1. Effectiveness of Irradiation in Controlling Pathogenic and Spoilage Microorganisms in Meats
Catherine N. Cutter
Department of Food Science
Pennsylvania State University

2. Overview
Effect of irradiation on pathogenic and spoilage microorganisms
Effect of irradiation on shelf life of fresh meats
Types of irradiated meat products
Future research needs

3. Effect of irradiation on pathogenic and spoilage microorganisms
Biological effects of irradiation on microorganisms
Factors affecting irradiation effectiveness against microorganisms
Radiation resistance

4. Biological effects of irradiation on microorganisms
Irradiation can directly impair critical cell functions or components (DNA)
Single strand breaks (repairable in most cases)
Double strand breaks (not repairable in most cases)

6. Biological effects of irradiation on microorganisms
Irradiation can indirectly form radiolytic products/free radicals from water (oH, oOH)
oOH radicals are responsible for 90% of DNA damage

7. Effect of irradiation on pathogenic and spoilage microorganisms
Biological effects of irradiation on microorganisms
Factors affecting irradiation effectiveness against microorganisms
Radiation resistance

8. Factors affecting irradiation effectiveness against microorganisms
Growth phase:
Some microorganisms (L. monocytogenes) are more susceptible to irradiation at low doses when irradiated during the logarithmic phase of growth then during the stationary phase

9. Factors affecting irradiation effectiveness against microorganisms
Type of food
The more complex the food, the greater the competition of the food for the energy and less for the microorganisms
Fat content of ground beef does not change the dose needed to eliminate E. coli O157:H7
C. jejuni was more resistant to irradiation in low fat frozen beef

10. Factors affecting irradiation effectiveness against microorganisms
Moisture content
The lower the water activity in a food, the less free radicals produced by water--> less DNA damage to microorganisms
Low water activity will reduce the ability of radiation resistant organisms to recover during storage

11. Factors affecting irradiation effectiveness against microorganisms
Temperature of food
Higher temperatures enhance the lethal effect of irradiation
Microorganism repair mechanisms are impaired at the higher temperatures
Freezing immobilizes and prevents diffusion of free radicals to microorganisms

12. Factors affecting irradiation effectiveness against microorganisms
Presence of oxygen
Higher oxygen concentration = greater lethal effect of radiation on microorganisms
Anaerobic conditions = less lethal effect of radiation on microorganisms
Storage conditions can enhance recovery of some microorganisms after irradiation

13. Effect of irradiation on pathogenic and spoilage microorganisms
Biological effects of irradiation on microorganisms
Factors affecting irradiation effectiveness against microorganisms
Radiation resistance

14. Approximate doses of radiation needed to kill various organisms

15. Radiation resistance
Gram negative bacteria < Gram positive bacteria/molds/yeast < spores and viruses
Differences in resistance are due to:
chemical and physical structure of microorganism
ability to recover from radiation injury

16. Effect of Irradiation on Pathogens Population (log10 CFU/g) - killed by :

17. Radiation resistance
Deinococcus radiodurans is highly resistant to irradiation
Acid resistant E. coli O157:H7 exhibit radiation resistance
Of pathogens tested in ground beef, C. jejuni has lowest resistance to irradiation; Salmonella spp. has the highest resistance

18. Typical radiation survival curves
Survivors
Time or Radiation Dose

19. Radurization
Irradiation applied to elicit a substantial reduction in number of spoilage organisms, thereby extending the shelf life of a food 3-4 times
Applied at dosage of kGy
5 kGy will eliminate most spoilage organisms

20. Radicidation
Irradiation is applied to reduce the number of non-spore forming pathogenic microorganisms (other than viruses) and parasites
Applied at dosage of kGy
Improves the hygienic quality of the food
Reduces the risk of public exposure to pathogens

21. Radappertization Applied at dosage of 25-60 kGy
Irradiation is applied to prepackaged, enzyme-inactivated foods to reduce the number and/or activity of microorganisms (12-D reduction in
C. botulinum spores)
Applied at dosage of kGy
In the absence of post-processing contamination, no microbial spoilage or toxicity should occur
Shelf stable without refrigeration

22. Overview
Effect of irradiation on pathogenic and spoilage microorganisms
Effect of irradiation on shelf life of fresh meats
Types of irradiated meat products
Future research needs

23. 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)

24. Shelf life extension of fresh meat

25. Overview
Effect of irradiation on pathogenic and spoilage microorganisms
Effect of irradiation on shelf life of fresh meats
Types of irradiated meat products
Future research needs

26. Types of meat products approved for irradiation
Refrigerated or frozen, uncooked meat or meat byproducts
Meat from cattle, sheep, swine, or goats, which is skeletal or which is found in the tongue, diaphragm, heart, or esophagus, with or without the accompanying and overlying fat. (It does not include the muscle found in the lips, snout, or ears.)

27. Types of meat products approved for irradiation
Mechanically deboned meat
Intact or ground meat
Hamburger
Certain defatted beef or pork products

28. Overview
Effect of irradiation on pathogenic and spoilage microorganisms
Effect of irradiation on shelf life of fresh meats
Types of irradiated meat products
Future research needs

29. Future research needs
Determination of processes (heat, antimicrobials, curing agents, etc.) that may affect radiation resistance of pathogens in fresh meats
The effect of multi-hurdle approach with irradiation to enhance pathogen reduction or improve shelf life in fresh meats

30. Future research needs
Determining effects of irradiation on different cooked meat products to inhibit organisms such as LM
Determining effects of atmospheres and packaging regimens on pathogens associated with cooked and fresh meats subjected to low dose irradiation

31. Societal Benefits of Irradiating Ground Beef
If 25% of ground beef supply (~2 billion pounds) is irradiated:
it would cost $88.5 million (assuming $0.05/lb); $28.3 million (assuming $0.02/lb)
25% of Salmonella spp. and E. coli O157:H7 infections would be prevented for saved medical costs of $56 million to $138 million

32. QUESTIONS?