Linoleic acid

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Not to be confused with linolenic acid or lipoic acid.
Linoleic acid
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Identifiers
CAS number 60-33-3 YesY
ChemSpider 4444105 YesY
UNII 9KJL21T0QJ YesY
KEGG C01595 YesY
ChEBI CHEBI:17351 YesY
ChEMBL CHEMBL267476 YesY
Jmol-3D images Image 1
Properties
Molecular formula 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]
Solubility in water 0.139 mg/L[2]
Vapor pressure 16 Torr at 229 °C[citation needed]
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
Flash point 112 °C (234 °F)[2]
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Linoleic acid (LA) is a polyunsaturated omega-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2 cis,cis-9,12. Chemically, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; with the first double bond located at the sixth carbon from the methyl end.[3]

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.[4]

The word "linoleic" comes 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.

Some medical research suggests that excessive levels of certain omega−6 fatty acids relative to certain omega-3 fatty acids, likely in conjunction with exogenous toxins, may have negative health effects.[citation needed]

In physiology[edit]

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 vegetable oils, comprising over half (by weight) of poppy seed, safflower, sunflower, corn, and soybean oils.[5]

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,[6] and poor wound healing in rats.[7]

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 release oleic acid upon death.[8]

Metabolism and eicosanoids[edit]

Linoleic Acid Metabolism.gif

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.[9]

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, a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to be inflammatory.[10] For example, both AA-derived thrombaxane and leukotrieneB4 are proaggretory and vasoconstrictive eicosanoids. 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.[11]

An increased intake of certain [12] omega–3 fatty acids with a decrease in omega-6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.[13]

One study monitoring two groups of survivors of myocardial infarction concluded “the concentration of alpha-linolenic acid was increased by 68%, in the experimental group, and that of linoleic acid reduced by 7%...the survivors of a first myocardial infarction, assigned to a Mediterranean alpha-linolenic acid rich diet, had a markedly reduced rate of recurrence, other cardiac events and overall mortality.” [14]

Uses[edit]

Industrial uses[edit]

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.

Reduction of linoleic acid yields linoleyl alcohol. Linoleic acid is a surfactant with a critical micel 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.[15][16][17]

Use in research[edit]

Linoleic acid 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 with different combinations of phenolics show that binary mixtures can lead to either a synergetic antioxidant effect or to an antagonistic effect.[18]

Linoleic acid may be linked to obesity by promoting overeating and damaging the arcuate nucleus in the brain's hypothalamus.[19]

Dietary sources[edit]

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 60%
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% [20]
Almonds 24%
Canola oil 21%
Chicken fat 18-23% [21]
Egg yolk 16%
Linseed oil 15%
Lard 10%
Olive oil 10% (3.5 - 21%) [22][23]
Palm oil 10%
Cocoa butter 3%
Macadamia oil 2%
Butter 2%
Coconut oil 2%
  average val

See also[edit]

References[edit]

  1. ^ a b c The Merck Index, 11th Edition, 5382
  2. ^ a b c d Record of CAS RN 60-33-3 in the GESTIS Substance Database from the IFA
  3. ^ David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_245.pub2
  4. ^ 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. 
  5. ^ "Nutrient Data Laboratory Home Page". USDA National Nutrient Database for Standard Reference, Release 20. U.S. Department of Agriculture, Agricultural Research Service. 2007. 
  6. ^ 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. 
  7. ^ 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. 
  8. ^ "Earth News: Ancient 'smell of death' revealed". BBC. 
  9. ^ 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. 
  10. ^ Piomelli, Daniele (2000). "Arachidonic Acid". Neuropsychopharmacology: The Fifth Generation of Progress. Retrieved 2009-04-16. 
  11. ^ 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. doi:10.1073/pnas.0905415106. PMC 2764734. PMID 19843694. 
  12. ^ Kinsella, JE; Lokesh, B; Stone, RA (1990). "Dietary n-3 polyunsaturated fatty acids and amelioration of cardiovascular disease: possible mechanisms". The American journal of clinical nutrition 52 (1): 1–28. PMID 2193500. 
  13. ^ Kinsella, John E., Lokesh, Belur, Stone, Richard A. (1990). "Dietary n-3 polyunsatruated fatty acids and amelioration of cardiovascular disease: possible mechanisms". American Journal of Clinical Nutrition 52 (1): 1–28. PMID 2193500. 
  14. ^ Michel, Renaud, Serge (1994). "Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease". Lancet 343: 8911. doi:10.1016/s0140-6736(94)92580-1. 
  15. ^ 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. 
  16. ^ 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. doi:10.1046/j.1365-2230.1998.00315.x. PMID 9692305. 
  17. ^ 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. doi:10.1080/080352502753711678. PMID 12113324. 
  18. ^ 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. doi:10.1007/s11746-003-0812-z. 
  19. ^ Janet Raloff (2012). "Tricks Foods Play". Science News Magazine 182 (7): 25–28. doi:10.1002/scin.5591820727. 
  20. ^ Oil, peanut, salad or cooking: search for peanut oil on http://www.nal.usda.gov/fnic/foodcomp/search/
  21. ^ 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. 
  22. ^ "Olive Oil : Chemical Characteristics". 
  23. ^ 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. doi:10.1021/jf049894n. PMID 15161211. 

External links[edit]