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Preservation by
irradiation
Syeda Rubeena Fatima
Introduction
• Utilization of radiations of various frequencies ranging from low frequency electric current
to high frequency gamma rays have been employed for food preservation.
• Ultraviolet radiations ionization radiations and microwave heating have been effectively
used for food preservation.
• The entire spectrum of radiation is divided into 2 categories
• low frequency, long wavelength, low quantum energy radiation ranges from radio waves
to infrared and their effect on microorganism is related to their thermal agitation of the
food
• Whereas high frequency short wavelength radiations have high quantum energies and
actually destroy organic compounds and microorganisms without heating the products.
• Microbial destruction without generation of high temperature is termed as cold
sterilization.
• In food industry short wavelength radiation can be further divided into two groups- low
frequency and low energy radiations such as ultraviolet has efficient energy only to excite
molecules and is employed in food industry and radiations of high frequencies have high
energy content and are capable of actually breaking individual molecules into ions hence
termed ionizing radiations
Ultraviolet irradiation
• Among all the electromagnetic radiations ultraviolet
irradiation has been the most widely used in food
industry.
• Radiations with wavelengths nearly 260 nm is
absorbed strongly by purines and pyrimidines and is
therefore the most germicidal.
• Ultraviolet radiations around 200nm is strongly
absorbed by oxygen, may result in production of
ozone and is ineffective against microorganisms.
Germicidal lamps
• The usual source of ultraviolet radiation in the
food industry is from quartz mercury vapor
lamps or low pressure mercury lamps which
emit radiations at 254nm.
• Radiations from these lamps include rays in
the visible range and those in the arrhythmic
range which have an irradiation effect on skin
and mucous membrane.
• The lamps are available in various sizes shapes
and power.
• The latest types releases only negligible
amount of ozone.
Factors influencing
effectiveness of UV
light
• only direct rays are effective
unless they come from special
reflectors and even then their
effectiveness is reduced.
• the factors that influence the
effectiveness of ultraviolet rays
are as follows.
Time of exposure
• The longer the time of exposure to a given
concentration the more effective the
treatment.
Intensity of UV
light
• The intensity of race reaching an object will depend upon
the power of the lamp the distance from the lamp to the
object and the kind and amount of interfering material in
the path of the rays.
• The intensity will increase with the power of the lamp.
• Intensity is measured as microwatts per square
centimeter µW/cm2
• the quantity or dose of irradiation actually absorbed by an
Organism or a product is expressed by the product of time
and intensity.
• Intensity of rays vary with distance from lamp.
• dust in the air or on the lamp reduces the effectiveness and
so do the atmospheric humidity
• over 80% relative humidity definitely reduces the
penetration through air but humidity is below 60% have
little effect. little effect
Penetration
• The nature of object or material being irradiated has important influence
on the effectiveness of the process.
• Penetration is reduced even by clear water which also exerts a positive
effect on microorganisms
• Dissolved mineral salts especially of iron and cloudiness generally reduces
the effectiveness of the rays
• Even a thin layer of fatty or greasy material cuts off the rays
• No penetrations through opaque material
• The rays affect only the outer surface of most irradiated foods directly
exposed to the lamp and do not penetrate to microorganisms inside the
food
Action on microorganisms
• the intensity of the race that reached the organisms at the time in which they act and the location of the
Organism determined that germicidal effects.
• each microorganism has a characteristic resistance to ultraviolet radiations which may vary with the face of
growth and physiological state of the cell
• The amount of ultraviolet radiation needed to destroy several different types of organisms varies the
location of the organisms during the test has a marked influence.
• example is is E coli in the air were killed in 10 seconds at 24 in with a 15 wat lamp but 20 seconds at 11
inches was necessary for bacteria on the surface on an Agar plate
• capsulation or clumping of bacteria increases their resistance
• bacterial endospores takes from two to five times as much exposure as the corresponding vegetative cells
• sometimes even the pigmentation also have a protective effect on the microorganism
• Yeast are two to five times more resistant then bacteria especially the pigmented Molds are more resistant
than nonpigmented molds
This Photo by Unknown author is licensed under CC BY-SA.
Applications in food industry
• the use of ultraviolet irradiation in food industry has been seen for specific
foods.
• examples of successful use of these rays include
• treatment of water used for beverages,
• ageing of meat,
• treatment of knives for slicing breads,
• treatment of bread and cakes,
• packaging of sliced bacon,
• sanitizing of eating utensils,
• preservation of growth of film eased on Pickles,
• vinegar and sauerkraut,
• killing of spores on sugar crystals and in syrups,
• storage and packing of cheese
• prevention of mold growth on walls and shelves and
• treatment of air used for or in storage and processing rooms.
Ionizing radiations
Kinds of ionizing radiations
• the radiations that are categorized as ionizing radiations include X-rays all gamma rays,
cathode or beat arrays, protons, neutrons and alpha particles.
• Neutrons result in residual radioactivity in foods and protons and alpha particles have
little penetration therefore these rays are not practical for use in food preservation.
• Xrays are penetrating electromagnetic waves which are produced by bombardment of
heavy metal target with cathode rays within an evacuated tube they are not currently
considered economical for use in food industry.
• gamma rays are like X-rays but are emitted from byproduct of atomic fusion or from
imitation of such byproducts.
• Beta rays are streams of electrons emitted from radioactive material electrons are
small negatively charged particles of uniform mass that form a part of atom. they are
deflected by magnetic and electric field their penetration depends upon the speed
with which they hit the target. The higher the charge of electron the deeper its
penetration
• cathode rays are streams of electrons from cathode of an evacuated tube first
practically these electrons are accelerated by artificial means. shins to images
Definition of new terms
• Roentgen (r) is the quantity of gamma radiation which produces one electrostatic unit of electric charge of
either side in a cubic centimeter of air under standard conditions.
• Roentgen-equivalent-physical is the quantity of ionizing energy which produces, per gram of tissue, an
amount of ionization equivalent to a roentgen. A megarep is 1 million rep. One r, or 1 rep, is equivalent to
the absorption of 83 to 90 erg per gram of tissue.
• The rad now is employed chiefly as the unit of radiation dosage, being equivalent to the absorption of 100
erg per gram of irradiated material. A megarad (Mrad) is 1 million rad, and a kilorad (Krad) is 1,000 rad.
• An electronvolt (eV) is the energy gained by an electron in moving through a potential difference of 1 volt. A
meV is 1 million electronvolts.
• A meV, then, is a measure of the intensity of the irradiation, and a rep is a measure of the absorbed energy
that is effective within the food.
• A Gray (Gy) equals 100 rads and is being used as a term to replace rads in some references.
• Radappertization is a term used to define "radiation sterilization" which would imply high dose treatments,
with the resulting product being shelf-stable.
• Radurization refers to "radiation pasteurization" low-dose treatments, where the intent is to extend a
product's shelf life.
• Radicidation also is a low-dose "radiation pasteurization" treatment, but with the specific intent being the
elimination of a particular pathogen.
• Picowaved is a term used to label foods treated with low-level ionizing radiation.
X-rays
• X-rays, gamma rays, and cathode rays are
equally effective in sterilization for
equal quantities of energy absorbed.
• X-rays and gamma rays have good
penetration, while cathode rays have
comparatively poor penetration.
• The greatest drawback at present to the use
of x-rays in food preservation is the low
efficiency and consequent high cost of their
production
Gamma Rays and
Cathode Rays
• These two types of rays are equally effective in
sterilization for equal quantities of energy absorbed
and apparently produce similar changes in the food
being treated.
• Chief sources of gamma rays are
(1) radioactive fission products of uranium and
cobalt,
(2) the coolant circulated in nuclear reactors, and
(3) other fuel elements used to operate a
nuclear reactor.
• Cathode rays usually are accelerated by special
electrical devices.
• The greater this acceleration (i.e., the more meV),
the deeper the penetration into the food.
This Photo by Unknown author is licensed under CC BY-SA-NC.
Penetration
• Gamma rays have good penetration but their
efficiency decreases exponentially with depth.
• they have been reported to be efficient up to 20
cm in most foods but this depth will depend on
the time of exposure.
• Cathode rays on the other hand have poor
penetration being effective at only 0.5 cm per
MeV when cross firing that is irradiation from
opposite side is employed.
• the absorption dose level in a material is not a
uniform decreasing fraction with depth and
rather builds up to a maximum at a depth equal
to about 1/3 of the total penetration and then
decreases to zero.
Efficiency
• as cathode rays are directional they can be
made to hit the food and therefore are used
with greater efficiency than gamma rays
which are constantly emitted in all direction
from the radioactive source.
• various estimates of maximal efficiency of
utilization of cathode raise range from 40
and 80% depending on the shape of the
irradiated material but only a maximum of
10 to 25% utilization efficiency is estimated
for gamma rays
• radioactive source of gamma rays decay
steadily and hence weaken with time.
Safety
• use of cathode rays present fewer health problems than the use of
gamma rays
• since cathode rays are directional and less penetrating can be turned
off for repair or maintenance work and present no hazard of
radioactive material after a fire explosion or other catastrophe.
• gamma rays are emitted in all direction are penetrating continuously
emitted and comes from radioactive source they require more
shielding to protect workers.
Effects on microorganisms
• The kind and species of organism
• The no of organism or spores present :The more organisms there are, the less
effective a given dose will be.
• Composition of food: Some constituents, e.g., proteins, catalase, and
reducing substances (nitrites, sulphites, and sulfhydryl compounds), may be
protective. Compounds that combine with the SH groups would be sensitizing.
Products of ionization may be harmful to the organisms.
• Presence of Oxygen: The effect of free oxygen varies with the organism, ranging
from no effect to sensitization of the organism. Undesirable "side reactions,"
are likely are intensified in the presence of oxygen and to be less frequent in a
vacuum or an atmosphere of nitrogen.
• The physical state of the food during irradiation. Both moisture content and
temperature affect different organisms in different ways.
• The condition of the organisms. Age, temperature of growth and sporulation,
and state vegetative or spore-may affect the sensitivity of the organisms.
Effects on food
• Radiation doses heavy enough to affect sterilization have been found to produce
undesirable "side reactions," or secondary changes, in many kinds of foods, causing
undesirable colors, odors, tastes, or even physical properties.
• Some of the changes produced in foods by sterilizing doses of radiation include
1. In meat, a rise in pH, destruction of glutathione, and an increase in carbonyl
compounds, hydrogen sulfide, and methyl mercaptan.
2. In fats and lipids, destruction of natural antioxidants, oxidation followed by
partial polymerization, and increase in carbonyl compounds.
3. In vitamins, reduction in most foods of levels of thiamine, pyridoxine, and vitamins B12,
C, D, E, and K: riboflavin and niacin are fairly stable. The lower the dosage of irradiation,
of course, the less frequent the undesirable effects on the food.
• Destruction of many of the food enzymes requires five to ten times the dosage of rays
needed to kill all the microorganisms.
• Enzyme action continues after all microorganisms have been destroyed unless a
special blanching treatment has preceded irradiation.
• The chief effect on the healthfulness of foods is the destruction of vitamins.
• The general nutrition of an irradiated food would be as good as that of a food processed
by other means to achieve the same shelf stability.
Applications
• Currently food irradiation has been approved only in a very limited
way in the United States.
• Low-level irradiation (I kilo Gray) can be used on fresh fruits and
vegetables to kill insects and to inhibit spoilage.
• Dry or dehydrated vegetables (herbs and spices) can be irradiated at
up to 30 kilo Gray to kill insects and bacteria
Microwave processing
• Microwave heating and processing of foods is becoming increasingly
popular, particularly at the consumer level.
• Microwaves are electromagnetic waves between infrared and radio waves.
Specific frequencies are usually at either 915 megacycles or 2,450
megacycles.
• The energy or heat produced by microwaves as they pass through a food is
a result of the extremely rapid oscillation of the food molecules to align
themselves with the electromagnetic field being produced.
• This rapid oscillation, or intermolecular friction, generates heat.
• The preservative effect of microwaves or the bactericidal effect produced is
really a function of the heat that is generated. But the destruction of
microorganisms is due to the heat produced by the excitation of food
molecules.
This Photo by Unknown author is licensed under CC
BY.

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Preservation by Irradiation.pptx

  • 2. Introduction • Utilization of radiations of various frequencies ranging from low frequency electric current to high frequency gamma rays have been employed for food preservation. • Ultraviolet radiations ionization radiations and microwave heating have been effectively used for food preservation. • The entire spectrum of radiation is divided into 2 categories • low frequency, long wavelength, low quantum energy radiation ranges from radio waves to infrared and their effect on microorganism is related to their thermal agitation of the food • Whereas high frequency short wavelength radiations have high quantum energies and actually destroy organic compounds and microorganisms without heating the products. • Microbial destruction without generation of high temperature is termed as cold sterilization. • In food industry short wavelength radiation can be further divided into two groups- low frequency and low energy radiations such as ultraviolet has efficient energy only to excite molecules and is employed in food industry and radiations of high frequencies have high energy content and are capable of actually breaking individual molecules into ions hence termed ionizing radiations
  • 3. Ultraviolet irradiation • Among all the electromagnetic radiations ultraviolet irradiation has been the most widely used in food industry. • Radiations with wavelengths nearly 260 nm is absorbed strongly by purines and pyrimidines and is therefore the most germicidal. • Ultraviolet radiations around 200nm is strongly absorbed by oxygen, may result in production of ozone and is ineffective against microorganisms.
  • 4. Germicidal lamps • The usual source of ultraviolet radiation in the food industry is from quartz mercury vapor lamps or low pressure mercury lamps which emit radiations at 254nm. • Radiations from these lamps include rays in the visible range and those in the arrhythmic range which have an irradiation effect on skin and mucous membrane. • The lamps are available in various sizes shapes and power. • The latest types releases only negligible amount of ozone.
  • 5. Factors influencing effectiveness of UV light • only direct rays are effective unless they come from special reflectors and even then their effectiveness is reduced. • the factors that influence the effectiveness of ultraviolet rays are as follows.
  • 6. Time of exposure • The longer the time of exposure to a given concentration the more effective the treatment.
  • 7. Intensity of UV light • The intensity of race reaching an object will depend upon the power of the lamp the distance from the lamp to the object and the kind and amount of interfering material in the path of the rays. • The intensity will increase with the power of the lamp. • Intensity is measured as microwatts per square centimeter µW/cm2 • the quantity or dose of irradiation actually absorbed by an Organism or a product is expressed by the product of time and intensity. • Intensity of rays vary with distance from lamp. • dust in the air or on the lamp reduces the effectiveness and so do the atmospheric humidity • over 80% relative humidity definitely reduces the penetration through air but humidity is below 60% have little effect. little effect
  • 8. Penetration • The nature of object or material being irradiated has important influence on the effectiveness of the process. • Penetration is reduced even by clear water which also exerts a positive effect on microorganisms • Dissolved mineral salts especially of iron and cloudiness generally reduces the effectiveness of the rays • Even a thin layer of fatty or greasy material cuts off the rays • No penetrations through opaque material • The rays affect only the outer surface of most irradiated foods directly exposed to the lamp and do not penetrate to microorganisms inside the food
  • 9. Action on microorganisms • the intensity of the race that reached the organisms at the time in which they act and the location of the Organism determined that germicidal effects. • each microorganism has a characteristic resistance to ultraviolet radiations which may vary with the face of growth and physiological state of the cell • The amount of ultraviolet radiation needed to destroy several different types of organisms varies the location of the organisms during the test has a marked influence. • example is is E coli in the air were killed in 10 seconds at 24 in with a 15 wat lamp but 20 seconds at 11 inches was necessary for bacteria on the surface on an Agar plate • capsulation or clumping of bacteria increases their resistance • bacterial endospores takes from two to five times as much exposure as the corresponding vegetative cells • sometimes even the pigmentation also have a protective effect on the microorganism • Yeast are two to five times more resistant then bacteria especially the pigmented Molds are more resistant than nonpigmented molds This Photo by Unknown author is licensed under CC BY-SA.
  • 10.
  • 11. Applications in food industry • the use of ultraviolet irradiation in food industry has been seen for specific foods. • examples of successful use of these rays include • treatment of water used for beverages, • ageing of meat, • treatment of knives for slicing breads, • treatment of bread and cakes, • packaging of sliced bacon, • sanitizing of eating utensils, • preservation of growth of film eased on Pickles, • vinegar and sauerkraut, • killing of spores on sugar crystals and in syrups, • storage and packing of cheese • prevention of mold growth on walls and shelves and • treatment of air used for or in storage and processing rooms.
  • 13. Kinds of ionizing radiations • the radiations that are categorized as ionizing radiations include X-rays all gamma rays, cathode or beat arrays, protons, neutrons and alpha particles. • Neutrons result in residual radioactivity in foods and protons and alpha particles have little penetration therefore these rays are not practical for use in food preservation. • Xrays are penetrating electromagnetic waves which are produced by bombardment of heavy metal target with cathode rays within an evacuated tube they are not currently considered economical for use in food industry. • gamma rays are like X-rays but are emitted from byproduct of atomic fusion or from imitation of such byproducts. • Beta rays are streams of electrons emitted from radioactive material electrons are small negatively charged particles of uniform mass that form a part of atom. they are deflected by magnetic and electric field their penetration depends upon the speed with which they hit the target. The higher the charge of electron the deeper its penetration • cathode rays are streams of electrons from cathode of an evacuated tube first practically these electrons are accelerated by artificial means. shins to images
  • 14. Definition of new terms • Roentgen (r) is the quantity of gamma radiation which produces one electrostatic unit of electric charge of either side in a cubic centimeter of air under standard conditions. • Roentgen-equivalent-physical is the quantity of ionizing energy which produces, per gram of tissue, an amount of ionization equivalent to a roentgen. A megarep is 1 million rep. One r, or 1 rep, is equivalent to the absorption of 83 to 90 erg per gram of tissue. • The rad now is employed chiefly as the unit of radiation dosage, being equivalent to the absorption of 100 erg per gram of irradiated material. A megarad (Mrad) is 1 million rad, and a kilorad (Krad) is 1,000 rad. • An electronvolt (eV) is the energy gained by an electron in moving through a potential difference of 1 volt. A meV is 1 million electronvolts. • A meV, then, is a measure of the intensity of the irradiation, and a rep is a measure of the absorbed energy that is effective within the food. • A Gray (Gy) equals 100 rads and is being used as a term to replace rads in some references. • Radappertization is a term used to define "radiation sterilization" which would imply high dose treatments, with the resulting product being shelf-stable. • Radurization refers to "radiation pasteurization" low-dose treatments, where the intent is to extend a product's shelf life. • Radicidation also is a low-dose "radiation pasteurization" treatment, but with the specific intent being the elimination of a particular pathogen. • Picowaved is a term used to label foods treated with low-level ionizing radiation.
  • 15. X-rays • X-rays, gamma rays, and cathode rays are equally effective in sterilization for equal quantities of energy absorbed. • X-rays and gamma rays have good penetration, while cathode rays have comparatively poor penetration. • The greatest drawback at present to the use of x-rays in food preservation is the low efficiency and consequent high cost of their production
  • 16. Gamma Rays and Cathode Rays • These two types of rays are equally effective in sterilization for equal quantities of energy absorbed and apparently produce similar changes in the food being treated. • Chief sources of gamma rays are (1) radioactive fission products of uranium and cobalt, (2) the coolant circulated in nuclear reactors, and (3) other fuel elements used to operate a nuclear reactor. • Cathode rays usually are accelerated by special electrical devices. • The greater this acceleration (i.e., the more meV), the deeper the penetration into the food. This Photo by Unknown author is licensed under CC BY-SA-NC.
  • 17. Penetration • Gamma rays have good penetration but their efficiency decreases exponentially with depth. • they have been reported to be efficient up to 20 cm in most foods but this depth will depend on the time of exposure. • Cathode rays on the other hand have poor penetration being effective at only 0.5 cm per MeV when cross firing that is irradiation from opposite side is employed. • the absorption dose level in a material is not a uniform decreasing fraction with depth and rather builds up to a maximum at a depth equal to about 1/3 of the total penetration and then decreases to zero.
  • 18. Efficiency • as cathode rays are directional they can be made to hit the food and therefore are used with greater efficiency than gamma rays which are constantly emitted in all direction from the radioactive source. • various estimates of maximal efficiency of utilization of cathode raise range from 40 and 80% depending on the shape of the irradiated material but only a maximum of 10 to 25% utilization efficiency is estimated for gamma rays • radioactive source of gamma rays decay steadily and hence weaken with time.
  • 19. Safety • use of cathode rays present fewer health problems than the use of gamma rays • since cathode rays are directional and less penetrating can be turned off for repair or maintenance work and present no hazard of radioactive material after a fire explosion or other catastrophe. • gamma rays are emitted in all direction are penetrating continuously emitted and comes from radioactive source they require more shielding to protect workers.
  • 20. Effects on microorganisms • The kind and species of organism • The no of organism or spores present :The more organisms there are, the less effective a given dose will be. • Composition of food: Some constituents, e.g., proteins, catalase, and reducing substances (nitrites, sulphites, and sulfhydryl compounds), may be protective. Compounds that combine with the SH groups would be sensitizing. Products of ionization may be harmful to the organisms. • Presence of Oxygen: The effect of free oxygen varies with the organism, ranging from no effect to sensitization of the organism. Undesirable "side reactions," are likely are intensified in the presence of oxygen and to be less frequent in a vacuum or an atmosphere of nitrogen. • The physical state of the food during irradiation. Both moisture content and temperature affect different organisms in different ways. • The condition of the organisms. Age, temperature of growth and sporulation, and state vegetative or spore-may affect the sensitivity of the organisms.
  • 21. Effects on food • Radiation doses heavy enough to affect sterilization have been found to produce undesirable "side reactions," or secondary changes, in many kinds of foods, causing undesirable colors, odors, tastes, or even physical properties. • Some of the changes produced in foods by sterilizing doses of radiation include 1. In meat, a rise in pH, destruction of glutathione, and an increase in carbonyl compounds, hydrogen sulfide, and methyl mercaptan. 2. In fats and lipids, destruction of natural antioxidants, oxidation followed by partial polymerization, and increase in carbonyl compounds. 3. In vitamins, reduction in most foods of levels of thiamine, pyridoxine, and vitamins B12, C, D, E, and K: riboflavin and niacin are fairly stable. The lower the dosage of irradiation, of course, the less frequent the undesirable effects on the food. • Destruction of many of the food enzymes requires five to ten times the dosage of rays needed to kill all the microorganisms. • Enzyme action continues after all microorganisms have been destroyed unless a special blanching treatment has preceded irradiation. • The chief effect on the healthfulness of foods is the destruction of vitamins. • The general nutrition of an irradiated food would be as good as that of a food processed by other means to achieve the same shelf stability.
  • 22. Applications • Currently food irradiation has been approved only in a very limited way in the United States. • Low-level irradiation (I kilo Gray) can be used on fresh fruits and vegetables to kill insects and to inhibit spoilage. • Dry or dehydrated vegetables (herbs and spices) can be irradiated at up to 30 kilo Gray to kill insects and bacteria
  • 23. Microwave processing • Microwave heating and processing of foods is becoming increasingly popular, particularly at the consumer level. • Microwaves are electromagnetic waves between infrared and radio waves. Specific frequencies are usually at either 915 megacycles or 2,450 megacycles. • The energy or heat produced by microwaves as they pass through a food is a result of the extremely rapid oscillation of the food molecules to align themselves with the electromagnetic field being produced. • This rapid oscillation, or intermolecular friction, generates heat. • The preservative effect of microwaves or the bactericidal effect produced is really a function of the heat that is generated. But the destruction of microorganisms is due to the heat produced by the excitation of food molecules. This Photo by Unknown author is licensed under CC BY.