Fatty acid

Fatty acids is the group name for aliphatic monocarboxylic acids with mostly unbranched carbon chain. The term " fatty acid " is based on the realization that natural fats and oils from the esters of long chain carboxylic acids are made with glycerin. From this perspective, fatty acids are also numbered among the lipids. Later, all other alkyl carboxylic acids and their unsaturated representatives were assigned to the fatty acids.

General

Fatty acids differ in the number of carbon atoms ( chain length) and - for unsaturated fatty acids - in the number and position of double bonds. We can separate fatty acids due to their chain lengths in lower (up to seven carbon atoms), medium ( eight to twelve carbon atoms) and higher (more than twelve carbon atoms). The historical naming as " fatty " suggests that an individual connection must once have been a component of fat to be a fatty acid. However, this is not necessarily the case. This term is used today compounds are collected chemical similarities.

Natural fatty acids are typically composed of an even number of carbon atoms and are unbranched. Exceptions to this, however, can be found in all kingdoms. The carbon chain must be at least four carbon atoms long, thus the butyric acid is the simplest natural fatty acid. Fatty acids with double bonds are called unsaturated fatty acids. The double bond is cis- configured in the rule. If there are more double bonds, they are usually separated by a CH2 group.

A wide variety of fatty acids ( more than 400 different structures, of which only about 10-12 are frequently ) occurs in the seed oils of the plant kingdom. Rare fatty acids that occur in larger percentages in seeds of certain plant families, can evolutionary relationships illustrate ( kinship, chemotaxonomy, evolution, see, for example, world economy) such as petroselinic acid, tariric, erucic acid, Cyclopentenfettsäuren and Cyclopropenfettsäuren. Some bacterial species can be distinguished by their fatty acid composition.

As essential fatty acids are called fatty acids, which requires an organism, but can not produce itself. Fatty acids are essential for mammals, which have one or more double bonds at positions higher than C-9 (numbered from the carbonyl carbon of ) because they lack the enzymes to insert such double bonds. For humans, these are, strictly speaking, only linoleic acid and α -linolenic acid.

Fatty acids are used in the food industry, primarily as a raw material for various emulsifiers such addition, however, as the carrier substances, separating agents (for example, in chewing gum ), or as coating agents (e.g., fruit ). You are in the EU as a food additive under the collective name without E 570 maximum limit ( quantum satis ) generally approved for food.

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

Saturated and unsaturated fatty acids

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

Unsaturated fatty acids have at least one double bond as alkenoic 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 are usually present in natural fatty acids in the cis configuration, will be a kink of about 30 ° in the hydrocarbon chain. Thus, the Van der Waals interaction is attenuated to other molecules; the melting point is reduced. Some unsaturated fatty acids are essential for human beings, since they can not be synthesized by the human body. These include fatty acids, which carry double bonds at specific positions, the omega -n- fatty acids. Here, n is a number describing the position of the double bonds. When counting from the omega " ω - end" of the carbon chain is counted, the faces of the carboxy group. Therefore, the double bond near the carboxyl group receives the greatest number; the position of the ω - end closest to the double bond determines the type of omega- n- fatty acid. The figure shows the ω - linolenic acid, the counting is shown in red. For the classification of the different groups of omega- n- fatty acids, only the first counted double bond is crucial.

In addition to unsaturated fatty acids in the cis- configuration occur in nature also fatty acids with trans- configured double bonds are present, the trans fatty acids. Glycerides of trans fatty acids are also obtained as a byproduct in the manufacture of margarine and are suspected to have harmful properties. In particular, in the literature, the negative influence of coronary heart disease is given.

If two or more double bonds - or more precisely the C = C double bonds - in a fatty before, these are usually - separated by a methylene group ( CH2 group ) - analogous to the one shown above right linolenic acid. However, there are also conjugated fatty acids, in which the double bonds are present close to each other, namely conjugated. The figure shows the octadeca - 9c, 11t - dienoic acid, the double bonds are conjugated before. Since one of the double bonds is present as a trans double bond, this compound is also a trans fatty acid. For the formation of these fatty acids are often bacteria in the digestive tract of ruminants cause. Conjugated fatty acids are therefore present in all dairy products.

Odd-numbered fatty acids

Fatty acids having an odd number of carbon atoms arise inter alia by the α - oxidation of fatty acids with even numbered carbon atoms. In humans, this concerns mainly the phytanic acid, which is subsequently degraded in the β - oxidation to propionyl -CoA.

Branched fatty acids

Lower fatty acids with branching in the carbon chain can be found in some essential oils. To contain the extracts of valerian esters of isovaleric acid.

Phytanic acid ( 3,7,11,15 - Tetramethylhexadecansäure ) is a branched-chain carboxylic acid that occurs as a degradation product of chlorophyll. In many foodstuffs (e.g., milk) traces of this compound can be found. The pathological inability to reduce these carboxylic acid leads to Refsum's syndrome.

Branched-chain fatty acids are found in the membranes of many prokaryotes. Their occurrence is used to identify a bacterial species and to explore family relationships of organisms. Especially fatty acids with a methyl group as a branch near the " ω - end" of the carbon chain are of importance, such as the iso- pentadecanoic acid ( methyl group on the penultimate carbon atom) and anteiso - pentadecanoic acid ( methyl group on the penultimate carbon atom). They come in small amounts in milk fat. It is assumed that they are produced by bacteria in the rumen and be absorbed by the cows and stored in the adipose tissue and in milk fat.

List of shorter fatty acids and mono- carboxylic acids

Fatty acids having a hydroxy group are present in the lipids of animals, plants and prokaryotes. There is often the hydroxy group on the second carbon atom (compare α -hydroxy carboxylic acids ). Also β -hydroxy fatty acids are present, as well as fatty acids, in which the functional group occurs in the middle of the carbon chain, as in the ricinoleic acid. Other functional groups with an oxygen atom, the epoxy group, the keto group, and furan, which are also found in fatty acids.

Fatty acids in the membrane lipids of bacteria exhibit some unusual ingredients in the molecule. To assign alicyclic fatty acids on a ring of hydrocarbons. This can be as cyclopropane, are in the middle of the carbon chain, as is the case with the mycolic acids or Lactobacillsäure. Furthermore, they may also have a keto group. Mycolic acids are also the longest naturally occurring fatty acids. They are attached to arabinogalactan via the murein in the bacterial cell wall.

Rings with six or seven carbon atoms ( cyclohexane or cycloheptane ) often find themselves at the end of the actual fatty acid chain, they are then referred to as omega - alicyclic ( ω - alicyclic ) fatty acids, the Greek lowercase letter ω is used as locant. Bacterial genus Alicyclobacillus is designated by these fatty acids, because it contains these lipids in the membrane in large amounts. An example is the omega Cyclohexyltridecansäure, a ω - alicyclic fatty acid with a cyclohexane group and a chain of 13 carbon atoms.

Metabolism

Transport

The free fatty acids are then transported in the bloodstream to the energy -requiring cells where it first with ATP consumption of coenzyme A ( CoA) bound (activated). This reaction is promoted by the hydrolysis of the resulting pyrophosphate to two phosphate (Pi).

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

Fatty acid degradation

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

In addition to mitochondrial fatty acid oxidation takes place recycling of fatty acids in peroxisomes. Above all, very long chain fatty acids are usually shortened there first, before they can be further processed in the mitochondria. This peroxisomal function is significant. A failure leads to adrenoleukodystrophy.

Fatty acid synthesis

Fatty acid synthesis takes place in contrast to the degradation in the cytosol. In higher organisms, all enzymes required for this are in a single -enzyme complex, fatty acid synthase, combined. In green plants, however, the construction up to a maximum of C 18 fatty acid mainly takes place in the plastids and is then only transported into the cytosol.

These malonyl -CoA is formed from acetyl -CoA with ATP consumption by carboxylation first. This is then converted to malonyl -ACP, because in contrast to the reduction used in the synthesis of acyl carrier protein ( ACP) instead of CoA as a carrier molecule. The subsequent condensation reaction is roughly considered a reversal of fatty acid oxidation ( β - oxidation). However, can be found in detail some significant differences that permit independent, targeted control of both operations.

Health significance

Both saturated and unsaturated fatty acids provide a lot of energy, support the immune system, reduce, inter alia, Depression and affect many other metabolic processes positively. Fats with a high content of medium chain fatty acids are easier to digest than those with long-chain fatty acids.

In addition, the German Nutrition Society ( DGE) has found in a recent evaluation of intervention studies with over 13 600 participants, that a high proportion of polyunsaturated fatty acids, together with a low proportion of saturated fatty acids, the risk of coronary heart disease (eg heart attack ) lowers. They thus confirmed results that Daniel Hecht and published in 1990. Cheap ratios of polyunsaturated to saturated fatty acids are found mainly in vegetable oils: safflower oil ( 74.5 % / 8.6 %), hemp oil (70 % / 10 % ), sunflower oil ( 60.7 % / 11.5%), soybean oil ( 61.0% / 13.4 %) and rape oil (27 % / 6%). The exceptions are coconut and palm kernel oil (1.4% / 86.5 %).

Unsaturated trans fatty acids have adverse effects on cholesterol levels. In particular by the reduction in the HDL -cholesterol level, while increasing the LDL cholesterol lipoprotein (a) levels, and pro-inflammatory effects, there is a negative effect on the endothelial function of the arterial walls. Also, there is speculation on a gain of insulin resistance and obesity, cell membrane changes and negative effects on coagulation. In addition, the evidence from observational studies of an association between trans fatty acids and risk for coronary heart disease is very convincing.

In populations that are located in the Mediterranean area, is the intake of monounsaturated fatty acids 16-29 % of total daily energy intake (especially in the form of oleic acid). Studies show that a replacement of saturated fat by carbohydrates, polyunsaturated or monounsaturated fatty acids reduces cardiovascular risk factors. Compared to carbohydrates to MUFAs had a positive effect on triglycerides, HDL - cholesterol and the ratio of total cholesterol: HDL - cholesterol from. Two meta-analyzes showed positive effects of an increased intake of monounsaturated fatty acids on cardiovascular risk factors following recently: systolic and diastolic blood pressure, glycated hemoglobin ( HbA1c) and fasting glucose.

The omega -6 fatty acids (eg linoleic acid, gamma - linolenic acid) and omega -3 fatty acids belong to the essential fatty acids because they can not be manufactured by the human organism itself. Linoleic acid in vegetable oils is ( sunflower oil, soybean oil, corn oil) in fairly high concentrations ( 50-70 % based on the total fatty acid content) before. Through dehydration and chain extension of the human body can convert linoleic acid via several intermediates to arachidonic acid. Arachidonic acid can be converted in the body to prostaglandins. Flax 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 synthesis of cell membranes and reduce blood fat and cholesterol levels.

Omega -6 fatty acids are usually on the arachidonic acid - metabolized to proinflammatory prostaglandins to anti-inflammatory omega -3 fatty acids - but not always or exclusively.

From the DGE is recommended to cover about 30 % of energy requirements with fat. 10 % should be covered with saturated fatty acids, 10 to 13% polyunsaturated monounsaturated and the rest with. The American Heart Association (ADA ), the European Authority for Food Safety Authority (EFSA ) and the American " Academy of Nutrition and Dietetics " recommend to take a less than 35 % of energy from fat, and the ADA, an energy intake of less than 20% to just unsaturated fatty acids is recommended. To keep the cardiovascular risk low, the ratio of omega-6 should be to omega -3 fatty acids maximum of 5:1. An international committee of experts headed by Professor Dr. Berthold Koletzko (Chairman of the Foundation Child Health ) has developed and published guidelines for the nutrition of mothers and babies. It describes the growing fetus increases long-chain, polyunsaturated fatty acids, called the LC - PUFA ( Long Chain polyunsaturated fatty acid), are required. These are in particular arachidonic acid (omega- 6 fatty acid AA) and docosahexaenoic acid (omega- 3 fatty acid, DHA). The fatty acids mentioned are included in bold sea fishing (eg herring, mackerel and salmon).

Substituted fatty acids with keto and hydroxy groups are present in tainted oils. They are toxic in part, for the human organism. Another important substituted fatty acid, ricinoleic acid is contained in the castor oil to about 80%. Castor oil is not absorbed in the intestine and therefore has a laxative.

Analysis of fatty acids

The modern qualitative and quantitative analysis of fatty acids in food chemistry and physiological research uses in general, the chromatographic method. For use come capillary gas chromatography, HPLC, and the coupling of this method with mass spectrometry. Most are the fatty acids in the form of suitable derivatives, such as, for example, the chromatographic separation of fatty acid methyl esters or their TMS derivatives. In special cases the classical columns and thin layer chromatography is also used today; so, the separation of isomers on silver nitrate thin layer chromatography.