alpha-Linolenic acid

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Not to be confused with linoleic acid.

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This article is about alpha-linolenic acid. For other uses, see Linolenic acid.
α-Linolenic acid
ALAnumbering.svg
Linolenic-acid-3D-vdW.png
Names
IUPAC name
(9Z,12Z,15Z)-9,12,15-Octadecatrienoic acid
Other names
ALA; Linolenic acid; cis,cis,cis-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid;[1] Industrene 120
Identifiers
463-40-1 YesY
ChEBI CHEBI:27432 YesY
ChEMBL ChEMBL8739 YesY
ChemSpider 4444437 YesY
DrugBank DB00132 YesY
1049
Jmol 3D model Interactive image
Interactive image
PubChem 5280934
UNII 0RBV727H71 YesY
  • InChI=1S/C18H30O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h3-4,6-7,9-10H,2,5,8,11-17H2,1H3,(H,19,20)/b4-3-,7-6-,10-9- YesY
    Key: DTOSIQBPPRVQHS-PDBXOOCHSA-N YesY
  • InChI=1/C18H30O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h3-4,6-7,9-10H,2,5,8,11-17H2,1H3,(H,19,20)/b4-3-,7-6-,10-9-
    Key: DTOSIQBPPRVQHS-PDBXOOCHBH
  • O=C(O)CCCCCCC\C=C/C\C=C/C\C=C/CC
  • CC/C=C\C/C=C\C/C=C\CCCCCCCC(=O)O
Properties
C18H30O2
Molar mass 278.44 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).
YesY verify (what is YesYN ?)
Infobox references

α-Linolenic acid (ALA) is an n−3 fatty acid, it is one of two essential fatty acids (EFAs), so called because they are necessary for health, and they cannot be produced within the human body. They must be acquired through diet. ALA is an omega-3 fatty acid found in seeds (chia, flaxseed, see also table below), nuts (notably walnuts), 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); its isomer GLA is 18:3 (n−6).

α-Linolenic acid 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), a polyunsaturated n−6 (omega-6) fatty acid.

History

α-Linolenic acid was first isolated by Rollett[3] as cited in J. W. McCutcheon's synthesis in 1942,[4] and referred to in Green and Hilditch's 1930s survey.[5] 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.[6]

Dietary sources

Seed oils are the richest sources of α-linolenic acid, notably those of 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).[7] Plant chloroplasts consisting of more than 95 percent of photosynthetic thylakoid membranes are highly fluid due to large abundance of linolenic acid, that shows up as sharp resonances in high resolution carbon-13 NMR spectra, invariably.[8] Some studies state that ALA remains stable during processing and cooking.[9] 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.[10] 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% [11]
Kiwifruit seeds Chinese gooseberry Actinidia chinensis 62% [11]
Perilla shiso Perilla frutescens 58% [11]
Flax linseed Linum usitatissimum 55% [11]
Lingonberry cowberry Vaccinium vitis-idaea 49% [11]
Camelina camelina Camelina sativa 35-45%
Purslane portulaca Portulaca oleracea 35% [11]
Sea buckthorn seaberry Hippophae rhamnoides L. 32% [12]
Hemp cannabis Cannabis sativa 20% [11]
Walnut English walnut / Persian walnut Juglans regia 10.4% [13]
Rapeseed canola Brassica napus 10% [2]
Soybean soya Glycine max 8% [2]
  †average value

Potential role in nutrition and health

Flax is a rich source of α-linolenic acid.

Although the best source of ALA is seeds, most seeds and seed oils are much richer in an n−6 fatty acid, linoleic acid. Exceptions include flaxseed (must be ground for proper nutrient absorption) and chia seeds. Linoleic acid is the other essential fatty acid, but it, and the other n−6 fatty acids, compete with n−3s for positions in cell membranes and have very different effects on human health. There is a complex set of essential fatty acid interactions.

α-Linolenic acid can only be obtained by humans 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 can also be synthesized by humans from dietary α-linolenic acid, but with an efficiency of only a few percent.[14] 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.[15][16] Conversion of ALA to DHA is higher in women than in men. [17]

A large 2006 study found no association between total α-linolenic acid intake and overall risk of prostate cancer.[18] Multiple studies[19][20] have shown a relationship between α-linolenic acid and an increased risk of prostate cancer. This risk was found to be irrespective of source of origin (e.g., meat, vegetable oil).[21] A recent (2009) meta-analysis, however, found evidence of publication bias in earlier studies, and concluded that if ALA contributes to increased prostate cancer risk, the increase in risk is quite small.[22]

Stability and hydrogenation

α-Linolenic acid is relatively more susceptible to oxidation and will become rancid more quickly than many other oils. Oxidative instability of α-linolenic acid is one reason why producers choose to partially hydrogenate oils containing α-linolenic acid, such as soybean oil.[23] Soybeans are the largest source of edible oils in the U.S., and 40% of soy oil production is partially hydrogenated.[24]

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.[25]

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.[26] 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.

Cardiovascular

There is some evidence ALA consumption might have a slight preventative effect against cardiovascular diseases.[27] The effect only registers through fish consumption; ALA taken in capsule form has no effect.[28]

See also

References

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  2. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 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
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 Seed Oil Fatty Acids – SOFA Database Retrieval
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.[dead link]
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  27. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  28. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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