Meat
PII:
SO309-1740(96)00001-0
Sciwwr, Vol. 43, Nos 34, 291-299, 1996
Copyright C 1996 Elsevier Science Ltd
Printed in Great Britain. All rights reserved
0309- I740/96 $15.00 + 0.00
ELSEVIER
Effects of Dietary a-Linolenic Acid on the Fatty Acid Composition,
Storage Stability and Sensory Characteristics of Pork Loin
D. U. Ahn,“* S. Lutzb & J. S. Sim’
“Animal Science Department,
Iowa State University, Ames, IA 50011, USA
“Processing Services Division, Agriculture Food Development
Centre,
Leduc, Alberta T9E 6M2, Canada
‘Deptartment
of Agricultural,
Food and Nutritional Science, University of Alberta, Edmonton,
Alberta T6G 2P5, Canada
(Received
5 September
1995: accepted
I I December
1995)
ABSTRACT
Ejects of dietary a-linolenic acid on the fatty acid composition, storage stability and sensory
characteristics of cooked pork were studied. Dietary cr-linolenic acid (LNA) significantly
(p < 0.05) increased the proportion of n-3 fatty acids and the degree of unsaturation in the
neutral lipids and phospholipids. The increases in n-3 fatty acids were observed in the total
lipids, triglycerides, phosphatidylethanolamine and phosphatidylcholine, and mainly consisted
of C18:3n3, C20:5n3 and/or C22:5n3.
The thiobarbituric acid reactive substances (TBARS) values (mg malondialdehyde per kg
meat) of cooked vacuum packaged loins remained below 1.5, but in loose packaged loins
TBA RS values increased more than 3 times those of 0 time values during 2-day storage at
4’C. The TBARS values of loins after LNA-enrichment were significantly higher than those
of the control in both vacuum and loose packaging, and the increase of unsaturation in fatty
acids had a strong prooxidant effect. The increase in dietary LNA enrichment increased oxidation (TBARS values) and had a detrimental efSect on the acceptability ofcookedpork loins
held for 2 days in loose packaging. Copyright c 1996 Elsevier Science Ltd
INTRODUCTION
The protective effects of n-3 lipids against cardiovascular
diseases, cancer and rheumatoid
arthritis (Addis, 1989; Fernandes & Venkatraman,
1993) have caused researchers to study
the dietary enrichment
of animal products and tissues with n-3 fatty acids. Sklan et al.
(1983) and Lin et al. (1989) reported that feeding different dietary fats affected the fatty
acid composition
of neutral lipids significantly
but phospholipid
composition
was influenced only slightly, and feeding diets with high n-3 fatty acids effectively enriched chicken
meat with n-3 fatty acids (Phetteplace & Watkins, 1989; Olomu & Baracos, 1991; Ajuyah
et al., 1993). However, one of the important
questions about n-3 polyunsaturated
fatty
acid enriched meat and meat products is their oxidative stability during storage and their
taste after cooking.
*To whom correspondence
should be addressed.
291
292
D. U. Ahn, S. Lutz, J. S. Sim
Research results indicated that the development
of lipid oxidation is closely related to
the availability
of oxygen, free ionic iron (Kanner et al., 1988; Ahn et al., 1993a), and the
nature, proportion,
and degree of unsaturation
of the fatty acids in the lipids (Lillard,
1986; Gunstone,
199 1). The fatty acid composition
of the phospholipids
of the muscle cell
membranes is especially important in determining
the oxidative stability of meat, since the
oxidative changes in meat are initiated mainly from the membrane components
of muscle
(Pikul et al., 1984; Buckley et al., 1989). Wilson et al. (1976) reported that the role of
triglycerides
in warmed-over
flavor is a minor one when compared
to that of phospholipids, and Igene & Pearson (1979) concluded that phosphatidylethanolamine
(PE) is
the most important
phospholipid
in the complex reaction that leads to warmed-over
flavor. They also showed that total lipid and total phospholipids
significantly
affected
TBA numbers, but flavor ratings of samples were not always consistent with the sensory
scores.
Ahn et al. (1993b, 1995) reported that the effects of prooxidants,
total lipid and fatty
acid composition
of meat patties were highly significant
only when oxygen was freely
accessible to the patties during storage, and that the lipid oxidation levels in raw meat,
before cooking, were very critical in determining
the lipid oxidation conditions
in cooked
meat.
The objectives of this research were to determine the effect of dietary cr-linolenic acid on
the fatty acid composition
of muscle, and to determine the effect of different packaging
systems on the storage stability and sensory characteristics
of cooked pork.
MATERIALS
AND
METHODS
Feeding and product preparations
Forty-eight
female piglets at 20 kg body weight (35 days old) were randomly allotted to
16 pens (three piglets per pen) and four experimental
diets (four pens per diet) containing
four levels of cr-linolenic acid (0, 1.5, 2.5 and 3.5%). Flax seed was used as a source of
cz-linolenic acid. The four experimental
diets were wheat-barley-soybean
meal based, and
all diets were isocaloric, isonitrogenous
and balanced to meet NRC (1988) requirements
for growing pigs. The trial was continued for 4 months, and feed and water were provided
ad libitum.
At the end of the 4 month feeding trial, pigs (100 kg body weight) were slaughtered at a
local processing plant, and chilled in a 4°C cold room for 24 hr. One pig from each pen
(four pigs per treatment)
was randomly
selected, transported
to a government
certified
meat packer and whole Longissimus dorsi (LD, loin) muscles from both sides of the carcass (approximately
1 kg total) were separated within 48 hr after slaughter.
Sample preparation for sensory and storage stability study
The LD muscles were brought to the Agriculture
Food Development
Center (Leduc,
Alberta) immediately
after deboning, and stored overnight at 4°C. The LD muscles were
wrapped with aluminum
foil and roasted in a pre-heated electric oven at 350°C until the
internal temperature
of the meat reached 85°C (approximately
100 min). After cooking,
half of the meat was vacuum packaged in two bags (1 bag for for 3 hr and another for
48 hr storage and analysis) within 15 min of cooking; the same amount was chilled at
room temperature
(22°C) for 15 min and then loosely packaged in two oxygen-permeable
plastic bags to obtain cooked meat with free oxygen accessibility. Samples were stored up
to 48 hr in a refrigerator (4°C).
Dietary,fht on the storage stability and sensory characteristics of pork
Measurement
of total fat, fatty acid composition
293
of lipid and lipid classes
Immediately
after cooking and packaging, the cooked meat was brought to the University
of Alberta laboratory along with approximately
20 g of raw loin pieces from each carcass.
Sampling for the total fat, fatty acid composition
and lipid classes was started within an
hour after the arrival of the samples. Two to three grams of sample were weighed into a
test tube with 20 ml Folch solution (chloroform:methanol=2:1;
Folch et al., 1957) and
homogenized
with a Polytron (Brinkman,
Type PT 10/35, Westbury, NY) for 5-10 s at
high speed. BHA (butylated hydroxy anisole) dissolved in 98% ethanol was added prior
to homogenization
at a level of 35 pg/mg fat. After filtration and phase separation,
the
top layer (methanol and water) of the solution was siphoned off. Five ml of the chloroform layer were put into a glass scintillation
vial, dried in a block heater (1 hr at 5O’C)
under nitrogen atmosphere,
and used for total fat and fatty acid composition.
The dried
lipids were redissolved with an appropriate
amount of chloroform to obtain a sample with
50 mg lipid/ml.
50 ~1 of the lipid solution
and 0.5 ml boron-trifluoride-methanol
methylation
solution were added into a screw capped tube, capped tightly and incubated
in a water bath at 90°C for 1 hr. After cooling to room temperature,
5 ml water and 5 ml
hexane were added to each tube, mixed well and left overnight for phase separation.
The fatty acid methyl esters of lipids were separated and quantified
by automated
gas
chromatography
with an on-column
injector (Model 3400, Varian, Sunnyvale,
CA) as
described in detail by Jiang et al. (1992).
The rest of the organic layer from the Folch preparation
was dried under nitrogen
atmosphere for 2 hr and redissolved with chloroform plus 2-3 drops of ethanol to obtain
a solution with approximately
150 mg lipid/ml. Two hundred ~1 of the resulting sample were
loaded onto precoated silica gel G plates (20x20 cm) that had been previously activated
by heating at 120°C for 2 hr. The plates were developed in two developing solutions. The
first developing
solution was chloroform:methanol:water
(65:25:4) and the plates were
incubated until the solvent front reached 10 cm from the origin (about 40 min). The plates
were air dried for 10 min and then incubated for about 20 min in a second tank containing a hexane and diethyl ester (4:l) solution. The plates were air dried and sprayed with
0.1% (w/v) 2’,7’-dichlorofluororescein
in ethanol. Triglycerides
(TG), phosphotidylethanolamine (PE) and phosphatidylcholine
(PC) were identified under UV light, scraped off
into screw-capped tubes, methylated and analysed for fatty acids as described above.
Thiobarbituric
acid analysis
TBARS (thiobarbituric
acid reactive substances) values of raw and cooked meat samples
were determined
3 and 48 hr (storage at 4°C) after cooking for the cooked, and 3 days
after slaughter for the raw meat samples. TBARS values were measured by the extraction
procedure of Salih et al. (1987) with some modifications
(Ahn et al., 1992).
Sensory test
Sensory tests of cooked loin muscle were conducted
3 and 48 hr after cooking. The
roasted loins were warmed up in a 700 watt microwave oven at full power immediately
before serving. A loin from each dietary treatment
was presented
to 13 panelists
(approximately
10 g per sample), and hence, four groups of 13 panelists
(total 52
untrained
panelists) tasted loins from each dietary treatment.
A 15 cm linear hedonic
scale, anchored with the words ‘like’ and ‘dislike’ at opposite ends, was used to rate the
samples on taste. The responses from the panelists were expressed in numerical
values
ranging from 0 (the lowest rating) to 15 (the highest rating) to the nearest 0.5 cm.
294
D. U. Ahn, S. Lutz, J. S. Sim
Statistics
The sensory data from four panel groups were pooled after finding no difference (p > 0.05)
among the sensory groups within a replication. TBARS and sensory values of loins with
different storage time were analyzed independently. The effect of packaging methods on
the TBARS and sensory values of loins within a dietary treatment was compared using
Student’s t-test, and the dietary effect within a packaging method was compared using
Student-Newman-Keuls multiple range test (SAS, 1986).
RESULTS
AND DISCUSSION
Effect of dietary fat on the fatty acid composition
of loin muscle
The composition of fatty acids in pork loin muscle was affected (p < 0.05) by the dietary CYlinolenic acid as reported earlier for muscles of broiler chickens (Ahn et al., 1995). The
major changes in loin muscle fatty acids caused by the dietary cx-LNA resulted in increases
in polyunsaturated fatty acids (PUFA), and decreases in saturated fatty acids (SAFA) and
Fatty Acid Composition
TABLE 1
(%) of the Total Lipids from Pork Loin Muscles
Treatments
from Different
Dietary
Dietary a-linolenic acid
Fatty acid
Control
1.5%
2.5%
1.37a
1.17b
1.14b
Cl6:O
Cl6:ln7
Cl8:O
Cl8:ln9
Cl8:2n6
Cl8:3n3
C20: 1n9
22.6Sa
2.66a
11.01
39.74a
15.64
1.54c
C20:2n6
C20:3n3
C20:3n6
C20:4n6
C20:5n3
C22:4n6
C22:5n3
C22:6n3
0.51a
0.15”
0.34a
2.40a
0.26b
0.32”
0.61b
0.32
35.03a
42.90=
22.07=
16.15
3.04”
2.88”
20.99b
2.14b
10.53
33.25b
16.61
8.54b
0.37b
0.4lb
0.72b
0.32a
l.80b
1.33a
0.19b
1.32a
0.30
32.70b
35.76b
31.54b
17.02
2.31ab
12.2lb
20.22b
1.93b
10.48
32.79b
15.38
12.26a
0.39b
0.39bC
1.07a
0.22b
1.02c
1.29a
0.09c
1.OSa
0.28
31.84b
35.llb
33.05a
15.77
1.33b
15.95”
c14:o
Total SAFA’
Total MUFA
Total PUFA
n6 di-unsaturated
n6 3 or more unsaturated
n3 3 or more unsaturated
0.50a
3.5%
SEM
1.15b
20.31b
1.95b
10.59
32.51b
15.42
12.27=
0.39b
o.35c
1.03”
0.23b
1.02c
1.32”
0.10’
1.07a
0.22
32.06b
34.85b
33.11”
15.77
1.35b
15.99a
0.02
0.14
0.05
0.12
0.42
0.29
0.34
0.01
0.01
0.03
0.01
0.09
0.06
0.01
0.05
0.02
0.24
0.45
0.19
0.29
0.17
0.38
‘Abbreviation:
SAFA, saturated fatty acid; MUFA, monounsaturated
fatty acid; PUFA, polyunsaturated
fatty acid; SEM, standard error of mean. n = 4.
“bcValues with different letters within a row of the same fatty acid are significantly
different
(p < 0.05).
Dietary fat on the storage stability and sensory characteristics of pork
295
monounsaturated fatty acids (MUFA). The increase in PUFA was caused by the increase
in n-3 fatty acids (Table 1). Among the n-3 fatty acids, the increase of cr-linolenic acid
(C18:3n3) was the most prominent, but the increases in C20:3n3, C20:5n3 and C22:5n3
were also significant. The amount of n-6 diunsaturated fatty acids were not affected by the
dietary fat (p > O.OS),and n-6 fatty acids with more than three double bonds decreased as
much as 0.551.5%, depending on the dietary treatments. The composition of fatty acids in
triglycerides (TG) was similar to that of the total lipids but the increases in C20:5n3
caused by dietary LNA were greater in the total lipids (Table 1). The proportion of triglycerides (TG) was higher (7-10%) in MUFA but lower (5-8%) in PUFA compared
with those of the total lipids (data not shown). The proportions of very long-chain fatty
acids (C22:5n3) in TG were very small ( < 0.2%).
The changes of fatty acids in PE were quite different from those of lipid and TG
(Table 3). Compared with lipid and TG, changes in the proportions of total MUFA and
PUFA caused by dietary LNA were relatively small. However, there were large changes in
the composition of fatty acids, especially in the PUFA with more than three unsaturations. Approximately l&13% of n-6 fatty acids with more than three double bonds were
replaced by the n-3 fatty acids with more than three double bonds, and the amount of
n-3 fatty acids comprised up to 25% of total PE fatty acids. Among the individual n-3
fatty acids, the increases in C18:3n3, C20:5n3 and C22:5n3 were the most prominent but
the increase in Cl8:3n3 was much smaller than that in lipid and TG. Among the individual
n-6 fatty acids, C20:4n6 was affected the most but others such as C20:2n6 and C22:4n6
were also reduced significantly by the dietary treatments (Table 2). The changes in fatty
acid composition of PE by dietary treatments were rather extensive. However, the changes
in the degree of unsaturation were not as large as in lipid and TG.
The composition of PC fatty acids was also affected by the dietary treatment but the
changes were relatively small compared with fatty acid changes in PE. The major changes
in the PC portion can be summarized as an increase in PUFA and decrease in MUFA.
The increase in PUFA was within n-3 PUFA group, which increase the degree of unsaturation of overall fatty acids in the PC portion (Table 3). As in PE, the increase in
C18:3n3 was the major increase in n-3 fatty acids in PC but was not as extensive as in lipid
and TG. Although, the proportions of changes in fatty acids in PC were smaller than those
of PE, its impact on the susceptibility of PC to lipid oxidation would be as high as that of
PE due to the increase in unsaturation by the replacement of MUFA by n-3 fatty acids.
The effect of dietary LNA on fatty acids of lipid, TG, PE and PC increased as the
amount of LNA enrichment increased. However, the LNA increase caused by 3.5%
dietary LNA was not different from that of 2.5%, indicating 2.5% was an adequate level
for the dietary enrichment for LNA in pork (Tables l-3).
Effect of dietary LNA, packaging and storage on the TBARS values of loins
The TBARS values of raw pork loin indicated that the meat used in this study was fresh,
and few oxidized products were formed even in the meat with high LNA enrichment
(Table 4). Although, the TBARS value of raw pork from the 3.5% dietary LNA was
higher (p < 0.05) than that of the control, the difference was very small. The low TBARS
values of cooked, vacuum packaged meat at 0 days storage indicated that cooking had a
very small effect on the TBARS values of the meat. In vacuum packaged meat at 0 time
storage, only meat from the 3.5% LNA treatment group had higher (JJ< 0.05) TBARS
values than loins from the other dietary LNA treatments. However, in loosely packaged
meat, all the dietary enrichment treatments resulted in higher @ < 0.05) TBARS values
than the control. Also, the TBARS values of loosely packaged loins were higher (p < 0.05)
than those of vacuum packaged loins.
296
D. U. Ahn, S. Lutz, J. S. Sim
TABLE 2
Fatty Acid Composition
(%) of Phosphatidylethanolamine
from Pork Loin Muscles from Different
Dietary Treatments
Dietary a-linolenic acid
Fatty acid
c14:o
C14:ln7
C16:O
C16:ln7
C18:O
C18:ln9
C18:2n6
C18:3n3
C18:3n6
c2o:o
C20: In9
C20:2n6
C20:3n3
C20:3n6
C20:4n6
C20: 5n3
C22:4n6
C22:5n3
C22:6n3
C22:6n3
Total SAFA’
Total MUFA
Total PUFA
n6 di-unsaturated
n6 3 or more unsaturated
n3 3 or more unsaturated
Control
1.5%
2.5%
3.5%
SEM
0.10
0.13
3.95
1.59
23.07
12.36”
25.44
0.92c
0.18”
0.09
0.19”
1.49a
0.21”
1.60”
20.60”
2.04c
1.63”
2.79b
1.42”
0.18
27.39
14.29”
58.32
26.93”
24.01a
7.38’
0.11
0.15
3.66
1.48
24.65
9.93b
23.42
5.09b
0.13b
0.07
0.14b
0.67b
0.62b
1.33b
11.83b
9.45b
0.54b
5.54a
1.08b
0.13
28.62
11.69b
59.69
24.09b
13.82b
21.78b
0.09
0.14
3.45
1.57
24.64
9.94b
24.65
6.62a
O.lOb
0.08
0.14b
o.39c
0.74a
1.05”
8.92”
10.99”
0.35b
5.18”
0.84b
0.14
28.39
11.79b
59.83
25.04”b
10.42c
24.37”
0.08
0.14
3.83
1.86
24.33
9.81b
23.02
6.41a
0.09b
0.08
0.12b
o.49c
0.76”
1.13c
9.43’
11.77a
0.37b
5.31”
0.84b
0.13
28.45
11.92b
59.63
23.51b
11.02’
25.10=
0.01
0.01
0.11
0.07
0.38
0.18
0.41
0.18
0.01
0.00
0.01
0.03
0.02
0.03
0.31
0.24
0.03
0.11
0.04
0.01
0.37
0.21
0.43
0.41
0.20
0.40
‘Abbreviation: SAFA, saturated fatty acid; MUFA, monounsaturated
fatty acid; PUFA, polyunsaturated fatty acid; SEM, standard error of mean. n = 4.
abcValues with different letters within a row of the same fatty acid are significantly different
(p < 0.05).
After 48 hr (2 days) of storage in the cold room (4”C), the TBARS values of cooked
loin from 2.5% and 3.5% dietary LNA were higher than those of the controls but the
highest TBARS value in vacuum packaged loin was lower than the critical limit (TBARS
value of 1.5) for the oxidized rancid flavor. With loose packaging, the TBARS values of
cooked loins stored for 48 hr were approximately three times higher than those of 3 hr
(0 day). The TBARS values of loins from LNA-enriched diets were higher than those of
the controls in both vacuum and loose packaging. The TBARS value of cooked loins
from 3.5% LNA enrichment was higher than those of 1.5% and 2.5% in loose packaging,
but was higher than that of 1.5% in vacuum packaging. Exclusion of oxygen contact from
meat shortly (within 15 min) after cooking was highly effective in preventing lipid oxidation
of cooked pork loins, even with highly unsaturated fat.
The role of triglycerides in warmed-over flavor is reported to be minor compared with
that of phospholipids (Wilson et al., 1976), and phospholipids
in muscle cell membranes
are responsible
for about 90% of lipid oxidation
in meat (Pikul et al., 1984; Buckley
Dietary fat on the storage stability and sensory characteristics of pork
Fatty
Acid
Composition
(%)
TABLE 3
of Phosphatidylcholine
from
Dietary Treatments
Pork
Loin
Muscles
297
from
Different
Dietary a-linolenic acid
Fatty acid
c14:o
C16:O
C16:ln7
C18:O
C18:ln9
C18:2n6
C18:3n3
C20: ln9
C20:2n6
C20:3n3
C20:3n6
C20:4n6
C20:5n3
C22:4n6
C22:5n3
C22:6n3
Total SAFAl
Total MUFA
Total PUFA
n6 di-unsaturated
n6 3 or more unsaturated
n3 3 or more unsaturated
Control
1.5%
2.5%
3.5%
SEA4
0.21
31.61
0.99
8.51
20.44”
29.75
0.86”
0.10”
0.29”
0.06
0.66”
4.30”
o.44c
0.30
0.55b
0.27a
40.33
22.20a
67.51c
30.04
35.29
2.18c
0.24
33.20
0.95
7.95
15.55b
29.98
5.12b
0.08b
0.12b
0.59
0.48b
2.22b
1.61b
0.12
0.94”
0.19b
41.39
17.08b
71.47b
30.10
32.92
8.45b
0.18
32.32
0.70
9.35
13.62b
30.07
6.77”
0.08b
0.18b
0.33
0.48b
2.16b
1 99”b
0:21
0.96a
0.16b
41.85
14.89b
73.56”
30.25
33.10
10.21a
0.20
32.02
0.86
9.04
13.83b
30.32
6.76
0.07b
O.llb
0.35
0.48b
2.lOb
2.27”
0.07
0.95”
0.16b
41.26
15.17b
74.01”
30.43
33.08
10.50a
0.01
0.54
0.04
0.27
0.38
0.47
0.23
0.00
0.01
0.08
0.02
0.11
0.07
0.04
0.03
0.01
0.48
0.42
0.23
0.47
0.25
0.25
‘Abbreviation:
SAFA, saturated fatty acid; MUFA, monounsaturated
fatty acid; PUFA, polyunsaturated
fatty acid; SEM, standard error of mean. n = 4.
abcValues with different letters within a row of the same fatty acid are significantly
different
(p < 0.05).
et al., 1989).
However, the results of the current research indicated that the composition of
fatty acids in the lipid of LNA-enriched loins was also very important in determining the
development of lipid oxidation of loosely packaged loins during storage. The increase of
three or more polyunsaturated fatty acids in TG (8-14.5%) and PC (46.5%) was much
greater than that of PE (1 S%), and the high TBARS values of loins from LNA-enriched
diets seemed to related mainly to the increase in n-3 polyunsaturated fatty acid of TG and
PC.
Effect of diets and packaging on the sensory evaluation of roasted loins
The sensory properties of the roasted loins at day 0 were not affected by the dietary
treatments, and the sensory scores were high (favorable) in all samples (Table 5). The
sensory score of vacuum packaged loins from the 2.5% LNA treatment was lower than
those of the control and 3.5% LNA, which can not be explained by relating it with
TBARS values of the meat. Considering the high sensory scores and very low TBARS
values of all the loins in vacuum packaging, this difference was not generated by the oxidation products in meat. The preference of the panelists for the flavor of freshly cooked
meats may have been the major factor.
D. U. Ahn, S. Lutz, J. S. Sim
298
Effect of Packaging
and Storage
TABLE 4
on the TBARS’ Values of Pork Loins from Different
Acid Dietary Treatments
Cooked, 0 day storage2
Dietary treatment
Raw
TBARS values (mg malondialdehydelkg meat)
0.12b
Control
1.5% LNA
0.15=b
2.5% LNA
0.19ab
3.5% LNA
0.21”
0.01
SEM
a-Linolenic
Cooked, 2 days storage
Vacuum pkg
Loose pkg
Vacuum pkg
Loose pkg
0.20b”
0.25b”
0.29b”
0.46=
0.02
0.56by
0.88=y
0.83”Y
0.91ay
0.02
0.23c”
0.35h”
0.52”b”
0.62=
0.03
1.8F
2.42by
2.75by
3.60ay
0.11
‘Abbreviation:
TBARS, 2-thiobarbituric
acid reactive substances;
LNA, a-linolenic
acid; SEM,
standard error of mean. n = 4.
2O day samples were analyzed 3 h after cooking and packaging while 2 day samples were analyzed at
48 h after cooking.
abcValues with different superscript letters within a column of the same packaging system are different (p < 0.05).
XYValues with different superscript
letters within a row of the same storage time are different
@ < 0.05).
Effect of Dietary
TABLE 5
a-Linolenic
Acid on the Taste (Hedonic Scores) of Roasted
Different Packaging and Storage Conditions
Pork
Loins
with
2 day storage
Dietary treatment
Control
1.5% LNA2
2.5% LNA
3.5% LNA
SEM
0 day’
Vacuum packaging
Loose packaging
9.29*
8.93
8.25
8.32
0.22
9.46”
7.95”b
7.66b
9.38””
0.23
8.66a
7.49”b
6.43bC
5.80cY
0.24
‘0 day samples were tasted 3 h after roasting while 2 day samples were stored at 4°C for 48 h and
reheated before serving. A total 208 untrained panelists (52 panelists per each storage and packaging
condition) participated
in this test.
2Abbreviation:
LNA, cr-linolenic acid; SEM, standard error of mean.
*The responses from the panelists were expressed in numerical values ranging from 0 (the lowest
rating) to I5 (the highest rating) to the nearest 0.5 cm.
“bcValues with different superscript letters within a column of the same meat type are significantly
different (p < 0.05).
XWalues with different superscript
letters within a row of the same packaging systems are significantly different (p < 0.05).
In loosely packaged
meat, the sensory scores decreased with the increasing amounts of
dietary LNA enrichment,
and 3.5% dietary LNA enrichment
created a lower sensory
score than those of the control and 1.5% LNA treatment.
Although the differences in
fatty acid composition
of loins from 2.5% and 3.5% LNA were not significant in most
cases, the TBARS and sensory values of these two groups were different. These differences
Dietary fat on the storage stability and sensory characteristics of pork
299
could have been generated by the increase in C22:5n3 in PE of the 3.5% LNA group. The
sensory results reflected the TBARS values of pork loins, and both sensory and TBARS
coincided well with the fatty acids composition
of pork loins.
CONCLUSION
Dietary LNA increased the proportion
of n-3 polyunsaturated
fatty acids in TG and PC
of pork loins significantly,
and was responsible
for the increase in the oxidation rates of
those meats. Although the role of triglycerides in lipid oxidation of meat is reported to be
minor compared with that of phospholipids,
the composition
of fatty acids in the lipid of
loins was also very important
in determining
the development
of lipid oxidation during
storage. The vacuum packaging soon after cooking was highly effective in preventing lipid
oxidation in cooked pork loins even with high polyunsaturated
fat, and the sensory results
coincided well with the TBARS values and the composition
of fatty acids in pork loins.
This study also indicated that cooking itself has little effect on the TBARS values of the
meat, but the exposure to air during the subsequent storage had a significant effect on the
development
of lipid oxidation in cooked meat.
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