JOURNAL OF FOOD SCIENCE
CHEMISTRY/BIOCHEMISTRY
Volatile Profiles of Raw and Cooked Turkey
Thigh as Affected by Purge Temperature
and Holding Time Before Purge
D. U. Ahn, C. Jo, and D. G. Olson
ABSTRACT
Effects of purge temperature and sample holding time on
volatile profiles were determined using a purge-and-trap/gas
chromatography unit with autosampler. Purge temperature
and sample holding time before purge influenced the profile
of volatiles in raw and cooked meat. The most notable changes
were observed when the purge temperature was increased
from 60⬚C to 80⬚C. Many of the changes in volatiles were
related to oxidation of lipids. We recommend that meat should
be purged at 40⬚C or 50⬚C (temperature at sensory analysis)
to minimize heat-induced production of volatiles and sample
purge should be done within 3h after sampling to reduce oxidative changes during sample holding time.
Key Words: purge-and-trap, dynamic headspace, purge
temperature, lipid oxidation, volatiles
INTRODUCTION
VOLATILES IN MEAT CONSTITUTE AN INTEGRAL PART OF ITS FLAVOR
(Girard and Nakai, 1991), which are influenced not only by odor
intensity but also by the kind and composition of flavor compounds in
the meat (Specht and Baltes, 1994; Bailey et al., 1994). Gas chromatography (GC)/mass spectrometry is widely used to analyze flavor
volatiles, and many sample preparation methods have been reported to
extract and trap volatiles from meat samples before GC analysis (Larick and Turner, 1990; Girard and Nakai, 1991; Ramarathnam et al.,
1993). Many extraction methods such as simultaneous distillation/
extraction, distillation/solvent extraction, or direct isolation (Tanchotikul and Hsieh, 1991; Ajuyah et al., 1993; Specht and Baltes, 1994)
require considerable sample preparation and/or exposure to high temperature conditions that may create changes in the organic compounds.
Damodaran and Kinsella (1981) and O’Neill and Kinsella (1988)
showed that conformational changes by heat or chemical treatment
could lessen the flavor (volatile) binding affinity and capacity of proteins. The headspace/GC (static and dynamic) method is a simple and
effective way to analyze volatiles because it uses a direct injection of
volatiles released from samples. However, the static headspace method requires a long equilibration time and the dynamic headspace methods usually use high temperature conditions, which could promote
production of artifacts by thermal degradation and lipid oxidation.
The purge-and-trap method extracts volatiles by flushing samples
with a continuous flow of inert (e.g., helium) gas and traps them with
a trap column (e.g., Tenax). The purge-and-trap method (EPA, 1994)
can be applied to extract and concentrate organic flavor compounds in
meat. The trapped volatiles can be directly desorbed or concentrated
using a cryofocusing unit before injection. The temperature of samples during holding and volatiles extraction can be adjusted, and the
process from extraction to GC analysis can be fully automated (Ahn et
al., 1997, 1998).
The authors are affiliated with the Dept. of Animal Science, Iowa State Univ.,
Ames, IA 50011-3150. Direct inquiries to Dr. D. U. Ahn.
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JOURNAL OF FOOD SCIENCE—Volume 64, No. 2, 1999
Ang et al. (1994) and Ahn et al. (1997) developed a dynamic
headspace GC method for volatiles in poultry meat using a purge-andtrap unit. They proved that the purge-and-trap dynamic headspace/GC
system could be useful in analyzing meat volatiles. The kind and
composition of volatile compounds in meat can vary widely not only
due to animal species but also to processing and sample preparation
methods (Girard and Nakai, 1991; Ramarathnam et al. 1993; Ang et
al., 1994; Sheldon et al., 1997). Purge temperature and oxygen contact
are the two most critical factors that influence volatile profiles in meat
(Spanier et al., 1994). Ang et al. (1994) reported that high end-point
cooking temperature produced more volatile compounds than low
end-point temperatures. Thus, high purge temperature also may influence the production of volatiles from meat samples during purge. The
purge-and-trap dynamic headspace/GC method uses a continuous
sweeping of volatiles in a sample vial by inert gas. Oxygen contact
with meat during sample preparation and holding periods is inevitable
because of oxygen in the headspace of the sample vial. Cooked meat
could easily be oxidized under aerobic conditions (Ahn et al., 1992).
Oxygen in a sample vial could oxidize the sample if held hours before
purging which would produce more volatiles than one purged immediately after sampling. Waiting time in an autosampler tray and high
purge temperature, therefore, could considerably influence volatile
profiles and misrepresent the true composition of volatiles.
The objective of our work was to determine the effects of sample
purge temperature and holding time in an autosampler tray before
purging, on the volatile composition of raw and cooked turkey thigh
analyzed with a purge-and-trap/GC method.
MATERIALS & METHODS
Sample preparation
Turkey thighs were purchased from a local grocery store, deboned,
and skinned. The deboned meat (⬇5 kg) was ground twice through a 3mm plate, and 40 patties (⬇100g each) were prepared from the ground
thigh meat. Twenty patties were used for raw thigh study, and another
20 patties were broiled in an electric oven (300⬚C) to internal temperature 78⬚C. Raw meat patties were vacuum packaged and stored at ⫺30⬚C
until used. The cooked patties were individually vacuum packaged in
oxygen-impermeable nylon/polyethylene bags (O2 permeability, 9.3
mL O2/m2/24 h at 0⬚C; Koch, Kansas City, MO) immediately after
cooking (within an h) and stored at ⫺30⬚C until used. One day before
analysis, raw or cooked meat samples were placed in a 4⬚C refrigerator
to thaw. Lipid oxidation was determined by the thiobarbituric acid reactive substances (TBARS) method (Ahn et al., 1998). A purge-and-trap
apparatus connected to a GC unit was used to trap and quantify volatile
compounds responsible for the off-flavors produced.
Volatiles analysis
To analyze the effects of purge temperature, meat samples were
purged at 40, 50, 60, and 80⬚C with helium gas. Individually vacuumpackaged raw (16) and vacuum-packaged cooked (16) turkey thigh
patties were used for the purge-temperature study and each patty was
replicated once. Meat samples were prepared and placed in a sample
tray immediately before analysis. Sample temperature was increased
to the target temperature in a sample holder before purging, and that
temperature was maintained throughout the purging period. To analyze the effects of sample holding time on volatile profiles, samples
for all 7 holding times were taken from one turkey thigh patty. Four
raw and four cooked meat patties were used, and samples were purged
at 32⬚C. Lipid oxidation and volatiles were determined after 0, 40, 80,
160, 320, 640, and 1280 min of holding at 4⬚C.
A Precept II and Purge-and-Trap Concentrator 3000 (TekmarDorham, Cincinnati, OH) were used to purge and trap volatiles from
samples. A GC (Model 6890; Hewlett Packard Co., Wilmington, DE)
equipped with a flame ionization detector (FID) was used. For volatiles analysis, 2g ground meat was placed into a 40-mL sample vial and
purged with helium gas (40 mL/min) for 11 min using the autosampling unit (Precept II) equipped with a robotic arm. Volatiles were
trapped using a Tenax/Silica gel/Charcoal column (Tekmar-Dorham,
Cincinnati, OH) and desorbed for 1 min at 220⬚C.
A split inlet (split ratio, 49:1) was used to inject volatiles into the
GC column (HP-Wax capillary column, 60 m, 0.25 mm i.d., and 0.25mm film thickness; Hewlett Packard Co., Wilmington, DE), and ramped
oven temperature conditions (32⬚C for 2 min, increased to 40⬚C at
2⬚C/min, increased to 70⬚C at 5⬚C/min, increased to 100⬚C at 10⬚C/
min, increased to 140⬚C at 20⬚C/min, increased to 200⬚C at 30⬚C/min,
and held for 3.5 min) were used. Inlet temperature was 220⬚C, and
detector was 280⬚C. Helium was the carrier gas, and column flow was
1.1 mL/min. Detector air, H2, and make-up gas (He) flows were set at
300 mL/min, 30 mL/min, and 28.8 mL/min, respectively. Standard
kits (aldehydes, ketones, alcohols, hydrocarbons, and alkenes C6C10) were purchased (Chromatography Research Supplies, Inc., Addison, IL), and a total of 49 standards (9 aldehydes, 11 alcohols, 13
ketones, and 16 hydrocarbones) were used to identify peaks. A few
unidentifiable peaks with the standards were identified using a Mass
Selective detector (MSD, Model 5973; Hewlett Packard Co., Wilmington, DE). GC-MSD analysis was performed with the column and
other purge-and-trap/GC conditions as above. The ionization potential of MSD was 70 eV and scan range was 50 to 550 m/e. The
identification of volatiles was achieved by comparing mass spectral
data with published data (Wiley Library, Hewlett Packard Co., Wilmington, DE). Analyses were replicated four times, the area of each
peak was integrated by using ChemStation software (Hewlett Packard
Co., Wilmington, DE), and the total peak area (pA*sec) was reported
as an index of volatiles generated from the meat samples.
Statistical analysis
The experiment was designed primarily to determine the effects of
sample temperature and sample holding time before purging on volatiles
production in raw and cooked turkey thigh. The effect of sample holding time before purging on lipid oxidation in raw and cooked thigh also
was determined. The major selected volatile components of raw and
cooked meat were analyzed independently by SAS® software (SAS
Institute, Inc., 1989). Analyses of variance were conducted to test the
effects of purge temperature and sample holding time before purge time
on volatiles production, and the Student-Newman-Keuls multiple range
test was used to compare differences among mean values. Mean values
and standard errors of the mean (SEM) were reported when necessary.
Significance of differences was defined at P⬍0.05.
RESULTS & DISCUSSION
Purge temperature
The amount of all major volatile components except pentanal and
1-octanol was influenced by the purge temperature of raw turkey
thigh meat (Table 1). The amount of total volatiles produced in raw
thigh meat gradually increased as purge temperature increased from
40⬚C to 80⬚C. However, only the raw samples purged at 80⬚C produced more total volatiles than those purged at lower temperatures.
The amount of total volatiles in raw meat purged at 80⬚C was 1.5- to 2fold more than those purged at lower temperatures. Among individual
volatiles the amounts of heptane, 2-propanone, 2-butanone, hexanal,
1-penten-3-ol, heptanal, 1-pentanol, octanal, cyclohexanone, 1-hex-
Table 1—Effect of purge temperature on production of volatiles in
raw turkey thigh meate
Purge temperature
Compound
40°C
50°C
60°C
80°C
SE
Peak area (pA ∞ sec)
2-Methylbutane, pentane
Heptane
Propanal
Octane
2-Propanone
2-Butanone
Pentanal
Tetradecane
Dimethylheptane
Trimethylhexane
Tridecane
Hexanal
1-Penten-3-ol
Heptanal
1-Pentanol
Octanal
Cyclohexanone
1-Hexanol
Nonanal
1-Heptanol
1-Octanol
Total volatiles
5.4b
2.2c
4.0b
1.1b
32.7b
43.3b
6.0
22.2a
21.0a
8.5b
21.8a
52.3b
1.1c
1.6b
5.6c
1.1b
1.1b
1.0c
3.8c
3.1d
1.7
241.6b
6.4b
5.5b
7.5a
2.2b
40.3b
44.5b
6.7
3.4b
2.0c
2.8c
2.4b
84.9a
1.9b
3.4ab
10.5b
2.3ab
2.4a
3.8b
8.4bc
5.5c
3.3
251.1b
13.8a
6.1b
7.8a
6.0a
43.8b
57.8b
6.0
3.0b
1.0c
2.8c
4.6b
101.1a
2.2b
4.9a
13.2b
3.2ab
2.4a
3.6b
17.4a
8.0b
2.0
311.3b
8.8b
12.5a
8.3a
1.7b
60.2a
141.1a
8.6
15.7a
13.6b
15.2a
24.0a
87.2a
3.2a
5.2a
21.1a
4.2a
2.8a
5.8a
12.5ab
10.3a
3.2
466.0 a
1.1
0.8
0.6
0.5
3.3
13.3
0.8
2.1
1.7
1.0
2.5
5.8
0.2
0.8
1.0
0.6
0.2
0.3
1.9
0.4
0.4
24.9
a-dDifferent letters within a row are significantly different (P< 0.05). SEM, standard error of the
mean.
eSamples (2 g) were purged immediately after sampling . Sample vials were held in a sample
holder and purged at the designated temperature. n = 4.
anol, nonanal, and 1-heptanol in raw samples showed increasing trends
with purge temperature, but the changes of 2-methylbutane+pentane
and alkanes (octane, tetradecane, dimethylheptane, trimethylhexane,
and tridecane) were not consistently related to temperature changes.
The production of octane and 2-methylbutane/penane were the highest
at 60⬚C, but the other alkanes were produced more at 40⬚C and 80⬚C
than at 50⬚C and 60⬚C. Changes of volatile composition were the
greatest when the purge temperature increased from 60⬚C to 80⬚C.
The temperature-independent changes of 2-methylbutane+pentane and
some alkanes at 40⬚C to 50⬚C to 60⬚C could not be explained.
In cooked thigh, the purge temperature-dependent changes of volatiles were more prominent and were considerably greater than those
in raw samples (Table 2). Except for dimethylheptane, trimethylhexane, tridecane, and 1-octanol, all other volatiles including total volatiles gradually increased as purge temperature increased. As in the raw
samples, the amounts of many volatile compounds changed considerably as the purge temperature increased 60⬚C to 80⬚C. Cooked thigh
purged at50⬚C, produced almost two times more total volatiles than
those purged at 40⬚C, and the amount of total volatiles produced at
80⬚C was about 5-fold greater than those produced at 40⬚C. Among
individual volatiles, hexanal increased the most, but the amounts of
other volatiles (except some alkanes) also increased greatly. As in the
raw samples, the production of alkanes (octane, tetradecane, dimethylheptane, trimethylhexane, and tridecane) was not consistent with
temperature changes (Table 2).
More than 1000 flavor compounds have been identified as flavor/
aroma compounds in commonly consumed meat specie-beef, pork,
poultry, and lamb (Ramarathnan et al., 1993). Such compounds are
produced by thermal degradations of sugar, amino acids, or nucleotides as well as Maillard reactions and lipid oxidation (Shahidi et al.,
1986; Specht and Baltes, 1994). However, the major volatile components we found were the reaction compounds from lipids with no
products derived from protein or sugar being produced. The major
reason for such relatively simple volatile composition compared with
other studies (Tanchotikul and Hsieh, 1991; Ajuyah et al., 1993; Specht
and Baltes, 1994) was due to our sampling method. Exhaustive distillation of meat at high temperatures does not represent the true volatile
composition and flavor characteristics of raw and cooked meat under
practical testing (e.g., sensory analysis) conditions. Lactones, aromatVolume 64, No. 2, 1999—JOURNAL OF FOOD SCIENCE 231
Volatile Profiles of Raw/Cooked Turkey Thighs . . .
Table 2—Effect of purge temperature on production of volatiles in
cooked turkey thigh meatd
Table 3—Effect of sample holding time in an autosampler tray before
purge on production of volatiles in raw turkey thigh meatf
Sample holding time (min)
Purge temperature
Compound
40°C
50°C
60°C
80°C
SE
Compound
0
40
80
Peak area (pA ∞ sec)
2-Methylbutane, pentane
Heptane
Propanal
Octane
2-Propanone
2-Butanone
Pentanal
2-Methylpentanal
Tetradecane
Dimethylheptane
Trimethylhexane
Tridecane
Hexanal
1-Penten-3-ol
Heptanal
1-Pentanol
Octanal
Cyclohexanone
1-Hexanol
Nonanal
1-Heptanol
1-Octanol
Total volatiles
60.9c
70.1b
33.0c
7.1c
54.5b
33.2b
44.8c
13.1c
29.7a
16.2ab
28.1a
28.0a
213.9c
3.1c
6.6c
10.1c
5.1c
5.9c
7.3b
7.1c
5.1c
5.1a
687.9c
120.2b
136.9b
88.7b
114.3b
72.0b
71.1b
15.7bc
19.6b
73.0b
76.7b
61.6b
66.7b
89.4bc
114.5b
13.6c
18.6b
3.1b
18.7a
10.8b
12.8b
4.5b
12.7b
2.8b
15.9a
629.6b
848.8b
6.0b
7.6b
12.9bc
18.0b
26.51b
35.4b
8.24c
10.9b
16.6b
21.9b
4.8b
5.6b
14.4bc
18.8b
13.81bc
20.5b
2.4b
2.1b
1290.4b
1665.5b
240.1a
300.9a
125.6a
37.7a
134.3a
235.2a
227.6a
24. 5a
22.2a
17.3a
18.2ab
25.5a
1460.9a
16.2a
45.8a
72.1a
33.6a
44.5a
16.3a
62.8a
64.3a
6.0a
3233.5a
160
320
640
1280 SEM
Peak area (pA x sec)
13.1
14.0
6.9
3.1
6.8
18.8
15.1
1.2
4.1
1.4
3.8
4.0
83.7
0.7
2.2
4.2
1.5
3.1
0.9
3.0
3.1
0.5
151.0
2-Methylbutane,
6.1c
7.9c
9.90c 11.2c 18.7b
26.4a 1.7
pentane
4.1c
2.0c
2.3c
4.4bc
5.5ab 7.2ab
8.3a 0.9
Heptane
1.0c
3.3cd 4.7cd
7.9cd 11.7bc 17.9ab 23.5a 2.2
Propanal
1.6d
2-Propanone
31.7
31.3 31.5
31.9
34.0 33.1
33.4
2.9
2-Butanone
39.5
38.1 38.1
39.8
41.2 37.4
35.5
7.3
Pentanal
1.8
1.3
1.0
1.3
1.2
1.1
1.0
0.2
2-Methylpentanal 14.0a
9.5ab 6.9ab
8.4ab
6.9ab 7.5ab
5.5b 1.8
Hexanal
18.9d 50.4cd 66.3cd 121.6cd 183.3bc 268.5ab 334.7a 33.8
5.0cd 6.7cd
9.9c
15.1b 19.7b
24.9a 1.7
1-Pentanol
3.1d
Cyclohexanone
0d
0d
1.5cd
2.9cd
5.3bc 8.3b
12.8a 1.1
1.0c
1.2c
1.7c
2.8b
3.5b
4.4a 0.3
1-Hexanol
1.0c
Nonanal
2.4
2.4
2.7
2.9
3.4
3.5
3.9
0.3
2.5e
3.2de
4.6d
7.2bc 9.0ab 11.2a 0.9
1-Heptanol
1.7e
Total volatiles
120.9d 152.8cd173.9cd 247.1cd 328.7bc 435.5ab 525.5a 45.6
a-eDifferent letters within a row are significantly different (P<0.05). SEM, standard error of the
mean.
fSamples (2g) were purged after holding in a sample tray (4°C) for designated times. Sample
purge temperature was 32°C. n = 4.
a-cDifferent letters within a row are significantly different (P<0.05). SEM, standard error of the
mean.
dSamples (2g) were purged immediately after sampling. Samples were held in a sample
holder and purged at the designated temperature. n = 4.
Table 4—Effect of sample holding time in an autosampler tray before
purge on production of volatiles in cooked turkey thigh meate
Sample holding time (min)
ic and nonaromatic heterocyclic compounds, sulfur-containing compounds, and furan compounds are important contributors to meaty
aroma notes of cooked meat (Chang and Peterson, 1977; Min et al.,
1979; Wasserman, 1979; Ruther and Baltes, 1994). However, few, if
any, sulfur-containing compounds, pyrazines, and furans were detected in cooked thigh meat under all purge temperature and holding time
conditions. That does not indicate protein or sugar derivatives are not
important components for the flavor/odor of meat. Most sulfur compounds had low odor thresholds (Wick et al., 1967; Angellini et al.,
1975) and could be important for off-odor production in meat. The
amounts of such compounds under our study conditions, however,
were negligible compared with lipid by-products.
A major reason for high volatile production with high purge temperatures is the acceleration of lipid oxidation during sample purge.
High temperature accelerates chemical reactions and oxygen in the
headspace of sample vials and it should have been the driving force
for lipid oxidations of thigh meat in the vial. Although a notable increase in total volatiles and change in volatile composition was observed as purge temperature of raw samples increased, the oxidative
changes of the cooked samples were faster than those of the raw
samples. The high susceptibility to lipid oxidation of cooked meat
compared with raw meat is well documented (Ahn et al., 1992, 1993).
Another reason for the higher volatiles production at high purge temperature would be the increased volatilities of more compounds, especially those with relatively hugh molecular weights. Thermal modification of meat proteins, especially in raw turkey thigh, and lower
binding affinity of structurally modified meat proteins to volatile compounds at high purge temperatures (O’Neill and Kinsella, 1987;
O’Neill and Kinsella, 1988) could explain the higher volatiles production in thigh meat purged at high temperature.
The amount and composition of volatile compounds in meat samples can vary widely with cooking temperature (Ang et al., 1994).
However, our results show that minor differences in analytical conditions, such as purge temperature within a given sample, can change
the profile of volatiles.
Sample holding time
More than 160 min sample holding time before purge can cause
a problem when volatiles are analyzed using a purge-and-trap/GC
232
JOURNAL OF FOOD SCIENCE—Volume 64, No. 2, 1999
Compound
0
40
80
160
320
640
1280 SEM
Peak area (pA x sec)
2-Methylbutane,
pentane
88.8d 99.9cd 107.3cd 131.3bcd 156.7abc171.9ab 198.7a 14.7
93.4bc 105.2bc 120.7ab 142.7a 8.8
Heptane
71.0c 74.3c 69.0c
Propanal
61.1d 71.7d 72.9d 100.7d 140.1c 173.2b 215.9a 1 1.2
2-Propanone
56.8
54.1 48.3
53.8
53.2 62.8
54.9
4.8
2-Butanone
36.2
36.3 34.4
38.7
36.1 35.0
31.9
2.2
91.0c 118.6bc 144.3ab 170.0a 13.2
Pentanal
69.2c 70.6c 66.9c
2-Methylpentanal 2.2
1.7
1.5
1.9
1.4
1.3
1.6
0.3
Hexanal
429.1d 530.6cd545.6cd 772.0c 1055.1b1181.8ab 1363.6a 80.2
26.8bc 32.1bc 42.5ab 48.7a 4.4
1-Pentanol
16.2c 19.1c 19.7c
Cyclohexanone
13.5b 15.9b 16.5b
28.3b
41.1a 49.2a
48.0a 4.0
3.2b
3.0b
4.7ab
4.3ab 5.1a
5.9a 0.5
1-Hexanol
3.1b
Nonanal
9.5
9.5
7.5
8.0
7.9
10.8
10.2
1.5
1-Heptanol
7.9b
9.5b
9.2b
13.2ab 16.9ab 26.7a
25.2a 3.6
Total volatiles
864.4c 996.4c1001.9c 1363.9c 1768.5b2025.2ab 2317.6a 129.2
a-dDifferent letters within a row are significantly different (P<0.05). SEM, standard error of the
mean.
eSamples (2 g) were purged after holding in a sample tray (4°C) for designated times. Sample
purge temperature was 32°C. n = 4.
unit equipped with an autosampler. The autosampler can be a source
of considerable experimental error due to the variation in time samples reside in the autosampler before being purged. With each purge
cycle of 30 min, a 48-position autosampler requires 24h from the
first to the last sample. Each vial has a 40 mL headspace of which
20% of gas in the headspace is oxygen. Thus oxidative changes can
occur while samples are in the autosampler causing artifact changes
in volatiles.
As expected, sample-holding time before purge influenced the
amount and composition of volatile components of raw meat (Table
3). The amounts of 2-methylbutane+pentane, heptane, propanal, hexanal, 1-pentanol, cyclohexanone, 1-hexanol, 1-heptanol, and total
volatiles gradually increased as holding time of raw samples before
analysis increased. However, the amounts of 2-propanone, 2-butanone, pentanal, 2-methylpentanal, and nonanal did not change.
Among individual volatile compounds, hexanal increased the most,
but other volatile components increased proportionally. Increases in
many volatile compounds were observed when raw samples were
Table 5—Changes of TBARS in raw and cooked turkey thigh meat
during sample holding timef
Sample holding time (min)
Meat type
Raw meat
Cooked meat
0
0.27e
1.35e
40
0.23e
2.14d
80
160
320
640
TBARS (mg MDA/kg meat)
0.57c
0.48d
0.65c
0.92b
2.92c
3.11c
3.56c
5.28b
1280 SEM
1.41a 0.03
6.51a 0.19
a-eDifferent letters within a row are significantly different (P<0.05). SEM, standard error of the
mean.
fSamples (5g) were put in 50-mL test tubes, capped tightly, and held at 4°C for designated
times before analysis. n = 4.
held for 320 min or longer, but volatiles did not increase significantly up to 160 min (Table 3).
Changes in volatiles in cooked samples during holding time were
similar to those of the raw samples except for pentanal (Table 4). The
amount of pentanal in the raw samples did not change with time, but in
cooked samples, a 3-fold increase occurred after 1280 min holding at
4°C. As in raw samples, increases in most of volatiles (including total
volatiles) were observed when cooked meat samples were held 320
min or longer. Although the rates of volatile increase in cooked samples during holding time were lower than those in the raw samples, the
amount of increased volatiles was much higher.
Oxidative changes in raw and cooked thigh occurred during sample
holding time (Table 5). Similar to the volatiles, TBARS values gradually
increased during holding time due to residual oxygen in the sample vial.
The increase of TBARS in raw and cooked samples during 1280-min
holding periods were 4- to 5-fold higher than those at 0 min. This
indicated that the amount of residual oxygen in the sample vial was high
enough to cause changes in volatile profiles of meat. Therefore, volatiles
of meat should be purged immediately after sampling if oxygen is not
removed from the headspace of the sample vial.
CONCLUSIONS
THE AMOUNT OF RESIDUAL OXYGEN IN SAMPLE VIALS MAY CAUSE
changes in volatile profiles of meat. Autosamplers can be a source of
considerable experimental error due to variations in time samples reside in the autosampler before being purged. Therefore, meat should
be purged at the meat temperature, and residual oxygen in sample vials
should be eliminated to prevent oxidative changes during sample holding time. If meat samples are to be held more than 3 h in an autosampler, procedures that can remove residual oxygen (e.g., oxygen absorber) in the sample vial should be employed. Flushing sample vials
with inert gas (e.g., helium or nitrogen) also may reduce the residual
oxygen in the sample vial.
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Ms received 5/29/98; revised 7/30/98; accepted 8/6/98.
Journal paper No. J - 17927 of the Iowa Agriculture & Home Economics Experiment Station, Ames,
IA 50011. Project No. 3322, and supported by the Food Safety Consortium.
Volume 64, No. 2, 1999—JOURNAL OF FOOD SCIENCE 233