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:

• Ionizing radiation Ionizing radiation • Surface pasteurization Surface pasteurization • Electronic pasteurization Electronic pasteurization • E-beam sterilization/pasteurizationE-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 SpectrumElectromagnetic Spectrum

Low Frequency

Long Wavelengths

High Frequency

Short Wavelengths

Sources of Ionizing irradiationSources of Ionizing irradiation

• Gamma sources of irradiationGamma sources of irradiation• X-ray machinesX-ray machines• Electron accelerators Electron accelerators

Gamma (Gamma () rays) rays

• energy comes from decay of radioactive energy comes from decay of radioactive isotopes isotopes – Cobalt-60 (half life of 5.3 years)Cobalt-60 (half life of 5.3 years)

• Produced by neutron bombardment Produced by neutron bombardment

– Cesium-137 (half life of 30 years)Cesium-137 (half life of 30 years)• By-product of spent nuclear fuelBy-product of spent nuclear fuel

Gamma (Gamma () rays) rays

• Isotope is contained and stored in pool of water Isotope is contained and stored in pool of water and raised when produce is to be exposed toand raised when produce is to be exposed to --raysrays

• facility is concrete chamber with 6-12’ thick walls facility is concrete chamber with 6-12’ thick walls • completely penetrates product and packaging completely penetrates product and packaging

(pallets)(pallets)

Electron-beamElectron-beam

• electricity is power source-switch on and off electricity is power source-switch on and off • uses stream of high-energy electrons uses stream of high-energy electrons

accelerated at near the speed of light accelerated at near the speed of light • electrons are showered on the product electrons are showered on the product • facilities are shielded with concrete or steel walls facilities are shielded with concrete or steel walls • penetrates approximately 2-3” of product and penetrates approximately 2-3” of product and

packaging packaging • ideal for thin ground beef patties 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 Factors affecting irradiation effectiveness against effectiveness against

microorganisms in foodsmicroorganisms in foods

• Growth phase of microorganism Growth phase of microorganism • Type of food (lean vs fat) Type of food (lean vs fat) • Moisture content (water level) Moisture content (water level) • Temperature of food (frozen vs heated) Temperature of food (frozen vs heated) • Presence of oxygen (aerobic vs anaerobic)Presence of oxygen (aerobic vs anaerobic)

Irradiation DosageIrradiation Dosage

• Dose - amount of energy transferredDose - amount of energy transferred– rad - old unit rad - old unit – gray (Gy) - new unit gray (Gy) - new unit – 1 kGy = 100,000 rad1 kGy = 100,000 rad

• 1 chest X-ray = .01 rad 1 chest X-ray = .01 rad • natural background = 0.1 rad/yearnatural background = 0.1 rad/year

Approximate doses of radiation needed Approximate doses of radiation needed to kill various organismsto kill various organisms

Organisms Dose (kGy)

Higher animals 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

IrradiationkGy 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

Meat product

Dose

kGry

Untreated shelf life

(days)

Irradiated

shelf life

(days)

Beef cuts 2 14-21 70

Ground beef 1.5 8-10 26-28

Pork loins 3 41 90

Ground pork 1 8 12

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 (Gamma () ray ) ray processing facilityprocessing facility

Gamma (Gamma () ray ) ray processing facilityprocessing facility

Electron-beamElectron-beam

DosimeterDosimeter

Levels of Food IrradiationLevels of Food Irradiation

• Radurization (low) < 1 kGy Radurization (low) < 1 kGy – vegetable sprouting, fruit ripening, insect sterilization vegetable sprouting, fruit ripening, insect sterilization

• Radicidation (medium) 1-10 kGy Radicidation (medium) 1-10 kGy – kills most pathogens and many food spoilage kills most pathogens and many food spoilage

organisms, kills insects and parasitesorganisms, kills insects and parasites–

• Rappertization (high) > 10kGy Rappertization (high) > 10kGy – can sterilize by killing all bacteria and virusescan sterilize by killing all bacteria and viruses

Technology ComparisonTechnology ComparisonElectron BeamElectron Beam Cobalt-60Cobalt-60

TechnologyTechnology

Focused beam of electrons (10 MeV energy)

Photons created from decay of radioactive material

AdvantagesAdvantages Safe ON/OFF

Cost efficient

In-Line capability

Compact systems

High dose rate = reduced oxidation

Increased ability to penetrate dense material

Process pallet load

DisadvantageDisadvantage 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

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