Fatty acids

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Example of a triglyceride in fat. The fatty acid residue marked blue is saturated, the green marked is single, the red marked triple unsaturated . In the center, the triple esterified glycerine can be seen in black .

Fatty acids are aliphatic monocarboxylic acids with mostly unbranched carbon chains that are either saturated or unsaturated . The term "fatty acids" is based on the knowledge that natural fats and oils consist of the esters of long-chain carboxylic acids with glycerine . From this point of view, fatty acids are also counted among the lipids . Later all other alkyl carboxylic acids and their unsaturated representatives were assigned to the fatty acids.

General and structure

Fatty acids differ in the number of carbon atoms (chain length) and - in the case of unsaturated fatty acids - in the number and position of double bonds . Due to their chain lengths, fatty acids can be broken down into lower , short-chain fatty acids (up to 6-8 carbon atoms) (SCFA; Short Chain Fatty Acids), the lower limit being interpreted differently here, either 1, 2, 3 or 4 carbon atoms, medium , medium-chain (6-8 to 12 C-atoms) (MCFA; Middle Chain Fatty Acids) and higher , long-chain (13 to 21 C-atoms) (LCFA; Long Chain Fatty Acids) fatty acids are divided. Fatty acids with more than 22 carbon atoms are also known as VLCFAs (Very Long Chain Fatty Acids).

The naming as "fatty acid" suggests that an individual compound must once have been a component of a fat in order to be a fatty acid, but this is not necessarily the case. Today, this term covers carboxylic acids with (chain-like) organyl groups.

Natural fatty acids usually consist of an even number of carbon atoms and are unbranched. Exceptions to this, however, can be found in all realms . One definition is that the carbon chain must be at least four carbon atoms long; thereafter butyric acid is the simplest natural fatty acid. Another definition uses the formula CH 3 (CH 2 ) x COOH, where x is the number of carbon atoms in the hydrocarbon chain; only three carbon atoms can be present here if x = 1, or only two if x = 0; however, when x = 0, strictly speaking, one cannot speak of a “chain”. Fatty acids with C = C double bonds are called "unsaturated". This double bond is usually cis -configured . If there are two or more double bonds, they are usually separated from one another by a methylene group (-CH 2 -).

A large variety of fatty acids (more than 400 different structures, of which only about 10–12 are common) occur - mostly in the form of triacylglycerides , i.e. esterified with glycerine - in the seed oils of the vegetable kingdom. Rare fatty acids, which occur esterified in larger percentages in seeds of certain plant families, can illustrate developmental relationships (kinship relationships, chemotaxonomy, evolution; see e.g. also world economy) such as petroselinic acid , tariric acid , erucic acid , cyclopentene fatty acids and cyclopropene fatty acids . Some types of bacteria can be differentiated based on their fatty acid composition.

Essential fatty acids refer to fatty acids that an organism needs but cannot produce itself. For mammals , those fatty acids are essential that have one or more double bonds at positions higher than C-9 (counting from the carbonyl carbon) because they lack the enzymes to insert such double bonds. Strictly speaking, these are only linoleic acid and α-linolenic acid for humans .

In the food industry, fatty acids are mainly used as raw materials for various emulsifiers , but also as carriers , separating agents (e.g. in chewing gum) or as coating agents (e.g. for fruit). They are generally approved in the EU as food additives with the collective name E 570 without maximum quantity restriction (quantum satis) for foodstuffs.

The sodium or potassium salts of the higher fatty acids are known as soaps and are used as surfactants .

Saturated and unsaturated fatty acids

Stearic acid , a saturated fatty acid

A saturated fatty acid ( SFA , of Engl. Saturated fatty acids ) is - as a group of alkanoic acids - a fatty acid that no double bonds between carbon atoms has. The saturated fatty acids form a homologous series with the empirical formula C n H 2n + 1 COOH.

Oleic acid , an unsaturated cis fatty acid
α-Linolenic acid , a polyunsaturated omega-3 fatty acid

Unsaturated fatty acids have as alkenoic acids , at least one C = C double bond ( MUFA , of Engl. Monounsaturated fatty acids ). Polyunsaturated fatty acids ( PUFA , of Engl. Polyunsaturated fatty acids ) have two or more double bonds between the carbon atoms of the chain. Since the double bonds in natural fatty acids are mostly in the cis configuration , there is a bend of around 30 ° in the hydrocarbon chain. As a result, the van der Waals interaction with other molecules is weakened; the melting point is lowered. Some unsaturated fatty acids are essential for humans because the human body cannot synthesize them but needs them. These include fatty acids that have double bonds in certain positions, the omega- n fatty acids .

A distinction is made between simple (monoic acids), double (dienoic acids), triple (trienoic acids) or poly (polyenoic acids) unsaturated fatty acids.

Nomenclature ( cis , trans , ω)

In the omega-n fatty acids, n stands for a number and describes the position of one of the double bonds. The omega-counting method, which is often used in food chemistry, counts from the “ ω- end” of the carbon chain that is opposite the carboxy group. The double bond near the carboxy group therefore receives the largest number; the position of the double bond closest to the ω end determines the type of omega n fatty acid. In the illustration of linolenic acid, the ω-counting method is shown in red . Only the double bond counted first is decisive for the classification into the various groups of omega n fatty acids.

Elaidic acid , an unsaturated trans fatty acid

In addition to unsaturated fatty acids in the cis configuration, in rare cases there are also fatty acids with trans -configured double bonds, the trans fatty acids . Glycerides of trans -fatty acids are sometimes produced as an undesirable by-product in margarine production and are suspected of having harmful properties. In particular, the negative influence on coronary heart disease is cited in the literature .

Rumenic acid Octadeca-9c, 11t-dienoic acid, a conjugated fatty acid

If there are several double bonds - more precisely C = C double bonds - in a fatty acid, these are usually - analogous to the linolenic acid shown above on the right - separated from one another by a methylene group ( CH 2 group ); these are then referred to as isolenic acids . Are the double bonds by two or more methylene groups separated from each other, it is called these particular fatty acids to - or polymethylene interrupted or non-methylene-interrupted Isolensäuren (NMI; Non-Methylene-Interrupted or PMI; poly-Methylene-Interrupted).

However, there are also conjugated fatty acids (conjugic acids) in which the double bonds are closer to one another, namely conjugated . In the illustration of the rumenic acid octadeca-9c, 11t-dienoic acid, the double bonds are conjugated. Since one of the double bonds is present here as a trans double bond , this is also a trans fatty acid. Bacteria in the digestive tract of ruminants are often responsible for the formation of these fatty acids . Conjugated fatty acids are therefore found in all dairy products.

Odd-numbered fatty acids

Fatty acids with an uneven number of carbon atoms are of little importance and arise, among other things, from α-oxidation from fatty acids with even-numbered carbon atoms. In humans, this mainly affects phytanic acid and pristanic acid , which are then broken down into propionyl-CoA in the β-oxidation .

Branched Fatty Acids

Isovaleric
acid
Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid)

Lower fatty acids with branches in the carbon chain are found in some essential oils . Valerian extracts contain esters of isovaleric acid .

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain carboxylic acid that occurs as a breakdown product of chlorophyll . Traces of this compound can be found in many foods (e.g. milk ). The pathological inability to break down this carboxylic acid leads to Refsum's syndrome .

Branched-chain fatty acids are found in the membranes of numerous prokaryotes . Their occurrence is used to identify a type of bacteria and to investigate related relationships between the organisms. Above all, fatty acids with a methyl group as a branch near the “ω-end” of the carbon chain are important, such as iso- pentadecanoic acid (methyl group on the penultimate carbon atom) and the anteiso- pentadecanoic acid (methyl group on the penultimate carbon atom). They are also found in small amounts in milk fat . It is assumed that they are produced by bacteria in the rumen and are ingested by the cows and stored in their fatty tissue or in milk fat.

Branched chain fatty acids are also known as (BCFA; Branched Chain Fatty Acids).

Cyclic fatty acids

Cyclic fatty acids or CFAM (Cyclic Fatty Acid Monomers) are fatty acids with an intramolecular ring of 3, 5 or 6 C units, saturated or with double bond (s) in the ring. E.g. sterculic acid and chaulmoogric acid; see under other fatty acids.

List of fatty acids and shorter monocarboxylic acids

Saturated fatty acids and shorter monocarboxylic acids
Number of carbon atoms: double bonds Common name Chemical name Gross formula Occurrence Melting point boiling point
1-0 Formic acid Methanoic acid HCOOH Widespread, in almost all organisms 8.3 ° C 101 ° C
2-0 acetic acid Ethanoic acid CH 3 COOH Vinegar (by oxidation of ethanol) 16.6 ° C 118 ° C
3-0 Propionic acid Propanoic acid C 2 H 5 COOH Intermediate product in methane fermentation −20.5 ° C 141 ° C
4-0 Butyric acid Butanoic acid C 3 H 7 COOH Milk fat , sweat, the simplest fatty acids −5.1 ° C 164 ° C
5-0 Valeric acid Pentanoic acid C 4 H 9 COOH Valerian root , wood vinegar −34 ° C 186 ° C
6-0 Caproic acid Hexanoic acid C 5 H 11 COOH Milk fat, arises from butyric acid fermentation −4 ° C 205 ° C
7-0 Enanthic acid Heptanoic acid C 6 H 13 COOH as an ester in calamus oil ( Acorus calamus ) −7.2 ° C 222 ° C
8-0 Caprylic acid Octanoic acid C 7 H 15 COOH Milk fat, coconut fat 16.5 ° C 239 ° C
9-0 Pelargonic acid Nonanoic acid C 8 H 17 COOH essential oil of Pelargonium roseum , cheese, fusel oil , wine 12.4 ° C 254 ° C
10-0 Capric acid Decanoic acid C 9 H 19 COOH Animal and vegetable fats 31.4 ° C 269 ​​° C
11: 0 - Undecanoic acid C 10 H 21 COOH Essential oils ( Iris and Quendel oil Thymus serpyllum ) 28.5-29.3 ° C 280 ° C
12: 0 Lauric acid Dodecanoic acid C 11 H 23 COOH Milk fat, vegetable fats 43.8 ° C 225 ° C (100 torr)
13: 0 - Tridecanoic acid C 12 H 25 COOH Vegetable oils 41.5 ° C 236 ° C (100 torr)
14: 0 Myristic acid Tetradecanoic acid C 13 H 27 COOH Milk fat, fish oil , animal and vegetable fats 54.2 ° C 250 ° C (100 Torr)
15: 0 - Pentadecanoic acid C 14 H 29 COOH Ruminant milk and body fat, fish oil 52.3 ° C 257 ° C (100 torr)
16: 0 Palmitic acid Hexadecanoic acid C 15 H 31 COOH Animal and vegetable fats 62.5-63 ° C 351.5 ° C
17: 0 Margaric acid Heptadecanoic acid C 16 H 33 COOH Animal and vegetable fats 61.3 ° C 227 ° C (100 torr)
18: 0 Stearic acid Octadecanoic acid C 17 H 35 COOH Animal and vegetable fats 69.2-69.9 ° C 350 ° C (dec.)
19: 0 - Nonadecanoic acid C 18 H 37 COOH Beef fat, dill ( Anethum graveolens ) 69.4 ° C 297 ° C (100 torr)
20: 0 Arachidic acid Eicosanic / icosanoic acid C 19 H 39 COOH in small amounts in plant seeds and animal fats 75.5 ° C 328 ° C (dec.)
21: 0 - Heneicosanoic acid C 20 H 41 COOH in fungi of the genus Armillaria (4–5% of the fatty acids) and in a few plants 74-75 ° C
22: 0 Behenic acid Docosanoic acid C 21 H 43 COOH in small amounts in plant seeds and animal fats, in Gaucher's disease 79.5-80.5 ° C
24: 0 Lignoceric acid Tetracosanoic acid C 23 H 47 COOH Wood, tar , peanut oil , some vegetable fats, part of the sphingomyeline 81.5-84.5 ° C
26: 0 Cerotic acid Hexacosanoic acid C 25 H 51 COOH Beeswax , carnauba wax , montan wax , wool sweat 87.7-88.5 ° C
28: 0 Montanic acid Octacosanoic acid C 27 H 55 COOH Montan wax , beeswax, china wax 91-93 ° C
30: 0 Melissic acid Triacontanoic acid C 29 H 59 COOH Beeswax, Selinum , Trichosanthes and Pericampylus species 92-94 ° C
32-0 Laccic acid Dotriacontanoic acid C 31 H 63 COOH in growing 96 ° C
34: 0 Geddic acid Tetratriacontanoic acid C 33 H 67 COOH in growing 98.4 ° C
Monounsaturated fatty acids
Number of carbon atoms: double bonds Common name Gross formula Position of
the
double
bond		 Occurrence Melting point Chemical name
11: 1 Undecylenic acid C 10 H 19 COOH 10 Salicornia brachiata (South Asian halophyte ) 24.5 ° C (10 Z ) - Undeca-10 enoic acid
14: 1 Myristoleic acid C 13 H 25 COOH 9 rare fatty acid in a few vegetable oils, e.g. B. in seeds of the genus Myristicaceae ( nutmeg family ) −4.5 ° C (9 Z ) - tetradeca- 9-enoic acid
16: 1 Palmitoleic acid C 15 H 29 COOH 9 Milk fat, animal depot fat, fish tran , vegetable fat 1 ° C (9 Z ) - hexadeca- 9-enoic acid
17: 1 Margaroleic acid C 16 H 29 COOH 9 Animal depot fat, vegetable fats 11.4-12.2 ° C, 14.5 ° C (9 Z ) -Heptadeca- 9-enoic acid
18: 1 Petroselinic acid C 17 H 33 COOH 6th in coriander oil ( real coriander ) 29.8 ° C (6 Z ) - Octadeca- 6 enoic acid
18: 1 Oleic acid (OA) C 17 H 33 COOH 9 in all natural fats 16 ° C (9 Z ) - Octadeca- 9-enoic acid
18: 1 Elaidic acid 1 C 17 H 33 COOH 9 in the fat of ruminants 44-45 ° C (9 E ) - Octadeca- 9-enoic acid
18: 1 Vaccenic acid C 17 H 33 COOH 11 in the fat of ruminants 44 ° C ( trans ), 14.5-15.5 ° C ( cis ) (11 E ) (11 Z ) - Octadeca-11 enoic acid
20: 1 Gadoleic acid C 19 H 37 COOH 9 Vegetable oils, cabbage species ( Brassica ); Rape and broccoli seed oil , mustard oil , fish oils 24.5 ° C (9 Z ) - Eicosa- 9-enoic acid
20: 1 Gondo acid C 19 H 37 COOH 11 in jojoba oil, soap tree plants (Sapindaceae), cabbage species ( Brassica ), rapeseed oil (old varieties), camelina oil 24 ° C (11 Z ) - Eicosa-11-enoic acid
22: 1 Cetoleic acid C 21 H 41 COOH 11 Vegetable oils, fish oils 32-33 ° C (11 Z ) - docosa-11-enoic acid
22: 1 Erucic acid C 21 H 41 COOH 13 Rapeseed oil (old varieties), mustard oil 33.5 ° C (13 Z ) - Docosa-13-enoic acid
24: 1 Nervonic acid C 23 H 45 COOH 15th Seed oil from the rare Malania oleifera tree in the Olacaceae family 42-43 ° C (15 Z ) - tetracosa-15-enoic acid
Polyunsaturated fatty acids
Number of carbon atoms: double bonds Common name Gross formula Position of
the
double
bonds		 Occurrence Melting point Chemical name
18: 2 Linoleic acid (LA) C 17 H 31 COOH 9.12 Vegetable oils, especially safflower oil , sunflower oil and grape seed oil −7 ° C (9 Z , 12 Z ) - Octadeca- 9,12- dienoic acid
18: 3 Alpha-Linolenic Acid 2 (ALA) C 17 H 29 COOH 9.12.15 some vegetable oils, especially linseed oil , walnut oil , hemp oil , rapeseed oil, and soybean oil −11 ° C (9 Z , 12 Z , 15 Z ) - Octadeca- 9,12,15-trienoic acid
18: 3 Gamma Linolenic Acid 2 (GLA) C 17 H 29 COOH 6,9,12 in a few vegetable oils such as borage oil , evening primrose oil and hemp oil −11 ° C (6 Z , 9 Z , 12 Z ) - Octadeca- 6,9,12- trienoic acid
18: 3 Calendulic acid C 17 H 29 COOH 8,10,12 Main fatty acid in the fatty vegetable seed oil of the marigold 40.5 ° C (8 E , 10 E , 12 Z ) - Octadeca- 8,10,12-trienoic acid
18: 3 Punicic acid C 17 H 29 COOH 9.11.13 in a few vegetable oils, e.g. B. in the seed oil of the pomegranate 43-44 ° C (9 Z , 11 E , 13 Z ) - Octadeca- 9,11,13-trienoic acid
18: 3 Alpha eleostearic acid C 17 H 29 COOH 9.11.13 in a few vegetable oils, e.g. B. Main fatty acid in the oil of the seeds of bitter melon ( Momordica spp.) And golden plum family ( Parinari spp.), As well as in tung oil ( Vernicia spp.) 49 ° C (9 Z , 11 E , 13 E ) - Octadeca- 9,11,13-trienoic acid
18: 3 Beta-eleostearic acid C 17 H 29 COOH 9.11.13 in a few vegetable oils, from the α -leostearic acid in the seed oils by isomerization 71.5 ° C (9 E , 11 E , 13 E ) - Octadeca- 9,11,13-trienoic acid
18: 4 Stearidonic acid C 17 H 27 COOH 6,9,12,15 Boraginaceae (Boraginaceae), primrose ( Primula spp.), Algae, fungi, spirulina , oils from marine animals, hemp seed, blackcurrant seed −57 ° C (6 Z , 9 Z , 12 Z , 15 Z ) - Octadeca- 6,9,12,15-tetraenoic acid
20: 4 Arachidonic acid C 19 H 31 COOH 5,8,11,14 Animal fats, fish oil −49.5 ° C (5 Z , 8 Z , 11 Z , 14 Z ) - Eicosa- 5,8,11,14- tetraenoic acid
20: 5 Eicosapentaenoic acid (timnodonic acid, EPA) C 19 H 29 COOH 5,8,11,14,17 Fish oils −53–54 ° C (5 Z , 8 Z , 11 Z , 14 Z , 17 Z ) - Eicosa- 5,8,11,14,17- pentaenoic acid
22: 2 Docosadienoic acid C 21 H 39 COOH 13.16 Cod liver oil , sunflower oil , rapeseed oil (old varieties)   (13 Z , 16 Z ) - docosa-13,16-dienoic acid
22: 4 Docosatetraenoic acid (adrenic acid, ADA) C 21 H 35 COOH 7,10,13,16 Fish oils   (7 Z , 10 Z , 13 Z , 16 Z ) - docosahexaenoic acid tetra 7,10,13,16-
22: 5 Docosapentaenoic acid , ( Clupa (no) donsäure ), (DPA-3) C 21 H 33 COOH 7,10,13,16,19
(4, 8, 12, 15, 19; 22: 5n-3)
(4, 7, 10, 13, 16; 22: 5n-6, osbond acid , DPA-6, OBA )		 Fish oils −78 ° C (7 Z , 10 Z , 13 Z , 16 Z , 19 Z ) - docosahexaenoic 7,10,13,16,19- pentanoic acid
22: 6 Docosahexaenoic acid (cervonic acid, clupanodonic acid, DHA) C 21 H 31 COOH 4,7,10,13,16,19 Fish oils −44 ° C (4 Z , 7 Z , 10 Z , 13 Z , 16 Z , 19 Z ) - docosahexaenoic 4,7,10,13,16,19- hexaenoic
24: 6 Tetracosahexaenoic acid (nisic acid) C 23 H 35 COOH 6,9,12,15,18,21 Fish oils (6 Z 9 Z , 12 Z , 15 Z , 18 Z , 21 Z ) -Tetracosa-6,9,12,15,18,21- hexaenoic
Remarks
1 Elaidic acid, the trans isomer of oleic acid, is produced during fat hardening for the production of margarine through the partial hydrogenation of polyunsaturated fatty acids in the course of isomerization . It occurs naturally in the fat of ruminants (milk, butter, beef tallow), as their rumen organisms also contain hydrogenating enzymes.
2 The linolenic acid isomer with the double bonds in positions 9, 12 and 15 (all in cis - configuration ) is alpha-linolenic acid , the isomer with the double bonds in positions 6, 9 and 12 (all in cis - Configuration) is called gamma-linolenic acid .

More fatty acids

Fatty acids with other functional groups or special bonds
Number of carbon atoms: functional group
double bonds		 Common name Gross formula Position of the
functional groups / bonds		 Occurrence Melting
point		 Chemical name
8: 0cy-Dis
disulfide -		 Lipoic acid C 8 H 14 S 2 O 2 5 (1,2- dithiolane , disulfide bridge ) Microorganisms, algae, liver 46-48 ° C 5 - [(3 R ) -1,2-dithiolan-3-yl] pentanoic acid
18: 0-9Br, 10Br, 12Br, 13Br
bromine - ( bromoalkane , haloalkane )		 Tetrabromostearic acid C 18 H 32 Br 4 O 2 9,10,12,13 (bromo group) Seed oil from Labiatae ( Eremostachys molucelloides ) 114.7-115.2 ° C 9,10,12,13-tetrabromooctadacanoic acid
18: 0-9Cl-10Cl
chlorine - ( chloroalkane , haloalkane)		 Dichlorostearic acid C 18 H 34 Cl 2 O 2 9.10 (chlorine group) European eel ( Anguilla anguilla ) 9,10-dichloroctadecanoic acid
18: 1cy
(18: 1-13-cp)
cyclopentene -		 Chaulmoogric acid C 18 H 32 O 2 13 (cyclopentene) Seed oil Hydnocarpus wightianus , Hydnocarpus kurzii 68.5 ° C-71 ° C 13-Cyclopent-2-enyl-tridecanoic acid
18: 1-delta-6a
triple bond 		Tariric acid C 18 H 32 O 2 6 (triple bond) Vegetable oils 49-50 ° C 6-octadecinic acid
18: 1-delta-9c-12,13-O
epoxy		 Vernolic acid C 18 H 32 O 3 9 (double bond)
12.13 ( epoxy group )		 Main fatty acid in vernonia oil (from seeds of sham asters ) 23-25 ​​° C (12 R , 13 S ) -12,13-epoxy-9-cis-octadecenoic acid
18: 1-delta-9c-12-OH
hydroxy		 Ricinoleic acid C 18 H 34 O 3 9 (double bond)
12 ( hydroxy group )		 Main fatty acid in castor oil 5 ° C (9 Z , 12 R ) -12-hydroxy-9-octadecenoic acid
18: 1-delta-9c-18-F
fluorine - ( fluoroalkane , haloalkane)		 Fluorooleic acid C 18 H 33 FO 2 9 (double bond)
18 (fluorine group)		 Seeds of Dichapetalaceae ( Dichapetalum toxicarium ) 13.5 ° C (9 Z ) -18-fluoro-9-octadecenoic acid
18: 2-delta-5.6allene
allenes -		 Laballenic acid C 18 H 32 O 2 5.6 ( cumulative double bond ) In species of mint Lamiaceae ( R ) -5,6-octadecadienoic acid
18: 3-delta-4-oxo-9c, 11t, 13t
double bond, carbonyl -		 α- licanic acid (couepic acid) C 18 H 28 O 3 9,11,13 (double bond)
4 ( keto group )
keto acid 		Main fatty acid in oiticica oil (from the seeds of Licania rigida ) 74-75 ° C 4-oxo (9 Z , 11 E , 13 E ) octadecatrienoic acid
18: 3-delta-9a, 11a, 17-E
triple bond, ethene -
 Isanoic acid C 18 H 26 O 2 9.11 (triple bond)
17 ( vinyl group )		 Isano oil (from the seeds of Ongokea gore ) 42 ° C Octadeca-17-en-9,11-diyric acid
18: 3-9-Oxa-8t, 10t, 12c
double bond, vinyl ether -		 Colnelic acid C 18 H 30 O 3 8,10,12 (double bond)
9 ( ether group )		 Plant leaves and roots (8 E ) -9 - [(1 E , 3 Z ) -1,3-nonadien-1-yloxy] -8-nonenoic acid
18: 4-delta-9c, 11t, 13t, 15c
double bond		 α- parinaric acid (octadecatetraenoic acid) C 18 H 28 O 2 9,11,13,15 (double bond) Rosaceae seed oil , Balsaminaceae 83.5 ° C (9 Z , 11 E , 13 E , 15 Z ) -Octadecatetraenoic acid
18: 4-delta-9a, 11a, 13a, 15a-17-OH
triple bond, hydroxy		 Minquartinic acid C 18 H 20 O 3 9,11,13,15 (triple bond)
17 (hydroxy group)		 Bark of Minquartia guianensis , Coula edulis 97 ° C ( S ) -17-Hydroxy-9,11,13,15-octadecatetrainic acid
19: 0-11,12-cpa
cyclopropyl -		 Lactobacillic acid C 19 H 36 O 2 11.12 (cyclopropane) Important fatty acid in Lactobacillus species 28-29 ° C (11 R , 12 S ) -Methylene octadecanoic acid
19: 0-2,6,10,14-tetra-Me (19: 0br4)
methyl-		 Pristanoic acid C 19 H 38 O 2 2,6,10,14 ( methyl group ; isoprenoid ) Animal fat, milk fat, fish oil (2 S , 6 R , 10 R ) -2,6,10,14-tetramethylpentadecanoic acid
19: 1-9,10-cpe
cyclopropene -		 Sterculic acid C 19 H 36 O 2 9.10 (cyclopropene) In plant seeds;
Stink tree ( Sterculia foetida ), Kapok tree ( Ceiba pentandra ), African baobab ( Adansonia digitata )		 18.2-18.3 ° C 8- (2-octylcyclopropen-1-yl) octanoic acid

Fatty acids with a hydroxy group are found in the lipids of animals, plants and prokaryotes. The hydroxyl group is often found on the second carbon atom (compare α- hydroxycarboxylic acids ). Β-hydroxy fatty acids also occur, as do fatty acids in which the functional group occurs in the middle of the carbon chain, such as ricinoleic acid. Further functional groups with an oxygen atom are the epoxy group , the keto group and the furan group , which can also be found in fatty acids.

Fatty acids in the membrane lipids of bacteria sometimes have unusual components in the molecule. So have alicyclic fatty acids on a ring of hydrocarbons. As cyclopropane , this can be in the middle of the carbon chain, as is the case with mycolic acids or lactobacillic acid . Furthermore, they can also have a keto group. Mycolic acids are also the longest naturally occurring fatty acids. They are bound to the murein in the bacterial cell wall via arabinogalactan .

Omega Cyclohexyltridecanoic Acid

Rings with six or seven carbon atoms ( cyclohexane or cycloheptane ) are often found at the end of the actual fatty acid chain; they are then referred to as omega-alicyclic (ω-alicyclic) fatty acids, with the Greek lowercase ω being used as locant . The bacterial genus Alicyclobacillus was named after these fatty acids because it contains them in large quantities in the membrane lipids. One example is omega-cyclohexyltridecanoic acid, an ω-alicyclic fatty acid with a cyclohexane residue and a chain with 13 carbon atoms.

metabolism

transport

Fatty acids are stored as triglycerides in adipose tissue. If necessary, indicated by the messenger substances adrenaline , noradrenaline , glucagon or ACTH , lipolysis takes place there.

The free fatty acids are then transported in the bloodstream to the energy-consuming cells, where they are first bound (activated) to coenzyme A (CoA) while consuming ATP . This reaction is driven by the hydrolysis of the resulting pyrophosphate to two phosphates (P i ).

Then they are bound  to carnitine by the enzyme carnitine acyltransferase I and actively transported into the matrix of the mitochondria , where they are bound to CoA again by carnitine acyltransferase II. This activation is necessary because fatty acids can diffuse through the mitochondrial membrane. Only actively transported fatty acids are used for the β-oxidation of the fatty acids. The acyl carnitine activation is not reversible, an activated fatty acid is broken down.

Fatty acid breakdown

In the matrix of the mitochondrion, the β-oxidation of the fatty acids to acetyl-CoA takes place, which can be used in the citric acid cycle to gain ATP. For prolonged periods of hunger or diets with very little carbohydrates , such as B. the Atkins diet , the fats are instead metabolized into ketone bodies .

In addition to the mitochondrial fatty acid oxidation, fatty acids are also utilized in the peroxisomes . Especially very long-chain fatty acids are usually shortened there first before they can be processed further in the mitochondria. This peroxisomal function is significant. Failure will lead to adrenoleukodystrophy .

Fatty acid synthesis

In contrast to its breakdown, fatty acid synthesis takes place in the cytosol . In higher organisms, all of the enzymes required for this are combined in a single enzyme complex, the fatty acid synthase . In green plants, however, the synthesis up to the C18 fatty acid takes place mainly in the plastids and is only then transported into the cytosol.

For this purpose, malonyl-CoA is first formed from acetyl-CoA with consumption of ATP by carboxylation . This is then converted to malonyl-ACP, because in contrast to the breakdown, acyl carrier protein (ACP) serves as a carrier molecule instead of CoA. The subsequent condensation reaction is roughly a reversal of fatty acid oxidation ( β-oxidation ). However, there are some significant differences in the details that allow independent, targeted control of both processes.

Characteristic fatty acids in microorganisms

Typical fatty acids can be used as biomarkers . Actinomycetes are Gram-positive bacteria that occur during the decomposition of organic material and, among other things, produce an earthy odor. Actinomycete fatty acids are occasionally branched at C10 with a methyl group, e.g. B. 16: 0 10-methyl and 18: 0 10-methyl. Actinomycetes living in the ground are e.g. B. Rhodococcus, Nocardia, Corynebacterium and Streptomyces . Gram-positive bacteria are e.g. B. also Bacillus spp. such as Bacillus cereus and Bacillus subtilis . The number of bacteria of Bacillus spp. increases in the rhizosphere . They form branched fatty acids like 15: 0 iso and 15: 0 anteiso.

Gram-negative bacteria are an important part of the rhizosphere and increase the availability of phosphate, iron and other minerals, some also produce fungicides . Gram-negative bacteria produce higher concentrations of monounsaturated fatty acids such as 16: 1 omega-7 and 18: 1 omega-9, most of which are further metabolized into cyclopropyl fatty acids such as 17: 0 cyclopropane and 19: 0 cyclopropane. Dimethylacetals (DMA) are formed under anaerobic conditions and can be used as biomarkers. Under strictly anaerobic conditions, such as during a flood, the number of facultative aerobic bacteria decreases and the number of anaerobic bacteria and archaea increases.

The fatty acids in the lipids of archaea are not linked by an ester bond , but by an ether bond . Mycorrhizal fungi form storage vesicles that contain , among other things, 18: 2 (ω-6c) and 16: 1 (ω-5c).

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Different fatty acids as biomarkers:

  • Saturated fatty acids ( english saturated fatty acids , SAFA)
  • Monounsaturated fatty acids (Engl. Monounsaturated fatty acids , MUFA)
    • 16: 1 ω5c (hexadecenonic acid) - mycorrhiza
    • Omega-5 and 7 position (e.g. 16: 1 ω7c, palmitoleic acid ) - Gram-negative bacteria
    • 16: 1 ω8c (8-hexadecenonic acid) - methane-oxidizing bacteria type I
    • 18: 1 ω8c (10-octadecenonic acid) - methane-oxidizing bacteria type II
    • Omega-9 position (e.g. 16: 1 ω9c, cis-7-palmitoleic acid) - Ectomycorrhizal fungi & Gram-positive bacteria
  • Polyunsaturated fatty acids (Engl. Polyunsaturated fatty acids , PUFA)
  • Cyclopropyl fatty acids (e.g. 19: 0 cyclo ω7c) - bacteria
  • Dimethyl acetals (e.g. 16: 0 DMA, hexadecanal dimethyl acetal) - Anaerobic bacteria

Health importance

Both saturated and unsaturated fatty acids provide a lot of energy, support the immune system, and reduce a. Depression and have a positive effect on many other metabolic processes. Fats with a high percentage of medium-chain fatty acids are easier to digest than those with long-chain fatty acids.

In an evaluation of intervention studies with over 13,600 participants in 2010, the German Nutrition Society (DGE) found that a high proportion of polyunsaturated fatty acids, together with a low proportion of saturated fatty acids, increased the risk of coronary heart disease (e.g. heart attack ) lowers. It confirmed results that Daniel and Hecht published in 1990. Favorable ratios of polyunsaturated to saturated fatty acids are found primarily in vegetable fats (e.g. safflower oil 74.5% / 8.6%, olive oil 86% / 14%, hemp oil 70% / 10%, sunflower oil 60.7% / 11 , 5% and soybean oil 61.0% / 13.4%; exceptions are coconut oil 1.4% / 86.5% and palm oil 17% / 83%), nuts and seeds (e.g. tahini 55% / 9% , Hazelnuts 54% / 5%).

Unsaturated trans fatty acids have a negative effect on cholesterol levels . In particular, the lowering of the HDL cholesterol level with a simultaneous increase in the LDL cholesterol lipoprotein (a) level and proinflammatory effects have a negative impact on the endothelial function of the arterial walls. There are also suspicions of an increase in insulin resistance and obesity , cell membrane changes and negative effects on blood clotting. In addition, the evidence from observational studies for a connection between trans fatty acids and an increased risk of coronary heart disease is very convincing. Foods with triglycerides containing trans fatty acids are often marked with the note “vegetable oil, partially hydrogenated” in the information on the ingredients .

In populations in the Mediterranean region, the intake of monounsaturated fatty acids is between 16 and 29% of the total daily energy intake (mainly in the form of oleic acid, e.g. olive oil ). Studies show that replacing saturated fatty acids with carbohydrates, monounsaturated or polyunsaturated fatty acids reduces cardiovascular risk factors. Compared to carbohydrates, MUFAs had a positive effect on triglycerides, HDL cholesterol and the total cholesterol: HDL cholesterol ratio. Two meta-analyzes showed positive effects of an increased intake of monounsaturated fatty acids on the following cardiovascular risk factors: systolic and diastolic blood pressure , glycated hemoglobin ( HbA1c ) and fasting glucose .

The omega-6 fatty acids (e.g. linoleic acid , gamma-linolenic acid ) and the omega-3 fatty acids belong to the essential fatty acids, as they cannot be produced by the human organism itself. In vegetable oils, linoleic acid (sunflower oil, soybean oil, corn oil) occurs in very high concentrations (50–70% based on the total fatty acid content). Through dehydration and chain extension, the human organism can convert linoleic acid through several intermediate stages to arachidonic acid . Arachidonic acid can be further converted to prostaglandins in the body. Linseed and hemp oil are rich in linolenic acid, arachidonic acid is only found in animal products such as liver, eggs and lard . The essential fatty acids are involved in the construction of cell membranes and lower blood fat and cholesterol levels.

Omega-6 fatty acids are mostly metabolized via arachidonic acid - but not always or exclusively - into prostaglandins that promote inflammation , while omega-3 fatty acids become anti-inflammatory.

The DGE recommends covering around 30% of the energy requirement with fat. 10% should be covered with saturated fatty acids, 10 to 13% with monounsaturated and the rest with polyunsaturated. The American Heart Society (ADA), the European Food Safety Authority (EFSA) and the American Academy of Nutrition and Dietetics recommend that less than 35% of the energy requirement be obtained from fat, with the ADA an energy intake of less than 20% from monounsaturated fatty acids recommends. To keep the cardiovascular risk low, the ratio of omega-6 to omega-3 fatty acids should be a maximum of 5: 1. An international commission of experts headed by Berthold Koletzko ( Children's Health Foundation ) has developed and published guidelines for the nutrition of mothers and babies. It describes that the growing fetus increasingly needs long-chain, polyunsaturated fatty acids, so-called LC-PUFA (Longchain polyunsaturated fatty acid). In particular, these are arachidonic acid (omega-6 fatty acid, AA) and docosahexaenoic acid (omega-3 fatty acid, DHA). The fatty acids mentioned are contained in fatty sea fish (e.g. herring , mackerel and salmon).

Substituted fatty acids with keto and hydroxy groups are present in spoiled oils. Some of them are poisonous for the human organism. Another important substituted fatty acid, ricinoleic acid , is about 80% in castor oil . Castor oil is not absorbed in the intestine and therefore has a laxative effect.

Analysis of fatty acids

The modern qualitative and quantitative analysis of fatty acids in food chemistry and in physiological research usually makes use of chromatographic methods. Capillary gas chromatography (after transesterification to the methyl ester), HPLC and the coupling of these processes with mass spectrometry are used . Usually the fatty acids are in the form of suitable derivatives , such as. B. the fatty acid methyl esters or their TMS derivatives, separated by chromatography. In special cases, classic column and thin-layer chromatography is still used today ; the isomers are separated by means of silver nitrate thin layer chromatography.

Count of fatty acids

The number of unbranched fatty acids (including shorter monocarboxylic acids) with different numbers of double bonds at different positions as a function of chain length obeys the Fibonacci sequence, which is very well known in number theory . Among other things, this follows from the fact that (with rare exceptions) there are no neighboring double bonds in fatty acids. Specifically, there is only one aliphatic monocarboxylic acid with one carbon atom: formic acid, one with two carbon atoms: acetic acid, two with three: propionic acid and acrylic acid , etc. With 18 carbon atoms there are 2,584 variants (of which stearic acid, oleic acid, linoleic acid and Linolenic acid are four examples).

Special fatty acids

literature

  • Wolf-H. Kunau: chemistry and biochemistry of unsaturated fatty acids. In: Angewandte Chemie . 88, 1976, pp. 97-111 ( doi: 10.1002 / anie.19760880402 ).
  • J. Ernst, WS Sheldrick, J.-H. Fuhrhop: The structures of the essential unsaturated fatty acids. Crystal structure of linoleic acid as well as evidence for the crystal structures of linolenic acid and arachidonic acid. In: Z. Naturforsch. 34b, 1979, pp. 706-711.
  • P. Nuhn , M. Gutheil, B. Dobner: Occurrence, biosynthesis and importance of branched fatty acids. In: Fette-Soap-Paint. 87, 1985, p. 135.
  • FD Gunstone, JL Harwood, FB Padley: The Lipid Handbook. Chapman and Hall, London / New York 1986, ISBN 0-412-24480-2 .

Web links

Commons : Fatty  - Album with pictures, videos and audio files
Wiktionary: Fatty acid  - explanations of meanings, word origins, synonyms, translations
Wikibooks: Saturated Fatty Acids Biosynthesis  - Learning and Teaching Materials
Wikibooks: Saturated Fat Breakdown  - Learning and Teaching Materials

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