Linoleic acid

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Linoleic acid
LAnumbering.png
Linoleic-acid-from-xtal-1979-3D-balls.png
Linoleic-acid-from-xtal-1979-3D-vdW.png
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 Edit this at Wikidata
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[citation needed]
Hazards
NFPA 704 (fire 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 ?)

Linoleic acid is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. 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.[4]

Linoleic acid is a polyunsaturated omega-6 fatty acid. It is a colorless or white 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.[5] It is one of two essential fatty acids for humans, who must obtain it through their diet.[6]

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

History[edit]

In 1844, F. Sacc, working at the laboratory of Justus von Liebig, isolated linoleic acid from linseed oil.[7][8] In 1886, K. Peters determined the existence of two double bonds.[9] Its essential role in human diet was discovered by G. O. Burr and others in 1930.[10] 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.[11]

In physiology[edit]

The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid.[12]

Metabolism and eicosanoids[edit]

Linoleic Acid Metabolism.gif

Linoleic acid is a precursor to arachidonic acid (AA) with elongation and saturation.[13] AA is the precursor to some prostaglandins,[14] leukotrienes (LTA, LTB, LTC), and thromboxane (TXA).[15]

The metabolism of LA to AA begins with the conversion of LA into gamma-Linolenic acid (GLA), effected by Δ6desaturase.[16] 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.[17]

Uses and reactions[edit]

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.[18]

Reduction of the carboxylic acid group of linoleic acid yields linoleyl alcohol.[19]

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

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.[20][21][22][23]

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

Dietary sources[edit]

Properties of vegetable oils[24][25]
Type Processing
treatment[26]
Saturated
fatty acids
Monounsaturated
fatty acids
Polyunsaturated
fatty acids
Smoke point
Total[24] Oleic
acid
(ω-9)
Total[24] α-Linolenic
acid
(ω-3)
Linoleic
acid
(ω-6)
ω-6:3
ratio
Avocado[27] 11.6 70.6 52–66[28] 13.5 1 12.5 12.5:1 250 °C (482 °F)[29]
Brazil nut[30] 24.8 32.7 31.3 42.0 0.1 41.9 419:1 208 °C (406 °F)[31]
Canola[32] 7.4 63.3 61.8 28.1 9.1 18.6 2:1 238 °C (460 °F)[31]
Coconut[33] 82.5 6.3 6 1.7 175 °C (347 °F)[31]
Corn[34] 12.9 27.6 27.3 54.7 1 58 58:1 232 °C (450 °F)[35]
Cottonseed[36] 25.9 17.8 19 51.9 1 54 54:1 216 °C (420 °F)[35]
Flaxseed/linseed[37] 9.0 18.4 18 67.8 53 13 0.2:1 107 °C (225 °F)
Grape seed   10.5 14.3 14.3   74.7 74.7 very high 216 °C (421 °F)[38]
Hemp seed[39] 7.0 9.0 9.0 82.0 22.0 54.0 2.5:1 166 °C (330 °F)[40]
Olive[41] 13.8 73.0 71.3 10.5 0.7 9.8 14:1 193 °C (380 °F)[31]
Palm[42] 49.3 37.0 40 9.3 0.2 9.1 45.5:1 235 °C (455 °F)
Peanut[43] 16.2 57.1 55.4 19.9 0.318 19.6 very high 232 °C (450 °F)[35]
Rice bran oil 25 38.4 2.2 34.4[44] 15.6 232 °C (450 °F)[45]
High-oleic safflower oil[46] 7.5 75.2 75.2 12.8 0 12.8 very high 212 °C (414 °F)[31]
Sesame[47] ? 14.2 39.7 39.3 41.7 0.3 41.3 138:1
Soybean[48] partially hydrogenated 14.9 43.0 42.5 37.6 2.6 34.9 13.4:1
Soybean[49] 15.6 22.8 22.6 57.7 7 51 7.3:1 238 °C (460 °F)[35]
Walnut oil[50] unrefined 9.1 22.8 22.2 63.3 10.4 52.9 5:1 160 °C (320 °F)[51]
Sunflower[52] 8.99 63.4 62.9 20.7 0.16 20.5 very high 227 °C (440 °F)[35]
Cottonseed[53] hydrogenated 93.6 1.5 0.6 0.2 0.3 1.5:1
Palm[54] hydrogenated 88.2 5.7 0
The nutritional values are expressed as percent (%) by mass of total fat.

Other occurrences[edit]

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.[55]

Health effects[edit]

Consumption of linoleic acid has been associated with lowering the risk of cardiovascular disease and premature death.[56]

See also[edit]

References[edit]

  1. ^ a b c The Merck Index, 11th Edition, 5382
  2. ^ a b c 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. ^ a b c d Record of CAS RN 60-33-3 in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  4. ^ "Fatty Acids". Cyber Lipid. Archived from the original on 28 October 2018. Retrieved 31 July 2017.
  5. ^ Mattes, RD (2009). "Is there a fatty acid taste?". Annu. Rev. Nutr. 29: 305–27. doi:10.1146/annurev-nutr-080508-141108. PMC 2843518. PMID 19400700.
  6. ^ 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.
  7. ^ F. Sacc (1844) "Ueber das Leinöl, seine physicalischen und chemischen Eigenscharften und seine Oxydationsproducte". Liebig Annalen, volume 51, pages 213-230.
  8. ^ F. Sacc (1845): "Expériences sur les propriétés physiques et chimiques de l'huile de Lin". SChweizer. Gesell. N. Dekschr., volume 7
  9. ^ (1886), Monatsch., volume 7, pages 522-
  10. ^ (1930: J Biol Chem, volume 86, pages 587-
  11. ^ 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
  12. ^ 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.
  13. ^ Whelan J, Fritsche K. (2013). "Linoleic acid". Adv Nutr. 4 (3): 311–312. doi:10.3945/an.113.003772. PMC 3650500. PMID 23674797.{{cite journal}}: CS1 maint: uses authors parameter (link)
  14. ^ Wlodawer, P; Samuelsson, B (1973). "On the organization and mechanism of prostaglandin synthetase". The Journal of Biological Chemistry. 248 (16): 5673–8. doi:10.1016/S0021-9258(19)43558-8. PMID 4723909.
  15. ^ Terano, Takashi; Salmon, John A.; Moncada, Salvador (1984). "Biosynthesis and biological activity of leukotriene B5". Prostaglandins. 27 (2): 217–32. doi:10.1016/0090-6980(84)90075-3. PMID 6326200.
  16. ^ Evidence suggests that infants must acquire Δ6desaturase breast milk. Breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LADavid 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–7S. doi:10.1093/ajcn/57.5.732S. PMID 8386433.
  17. ^ 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.
  18. ^ Ulrich Poth (2002). "Drying Oils and Related Products". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_055.
  19. ^ Adkins, Homer; Gillespie, R. H. (1949). "Oleyl Alcohol". Organic Syntheses. 29: 80. doi:10.15227/orgsyn.029.0080.
  20. ^ 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.
  21. ^ Letawe, C; Boone, M; Pierard, GE (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.
  22. ^ Ando, H; Ryu, A; Hashimoto, A; Oka, M; Ichihashi, M (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.
  23. ^ Darmstadt, GL; Mao-Qiang, M; Chi, E; Saha, SK; Ziboh, VA; Black, RE; Santosham, M; Elias, PM (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.
  24. ^ a b c "US National Nutrient Database, Release 28". United States Department of Agriculture. May 2016. All values in this table are from this database unless otherwise cited.
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  26. ^ "USDA Specifications for Vegetable Oil Margarine Effective August 28, 1996" (PDF).
  27. ^ "Avocado oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  28. ^ Feramuz Ozdemir; Ayhan Topuz (May 2003). "Changes in dry matter, oil content and fatty acids composition of avocado during harvesting time and post-harvesting ripening period" (PDF). Elsevier. Retrieved 15 January 2020.
  29. ^ Marie Wong; Cecilia Requejo-Jackman; Allan Woolf (April 2010). "What is unrefined, extra virgin cold-pressed avocado oil?". Aocs.org. The American Oil Chemists’ Society. Retrieved 26 December 2019.
  30. ^ "Brazil nut oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  31. ^ a b c d e Katragadda, H. R.; Fullana, A. S.; Sidhu, S.; Carbonell-Barrachina, Á. A. (2010). "Emissions of volatile aldehydes from heated cooking oils". Food Chemistry. 120: 59–65. doi:10.1016/j.foodchem.2009.09.070.
  32. ^ "Canola oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  33. ^ "Coconut oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  34. ^ "Corn oil, industrial and retail, all purpose salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  35. ^ a b c d e Wolke, Robert L. (16 May 2007). "Where There's Smoke, There's a Fryer". The Washington Post. Retrieved 5 March 2011.
  36. ^ "Cottonseed oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  37. ^ "Linseed/Flaxseed oil, cold pressed, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  38. ^ Garavaglia J, Markoski MM, Oliveira A, Marcadenti A (2016). "Grape Seed Oil Compounds: Biological and Chemical Actions for Health". Nutrition and Metabolic Insights. 9: 59–64. doi:10.4137/NMI.S32910. PMC 4988453. PMID 27559299.
  39. ^ Callaway J, Schwab U, Harvima I, Halonen P, Mykkänen O, Hyvönen P, Järvinen T (April 2005). "Efficacy of dietary hempseed oil in patients with atopic dermatitis". The Journal of Dermatological Treatment. 16 (2): 87–94. doi:10.1080/09546630510035832. PMID 16019622. S2CID 18445488.
  40. ^ "Smoke points of oils" (PDF).
  41. ^ "Olive oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  42. ^ "Palm oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  43. ^ "FoodData Central". fdc.nal.usda.gov.
  44. ^ Orthoefer, F. T. (2005). "Chapter 10: Rice Bran Oil". In Shahidi, F. (ed.). Bailey's Industrial Oil and Fat Products. Vol. 2 (6 ed.). John Wiley & Sons, Inc. p. 465. doi:10.1002/047167849X. ISBN 978-0-471-38552-3.
  45. ^ "Rice bran oil". RITO Partnership. Retrieved 22 January 2021.
  46. ^ "Safflower oil, salad or cooking, high oleic, primary commerce, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  47. ^ "Oil, sesame, salad or cooking". FoodData Central. fdc.nal.usda.gov.
  48. ^ "Soybean oil, salad or cooking, (partially hydrogenated), fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  49. ^ "Soybean oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  50. ^ "Walnut oil, fat composition, 100 g". US National Nutrient Database, United States Department of Agriculture.
  51. ^ "Smoke Point of Oils". Baseline of Health. Jonbarron.org.
  52. ^ "FoodData Central". fdc.nal.usda.gov.
  53. ^ "Cottonseed oil, industrial, fully hydrogenated, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  54. ^ "Palm oil, industrial, fully hydrogenated, filling fat, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  55. ^ "Earth News: Ancient 'smell of death' revealed". BBC. 9 September 2009.
  56. ^ Li J, Guasch-Ferré M, Li Y, Hu FB. (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.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Further reading[edit]

External links[edit]