Science of Irradiation of meat - University of Tennessee
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 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
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
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
Contains 10 microorganisms 1 microorganism survives Irradiation kGy dose 2 D value 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) Irradiated shelf life (days) 2 14-21 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
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 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
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