JFS: Food Chemistry and Toxicology
Lipid Oxidation, Volatiles, and Color Changes in
Irradiated Raw Turkey Breast During Frozen Storage
ABSTRACT: Raw turkey breasts were aerobically or vacuum-packaged, irradiated with a linear accelerator, and
frozen for 0, 1.5, or 3 mo. Lipid oxidation, volatiles, color values, gas production, and oxidation-reduction potential of the samples were determined. Irradiation produced off-odor volatiles associated with lipid oxidation
and sulfur-volatiles; the off-odor was much higher in aerobic packaging. Volatiles increased with irradiation
dose, aerobic packaging, and storage time. Irradiation increased stable pink color with both aerobic and vacuumpackaging. Irradiation increased the production of carbon monoxide (CO) and reducing property, indicating
that CO-myoglobin could be responsible for the pink color. Lipid oxidation and color changes were not related in irradiated frozen turkey.
Keywords: irradiation, lipid oxidation, volatiles, color, frozen turkey
Introduction
I
RRADIATION IS AN EFFICIENT METHOD TO
inactivate spoilage and pathogenic microorganisms present in meat. Low doses
(< 10 kGy) of radiation can kill at least
99.9% of Salmonella and an even higher
percentage of Escherichia coli O157:H7 in
poultry meats (Olson 1998). When molecules absorb ionizing energy they become
reactive and form ions or free radicals that
react to form stable radiolytic products
(Woods and Pikaev 1994). The radiolytic
products are neither toxicologically
unique nor significant in the quantities
found in irradiated foods (Thayer 1990),
but they can influence several meat qualities.
Quality deterioration in irradiated
meat is associated with oxidative reactions
induced by free radicals and their derivatives. Free radicals produced by irradiation promote lipid oxidation and generate
characteristic off-odor in meats. Hashim
and others (1995) showed that irradiating
raw chicken breast and thigh produced a
characteristic bloody and sweet aroma
that remained after the thighs were
cooked, but was not detectable after the
breasts were cooked. Ahn and others
(2000a) reported that sulfur-containing
compounds, not lipid oxidation-dependent volatiles, were responsible for most
of the irradiation off-odor in frozen pork,
but the compounds volatilized quickly
during storage under aerobic conditions.
Irradiation produced new volatile compounds from oil emulsions containing
leucine, valine, isoleucine, phenylalanine,
© 2002 Institute of Food Technologists
jfsv67n6p2061-2066ms20010443-AF.p65
2061
methionine, or cysteine. This indicates
that radiolytic products of protein can
play an important role in off-odor generation of irradiated meat (Jo and Ahn 2000).
Irradiation also affects meat color. Radiolytic products can cause oxidation of
myoglobin as well as lipids, leading to discoloration (Murano 1995). Irradiation increased redness in poultry breast meat,
and the increased red or pink color was
stable during refrigerated storage (Millar
and others 2000). The reason red color increased in irradiated poultry breast is not
yet clear. Ahn and others (1998) reported
that the increase of redness in meat by irradiation varies depending upon species,
muscle type, irradiation dose, and packaging conditions. According to our preliminary study, irradiation of meat increased
reducing property and produced carbon
monoxide (CO). CO has strong affinity to
heme pigments and increases their intensity of red or pink color.
Lipid oxidation, volatiles, and color
changes have been determined in many
previous irradiation studies, but little information is available on those changes in
irradiated turkey white muscles, especially in the frozen state. The frozen condition can inhibit the transport of free radicals and slow down the oxidative
reactions inducing meat quality deterioration. Taub and others (1979) reported
that, with less mobility in the frozen state,
free radicals tend to recombine to form
the original substances rather than diffuse
through the food and react with other
food components.
The objectives of this study were to determine the effects of irradiation dose,
packaging, and frozen storage on lipid oxidation, volatiles, and color changes in irradiated frozen turkey breast and to elucidate the compounds responsible for the
characteristic off-odor and color changes
of irradiated frozen turkey breast meat.
The result of this study will be helpful for
poultry industry willing to use irradiation
technology.
Materials and Methods
Sample preparation
Turkey breast muscles (pectoralis major) were obtained from 50 turkeys slaughtered in the Meat Lab at Iowa State Univ.
The breast muscles from 8 turkeys were
pooled and used as a replication, and 4
replications were prepared. Breast muscles sliced into 3-cm-thick steaks (70 to 80
g each) and individually packaged in either polyethylene oxygen-permeable (4 ⫻
6 inches; 2 MIL; Associated Bag Co., Milwaukee, Wis., U.S.A.) or oxygen-impermeable vacuum bags (nylon/polyethylene,
9.3 mL O2/m 2/24 h at 0 ⬚C; Koch, Kansas
City, Mo., U.S.A.). Samples were irradiated
at 0, 2.5, or 5 kGy using a Linear Accelerator (Circe IIIR; Thomson CSF Linac, SaintAubin, France) with 10 MeV of energy, 10
kW of power level, and 95.5 kGy/min of
average dose rate. The max/min ratio was
approximately 1.25 for 2.5 kGy and 1.43 for
5 kGy. Alanine dosimeters were attached
to the top and bottom surfaces of a sample
and read using a 104 Electron Paramag-
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Food Chemistry and Toxicology
K.C. NAM, S.J. HUR, H. ISMAIL, AND D.U. AHN
Volatiles and color in irradiated frozen turkey . . .
Food Chemistry and Toxicology
netic Resonance Instrument (Bruker Instruments Inc., Billerica, Mass., U.S.A.) to
check the applied dose. The turkey breast
samples were stored in a dark freezer room
(-40 ⬚C) for 3 mo. Lipid oxidation, color, and
oxidation-reduction potential (ORP) of
meat samples were determined at 0, 1.5,
and 3 mo of storage and volatile compounds and gas production were determined at 0 and 3 mo. The samples at 0 mo
were also frozen (-40 ⬚C) for at least 3 h before analysis to compensate for the effect
of freezing and thawing.
Analysis of 2-thiobarbituric acidreactive substances (TBARS) values
Lipid oxidation was determined by the
TBARS method (Ahn and others 1998). A
minced sample (5 g) was placed in a 50mL test tube and homogenized with 15
mL deionized distilled water (DDW) using
a Brinkman Polytron (Type PT 10/35;
Brinkman Instrument Inc., Westbury, N.Y.,
U.S.A.) for 15 s at high speed. The meat
homogenate (1 mL) was transferred to a
disposable test tube (13 ⫻ 100 mm), and
butylated hydroxytoluene (7.2%, 50 ␮L)
and thiobarbituric acid/trichloroacetic
acid (20 mM TBA and 15% (w/v) TCA) solution (2 mL) were added. The mixture was
vortexed and then incubated in a 90 ⬚C
water bath for 15 min to develop color. After cooling for 10 min in cold water, the
sample was vortexed and centrifuged at
3000 ⫻ g for 15 min at 5 ⬚C. The absorbance of the resulting upper layer was
read at 531 nm against a blank (1 mL DDW
and 2 mL TBA/TCA solution). The
amounts of TBARS were expressed as mg
of malondialdehyde per kg of meat.
focused in a cryofocusing module
(-100 ⬚C) and then thermally desorbed
into a column for 30 s at 220 ⬚C.
An HP-624 column (7.5 m, 0.25 mm i.d.,
1.4 ␮m nominal), an HP-1 column (52.5 m,
0.25 mm i.d., 0.25 ␮m nominal; HewlettPackard Co., Wilmington, Del., U.S.A.) and
an HP-Wax column (7.5 m, 0.250 mm i.d.,
0.25 ␮m nominal) were connected using a
zero dead-volume column connector (J&W
Scientific, Folsom, Calif., U.S.A.) and used
for the volatile analysis. Ramped oven
temperature was used to improve volatile
separation. The initial oven temperature
of 0 ⬚C was held for 2.50 min. After that,
the oven temperature was increased to 15
⬚C at 2.5 ⬚C per min, increased to 45 ⬚C at
10 ⬚C per min, increased to 110 ⬚C at 20 ⬚C
per min, and then increased to 210 ⬚C at 10
⬚C per min and was held for 2.5 min at that
temperature. Constant column pressure
at 20.5 psi was maintained. The ionization
potential of the mass-selective detector
(Model 5973; Hewlett-Packard Co., Wilmington, Del., U.S.A.) was 70 eV and the
scan range was 18.1 to 350 m/z. Identification of volatiles was achieved by comparing mass spectral data of samples with
those of the Wiley library (Hewlett-Packard Co., Wilmington, Del., U.S.A.). Standards, when available, were used to confirm
the
identification
by
the
mass-selective detector. The area of each
peak was integrated using ChemStation
software (Hewlett-Packard Co., Wilmington, Del., U.S.A.), and the total peak area
(total ion counts ¥ 104) was reported as an
indicator of volatiles generated from the
meat samples.
Color measurement
Analysis of volatile compounds
A purge-and-trap apparatus (Precept II
and Purge & Trap Concentrator 3000; Tekmar-Dohrmann, Cincinnati, Ohio, U.S.A.)
connected to a gas chromatograph/mass
spectrometer (GC/MS; Hewlett-Packard
Co., Wilmington, Del., U.S.A.) was used to
analyze volatiles responsible for the offodor in samples (Ahn and others 2001). A
minced sample (3 g) was placed in a 40mL sample vial, and the vials were then
flushed with helium gas (40 psi) for 5 s to
remove oxygen from sample vials. The
maximum holding time of a sample in a
refrigerated (4 ⬚C) loading tray was less
than 4 h to minimize oxidative changes
during the waiting period before analysis.
The meat sample was purged with helium
gas (40 mL/min) for 14 min at 40 ⬚C. Volatiles were trapped using a Tenax column
(Tekmar-Dohrmann, Cincinnati, Ohio,
U.S.A.) and desorbed for 2 min at 220 ⬚C,
2062
CIE color values were measured on the
sample surface using a LabScan colorimeter (Hunter Associated Labs. Inc., Reston,
Va., U.S.A.) that had been calibrated
against a black and a white reference tile
covered with the same packaging materials used for samples. The CIE L- (lightness), a- (redness), and b- (yellowness)
values were obtained using an illuminant
A (light source). An average value from
both upper and bottom locations on a
sample surface was used for statistical
analysis.
Measurement of oxidationreduction potential (ORP)
A pH/ion meter (Accumet 25; Fisher
Scientific, Fair Lawn, N.J., U.S.A.) was
used to measure ORP. A platinum electrode filled with an electrolyte solution (4
M KCl solution saturated with AgCl) was
tightly inserted at the center of a meat
sample (about 100 g). To minimize the effect of air, the smallest possible pore was
made by a cutter before the insertion of an
electrode. To compensate for the effect of
temperature, a temperature-reading sensor was also inserted. ORP readings (mV )
were recorded at exactly 2 min after inserting the electrode into a sample.
Analysis of gas production
Minced meat sample (10 g, 1 to 2 mm
thick) was placed in a 24-mL wide-mouth
screw-cap
glass
vial
with
a
Teflon*fluorocarbon resin/silicone septum (I-Chem Co., New Castle, Del.,
U.S.A.). The vial was microwaved for 10 s
at full power to release gas compounds
from the meat sample. After 5 min of cooling at room temperature, the headspacegas (200 ␮L) was withdrawn using an airtight syringe and injected into a split inlet
(split ratio, 9:1) of a GC. A Carboxen-1006
Plot column (30 m ⫻ 0.32 mm i.d.; Supelco, Bellefonte, Pa., U.S.A.) and a ramped
oven temperature was used (50 ⬚C, increased to 160 ⬚C at 25 ⬚C/min). Helium
was the carrier gas at a constant flow of 2.4
mL/min. Flame ionization detector (FID)
equipped with a nickel catalyst (Hewlett
Packard Co., Wilmington, Del., U.S.A.) was
used as a detector and the temperatures of
inlet, detector, and nickel catalyst were
250, 280, and 375 ⬚C, respectively. Detector
air, H 2, and make-up gas (He) flows were
400, 40, and 50 mL/min, respectively. The
identification of gas compounds was
achieved using standard gases (CO; Aldrich, Milwaukee, Wis., U.S.A.; CH4 and
CO2; Praxair, Danbury, Conn., U.S.A.); and
a GC-MS (Model 5873; Hewlett Packard
Co., Wilmington, Del., U.S.A.). To quantify
the amount of a gas released, a peak area
(pA*s) was converted to a gas concentration (ppm) contained in the headspace (14
mL) of a 10-g meat sample compared to
the carbon dioxide concentration existing
in air (330 ppm).
Statistical analysis
A factorial design (2 packaging ⫻ 3 irradiation dose ⫻ 3 storage time) was
used to determine the effects of irradiation, packaging, and storage time on lipid oxidation, volatile compounds, color,
ORP, and gas production in turkey breast
during the frozen storage. Data were analyzed using SAS software (SAS Institute
Inc. 1995) by the generalized linear model procedure; Student-Newman-Keul’s
multiple range test was used to compare
the mean values. Mean values and standard error of the means (SEM) were reported (P < 0.05).
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Volatiles and color in irradiated frozen turkey . . .
Table 1—The TBARS of raw turkey breast with different packaging, irradiation
dose, and storage time at -40 ⬚C
TBARS values
Under frozen conditions, irradiation increased lipid oxidation in both vacuumand aerobically packaged raw turkey
breast during storage (Table 1). In aerobically packaged meat, irradiation increased
the TBARS values of turkey breast regardless of irradiation dose, but storage time
did not. Hydroxyl radicals formed from
water molecules in all meat conditions by
irradiation were reported to be site-specific because of their short half-life (10-6 sec)
(Gray and others 1996). Thus, the minimal
lipid oxidation detected in frozen turkey
after irradiation should be due to the limited mobility of free radicals in frozen
states. The changes of TBARS in vacuumpackaged turkey breast was inconsistent
with storage time, but the irradiated turkey breasts had higher TBARS values than
the nonirradiated at 1.5 and 3 mo of frozen storage.
Volatile compounds
The lipid oxidation expressed by
TBARS value did not differ much between
irradiated and nonirradiated meat samples, but production of volatiles did. Aliphatic hydrocarbons composed of not
more than 5 carbons were predominant
volatiles in raw turkey breast before storage (Table 2). Irradiation as well as packaging was a crucial factor influencing the
profiles of volatiles and their production
in raw turkey breast (p < 0.01).
In aerobically packaged turkey breast,
irradiation increased the amounts of volatiles found in nonirradiated samples. Sulfur (S)-containing volatiles are regarded as
major compounds responsible for the
characteristic off-odor in irradiated meats.
Acetaldehyde and dimethyl sulfide were
found in turkey breasts irradiated at both
2.5 and 5.0 kGy. However, dimethyl disulfide was found only in turkey breasts irradiated at 5 kGy. Ahn and others (2000b) reported that S-containing volatiles such as
2,3-dimethyl disulfide produced by radiolytic amino acids were responsible for
the off-odor in irradiated pork. They also
assumed that the off-odor volatiles in irradiated pork were the result of compounding effects of volatiles from lipid oxidation
and other reactions such as radiolysis of
amino acid side chains. Jo and Ahn (2000)
also found that 2,3-dimethyl disulfide was
produced from irradiated oil emulsion
containing methionine. There was a great
difference in the amount of S-containing
volatiles in turkey breast irradiated at 2.5
kGy and 5 kGy. Therefore, the production
Storage
0 mo
1.5 mo
3 mo
SEM
0
mg malondialdehyde/kg meat
Aerobic packaging
Vacuum-packaging
2.5 kGy 5 kGy SEM
0
2.5 kGy 5 kGy
SEM
0.33b
0.33b
0.37b
0.06
0.41a
0.42a
0.43a
0.04
0.46a
0.45a
0.45a
0.04
0.02
0.08
0.03
0.34x
0.32bx
0.27by
0.01
0.35y
0.38ax
0.34ay
0.01
0.38x
0.37ax
0.32ay
0.01
0.01
0.01
0.01
a, bValues with different letters within a row with same packaging are significantly different (p < 0.05)
x, yValues with different letters within a column are significantly different (p < 0.05)
Table 2—The volatile compounds of raw turkey breast with different packaging
and irradiation dose at 0 mo of storage at -40 ⬚C
Volatile
compounds
0
2-Methylpropane
0c
1-Butene
0c
Butane
85c
Acetaldehyde
0b
1-Pentene
0b
Pentane
1516b
2-Pentene
0
Propanal
0
2-Propanone
26287
Dimethyl sulfide
0b
1-Hexene
0
Hexane
0
2-Butanone
0
Dimethyl disulfide
0b
Total
27888
Aerobic packaging
2.5 kGy
5 kGy
SEM
584b
1933b
1226b
458ab
0b
5458a
0
0
24502
1727a
0
0
0
0b
35888
819a
2863a
2034a
890a
273a
5593a
0
0
22582
1720a
0
0
0
296a
37070
45
357
119
204
13
446
6698
165
51
8098
0
0c
0c
145c
0c
0c
3871
0b
0b
4761b
431b
0b
0b
0b
0b
9208c
Vacuum-packaging
2.5 kGy
5 kGy SEM
258b
807a
68
1806b
6152a 218
1303b
2727a 190
607b
1556a 289
289b
776a
60
6093
7282
725
0b
103a
35
0b
172a
57
31144ab 38036a 838
1392b
4096a
58
0b
345a
8
0b
444a
29
0b
2778a 261
31b
481a
66
41923b 65755a 2902
Total ion counts ⫻ 104
a-cValues with different letters within a row with same packaging are significantly different (p < 0.05)
of S-containing volatiles of turkey breast
meat at 0 mo, especially with vacuum
packaging, was highly irradiation dose-dependent.
In nonirradiated samples, vacuumpackaged turkey breast at 0 mo produced
less volatile compounds than aerobically
packaged (p < 0.01). After irradiation, on
the other hand, vacuum-packaged turkey
breast produced as much or more volatile
compounds than the aerobically packaged
(p < 0.05). The volatile species and their
amounts were very sensitive to irradiation
dose in both vacuum- and aerobically
packaged meats. Vacuum-packaged turkey
breasts irradiated at 5 kGy produced more
hydrocarbons, acetaldehyde, dimethyl
sulfide, and dimethyl disulfide than those
irradiated at 2.5-kGy. Propanal, a main lipid oxidation product was detected only in
turkey breast irradiated at 5 kGy. Sudarmadji and Urbain (1972) reported that the
threshold dose for irradiation odor was 1.5
kGy for turkey meat. The irradiation dosage, therefore, was an important parameter that determines the volatile profile and
its production.
After 3 mo of frozen storage, most volatiles existing at 0 mo increased and a few
volatiles were newly generated in aerobically packaged turkey breast (Table 3). 2Propanone content decreased drastically,
but the amount of total volatiles increased
after 3 mo of storage at -40 ⬚C. Irradiation
increased the amounts of most hydrocarbons and aldehydes in aerobically packaged turkey breast. Greater amounts of hydrocarbons
(1-butene,
1-pentene,
2-pentene, and hexane), short chain-aldehydes (acetaldehyde, propanal, and 2-methylpropanal) and a ketone (2-butanone)
were detected in turkey breast as the irradiation dose increased. Turkey breasts irradiated at 5 kGy produced 2-methylbutanal and 3-methylbutanal, but those
irradiated at 2.5 kGy did not. Two S-containing volatiles (methanethiol and methylthioethane) were newly generated in
aerobically packaged, irradiated turkey
breast after 3 mo of storage. Irradiated turkey breast had a considerable amount of
dimethyl disulfide, a representative offodor volatile in irradiated meat after 3 mo
of storage. Most of the S-containing volatiles produced by irradiation usually evaporated during the refrigerated storage under aerobic packaging conditions (Ahn
and others 2001). Thus, the aerobic pack-
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Food Chemistry and Toxicology
Results and Discussion
Volatiles and color in irradiated frozen turkey . . .
Table 3—The volatile compounds of raw turkey breast with different packaging
and irradiation dose at 3 mo of storage at -40 ⬚C
Food Chemistry and Toxicology
aging was more beneficial in reducing offodor during refrigerated storage. On the
contrary, the S-volatiles in frozen temperature did not decrease under aerobic conditions. A considerable amount of dimethyl disulfide increased in mainly aerobic
packaging at 3 mo.
Vacuum-packaged turkey breast was
more resistant to volatile production than
the aerobically packaged during the 3-mo
frozen storage (p < 0.01) (Table 3). The
amount of dimethyl disulfide in vacuumpackaged turkey breasts was only about
one-tenth of that in aerobically packaged.
Compared to the amount before storage,
dimethyl disulfide did not increase much
after 3 mo of frozen storage under vacuum
conditions. Acetaldehyde and 2-propanone were still predominant volatiles in
vacuum-packaged, irradiated turkey
breast at 3 mo. In conclusion, the exclusion of oxygen could inhibit or reduce the
volatile production responsible for the irradiation odor as well as total volatiles
during the 3 mo of frozen storage.
2-Methylpropane
1-Butene
Butane
Acetaldehyde
Methanethiol
1-Pentene
Pentane
2-Pentene
Propanal
2-Propanone
Dimethyl sulfide
2-Methylpropanal
Hexane
Butanal
Methylthioethane
2-Butanone
3-Methylbutanal
2-Methylbutanal
Dimethyl disulfide
Total
Development of pink color
Table 4—The CIE color values of raw turkey breast with different packaging, irradiation dose, and storage time at -40 ⬚C
The color values of frozen turkey breast
were compared for the effect of irradiation, packaging, and storage time (Table
4). Irradiation changed the color of raw
turkey breast to red or pink and the changes occurred evenly over the entire meat
samples. Irradiation increased redness (avalues) of turkey breast in an irradiationdose-dependent manner under both
packaging conditions, but vacuum-packaged turkey had higher redness than the
aerobically packaged (p < 0.05). The increased redness of irradiated turkey breast
was stable during the frozen storage. The
result agrees with the report that irradiated vacuum-packaged meat can develop a
fairly stable pink color in turkey breasts
(Lynch and others 1991). Although the
redness of nonirradiated turkey breast
also increased after the 3 mo of frozen
storage, irradiated turkeys still had higher
a-values than nonirradiated under both
packaging conditions. The color of vacuum-packaged, irradiated turkey breast
looked pinker at 3 mo than at 0 mo.
The irradiation effect on lightness (L-value) of turkey breast was inconsistent, but
gradually increased during the frozen storage under both packaging conditions.
Therefore, the pink color of irradiated turkeys after 3 mo of storage was more distinct
because of the increased L-value as well as
a-value. Irradiation did not affect the yellowness (b-value) of raw turkey breast in both
packaging conditions, but b-values also increased during the 3 mo of frozen storage.
2064
Volatile
compounds
Aerobic packaging
2.5 kGy
5 kGy
SEM
0c
497b
822a
0c
1704b
3152a
1072c
2033b
3230a
9577c 43924b 83204a
0c
2602b
4607a
0c
343b
607a
18012b 23083ab 31682a
0c
141b
314a
2916b
4092ab
6628a
10368
28440
23531
0b
612a
344b
c
b
147
1786
3881a
0
129
250
0c
358b
751a
0
0
142
0c
1097b
2509a
0
0
529
0
0
708
0b
2526a
2894a
b
a
42092 113367 169785a
56
142
279
4331
138
75
3236
19
841
5763
50
457
97
102
47
252
176
237
681
17483
0
0
0c
507b
989a
49
0c
1939b
4735a
579
798c
2306b
3471a
254
11862b 49189a 68277a 5580
0
0
0
0b
243b
569a
97
17611
20984
17677 5601
0
0
0
1311b
4761b
4588a
493
472b 21309a
2639b 3166
524
427
261
186
0b
809ab
1211a
290
0
0
0
0b
179a
0b
59
0
0
0
0
227
0
75
0
0
0
0
0
0
0b
341a
258a
31
b
a
a
33085 103703 103735 16411
Total ion counts ⫻ 104
a-cValues with different letters within a row with same packaging are significantly different (p < 0.05)
Storage
L-value
0 mo
1.5 mo
3 mo
SEM
a-value
0 mo
1.5 mo
3 mo
SEM
b-value
0 mo
1.5 mo
3 mo
SEM
0
Aerobic packaging
2.5 kGy
5 kGy
SEM
0
2064
Vacuum-packaging
2.5 kGy 5 kGy
SEM
51.7y
49.0ay
61.4x
1.3
49.0y
46.8by
58.8x
0.8
51.0y
47.8abz
57.7x
1.0
1.3
0.5
1.2
47.9y
48.1ay
53.1x
48.6y
45.6by
55.3x
0.9
48.6y
46.2abz
55.0x
1.1
1.0
0.6
0.9
0.5
3.2cz
4.6by
6.6cx
0.3
5.0by
6.0ay
9.0bx
0.3
6.5ay
6.7ay
10.3ax
0.4
0.4
0.2
0.3
3.0by
3.7by
8.4bx
0.3
6.2az
7.7ay
10.0ax
0.3
7.0ay
7.9ay
10.7ax
0.4
0.4
0.3
0.4
5.7z
8.5y
10.4bx
0.4
5.3z
7.5y
12.4ax
0.4
6.1z
8.3y
12.5ax
0.4
0.3
0.3
0.5
4.8z
6.1y
11.3x
0.3
4.9y
5.8y
11.2x
0.3
0.3
0.3
0.4
4.8z
6.2y
11.4x
0.4
a-cValues with different letters within a row with same packaging are significantly different (p < 0.05)
x-zValues with different letters within a column with same color value are significantly different (p < 0.05)
Oxidation-reduction potential
The oxidation status of heme iron and
the binding of a sixth ligand molecule to
heme pigment are main factors determining fresh meat color. Stronger reducing
conditions are needed for heme pigment
to bind a sixth ligand, which can impart
pink color in turkey breast. Irradiation decreased oxidation-reduction potential
(ORP) of turkey breast meat under both
aerobically and vacuum-packaged conditions (Table 5). Irradiation could provide
the turkey breast with strongly reduced
properties. The result indicated that the
ferric iron of heme pigments in irradiated
turkey breast might be converted to the
ferrous form by the aid of increased reducing properties. Swallow (1984) reported that hydrated electrons, radiolyzed
radicals produced by irradiation, could
act as a very powerful reducing agent, and
reacted with ferricytochrome and produced ferrocytochrome.
The ORP values increased with increasing storage time, which means more oxidizing opportunities increased. The increase was more severe in aerobically
packaged turkey breast, thus there was no
difference of ORP between irradiated and
nonirradiated samples after 3 mo of storage at -40 ⬚C. Color a-values in irradiated
turkey breast, however, were still higher
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Volatiles and color in irradiated frozen turkey . . .
Formation of CO-heme pigment
Among the gas compounds detected in
irradiated turkey breast at 0 mo (Table 6),
the amounts of CO and methane (CH4)
showed the irradiation dose-dependent
increases. CO has a strong affinity to heme
pigments and, thus, it can be a sixth ligand
of heme pigments. Fresh meat exposed to
low levels of carbon monoxide gas turned
to red color with the formation of COmyoglobin. Therefore, the CO produced
by irradiation could be the reason for red
or pink color in irradiated turkey breast.
The amount of CO in turkey breast decreased after 3 mo of storage at -40 ⬚C under both packaging conditions, but the decrease was greater under aerobic
conditions (P < 0.05). Greater increase in
redness was found mainly in vacuumpackaged than aerobically packaged, irradiated meats. Luchsinger and others
(1996) found that the increased red color
was more intense and stable under vacuum-packaging than aerobic conditions
during refrigerated storage. Nevertheless,
the distinct pink color of aerobically packaged, irradiated turkey breast can be attributed to the frozen state, which retarded the detachment of CO from heme
pigments and maintained the CO-heme
pigment complex during the storage. Only
one type of heme pigment, however, cannot explain all the color changes in irradiated, frozen turkey breast. More work is
needed to identify other ligand compounds or mechanisms that can contribute color changes in irradiated turkey
breast.
Lipid oxidation and color change
Renerre and others (1992) reported
that lipid and pigment oxidation are closely coupled, and lipid oxidation is a promoter of myoglobin oxidation. However, it
is not always possible to deduce whether
the pigment oxidation caused lipid oxidation. In this frozen meat study, lipid oxidation and color change in irradiated frozen
meat were not closely related (Table 1 and
4). Irradiation promoted reactions associated with lipid oxidation and off-odor production, and the reactions were more severe under aerobic than vacuum
conditions. However, the distinct red or
pink color produced by irradiation was stable and even increased during the frozen
Table 5—The oxidation-reduction potential (ORP) of raw turkey breast with different packaging, irradiation dose, and storage time at -40 ⬚C
Storage
0 mo
1.5 mo
3 mo
SEM
0
-23az
71x
28y
2
Redox potential (mV)
Aerobic packaging
Vacuum-packaging
2.5 kGy
5 kGy SEM
0
2.5 kGy
5 kGy SEM
-188by
66x
33x
16
-172bz
93x
14y
7
-71az
-5ay
35ax
8
13
9
7
-154bz
-32by
1bx
8
-201cz
-60cy
-9bx
5
a-cValues with different letters within a row with same packaging are significantly different (p < 0.05)
x-zValues with different letters within a column are significantly different (p < 0.05)
Table 6—The gas production of raw turkey breast with different packaging, irradiation dose, and storage time at -40 ⬚C
Storage
0
Aerobic packaging
2.5 kGy
5 kGy
Vacuum-packaging
2.5 kGy
5 kGy
SEM
0
2065
SEM
102
13
0cy
79cx
3
568bx
244by
43
917ax
380ay
36
16
13
13
1
0c
0c
0
139bx
43by
13
260ax
79ay
12
3
3
(ppm1)
Carbon monoxide
0 mo
0by
426ax
3 mo
56cx
172by
SEM
3
23
Methane (ppm1)
0 mo
0b
43ax
3 mo
0c
7by
SEM
0
3
Carbon dioxide (%1)
0 mo
3.1x
2.1x
3 mo
0.6y
0.7y
SEM
0.2
0.1
564a
257a
125
73ax
13ay
13
2.1x
0.8y
0.9
0.3
0.1
10.6bx
2.0y
0.3
13.1ax
2.7y
0.8
13.5ax
2.5y
0.4
0.5
0.2
1Gas concentration in 14 mL headspace from 10 g meat.
a-cValues with different letters within a row with same packaging are significantly different (p < 0.05)
x, yValues with different letters within a column with same gas are significantly different (p < 0.05)
storage regardless of packaging types. The
initial red or pink pigments formed by irradiation were stable against oxidative
changes during storage. Therefore, it
could be concluded that free radical species produced by irradiation promoted
lipid oxidation and volatile production,
but created reduced conditions for complex formation between radiolytic gas
(CO) and heme pigments. Woods and Pikaev (1994) also reported that the free radicals formed by irradiation might be divided into reducing (eaq-, H) and oxidizing
species (OH·, O 2-, and H 2O2). Therefore,
the major reactions in irradiated meats
can be dependent upon the type of meat
components reacting with free radicals.
Conclusions
I
RRADIATION PRODUCED OFF - ODOR BY
promoting lipid oxidation and producing radiolytic products of amino acids and
generated stable pink color by forming
CO-heme pigment complex in irradiated
frozen turkey breast. The off-odor produced by irradiation was more serious in
aerobically packaged, frozen-stored turkey breast. Thus, vacuum packaging will
be more beneficial in reducing off-odor for
frozen-stored turkey breast. Sensory eval-
uations are needed now to learn about
consumer response to the pink color of irradiated frozen raw turkey breast.
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Food Chemistry and Toxicology
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MS 20010443, Submitted 8/14/01, Accepted 10/11/01, Received 10/11/01
The authors are with the Animal Science Dept., Iowa State Univ., Ames,
Iowa 50011-3150. Direct inquiries to author Ahn (E-mail: duahn@
iastate.edu).
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