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Introduction
• Food irradiation is a processing technique that
exposes food, usually pre-packaged to avoid
further contamination, to high-energy ionising
radiation
• Types of food irradiated:
Why irradiate food?
• Prolong shelf life by preventing food borne diseases
• Delay ripening and aging in fruit and vegetables
• Stop vegetables from germinating and sprouting
• Disinfect grain, dried fruit, nuts and vegetables by killing invading insects
• Improve re-hydration of foodstuffs
Irradiation and polymers
• Effect of irradiation on basic polymers has been studied e.g. polyolefins
C R
R
R
R
C
R
R
R
.O2
C OO
R
R
R
.
C OH
R
R
R
C C
H
H H
H
C OOH
R
R
Renergy
unstable
+ other hydrocarbons
C
R
R
R
C
R
R
R
+ other hydrocarbons
C
O
OHR
C
O
ORRC
O
HR
Irradiation and plastic packaging
• Foods are generally irradiated in their packaging to avoid further contamination
• Food packaging materials contain additives – Adhesives, inks, plasticisers, photoinitiators,
lubricants, catalysts, surfactants, antioxidants…...
• Irradiation of food packaging may pose problems not evident from studies on basic polymers
Project
• Analytical screening studies on irradiated
food packaging
– Investigate ‘finished’ plastic packaging systems
before and after irradiation
– Radiolytic products
• Identification
• Estimated quantification
– Effect on radiolytic products upon changing
irradiation parameters
• Irradiation type
• Irradiation dose
• Irradiation dose rate
Experimental set-up
• 15 materials selected to cover a range of:
– Plastic types
– Packaging types
– Foodstuffs
• Irradiation experiments
– Carried out by Synergy Health (formerly Isotron, UK)
– Scoping study
• Vials, caps and septa all tested first
• Dosimeters in empty vials to allow correction factors to be
calculated
Analytical screening of packaging
• Samples tested before and after irradiation
• Combination of techniques to allow detection
of a wide variety of compounds with different
chemical and physical properties
– Direct analysis by headspace GC-MS
– Solvent extraction followed by GC-MS and
LC-TOF-MS
Effect of irradiation - Identification
of compounds by GC-MS
PVC packaging dichloromethane extract
8.50 9.00 9.50 10.00 10.50 11.00 11.50 12.00 12.50 13.00 13.50 14.00
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
Time-->
Abundance
Library match to 2-decenal
30 40 50 60 70 80 90 100 110 120 130 140 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
m/z-->
Abundance
41
55
70
83
60
98
115 129 110
93 121 136 65 77
Control
Electron beam
Gamma
Peak formed upon irradiation
Effect of irradiation - Identification
of compounds by LC-TOF-MS
Control
Gamma
Electron beam
PVC packaging acetonitrile extract
6 x10
2
4
6
1 1
6 x10
2
4
6
1 1
6 x10
2
4
6
1 1
Counts vs. Acquisition Time (min)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Peak formed upon irradiation
Control
Gamma
Electron beam
Effect of irradiation - Identification
of compounds by LC-TOF-MS
5 x10
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Counts vs. Mass-to-Charge (m/z)
485 490 495 500 505 510 515 520 525 530
Formula Calculated
mass
Mass error
(ppm)
Score
C24H40O10 489.2694 0.18 96
506.2973
[M+NH4]+ 511.2526
[M+Na]+
527.2266
[M+K]+
489.2693
[M+H]+ – Software to carry out data
comparison and determine
statistical significance
e.g. MassProfiler (Agilent)
PVC packaging acetonitrile extract
Effect of irradiation – Potential
migration levels at 10 kGy
• PP tray
• Non-intentionally added substances (NIAS)
• Additional substances detected above level of
interest for NIAS
Number of peaks by HS-GC-MS prior to irradiation 16
Number of peaks affected by irradiation 8
Number of additional peaks after irradiation 4
Concentration range of peaks
formed after irradiation
(mg/kg in packaging) 0.1 - 200
(mg/kg)# 0.004 - 8
# Worse case migration assuming total transfer and using actual food/packaging ratio
Effect of irradiation – Summary
• Irradiation induced degradation of packaging
– Products from phosphite additives detected
– Plasticiser compounds present after irradiation
• Irradiation effecting polymer structure to allow easier
release
• Many more radiolytic products present by
GC-MS than LC-TOF-MS
• PVC, PE and PP largest number of radiolytic
products
Effect of irradiation type and
dose rate
• Gamma ray vs. electron beam (10 kGy)
– Quantities of oxidative compounds generally higher
by gamma irradiation
– Intense electron beam at higher dose rate reducing
oxygen levels so fast it cannot be replenished fast
enough by diffusion from surrounding air
• Dose rate – gamma irradiation at 0.4 kGy/hour
and 1.85 kGy/hour
– No major differences detected in the effects of any
substances (over a wide concentration range)
measured by any of the analytical techniques
Effect of irradiation dose – No change in concentration
PP packaging HS-GC-MS analysis
– Substance may
be radiolytically
stable
– Irradiation dose
may not be high
enough to induce
change
21.00 21.20 21.40 21.60 21.80 22.00 22.20 22.40 22.60
0
200000
400000
600000
800000
1000000
1200000
1400000
1600000
1800000
2000000
2200000
2400000
2600000
2800000
3000000
3200000
3400000
3600000
3800000
4000000
4200000
4400000
Time-->
Abundance
C13 alkane
10 kGy
3 kGy
1 kGy
7 kGy
Control
Effect of irradiation dose –
Decrease in concentration
13.00 13.50 14.00 14.50 15.00 15.50 16.00 16.50 17.00 17.50
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
Time-->
Abundance
10 kGy
3 kGy
1 kGy
7 kGy
Control
heptanal
PVC packaging HS-GC-MS analysis
– Compounds may
be breaking down
due to the high
energy irradiation
– Compounds may
be participating in
radiolytically
induced reactions
with other
compounds
9.00 9.50 10.00 10.50 11.00 11.50 12.00 12.50 13.00 13.50 14.00
0
1000000
2000000
3000000
4000000
5000000
6000000
7000000
8000000
9000000
1e+07
1.1e+07
1.2e+07
1.3e+07
1.4e+07
1.5e+07
Time-->
Abundance
Effect of irradiation dose –
Increase in concentration
PP packaging HS-GC-MS analysis
– Larger
compounds may
be breaking down
due to the high
energy irradiation
– Compounds may
be forming in
radiolytically
induced reactions
10 kGy – 211 mg/kg PP
3 kGy – 79 mg/kg PP
1 kGy – 27 mg/kg PP
7 kGy – 193 mg/kg PP
Control - ND
1,1-Diethoxy-ethane
Summary
• Analytical screening using state-of-the-art
technologies on ‘finished’ food packaging before and
after irradiation
– Radiolytic products detected
– Detection of substances indicative of breakdown of
packaging materials
– Estimated worse case migration concentrations for NIAS up
to 8 ppm
– Levels of oxidative compounds generally higher by gamma
irradiation
– Irradiation dose effects extent of radiolytic product
formation/loss
Acknowledgements
Fera
• Emma Bradley
• Nick Harmer
• Irene Leon
• Liam Lister
• Dennis Speck
• Laurence Castle
Food Standards Agency
• Funding for Project
A03068
• Edward Potter
Full details will be given
in the paper for the
conference issue of FAC
Thank you for your attention!
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