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STRUCTURE OF ANIMAL FATS



The table below gives the stereospecific distribution of fatty acids in triacylglycerols of depot fats in man and some animals.



 

sn

14:0

16:0

16:1

18:0

18:1

18:2

20:1

22:1

20:5

22:5

22:6


Man

1
2
3

4
11
1

39
10
25

5
11
4

10
2
9

33
50
51

3
9
5

          


Rat

1
2
3

2
1
2

32
10
27

5
4
5

9
1
7

32
37
37

15
45
17

          


Pig

1
2
3

2
4
1

16
59
2

3
4
3

21
3
10

44
17
65

12
8
24

          


Chicken

1
2
3

2
1
1

25
15
24

12
7
12

6
4
6

33
43
35

14
23
14

          


Herring

1
2
3

6
10
4

12
17
7

13
10
5

1
1
1

16
10
8

3
3
1

25
6
20

14
5
50

3
18
4

1
3
1

1
13
1


Cod

1
2
3

6
8
4

15
16
7

14
12
14

6
1
1

28
9
23

2
2
2

12
7
17

6
5
7

2
12
13

1
3
1

1
20
6

Menhaden		 1
2
3		 12
10.5
5		 24
20
7		 18
10.5
9		 1
2
4		 13
7.5
13;5		 1
0.5
3		 1
0.5
2		   3
17.5
16		 1
3
2		 4
17
6

Seal Blubber		 1
2
3		 2
8
0		 3
12
3		 8
35
12		 1
2
1		 38
23
18		 0
1
2		 13
4
17		 3
0
3		 8
2
11		 4
1
8		 10
2
18


Seal

1
2
3

4
11
1

11
13
4

15
30
14

1
1
1

29
30
26

1
3
1

18
3
16

8
1
7

3
1
8

2
1
6

3
1
10

Seal blubber and menhaden : data from Wanasundara U et al., J Food Lipids 1997, 4, 51

It can be seen that, as in vegetal oils, the external positions are generally occupied by saturated fatty acids, except in pig where palmitic acid is more abundant at the 2 position. Monoenes are differently distributed, oleic acid being more abundant at positions 2 and 3 in man, at positions 1 and 3 in pig and 2 in chicken. The distribution of 18:2 is also species specific. It must be noticed that fat depots in marine animals are rich in polyunsaturated fatty acids and long-chain monoenes. Results indicate that the stereospecific location of the polyunsaturated fatty acids is in the position 2 (also 3 for 20:5n-3 in cod) in fish but in position 3 for mammals (same in seal, whale and polar bear) or in positions 1 and 3 (seal blubber). This raises the question of the availability of these fatty acids from food expecting a benefic effect on diverse human functions.

Oils from fish and marine mammals are characterized by a large range of fatty acids from 12 to 26 carbon atoms and 0 to 6 double bonds. The bulk of the fatty chains is contributed by saturated (15-25%), monoenes (35-60%) and polyenes (25-40%). Among polyunsaturated, 20:5n-3 and 22:6n-3 are the most prevalent. The study of the structure of the triacylglycerol molecules of marine oils is complex because of their multiplicity and the low and differential hydrolysis by lipases of positions occupied by 20:5 or 22:6n-3, the use of the Grignard reagent being required.
From the above data obtained by chemical degradation as well as those obtained with nuclear magnetic resonance spectroscopy (Aursand M et al., JAOCS 1995, 72, 293), it may be inferred that fish and mammal oils have distinct positional distributions of w3 fatty acids. As an example, in Salmon, cod or herring, 22:5 and DHA are concentrated in the b-position (sn-2), while, in mammals, they are mainly found in the a-position (sn-1,3). This may be important in considering the bioavailability of these important fatty acids after ingestion of marine foods from various origins.


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