Mechanisms of Pink Color Formation in Irradiated Precooked Turkey Breast Meat
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JFS: Food Chemistry and Toxicology
Mechanisms of Pink Color Formation in
Irradiated Precooked Turkey Breast Meat
K.C. NAM AND D.U. AHN
ABSTRACT: Precooked turkey breast meat was aerobically packaged or vacuum-packaged and irradiated at 0, 2.5,
Food Chemistry and Toxicology
or 5.0 kGy. CIE color, reflectance, oxidation-reduction potential (ORP), gas production, and lipid oxidation were
determined at 0, 7, and 14 d. Irradiation increased redness of vacuum-packaged meat, and the redness was distinct
and stable under vacuum. Irradiation decreased ORP and produced carbon monoxide (CO). This indicated that the
pink color was caused by the heme pigment-CO complex formation. The reflectance of meat and the absorption
spectra of myoglobin solution supported the assumption that denatured CO-myoglobin is the pigment in irradiated
precooked turkey breast.
Keywords: irradiation, color, orp, co, precooked turkey breast
Introduction venting the color problem in irradiated duced by irradiation can be responsible
C OLOR IS THE MAJOR SENSORY ATTRIBUTE
determining consumer acceptance of
meat. The normally expected color for
cooked meat. Nanke and others (1998)
speculated that the pink color produced in
irradiated raw pork and turkey was in-
for the pink color forming in precooked
turkey breast.
Color changes in irradiated raw meats
cooked poultry breast meat is grayish duced by the formation of an oxymyoglo- have been reported in many irradiation
brown. Whenever cooked poultry breast bin-like pigment. Millar and others (1995) studies, but little information is available
meat shows pink or red color, consumers found that irradiated chicken breasts un- on the color changes of cooked meat. The
suspect that the meat is undercooked or derwent a definite change during irradia- increase of redness by irradiation in raw
contaminated. The pink defect in cooked tion from the usual brown/purple color to meats varies depending on species, mus-
meat could be produced by incompletely a more vivid red/pink color, and postulat- cle type, irradiation dose, and packaging
denatured myoglobin or oxymyoglobin, ed that the red/pink color might be a fer- environment (Ahn and others 1998a). No
reduced globin hemochromes of well- rous myoglobin derivative such as car- attempt, however, was made to elucidate
cooked meat, contamination with nitrite or boxy-myoglobin or nitric oxide-myoglobin the mechanisms of color changes and to
nitrate, or the absorption of combustion rather than oxymyoglobin. These studies, characterize the color compounds in irra-
gases such as nitric oxide (NO) or carbon however, were conducted with fresh meat, diated precooked meat. To identify the
monoxide (CO) (Cornforth and others and the identification and characteriza- pigment in irradiated precooked meat
1986). This pink defect should be focused tion of the pigments produced by irradia- would be important to establish methods
on poultry breast meat because it is more tion were not done. to control or modify the color in irradiated
susceptible to pink color formation than The denatured heme pigments in cooked meat.
highly pigmented beef in the presence of cooked poultry breast muscles are chemi- The objectives of this study were to de-
sodium nitrate (Heaton and others 2000). cally determined by the status of heme termine the effects of packaging and stor-
Irradiation is an excellent method to iron and the sixth ligand molecule at- age on pink color formation in irradiated
improve microbial safety of meat, but it tached to heme-iron. Ahn and Maurer precooked turkey breast and to elucidate
can have a negative effect on meat color, (1990a,b) reported that many ligands can the mechanism involved in the generation
especially that of cooked meat. Irradiated bind with denatured heme pigments and of color compounds responsible for the
raw chicken and turkey breast muscles that the binding of heme pigments with pink defect.
had increased redness and the increased ligands could increase the intensity of
pink color was stable during refrigerated pink color in oven-roasted turkey breast. Materials and Methods
storage (Millar and others 1995; Nanke For denatured heme pigments to impart a
and others 1998). The brown color of pink color in fully cooked meat, irradiation Sample preparation and
cooked meat can also be partially convert- should provide reducing conditions plus irradiation
ed to red by ionizing radiation. Hanson ligand molecule(s) with strong binding af- Pectoralis major muscles from 50 tur-
and others (1963) observed an objection- finity to the heme iron. Nam and Ahn keys were randomly grouped for 8 replica-
able red color in radiation-sterilized (2002) found that irradiation of raw turkey tions. The muscles were ground twice
cooked chicken meat in the absence of ox- breast decreased oxidation-reduction po- through a 3-mm plate and meat rolls (di-
ygen. Jo and others (2000) found a signifi- tential (ORP) and produced gas com- ameter 12cm, length 20cm) were pre-
cant increase in redness in cooked irradi- pounds that can act as a sixth ligand of pared. The rolls were then cooked in a
ated pork sausages. myoglobin. Therefore, we can hypothesize smoke house to an internal temperature
Identifying the pigment responsible that production of certain gas compounds of 75 8C. After chilling in running cold wa-
for the pink color is a prerequisite to pre- and increased reducing conditions in- ter for 1 hr, the rolls were sliced to 2.5-cm-
600 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 2, 2002 © 2002 Institute of Food TechnologistsColor of irradiated precooked turkey meat . . .
thick pieces, then aerobically repackaged a pH/ion meter (Accumet 25; Fisher Scien- mainly analyzed during the storage.
in polyethylene oxygen-permeable (4” 3 tific, Fair Lawn, N.J., U.S.A.). A platinum The method of Furuta and others (1992)
6”, 2-mil, Associated Bag Company, Mil- electrode filled with a 4M KCl solution sat- was modified to detect carbon-related gas-
waukee, Wis.,U.S.A.) or vacuum-packaged urated with AgCl was tightly inserted in es. Minced meat portions (10 g, 1 to 2 mm
in oxygen-impermeable bags (nylon/poly- the center of a meat sample. A small pore thick) was placed in a 24-mL wide-mouth
ethylene, 9.3 mL O2/m2/24 hr at 0 8C; was made by a cutter before the insertion screw-cap glass vial with a
Koch, Kansas City, Mo.,U.S.A.). After pack- of an electrode to minimize effect of oxy- Teflon*fluorocarbon resin/silicone septum
aging, the meat portions were irradiated gen in air. A temperature-reading sensor (I-Chem Co., New Castle, De., U.S.A.). The
using a Linear Accelerator (Circe IIIR; Th- was also inserted to compensate for the vial was microwaved for 10 s at full power to
omson CSF Linac, Saint-Aubin, France). temperature effect. ORP readings (mV ) release gas compounds from meat sample.
The target doses of irradiation were 0, 2.5, were recorded in exactly 3 min after the in- After 5 min cooling in room temperature,
and 5.0 kGy. The energy and power level sertion of an electrode to stabilize and the headspace-gas (200 mL) was withdrawn
used were 10 MeV and 10 kW, respectively, equilibrate the reaction between elec- using an air-tight syringe and injected into
Food Chemistry and Toxicology
and the average dose rate was 95.5 kGy/ trode and sample. a split inlet (split ratio 9:1) of a GC. A Car-
min. The max/min ratio was approximate- Lipid oxidation was determined by the boxen-1006 Plot column (30 m 3 0.32 mm
ly 1.28 for 2.5 kGy and 1.18 for 5.0 kGy. To method of thiobarbituric acid-reactive i.d.; Supelco (Bellefonte, Penn., U.S.A.) was
confirm the target dose, 2 alanine dosime- substances ( TBARS) measurement (Ahn used, and a ramped oven temperature was
ters per cart were attached to the top and and others 1998b). Minced meat (5 g) was programmed (50 8C, increased to 180 8C at
bottom surface of a sample. The alanine placed in a 50-mL test tube and homoge- 25 8C/min, increased to 200 8C at 508 C/
dosimeter was read using a 104 Electron nized with 15 mL deionized distilled water min). Helium was the carrier gas used at a
Paramagnetic Resonance Instrument (DDW ) using a Brinkman polytron ( Type constant flow of 2.4 mL/min. FID equipped
(Bruker Instruments Inc., Billerica, PT 10/35; Brinkman Instrument Inc., with a nickel catalyst (Hewlett-Packard Co.,
Mass.,U.S.A.). The irradiated samples Westbury, N.Y., U.S.A.) for 15 s at high Wilmington, Del., U.S.A.) was used and the
were stored at 4 8C for up to 14 d. During speed. The meat homogenate (1 mL) was temperatures of inlet, detector, and nickel
the storage, samples were exposed to a transferred to a disposable test tube (13 3 catalyst were set at 250, 280, and 375 8C, re-
light source (Philips, fluorescent 40W 100 mm) and butylated hydroxytoluene spectively. Detector (FID) air, H2, and
Cook White). Color value, reflectance (7.2%, 50 mL) and thiobarbituric acid/ make-up He gas flows were 400, 40, and 50
scanning, gas production, ORP, and lipid trichloroacetic acid (15 mM TBA/15% TCA) mL/min, respectively. The identification of
oxidation of the samples were determined solution (2 mL) were added. The mixture gaseous compounds was achieved using
at 0, 7, and 14 d of storage. was vortexed and then incubated in a standard gases and GC-MS (Model 5873;
90 8C water bath for 15 min to develop col- Hewlett-Packard Co.), and the area of each
Color measurement and or. After cooling for 10 min in cold water, peak was integrated by using Chemstation
reflectance scanning the sample was vortexed and centrifuged software (Hewlett-Packard Co.). To quanti-
The surface and internal CIE color L- at 3,000 3 g for 15 min at 5 8C. The result- fy the amount of a gas released, a peak
(lightness), a-(redness), and b-(yellow- ing upper layer was determined at 531 nm area (pA*sec) was converted to a concen-
ness) values of samples were obtained against a blank containing 1 mL DDW and tration (ppm) of gas in the headspace (14
(AMSA 1991) with a LabScan spectropho- 2 mL TBA/TCA solution. The amounts of mL) from 10 g meat compared to CO2 con-
tometer (Hunter Associated Labs., Inc. Re- TBARS were expressed as mg malondial- centration (330 ppm) in air.
ston, Va., U.S.A.) that had been calibrated dehyde per kg meat.
against a black and a white reference tile Absorption spectra of myoglobin
covered with the same packaging bags Analysis of gas compounds derivatives
used for samples. For the internal color Carbon monoxide (CO), nitric oxide To compare the reflectance minima of
measurements, the center of meat samples (NO), and hydrogen sulfide (H2S) gas stan- meat samples with absorption maxima of
was cut immediately before reading. An av- dards were purchased from Aldrich (Mil- natural and denatured myoglobin deriva-
erage value from 2 random locations on waukee, Wis., U.S.A.), and hydrogen (H 2), tives were prepared. Equine myoglobin
each sample surface was used for statistical methane (CH 4), and carbon dioxide (CO 2) (Sigma Chemical Co., St. Louis, Mo.,
analysis. Reflectance spectra were ob- from Praxair (Danbury, Conn., U.S.A.) to U.S.A.) was dissolved in 0.1 M citrate-
tained from the scanning mode of the Lab- identify gas compounds generated by irra- phosphate buffer (pH 6.0) to make 2 mg/
Scan spectrophotometer over the range of diation in meat samples. The standard gas- mL myoglobin solution. Myoglobin solu-
400 to 700 nm wavelength with an interval es were analyzed using a gas chromato- tion (3 mL) was placed in a wide-mouth
of 10 nm. Reflectance spectra at 7 days graph (GC, Model 6890; Hewlett-Packard screw-cap glass vial with a Teflon*fluoro-
were reported here. Illuminant source and Co., Wilmington, Del., U.S.A., USA) carbon resin/silicone septum. Half of the
other conditions were the same as in mea- equipped with either flame ionization de- samples were microwaved for 15 s to dena-
suring CIE color values. Data from 8 reflec- tector or thermal conductivity detector with ture the protein. The solution was convert-
tance spectra at each wavelength were av- or without a Nickel catalyst. A Supel-Q or ed to a reduced form by adding 200 mL so-
eraged by treatment and converted into a Carboxen-1006 Plot column (30 m 3 0.32 dium hydrosulfite (10% Na 2S2O 4).
reflectance curve using an Excel program mm i.d.; Supelco, Bellefonte, Pa., U.S.A.) Immediately after injection of the ligand
(Microsoft Corp., Seattle, Wash.,U.S.A.). was used to determine sulfur or carbon gas gas (3 mL; oxygen, carbon monoxide, or ni-
compounds, respectively. Among the gas tric oxide) into the pigment solution (using
ORP and lipid oxidation compounds detected in meat samples, the an air-tight syringe), the solution was
The method of Moiseeve and Corn- production of carbon monoxide, methane, scanned in the range of 400 to 700 nm us-
forth (1999) was modified to determine and carbon dioxide were irradiation dose- ing a spectrophotometer (Beckman DU
the change of ORP in meat samples using dependent. Thus, these carbon gases were 640; Beckman Instruments, Inc., Fuller-
Vol. 67, Nr. 2, 2002—JOURNAL OF FOOD SCIENCE 601Color of irradiated precooked turkey meat . . .
Table 1—CIE color values of precooked turkey breast meat with different pack- ported. Significance was defined at p
aging, irradiation dose, and storage 0.05. Pearson’s correlation coefficients be-
Aerobic packaging Vacuum packaging tween color values, irradiation dose, stor-
age time, ORP, CO, and TBARS within the
Storage 0 2.5 kGy 5.0 kGy SEM1 0 2.5 kGy 5.0 kGy SEM
same packaging environment were calcu-
Surface color lated.
L-value
0 Week 81.25 80.23 81.37 0.44 81.28 80.60 80.81 0.57
1 Week 80.73 80.87 80.92 0.55 81.33 80.97 80.60 0.79 Results and Discussion
2 Week 81.21 81.06 81.29 0.42 79.58b 80.61ab 81.52a 0.53
SEM 0.50 0.50 0.41 0.50 0.66 0.74 Color values
a-value Irradiation increased the redness (a-
0 Week 6.85x 7.39x 7.42x 0.21 7.24by 9.67ax 9.87a 0.29
value) of precooked turkey breast except
1 Week 6.25y 6.28y 6.86y 0.33 7.36cy 8.49by 9.76a 0.20
2 Week 6.06y 6.04y 6.43y 0.34 8.16bx 9.71ax 10.08a 0.19 for the surface color with aerobic packag-
Food Chemistry and Toxicology
SEM 0.28 0.29 0.32 0.20 0.26 0.23 ing ( Table 1). The increased redness was
b-value more distinct in vacuum than under aero-
0 Week 18.82 ay 18.54 ay 17.96by 0.18 19.07 ax 17.52b 16.99 bx 0.20 bic condition, and it was also greater in-
1 Week 18.57 ay 17.72 bz 17.58by 0.13 17.85 ay 16.69b 14.81cz 0.28
side than on the surface. With aerobic
2 Week 19.59x 19.43x 19.75x 0.24 19.10 ax 17.77b 15.98cxy 0.39
SEM 0.19 0.20 0.19 0.25 0.36 0.28 packaging, irradiation did not influence
Internal color the surface color of cooked turkey breast.
L-value The surface color was grayish brown re-
0 Week 83.98xy 83.82 82.99 0.78 84.36a 84.78a 81.49b 0.80 gardless of irradiation, and the a-values
1 Week 84.91x 82.66 82.84 0.66 83.50 84.01 81.39 0.94
2 Week 81.79y 82.16 81.85 1.03 82.79 82.41 82.98 0.59 decreased due to color oxidation during
SEM 0.77 0.93 0.80 0.69 0.77 0.89 storage. The pink color intensity of the in-
a-value side of cooked meat was stronger in irradi-
0 Week 8.09c 9.16bx 10.81ax 0.24 7.84cy 9.47b 12.40 ax 0.45 ated meat than the nonirradiated, and the
1 Week 8.56b 9.85ax 10.50ax 0.38 9.42bx 9.79b 11.55 ax 0.21 a-value was irradiation dose-dependent.
2 Week 8.48 7.84y 8.10y 0.46 7.04cy 8.82b 9.40ay 0.17
SEM 0.36 0.37 0.40 0.30 0.27 0.62 The pink color inside of aerobically pack-
b-value aged meat, however, mostly discolored to
0 Week 14.96x 15.88x 14.97x 0.29 15.65y 15.82x 15.94x 0.46 brown or yellow regardless of irradiation at
1 Week 14.58x 15.49x 15.39x 0.33 16.65x 15.86x 16.11x 0.48 2 weeks because of pigment oxidation.
2 Week 13.53y 14.12y 13.69y 0.36 13.82z 13.28y 12.75y 0.34
Under vacuum packaging, the in-
SEM 0.25 0.39 0.33 0.26 0.46 0.53
creased redness was irradiation dose-de-
1 Standard error of the means.
pendent both at surface and inside, and it
was stable during the storage. The in-
creased pink color was not occurred in any
Table 2—Oxidation-reduction potential (ORP) and TBARS values in precooked localized area, but was uniformly found
turkey breast meat with different packaging, irradiation dose, and storage throughout the meat. The result is consis-
Aerobic packaging Vacuum packaging tent with that of Luchsinger and others
Storage 0 2.5 kGy 5.0 kGy SEM1 0 2.5 kGy 5.0 kGy SEM (1991) who reported that increased red
color in irradiated pork was more intense
ORP (mV)
0 Week -19ay -49by -62by 6 -48ay -71ay -104by 8 and stable with vacuum packaging than
1 Week 102ax 68bx 75bx 7 -49ay -53bxy -50abx 7 aerobic conditions during refrigerated
2 Week 113ax 84bx 82bx 4 -18ax -41abx -59bx 8 storage. Satterlee and others (1971) re-
SEM 7 6 4 4 5 11 ported that the presence of air slightly in-
TBARS (mg malondialdehyde/kg meat)
0 Week 2.01y 4.09y 3.71z 0.39 1.49x 1.22 1.05 0.14
hibited the formation of red color in irradi-
1 Week 7.11x 9.43x 6.25y 0.80 1.88ax 1.27b 1.30b 0.08 ated bovine metmyoglobin solutions.
2 Week 6.91 bx 9.76ax 9.83ax 0.77 1.01y 0.93 0.98 0.08 Therefore, the red color formed by irradia-
SEM 0.51 0.90 0.60 0.12 0.07 0.09 tion produced in mainly anoxic conditions
1 Standard error of the means. and the pigment generated by irradiation
a,bDifferent letters within a row with same packaging are different (p , 0.05).
x-zDifferent letters within a column with same irradiation dose are different (p , 0.05). cannot be regarded as only an oxygen-re-
lated pigment.
The lightness (L-value) of precooked
turkey breast was not much different re-
ton, Ca., U.S.A.). The scanning interval mine the effects of irradiation, packaging, gardless of packaging, irradiation, and
was 1 nm and the experiments were repli- and storage time on color change, gas pro- storage time. Irradiation decreased the
cated 4 times. Absorbance data at each duction, ORP, and lipid oxidation in sam- surface yellowness (b-value) of precooked
wavelength were averaged and converted ples during the 14 d of storage. Data were turkey breast with both vacuum and aero-
into a graph using a spreadsheet program analyzed using SAS software (SAS 1985) by bic packaging. Regardless of irradiation, b-
(Excel, Microsoft Corp., Seattle, Wash., the generalized linear model procedure; value of aerobically packaged meat sur-
U.S.A.). the Student-Newman-Keuls’ multiple face increased, but that of the inside
range test was used to compare differenc- decreased with storage. The internal color
Statistical analysis es among means. Mean values and stan- a-values were higher than those of surface
The experimental design was to deter- dard error of the means (SEM) were re- whereas the internal color b-values were
602 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 2, 2002Color of irradiated precooked turkey meat . . .
lower than those of surface. This results ation. Irradiation and storage time did not TBARS values in aerobically packaged
show that the pigment inside the meat affect the lipid oxidation in vacuum-pack- meat partially explained the low a-values
was not fully denatured. aged meat. Although lipid oxidation was compared with the vacuum-packaged.
not directly related to the pink color of irra- Lipid oxidation proceeded along with pig-
ORP and lipid oxidation diated precooked turkey breast, the high ment oxidation during aerobically pack-
ORP and lipid oxidation (TBARS) were
determined to elucidate oxidative chang-
es in heme pigments of precooked turkey
breast ( Table 2). Irradiation decreased
ORP of precooked turkey breast in both
(a)
aerobic and vacuum packaging, but vacu-
um-packaged turkey breast had signifi-
cantly lower ORP value than the aerobical-
Food Chemistry and Toxicology
ly packaged at 0 wk. Cornforth and others
(1986) reported that hemochrome forma-
tion was promoted by reducing conditions
and prevented by oxidizing conditions.
Shahidi and others (1991) showed that ir-
radiation increased the reducing potential
of sodium ascorbate. We presume that ir-
radiation and anaerobic conditions can
provide heme pigments in meat with
strongly reducing environments. We also
believe that both undenatured and dena-
tured heme pigments in cooked turkey
may have been involved in heme-complex
formations (with ligands available under
the conditions), which will be important
for the pink color formation. Swallow
(1984) reported that hydrated electrons, a
radiolyzed radical produced by irradia-
tion, could act as a very powerful reducing
agent, and react with ferricytochrome to
produce ferrocytochrome. The decreased
ORP by irradiation in aerobically packaged
meat, however, was not low enough to pro- (b)
duce the distinct pink color.
The ORP increased faster under aerobic
than vacuum conditions during storage.
Within each packaging condition, however,
irradiated samples had lower ORP than the
nonirradiated during the storage. Vacuum
packaging maintained the decreased ORP
conditions produced by irradiation during
the 14 d of storage. The color of irradiated
meat was still pinker than nonirradiated
ones even after 14 d of storage under vacu-
um. The surface pink color generated by ir-
radiation was stable during the storage
with vacuum packaging. This indicated
that some compounds that can make the
sixth ligand of heme pigments were gener-
ated by irradiation.
TBARS values were not directly related
to the pink color generated by irradiation.
Irradiation and storage effects on lipid oxi-
dation were detected only in aerobically
packaged turkey breast. With aerobic
packaging, precooked irradiated turkey
breast had higher TBARS values than the
nonirradiated. The TBARS values of aero- Figure 1—Reflectance spectra of aerobically packaged precooked turkey breast
bically packaged meat increased with stor- meat as affected by irradiation dose at 7 days of storage (A, surface; B, in-
age and the increase was greater by irradi- side).
Vol. 67, Nr. 2, 2002—JOURNAL OF FOOD SCIENCE 603Color of irradiated precooked turkey meat . . .
Table 3—Gas production in precooked turkey breast meat with different pack- redness in meat with increasing cooking
aging, irradiation dose, and storage temperature results from progressive de-
Aerobic packaging Vacuum packaging naturation of pigments and the brown col-
or in cooked meat is occurred due to oxida-
Storage 0 2.5 kGy 5.0 kGy SEM1 0 2.5 kGy 5.0 kGy SEM
tion and denaturation of heme pigments
Carbon monoxide (ppm 2 ) (Judge and others 1989). Thus, for cooked
0 Week 220cx 319bx 456ax 16 227cx 370bx 575ax 12
1 Week 230bx 210by 261ay 22 154cy 336bxy 558ax 14 to maintain stable pink color, strongly re-
2 Week 134y 181y 227y 30 130cy 289by 450ay 18 ducing conditions are required. During
SEM 21 25 23 14 14 16 the storage, the amount of CO decreased
Methane (ppm) in aerobically packaged irradiated turkey
0 Week 5cy 13bx 26ax 1 4c 34b 67ax 1 breast. Most CO gas produced by irradia-
1 Week 9x 8y 9y 3 4c 29b 54ay 1
2 Week 8x 8y 7y 3 3c 26b 52ay 1 tion escape and/or dilute under aerobic
SEM 1 1 1 1 1 2 conditions. Under vacuum-packaged con-
Food Chemistry and Toxicology
Carbon dioxide (ppm) ditions, on the other hand, almost all the
0 Week 3483by 4029b 5041a 192 5970bx 7300abx 8732ax 417 CO formed by irradiation and the pink ir-
1 Week 3922y 3661 3983 258 6280bx 6632bxy 7967axy 384
radiation color remains in the meat, even
2 Week 8496x 3683 5961 1377 4874by 5841ay 6522ay 180
SEM 816 159 1155 294 285 477 after 14 d of storage.
1 Standard error of the means. Although small, the amounts of CH4 in-
2 Gas concentration in headspace (14 mL) from 10 g meat. creased with irradiation and it was more ir-
a-cDifferent letters within a row with same packaging are different (p , 0.05).
x-zDifferent letters within a column with same irradiation dose are different (p , 0.05). radiation dose-dependent than CO at 0
wk. Therefore, CH4 can be used as an indi-
cator for irradiation dose. Furuta and oth-
ers (1992) also reported that radiolytic CO
Table 4—Pearson correlation coefficientsa between color values and other fac- gas was detected in irradiated beef, pork,
tors in precooked turkey breast meat
and poultry meat. CO 2 was also detected
Aerobic packaging Vacuum packaging in meat in proportion to irradiation dose.
L–value a–value b–value L–value a–value b–value However, it cannot be used as an irradia-
Surface color tion indicator because it is commonly used
Irradiation dose –0.12 0.46 –0.38 –0.32 0.88** –0.87** as a gas mixture for modified atmosphere
Storage time –0.03 –0.83** 0.51 –0.32 0.05 0.12 packaging of meat. Seideman and others
ORP b 0.12 –0.88** 0.38 –0.41 –0.55 0.45 (1984) reported that CO2 was beneficial in
TBARS value 0.08 –0.70* 0.31 0.52 –0.77* 0.25 suppressing bacterial growth, but it in-
Carbon monoxide 0.06 0.85** –0.60 0.21 0.76* –0.73*
Internal color duced a grayish tinge in fresh meat,
Irradiation dose –0.19 0.40 0.12 0.05 0.80* 0.05 whereas CO2 gas had no significant effect
Storage time –0.64* –0.34 –0.76* 0.25 –0.40 –0.80* on the discoloration of the red color in irra-
ORP –0.55 –0.33 –0.55 0.26 –0.79* –0.39 diated precooked turkey breast.
TBARS value –0.53 –0.36 –0.50 0.33 0.12 0.71*
Carbon monoxide 0.07 0.69* 0.52 –0.55 0.88** 0.11
Reflectance spectra
a n = 72.
b Oxidation reduction potential. The reflectance spectra of aerobically
*Value with significant correlation (p , 0.05). packaged precooked turkey breast were
**Value with significant correlation (p , 0.01).
different on the surface than on the in-
side. On the surface of aerobically pack-
aged precooked turkey breast, irradiation
aged storage. sponsible for the pink color in irradiated did not affect the reflectance spectra (Fig-
Therefore, ORP of meat is better indi- precooked turkey breast. Watts and others ure 1A). The spectra did not show any
cator than TBARS values to express the re- (1978) reported that fresh raw meat ex- characteristic reflectance minima between
ducing conditions produced by irradia- posed to low levels of CO gas turned red 500- and 600-nm regions. Thus, the pig-
tion. Free radicals produced by irradiation color with the formation of CO-myoglobin, ments should consist mostly of denatured
promoted the lipid oxidation of precooked which is similar to the deep red color of metmyoglobin or hemichrome.
turkey breast meat, while generated a re- blood of persons poisoned by CO inhala- The inside of aerobically packaged
ducing condition for heme pigments in ir- tion. Irradiation generated CO in both aer- nonirradiated meat, however, had a reflec-
radiated meat. obically and vacuum-packaged meat, but tance minimum, while 5-kGy-irradiated
vacuum-packaged turkey breast showed meat had 2 distinct reflectance minima
Production of gas compounds more CO value than aerobically packaged. between 500- and 600-nm regions (Figure
Irradiation, as well as cooking, pro- The CO generated by cooking did not 1B). This indicated that the main pigment
duced carbon-containing gases such as influence the redness of nonirradiated in nonirradiated meat samples should be
CO, CH 4, and CO 2 (Table 3). The gases cooked turkey breast, but the CO pro- denatured reduced-heme pigment,
were also detected in nonirradiated meat duced by irradiation significantly in- whereas the pigments in irradiated ones
samples, but they increased proportional- creased the redness via the formation of would be denatured heme pigments with
ly with irradiation dose. CO is a strong field CO-heme pigment complex. The ORP of the sixth ligand occupied. The reflectance
ligand to heme pigments, whereas CH4 or nonirradiated cooked turkey breast was minima of irradiated precooked meat be-
CO2 is a very stable gas. Therefore, CO can too high for the heme pigments to form came shaper with increasing irradiation
form complexes with heme pigments re- complexes with ligands. Progressive loss of dose. Irradiated samples had higher re-
604 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 2, 2002Color of irradiated precooked turkey meat . . .
flectance values than the nonirradiated at reflectance spectra of irradiated meat reflectance minima at 550 and 570 nm in-
630- and 650-nm regions at which red col- were similar (Figure 2A and 2B). But nonir- side. Irradiated precooked turkey breast
or represents (AMSA 1991). radiated meat samples had a reflectance had 2 distinct reflectance minima at 540
Under vacuum, the surface and inside minimum at 550 nm on the surface and 2 and 565 nm. The wavelengths of reflec-
tance minima in 5-kGy-irradiated meat
samples were shorter than those of 2.5-
kGy-irradiated meats. Thus, irradiation
shifted the reflectance minima into short-
a) er wavelengths. The reflectance minima
were sharper with increasing irradiation
dose, and irradiated samples had higher
reflectance values than the nonirradiated
Food Chemistry and Toxicology
ones at the red color region, which provide
a strong color contrast. Tarladgis and
Ehtashan-Ud-Din (1965) reported that
the absorption maxima of both a- and b-
bands shifted to shorter wavelengths with
radiation, while that of Soret (400 nm)
band moved toward longer wavelength.
The shifted reflectance minima in irra-
diated precooked turkey breast were com-
pared with the absorption maxima of nat-
ural and denatured myoglobin derivatives
(Figure 3A and 3B). When reduced-myo-
globin solution was flushed with CO, O2, or
NO, the absorption minima of CO-myoglo-
bin (541, 577 nm) were positioned at
shorter wavelengths than those of oxy-
myoglobin (543, 580 nm) or NO-myoglo-
bin (547, 578 nm), respectively. The ab-
sorption spectra of denatured myoglobin
solution showed that O2 and NO gas could
little bind to denatured myoglobin where-
as CO had strong binding capability to the
b) denatured heme pigment (Figure 3B).
Therefore, CO detected in irradiated meat
samples can be considered as a sixth
ligand of denatured heme pigment, and
denatured CO-myoglobin can be suggest-
ed as a heme pigment responsible for the
pink color in irradiated vacuum-packaged
precooked turkey breast.
Correlation
Table 4 shows Pearson correlation coef-
ficients between CIE color values and other
factors in irradiated precooked turkey
breast. In vacuum-packaged precooked
turkey breast, the a-values of both surface
and inside were positively correlated with
the irradiation dose and the amount of CO
gas produced. Although significant correla-
tion between a-value and ORP was found
in only inside meat color, the increased a-
values by irradiation were highly correlated
with ORP of meat surface at 0 wk (r = -0.73).
Therefore, the increased a-values of irradi-
ated precooked meat with vacuum packag-
ing could be attributed to the decreased
ORP and the formation of heme pigment-
Figure 2—Reflectance spectra of vacuum-packaged precooked turkey breast CO complex. The result also showed that
meat as affected by irradiation dose at 7 days of storage (A, surface; B, in-
the pink pigment formed by irradiation
side)
was considerably stable against the oxida-
Vol. 67, Nr. 2, 2002—JOURNAL OF FOOD SCIENCE 605Color of irradiated precooked turkey meat . . .
tion during the storage. In aerobically Conclusions irradiation provides reducing conditions
packaged precooked turkey breast, the a-
value of meat surface was not affected by
irradiation because of oxidation.
T HE MECHANISM OF COLOR CONVERSION OF
precooked turkey breast meat by ion-
izing radiation can be explained as follows:
and produces CO to which heme pigments
can bind and increase the intensity of
pink color. Therefore, CO-heme pigment
can be a major color component responsi-
ble for the pink color in irradiated pre-
cooked turkey breast, and the pigment
formed was stable with vacuum packag-
a) ing. Nevertheless, CO-Mb alone cannot
explain all the irradiated meat color. More
precise and broader analytical techniques
are needed to identify and characterize
Food Chemistry and Toxicology
other specific heme compounds produced
by irradiation.
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