Linoleic acid
Names
Preferred IUPAC name
(9Z,12Z)-Octadeca-9,12-dienoic acid
Other names
cis,cis-9,12-Octadecadienoic acid
C18:2 (Lipid numbers)
Identifiers
3D model (JSmol)
3DMet
1727101
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.428
EC Number
  • 200-470-9
57557
KEGG
UNII
  • InChI=1S/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9- checkY
    Key: OYHQOLUKZRVURQ-HZJYTTRNSA-N checkY
  • InChI=1/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9-
    Key: OYHQOLUKZRVURQ-HZJYTTRNBX
  • CCCCC/C=C\C/C=C\CCCCCCCC(=O)O
Properties
C18H32O2
Molar mass 280.452 g·mol−1
Appearance Colorless oil
Density 0.9 g/cm3[1]
Melting point −12 °C (10 °F)[1]
−6.9 °C (19.6 °F)[2]
−5 °C (23 °F)[3]
Boiling point 229 °C (444 °F) at 16 mmHg[2]
230 °C (446 °F) at 21 mbar[3]
230 °C (446 °F) at 16 mmHg[1]
0.139 mg/L[3]
Vapor pressure 16 Torr at 229 °C
Acidity (pKa) 9.24[4]
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
2
1
0
Flash point 112 °C (234 °F)[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Linoleic acid (LA) is an organic compound with the formula HOOC(CH
2)
7CH=CHCH
2CH=CH(CH
2)
4CH
3. Both alkene groups are cis. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 cis-9,12. A linoleate is a salt or ester of this acid.[5]

Linoleic acid is a polyunsaturated omega-6 fatty acid. It is a colorless liquid that is virtually insoluble in water but soluble in many organic solvents.[2] It typically occurs in nature as a triglyceride (ester of glycerin) rather than as a free fatty acid.[6] It is one of two essential fatty acids for humans, who must obtain it through their diet,[7] and the most essential, because the body uses it as a base to make the others.

The word "linoleic" derives from the Latin linum "flax" + oleum "oil", reflecting the fact that it was first isolated from linseed oil.

History

In 1844, F. Sacc, working at the laboratory of Justus von Liebig, isolated linoleic acid from linseed oil.[8][9] In 1886, K. Peters determined the existence of two double bonds.[10] Its essential role in human diet was discovered by G. O. Burr and others in 1930.[11] Its chemical structure was determined by T.P. Hilditch and others in 1939, and it was synthesized by R. A. Raphael and F. Sondheimer in 1950.[12]

In physiology

The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid.[13]

Metabolism and eicosanoids

Linoleic acid (LA: C
18H
32O
2; 18:2, ω-6) is a precursor to arachidonic acid (AA: C
20H
32O
2; 20:4, ω-6) with elongation and unsaturation.[13] AA is the precursor to some prostaglandins,[14] leukotrienes (LTA, LTB, LTC), thromboxane (TXA)[15] and the N-acylethanolamine (NAE) arachidonoylethanolamine (AEA: C
22H
37NO
2; 20:4, ω-6),[16] and other endocannabinoids and eicosanoids.[17]

The metabolism of LA to AA begins with the conversion of LA into gamma-linolenic acid (GLA), effected by Δ6-desaturase.[18] GLA is converted to dihomo-γ-linolenic acid (DGLA), the immediate precursor to AA.

LA is also converted by various lipoxygenases, cyclooxygenases, cytochrome P450 enzymes (the CYP monooxygenases), and non-enzymatic autoxidation mechanisms to mono-hydroxyl products viz., 13-Hydroxyoctadecadienoic acid, and 9-Hydroxyoctadecadienoic acid; these two hydroxy metabolites are enzymatically oxidized to their keto metabolites, 13-oxo-octadecadienoic acid and 9-oxo-octadecdienoic acid. Certain cytochrome P450 enzymes, the CYP epoxygenases, catalyze oxidation of LA to epoxide products viz., its 12,13-epoxide, vernolic acid, and its 9,10-epoxide, coronaric acid. These linoleic acid products are implicated in human physiology and pathology.[19]

Hydroperoxides derived from the metabolism of anandamide (AEA: C
22H
37NO
2; 20:4,n-6), or its linoleoyl analogues, are by a lipoxygenase action found to be competitive inhibitors of brain and immune cell FAAH, the enzyme that breaks down AEA and other endocannabinoids, and the compound linoleoyl-ethanol-amide (C
20H
37NO
2; 18:2,n-6), an N-acylethanolamine, - the ethanolamide of linoleic acid (LA: C
18H
32O
2; 18:2, n-6) and its metabolized incorporated ethanolamine (MEA: C
2H
7NO),[20] is the first natural inhibitor of FAAH, discovered.[21][22]

Uses and reactions

Linoleic acid is a component of quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the lability of the doubly allylic C−H groups (−CH=CH−CH2−CH=CH−) toward oxygen in air (autoxidation). Addition of oxygen leads to crosslinking and formation of a stable film.[23]

Reduction of the carboxylic acid group of linoleic acid yields linoleyl alcohol.[24]

Linoleic acid is a surfactant with a critical micelle concentration of 1.5 x 10−4 M @ pH 7.5.

Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, skin-lightening and moisture retentive properties when applied topically on the skin.[25][26][27][28]

Linoleic acid is also used in some bar of soap products.

Dietary sources

It is abundant in safflower, and corn oil, and comprises over half their composition by weight. It is present in medium quantities in soybean oils, sesame, and almonds.[29][30]

Name% LA†ref.
Salicornia oil75%
Safflower oil72-78%[31]
Evening Primrose oil65-80%[32]
Melon seed oil70%
Poppyseed oil70%
Grape seed oil69.6%
Prickly Pear seed oil63%
Artichoke oil60%
Hemp oil54.3%[33]
Wheat germ oil55%
Cottonseed oil54%
Corn oil51.9%[34]
Walnut oil51%
Soybean oil50.9%[35]
Sesame oil45%
Pumpkin seed oil42-59%[36]
Rice bran oil39%
Argan oil37%
Pistachio oil32.7%
Peach oil29%[37]
Almonds24%
Canola oil17.8%[38]
Sunflower oil20.5%[39]
Chicken fat18-23%[40]
Peanut oil19.6%[41]
Egg yolk16%
Linseed oil (flax), cold pressed14.2%[42]
Lard10%
Palm oil10%
Olive oil8.4%[43]
Cocoa butter3%
Macadamia oil2%
Butter2%
Coconut oil2%
  †average val

Other occurrences

Cockroaches release oleic and linoleic acid upon death, which discourages other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death.[44]

Health effects

Consumption of linoleic acid has been associated with lowering the risk of cardiovascular disease, diabetes and premature death.[45][46][47] There is high-quality evidence that increased intake of linoleic acid decreases total blood cholesterol and low-density lipoprotein.[48]

The American Heart Association advises people to replace saturated fat with linoleic acid to reduce CVD risk.[49]

See also

References

  1. 1 2 3 The Merck Index, 11th Edition, 5382
  2. 1 2 3 William M. Haynes (2016). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton: CRC Press. pp. 3–338. ISBN 978-1-4987-5429-3.
  3. 1 2 3 4 Record of CAS RN 60-33-3 in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  4. ↑ J.R. Kanicky and D.O. Shah (2002): "Effect of Degree, Type, and Position of Unsaturation on the pKa of Long-Chain Fatty Acids". Journal of Colloid and INterface Science, volume 256, pages 201-207, doi:10.1006/jcis.2001.8009
  5. ↑ "Fatty Acids". Cyber Lipid. Archived from the original on 28 October 2018. Retrieved 31 July 2017.
  6. ↑ Mattes, Richard D. (2009). "Is there a fatty acid taste?". Annual Review of Nutrition. 29: 305–327. doi:10.1146/annurev-nutr-080508-141108. PMC 2843518. PMID 19400700.
  7. ↑ Simopoulos, Artemis P. (2008). "The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases". Experimental Biology and Medicine. 233 (6): 674–688. doi:10.3181/0711-mr-311. PMID 18408140. S2CID 9044197.
  8. ↑ F. Sacc (1844) "Ueber das Leinöl, seine physicalischen und chemischen Eigenscharften und seine Oxydationsproducte". Liebig Annalen, volume 51, pages 213-230.
  9. ↑ F. Sacc (1845): "Expériences sur les propriétés physiques et chimiques de l'huile de Lin". SChweizer. Gesell. N. Dekschr., volume 7
  10. ↑ (1886), Monatsch., volume 7, pages 522-
  11. ↑ (1930: J Biol Chem, volume 86, pages 587-
  12. ↑ R. A. Raphael and Franz Sondheimer (1950): "The synthesis of long-chain aliphatic acids from acetylenic compounds. Part III. The synthesis of linoleic acid". Journal of the Chemical Society (Resumed), article 432, doi:10.1039/jr9500002100
  13. 1 2 Whelan, Jay; Fritsche, Kevin (May 2013). "Linoleic Acid". Advances in Nutrition. 4 (3): 311–312. doi:10.3945/an.113.003772. PMC 3650500. PMID 23674797.
  14. ↑ Wlodawer, Paulina; Samuelsson, Bengt (25 August 1973). "On the organization and mechanism of prostaglandin synthetase". The Journal of Biological Chemistry. 248 (16): 5673–5678. doi:10.1016/S0021-9258(19)43558-8. PMID 4723909.
  15. ↑ Terano, Takashi; Salmon, John A.; Moncada, Salvador (February 1984). "Biosynthesis and biological activity of leukotriene B5". Prostaglandins. 27 (2): 217–232. doi:10.1016/0090-6980(84)90075-3. PMID 6326200.
  16. ↑ Murru, Elisabetta; Lopes, Paula A.; Carta, Gianfranca; Manca, Claudia; Abolghasemi, Armita; Guil-Guerrero, José L.; Prates, José A. M.; Banni, Sebastiano (15 February 2021). "Different Dietary N-3 Polyunsaturated Fatty Acid Formulations Distinctively Modify Tissue Fatty Acid and N-Acylethanolamine Profiles". Nutrients. 13 (2): 625. doi:10.3390/nu13020625. ISSN 2072-6643. PMC 7919039. PMID 33671938.
  17. ↑ Salem, Norman; Van Dael, Peter (27 February 2020). "Arachidonic Acid in Human Milk". Nutrients. 12 (3): 626. doi:10.3390/nu12030626. ISSN 2072-6643. PMC 7146261. PMID 32121018.
  18. ↑ Evidence suggests that infants must acquire Δ6-desaturase breast milk. Breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA. David F. Horrobin (1993). "Fatty acid metabolism in health and disease: the role of Δ-6-desaturase". American Journal of Clinical Nutrition. 57 (5 Suppl): 732S–737S. doi:10.1093/ajcn/57.5.732S. PMID 8386433.
  19. ↑ Jandacek, Ronald J. (20 May 2017). "Linoleic Acid: A Nutritional Quandary". Healthcare. 5 (2): 25. doi:10.3390/healthcare5020025. ISSN 2227-9032. PMC 5492028. PMID 28531128.
  20. ↑ PubChem. "Linoleoyl ethanolamide". pubchem.ncbi.nlm.nih.gov. Retrieved 29 October 2022.
  21. ↑ Maccarrone, Mauro; Stelt, Marcelis van der; Rossi, Antonello; Veldink, Gerrit A.; Vliegenthart, Johannes F. G.; Agrò, Alessandro Finazzi (27 November 1998). "Anandamide Hydrolysis by Human Cells in Culture and Brain *". Journal of Biological Chemistry. 273 (48): 32332–32339. doi:10.1074/jbc.273.48.32332. hdl:1887/50863. ISSN 0021-9258. PMID 9822713.
  22. ↑ Scala, Coralie Di; Fantini, Jacques; Yahi, Nouara; Barrantes, Francisco J.; Chahinian, Henri (22 May 2018). "Anandamide Revisited: How Cholesterol and Ceramides Control Receptor-Dependent and Receptor-Independent Signal Transmission Pathways of a Lipid Neurotransmitter". Biomolecules. 8 (2): 31. doi:10.3390/biom8020031. ISSN 2218-273X. PMC 6022874. PMID 29789479.
  23. ↑ Ulrich Poth (2002). "Drying Oils and Related Products". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_055. ISBN 978-3527306732.
  24. ↑ Adkins, Homer; Gillespie, R.H. (1949). "Oleyl Alcohol". Organic Syntheses. 29: 80. doi:10.15227/orgsyn.029.0080.
  25. ↑ Diezel, W.E.; Schulz, E.; Skanks, M.; Heise, H. (1993). "Plant oils: Topical application and anti-inflammatory effects (croton oil test)". Dermatologische Monatsschrift. 179: 173.
  26. ↑ Letawe, C.; Boone, M.; Pierard, G.E. (March 1998). "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones". Clinical and Experimental Dermatology. 23 (2): 56–58. doi:10.1046/j.1365-2230.1998.00315.x. PMID 9692305. S2CID 28594076.
  27. ↑ Ando, Hideya; Ryu, Atsuko; Hashimoto, Akira; Oka, Masahiro; Ichihashi, Masamitsu (March 1998). "Linoleic acid and α-linolenic acid lightens ultraviolet-induced hyperpigmentation of the skin". Archives of Dermatological Research. 290 (7): 375–381. doi:10.1007/s004030050320. PMID 9749992. S2CID 23036319.
  28. ↑ Darmstadt, Gary L.; Mao-Qiang, M.; Chi, E.; Saha, S.K.; Ziboh, V.A.; Black, R.E.; Santosham, M.; Elias, P.M. (2002). "Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries". Acta Paediatrica. 91 (5): 546–554. CiteSeerX 10.1.1.475.1064. doi:10.1080/080352502753711678. PMID 12113324.
  29. ↑ "Nutrient Data Laboratory Home Page". USDA National Nutrient Database for Standard Reference, Release 20. U.S. Department of Agriculture, Agricultural Research Service. 2007. Archived from the original on 14 April 2016.
  30. ↑ Kaur, Narinder; Chugh, Vishal; Gupta, Anil K. (October 2014). "Essential fatty acids as functional components of foods- a review". Journal of Food Science and Technology. 51 (10): 2289–2303. doi:10.1007/s13197-012-0677-0. PMC 4190204. PMID 25328170.
  31. ↑ Hall III, C. (2015). Wrigley, Colin W.; Corke, Harold; Seetharaman, Koushik; Faubion, Jonathan (eds.). Encyclopedia of Food Grains. Academic Press. ISBN 978-0-12-394786-4.
  32. ↑ "Evening Primrose Oil for Menopause does it help". 26 January 2018.
  33. ↑ Oomah, B. Dave; Busson, Muriel; Godfrey, David V; Drover, John C. G (1 January 2002). "Characteristics of hemp (Cannabis sativa L.) seed oil". Food Chemistry. 76 (1): 33–43. doi:10.1016/S0308-8146(01)00245-X.
  34. ↑ "FoodData Central". fdc.nal.usda.gov.
  35. ↑ "FoodData Central". fdc.nal.usda.gov.
  36. ↑ Nawirska-Olszańska A, Kita A, Biesiada A, Sokół-Łętowska A, Kucharska AZ. (2013). "Characteristics of antioxidant activity and composition of pumpkin seed oils in 12 cultivars". Food Chemistry. 139 (1–4): 155–161. doi:10.1016/j.foodchem.2013.02.009. PMID 23561092.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  37. ↑ Wu, Hao; Shi, John; Xue, Sophia; Kakuda, Yukio; Wang, Dongfeng; Jiang, Yueming; Ye, Xingqian; Li, Yanjun; Subramanian, Jayasankar (2011). "Essential oil extracted from peach (Prunus persica) kernel and its physicochemical and antioxidant properties". LWT - Food Science and Technology. 44 (10): 2032–2039. doi:10.1016/j.lwt.2011.05.012.
  38. ↑ "FoodData Central". fdc.nal.usda.gov.
  39. ↑ "FoodData Central". fdc.nal.usda.gov.
  40. ↑ M. K. Nutter, E. E. Lockhart and R. S. Harris (1943). "The chemical composition of depot fats in chickens and turkeys". Journal of the American Oil Chemists' Society. 20 (11): 231–234. doi:10.1007/BF02630880. S2CID 84893770.
  41. ↑ "FoodData Central". fdc.nal.usda.gov.
  42. ↑ "FoodData Central". fdc.nal.usda.gov.
  43. ↑ "FoodData Central". fdc.nal.usda.gov.
  44. ↑ "Earth News: Ancient 'smell of death' revealed". BBC. 9 September 2009.
  45. ↑ Li, Jun; Guasch-Ferré, Marta; Li, Yanping; Hu, Frank B. (2020). "Dietary intake and biomarkers of linoleic acid and mortality: systematic review and meta-analysis of prospective cohort studies". The American Journal of Clinical Nutrition. 112 (1): 150–167. doi:10.1093/ajcn/nqz349. PMC 7326588. PMID 32020162.
  46. ↑ Marangoni, Franca; Agostoni, Carlo; Borghi, Claudio; Catapano, Alberico L.; Cena, Hellas; Ghiselli, Andrea; La Vecchia, Carlo; Lercker, Giovanni; Manzato, Enzo; Pirillo, Angela; Riccardi, Gabriele; Risé, Patrizia; Visioli, Francesco; Poli, Andrea (2020). "Dietary linoleic acid and human health: Focus on cardiovascular and cardiometabolic effects". Atherosclerosis. 292: 90–98. doi:10.1016/j.atherosclerosis.2019.11.018. PMID 31785494. S2CID 208516015.
  47. ↑ Mousavi, Seyed Mohammad; Jalilpiran, Yahya; Karimi, Elmira; Aune, Dagfinn; Larijani, Bagher; Mozaffarian, Dariush; Willett, Walter C.; Esmaillzadeh, Ahmad (2021). "Dietary Intake of Linoleic Acid, Its Concentrations, and the Risk of Type 2 Diabetes: A Systematic Review and Dose-Response Meta-analysis of Prospective Cohort Studies". Diabetes Care. 44 (9): 2173–2181. doi:10.2337/dc21-0438. PMID 34417277. S2CID 237255109.
  48. ↑ "Systematic review of the evidence for relationships between saturated, cis monounsaturated, cis polyunsaturated fatty acids and selected individual fatty acids, and blood cholesterol concentration". foodstandards.gov.au. Retrieved 10 January 2023.
  49. ↑ Sacks FM, Lichtenstein AH, Wu JH, Appel LJ, Creager MA, Kris-Etherton PM, Miller M, Rimm EB, Rudel LL, Robinson JG, Stone NJ, Van Horn LV (July 2017). "Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association". Circulation. 136 (3): e1–e23. doi:10.1161/CIR.0000000000000510. PMID 28620111. S2CID 367602.

Further reading

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