Chemistry:α-Linolenic acid

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α-Linolenic acid
ALAnumbering.svg
Linolenic-acid-3D-vdW.png
Names
Preferred IUPAC name
(9Z,12Z,15Z)-Octadeca-9,12,15-trienoic acid[1]
Other names
ALA; LNA; Linolenic acid; cis,cis,cis-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-9,12,15-Octadecatrienoic acid; Industrene 120
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
UNII
Properties
C18H30O2
Molar mass 278.436 g·mol−1
Density 0.9164 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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α-Linolenic acid, also known as alpha-Linolenic acid (ALA) (from Greek alpha meaning "first" and linon meaning flax), is an n−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, walnuts, chia, hemp, and many common vegetable oils.

In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid.[2] In physiological literature, it is listed by its lipid number, 18:3, and (n−3). It is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the n end. Thus, α-linolenic acid is a polyunsaturated n−3 (omega-3) fatty acid. It is an isomer of gamma-linolenic acid (GLA), an 18:3 (n−6) fatty acid (i.e., a polyunsaturated omega-6 fatty acid with three double bonds).

Etymology

The word linolenic is an irregular derivation from linoleic, which itself is derived from the Greek word linon (flax). Oleic means "of or relating to oleic acid" because saturating linoleic acid's omega-6 double bond produces oleic acid. Similarly saturating one of linolenic acid's double bonds produces linoleic acid.

Dietary sources

Seed oils are the richest sources of α-linolenic acid, notably those of hempseed, chia, perilla, flaxseed (linseed oil), rapeseed (canola), and soybeans. α-Linolenic acid is also obtained from the thylakoid membranes in the leaves of Pisum sativum (pea leaves).[3] Plant chloroplasts consisting of more than 95 percent of photosynthetic thylakoid membranes are highly fluid due to the large abundance of ALA, evident as sharp resonances in high-resolution carbon-13 NMR spectra.[4] Some studies state that ALA remains stable during processing and cooking.[5] However, other studies state that ALA might not be suitable for baking as it will polymerize with itself, a feature exploited in paint with transition metal catalysts. Some ALA may also oxidize at baking temperatures.[6] ALA percentages in the table below refer to the oils extracted from each item.

Common name Alternate name Linnaean name % ALA†(of oil) ref.
Chia chia sage Salvia hispanica 64% [7]
Kiwifruit seeds Chinese gooseberry Actinidia chinensis 62% [7]
Perilla shiso Perilla frutescens 58% [7]
Flax linseed Linum usitatissimum 55% [7]
Lingonberry cowberry Vaccinium vitis-idaea 49% [7]
Camelina camelina Camelina sativa 35–45%
Purslane portulaca Portulaca oleracea 35% [7]
Sea buckthorn seaberry Hippophae rhamnoides L. 32% [8]
Hemp cannabis Cannabis sativa 20% [7]
Walnut English walnut / Persian walnut Juglans regia 10.4% [9]
Rapeseed canola Brassica napus 10% [2]
Soybean soya Glycine max 8% [2]
  †average value

Metabolism

Flax is a rich source of α-linolenic acid.

α-Linolenic acid can be obtained by humans only through their diets, because the absence of the required 12- and 15-desaturase enzymes makes de novo synthesis from stearic acid impossible. Eicosapentaenoic acid (EPA; 20:5, n−3) and docosahexaenoic acid (DHA; 22:6, n−3) are readily available from fish and algae oil, and play a vital role in many metabolic processes. These also can be synthesized by humans from dietary α-linolenic acid: ALA → stearidonic acid → eicosatetraeonic acid → eicosapentaenoic acid → docosapentaenoic acid → tetracosapentaenoic acid → 6,9,12,15,18,21-tetracosahexaenoic acid → docosahexaenoic acid, but with an efficiency of only a few percent.[10] Because the efficacy of n−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of α-linolenic acid conversion, DHA synthesis from α-linolenic acid is even more restricted than that of EPA.[11] Conversion of ALA to DHA is higher in women than in men.[12]

Stability and hydrogenation

Compared to many other oils, α-linolenic acid is more susceptible to oxidation and will become rancid more quickly. Oxidative instability of α-linolenic acid is one reason why producers choose to partially hydrogenate oils containing α-linolenic acid, such as soybean oil.[13] Soybeans are the largest source of edible oils in the U.S., and, as of a 2007 study, 40% of soy oil production was partially hydrogenated.[14]

However, when partially hydrogenated, part of the unsaturated fatty acids become unhealthy trans fats. Consumers are increasingly avoiding products that contain trans fats, and governments have begun to ban trans fats in food products. These regulations and market pressures have spurred the development of low-α-linolenic acid soybeans. These new soybean varieties yield a more stable oil that doesn't require hydrogenation for many applications, thus providing trans fat-free products, such as frying oil.[15]

Several consortia are bringing low-α-linolenic acid soy to market. DuPont's effort involves silencing the FAD2 gene that codes for Δ6-desaturase, giving a soy oil with very low levels of both α-linolenic acid and linoleic acid.[13] Monsanto Company has introduced to the market Vistive, their brand of low α-linolenic acid soybeans, which is less controversial than GMO offerings, as it was created via conventional breeding techniques.[citation needed]

Health

ALA consumption is associated with a lower risk of cardiovascular disease and a reduced risk of fatal coronary heart disease.[16][17] Dietary ALA intake can improve lipid profiles by decreasing triglycerides, total cholesterol, high-density lipoprotein, and low-density lipoprotein.[18] A 2021 review found that ALA intake is associated with a reduced risk of mortality from all causes, cardiovascular disease, and coronary heart disease but a slightly higher risk of cancer mortality.[19]

History

In 1887, linolenic acid was discovered and named by the Austrian chemist Karl Hazura of the Imperial Technical Institute at Vienna (although he did not separate its isomers).[20] α-Linolenic acid was first isolated in pure form in 1909 by Ernst Erdmann and F. Bedford of the University of Halle an der Saale, Germany,[21] and by Adolf Rollett of the Universität Berlin, Germany,[22] working independently, as cited in J. W. McCutcheon's synthesis in 1942,[23] and referred to in Green and Hilditch's 1930s survey.[24] It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of [(Z-Z)-nona-3,6-dien-1-yl]triphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis.[25]

See also

References

  1. ↑ Loreau, O; Maret, A; Poullain, D; Chardigny, JM; Sébédio, JL; Beaufrère, B; Noël, JP (2000). "Large-scale preparation of (9Z,12E)-[1-13C]-octadeca-9,12-dienoic acid, (9Z,12Z,15E)-[1-13C]-octadeca-9,12,15-trienoic acid and their 1-13C all-cis isomers". Chemistry and Physics of Lipids 106 (1): 65–78. doi:10.1016/S0009-3084(00)00137-7. PMID 10878236. 
  2. ↑ 2.0 2.1 2.2 Beare-Rogers (2001). "IUPAC Lexicon of Lipid Nutrition". http://www.iupac.org/publications/pac/2001/pdf/7304x0685.pdf. 
  3. ↑ Chapman, David J.; De-Felice, John; Barber, James (May 1983). "Growth temperature effects on thylakoid membrane lipid and protein content of pea chloroplasts 1". Plant Physiol 72 (1): 225–228. doi:10.1104/pp.72.1.225. PMID 16662966. 
  4. ↑ YashRoy R.C. (1987) 13-C NMR studies of lipid fatty acyl chains of chloroplast membranes. Indian Journal of Biochemistry and Biophysics vol. 24(6), pp. 177–178.https://www.researchgate.net/publication/230822408_13-C_NMR_studies_of_lipid_fatty_acyl_chains_of_chloroplast_membranes?ev=prf_pub
  5. ↑ Manthey, F. A.; Lee, R. E.; Hall, C. A. (2002). "Processing and cooking effects on lipid content and stability of alpha-linolenic acid in spaghetti containing ground flaxseed.". J. Agric. Food Chem. 50 (6): 1668–71. doi:10.1021/jf011147s. PMID 11879055. 
  6. ↑ "OXIDATIVE STABILITY OF FLAXSEED LIPIDS DURING BAKING". http://serials.unibo.it/cgi-ser/start/it/spogli/df-s.tcl?prog_art=3832218&language=ITALIANO&view=articoli. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 "Seed Oil Fatty Acids – SOFA Database Retrieval". http://sofa.mri.bund.de/. 
  8. ↑ Li, Thomas S. C. (1999). "Sea buckthorn: New crop opportunity". Alexandria, VA: ASHS Press. pp. 335–337. http://www.hort.purdue.edu/newcrop/proceedings1999/v4-335.html. Retrieved 2006-10-28. 
  9. ↑ "Omega-3 fatty acids". University of Maryland Medical Center. http://www.umm.edu/altmed/articles/omega-3-000316.htm. 
  10. ↑ Breanne M Anderson; David WL Ma (2009). "Are all n-3 polyunsaturated fatty acids created equal?". Lipids in Health and Disease 8 (33): 33. doi:10.1186/1476-511X-8-33. PMID 19664246. 
  11. ↑ Shiels M. Innis (2007). "Fatty acids and early human development". Early Human Development 83 (12): 761–766. doi:10.1016/j.earlhumdev.2007.09.004. PMID 17920214. 
  12. ↑ Burdge, GC; Calder, PC (2005). "Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults". Reproduction, Nutrition, Development 45 (5): 581–597. doi:10.1051/rnd:2005047. PMID 16188209. http://rnd.edpsciences.org/articles/rnd/pdf/2005/05/r5505.pdf. Retrieved 4 November 2018. 
  13. ↑ 13.0 13.1 Kinney, Tony. "Metabolism in plants to produce healthier food oils (slide #4)". http://www.metabolicengineering.gov/me2005/Kinney.pdf. 
  14. ↑ Fitzgerald, Anne; Brasher, Philip. "Ban on trans fat could benefit Iowa". Truth About Trade and Technology. http://www.truthabouttrade.org/article.asp?id=6669. Retrieved 2007-01-03. 
  15. ↑ Monsanto. "ADM to process Monsanto's Vistive low linolenic soybeans at Indiana facility". http://www.monsanto.com/monsanto/layout/media/06/01-12-06.asp. 
  16. ↑ "Impact of α-Linolenic Acid, the Vegetable ω-3 Fatty Acid, on Cardiovascular Disease and Cognition". Advances in Nutrition 13 (5): 1584–1602. 2022. doi:10.1093/advances/nmac016. PMID 35170723. PMC 9526859. https://academic.oup.com/advances/article/13/5/1584/6529227. 
  17. ↑ "α-Linolenic acid and risk of cardiovascular disease: a systematic review and meta-analysis". Am. J. Clin. Nutr. 96 (6): 1262–73. December 2012. doi:10.3945/ajcn.112.044040. PMID 23076616. 
  18. ↑ "Effects of α-linolenic acid intake on blood lipid profiles：a systematic review and meta-analysis of randomized controlled trials". Critical Reviews in Food Science and Nutrition 61 (17): 2894–2910. 2020. doi:10.1080/10408398.2020.1790496. PMID 32643951. https://www.tandfonline.com/doi/abs/10.1080/10408398.2020.1790496. Retrieved 14 December 2021. 
  19. ↑ "Research Dietary intake and biomarkers of alpha linolenic acid and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of cohort studies". The BMJ 375: n2213. 2021. doi:10.1136/bmj.n2213. PMID 34645650. PMC 8513503. https://www.bmj.com/content/375/bmj.n2213. Retrieved 14 December 2021. 
  20. ↑ Hazura, K. (1887). "Über trocknende Ölsäuren IV. Abhandlung" (in de). Monatshefte für Chemie 8: 260–270. doi:10.1007/BF01510049. https://babel.hathitrust.org/cgi/pt?id=uiug.30112025862258&view=1up&seq=272. Retrieved 1 November 2020.  Linolenic acid is named on p. 265: "Für die Säure C18H32O2 schlage ich den Namen Linolsäure, für die Säure C18H30O2 den Namen Linolensäure vor." (For the acid C18H32O2 I suggest the name "linolic acid"; for the acid C18H30O2 [I suggest] the name "linolenic acid".) Linolenic acid is discussed on pp. 265-268.
  21. ↑ See:
  22. ↑ Rollett, A. (1909). "Zur Kenntnis der Linolensäure und des Leinöls". Zeitschrift für physiologische Chemie 62 (5–6): 422–431. doi:10.1515/bchm2.1909.62.5-6.422. https://zenodo.org/record/1448776. Retrieved 1 July 2019. 
  23. ↑ J. W. McCutcheon (1955). "Linolenic acid". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv3p0531. ; Collective Volume, 3, pp. 351 
  24. ↑ Green, TG; Hilditch, TP (1935). "The identification of linoleic and linolenic acids". Biochem. J. 29 (7): 1552–63. doi:10.1042/bj0291552. PMID 16745822. 
  25. ↑ Sandri, J.; Viala, J. (1995). "Direct preparation of (Z,Z)-1,4-dienic units with a new C6 homologating agent: synthesis of alpha-linolenic acid". Synthesis 1995 (3): 271–275. doi:10.1055/s-1995-3906. 



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