JFS C: Food Chemistry
C: Food Chemistry
Fat Content Influences the Color, Lipid Oxidation,
and Volatiles of Irradiated Ground Beef
H.A. ISMAIL, E.J. LEE, K.Y. KO, AND D.U. AHN
ABSTRACT: Ground beef with 10%, 15%, or 20% fat were added with none, 0.05% ascorbic acid + 0.01% αtocopherol, or 0.05% ascorbic acid + 0.01% α-tocopherol + 0.01% sesamol, and irradiated at 0 or 2.5 kGy. The meat
samples were displayed under fluorescent light for 14 d at 4 ◦ C. Color, lipid oxidation, volatiles, oxidation-reduction
potential (ORP), and carbon monoxide (CO) production were determined during storage. Irradiation increased lipid
oxidation and total volatiles of ground beef regardless of fat contents. Ascorbic acid + α-tocopherol + sesamol treatment was the most effective in reducing lipid oxidation during storage. The production of ethanol in nonirradiated
ground beef increased dramatically after 7 d of storage due to microbial growth. Total aldehydes and hexanal in∗
creased drastically in irradiated control over the storage period, but hexanal increased the most by irradiation. L values was decreased by irradiation, but increased in all meat regardless of fat contents as storage period increased.
∗
Irradiation reduced the redness, but fat contents had no effect on the a -value of ground beef. Sesamol lowered, but
ascorbic acid + α-tocopherol maintained the redness of irradiated beef up to 2 wk of storage. The yellowness of meat
was significantly decreased by irradiation. The reducing power of ascorbic acid + α-tocopherol lasted for 3 d, after
which ORP values increased. Irradiation increased CO production regardless of fat content in ground beef. In conclusion, up to 20% fat had no effect on the quality change of irradiated ground beef if ascorbic acid + α-tocopherol
was added.
Keywords: antioxidants, fat content, ground beef, irradiation, quality parameters
Introduction
100 times greater than that of metmyoglobin (Hargrove and Olson
1996). The ORP of meat determines the status of iron in heme pigments and lowering ORP favors CO-Mb complex formation, which
intensifies the redness of heme pigments. The ORP of meats decreased after irradiation but increased rapidly after aerobic storage
(Hannah and Simic 1985; Nam and Ahn 2002a, 2002b). The affinity
of CO to heme pigments reduced by the rapid increases of ORP in
irradiated meat under aerobic condition. Although the amount of
CO produced and the changes in ORP in beef are not much different from those from light meat (Kim and others 2002b), the color
of irradiated beef after irradiation becomes brown/gray instead of
pink, especially under aerobic conditions (Nanke and others 1999;
Nam and Ahn 2003b).
Lipid oxidation is a major cause of quality deterioration in meat
and meat products (Asghar and others 1988; Ladikos and Lougovois 1990). The 2-thiobarbituric acid reactive substances (TBARS)
test is the most commonly used method to measure lipid oxidation in meat. Rancid odor was first perceived by sensory panelists
when thiobarbituric acid (TBA) number was between 0.5 and 1, and
this level has been serving as a guide for interpreting TBA test results (Tarladgis and others 1960). Ahn and others (1998) reported
that irradiation and high-fat content accelerated the lipid oxidation in raw meat during storage. Oxygen availability during storage,
however, was more important than irradiation on the lipid oxidation and color values of raw patties. Irradiated meat produced more
volatiles than nonirradiated patties, and the proportion of volatiles
varied by the packaging-irradiation conditions of patties.
Irradiation produced characteristic off-odor in all meat species,
and that odor was not related to lipid oxidation (Ahn and others 1997). Irradiation off-odor had been described by several
MS 20090031 Submitted 1/13/2009, Accepted 4/13/2009. Authors are with researchers as “bloody and sweet” (Hashim and others 1995),
Dept. of Animal Science, Iowa State Univ., Ames, Iowa 50011-3150, U.S.A.
“burned oil” or “burned feather” (Heath and others 1990), and
Direct inquiries to author Ahn (E-mail: duahn@iastate.edu).
“barbecued corn-like” odor (Ahn and others 2000b). Patterson and
C
olor changes, accelerated lipid oxidation, and off-odor production are the main changes that occur in ground beef as a result of irradiation. Because these are the major quality parameters,
consumer decisions to purchase irradiated meat will be affected by
these changes. It was reported that 74% of consumers indicated
that meat color was important in making their purchase decision
where they associated bright red color with freshness (Lynch and
others 1986). Over 700 million dollars per year could be lost in beef
at retail level in the United States because of discoloration alone
(Liu and others 1995). Color changes, caused by irradiation, are different among different meat species (Satterelee and others 1971;
Luchsinger and others 1996; Ahn and others 1998). While light meat
such as pork and poultry breast developed pink color when irradiated, dark meat such as beef became brown or gray color (Millar and others 1995; Ahn and others 1998; Nanke and others 1998;
Kim and others 2002a; Nam and Ahn 2003a). Nam and Ahn (2002a)
claimed that the formation of CO-heme pigment complex was
the cause of the pink color formed in irradiated precooked turkey
breast. The claim was based on the fact that irradiation decreased
oxidation-reduction potential (ORP) and produced carbon monoxide (CO). They supported their claim by the reflectance spectra of
meat and the absorption spectra of myoglobin solution.
Considerable amount of CO gas was produced as a result of radiolysis of organic component, such as alcohols, aldehydes, ketones,
carboxylic acids, amides, and esters, in irradiated frozen meat and
poultry (Furuta and others 1992; Woods and Pikaev 1994). Reactivity of myoglobin toward diatomic ligands such as oxygen, nitric oxide, and CO is different. The affinity of CO to ferrous myglobin was
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JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 6, 2009
R
Institute of Food Technologists
doi: 10.1111/j.1750-3841.2009.01207.x
C 2009
Further reproduction without permission is prohibited
Stevenson (1995) reported that dimethyl trisulfide was the main offodor compound in irradiated chicken followed by cis-3-and trans6-nonenals, cot-1-en-3-one, and bis (methylthio-) methane, while
others (Jo and Ahn 2000; Ahn and Lee 2002; Fan and others 2002) reported that there are many other sulfur and nonsulfur compounds
related to irradiation odor. Ahn and Lee (2002) showed that sulfur
amino acids were the most susceptible to changes by irradiation.
Ahn (2002) reported that sulfur compounds produced from the
side chains of methionine and cysteine were the most important
volatiles for off-odor production in irradiated meat. Sulfur compounds were not only produced by the radiolytic cleavage of side
chains (primary reaction) of sulfur amino acids, but also by the secondary reactions of the primary sulfur compounds with other compounds around them. Among the sulfur amino acids, methionine
was the major source for the sulfur volatiles, and more than 99% of
sulfur compounds produced by irradiation were from methionine.
The objective of this study was to determine the effect of ascorbic
acid and selected antioxidants on the color, lipid oxidation, and offodor volatiles of ground beef with different fat content.
Materials and Methods
Sample preparation
Eight blocks of beef top rounds from 8 different animals were
bought from a local packing plant and used for the study. Each
meat block was trimmed of any visible fat. Meat blocks from 2 animals were combined, ground through a 6-mm plate, and treated
as a replication. High-fat beef trimmings were also bought from the
same packing plant and used to adjust fat content of ground beef
for the study. High-fat trimmings were also ground through a 6mm plate, the fat content determined, and appropriate amounts
of ground fat trimmings were added to the ground beef to make
ground beef containing 10%, 15%, and 20% fat. Ground meat from
each of the 4 replications was divided into 6 portions and ground
separately twice through a 3-mm plate. Three portions of them
were used for irradiation and the other 3 portions for nonirradiation. For both irradiated and nonirradiated meat, 1 of the following antioxidant treatments was added: (1) control, (2) meat added
with 0.05% (w/w) L-ascorbic acid (Fisher Scientific, Fair Lawn, N.J.,
U.S.A.) + 0.01% α-tocopherol (Aldrich Chemical Co., Milwaukee,
Wis., U.S.A.), (3) meat added with 0.05% (w/w) L-ascorbic acid +
0.01% α-tocopherol + 0.01% sesamol (3,4-methylenedioxyphenol;
Sigma, St. Louis, Mo., U.S.A.). The ground beef were then mixed for
2 min in a bowl mixer (Model KSM 90; Kitchen Aid Inc., St. Joseph,
Mich., U.S.A.), and beef patties (approximately 50 g) were prepared.
Patties were placed individually on Styrofoam trays and wrapped
with clear stretch, oxygen-permeable meat film RMF-61 Hy (Borden Div., Borden Packaging and Industrial Products Inc., North
Andover, Mass., U.S.A.), using a single-roll overwrapper, Model
600A (Heat Sealing Equipment Manufacturing Co., Cleveland, Ohio,
U.S.A.). A α-tocopherol was dissolved in corn oil first, and then oil
emulsion (water-in-oil) was prepared using water or the aqueous
solutions of ascorbate and/or sesamol before use. All the antioxidant treatments were on w/w basis and final concentrations. Prepared patties were stored overnight at 4 ◦ C, and irradiated the next
morning.
Ionizing radiation
Wrapped beef patties were irradiated at 2.5 kGy using a linear accelerator facility (Circe IIIR; Thomson CSF Linac, St. Aubin, France)
with 10 MeV of energy and 5.6 kW of power level. The average
dose rate was 67.9 kGy/min. Alanine dosimeters 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 dose
range absorbed by meat samples was 2.40 to 2.92 kGy (max/min ratio 1.22). The nonirradiated control samples were exposed to ambient temperature of linear acceleration facility while other samples
were being irradiated. After irradiation, the irradiated and nonirradiated meat samples were immediately returned to a 4 ◦ C cold
room where they were displayed in a single layer on illuminated
racks under standard fluorescent light (1000 lux, Philips, fluorescent light 40W Cool White) for 14 d. Incident light reaching the
sample surface had an intensity of 2018 lux. Color, lipid oxidation,
volatile analysis, ORP, and CO production were determined at 0, 3,
7, and 14 d of storage.
Thiobarbituric acid-reactive substances (TBARS)
measurement
Lipid oxidation was determined using a TBARS method (Ahn
and others 1999). Five grams of ground beef were weighed into a
50-mL test tube and homogenized with 50 μL butylated hydroxytoluene (7.2%) and 15 mL of deionized distilled water (DDW) using a Polytron homogenizer (Type PT 10/35, Brinkman Instruments
Inc., Westbury, N.Y., U.S.A.) for 15 s at high speed. One milliliter
of the meat homogenate was transferred to a disposable test tube
(13 × 100 mm), and thiobarbituric acid/trichloroacetic acid (15 mM
TBA/15% TCA, 2 mL) was added. The mixture was vortex mixed and
incubated in a boiling water bath for 15 min to develop color. Then
samples were cooled in the iced water for 10 min, mixed again, and
centrifuged for 15 min at 2500 × g at 4 ◦ C. The absorbance of the
resulting supernatant solution was determined at 531 nm against
a blank containing 1 mL of DDW and 2 mL of TBA/TCA solution.
The amounts of TBARS were expressed as milligram of malondialdehyde (MDA) per kilogram of meat.
Volatile compounds
A purge-and-trap apparatus (Solartek 72 and Concentrator 3100;
Tekmar–Dohrmann, Cincinnati, Ohio, U.S.A.) connected to a gas
chromatograph/mass spectrometer (HP 6890/HP 5973; Hewlett
Packard Co., Wilmington, Del., U.S.A.) was used to analyze volatiles
produced. The ground meat sample (3 g) was placed in a 40-mL
sample vial, and the vial was flushed with helium gas (40 psi) for
5 s. The maximum waiting time of a sample in a refrigerated (4 ◦ C)
holding tray was less than 4 h to minimize oxidative changes before
analysis (Ahn and others 2001). The meat sample was purged with
helium gas (40 mL/min) for 14 min at 40 ◦ C. Volatiles were trapped
using a Tenax–charcoal–silica column (Tekmar–Dohrmann) and
desorbed for 2 min at 225 ◦ C, focused in a cryofocusing module
(−80 ◦ C), and then thermally desorbed into a capillary column for
60 s at 225 ◦ C.
An HP-624 column (8.5 m × 0.25 mm i.d., 1.4 μm nominal), an
HP-1 column (60 m × 0.25 mm i.d., 0.25 μm nominal; HewlettPackard), and an HP-Wax column (6.5 m × 0.25 mm i.d., 0.25 μm
nominal) were connected using zero dead-volume column connectors (J&W Scientific, Folsom, Calif., U.S.A.). Ramped oven temperature was used to improve volatile separation. The initial oven
temperature of 30 ◦ C was held for 6 min. After that, the oven temperature was increased to 60 ◦ C at 5 ◦ C/min, increased to 180 ◦ C
at 20 ◦ C/min, increased to 210 ◦ C at 15 ◦ C/min, and then was held
for 5 min at the temperature. Constant column pressure at 22.5 psi
was maintained. The ionization potential of the mass selective detector (Model 5973; Hewlett Packard Co.) was 70 eV, and the scan
range was 19.1 to 400 m/z. Identification of volatiles was achieved
by comparing mass spectral data of samples with those of the Wiley Library (Hewlett Packard Co.). Standards were used to confirm
Vol. 74, Nr. 6, 2009—JOURNAL OF FOOD SCIENCE
C433
C: Food Chemistry
Fat content and irradiated beef quality . . .
Fat content and irradiated beef quality . . .
the identification by the mass-selective detector. The area of each
peak was integrated using the ChemStation (Hewlett Packard Co.),
and the total peak area (pA∗ s × 104 ) was reported as an indicator of
volatiles generated from the sample.
Color measurement
C: Food Chemistry
The color of meat was measured on the surface of meat samples
using a Labscan spectrophotometer (Hunter Assoc. Labs Inc., Reston, Va., U.S.A.) that had been calibrated against white and black
reference tiles covered with the same film as those used for meat
samples. CIE L∗ —(lightness), a∗ —(redness), and b∗ —(yellowness)
values were obtained (AMSA 1991) using an illuminant A (light
source). Area view and port size were 0.64 and 1.02 cm, respectively.
An average value from 2 random readings on the sample surface
was used for statistical analysis.
Oxidation-reduction potential
The method of Moiseeve and Cornforth (1999) was used in determining the change of ORP in meat. A pH/ion meter (Accumet
25, Fisher Scientific) connected to a platinum electrode filled with
a 4 M-KCl solution saturated with AgCl was tightly inserted in the
center of meat sample. To minimize the effect of air, the smallest
possible pore was made before inserting the electrode and recording the ORP readings (mV).
into a splitless inlet of a GC (Model 6890; Hewlett Packard Co.). A
Carboxen-1006 Plot column (30 m × 0.32 mm id; Supelco, Bellefonte, Pa., U.S.A.) was used. Helium was used as a carrier gas at a
constant flow of 1.8 mL/min and oven conditions were set at 120 ◦ C.
A FID equipped with a Nickel catalyst (Hewlett Packard Co.) was
used for the methanization of CO and CO 2 , and the temperatures
of inlet, detector, and Nickel catalyst were 250, 280, and 375 ◦ C, respectively. Detector (FID) air, H 2 , and make-up gas (He) flows were
350, 35, and 40 mL/min, respectively. The identification of CO was
achieved using standard gas and a GC/MS, and the area of each
peak was integrated using Chemstation software (Hewlett Packard
Co.). To quantify the amounts of gas released, peak areas (pA∗ s)
were converted to the concentrationx (ppm) of gas in the sample
headspace (14 mL) using CO 2 concentration (330 ppm) in air.
Statistical analysis
The experiment was a complete randomized design with 4 replications. Data were analyzed by the procedures of generalized linear
model of SAS (SAS Inst. 1995). Student–Newman–Keuls’ multiplerange test was used to compare the mean values of treatments.
Mean values and standard error of the means (SEM) were reported.
Significance was defined at P < 0.05. Analysis of variance (ANOVA)
was used to determine the effects of fat content, irradiation, additives, and storage period on lipid oxidation, color, CO production,
and ORP of ground beef.
Carbon monoxide
To measure CO produced by irradiation, CO gas was purchased
from Aldrich Chemical Co. The standard gas was analyzed using
a gas chromatograph (GC, Model 6890; Hewlett Packard Co.) with
a flame ionization detector (FID). Meat sample (10 g) was placed
in a 24-mL glass vial, and the vials were flushed with helium gas
(40 psi) for 5 s to minimize experimental errors due to air incorporation, then samples were microwaved for 10 s at full power. Ten
minutes after microwave heating, the headspace gas of each sample (200 μL) was withdrawn using an airtight syringe and injected
Results and Discussion
Lipid oxidation
TBARS values of nonirradiated beef patties were not significantly
different from those of irradiated ones at Day 0. As storage time increased, however, irradiated patties showed higher TBARS values
than nonirradiated ones and some of the patties treated with additives showed significant differences (Table 1). Jo and others (1999)
reported that TBARS values increased with increased fat content
Table 1 --- TBARS values of beef added with different additives and fat contents during storage at 4 ◦ C.
10% fat
Non-IR
IR
15% fat
SEM
Non-IR
IR
20% fat
SEM
Non-IR
IR
SEM
mg MDA/kg meat
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Day 7
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
2.17a
0.72b
0.64b
0.16
2.41a
0.9b
0.71b
0.15
0.24
0.08
0.07
1.92a
0.80b
0.64b
0.15
2.11a
0.96b
0.73b
0.18
0.24
0.13
0.09
1.98a
0.79b
0.77b
0.17
2.19a
0.98b
0.81b
0.17
0.26
0.10
0.10
3.36a
0.87b
0.66b
0.37
4.10a
1.12b
0.69b
0.25
0.52
0.14
0.07
3.20a
0.76b
0.69b
0.13
4.10a
0.90b
0.72b
0.25
0.27
0.20
0.05
3.11ay
0.93b
0.76b
0.20
4.31ax
1.33b
0.88b
0.28
0.25
0.32
0.11
6.53a
1.76by
0.71c
0.20
5.82a
2.99bx
0.69c
0.32
0.38
0.24
0.08
4.30ay
1.56b
0.67by
0.27
6.28ax
2.19b
1.10cx
0.41
0.43
0.42
0.06
5.15a
2.37b
0.85b
0.49
5.25a
1.76b
0.65c
0.27
0.62
0.27
0.11
5.62a
2.9b
0.59by
0.36
7.52a
3.79b
1.82cx
0.53
0.60
0.45
0.22
4.55ay
2.35b
0.64by
0.34
7.26ax
2.60b
1.76cx
0.35
0.40
0.40
0.19
4.98ay
2.48b
0.72cy
0.19
8.16ax
3.15b
1.46cx
0.52
0.62
0.21
0.18
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
x and y
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JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 6, 2009
in cooked pork sausages. Irradiation accelerated lipid oxidation in
meat stored only under aerobic conditions (Katusin-Razem and
others 1992; Ahn and others 2000a).
Ascorbic acid + α-tocopherol and ascorbic acid + α-tocopherol
+ sesamol treatments were effective in reducing lipid oxidation of
beef. Adding sesamol to ascorbic acid + α-tocopherol made them
more effective in preventing oxidative changes during storage under aerobic conditions, especially at 7 and 14 d. As storage time
increased, overall lipid oxidation increased, and the rate of lipid
oxidation was faster in irradiated than nonirradiated beef (P <
0.05). Buckley and others (1995) and Liu and others (1995) reported
that tocopherol is a major antioxidant in cells and protect cell membrane fatty acids and cholesterol from the damages caused by free
radicals such as hydroxyl and superoxide radicals. Tocopherol content in meat products varies depending upon adding vitamin E to
the diet or meat during product processing. Jo and others (1999)
found that at 0 day, irradiated meat had higher TBARS than nonirradiated ones, but as storage time increased the difference in TBARS
values disappeared. The effect of antioxidants in ground beef was
more distinct after 7 d of storage than at 0 d. The antioxidant effect of ascorbic acid + tocopherol started to decrease at 7 d of
storage, but that of ascorbic acid + tocopherol + sesamol still remained strong even at 14 d of storage. This indicated that adding
ascorbic acid + tocopherol was not good enough to prevent oxidative changes in irradiated ground beef stored more than 3 d under
aerobic conditions. Thus, addition of another antioxidant such as
sesamol and other natural such as gallate, ferulic acid, and quercetine may be necessary to prevent oxidative changes in ground beef
for longer than 3 d. Thayer and others (1993) and Lakritz and others (1995) reported that irradiation generates free radicals that can
destroy the antioxidants in muscle and consequently will reduce
storage stability and increase the production of off-flavor in meat.
Nam and Ahn (2003b) also showed that addition of sesamol + αtocopherol was effective in preventing lipid oxidation in aerobically
or double-packaged irradiated raw and cooked turkey breast. Storage stability of raw meat can be improved by increasing vitamin
E concentration in processed products (Ajuyah and others 1993;
Winne and Dirinck 1996).
Volatiles production
Irradiation increased the amounts of hydrocarbons, ketones,
toluene, and total volatiles in ground beef at 0 d regardless of fat
Table 2 --- Production of hydrocarbons, ketones, toluene, and total volatiles from beef with different additives and fat
contents during storage at 4 ◦ C.
A±E
Control
Storage/Fat (%)
Compound
Non-IR
IR
Non-IR
A±E±S
IR
Non-IR
IR
SEM
(Total ion counts × 104 )
13994a
5256c
8917ab
5996bc
498a
0b
38465a
15134d
13414a
5767b
9598a
5721b
469a
0b
34468a
15190c
12937a
7351b
8635a
5869b
507b
0c
38073a
17756c
13331a
8526bc
9014
20994
213b
0c
66099ab
101189a
12410a
11917a
559a
32369b
13087a
10282a
454a
31633a
13624a
10680a
590a
34297ab
11207ab
7255
260a
31054b
5255c
5936bc
0b
15839d
5717b
5124b
0b
17961c
5900b
5416b
0c
19618c
4024d
19753
0c
57282ab
10033b
11076a
542a
32940b
10847a
9983a
529a
27712ab
10924a
9792a
567a
30224b
10607ab
6394
227b
22495b
1224
710
44
2364
1224
710
44
2364
860
671
19
1425
1119
3786
9
12370
Hydrocarbons
Ketones
Toluene
Total volatiles
Hydrocarbons
Ketones
Toluene
Total volatiles
Hydrocarbons
Ketones
Toluene
Total volatiles
Hydrocarbons
Ketones
Toluene
Total volatiles
5317c
5176c
0b
22328c
8929ab
6030b
0b
22890bc
4883b
5784b
0c
20984c
6448cd
15565
0c
98808a
Day 7
15% fat
Hydrocarbons
Ketones
Toluene
Total volatiles
8274bc
26332a
0c
109784a
14103a
6724b
1397a
48719bc
8241bc
13962ab
0c
66890abc
9417bc
7282b
1380a
32553c
5328c
22541a
0c
82163ab
11361ab
6690b
1166b
23477c
1162
3691
48
12351
Day 7
20% fat
Hydrocarbons
Ketones
Toluene
Total volatiles
9178bc
18877
0c
86024a
15660a
7243
226b
55025b
11962ab
19448
0c
101202a
12402ab
5905
244b
26509c
6185c
23416
0c
79767a
14041ab
7552
265a
27251c
1269
5292
8
7660
Day 14
10% fat
Hydrocarbons
Ketones
Toluene
Total volatiles
Hydrocarbons
Ketones
Toluene
Total volatiles
Hydrocarbons
Ketones
Toluene
Total volatiles
12581ab
39087
0c
189771ab
13639bc
15324
0b
150441
18137a
15732
0c
143248a
14999a
10978
196b
86357bc
20059a
9616
222a
72916
22413a
13734
218b
75060ab
9053b
33349
0c
168110ab
12485bc
17370
0b
172615
8611b
24393
0c
129731ab
14734a
9388
232a
56482c
16264ab
7730
208a
51344
21345a
8621
277a
59546b
10513ab
45151
0c
225566a
10565c
26302
0b
174239
8496b
27966
0c
134083ab
12653ab
8672
246a
28871c
11879bc
9985
229a
46174
18975a
9707
233b
69506ab
1075
12471
11
29459
1290
4540
7
36115
2245
7750
13
18057
Day 0
10% fat
Day 0
15% fat
Day 0
20% fat
Day 7
10% fat
Day 14
15% fat
Day 14
20% fat
Values with different superscripts within a row are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means (n = 4).
Hydrocarbons: 2-methyl-butane, pentane, 1,3-pentadiene, pentene, hexane, 1-hexene, 1-heptene, heptane, octane, 2-octene, nonane.
Ketones: 2-propanone, 2,3-butanedione, 2-butanone, 2-heptanone.
a and b
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C435
C: Food Chemistry
Fat content and irradiated beef quality . . .
Fat content and irradiated beef quality . . .
C: Food Chemistry
contents or additive treatments. At 7 and 14 d, irradiated ground
beef produced higher amount of hydrocarbons than nonirradiated
ones in general, but the differences were not always significant. Unlike at 0 d, the production of ketones and total volatiles in nonirradiated ground beef at 7 and 14 d was greater than that in irradiated
ones but was not significant in many cases. Toluene was produced
only in irradiated meat. Additives had no effect on the production
of hydrocarbons, ketones, toluene, and total volatiles in ground
beef (Table 2). Among the volatiles, alcohols and aldehydes were affected the most by irradiation, additives, and storage. The amount
of alcohols greatly increased at 7 d in nonirradiated beef regardless of additive treatments and increased further at 14 d (Table 3).
Ethanol was mainly responsible for the increase in alcohols content
in nonirradiated ground beef over the storage periods probably due
to microbial growth in the meat during storage. Similar trends were
found in ground beef with different aging time (Ismail and others
2008). Zhu and others (2008) showed that irradiating ready-to-eat
(RTE) turkey hams and breast roll at 2 kGy greatly reduced the number of naturally occurring bacteria during refrigerated storage. The
production of aldehydes increased as storage time increased, but
the increase was the most significant in irradiated control meats
(no additives). Addition of antioxidants, especially sesamol + ascorbic + α-tocopherol, to ground beef was effective in preventing aldehydes production during storage (Table 3). Among the aldehydes,
hexanal increased the most by irradiation and storage. Hexanal is a
common indicator of lipid oxidation in meat (Ahn and others 1999).
Ground beef with low fat content (10%) produced greater amount
of aldehydes than that with higher fat content (20%) at 14 d of storage (Table 3). In general, however, fat content had little effect on the
production of volatiles in irradiated and nonirradiated ground beef
during storage.
Usually, sulfur volatiles such as sulfur-methyl ester ethanethioic
acid, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide
are newly generated by irradiation. These volatiles, however, were
detected at very low levels in this study. Ahn and others (2000a) reported that the amount and production of sulfur volatiles are highly
dependent upon irradiation dose, meat species, and muscle types
(Ahn and Lee 2002). The intensity of irradiation off-odor diminished over storage period as the sulfur volatiles disappeared during
storage under aerobic conditions (Nam and Ahn 2003a).
Color values
The lightness (L∗ -values) of ground beef was affected by irradiation (Table 4). Initially at irradiation decreased L∗ -values of
beef patties treated with no additives regardless of fat contents.
At 14 d, the lightness of irradiated controls patties increased in all
fat contents compared with nonirradiated controls. Fat contents
Table 3 --- Production of alcohols and aldehydes of beef with different additives and fat contents during storage at
4 ◦ C.
10% fat
Compound
Non-IR
IR
15% fat
SEM
Non-IR
IR
20% fat
SEM
Non-IR
IR
SEM
(Total ion counts × 10 )
4
Alcohols
After 0-d storage
Cont.
6267
A+E
3327
A+E+S
3977
SEM
1401
After 7-d storage
Cont.
61331a
A+E
58820a
A+E+S
31923a
SEM
20814
After 14-d storage
Cont.
125396a
A+E
117342a
A+E+S
154207a
SEM
50494
Aldehydes
After 0-d storage
Cont.
5568x
A+E
556by
A+E+S
671by
SEM
547
After 7-d storage
Cont.
15464
A+E
12850
A+E+S
1582
SEM
6368
After 14-d storage
Cont.
12706b
A+E
8366
A+E+S
15695a
SEM
4539
6643
5566
9258
1260
1476
696
1632
4916b
3541
6786
1955
6542a
5981
5202
922
427
928
2442
5645
4279
8099
1510
8661
7498
7377
1770
1667
1435
1813
16565bx
16460bxy
10439by
1729
11212
6021
4270
55259a
38862a
51737a
20395
13193bx
12425ax
17217ay
806
6677
5687
3021
47611a
56534a
47604a
17769
9565b
15374b
12122b
899
6952
4484
3864
33314b
33811b
39784b
2745
11959
14653
6431
115636a
136097a
130720a
53921
32422b
38812b
43373b
7186
17011
12242
22581
106083a
93581a
94059a
28026
22161b
24494b
36476b
11505
8845
21144
20943
8414x
1917ay
2030ay
769
1142
89
155
3843x
161by
644by
487
6258x
2184ay
1494ay
597
912
181
159
6102bx
597by
624by
481
9557ax
3010ay
2610ay
544
815
239
264
32329x
6312y
996y
4027
8719
3011
256
19920x
5825y
2558y
2346
19819x
8787xy
1240y
4226
5124
2919
514
10358b
13258
2563
3497
24944ax
3474y
1529y
2509
3181
4175
490
48224ax
17476y
868bz
4773
6587
3055
3515
5842b
6664
6652a
1801
26008ax
14900y
1500bz
3166
3074
2942
1341
3296b
3145
3563
464
29646ax
4524y
3908y
1679
1710
718
1053
with different superscripts within a row with the same fat content are significantly different (P < 0.05).
Values with different superscripts within a column of the same storage time are significantly different (P < 0.05).
Non-IR = nonirradiated samples, IR = irradiated samples; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means (n = 4).
Alcohols: ethanol, 1-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 2-methyle-1-propanol, 2-methyl-1-propanol, hexanol, 3-methyl-1-butanol.
Aldehydes: acetaldehyde, propanal, 2-methyl-propanal, 3-methyl-butanal, pentanal, hexanal, heptanal.
a and b
Values
x to z
C436
JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 6, 2009
influenced the lightness of both irradiated and nonirradiated beef,
where L∗ -values increased as fat contents increased throughout the
storage period. Adding ascorbic acid + α-tocopherol decreased the
lightness of beef, but this effect was not consistent. Patties treated
with sesamol + ascorbic + α-tocopherol had lower L∗ -values compared to those without sesamol.
Irradiation reduced the redness (a∗ -values) of ground beef at 0 d
(Table 5). As storage period increased, however, irradiation did not
show any effect on beef redness. As the fat content increased, a∗ values of nonirradiated control patties decreased at both 0 and 3 d
of storage. At 7 d, the influence of fat was not consistent and at 14 d,
a∗ -values of nonirradiated control increased as the fat content increased. Ascorbic acid + α-tocopherol maintained the redness of irradiated patties at 0 and 3 d of storage. As storage period increased
to 7 and 14 d, however, the effectiveness of the additive to keep the
red color decreased. Redness values of patties treated with sesamol
were lower than those treated with ascorbic acid + α-tocopherol,
with very few exceptions.
The yellowness (b∗ -values) of beef were decreased by irradiation,
regardless of fat contents at 0 d (Table 6). As storage time increased,
there was not much irradiation effect on b∗ -values. At 14 d, however,
patties with higher fat content showed higher b∗ -values. Ascorbic
Table 4 --- CIE color L∗ -values of beef with different additives, fat contents, and storage times at 4 ◦ C.
10% fat
Non-IR
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Cont.
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
IR
15% fat
SEM
Non-IR
IR
20% fat
SEM
Non-IR
IR
SEM
51.5w
51.8w
50.8w
0.3
48.4x
47.9x
47.3y
0.7
0.5
0.6
0.4
52.8w
52.4w
51.8w
0.6
50.1x
48.7x
48.6y
0.7
0.6
0.8
0.6
53.7uw
55.0w
53.9w
0.6
51.1x
52.1x
50.8x
0.5
0.5
0.6
0.6
50.7w
49.9
49.1w
0.8
49.9awx
50.5a
46.5bx
0.5
0.7
0.6
0.4
51.0a
51.4a
48.2b
0.8
50.1
50.0
50.1
1.2
0.8
0.7
0.9
50.8w
51.2
51.1
0.8
53.9aw
49.9b
49.9b
0.9
0.6
0.8
0.7
45.8
47.6
46.5
1.5
48
47.4
46.3
1.4
1.2
1.3
0.8
49.7a
51.2aw
46.6bwx
0.9
50.7a
50.5aw
45.7bx
0.7
0.8
0.8
0.6
52.0ax
52.0aw
46.1bx
0.9
53.5aw
48.3bx
48.6bwx
1.2
0.4
0.7
1.2
45.7y
45.2
44.3x
0.8
50.7aw
48.9ab
46.6bw
0.9
0.7
0.8
0.4
46.9x
49.1
45.7
0.9
52.8aw
50.4a
45.4b
1.0
0.7
1.0
0.8
50.3abx
52.6a
48.2bx
0.9
54.8w
54.4
50.9w
1.5
1.1
1.0
0.7
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
w to z
Table 5 --- CIE color a∗ -values of beef with different additives, fat contents, and storage times at 4 ◦ C.
10% fat
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Day 7
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
15% fat
20% fat
Non-IR
IR
SEM
Non-IR
IR
SEM
Non-IR
IR
SEM
24.8cw
28.7aw
26.7bw
0.5
14.5cx
16.8bx
18.0ax
0.3
0.7
0.4
0.3
25.5cw
29.9aw
27.4bw
0.4
14.9cy
17.5bx
18.9ax
0.3
0.3
0.4
0.4
26.2w
27.8w
26.5w
0.5
15.5cy
16.5bx
19.3ax
0.3
0.5
0.4
0.6
14.8cw
26.3aw
20.9bx
0.8
11.3bx
20.2ax
19.9ax
0.3
0.8
0.5
0.4
11.5cx
27.3aw
20.5bx
0.4
11.2cx
21.4ax
18.9by
0.5
0.5
0.5
0.4
10.9c
26.3aw
19bx
0.6
11.4b
21.4ax
20.2awx
0.6
0.5
0.6
0.5
9.8abx
9.5bz
10.4ay
0.2
9.7bx
13.6ax
14.2ax
0.6
0.2
0.5
0.3
9.4bx
9.9ay
10.3ay
0.1
9.8cwx
16.7ax
12.6bx
0.7
0.2
0.6
0.3
9.7bx
9.3by
10.7ay
0.3
9.7cx
17.1ax
14.1bx
0.7
0.2
0.6
0.4
10.8x
9.7x
11.1x
0.7
9.5bx
9.6bx
10.8ax
0.4
0.7
0.6
0.5
11.4bx
12.6ay
13.5aw
0.4
9.2by
11.2ay
9.3bx
0.4
0.4
0.6
0.4
13.4w
12.2x
11.9x
0.5
9.3bx
9.8by
10.6ay
0.2
0.7
0.5
0.4
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
w to z
Vol. 74, Nr. 6, 2009—JOURNAL OF FOOD SCIENCE
C437
C: Food Chemistry
Fat content and irradiated beef quality . . .
Fat content and irradiated beef quality . . .
C: Food Chemistry
acid + α-tocopherol increased the yellowness of beef patties at 0 decrease was inconsistent. The production of CO was irradiation
and 3 d of storage, but had no effect on the b∗ -values of beef after dose-dependent, and similar amounts of CO were produced from
meats from different animal species (Nam and Ahn 2002a; Lee
3 d of storage.
and Ahn 2004). The mechanisms of color changes in irradiated
dark meat are different from those in light meat. Dark meat has
CO and ORP
Irradiation increased the production of CO regardless of fat con- about 10 times higher pigment than light meat. The amount of CO
tents (Table 7). The amount of CO decreased over storage pe- produced by irradiation, however, is similar in both meats (Kim
riod, and no differences between irradiated and nonirradiated and others 2002b). So the percentages of CO-heme to total meat
beef patties were found at 7 and 14 d of storage. Treating beef pigment are different. Animal species, muscle type, irradiation
with antioxidants decreased the amount of CO produced, but the dose, and packaging type affect color changes in irradiated meat
Table 6 --- CIE color b∗ -values of beef with different additives, fat contents, and storage times at 4 ◦ C.
10% fat
Non-IR
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Day 7
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
15% fat
20% fat
IR
SEM
Non-IR
IR
SEM
Non-IR
IR
SEM
21.2bw
23.5aw
22.7abw
0.6
15.9bx
16.9abx
17.9ax
0.4
0.6
0.4
0.4
22.3cw
26.1aw
24.4bw
0.5
17.7bx
18.5ax
19.1ax
0.3
0.4
0.5
0.4
23.8w
24.2w
24.2w
0.5
18.5aby
17.6bx
19.5ax
0.5
0.5
0.4
0.6
18.4cw
22.5aw
20.5bx
0.6
16.4cx
18.5by
20.6ax
0.5
0.5
0.6
0.5
18.9c
24.6aw
20.5bx
0.5
18.5b
21.3ax
20.4ax
0.4
0.4
0.6
0.4
19.9b
24.3aw
20.2bx
0.6
19.4b
20.7ay
21.4awx
0.4
0.5
0.4
0.5
18.7x
18.7x
18.7x
0.5
19.3x
18.0x
18.8x
0.4
0.5
0.8
0.3
19.5a
19.7ax
18.1bx
0.4
19.9
19.7x
18.4x
0.6
0.4
0.6
0.4
19.9
19.2x
19.4x
0.4
20.3
19.6x
19.2x
0.5
0.4
0.5
0.3
18.8x
17.9x
19.4w
0.7
19.7ax
17.5bx
16.5bx
0.5
0.4
0.5
0.5
20.7x
21.4w
20.4w
0.4
19.4ay
17.9ax
14.9by
0.6
0.4
0.4
0.6
22.7aw
21.1bw
20.2bw
0.3
19.9x
17.9x
18.3x
0.6
0.4
0.4
0.4
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
w to z
Table 7 --- CO production from beef with different additives, fat contents, and storage times at 4 ◦ C.
(Unit: ppm)
10% fat
Non-IR
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Day 7
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
IR
15% fat
SEM
Non-IR
IR
20% fat
SEM
Non-IR
IR
SEM
86.32a
37.92by
43.85by
9.23
132.46
101.22x
110.92x
12.21
13.98
10.07
7.39
60.62y
39.64y
45.06y
7.47
144.82x
116.42x
100.40x
12.01
8.06
11.50
10.15
52.08y
42.36y
48.49y
7.59
146.03x
118.66x
143.83x
15.72
15.27
6.50
13.47
53.41y
34.50
36.84y
6.19
106.36x
87.13
84.06x
13.67
9.29
15.26
4.32
47.44ay
37.32aby
28.72by
4.65
126.57ax
87.28abx
64.57bx
13.42
14.98
8.17
3.41
38.51y
21.89y
17.67y
6.58
97.86x
83.90x
85.06x
10.68
10.25
10.36
4.87
26.69y
27.45y
34.70
5.53
58.9abx
83.73ax
40.68b
8.49
8.06
6.19
7.12
46.50y
28.1y y
26.95
5.89
78.30ax
76.99ax
34.65b
6.69
5.15
7.19
6.40
28.37
20.06y
12.14y
6.91
60.68
62.26x
63.87x
6.70
10.56
2.72
4.47
26.36
26.12y
26.98
7.77
41.07
45.58x
36.9
4.24
4.53
4.21
8.90
32.86
20.84y
23.84
5.33
54.64
65.50x
30.95
10.49
10.04
9.35
4.43
21.29y
18.45y
11.86y
2.53
52.33x
58.92x
47.41x
7.82
3.56
3.08
8.89
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
w to y
C438
JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 6, 2009
Fat content and irradiated beef quality . . .
Table 8 --- ORP values of beef with different additives and fat contents during storage at 4 ◦ C.
(Unit: mV)
Non-IR
Day 0
Cont.
A+E
A+E+S
SEM
Day 3
Cont.
A+E
A+E+S
SEM
Day 7
Cont.
A+E
A+E+S
SEM
Day 14
Cont.
A+E
A+E+S
SEM
IR
15% fat
20% fat
SEM
Non-IR
IR
SEM
Non-IR
IR
SEM
90.08a
22.65b
19.73b
5.21
107.20a
26.93b
20.88b
5.34
8.00
1.82
4.04
81.48a
16.93b
15.18b
5.57
97.93a
10.58b
13.98b
6.18
8.86
3.20
3.88
81.05a
9.10b
14.53b
10.07
94.65a
13.40b
18.20b
11.18
17.31
4.12
4.78
118.38a
58.68b
22.92b
11.45
121.28a
36.43b
44.03b
10.25
10.33
12.83
9.11
97.8ay
39.00by
88.73a
14.35
156.55ax
78.28bx
92.90b
4.91
16.06
6.24
6.93
84.00ay
27.58by
56.53ab
11.16
135.60ax
109.48ax
85.63b
8.59
11.63
2.15
12.55
136.03a
66.80by
97.83aby
16.02
180.55a
131.68bx
131.65x
7.14
13.63
15.79
5.13
83.33
80.55
85.25
11.15
134.03
102.60
107.20
14.77
18.27
9.45
9.46
44.40y
43.13x
33.88y
11.68
131.78ax
83.98bz
90.93bx
8.45
8.83
11.69
9.87
−6.10y
70.05y
48.33y
35.04
171.18x
168.70x
157.80x
7.63
37.26
17.03
15.81
−3.60y
22.28
11.83y
18.42
152.65x
128.85x
135.60x
10.58
15.76
15.71
13.49
−19.10y
1.05y
−20.25y
21.85
160.48x
155.98x
134.68ax
13.65
28.62
5.42
12.13
with different letters within a column of each storage period are significantly different (P < 0.05).
Values with different letters within a row of each fat percent are significantly different (P < 0.05).
Non-IR = nonirradiated samples; IR = irradiated samples; Cont. = control; A = ascorbic acid; E = vitamin E; S = sesamol; SEM = standard error of the means
(n = 4).
a to c
Values
x and y
(Satterelee and others 1971; Luchsinger and others 1996; Ahn and
others 1998): CO-heme pigment represents only a small portion of
pigments in irradiated dark meat such as ground beef, while it represents the majority of pigments in irradiated light meat. Thus, light
meat such as poultry and pork produce pink color while dark meat
produces brown or gray color after irradiation (Millar and others
1995; Ahn and others 1998; Nanke and others 1998; Kim and others
2002a).
ORP values were influenced by irradiation and additives during
the first 7d of storage but the change became inconsistent at 14 d
of storage (Table 8). Ascorbic acid + α-tocopherol was effective in
lowering ORP values regardless of fat contents. The reducing power
of ascorbic acid maintained lower ORP values for 3 d after irradiation. Sesamol + ascorbic acid + α-tocopherol had similar effect to
ascorbic acid alone. In nonirradiated patties, ORP values decreased
as fat contents increased. In the irradiated sample, the influence of
fat content on ORP was inconsistent. ORP played an important role
in color change of meat, because low ORP value maintains heme
pigments in ferrous form, which is stronger in color intensity than
that of ferric form and enables CO-heme pigment complex formation, which intensifies the red color intensity further. Because of its
reducing capability, ascorbic acid inhibited the oxidation of myoglobin, and thus prevented the development of brown color in nonirradiated meat (Wheeler and others 1996; Lee and others 1999;
Sanchez-Escalante and others 2001).
I
Conclusions
rradiation increased both lipid oxidation and total volatiles, especially aldehydes, but decreased redness of ground beef over
the 14-d storage period regardless fat content. The production of
alcohol greatly increased in nonirradiated ground beef during storage due to microbial growth. Adding antioxidants such as ascorbic
acid + α-tocopherol was effective in minimizing lipid oxidation,
volatile production and color changes in irradiated ground beef,
but fat content had little effect on the quality parameters of irradiated and nonirradiated ground beef. Therefore, up to 20% fat would
not affect quality changes of irradiated ground beef if ascorbic acid
+ α- tocopherol is added.
Acknowledgment
The study has been supported by the Natl. Integrated Food Safety
Initiative/USDA (USDA Grant 2002-5110-01957), Washington, D.C.
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