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Effects of Irradiation on Safety and Quality of Fresh-

cut Fruits and VegetablesPresented at the Fresh-Cut Workshop

UC DavisSeptember 17, 2008

Anuradha PrakashProfessor, Food Science

Chapman University

What is irradiationTypes of irradiationHow irradiation worksRegulationsIrradiation of fresh-cut fruits and vegetables

Effects on pathogensEffects on quality and nutrient content

Benefits and limitations

What is irradiationThe process in which the food is exposed to

predetermined levels of radiation energy with either a radioactive source, or

electron beams or x-raysForm of ionizing radiation

1 rad = 1 erg/g, 1 Gy = 1 J/kg or 100 rads, 1 kGy = 1000 Gy

The Electromagnetic Spectrum

Gamma Irradiation

Cobalt 60 and Cesium 137Demonstrated reliability, efficiency, safety Experience with large scale applicationsHigh penetration depthFairly good uniformity of dose

Electron beam irradiationMachine generated primary electrons accelerated to 99% speed of light to produce energies of 5, 7.5, or 10 MeV with beam power of upto 10 kW (higher power = higher thoroughput = lower unit cost)Limited penetration depth

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Electron beam unit X-ray

When electrons strike a metal plate, x-rays are generatedSame as gamma raysHigh penetration depthInefficient conversion of electron beam to x-rays (~8%)

Compton Effect

•Absorbed energy leads to ionization and excitation of atoms•Resultant low energy photon and ejected electrons cause further excitations and ionizations•These primary processes occur in 10-6 sec•Secondary processes: various reactions of primary species which result in ultimate molecular products

Irradiation: Mechanism of Action

Direct effectsDue to direct contact of high energy rays with specific molecule or cell e.g. DNA

Indirect effectsProduce ion pairs and free radicalsProduced mostly by products of water radiolysishydroxyl radicals .OH (strong oxidizing agent)solvated electrons e-

aq (strong reducing agent)hydrogen radicals .H (strong reducing agent)

Effect on microorganismsEffect on DNA and RNAEffect on structure of cell membrane

www.radiation-scott.org/radsource/4341-3.gif www.molecularexpressions.com

Effect on microorganismsMost pathogens have low toleranceSpores are more resistantD-value (irradiation dose necessary to destroy 1 log cycle) varies with productRecovery of organismsEffect on spoilage organisms

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Effect on microorganismsLogarithmic reductionD10 value: amount of radiation required to reduce the population of a specific bacterium by 90% (1 log cycle)Most bacterial pathogens have low tolerance

Sample D values(Molins, 2001. Food Irradiation)

0.190-5C, vacuum

Ground turkeyCampylobacter jejuni

2OystersHepatitis A

0.25AmbientBufferAspergillusglaucus

1.4AmbientBeef stewCl. botulinum

0.70AmbientGround beefS. enteritidis0.4912 CChickenL. mono

0.242-5CGround beefE. coli O157:H7

D10(kGy)TempMediumBacterium

D values of pathogens on lettuce (Niemira 2007. Data presented at the Irradiation Stakeholders meeting)

Internalized cells(Niemira IFT 2007)

0.37b0.12bGreen leaf

*Published D10 values, taken from Niemira et al. 2002. (1)Within a column, values with the same letter are not different (ANCOVA, P<0.05)

0.35a0.12bRed leaf

0.45b0.14aBoston

0.30a0.14aIceberg

InternalizedSurface*Lettuce type

E. coli O157:H7 D10 value, kGy

Inactivation of leaf-internalized E. coliO157:H7(Niemira, IAFP 2007)

Baby spinach Romaine lettuce

D values vary with bacterial strainSalmonella strains in diced tomatoes

01

2345

67

0 0.3 0.6 0.9 1.2

Irradiation dose (kGy)

log

CFU

/gm

Montevideo Hartford Cocktail

D=0.14 kGy

D=0.36 kGy

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Reduction of E. coli O157:H7 in Cilantro Irradiated at 1.4 kGy

0

2

4

6

8

No wash Water wash Chlorine Irradiation Chlorine +irradiation

log

cfu/

g

No Recovery RecoveryDay 6

Cilantro Effect of Irradiation on Background Microflora

Total Aerobic Plate Counts on Non-inoculated Cilantro Irradiated 1.4 kGy

0

2

4

6

8

No Wash Water Only Chlorine Only Irradiation Only C+I

Treatment

Log1

0 C

FU/g

D3

D6

Effect on quality

Appearance of spinach—non-irradiated (0 kGy, left) and irradiated (1 kGy, right)—after 14 days of storage at 4°C.Fan, Niemira, Prakash. 2008. Food Technology.

•Appearance and leakage•Texture•Color•Flavor and aroma•Wound response

•Respiration rate•Ethylene•Phenol biosynthesis

•Lipid oxidation•Cellular integrity

Fan and Sokorai 2005. Postharvest Biol. Technol. 36.

4.9b3.9aCelery

5.3b3.7aGreen onion

4.3a4.0aRed leaf lettuce

8.5a8.5aCarrots

8.0a7.8aAlfalfa sprouts

6.0a6.8aRomaine lettuce

6.9b5.0aSpinach

6.2a6.8aIceberg lettuce

6.2a5.5aCilantro

7.1b5.4aGreen leaf lettuce

7.6a6.2bParsley

6.5a5.8bEndive

8.2a8.4aRed cabbage

8.5a8.5aBroccoli

1 kGyControl Vegetables

Visual Quality of Non-irradiated (Control) and Irradiated (1 kGy) Fresh-cut Vegetables after 14 days storage at 4°C. 9 =excellent, 1=unusable.

Fan and Sokorai 2005.

Diced tomato texture

Control 0 kGy

Control 1 kGy

0.2% CaCl 0 kGy

0.2% CaCl 1 kGy

1% CaCl 0 kGy

1% CaCl 1 kGy

2% CaLac 0 kG

y

2% CaLac 1 kG

y

% F

irmne

ss

0

25

50

75

100

125

150

175

200

225Day 1 Day 8

5

Overall Visual Quality

02468

1012

0 5 10 15

Day

Scor

e

Control 1%CaCl2 IR(1kGy) IR+Ca

Effect on nutritional value

Folic acidThiamineVitamin CVitamin A (carotenoids)Vitamin E

69198199265Spinach

15.7343974Red leaf lettuce

157115538528Cilantro

855855902926Broccoli

1 kGy0 kGy1 kGy0 kGy

Day 14Day 1

Vitamin C content (µg/g fresh weight)Fan and Sokorai. J. Food Science. 2008.

RegulationsDefined as food additiveFDA has main regulatory responsibility, also USDA (FSIS and APHIS)Labeled with a radura (no size specification) and the words “Treated with irradiation” or “Treated by irradiation”Required for retail, finished products or foods destined for further processing, not required for minor ingredients

Food Irradiation - 21CFR § 179Fresh Pork 0.3 - 1.0 kGyFresh/frozen Poultry 3.0 kGy maxEnzyme preparations 10.0 kGy maxSpices, dehydrates 30.0 kGy maxFresh foods 1.0 kGy max

Control PestsMaturation Inhibition

NASA space food 44.0 kGy minFresh/frozen Red Meat 4.5 or 7.0 kGy maxEggs 1.5 kGyPet Feed <50.0 kGyReady-to-eat foods <10 kGy

Under reviewIceberg lettuce, spinach* 4 kGy

* For control of food borne pathogens and extension of shelf-life

PackagingFDA has approved 10 polymeric materials for irradiationIrradiation dose not to exceed 3 kGyPackaged food is irradiated in an oxygen free environment orFood is frozen and under vacuumSome additives used in packaging not approved

Process Optimization

% E

ffect

0

10

20

30

40

50

60

70

80

90

100

Maximum tolerance level for detriment

Minimum acceptable level for desired benefit

Process optimization may move dose response for detrimentProcess

optimizationmay improvedose response forbenefit

Dmax must be less than thisDmin must be greaterthan this

Acceptablerange

Dose

Dose responsefor beneficial effects

Dose responsefor detrimental effects

The illustrated Dmin and Dmax represent the ‘allowed’ range of dose. The ‘actual’ rangedelivered by the irradiator must fall within the ‘allowed’ range.

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BenefitsCold processFood can be processed in final package reducing risk of post-processing contaminationLeaves no residueCan be combined with other treatmentsApproved quarantine treatmentEnhances safetyIncreases shelf-life

Adoption of technologyCapital investment and per unit costsSpace requirements/maintenance/energy costsThroughput/batch sizePackage configurationsRegulatory approvalExtension of shelf-lifeConsumer attitudes