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Which Beef has the Best Nutritional Value?
BPX70 FAME Columns
Dr. Brian Siebert and his Group from the University of Adelaide, Department of Animal Science.
TECHNICAL ARTICLE
The interaction between nutrition and heart disease has focused recent research on the role of M.I.F.A.,
Metabolically Important Fatty Acids. We have learned, for instance, about the dangers of a diet high in
saturated fats and also the need for intake of polyunsaturated acids, in particular the cis-polyunsaturated
acids. The ability to monitor foodstuffs themselves, or better still the primary food intake, for fatty acids
and their metabolites, will allow researchers to modify and ultimately reduce the human intake levels of
undesired fatty acids.
The monitoring of these polyunsaturated acids, in particular the C18 acids in "natural" products such as
meat, is not easy and much attention has been paid to the development and optimization of GC analysis
to do this. In the following article, a BPX70 - FAME optimized capillary column, was used to monitor the
fatty acid levels in cattle tissue which have been pasture fed and animals raised on concentrate diets
(cereals) in the feedlot.
SGE wishes to thank Dr. Brian Siebert and his Group from The University of Adelaide, Department of
Animal Science for the following article:
To a large extent, improving meat quality by genetic
selection will rely on increasing the proportion of
oleic acid (C18:1ω9) in cattle fat, a trait associated
with flavor, health properties and value. Total monounsaturated fatty acid content of beef can range from
30-70% depending on its origin. At 70%, the lipid
present is similar to olive oil.
Despite the low levels in cattle storage fat, the
situation is different when we examine the membrane
phospholipid fatty acids. Cattle grazing in the field
have linoleic levels of about 8-12% and linolenic
levels of 1-2%. When raised on a feed lot, linoleic
values can rise to near 30%, well above the low
values found in storage fat (Figure 1 and 2).
Apart from the high concentration of oleic acid in the
triacylglycerols of some animals, one curious finding
concerns the proportions of the two polyunsaturated
fatty acids found in the triacylglycerol and
phospholipid fractions. Since beef cattle, like all
mammals, cannot synthesize linoleic (C18:2ω6) and
linolenic (C18:3ω3), it is essential that they receive
them in their feed.
Despite the low levels of essential fatty acids in their
storage fat, cattle do not appear to suffer any clinical
effects due to these deficiencies. This is probably due
to the fact that the concentration in their muscle
phospholipid is surprisingly high (Table 1) under
grazing conditions and higher under concentrated
feeding. It appears that ruminants, despite consuming
feedstuffs relatively low in essential fatty acids and
despite converting most of what they consume into
more saturated fats, have a very efficient conversion
mechanism for retaining and incorporating essential
unsaturated fatty acids into structural membranes of
their tissue cells.
The saturated fats we consume in red meat and dairy
products are largely the result of hydrogenation of feed
lipids in the forestomach of these animals. Forages
usually do not contain a great deal of lipid (3-4%)
although some cereals and oil seeds contain
considerably more. It is considered that almost all
(more than 95%) of linoleic and linolenic in feeds are
converted to oleic and stearic. The result is that the
concentration of linoleic seldom rises above 2% in the
triacylglycerol fraction of fat tissue in cattle. A pig fed
on similar feed would have a linoleic level in adipose
tissue near 14% and human levels range from
8% to 16%.
Summary
BPX70 enables detailed monitoring of fats, which
show a significant variation in some fatty acid levels
between animal breeds that mature at different rates
and are subjected to controlled feeding regimes. The
initial findings from this study indicate that cereal
feedlot cattle have a higher level of unsaturated fatty
acids contributing to better nutritional health.
The ability to monitor these levels will also enable researchers to
improve meat quality by selective breeding or isolation of the
genes responsible for particular lipid profiles. Detailed analysis
indicates that early maturing cattle have more monounsaturated
fatty acids in adipose tissue while late maturing animals have
more polyunsaturates, particularly linoleate, in their
structural lipid.
Figure 1. FAME Analysis of Tissue from Pasture Fed
Cattle
1
2
7
5
9
12
13
10
3
15
11
4
Figure 2. FAME Analysis of Tissue from
Feedlot Fed Cattle
Table 1. Fatty Acid Levels in Muscle Tissue from
Pasture and Feedlot Fed Cattle
(% of total - normalised values)
Fatty Acid
Peak No.
Pasture
Feedlot
16DMA*
1
1.0
5.7
16:0 ( )
2
23.6
17.1
16:1 (9)
3
1.5
0.9
18DMA*
4
1.2
3.2
18:0 ( )
5
16.1
13.3
18:1 (9)t
6
0
2.1
18:1 (9)c
7
23.9
12.1
18:1 (7)t
8
1.8
2.4
18:2 (6)
9
13
28.7
18.3 (3)
10
2.6
0.7
20.3 (3)
11
1.7
2.7
20:4 (6)
12
7.6
9.5
20:5 (3)
13
4
0.8
22:4
14
0
trace
22:5 (3)
15
2
0.8
100.0
100
* Di-methyl acetal derivative of fatty aldehyde
9
2
CONDITIONS FOR FIGURES 1 & 2
5
7
1
12
4
Phase:
Column:
Initial Temperature:
Program Rate:
Final Temperature:
Carrier Gas:
Detector:
Injection Mode:
BPX70, 0.25µm film
25m x 0.32mm ID
150°C
2°C/min., 20 mins
190°C
He, 40 Kpa
FID,
Split, 0.1µL injection
Part No.
054606
8
6
11
3
10
14
13
15
BPX70 CAPILLARY COLUMNS ORDERING INFORMATION
ID
mm
film
micron
12 metre
15 metre
25 metre
30 metre
50 metre
60 metre
120 metre
0.22
0.25
054601
-
054602
054612
054603
054613
-
0.25
0.25
-
054621
-
054622
-
054623
054624
0.32
0.25
054605
-
054606
054616
054607
054617
-
0.53
0.50
054609
054619
054610
054620
-
-
-
Developed in conjunction with CSIRO Australia