Food IrradiationCurrent Research and State of the Art

Brendan A. Niemira, Xuetong Fan, Christopher H. Sommers, Ignacio Alvarez

United States Department of AgricultureAgricultural Research Service Eastern Regional Research Ctr.

Wyndmoor, PA, USA

Food Irradiation• Overview and brief comparison of food

irradiation technologies• Research areas

– Microbiology of irradiated produce– Biofilms– Sensory and quality properties– Shell eggs and liquid egg products– Ready to eat meats and prepared meals– Toxicology

• Summary

Food Irradiation - Overview• Treatment of meats, seafood and produce with

high-energy particles (gamma, X-ray, E-beam)– inactivate insect pests– eliminate spoilage organisms and human pathogens– extend shelf life

• 60+ years of research by governments, industry and academia

• Irradiated food is safe, wholesome and nutritious• Endorsed by leading public health organizations

(WHO, USDA, FDA, FSIS, ADA, CDC, etc.)

How is food irradiated?• Product to be irradiated is handled with the same

care and attention to cleanliness as ever

• Irradiation is intended to complement, not substitute for, proper food handling procedures

• Product is exposed to high energy electrons or high energy photons, either on-site, or at another location– Contracting, shipment, transshipment add costs to

final product

Electron beam

X-rays

High-density metal target(must be cooled)

Gamma rays

Radioactive material:cobalt-60 or cesium-137

Technologies - Summary

Mode of Action• Largest target in organisms is water• High energy electrons break water molecules

into OH• and O• radicals, which disrupt membranes, proteins and nucleic acids

• DNA is also broken directly• High energy photons interact with atoms to eject

high energy electrons• Penetration of photons is much greater than for

electrons - implications for how material is processed

The Max/Min Ratio

Maximum dose

Minimum dose

(GROUNDBEEF

PATTIES)

The Max/Min Ratio

• Packaging is appropriate– complete penetration of e-beam

from above and below– relatively even dosage, low

Max/Min ratio

• Improper packaging & processing - too thick!– incomplete penetration of e-beam– uneven dosage, high Max/Min

ratio

Microbiology of Irradiated Produce

Response and efficacy• Lettuce

– D10 values on shredded iceberg lettuce• E. coli O157:H7: ~0.11 kGy• Salmonella: ~0.2 kGy (Goularte et al., 2004, Rad Phys Chem 71:155-

159)

– D10 values on green leaf lettuce• NalS E. coli O157:H7: ~0.18 kGy• NalR E. coli O157:H7: ~0.10-0.12 kGy (Niemira 2005. J. Food

Sci 79(2):M121-4)

– 5.5 kGy + chlorination 5.4 log reduction of E. coli O157:H7 (Foley et al., 2002. Rad Phys Chem 63:391-396.)

B. Niemira

B. Niemira

Post-irradiation phenomena• Endive

– L. monocytogenes regrew to control levels in storage following 0.42kGy (a 2 log10 reduction).

– Higher dose (0.84 kGy) suppressed the pathogen throughout the 19 d of the storage period (Niemira et al., 2003. J Food Prot 66:993-998.)

L. mono.

TAPC

B. Niemira

Post-irradiation phenomena• Respiration rates of most MAP vegetables are

not significantly affected by low dose irradiation– changes to packaging are not indicated

• Endive + MAP– Dose equivalent to 1-3 log10 reductions allowed

regrowth of L. monocytogenes– Irradiation + reduced-O2, enhanced-CO2 packaging

scheme effectively suppressed this capacity, and prevented the pathogen from regrowing. (Niemira et al., 2004. Rad Phys Chem 72(1):41-48.)

B. Niemira

L. mono. on endive: Irradiation + MAP

B. Niemira

• Phytoplane bacteria are biofilm associated• Biofilms protect against chemical and many

physical antimicrobial processes• Often requires 10x, 100x, 1000x exposure to get

equivalent kill• Planktonic and biofilm-associated Salmonella are

equally susceptible to irradiation (Niemira and Solomon. 2005. Appl. Environ. Microbiol. 71(5):2732-2736)

• Effect on structure? Attachment strength? Efficacy of co-applied antimicrobials?

Biofilms: the great unknown

B. Niemira

Irradiated biofilms

• Irradiation changes the internal structure of Salmonella biofilms– shifts in region of

highest density

– cell distributions

• Behavior of commensal & background microflora biofilms not known B. Niemira

• Response of other pathogen biofims• Complex microecologies

– mixed species biofilms of pathogens + commensal/phytoplane background organisms

– recovery, injury repair, regrowth, predation, competition?

• Synergy of multiple interventions

• Substrate effects

Biofilms: the great unknown

Sensory and Quality Attributes of Irradiated Foods

Dose Threshold and Endogenous Antioxidant Capacity of Fresh-cut Vegetables

0.3

0.6

0.9

1.2

1

2

Ele

ctro

lyte

leak

age

(%)

1

2

3

4

0

2

4

Radiation dose (kGy)

0 1 2 31

2

3

4

2

4

6

X Data

0

4

8

Ele

ctro

lyte

leak

age

(%)

0

2

4

0

4

8

12

0 1 2 30

3

6

Broccoli

Red cabbage

Parsley

Romaine lettuce

Iceberg lettuce

Spinach

Celery

Cilantro

Green onions

Carrots

X. Fan

X. Fan

Dose (kGy)

0 1 2 3

Vita

min

C (

g/g

)

30

60

90

120

Dose (kGy)

0 1 2 3Ant

ioxi

dant

s (

mol

/g)

2.00

2.25

2.50

2.75

3.00

Nutritional Quality of Alfalfa Sprouts Grown from

Irradiated Seeds

X. Fan

Effect of Ionizing Radiation on Sensory, Nutritionaland Microbiological Quality of Fresh-cut GreenOnions Leaves after 9 Days Storage at 3 °CDose(kGy)

Visual(9-1)

Texture(kg)

Aroma(5-1)

Decay(%)

MicrofloraLog (CFU/g)

0 7.2 a 25.1 a 3.1 a 12.7 ab 5.9 a1 7.4 a 24.0 a 3.3 a 8.3 c 4.0 b2 7.0 a 23.0 a 3.1 a 10.2 bc ND3 7.1 a 21.2 a 3.1 a 14.3 a ND

Means with same letters are not significant different (P<0.05).

X. Fan

Volatile Sulfur Compounds from Turkey Bologna Irradiated at 0 and at 3 kGy

min0 2.5 5 7.5 10 12.5 15 17.5 20 22.5

counts

200000

400000

600000

800000

1000000

1200000

AIB1 B, (C0W0K400.D)

min0 2.5 5 7.5 10 12.5 15 17.5 20 22.5

counts

200000

400000

600000

800000

1000000

1200000

AIB1 B, (C0W3K400.D)

0 kGy

3 kGy1

2 3 5

6

4

X. Fan

Irradiation-Induced malondialdehyde, formaldehdye, and acetaldehdye in Fresh Apple Juice

X. Fan

Irradiation and Heat Treatment of Whole and Liquid Eggs

Eggs and egg products are responsible for an estimated 230,000 cases of foodborne illnesses each year, resulting in economic losses and representing a consistent and serious obstacle to the well-being of consumers

Salmonella and mainly serovar Enteritidis is the leading cause of all egg-related foodborne illnesses

Ionizing radiation can inactivate Salmonella spp. in shell eggs and egg products.

Irradiation of eggs: background

I. Alvarez

WSE

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 0.5 1 1.5 2 2.5 3 3.5

Dose (kGy)

Log

N/N

oS. anatum

S. dublin

S. enteritidis

S. newport

S. senftenberg

S. typhimurium

Whole Shell Egg

137Cs irradiator, dose rate of 0.095 kGy/min, 4ºC I. Alvarez

IR Salmonella

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

0 0.5 1 1.5 2 2.5 3 3.5

IR dose (kGy)

Log

N/N

o

S. anatumS. dublinS. enteritidisS. newportS. senftenbergS. typhimurium

Liquid whole egg

137Cs irradiator, dose rate of 0.095 kGy/min, 4ºC I. Alvarez

Shell eggs

- US FDA Approves Irradiation of Shell Eggs 3.0 kGy (21 CFR Part 179, vol. 65, No. 141, p. 45280)

- Problem: Internal quality properties decreases with irradiation dose.

0 kGy 0.3 kGy 0.5 kGy

1.0 kGy 2.0 kGy 3.0 kGy

Will consumers accept IR shell egg? I. Alvarez

Egg products – LIQUID WHOLE EGG

- Heat pasteurization to obtain Salmonella-free LWE: 60ºC/3.5 min (FDA) (CFR 590.570, p. 765).

-Very heat resistant Salmonella serotypes

-More intensive treatments reduce LWE quality (57ºC – coagulation of some soluble proteins)

0

1

2

3

4

5

6

7

8

9

10

11

Salmonella Enteritidis Salmonella Senftenberg

Lo

g c

ycle

s o

f in

acti

vati

on

9 log FDA

(60ºC/3.5 min)

I. Alvarez

Egg products – LIQUID WHOLE EGG

- 3.0 kGy enables to reduce 9 log cycles population of Salmonella.

- However, doses > 1.5 kGy reduce LWE quality properties (color, off-flavor)

-HEAT followed by IRRADIATION – additive lethal effectnot available equipment for the industrial process

- IRRADIATION followed by HEAT- synergistic lethal effect- most viable immediate industrial option- available equipment for the industrial process

I. Alvarez

LWE

Holding tuve

Heat pasteurizer

Egg products – LIQUID WHOLE EGG

COMBINING TREATMENTS

IRRADIATION followed by HEATIRRADIATION followed by HEAT- synergistic lethal effect- most viable immediate industrial option: available equipment for the industrial

process S. senftenberg

0

1

2

3

4

5

6

7

8

1 kGy + 60C/3.5 min 1 kGy + 58.8C/3.5 min

Lo

g c

ycle

s o

f in

acti

vati

on

IR

HEAT

IR+HEAT

I. Alvarez

MODELIZATION OF THE COMBINING TREATMENTS

Salmonellainactivation= IR/0.67 kGy + Time/(299-9.8T+0.08T^2+4.4*IR+0.07*IR*T)

T: temperature (55 – 57ºC)

IR: irradiation dose (0.1 – 1.5 kGy)

Dotted and thick lines represents the TDT curves for Salmonella Enteritidis-Typhimurium and for Senftenberg, respectively.

Egg products – LIQUID WHOLE EGG - COMBINING TREATMENTS: IRRADIATION followed by HEATIRRADIATION followed by HEAT

Combinations time-temperature to inactivate 5 log of any Salmonella Enteritidis, Senftenberg or Typhimurium

I. Alvarez

55 56 57 58 59 600.0

0.5

1.0

1.5

2.0

Temperature ( C)

Lo

g1

0 T

ime

(min

)

S. senftenbergS. enteritidis – S. typhimurium

0.1 kGy0.3 kGy0.5 kGy1.0 kGy1.5 kGy

3.5 min

Irradiation + HeatSalmonella enteritidis

(A) Non-treated native cells

(B) subcultured cells after 1.5 kGy

(C) subcultured cells after 1.5 kGy and 55ºC/21 min

(D) subcultured cells after 1.5 kGy and 60ºC/2 min.

I. Alvarez

S. senftenberg

012

3456

789

10

111213

1 kGy + 60C/3.5 min 0.3 kGy + 57C/3.5 min

Lo

g c

ycle

s o

f in

acti

vati

on

IR

HEAT

IR+HEAT

IR+HEAT+ 0.5 mM CARVACROL

Egg products – LIQUID WHOLE EGG

COMBINING TREATMENTS - IRRADIATION followed by IRRADIATION followed by HEAT in LWE added with ADDITIVESHEAT in LWE added with ADDITIVES

- Nisin - Nisin + carvacrol- Carvacrol - EDTA + carvacrol- EDTA - EDTA + nisin- Sorbic acid - EDTA + nisin + carvacrol

I. Alvarez

Microbiological Safety of Irradiated Ready-To-Eat Foods

Irradiated Ready to Eat Meals• Reduction of pathogens in complex ready-to-eat

(RTE) foods– deli meats, assembled meals, sandwiches

• New challenge from a food safety standpoint– highly processed– typically eaten with little or no preparation– must have a low in-package risk profile

• Influences on efficacy– composition of meal– physical location of the contaminating bacteria

C. Sommers

0% SDA/0% PL - Palcam

Week

0 1 2 3 4 5 6 7 8

log

10

CF

U/g

123456789

10

0% SDA/0% PL - TSA

Week

0 1 2 3 4 5 6 7 8

log

10

CF

U/g

123456789

10

Proliferation of L. monocytogenes on beef fine emulsion sausage at 0. 1.5 and 3.0 kGy during 8 weeks refrigeratedstorage (9oC).

L. monocytogenes can proliferate following a radiation dose of 1.5 kGy, that provides a 2.5 log reduction, but not at 3.0 kGy, a 5 log reduction.

Sommers et al. 2003. J Food Prot. 66(11):2051-2056 C. Sommers

Proliferation of L. monocytogenes on beef fine emulsion sausage that contains sodium diacetate and potassium lactate at 0. 1.5 and 3.0 kGy during 8 weeks refrigerated storage (9oC).

0.15% SDA/2% PL - Palcam

Week

0 1 2 3 4 5 6 7 8

log

10 C

FU

/g

123456789

10

0.15% SDA/2% PL - TSA

Week

0 1 2 3 4 5 6 7 8

log

10 C

FU

/g

123456789

10

Use of 0.15% sodium diacetate and 2% potassium lactate prevents growth of L. monocytogenes and spoilage bacteria in combination with irradiation during long-term storage.Sommers et al. 2003. J Food Prot. 66(11):2051-2056

C. Sommers

Significant inactivation of hlyA was achieved only at radiation dose (>2 kGy) sufficient to achieve a 3-4 log reduction of the pathogen. Sommers et al. 2003. J Food Prot. 66(11):2051-2056

Radiation Dose (kGy)

0.0 0.5 1.0 1.5 2.0 2.5

% h

lyA

Ne

gativ

e C

olo

nie

s

0.00.51.01.52.02.53.03.5

Radiation Dose (kGy)

0.0 0.5 1.0 1.5 2.0 2.5Lo

g R

atio

Sur

v. (

N/N

o)

-5

-4

-3

-2

-1

0

D100.65 R2=0.97

How virulent is irradiated Listeria monocytogenes?

L. monocytogenes inoculated onto beef frankfurters, irradiated, and plated on blood agar to assess function of the hylA (hemolysin) virulence gene.

C. Sommers

Toxicological Safety of Irradiated Foods

Toxicological Safety

• Irradiated foods have tested exhaustively

• Numerous short-term, medium-term and long-term (multigenerational) animal feeding studies

• Chemical and biochemical analyses

• WHO determined in 1998 that foods treated at any dose posed no exceptional risk to consumers

• As chemical analysis methods improve, the debate on the toxicological safety of irradiated foods continues.

C. Sommers

Toxicological Safety

• IR induces changes in the chemistry of treated foods– formation of chemical byproducts, some of which are

known toxins

• Vast majority of radiolytic products are also found in unprocessed foods and in foods treated with conventional processing techniques

• Unique radiolytic products, i.e. chemicals byproducts which are only formed in foods by IR, have been a topic of recurrent attention.

C. Sommers

Toxicological Safety

• 2-alkylcyclobutanones (2-ACBs)• Generated at low levels in irradiated meats and

poultry• Observed to cause damage to DNA under certain

laboratory conditions• Most significant is 2-dodecylcyclobutanone (2-

DCB)

C. Sommers

H3C

CH2

CH2

CH2

CH2

CH2 CH2

CH2

CH2

CH2 CH2

CH2 CH2

CH2 CH2 OH

C

O

Palmitic Acid

H3C

CH2

CH2

CH2

CH2

CH2 CH2

CH2

CH2

CH2 CH2

CH2CH2

CH

CH2

C O2-DCB

• Produced by irradiation of fat containing foods.1

• 0.1 – 0.2 g/g of fat in meats. • Produced equivocal results for genotoxicity in the Comet Assay.2, 3

C. Sommers

Genotoxicity of 2-dodecylcyclobutanone (2-DCB)

• LeTellier and Nawar. (1972) Lipids. 1: 75-76.

• Delincee and Pool-Zobel. (1998) Radiat. Phys. Chem. 52: 39-42.

• Delincee et al. (1999) Lebensmittelbestralung 5. Deustche Tagung, Kahlruhe, Behichte der Bundesforcheshungsanstalt fur Ernarung. BFE-R—99-01. 11- 12 Nov. 1999, pp 262 – 269.

Toxicological Safety

• 2-dodecylcyclobutanone (2-DCB)– review of literature suggests that improper tests do

not allow any conclusions to be drawn(Smith and Pillai. 2004. Food Technology. 58 (11), 48-55.)

– analysis using more appropriate tests indicates no meaningful risk posed (Sommers and Mackay. 2005. J Food Sci. 70:C254-257)

• In vitro toxicology is one piece of information– accurate, appropriate tests are essential

• Many factors determine actual potential for risk

C. Sommers

Summary

• Irradiation has shown promise to improve the safety, sensory properties and shelf-life of a wide variety of foods

• An underutilized tool

• Consumer understanding, acceptance is key

• Challenge for processors and food scientists: derive benefits within limitations of technology– Singly or in combination with other treatments– Varying preparation methods, storage conditions, and

market forces

Resources for more information• IFT - Scientific Status Summary

– http://www.ift.org/publications/docshop/ft_shop/11-04/11_04_pdfs/11-04-sss-irradiation.pdf

• USDA’s Food and Nutrition Service– www.fns.usda.gov/fdd/foodsafety/irradiation

• CDC– www.cdc.gov/ncidod/dbmd/diseaseinfo/foodirradiation

• FDA– www.fda.gov/opacom/catalog/irradbro

• American Medical Association, National Food Processors Association, American Dietetic Association, many others

Resources for more information• USDA-ARS-ERRC Food Safety

Intervention Technologies Research Unit– Dr. Howard Zhang, Research Leader– http://www.arserrc.gov/www/fsit/

• Food irradiation group– Dr. Brendan A. Niemira

(bniemira@errc.ars.usda.gov)– Dr. Xuetong Fan – Dr. Christopher Sommers

USDA-ARS - Eastern RegionalResearch Center, Wyndmoor, PA