Fatty acid nomenclature B

begins to count at the most oxidized carbon atom; hence the C atom of the carboxyl group is designated as "1." An accurate description of a fatty acid contains at a minimum the number of C atoms and the number as well as the position of any double bonds. An m (or n) indicates the position of the first double bond, counting from the methyl end. The correct spelling of linoleic acid, an 18 C atom fatty acid with two double bonds in C9 and C12 is: linoleic acid (18:2; 9, 12, m-6).

Longer, naturally occurring fatty acids always have an even number of carbon atoms. This is due to their synthesis from C2 units.

The following applies to fatty acids in general: the longer the chain and the fewer double bonds, the harder the fat. The shortest fatty acid contained in lip-ids is butyric acid (4:0). When released from fats such as butter during aging, due to its short-chain nature, it is not just liquid but sometimes gaseous (smell of butyric acid). The long-chain, saturated fatty acids occur exclusively in solid fats or as a result of the hydrogenation of unsaturated fatty acids. The animal body is able to synthesize its own fatty acids but unable to introduce double bonds beyond C9. Long-chain, polyunsaturated fatty acids (PUFA) are therefore essential and must be obtained from foods. The most important essential fatty acids are linoleic acid (18:2; 9, 12, m-6) and a-linolenic acid (18:3; 9, 12, 15, m-3). The human body can make longer, polyunsaturated fatty acids from these two precursors by chain extension and desaturation (e. g., arachidonic acid, (ARA) 20:4; 5, 8, 11, 14; m-6, eicosapentaenoic acid (EPA), 20:5; 5, 8, 11, 14, 17; m-3, docosahexae-noic acid (DHA), 22:6; 4, 7, 10, 13, 16, 19; m-3). Nutritional supply of these higher-level homologues can partially replace linoleic and a-linolenic acid.

Fatty Acids 87

- A. Fatty Acid Structure cis-Double bond cis-Double bond

Lauric Supply Chain
|- B. Fatty Acids

Fatty acids

Number of C atoms

Number of double bonds

Double bond positions from carboxyl end

Saturated

( x

y ;

a, b, c, d... )

Butyric acid

4

^H 0

Valerianic acid

5 ^H

^H 0 ^^H

Caproic acid

6 ^H

^H 0

Caprylic acid

__ 8 __

^H 0

Capric acid

10

^H 0 ^^H

Lauric acid

12

^H 0

Myristic acid

14

^H 0 ^^H

Palmitic acid

16

^H 0

Stearic acid

18

^H 0 ^^H

Arachidic acid

20

^H 0

Behenic acid

22

^H0 ^^H

Monounsaturated

( x

y;

a, b, c, d... )

Oleic acid

18

1

9

Erucic acid

22

1

13

Nervonic acid

24

1

15

Polyunsaturated

( x

y;

a, b, c, d... )

Linoleic acid

18

2

9, 12,

a-Linolenic acid

18

3

9, 12, 15,

Arachidonic acid

20

4

5, 8, 11,14,

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