effects of irradiation on safety and quality of fresh-...
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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