Transcript Effectiveness of Irradiation in Controlling Pathogens in Meats

Effectiveness of Irradiation in
Controlling Pathogenic and
Spoilage Microorganisms in
Meats
Catherine N. Cutter
Department of Food Science
Pennsylvania State University
Overview
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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
Effect of irradiation on
pathogenic and spoilage
microorganisms
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Biological effects of irradiation on
microorganisms
Factors affecting irradiation
effectiveness against microorganisms
Radiation resistance
Biological effects of
irradiation on microorganisms
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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)
Biological effects of
irradiation on microorganisms
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Irradiation can indirectly form
radiolytic products/free radicals from
water (oH, oOH)
• oOH radicals are responsible for 90%
of DNA damage
Effect of irradiation on
pathogenic and spoilage
microorganisms
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Biological effects of irradiation on
microorganisms
Factors affecting irradiation
effectiveness against microorganisms
Radiation resistance
Factors affecting irradiation
effectiveness against
microorganisms
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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
Factors affecting irradiation
effectiveness against
microorganisms
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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
Factors affecting irradiation
effectiveness against
microorganisms
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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
Factors affecting irradiation
effectiveness against
microorganisms
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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
Factors affecting irradiation
effectiveness against
microorganisms
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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
Effect of irradiation on
pathogenic and spoilage
microorganisms
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Biological effects of irradiation on
microorganisms
Factors affecting irradiation
effectiveness against microorganisms
Radiation resistance
Approximate doses of
radiation needed to kill
various organisms
Organisms
Higher animals
Dose (kGy)
0.005 to 0.10
Insects
0.01 to 1
Non-spore forming
bacteria
Bacterial spores
0.5 to 10
Viruses
10 to 200
10 to 50
Radiation resistance
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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
Effect of Irradiation on
Pathogens
Population (log10 CFU/g) - killed by :
pathogen
0.50 Gy 1.0 kGy 1.5 kGy 2.0 kGy 2.5 kGy
E.coli 0157
1.64
3.26
4.89
6.51
8.14
Salmonella
0.62
1.25
1.88
2.50
3.13
C. jejuni
2.13
4.26
6.38
8.51
10.64
L. mono.
0.82
1.64
2.46
3.28
4.10
S. aureus
1.10
2.21
3.11
4.42
5.12
Beuchat, Brackett and Doyle, 1993
Radiation resistance
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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
Typical radiation survival
curves
9
High Dose Radiation
8
7
Radiation Sensitive
6
Radiation Resistant
5
4
3
2
1
0
Time or Radiation Dose
Radurization
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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
Radicidation
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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
Radappertization
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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
Overview
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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
Effect of irradiation on
shelf life of fresh meats
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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
(kGy)
Beef
2.5
Untreated
shelf life
(days)
2-3
Irradiated shelf
life (days)
Beef top round
2.0
8-11
28
Beef burgers
1.54
8-10
26-28
Beef cuts
2.0
N/A
70
Corned beef
4.0
14-21
35
Pork loins
3
41
90
Ground pork
1
8
11.5
Lamb (Whole/minced)
2.5
7
28-35
9
Overview
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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
Types of meat products
approved for irradiation
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Refrigerated or frozen, uncooked
meat or meat byproducts
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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.)
Types of meat products
approved for irradiation
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Mechanically deboned meat
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Intact or ground meat
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Hamburger
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Certain defatted beef or pork
products
Overview
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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
Future research needs
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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
Future research needs
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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
Societal Benefits of
Irradiating Ground Beef
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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
QUESTIONS?