Effectiveness of Irradiation in Controlling Pathogenic

and Spoilage Microorganisms in Meats

Catherine N. CutterDepartment of Food Science

Pennsylvania State University

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

Biological effects of irradiation on microorganisms

Factors affecting irradiation effectiveness against microorganisms

Radiation resistance

Effect of irradiation on pathogenic and spoilage

microorganisms

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)

Irradiation can indirectly form radiolytic products/free radicals from water (oH, oOH)• oOH radicals are responsible for

90% of DNA damage

Biological effects of irradiation on

microorganisms

Biological effects of irradiation on microorganisms

Factors affecting irradiation effectiveness against microorganisms

Radiation resistance

Effect of irradiation on pathogenic and spoilage

microorganisms

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

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

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

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

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

Factors affecting irradiation effectiveness against microorganisms

Biological effects of irradiation on microorganisms

Factors affecting irradiation effectiveness against microorganisms

Radiation resistance

Effect of irradiation on pathogenic and spoilage

microorganisms

Approximate doses of radiation needed to kill

various organismsOrganisms Dose (kGy)

Higher animals 0.005 to 0.10

I nsects 0.01 to 1

Non-spore f ormingbacteria

0.5 to 10

Bacterial spores 10 to 50

Viruses 10 to 200

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

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

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

0

1

2

3

4

5

6

7

8

9

High Dose Radiation

Radiation Sensitive

Radiation Resistant

Typical radiation survival curves

Surv

ivors

Time or Radiation Dose

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

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

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

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

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)

Meat productDose(kGy)

Untreatedshelf life

(days)

I rradiated shelflife (days)

Beef 2.5 2- 3 9

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

Shelf life extension of fresh meat

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

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.)

Types of meat products approved for irradiation

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

products

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

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

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

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

QUESTIONS?