Meat Science 88 (2011) 184–188
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Meat Science
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m e a t s c i
Dose-dependent changes of chemical attributes in irradiated sausages
K.C. Nam a, E.J. Lee b, D.U. Ahn b,c, J.H. Kwon d,⁎
a
Department of Animal Science & Technology, Sunchon National University, Suncheon 540-742, Republic of Korea
Department of Animal Science, Iowa State University, Ames, IA 50010-3150, USA
c
Major of Biomodulation, Seoul National University, Seoul 151-742, Republic of Korea
d
Department of Food Science and Technology, Kyungpook National University, Daegu 702-701, Republic of Korea
b
a r t i c l e
i n f o
Article history:
Received 11 August 2010
Received in revised form 11 December 2010
Accepted 14 December 2010
Available online 23 December 2010
Keywords:
Sausages
Irradiation
Volatile compounds
Hydrocarbons
Dimethyl disulfide
Detection markers
a b s t r a c t
To determine the effects of irradiation on the chemical attributes of sausages, TBARS values, volatile
compounds, gaseous compounds, and hydrocarbons of vacuum-packaged sausages were analyzed during 60 d
of refrigerated storage. A sulfur-containing volatile (dimethyl disulfide), a gas (methane), and radiationinduced hydrocarbons (1-tetradecene, pentadecane, heptadecane, 8-heptadecene, eicosane, 1, 7-hexadecadiene, hexadecane) were mainly detected in irradiated sausages and the concentrations of these compounds
were irradiation dose-dependent with R2 = 0.9585, 0.9431, and 0.9091–0.9977, respectively. Especially
methane and a few hydrocarbons were detected only in irradiated sausages and their amounts were dosedependent. On the other hand, TBARS values, other off-odor volatiles (carbon disulfide, hexanal), and gases
(carbon monoxide, carbon dioxide) were found both in irradiated and nonirradiated sausages. Therefore, it is
suggested that radiation-induced hydrocarbons (1-tetradecene, pentadecane, heptadecane, 8-heptadecene,
eicosane, 1, 7-hexadecadiene, hexadecane), dimethyl disulfide, and methane can be used as markers for
irradiated sausages.
© 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved.
1. Introduction
Food irradiation is currently used in about 40 countries to improve
microbiological safety and shelf-life of food. The basic principle of food
irradiation is that the high energy electrons break water molecules in
biological materials and produce free radicals such as hydrated
electrons, hydrogen and hydroxyl radicals (Taub, 2001), which can
react with food components (fatty acids, proteins, or amino acids).
The free radicals generated by irradiation are the main compounds
that kill pathogenic microorganisms in foods and initiate various
chemical reactions causing potential quality changes in meat products
(Farkas, 2006; Nam et al., 2006; Thayer, 1990). Irradiation-induced
quality changes in meat products include color changes, production of
off-odors and acceleration of lipid oxidation (Ahn, 2002; Ahn, Olson,
Jo, Love, & Jin, 1999; Nam & Ahn, 2003).
The Food and Agriculture Organization of the United Nations, the
International Atomic Energy Agency, and the World Health Organization (FAO/IAEA/WHO) reported that low-dose irradiation at less
than 10 kGy presents no toxicological hazard and introduces no
special nutritional or microbiological changes; hence toxicological
testing of foods so treated is no longer required (WHO, 1981).
Nevertheless, some consumers are concerned about the reactions
⁎ Corresponding author. Tel.: +82 53 950 5775; fax: +82 53 950 6772.
E-mail address: jhkwon@knu.ac.kr (J.H. Kwon).
taking place in food products induced by irradiation and the
compounds produced, while others are looking for the safety margins
that irradiation can bring to their food products. The consumers'
concern, however, is making it difficult for the industry to practice
irradiation technology to achieve food safety benefits (Kwon, Kwon,
Nam, Lee, & Ahn, 2008). Delincee (2002) asserts that consumers
would want to know whether what they are eating is irradiated or not
and which dose was applied. To provide freedom to consumers to
choose the type of products they prefer informative labeling is
needed. Irradiation effectiveness depends on the dose provided to the
food (Arvanitoyannis, Stratakos, & Mente, 2009).For informative
labeling, however, markers to identify irradiated foods need to be
developed. When foods were irradiated free fatty acids and
triglycerides decompose to hydrocarbons (Cn − 1 and Cn − 2) and 2alkylcyclobutanones (Kim et al., 2004; Stevenson, 1992). The
radiolytic products of lipids have been used as markers to determine
whether food has been irradiated or not, they have also been applied
to estimate the absorbed dose (Boyd, Crone, Hamilton, & Hand, 1991;
Lee, Byun, & Kim, 2000).
Different types of meat products including sausages are approved
for irradiation to control microbial growth and to extend their shelflife in many countries. Although many studies to determine various
chemical reactions have been performed (Gadgil, Hachmeister,
Smith, & Kropf, 2002; Kwon et al., 2008), they have been focused
mainly on fresh rather than processed meat products. The reactions
induced by irradiation will be more complex in processed meats as
0309-1740/$ – see front matter © 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.meatsci.2010.12.023
K.C. Nam et al. / Meat Science 88 (2011) 184–188
185
Table 1
TBARS (mg malonaldehyde/kg) values of irradiated sausages during storage at 4 °C.
Storage
time
(day)
0
60
Irradiation dose (kGy)
0
2.5
5
10
0.56 ± k0.07by
0.81 ± 0.08bx
0.81 ± 0.10ax
0.80 ± 0.02bx
0.94 ± 0.06ax
0.89 ± 0.04abx
0.94 ± 0.04ax
0.97 ± 0.03ax
Regression
expressionn
Coefficient
(R2)
Y = 0.0349x + 0.66
Y = 0.0177x + 0.79
0.6902
0.9092
k
Mean ± standard deviation from 3 replications.
Y: TBARS, x: irradiation dose.
a,b
Means with the same superscripts in each row are not significantly different (p b 0.05).
x,y
Means with the same superscripts in each column are not significantly different (p b 0.05).
n
they contain many additives. Feasible and stable chemical parameters, which can be used as irradiation markers for processed
meats such as sausages, have not been fully developed, especially
during long-term storage.
The objective of the present study was to determine the impact of
irradiation on the production of radiation-induced chemicals, or
changes that can be used as tools for identification of irradiated
sausages. This study also aimed to determine the correlation
coefficients between irradiation dose and subsequent changes in
some chemical attributes during storage of sausages to assess their
dose dependency.
2. Materials and methods
2.1. Sample preparation
Commercial sausages (29% fat content) made with turkey and pork
(Oscar Mayer, Wieners) were purchased from a local market. The
packaged sausages were opened and then re-packaged in oxygenimpermeable nylon/polyethylene bags (9.3 mL O2/m2/24 h at 0 °C,
Koch, Kansas City, MO), and stored overnight at 4 °C before
irradiation. The samples were irradiated at 0, 2.5, 5 or 10 kGy using
a linear accelerator (Circe IIIR, Thomson CSF Linac, France) with
10 MeV energy, 10.2 kW power level, and an average dose rate of
107 kGy/min. To confirm the target dose, two alanine dosimeters per
sample cart were attached to the top and bottom surfaces of the
sample. The samples for 0 d were analyzed 12 h after irradiation and
the rest were stored at 4 °C for 60 d.
2.2. 2-Thiobarbituric acid reactive substances (TBARS)
Lipid oxidation was determined by the modified TBARS method of
(Jo & Ahn, 2000). Five g of sausages were weighed in a 50-mL test tube
and homogenized with 15 mL of deionized distilled water (DDW)
using a Polytron homogenizer (Type PT 10/35, Brinkman Instruments
Inc., Westbury, NY, USA) for 10 s at the highest speed. One milliliter of
the sausage homogenate was transferred to a disposable test tube
(13 × 100 mm), and butylated hydroxyanisole (7.2% in ethanol, w/v,
50 μL) and thiobarbituric acid/trichloroacetic acid (20 mM TBA/15%
TCA, 2 mL) were added. The mixture was vortex-mixed and then
incubated in a 90 °C water bath for 15 min to develop color. Then, the
sample was cooled in cold water for 10 min, vortex-mixed again, and
centrifuged for 15 min at 3000 ×g. The absorbance of the resulting
supernatant solution was determined at 532 nm against a blank
containing 1 mL of DDW and 2 mL of TBA/TCA solution. The amounts
of TBARS were expressed as milligrams of malonaldehyde per
kilogram of sausages.
2.3. Volatile compounds
A dynamic headspace analysis was performed using a vial
autosampler (Solatek 72 Multimatrix, Tekmar-Dohrmann, Cincinnati,
OH) and a Purge-and-Trap concentrator (3100, Tekmar-Dohrmann)
as described by Ahn et al. (1999). A gas chromatograph (GC, Model
6890, Agilent Technologies Co., Wilmington, DE) equipped with a
mass selective detector (MSD, Model 5973, Agilent Technologies Co.)
was used to qualify and quantify volatile compounds. Minced sample
(1 g) was transferred to a 40-mL sample vial, and the headspace was
flushed with helium (99.999% purity) for 5 s to minimize oxidative
changes during the period before analysis. Samples were purged
with helium (40 mL/min) for 15 min at 40 °C. Volatile compounds
were trapped using a Tenax/silica/charcoal column (Tekmar-Dohrmann),
focused in a cryofocusing module (−80 °C), and then thermally desorbed
into a GC column for 60 s at 220 °C. A modified column was used to
improve separation of volatiles. An HP-Wax (7.5 m, 250 μm i.d., 0.25 μm
nominal) column was combined with an HP-5 column (30 m, 250 μm i.d.,
0.25 μm nominal) using a Glass Press-fit connector (Hewlett Packard Co.).
A ramped oven temperature was used (7 °C for 2.5 min, increased to 25 °C
at 3 °C/min, to 120 °C at 10 °C/min, and to 200 °C at 20 °C/min). Liquid
nitrogen was used to cool the oven below ambient temperature. Helium
was the carrier gas at a constant column pressure of 20.5 psi. The
temperature of the transfer lines was maintained at 155 °C. The ionization
potential of the MS was 70 eV; the scanned mass range was 46.1 to 550 to
eliminate the carbon dioxide peak, and the scan velocity was 2.94 scan/s.
The identification of off-odor volatiles was achieved by comparing mass
spectral data with those of the Wiley/NIST-98 (5th ed., Agilent
Technologies Co.).
2.4. Gas compounds
Gases were analyzed by the modified method of Nam and Ahn
(2002). Minced sausage (10 g) was placed in a 24-mL screw-cap glass
vial with a Teflon*fluorocarbon resin/silicone septum (I-Chem. Co.,
New Castle, DE, USA). The vial was micro-waved for 10 s at full power
(1200 W) to release gases from the sample. After 5 min of cooling at
ambient temperature, the headspace (200 μL) was withdrawn using
an airtight syringe and injected into a gas chromatograph (HP 6890,
Hewlett Packard Co., Wilmington, DE, USA). A Carboxen-1006 Plot
column (30 m × 0.32 mm i.d., Supelco, Bellefonte, PA, USA) was used
to analyze the gases produced by irradiation in the sausages. The oven
temperature was 120 °C and helium was the carrier gas at a constant
flow of 2.4 mL/min. A flame ionization detector equipped with a
Nickel catalyst (Agilent Technologies Co., Wilmington, DE) was used,
and the temperatures of inlet, detector and Nickel catalyst (Agilent
Technologies Co.) were set at 250, 280 and 375 °C, respectively.
Detector air, hydrogen and make-up gas (He) flows were 400, 40 and
50 mL/min, respectively. The identification of compounds was
achieved using standard gases (CO, Aldrich, Milwaukee, WI, USA;
CH4 and CO2, Praxair, Danbury, CT, USA) and a GC/MS (Model 5873,
Agilent Technologies Co.). The area of each peak was integrated using
the Chemstation software (Agilent Technologies Co.). To quantify the
amounts of gases released, each peak area (pA*s) was converted to a
gas concentration (ppm) contained in the headspace (14 mL) of 10 g
samples using the concentration of CO2 in air (330 ppm).
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K.C. Nam et al. / Meat Science 88 (2011) 184–188
Table 2
Volatile compounds (total ion counts × 104) of irradiated sausages during storage at 4 °C.
Irradiation dose (kGy)
Dimethyl disulfide
Hexanal
Carbon disulfide
Storage time (day)
0
60
0
60
0
60
m
k
1974.33 ± 46.29az
2625.67 ± 67.93ay
2988.67 ± 47.96ax
7274.00 ± 87.00aw
Y = 1626.2x − 349.84
0.7595
1336.33 ± 71.77ax
2766.00 ± 162.25awx
2978.67 ± 196.17aw
3541.33 ± 155.64bw
Y = 682.77x+948.67
0.8824
–
–
–
–
10,748.00 ± 1173.38ax
16,102.33 ± 1277.86aw
18,368.67 ± 1437.28aw
12,012.00 ± 1374.16ax
Y = 605.83x+12,793
0.0487
16.67 ± 28.87az
127.00 ± 7.55by
170.00 ± 18.03bx
322.00 ± 9.00bw
Y = 95.899x − 80.83
0.9585
–
718.67 ± 58.29ax
1111.33 ± 73.51aw
989.00 ± 48.00aw
Y = 335.97x − 135.17
0.7596
0
2.5
5
10
Regression expressionn
Coefficient (R2)
k
Mean ± standard deviation from 3 replications.
Y: volatile production, x: irradiation dose.
Not detected.
a,b
Means with the same superscripts in each row are not significantly different (p b 0.05).
w-z
Means with the same superscripts in each column are not significantly different (p b 0.05).
n
m
2.5. Hydrocarbons
Hydrocarbons were analyzed by the modified method of the
European Committee for standard (1996). Five to eight g of sausage,
depending on fat content, were homogenized with 10 times their
volume of solvent (hexane, w/v) and 15 g of anhydrous sodium
sulfate in a centrifuge tube, kept overnight and then centrifuged at
2000 ×g for 20 min at 4 °C. The supernatant was collected and the
extraction solvent (hexane) was removed using a rotary vacuum
evaporator (Büchi, Switzerland) at 35 °C. The extracted fat was placed
in N2 filled vials, and stored at −20 °C. Separation of hydrocarbons
was performed on a florisil column (200 × 20 mm). One gram of
extracted fat was mixed with an internal standard (n-eicosane,
4 ppm), applied to the florisil column, and eluted with 60 mL hexane
at a flow rate of 3 mL/min. The eluted hexane was concentrated to
2 mL using a rotary vacuum evaporator and further concentrated to
0.5 mL using nitrogen gas. A gas chromatograph/mass spectrometer
(GC/MS; Agilent Technologies Co., Wilmington, DE, USA) was used to
analyze the hydrocarbons.
To identify the hydrocarbons, an HP-5MS column (30 m × 0.25 mm
i.d., 0.25 μm nominal, J & W Scientific, Folsom, CA, USA) was used.
Ramped oven temperature was used to separate hydrocarbons. The
initial temperature (60 °C) was increased to 170 °C at 25 °C/min, to
205 °C at 2 °C/min, and then to 270 °C at 10 °C/min. Constant column
flow (1.5 mL/min) was used and the inlet temperature was set at
250 °C. To analyze hydrocarbons, 2 μL of sample was injected in
splitless mode for 2 min and then the inlet was changed to split mode
(20:1). Hydrocarbons were identified by comparing retention time
and mass spectrum of peaks with authentic standards. Hydrocarbon
standards, including 1-tetradecene (C14:1), pentadecane (C15:0), 1-
hexadecene (C16: 1), 1, 7-hexadecadiene (16:2), heptadecane
(C17:0), 8-heptadecene (C17:1) and eicosane (C20:5), were purchased from TeLA (Berlin, Germany). The concentration of each
hydrocarbon in fat was determined using an internal standard. The
ionization potential of the mass selective detector (Model 5973;
Hewlett-Packard) was 70 eV, and the scan range was 30.1 to 350 m/z.
Identification of hydrocarbons was achieved by comparing retention
times and mass spectral data of samples with those of hydrocarbon
standards based on the Wiley library (Agilent Technologies). The
concentration of each hydrocarbon in the fat was determined using neicosane (4 μg/mL) as an internal standard.
2.6. Statistical analysis
The experiment was designed to determine the dose-dependent
changes of chemical compounds such as TBARS, volatiles, gases, and
hydrocarbons in irradiated sausages. Their changes during the storage
were analyzed independently by SAS software (SAS Institute, 2001).
Student–Newman–Keul's multiple range tests were used to compare
the differences of the mean values of treatments (p b 0.05). The
relationship between irradiation dose and each parameter was
evaluated using correlation coefficients.
3. Results and discussion
3.1. TBARS
Irradiation at 2.5 kGy or higher increased the TBARS values of the
sausages, but there were no significant differences among sausages
with different irradiation doses (Table 1). Many studies report that
Table 3
Gaseous compounds in irradiated sausages during storage at 4 °C.
Irradiation dose (kGy)
0
2.5
5
10
Regression expressionn
Coefficient (R2)
k
CO (ppm)
CH4 (ppm)
CO2 (mg/g)
Storage time (day)
Storage time (day)
Storage time (day)
0
60
0
60
0
60
k
75.33 ± 8.62az
101.67 ± 6.66ay
232.33 ± 13.32aw
165.67 ± 7.77ax
Y = 10.183x+99.198
0.3837
m
–
14.00 ± 1.00ay
39.67 ± 8.77ax
50.00 ± 7.81aw
Y = 5.1086x+3.4
0.9121
0.25 ± 0.03bx
0.27 ± 0.08bx
0.61 ± 0.19bw
0.43 ± 0.03bwx
Y = 0.0222x+0.2916
0.3102
35.77 ± 47.16aw
15.84 ± 1.01aw
26.68 ± 2.37aw
15.77 ± 1.18aw
Y = − 1.4773x+29.98
0.4277
3.63 ± 0.67 bz
7.20 ± 0.78by
14.97 ± 1.88bx
16.1 ± 1.00bw
Y = 1.2898x+4.832
0.8314
–
0.83 ± 0.12by
2.87 ± 0.59bx
4.10 ± 0.26bw
Y = 0.4261x+0.086
0.9431
Mean ± standard deviation from 3 replications.
Y: gas production, x: irradiation dose.
Not detected.
a,b
Means with the same superscripts in each row are not significantly different (p b 0.05).
w-z
Means with the same superscripts in each column are not significantly different (p 0.05).
n
m
–
0.35 ± 0.01az
0.82 ± 0.03by
1.34 ± 0.10bx
Y = 0.1352x
+0.036
0.9844
0.9977
Coefficient (R2)
Mean ± standard deviation from 3 replications.
n
Y: hydrocarbon production, x: irradiation dose.
m
Not detected.
a,b
Means with the same superscripts in each row are not significantly different (p b 0.05).
x-z
Means with the same superscripts in each column are not significantly different (p b 0.05).
k
0
–
0.43 ± 0.03az
1.17 ± 0.12ay
2.68 ± 0.23ax
Y = 0.2743x
− 0.13
0.9898
60
–
0.39 ± 0.07bz
0.84 ± 0.03by
1.55 ± 0.15bx
Y = 0.1557x=0.014
0
–
0.09 ± 0.02az
2.40 ± 0.11ay
3.74 ± 0.37ax
Y = 0.3747x
+0.168
0.9762
60
0.76 ± 0.12bz
0.83 ± 0.08bz
0.98 ± 0.06by
1.14 ± 0.08bx
Y = 0.0392x
+0.756
0.9832
0.87 ± 0.34az
0.96 ± 0.05az
1.25 ± 0.07ay
2.15 ± 0.17ax
Y = 0.1329
+0.726
0.9423
0
k
3.2. Volatile compounds
–
–
0.67 ± 0.04ay
1.74 ± 0.06bx
Y = 0.1866x
− 0.214
0.9429
60
187
irradiation promotes lipid oxidation in meats and meat products,
which were dependent on irradiation dose, packaging conditions, and
presence of antioxidants (Ahn et al., 1999; Jo & Ahn, 2000). However,
no significant differences between sausages with different doses were
found, indicating that TBARS values cannot be used to determine
irradiation dose applied to sausages.
After 60 d of refrigerated storage, the TBARS values did not
increase in the irradiated sausages, which can be attributed to the
anaerobic storage conditions of the samples. The TBARS increase in
non-irradiated sausages at 60 d was significant, but small. There was
little TBARS difference between non-irradiated and irradiated sausages at 60 d. Therefore, TBARS values cannot be used as an indicator
to determine irradiation dose, especially in vacuum-packaged meat
products. Other reports have indicated that irradiation accelerates
lipid oxidation in meat and meat products stored under aerobic
conditions (Nam & Ahn, 2003; Nam et al., 2007).
–
–
2.20 ± 0.07ay
5.72 ± 0.09ax
Y = 0.6135x
− 0.704
0.9408
0
60
–
0.18 ± 0.01az
0.99 ± 0.03ay
2.06 ± 0.13ax
Y = 0.217x
− 0.142
0.9728
–
0.04 ± 0.01az
0.16 ± 0.01by
0.72 ± 0.1bx
Y = 0.0745x
− 0.096
0.9091
0
–
0.05 ± 0.01az
0.87 ± 0.05ay
1.87 ± 0.06ax
Y = 0.2006x
− 0.18
0.9523
60
–
0.17 ± 0.01az
0.24 ± 0.01by
0.61 ± 0.04bx
Y = 0.0597x
− 0.006
0.9805
0
m
C17:1
C16:1
C16:2
C15:0
Storage period (day)
C14:1
Irradiation dose (kGy)
Table 4
Hydrocarbons (μg/g fat) in irradiated sausages during storage at 4 °C.
0
2.5
5
10
Regression expressionn
C17:0
60
K.C. Nam et al. / Meat Science 88 (2011) 184–188
Irradiation increased many of the volatiles found in non-irradiated
sausages and generated a few not found in non-irradiated samples
(Table 2). Although all the volatile compounds detected are not
described in the table, important new volatiles in the irradiated
samples include carbon disulfide, dimethyl disulfide, and dimethyl
trisulfide. Such sulfur-containing volatiles are mainly responsible for
the characteristic irradiation off-odor in irradiated pork (Nam et al.,
2007). Ahn (2002) reported that the sulfur-volatile compounds in
irradiated meat are produced by radiolytic degradation of sulfurcontaining amino acids such as cysteine and methionine.
Dimethyl disulfide, the most dominant sulfur volatile, was only
detected in irradiated sausages, and thus could be an excellent marker
to distinguish irradiated from non-irradiated sausages. Even though
there was no significant difference between 5 and 10 kGy treated
samples, dimethyl disulfide tended to increase with irradiation dose.
The production of sulfur volatiles in irradiated meats is highly
dependent on the conditions during storage, and these volatiles are
very volatile and disappear during aerobic storage (Nam & Ahn,
2003). Considerable amounts of dimethyl disulfide, however, were
still detected in irradiated sausages and the amounts were highly
dose-dependent (R2 = 0.9585) after 60 d of storage. The samples in
the present study were vacuum-packaged and then irradiated, and
thus the sulfur volatiles produced by irradiation remained inside the
pack during storage.
The most representative volatile compounds increased by irradiation were aldehydes and hexanal was the most dominant. Although
hexanal was detected in all the samples regardless of irradiation, the
amounts detected were highly dose-dependent. After 60 days, the
amounts of hexanal did not increase but were still dose-dependent. As
shown by the TBARS values, lipid oxidation did not progress
significantly during anaerobic storage. Therefore, TBARS values or
aldehydes cannot be considered good markers for irradiated sausages,
even though they tend to increase on irradiation irradiation.
3.3. Gas compounds
Carbon monoxide was detected both in non-irradiated and
irradiated samples and the amount produced tended to be dosedependent. After 60 days of storage, however, the amounts of carbon
monoxide increased in all samples and the dose-dependency
decreased (Table 3). Nam and Ahn (2002) reported the amount of
carbon monoxide decreased in aerobically packaged irradiated turkey
breast after 2 wk of storage and the production of carbon monoxide in
non-irradiated samples was attributed to microbial growth. On the
other hand, methane was found only in irradiated sausages in a dosedependent manner (R2 = 0.9431). The dose-dependent production of
methane was maintained during the 60 days of storage under vacuum
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K.C. Nam et al. / Meat Science 88 (2011) 184–188
conditions (R2 = 0.9121). Methane was not detected in non-irradiated
sausage at 60 days. The production of carbon dioxide was inconsistent
in all samples. Therefore, methane can be used as an irradiation
marker for sausages.
3.4. Radiolytic hydrocarbons
The fatty acids in the sausages were mainly C18:1 (33–38%),
followed by C18:2 (19–28%), C16:0 (18–21%) and C18:0 (7–9%), and their
compositions were not changed by irradiation (data not shown).
Similar results regarding fatty acid composition were reported by
Príncipe, Pérez and Croci (2009) for gamma-irradiated toothfish
samples. Two main types of hydrocarbons (Cn − 1 and Cn − 2, 1-ene)
are produced on irradiation (EN 1784, 1996). Hydrocarbons including
1-tetradecene (C14:1), pentadecane (C15:0), heptadecane (C17:0), 8heptadecene (C17:1), and eicosane (C20:5) were detected only in
irradiated sausages (Table 4). 1, 7-Hexadecadiene (C16:2) was found
only in sausages irradiated at N5 kGy. Hexadecene (C16:1) was
detected in non-irradiated samples but the amount increased with
irradiation dose. Comparable results were reported, using EN 1784
protocol, in irradiated dried Pollack (Kwon et al., 2004), seasoned
filefish (Kwon et al., 2007), and peanuts (Li et al., 2011). Boyd et al.
(1991) and Gadgil et al. (2002) found such radiation induced
hydrocarbon production in raw meats. Kim et al. (2004) found that
authentic fatty acids were decomposed at the α-carbon position by
irradiation and Cn − 1 hydrocarbons were formed in higher concentration than Cn − 2. Overall, the concentrations of hydrocarbons in
sausages increased linearly with irradiation dose up to 10 kGy, and
their profiles were not influenced by fat content.
The radiation-induced hydrocarbons decreased with storage, but
still were detectable after 60 days, resulting in very high correlation
coefficients (R2 = 0.9091–0.9977). These hydrocarbons from fatty
acids were not formed on cooking or oxidation, but only in irradiated
fat-containing foods (Kim et al., 2004; Nawar, Champagne, Dubravic,
& LeTellier, 1969; Stevenson, 1992). In general sausages have over 20%
fat, and thus hydrocarbons can be used as irradiation markers for
sausages.
4. Conclusion
Irradiation is an excellent tool to secure microbiological safety of
foods, but it is a complex process that impacts on the physicochemical
characteristics of the food. A sulfur-containing volatile (dimethyl
disulfide), a gas (methane), and radiation-induced hydrocarbons (1tetradecene, pentadecane, heptadecane, 8-heptadecene, eicosane, 1, 7hexadecadiene, hexadecane) were only detected in irradiated sausages,
and the concentrations of the compounds were dose-dependent. The
production of dimethyl disulfide, methane, and a few hydrocarbons was
highly dose-dependent (R2 = 0.9585, 0.9431, and 0.9091–0.9977,
respectively) and were detected in sausages irradiated at N2.5 kGy.
Therefore, methane, dimethyl disulfide and hydrocarbons are suggested
as specific markers of irradiation in sausages. On the other hand, TBARS,
off-odor volatiles (carbon disulfide, hexanal), carbon monoxide, and
carbon dioxide were found in non-irradiated as well as irradiated
sausages, in amounts that were not dose-dependent.
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