α-linolenic acid
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| Structural formula with the numbering of selected carbon atoms | |||||||||||||||||||
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| Surname | α-linolenic acid | ||||||||||||||||||
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| Molecular formula | C 18 H 30 O 2 | ||||||||||||||||||
| Brief description |
colorless liquid |
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| properties | |||||||||||||||||||
| Molar mass | 278.44 g mol −1 | ||||||||||||||||||
| Physical state |
liquid |
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| density |
0.92 g cm −3 |
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| Melting point |
−11 ° C |
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| boiling point |
232 ° C (23 h Pa ) |
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| Refractive index |
1.480 (20 ° C) |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C | |||||||||||||||||||
Alpha-linolenic acid ( alpha-linolenic acid , often just linolenic acid or ALA for short after the English name a lpha- L inolenic a cid) is a tri- unsaturated fatty acid with 18 carbon atoms. It is an (all- cis ) -octadeca-9,12,15-trienoic acid, abbreviated as C18: 3 (9c, 12c, 15c) and belongs to the group of omega-3 fatty acids . It is a so-called trienoic acid and an isolenic acid because the three double bonds are each separated by a methylene group .
Several other fatty acids also have the word linolenic acid in their names, but they differ chemically. For example, the gamma-linolenic acid [(all- cis ) -Octadeca-6,9,12-trienoic acid, GLA], abbreviation: [18: 3 (ω − 6)], as well as the dihomogamma linolenic acid [(all- cis ) -Eicosa-8,11,14-trienoic acid, DGLA] to the group of omega-6 fatty acids. Abbreviation: [20: 3 (ω − 6)], the latter also consisting of 20 instead of 18 carbon atoms. Finally, linoleic acid, which is similar in name to linolenic acid , has one less double bond than linolenic acid and belongs to the group of omega-6 fatty acids. It is thus a octadeca-9,12- diene acid.
The name linolenic acid is derived from the Greek word linos for flax (flax).
Occurrence
Linolenic acid is found as an ester chemically bound in many triglycerides , which make up the main part of natural fats and oils. The triglycerides of a number of naturally obtained vegetable oils are rich in linolenic acid residues. These include oil from the Iberian scorpionfish (up to 70% of the fatty acid residues), chia oil (approx. 60%), perilla oil (31–42%), linseed oil (56–71%), hemp oil (28%) , Walnut oil (approx. 15%), rapeseed oil (5–16%) and soybean oil (4–11%). Some vegetable oils only contain small amounts (up to 1.5%); these include sunflower oil , olive oil and grapeseed oil (less than 1% linolenic acid, 72% linoleic acid ). Animal sources are horse fat (approx. 30%) and pork lard (<1.5%).
Contrary to popular belief, these natural fats and oils do not contain free linolenic acid, but their glycerol esters .
Extraction and presentation
The fatty acid can be obtained from the corresponding triglycerides by alkaline saponification , by boiling the corresponding fats or oils with alkalis . Since the natural fats and oils always contain many different fatty acids, the resulting mixture is usually separated. Commercially it is obtained primarily from linseed oil .
properties
Physical Properties
Linolenic acid, carefully cleaned and stored under exclusion of air, is a colorless, oily and almost odorless liquid. The molar mass is 278.43 g · mol −1 and the density 0.91 g · cm −3. It has a melting point of −11 ° C and a boiling point of 232 ° C (at 23 mbar). The fatty acid is insoluble in water, but works well in many organic solvents.
Chemical properties
Linolenic acid is very sensitive to oxidation and quickly ages in the air, turning yellow, which is due to the formation of hydroperoxides. In the further course of the oxidation, resinification occurs with the formation of varnish ; this process is also known as drying .
Biological importance
Alpha-linolenic acid (ALA) is an essential nutrient that is required for the formation of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). ALA also plays an important role in inflammatory processes. It is processed into EPA by the same enzymes that produce dihomogammalinolenic acid (DGLA) and arachidonic acid (AA) from linoleic acid . In turn, anti-inflammatory eicosanoids are formed from DGLA and EPA (series 1 and series 3), while arachidonic acid is used to form pro-inflammatory series 2 eicosanoids. So ALA is anti-inflammatory as it is
- 1. Attracts enzyme activity that would otherwise produce arachidonic acid and
- 2. The anti-inflammatory series 3 eicosanoids are formed from it.
Studies show that around 5–10% of the ingested α-linolenic acid is converted into EPA and 2–5% into DHA. Other studies speak of conversion rates to EPA and DHA less than 5%. One study concludes that the ALA to DHA conversion rate is less than 1%. A study by the Royal Adelaide Hospital in Australia shows that vegetable oil rich in α-linolenic acid, together with a diet low in linoleic acid , increases tissue EPA levels in a manner similar to that of supplementation with fish oil. The International Society for the Study of Fatty Acids and Lipids (ISSFAL) denies an increase in the DHA level in the blood through supplementation of additional ALA - with the exception of infants . Barcel-Coblijn & Murphy, on the other hand, come to the conclusion that the body can produce sufficient DHA if enough α-linolenic acid (> 1200 mg) is consumed per day. A 2016 review examining ALA to DHA conversion rates concluded that ALA is an unsuitable substitute for DHA.
proof
To determine the content of the linolenic acid components in the triglycerides, these are first transesterified to the methyl esters of the fatty acids . The fatty acid methyl esters are usually separated by gas chromatography .
In addition, the unsaturated isomers can be separated using silver nitrate thin-layer chromatography.
use
Acylglycerols of linolenic acid and linoleic acid are used as additives to varnishes and other drying oils for coatings (varnishes, etc.).
Individual evidence
- ↑ Entry on LINOLENIC ACID in the CosIng database of the EU Commission, accessed on March 21, 2020.
- ↑ a b c d e f g h Entry on linolenic acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 25, 2014.
- ↑ a b c d e f Entry on α-linolenic acid in the GESTIS substance database of the IFA , accessed on January 6, 2008(JavaScript required) .
- ↑ a b Linolenic acid data sheet from Sigma-Aldrich , accessed on May 29, 2011 ( PDF ).
- ↑ Species portrait "Iberian dragon head" ( Memento of the original from December 18, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. in the information system for renewable raw materials (INARO).
- ↑ Peter N. Mascia (Ed.), Jürgen Scheffran (Ed.), Jack M. Widholm (Ed.): Plant Biotechnology for Sustainable Production of Energy and Co-Products. Volume 66 of the series Biotechnology in Agriculture and Forestry , Springer, 2010, ISBN 978-3-642-13439-5 , p. 235.
- ↑ Entry on perilla oil. In: Römpp Online . Georg Thieme Verlag, accessed on May 23, 2011.
- ↑ German Society for Fat Science: Fatty Acid Composition of Important Vegetable and Animal Edible Fats and Oils ( Memento of the original from December 22, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF).
- ↑ Robert Ebermann, Ibrahim Elmadfa: Textbook food chemistry and nutrition. Springer-Verlag / Vienna, 2008, ISBN 978-3-211-49348-9 , p. 648 ( limited preview in the Google book search).
- ↑ keyword "α-Linolenic Acid" In Hans Zoebelein (ed.): Dictionary of Renewable Resources. 2nd edition, Wiley-VCH, Weinheim and New York 1996, ISBN 3-527-30114-3 , p. 92.
- ^ Siegfried Hauptmann : Organic Chemistry , 2nd reviewed edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1985, ISBN 3-342-00280-8 , pp. 653-654.
- ↑ a b J. T. Brenna, N. Salem, AJ Sinclair, SC Cunnane: alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans. In: Prostaglandins, leukotriene, and essential fatty acids. Volume 80, number 2-3, 2009, pp. 85-91, doi : 10.1016 / j.plefa.2009.01.004 , PMID 19269799 (review).
- ↑ Breanne M Anderson, David WL Ma: Are all n-3 polyunsaturated fatty acids created equal ?. In: Lipids in Health and Disease. 8, 2009, p. 33, doi : 10.1186 / 1476-511X-8-33 .
- ↑ JT Brenna: Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man. In: Current opinion in clinical nutrition and metabolic care. Volume 5, Number 2, 2002, pp. 127-132, PMID 11844977 .
- ↑ E. Mantzioris, MJ James, RA Gibson, LG Cleland: Dietary substitution with alpha-linolenic acid-rich vegetable oil Increases eicosapentaenoic acid Concentrations in tissues. In: The American journal of clinical nutrition. Volume 59, Number 6, 1994, pp. 1304-1309, PMID 7910999 .
- ↑ Gwendolyn Barcel-Coblijn, Eric J. Murphy: Alpha-linolenic acid and its conversion to longer chain n-3 fatty acids: Benefits for human health and a role in maintaining tissue n-3 fatty acid levels. In: Progress in Lipid Research. 48, 2009, pp. 355-374, doi : 10.1016 / j.plipres.2009.07.002 .
- ↑ EJ Baker, EA Miles, GC Burdge, P. Yaqoob, PC Calder: Metabolism and functional effects of plant-derived omega-3 fatty acids in humans. In: Progress in lipid research. Volume 64, 2016, pp. 30-56, doi : 10.1016 / j.plipres.2016.07.002 , PMID 27496755 (review).
- ↑ B. Breuer, T. Stuhlfauth, HP Fock: Separation of fatty acids or methyl esters including positional and geometric isomers by alumina thin-layer chromatography. In: J. of Chromatogr. Science. 25: 302-306 (1987); doi : 10.1093 / chromsci / 7/25/302 .
