Linoleic acid

Linoleic acid
Names
IUPAC name
(9Z,12Z)-9,12-Octadecadienoic acid
Other names
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.000.428
KEGG
UNII
Properties
C18H32O2
Molar mass 280.45 g·mol−1
Appearance Colorless oil
Density 0.9 g/cm3[1]
Melting point −5 °C (23 °F)[2]
−12 °C (10 °F)[1]
Boiling point 230 °C (446 °F) at 21 mbar[2]
230 °C (446 °F) at 16 mmHg[1]
0.139 mg/L[2]
Vapor pressure 16 Torr at 229 °C
Hazards
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
1
2
0
Flash point 112 °C (234 °F)[2]
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

Linoleic acid (LA), a carboxylic acid, is a polyunsaturated omega-6 fatty acid, an 18-carbon chain with two double bonds in cis configuration. A shorthand notation like "18:2 (n-6)" or "18:2 cis-9,12" may be used in literature.[3] It occurs in nature as a triglyceride ester, free fatty acids are typically low in foods.[4]

Linoleic acid belongs to one of the two families of essential fatty acids, which means that the human body cannot synthesize it from other food components.[5]

The word "linoleic" derived from the Greek word linon (flax). Oleic means "of, relating to, or derived from oil of olive" or "of or relating to oleic acid" because saturating the omega-6 double bond produces oleic acid.

In physiology

LA is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins, leukotrienes (LTA, LTB, LTC), and thromboxane (TXA). It is found in the lipids of cell membranes. It is abundant in many nuts, fatty seeds (flax seeds, hemp seeds, poppy seeds, sesame seeds, etc.) and their derived vegetable oils; comprising over half (by weight) of poppy seed, safflower, sunflower, corn, and soybean oils.[6]

LA is converted by various lipoxygenases, cyclooxygenases, certain cytochrome P450 enzymes (the CYP monooxygenases), and non-enzymatic autooxidation 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, metabolize LA to epoxide products viz., its 12,13-epoxide, Vernolic acid and its 9,10-epoxide, Coronaric acid. All of these LA products have bioactivity and are implicated in human physiology and pathology as indicated in the cited linkages.

Linoleic acid is an essential fatty acid that must be consumed for proper health. A diet only deficient in linoleate (the salt form of the acid) causes mild skin scaling, hair loss,[7] and poor wound healing in rats.[8]

Along with oleic acid, linoleic acid is released by cockroaches upon death which has the effect of preventing other roaches from entering the area. This is similar to the mechanism found in ants and bees, which also release oleic acid upon death.[9]

Metabolism and eicosanoids

The first step in the metabolism of LA is performed by Δ6desaturase, which converts LA into gamma-linolenic acid (GLA).

There is evidence suggesting that infants lack Δ6desaturase of their own, and must acquire it through breast milk. Studies show that breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA.[10]

GLA is converted to dihomo-gamma-linolenic acid (DGLA), which in turn is converted to arachidonic acid (AA). One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids during the inflammatory response and during physical activity; eicosanoids are a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to promote (not cause) inflammation and promote growth during and after physical activity in healthy humans.[11] For example, both AA-derived thrombaxane and leukotrieneB4 are proaggregatory and vasoconstrictive eicosanoids during inflammation. The oxidized metabolic products of linoleic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1, the capsaicin receptor, and through this might play a major role in hyperalgesia and allodynia.[12]

There are some suggested negative health effects related to this inflammation promoting function of linoleic acid as an omega-6 fatty acid.

Uses

Industrial uses

Linoleic acid is used in making quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the easy reaction of the linoleic acid with oxygen in air, which leads to crosslinking and formation of a stable film called linoxyn.

Reduction of linoleic acid yields linoleyl alcohol. 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, and moisture retentive properties when applied topically on the skin.[13][14][15]

Use in research

Linoleic acid lipid radicals can be used to show the antioxidant effect of natural phenols. Experiments on linoleic acid subjected to 2,2′-azobis (2-amidinopropane) dihydrochloride induced oxidation of linoleic acid; hence producing lipid radicals and then the use of different combinations of phenolics show that binary mixtures can lead to either a synergetic antioxidant effect or to an antagonistic effect towards the lipid radicals. Research like this is useful in discovering which phenols prevent the autoxidation of lipids in vegetable oils.[16]

Dietary sources

Note: Unless cited, none of these percentages have been verified by scientific research.

Name% LA†ref.
Salicornia oil 75%
Safflower oil 74.62%
Evening Primrose oil 73%
Poppyseed oil 70%
Grape seed oil 69.6%
Sunflower oil 65.7%
Barbary Fig Seed Oil 65%
Hemp oil 54.3% [17]
Corn oil 59%
Wheat germ oil 55%
Cottonseed oil 54%
Soybean oil 51%
Walnut oil 51%
Sesame oil 45%
Rice bran oil 39%
Argan oil 37%
Pistachio oil 32.7%
Peanut oil 32% [18]
Peach oil 29% [19]
Almonds 24%
Canola oil 21%
Chicken fat 18-23% [20]
Egg yolk 16%
Linseed oil 15%
Lard 10%
Olive oil 10% (3.5 - 21%) [21][22]
Palm oil 10%
Cocoa butter 3%
Macadamia oil 2%
Butter 2%
Coconut oil 2%
  †average val

See also

References

  1. 1 2 3 The Merck Index, 11th Edition, 5382
  2. 1 2 3 4 Record of CAS RN 60-33-3 in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ↑ http://www.cyberlipid.org/fa/acid0001.htm
  4. ↑ www.ncbi.nlm.nih.gov/pmc/articles/PMC2843518
  5. ↑ Burr, G.O., Burr, M.M. and Miller, E. (1930). "On the nature and role of the fatty acids essential in nutrition" (PDF). J. Biol. Chem. 86 (587): 1–9.
  6. ↑ "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.
  7. ↑ Cunnane S, Anderson M (1 April 1997). "Pure linoleate deficiency in the rat: influence on growth, accumulation of n-6 polyunsaturates, and (1-14C) linoleate oxidation". J Lipid Res. 38 (4): 805–12. PMID 9144095. Retrieved 2007-01-15.
  8. ↑ Ruthig DJ & Meckling-Gill KA (1 October 1999). "Both (n-3) and (n-6) fatty acids stimulate wound healing in the rat intestinal epithelial cell line, IEC-6". Journal of Nutrition. 129 (10): 1791–8. PMID 10498749. Retrieved 2007-01-15.
  9. ↑ "Earth News: Ancient 'smell of death' revealed". BBC.
  10. ↑ David F. Horrobin (1993). "Fatty acid metabolism in health and disease: the role of Δ-6-desaturase". American Journal of Clinical Nutrition. 57: 732S–7S.
  11. ↑ Piomelli, Daniele (2000). "Arachidonic Acid". Neuropsychopharmacology: The Fifth Generation of Progress. Archived from the original on 15 July 2006. Retrieved 2009-04-16.
  12. ↑ Patwardhan, AM; Scotland, PE; Akopian, AN; Hargreaves, KM (2009). "Activation of TRPV1 in the spinal cord by oxidized linoleic acid metabolites contributes to inflammatory hyperalgesia". Proceedings of the National Academy of Sciences of the United States of America. 106 (44): 18820–4. PMC 2764734 Freely accessible. PMID 19843694. doi:10.1073/pnas.0905415106.
  13. ↑ 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.
  14. ↑ Letawe, C; Boone, M; Pierard, GE (March 1998). "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones". Clinical & Experimental Dermatology. 23 (2): 56–58. PMID 9692305. doi:10.1046/j.1365-2230.1998.00315.x.
  15. ↑ 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. PMID 12113324. doi:10.1080/080352502753711678.
  16. ↑ Peyrat-Maillard, M. N.; Cuvelier, M. E.; Berset, C. (2003). "Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation: Synergistic and antagonistic effects". Journal of the American Oil Chemists' Society. 80 (10): 1007–1012. doi:10.1007/s11746-003-0812-z.
  17. ↑ Oomah, B. Dave; Busson, Muriel; Godfrey, David V; Drover, John C. G (2002-01-01). "Characteristics of hemp (Cannabis sativa L.) seed oil". Food Chemistry. 76 (1): 33–43. doi:10.1016/S0308-8146(01)00245-X.
  18. ↑ Oil, peanut, salad or cooking: search for peanut oil on "Archived copy". Archived from the original on 3 March 2015. Retrieved 2009-09-16.
  19. ↑ "Essential oil extracted from peach (Prunus persica) kernel and its physicochemical and antioxidant properties". LWT - Food Science and Technology. 44: 2032–2039. doi:10.1016/j.lwt.2011.05.012.
  20. ↑ 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.
  21. ↑ "Olive Oil : Chemical Characteristics".
  22. ↑ Beltran; Del Rio, C; Sánchez, S; Martínez, L (2004). "Influence of Harvest Date and Crop Yield on the Fatty Acid Composition of Virgin Olive Oils from Cv. Picual" (PDF). J. Agric. Food Chem. 52 (11): 3434–3440. PMID 15161211. doi:10.1021/jf049894n.

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