Effectiveness of Irradiation in Controlling Pathogens in Meats

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

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Effect of irradiation on pathogenic and spoilage
microorganisms

• Biological effects of irradiation on
  microorganisms
• Factors affecting irradiation effectiveness
  against microorganisms
• Radiation resistance

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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)

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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

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Effect of irradiation on pathogenic and spoilage
microorganisms

• Biological effects of irradiation on
  microorganisms
• Factors affecting irradiation effectiveness
  against microorganisms
• Radiation resistance

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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

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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 O157H7
• C. jejuni was more resistant to irradiation in
  low fat frozen beef

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Factors affecting irradiation effectiveness
against microorganisms

• Moisture content
• The lower the water activity in a food, the less
  free radicals produced by water--gt less DNA
  damage to microorganisms
• Low water activity will reduce the ability of
  radiation resistant organisms to recover during
  storage

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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

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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

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Effect of irradiation on pathogenic and spoilage
microorganisms

• Biological effects of irradiation on
  microorganisms
• Factors affecting irradiation effectiveness
  against microorganisms
• Radiation resistance

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Approximate doses of radiation needed to kill
various organisms
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Radiation resistance

• Gram negative bacteria lt Gram positive
  bacteria/molds/yeast lt spores and viruses
• Differences in resistance are due to
• chemical and physical structure of microorganism
• ability to recover from radiation injury

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Effect of Irradiation on Pathogens Population
(log10 CFU/g) - killed by
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Radiation resistance

• Deinococcus radiodurans is highly resistant to
  irradiation
• Acid resistant E. coli O157H7 exhibit radiation
  resistance
• Of pathogens tested in ground beef, C.
  jejuni has lowest resistance to irradiation
  Salmonella spp. has the highest resistance

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Typical radiation survival curves
Survivors
Time or Radiation Dose
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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 0.5-10 kGy
• 5 kGy will eliminate most spoilage organisms

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Radicidation

• Irradiation is applied to reduce the number of
  non-spore forming pathogenic microorganisms
  (other than viruses) and parasites
• Applied at dosage of 3.0-10 kGy
• Improves the hygienic quality of the food
• Reduces the risk of public exposure to pathogens

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Radappertization

• 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 25-60 kGy
• In the absence of post-processing contamination,
  no microbial spoilage or toxicity should occur
• Shelf stable without refrigeration

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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

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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)

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Shelf life extension of fresh meat
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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

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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.)

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Types of meat products approved for irradiation

• Mechanically deboned meat
• Intact or ground meat
• Hamburger
• Certain defatted beef or pork products

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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

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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

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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

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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 O157H7
  infections would be prevented for saved medical
  costs of 56 million to 138 million

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QUESTIONS?