dissociate covalent bonds
in organic molecules.
– Single bonds: 1.5eV to 6.2eV, Double bonds: 4.4eV to 7.4eV,
Triple bonds: 8.5eV to 11.2eV.

12. CLASSIFICATION OF PLASMA
Temperature
•Thermal plasma/Hot plasma
•Non – thermal plasma/Cold plasma
Mode: Microwave
•Gliding arc
•Corona discharge
•Dielectric barrier discharge
Pressure
•Low pressure
•Atmospheric pressure
•High pressure

13. HOT PLASMA
– Temperature of thermal plasma at atmospheric pressure
generally are above 6000K.
– Can be indirectly applied to food, i.e., at a distance from the
plasma source ensuring that the temperature remains within the
desired range.
– Applications:
1. Destruction of hazardous waste.
2. Extraction of metals.
3. Refining of metals.
4. Synthesis of fine ceramic powders.
5. Spray coatings.

14. COLD PLASMA
– A cold plasma (CP) is one of in which the thermal motion of the ions can be
ignored. Consequently there is no pressure force, the magnetic force can be
ignored and only the electric force is considered to act on the particles. These
plasmas are called “cold” as the temperature in the plasma reactor stays near
room temperature.
– It is designed for the inactivation of pathogenic microorganisms and food
safety improvement.
– Ionized gas that comprises a large number of different species such as
electrons, positive and negative ions, free radicals, electrons and gas atoms,
photons and it is suitable to be used in processes for which high temperature
is not recommended.
– It is applied in the food industry including for decontamination of raw
agricultural products like apple, lettuce, almond, mangoes and melon, egg
surface and real food system like cooked meat and cheese, etc.

15. COLD PLASMA AND
COLD PLASMA STERILIZATION
– A cold plasma (CP) is one in which the thermal motion of the ions can
be ignored. Consequently there is no pressure force, the magnetic force
can be ignored and only the electric force is considered to act on the
particles.
– These plasmas are said cold because the temperature in the plasma
reactor stays near room temperature.
– Cold plasma sterilization is designed for the inactivation of pathogenic
microorganisms and food safety improvement.
– The ionized gas that comprises a large number of different species such
as electrons, positive and negative ions, free radicals, electrons and gas
atoms, photons and it is suitable to be used in processes for which high
temperature is not recommended.
– Applied in food industry including decontamination of raw agricultural
products, egg surface and read food system, etc.

16. CP PROCESSING OF FOOD AND
FOOD RELATED PRODUCTS
Studied Effect Target System
Inactivation of Bacteria
Apples, melons, lettuce,
mangoes, bell pepper, apple
juice, sliced cheese, ham,
almonds, etc.
Inactivation of Fungi
Hazelnut, peanut, pistachio
nut
Inactivation of Fungi in Seed
Germination
Seeds of wheat, beans, lentils,
barley, oats, soybean,
chickpea, rye and corn
Degradation of Organic
Compounds/Macromolecules
Mycotoxins, starch,
pesticides, proteins

17. MECHANISM OF MICROBIAL
INACTIVATION
– The ability of atmospheric discharge
cold plasma to sterilize surfaces is well
established.
– The combination of electron and ion
bombardment, thermal effect, free
radical production and local exposure
UV.
– All the above act in concert to disrupt
microorganism’s cell membranes.
– This leads to changes in microorganism’s
structure like denaturation of proteins
and damage to bacterial DNA.

18. APPLICATIONS
CASE STUDY ON MEAT
Meat Type MAP Gas
Initial Bacterial
load
Log CFU/g
Reduction day
0
Reduction end
of Study
Days within
acceptable
limits
Current shelf
life
Target Shelf life
log
CFU/g
%
Log
CFU/g
%
Lamb chop CO2/O2 5.97 0.17 2 0.30 50 13 8 10 to 13
Pork loin CO2/O2 5.76 0.81 85 2.58 99.7 14 10 12 to 15
Turkey CO2/O2 4.94 0.41 61 0.81 84 15 to 20 21 28 to 35

19. APPLICATIONS
CASE STUDY ON RAW CHICKEN
– Campylobacter and Salmonella contaminate over 70% of raw chicken meat.
– Applied a cold plasma to uncooked chicken for different time period.
– 3.5 log reduction of bacterial from both skinless chicken and chicken skin itself.
Plasma Exposure Time (s)
Skinless Chicken Breast Chicken with Skin
Salmonella enterica Campylobacter jejuni Salmonella enterica Campylobacter jejuni
0 7.67 ± 0.29 9.56 ± 0.54 8.00 ± 1.03 8.00 ± 0.34
5 - - 7.33 ± 1.13 3.11 ± 0.44
10 - - 4.22 ± 1.32 -
15 - - 6.00 ± 1.32 -
20 - - 3.33 ± 1.49 -

20. APPLICATIONS
CASE STUDY ON EGGS
– Maximum reaction of 2.2 to 2.5 and
4.5 log
CFU
egg shell
in Salmonella
enteritidis levels following a 90
minutes of treatment at 35% and 65%
RH respectively.
– Salmonella typhimurium, with an
overall reduction of 3.5 log
CFU
egg shell
,
after 90 minutes treatment.
– 99.5% of bacteria on the egg shell.
Egg yolk and egg white remain
unaffected.

21. MICROBIAL INACTIVATION
USING PLASMA
Microorganism Treatment Medium Atmosphere Logarithmic Reduction
Bacillus atrophaeus PET foils Air 5.1 – 5.4
Bacillus pumilus PET foils Air 5.5 – 5.9
Bacillus cereus
Peptone water media
pH 5 to 7 on microscopic
slides
Air 2.8 – 3.9
Salonella Peptone water Air ~ 7
Listeria monocytogenes PET
Peptone media
pH 5 to 7 on microscopic
slides
Air 2.1 – 4.5
Staphylococcus aureus PET foils Air > 6.9
Escherichia coli PET foils Air 5.6 – 6.4
Aspergillus niger PET foils Air 3.0 – 3.6

22. ADVANTAGES AND
DISADVANTAGES
ADVANTAGES
– Decontamination of products
– Highly cost effective
– Environmental and economically beneficial
– Pollution control applications
– Reliable and user friendly
– Milk surface decontamination technology for
products such as cut vegetables and fresh meats
– Disinfect surfaces before packaging or included as
part of packaging process
DISADVANTAGES
– Cold plasma are the relatively early state of
technology development
– Important aspects of this technology are still
immature
– Optimization and scale up to commercial
treatment levels require more complete
understanding of these chemical processes
– High investment
– Variety and complexity of the necessary
equipment

23. FUTURE RESEARCH AND
CONCLUSION
FUTURE RESEARCH
– Further optimization and technology development
to determine the antimicrobial efficacy
– Characterization of the antimicrobial compounds
– Detailed examinations of the sensory properties
of cold plasma treated produce
– More information on the economics of the
process using larger scale equipment
CONCLUSION
– Emerging non – thermal technology
– Microbial destruction and surface modification of
substrate
– High efficacy, preservation and does not introduce
toxicity to the medium
– Effective at ambient temperatures
– No or minimum thermal effects on the nutritional
and sensory parameters of food with no chemical
residues

24. THANK YOU
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