JFS:
Food Chemistry and Toxicology
Color, Oxidation-Reduction Potential,
and Gas Production of Irradiated Meats
from Different Animal Species
Y.H. K IM , K.C. N AM , AND D.U. A HN
Food Chemistry and Toxicology
ABSTRACT: Turkey breasts, pork loins, and beef loins were aerobically or vacuum-packaged and electron beamirradiated at 3 kGy. Irradiation increased the redness of turkey breast regardless of packaging or storage. Irradiation
drastically decreased the redness of aerobically packaged beef loin. Irradiated meats produced higher amounts of
CO and CH4 than nonirradiated. The oxidation-reduction potential (ORP) of meats decreased after irradiation, but
increased during the storage. Little differences in CO and ORP values among the irradiated meats from different
species were detected. This indicated that CO and ORP were not the only factors involved in the color changes of beef
loin by irradiation.
Keywords: irradiation, animal species effect, color, gas production, packaging
Introduction
M
EAT COLOR, PRIMARILY INFLUenced by the concentration and
chemical states of heme pigments of individual animals (Seideman and others
1984; Kropf 1993), is one of the most important quality attributes for consumer
acceptance. The color changes in irradiated raw meat differ significantly by animal
species (Nanke and others 1998, 1999).
Ahn and others (1998) showed that the increase of redness in irradiated pork varied
depending on muscle type, irradiation
dose, and packaging type. Millar and others (1995) also reported that irradiating
poultry meat increased the redness, which
was stable during the refrigerated storage.
The stability of meat color is closely related to the inherent oxygen consumption
rates, oxidation-reduction potential, metmyoglobin reducing capacity, and metmyoglobin reductase activity of muscles
(Reddy and Carpenter 1991; Kropf 1993;
Madhavi and Carpenter 1993; McMillin
1996). Nam and Ahn (2002) found that irradiation decreased the oxidation-reduction potential and produced carbon monoxide (CO) in turkey breast meat. Furuta
and others (1992) also detected CO production in irradiated frozen meats, and
suggested using radiolytic CO as a probe
for irradiated frozen meat and poultry.
Nam and Ahn (2002) reported that COmyoglobin is responsible for the development of pink color in irradiated poultry
meat, while Millar and others (1995) suggested that vivid pink/red or red/pink col-
1692
or of irradiated chicken breast meat might
be a ferrous myoglobin derivative, such as
carboxy-myoglobin or nitric oxide-myoglobin other than oxymyoglobin. All these
studies were focused mainly on poultry
meats because irradiation was permitted
only in poultry meats (Federal Register
1990) until red meats were approved in
1998. The irradiation doses permitted for
the effective safety of meat range between 1.5 and 3.0 kGy for poultry, 2.5 and
4.5 kGy for fresh red meats, and 4.5 and
7.0 kGy for frozen red meats.
The objective of this study was to determine the changes in color values, oxidation-reduction potential, and gas production in meats from different animal
species by irradiation.
Materials and Methods
Sample preparation
Turkey breasts, pork loins, and beef
loins were purchased from four local grocery stores. The meat blocks purchased
from each grocery store were treated as a
replication for animal species. The meats
were sliced to 3-cm-thick steaks and individually packaged in either polyethylene
oxygen-permeable packaging bags (4 ´ 6
in; Associated Bag Company, Milwaukee,
Wis., U.S.A.) or vacuum-packaging bags
(nylon/polyethylene, 9.3 mL O 2/m 2/24
hours at 0 °C; Koch, Kansas City, Mo.,
U.S.A.). The packaged meats were irradiated at 3 kGy using a Linear Accelerator Facility (LAF; Circe IIIR; Thomson CSF Linac,
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St. Aubin, France) with 10 MeV of energy
and 10 kW of power level at 93.5 kGy/min.
of average dose rate. The dose range absorbed by meat samples was 3.959 to
3.161 kGy (max/min. ratio was 1.25). Alanine dosimeters (Bruker Instruments Inc.,
Billerica, Mass., U.S.A.) were placed on the
top and bottom surfaces of a sample and
were read using a 104 Electron Paramagnetic Resonance Instrument (Bruker Instruments Inc., Billerica, Mass., U.S.A.) to
check the absorbed dose. The control (0
kGy) samples were exposed to ambient
temperature of the LAF while other meats
were irradiated. After irradiation, the irradiated and nonirradiated meat samples
were immediately returned to a 4 °C cold
room and stored for 7 days. Color, ORP values, and gas production of meat samples
were determined at 0 and 7 days of storage.
Color measurement
CIE (Commission Internationale de
l’Eclairage) color values were measured on
the surface of meat samples using a LabScan colorimeter (Hunter Associated Labs.
Inc., Reston, Va., U.S.A.) with an 1.225-cm
aperture using an illuminant A. The colorimeter was calibrated against a black and
a white reference tile covered with the
same packaging bags used for samples.
The color L* (lightness), a* (redness), and
b* (yellowness) values were obtained using a setting of illuminant A (AMSA 1991).
An average value from 2 random locations
on each sample surface was used for sta© 2002 Institute of Food Technologists
7/10/2002, 9:00 AM
Table 1—CIE color L* values of turkey, pork, and beef with different irradiation, packaging, and storage time.a
Storage
(day)
Turkey
0 kGy
3 kGy
Aerobic packaging
0
47.76a
7
47.84a
SE
0.87
Vacuum-packaging
0
47.80 ax
7
46.04 ay
SE
0.58
Pork
Beef
3 kGy
0 kGy
3 kGy
0 kGy
SE
48.30a
46.41a
0.72
46.47a
47.62a
0.92
46.30a
48.02a
1.15
41.87b
43.99a
1.18
42.55 bx
36.10 by
1.22
1.03
1.02
47.96 ax
46.15 ay
0.58
46.60a
46.92a
1.10
45.30a
46.46a
1.18
36.86b
39.75b
1.28
39.41b
39.46b
1.79
0.95
1.34
a Different letters (a, b) within the same row are significantly different ( P < 0.05). n = 4.
Different letters (x, y) within a column of the same packaging are significantly different ( P < 0.05).
SE = standard error of the means.
Table 2—CIE color a* values of turkey, pork, and beef with different irradiation, packaging, and storage time.a
Storage
(day)
Turkey
0 kGy
3 kGy
Aerobic packaging
0
3.74e
7
3.53d
SE
0.26
Vacuum-packaging
0
2.71dy
7
4.11ex
SE
0.22
Pork
Beef
3 kGy
0 kGy
3 kGy
0 kGy
SE
4.99d
5.58c
0.19
6.82c
7.40c
0.46
6.93c
6.24c
0.38
24.90 ax
15.00 ay
0.95
10.40 by
19.77 bx
0.57
0.33
0.67
6.03cy
7.72cdx
0.45
5.37c
6.87d
0.51
6.74cy
8.64cx
0.48
19.15 ay
20.30 ax
0.26
15.09 by
17.20 bx
0.62
0.43
0.47
a Different letters (a-e) within the same row are significantly different ( P < 0.05). n = 4.
Different letters (x, y) within a column of the same packaging are significantly different ( P < 0.05).
SE = standard error of the means.
Table 3—CIE color b* values of turkey, pork, and beef with different irradiation, packaging, and storage times.a
Storage
(day)
Turkey
0 kGy
3 kGy
Aerobic packaging
0
6.43dy
7
8.90bx
SE
0.60
Vacuum-packaging
0
5.96b
7
5.58c
SE
0.54
Pork
0 kGy
6.94cdy
8.35cy
9.47bx 11.09 bx
0.26
0.46
5.76b
6.11c
0.44
6.55by
8.68bx
0.54
3 kGy
0 kGy
Beef
3 kGy
SE
8.25cy
10.63 bx
0.76
21.03a
19.26a
0.64
14.21 by
20.99 ax
0.66
0.48
0.68
4.87by
8.22bx
0.49
10.83 ay
13.56 ax
0.45
9.46ay
12.33 ax
0.67
0.50
0.55
a Different letters (a-d) within the same row are significantly different ( P < 0.05). n = 4.
Different letters (x, y)within a column of the same packaging are significantly different ( P < 0.05).
SE = standard error of the means.
tistical analysis. To determine the overall
color changes by irradiation, a numerical
total color difference (DE) was calculated
using the following equation:
DE = [(L* ir - L* nonir)2 + (a* ir - a* nonir)2 +
(b*ir - b* nonir)2]1/2
Oxidation-reduction potential
(ORP) measurement
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
saturated with AgCl) was tightly inserted
into the center of the meat block sample
(100 g). To minimize the effect of air, the
smallest possible pore was made by a cutter before inserting the electrode. A temperature-reading sensor was also inserted
to compensate for the effect of temperature. ORP readings (mV ) were recorded at
exactly 2 min. after inserting the electrode
into a sample.
vial was microwaved at 1.55 kW for 10 s to
release gas compounds from the meat
sample. After 5 min of cooling in an ambient temperature (22 °C), the headspace
(200 mL) was withdrawn using an airtight
syringe and injected into a split inlet (split
ratio, 9:1) of a GC (HP 6890, Hewlett Packard Co., Wilmington, Del., U.S.A.). A Carboxen-1006 Plot column (30 m ´ 0.32-mm
i.d.; Supelco, Bellefonte, Pa., U.S.A.) was
used and a ramped oven temperature was
programmed (initial temperature, 50 °C;
increased to 160 °C at 25 °C/min). Helium
was the carrier gas at a constant flow of 2.4
mL/min. A flame ionization detector (FID)
connected to a nickel catalyst (Hewlett
Packard Co.) was used, and the temperatures of inlet, detector, and nickel catalyst
were set at 250, 280, and 375 °C, respectively. Detector (FID) air, hydrogen, and
make-up gas (He) flows were 400, 40, and
50 mL/min, respectively. The identification of gaseous 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
(GAS CHROMATOGRAPH-MASS SPECTROGRAPH) (Model 5873; Hewlett Packard Co.). The area of each peak was integrated by using Chemstation software
(Hewlett Packard Co.). 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 10-g meat samples, compared
with the CO2 concentration existing in air
(330 ppm).
Statistical analysis
The experiment was designed to determine the effects of irradiation, packaging,
and storage time on color, ORP, and gas
production of turkey, pork, and beef during 7 days of storage. Data were analyzed
using the generalized linear model procedure of SAS software (SAS Institute 1989).
Student-Newman-Keul’s multiple range
test was used to compare differences
among mean values of meats from different animal species receiving different irradiation doses, and Student’s t-test was
used to compare the mean values between storage times. Mean values and
standard error of the means (SE) were reported. Significance was defined at P <
0.05.
Results and Discussion
Gas production measurement
A minced meat sample (10 g, 1 to 2 mm
thick) was placed into a 24-mL widemouth screw-cap glass vial with a Teflon
fluorocarbon resin/silicone septum (IChem Co., New Castle, Del., U.S.A.). The
Color
The CIE color L*, a*, and b* values of
fresh turkey, pork, and beef were compared to determine the effects of irradia-
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Food Chemistry and Toxicology
Irradiation and color changes—species effect…
Irradiation and color changes—species effect…
Food Chemistry and Toxicology
tion, packaging, and storage ( Tables 1
through 3). The L* values of turkey and
pork were similar, but that of beef was always lower than turkey and pork. With aerobic packaging, irradiation and storage
had no effect on color L* values of turkey
and pork. However, the L* value of irradiated beef decreased significantly after 7
days of storage, and irradiated beef had a
lower L* value than nonirradiated after 7
days of storage (Table 1). These results are
similar to those of Nanke and others
(1999) who reported color L* values for
pork and turkey were unaffected by irradiation, but color L* values for beef were affected. In vacuum packaging, irradiation
and storage did not affect color L* values
of pork and beef, but the L* values of turkey decreased significantly after storage
(Table 1).
The color a* values for fresh turkey,
pork, and beef were significantly different
and the intensity of redness was the highest in beef, followed by pork and turkey
(Table 2). The irradiation effect on color a*
values of turkey, pork, and beef was not
universal. At storage 0 days, irradiation increased the color a* value of turkey, did
not affect it for pork, and decreased it for
beef, regardless of packaging type. In the
case of storage for 7 days, beef showed different color a* values according to packaging type. That is, irradiated beef in aerobic
packaging showed slightly increased color
a* values, while a* values decreased in
vacuum packaging (Table 2). These results were similar (1) to those of Luchsinger and others (1996) who reported that color a* values of aerobically packaged pork
chops were not different at 0 days and 3
days but decreased at 7 days, (2) to those
of Nanke and others (1999) and Luchsinger and others (1997) who reported that color a* values of irradiated beef were lower
than those of the nonirradiated beef control, and (3) to those of Nanke and others
(1998) and Millar and others (1995) who
reported that irradiation increased the red
color of turkey. Storage effect on color a*
values of turkey, pork, and beef showed
clearly in vacuum-packaged meats. The
color a* values of turkey, pork, and beef in
vacuum packaging were slightly increased
after 7 storage days regardless of irradiation, but in aerobic packaging they did not
show a consistent trend.
Fresh turkey and pork showed similar
color b* values, but beef showed significantly higher color b* values than those of
turkey and pork. Irradiation had no significant effect on color b* values in meat species except for decreasing b* values in
beef at storage 0 days with aerobic pack1694
Table 4—Numerical total color difference (⌬Ea) of turkey, pork, and beef with
different packaging and storage times.b
Storage
Turkey
Aerobic packaging
0
7
SE
Vacuum-packaging
0
7
SE
Pork
1694
SE
1.45by
2.56bx
0.10
0.23by
1.31bx
0.10
16.04 ax
9.38ay
0.59
0.54
0.54
3.33b
3.65
0.11
2.53bx
1.89y
0.54
4.99ax
3.35y
0.83
0.16
0.32
aDE = [(L* - L*
2
2
2 1/2; ir, irradiated; nonir, nonirradiated.
ir
nonir) + (a* ir - a* nonir) + (b* ir - b* nonir) ]
b Different letters (a, b) within the same row are significantly different ( P < 0.05). n = 4.
Different letters (x, y) within a column of the same packaging are significantly different ( P < 0.05).
SE = standard error of the means.
Table 5—Production of CO, CH 4 , and CO 2 from turkey, pork, and beef by
irradiation.a
Turkey
0 kGy
Beef
0 kGy
CO
CH4
——————————————— (ppm) —————————————————
30.6c
931.6ab
21.0c
779.2b
21.5c
1246.0a 126.8
1.8b
303.3a
1.2b
317.2a
2.2b
387.8a
42.7
——————————————— (ppm) —————————————————
3.6c
8.0ab
5.1bc
9.4a
4.9bc
0.8
4.8bc
CO2
3 kGy
Pork
Gas
3 kGy
0 kGy
3 kGy
SE
a Different letters (a-c) within the same row are significantly different ( P < 0.05). n = 4.
SE = standard error of the means.
aging. But storage increased color b* values regardless of packaging types except
for turkey in vacuum packaging (Table 3).
These results did not confirm the results
of Luchsinger and others (1996) who reported that yellowness decreased as display time increased for aerobically packaged pork chops regardless of irradiation
dose, or of Nanke and others (1999) who
reported that color b* values of irradiated
pork decreased at 1.5 kGy and 3.0 kGy
compared with the nonirradiated control.
Numerically calculated total color difference (DE) showed that the color changes
by irradiation were greater in beef than in
turkey or pork (Table 4). The color change
of beef by irradiation was more distinct in
aerobic than in vacuum conditions.
Tables 1 to 3 show that the redness of
turkey was influenced by both irradiation
and storage day, but the lightness and yellowness were more influenced by storage
day than irradiation. In pork, the irradiation and storage day did not affect the
lightness, but yellowness was significantly
affected by storage day. On the other
hand, the lightness, redness, and yellowness of beef were generally affected by
both irradiation and storage day. Though
there are some data on irradiated meat
color, an exact explanation concerning the
development of meat color by irradiation
has not yet been provided. Until now, the
development of red or pink color of irradi-
ated poultry meats seemed to be caused
by ferrous myoglobin derivatives such as
carboxy-myoglobin, nitric oxide-myoglobin, or CO2-myoglobin other than oxymyogolobin (Millar and others 1995; Nam and
Ahn 2001).
Gas production
Irradiation increased the productions
of CO and CH4 significantly but decreased
the production of CO2 (Table 4). The productions of CO and CH4 gases of irradiated meats did not show significant differences between turkey and pork, while the
amounts of CO 2 produced by irradiation
were in the order of beef, pork, and turkey.
Furuta and others (1992) suggested
that CO gas acts as a probe of irradiated
meats, and reports showed that CO is one
of the major radiolytic gases arising from
irradiated foodstuffs (Pratt and Kneeland
1972; Simic and others 1979). Nam and
Ahn (2002) suggested that the red or pink
color of irradiated poultry meat was due to
the CO produced by irradiation, and CO
has very strong affinities to heme pigments to form CO-myoglobin. CO and CH4
produced by irradiation correlated positively with CIE color a* and b* values, but
negatively with the color L* value for irradiated meats, regardless of packaging
types and storage days. The correlation
between the production of CO and the
CIE color values supported the findings of
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Table 6 —Oxidation-reduction potential of turkey, pork, and beef with irradiation, packaging and storage.a
Turkey
Gas
Pork
0 kGy
Aerobic packaging
0
-35.25a
7
-71.25b
SE
11.27
Vacuum-packaging
0
-91.00a
7
-82.25a
SE
13.87
Beef
3 kGy
0 kGy
3 kGy
-196.75 cy
26.25 ax
18.05
-84.75ab
-83.50 b
17.22
-133.50 bcy
-13.25abx
28.87
-377.00 cy
-113.00abx
22.08
-121.75ab
-188.75b
34.43
0 kGy
3 kGy
-69.25ab -129.75 bcy
-37.50ab
30.25 ax
23.18
23.18
-308.25 cy -137.00ab -243.25 bc
-162.00abx -107.00ab -88.75 a
37.13
17.16
46.90
SE
21.44
20.63
37.94
21.77
a Different letters (a-c) within the same row are significantly different ( P < 0.05). n = 4.
Different letters (x, y) within a column of the same packaging are significantly different ( P < 0.05).
SE = standard error of the means.
Nam and Ahn (2002), but the CH4 produced by irradiation also seemed to be related to irradiated meat color.
lyzed radicals seemed rather to accelerate
the oxidizing properties.
Oxidation-reduction potential
OLOR IS ONE OF THE MOST IMPOrtant attributes that determines consumer acceptance of meat. Irradiation induces different CIE color values, gas production, and ORP in meats from different
animal species. It is suggested that the development of irradiated meat color is concerned with gas production, especially CO
gas produced by irradiation. An exact explanation concerning the development of
irradiated meat color is still needed.
The ORP values of fresh turkey, pork,
and beef were not significantly different,
but showed lower values in vacuum packaging than in aerobic packaging, regardless of irradiation and storage days (Table
5). Irradiation decreased the ORP values
of meats, especially in turkey, at storage 0
day. But the ORP values of irradiated
meats at storage 7 days were higher than
those of fresh meats. These results were
not consistent with the irradiated meat
color values shown in Tables 1 through 3,
but agreed with the findings by Nam and
Ahn (2002) who reported that irradiation
decreased the ORP values of turkey breast
and increased the ORP to positive values
with increased storage time. It was supposed that the radiolyzed radicals produced by irradiation might act as a powerful reducing agent, which reacted with
ferricytochrome to produce ferrocytochrome (Swallow 1984) at the beginning of
irradiation, but as time elapsed, the radio-
Conclusions
C
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MS 20010438 Submitted 9/22/01, Accepted 10/8/01,
Received 10/9/01
Author Kim is with the Korea Food Research Institute, Songnam-Si, Kyonggi-Do, Korea 463-420.
Authors Nam and Ahn are with the Animal Science Dept., Iowa State Univ., Ames, IA 50011-3150.
Direct inquiries to author Ahn (E-mail:
duahn@iastate.edu).
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Irradiation and color changes—species effect…