Transcript Science of Irradiation of meat

What is Food Irradiation
• Food irradiation is a process in which food
products are exposed to a controlled amount of
radiant energy to increase the safety of the food
and to extend shelf life of the food
• Like pasteurization of milk and pressure cooking
of canned foods, treating food with ionizing
radiation can kill bacteria and parasites that
would otherwise cause foodborne disease.
Irradiation….also known as:
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Ionizing radiation
Surface pasteurization
Electronic pasteurization
E-beam sterilization/pasteurization
Ionizing radiation
• When radiation strikes other material, it
transfers energy.
• This can cause heating, as with microwave
cooking, or if there is enough energy, it can
knock electrons out of the material
bombarded, breaking the molecular
structure-thus leaving ions (free radicals)
hence the name ionizing radiation.
Electromagnetic Spectrum
High Frequency
Short Wavelengths
Low Frequency
Long Wavelengths
Sources of Ionizing irradiation
• Gamma sources of irradiation
• X-ray machines
• Electron accelerators
Gamma () rays
• energy comes from decay of radioactive
isotopes
– Cobalt-60 (half life of 5.3 years)
• Produced by neutron bombardment
– Cesium-137 (half life of 30 years)
• By-product of spent nuclear fuel
Gamma () rays
• Isotope is contained and stored in pool of water
and raised when produce is to be exposed to rays
• facility is concrete chamber with 6-12’ thick walls
• completely penetrates product and packaging
(pallets)
Electron-beam
• electricity is power source-switch on and off
• uses stream of high-energy electrons
accelerated at near the speed of light
• electrons are showered on the product
• facilities are shielded with concrete or steel walls
• penetrates approximately 2-3” of product and
packaging
• ideal for thin ground beef patties
How ionizing radiation works
• Electrons disrupt the DNA chain either destroying
or preventing reproduction of the organism
Factors affecting irradiation
effectiveness against
microorganisms in foods
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Growth phase of microorganism
Type of food (lean vs fat)
Moisture content (water level)
Temperature of food (frozen vs heated)
Presence of oxygen (aerobic vs anaerobic)
Irradiation Dosage
• Dose - amount of energy transferred
– rad - old unit
– gray (Gy) - new unit
– 1 kGy = 100,000 rad
• 1 chest X-ray = .01 rad
• natural background = 0.1 rad/year
Approximate doses of radiation needed
to kill various organisms
Organisms
Higher animals
Dose (kGy)
0.005 to 0.1
Insects
0.01 to 1
Non-spore forming bacteria
0.5 to 10
Bacterial spores
10 to 50
Viruses
10 to 200
Typical irradiation
D-values of pathogens
kGy
Organism
Fresh (refrigerated)
Frozen
Camplobacter jejuni
0.08 – 0.20
0.21 – 0.32
E. Coli O157:H7
0.24 – 0.27
0.31 – 0.44
Staphlococcus aureus
0.26 – 0.60
0.30 – 0.45
Salmonella spp.
0.30 – 0.80
0.40 – 1.30
Listeria monocytogenes
0.27 – 1.00
0.52 – 1.30
D-value is equivalent to radiation dose required
to reduce a bacterial population 90%
Typical irradiation
D-values of pathogens
kGy
Organism
Fresh (refrigerated)
Clostridium botulinum
spores
1.00 – 3.60
Toxoplasma
0.40 – 0.70
Trichinella spiralis
0.30 – 0.60
D-value is equivalent to radiation dose required
to reduce a bacterial population 90%
Destruction of microorganisms
Irradiation
kGy dose
1 D value
Contains 10
microorganisms
1 microorganism survives
Irradiation
kGy dose
2 D value
Contains 10
microorganisms
1 microorganism survives/ 10 steaks
Pasteurization
• To reduce microorganisms but not to sterilize the
product
• Purpose is to destroy pathogenic
microorganisms to make food safe
• This is normally 5 to 7 D values
Effect of irradiation on shelf life of fresh
meats
• Spoilage organisms, especially pseudomonads,
are susceptible to low dose irradiation
• Spoilage of low dose irradiated meats may be
due to yeast, LAB, or Moraxella spp. (increased
lag time)
Shelf life extension of fresh meat
Dose
kGry
Untreated
shelf life
(days)
2
14-21
Irradiated
shelf life
(days)
70
1.5
8-10
26-28
Pork loins
3
41
90
Ground pork
1
8
12
Meat product
Beef cuts
Ground beef
How does irradiation
food processing operation work?
• Food is packed in containers and moved by
conveyer belt into a shielded room.
• Food is exposed briefly to a radiant-energy source.
(The amount of energy depends on the food.)
• Food is left virtually unchanged, but the number of
harmful bacteria, parasites and fungi is reduced and
may be eliminated.
Gamma () ray
processing facility
Gamma () ray
processing facility
Electron-beam
Dosimeter
Levels of Food Irradiation
• Radurization (low) < 1 kGy
– vegetable sprouting, fruit ripening, insect sterilization
• Radicidation (medium) 1-10 kGy
– kills most pathogens and many food spoilage
organisms, kills insects and parasites
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• Rappertization (high) > 10kGy
– can sterilize by killing all bacteria and viruses
Technology Comparison
Electron Beam
Cobalt-60
Focused beam of
electrons (10 MeV energy)
Photons created from decay of
radioactive material
Advantages
Safe ON/OFF
Cost efficient
In-Line capability
Compact systems
High dose rate = reduced
oxidation
Increased ability to penetrate
dense material
Process pallet load
Disadvantage
Reduced ability to
penetrate dense
material (3 ½ in. of highly
dense product – approx. 8
meat patties high)
Cannot be turned OFF – always
emitting gamma radiation
Requires source disposal and
replenishment
Low dose rate = increased
oxidation
Consumer perception
Technology
Meat Irradiation
• December 23, 1999 Federal Register
• Effective date – February 22, 2000
• Ionizing radiation approved for use
– Cobalt-60, Cesium-137, X-ray machines, Electron
accelerators
• Dosage
– 4.5 kGy if refrigerated
– 7.0 kGy if frozen
Safety and efficacy of
food irradiation
• The following statements are in the Federal Register (12/23/1999)
• The safety and efficacy of food irradiation, as demonstrated by
numerous experiments and studies, is widely accepted by Federal
regulatory agencies and national and international food and public
health organizations
• FDA examined numerous studies on the chemical effects of
radiation, the impact of radiation on nutrient content of foods,
potential toxicity concerns and effects on microorganisms in or on
irradiated products. FDA concluded that irradiation is safe in
reducing disease-causing microbes in or on meat food products and
it does not compromise the nutritional quality of treated products.
• The World Health Organization, Food and Agriculture Organization,
American Medical Association and American Dietetic Association
endorse food irradiation
Web sites of interest
• http://www.fsis.usda.gov/OA/topics/irrmenu.htm
• http://www.acsh.org/publications/booklets/irradiated.pdf
• http://www.ers.usda.gov/Topics/view.asp?T=102818
• http://www.fda.gov/opacom/catalog/irradbro.html
• http://www.fsis.usda.gov/OA/topics/irrad-risk.htm