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Essential nutrient
Linoleic acid
Другие языки:

    Linoleic acid

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    Not to be confused with linolenic acid, alpha-linolenic acid, lipoic acid, or linolelaidic acid.

    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
    EC Number
    • 200-470-9
    57557
    KEGG
    PubChem CID
    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
    Melting point −12 °C (10 °F)
    −6.9 °C (19.6 °F)
    −5 °C (23 °F)
    Boiling point 229 °C (444 °F) at 16 mmHg
    230 °C (446 °F) at 21 mbar
    230 °C (446 °F) at 16 mmHg
    0.139 mg/L
    Vapor pressure 16 Torr at 229 °C
    Acidity (pKa) 9.24
    Hazards
    NFPA 704 (fire diamond)
    2
    1
    0
    Flash point 112 °C (234 °F)
    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 (LA) is an organic compound with the formula HOOC(CH
    2    )
    7    CH=CHCH
    2    CH=CH(CH
    2    )
    4    CH
    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.

    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. It typically occurs in nature as a triglyceride (ester of glycerin) rather than as a free fatty acid. It is one of two essential fatty acids for humans, who must obtain it through their diet, 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. In 1886, K. Peters determined the existence of two double bonds. Its essential role in human diet was discovered by G. O. Burr and others in 1930. 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.

    In physiology

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

    Metabolism and eicosanoids

    Linoleic Acid Metabolism.gif

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

    The metabolism of LA to AA begins with the conversion of LA into gamma-linolenic acid (GLA), effected by Δ6desaturase. 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.

    Hydroperoxides derived from the metabolism of anandamide (AEA: C
    22    H
    37    NO
    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
    20    H
    37    NO
    2    ; 18:2,n-6), an N-acylethanolamine, - the ethanolamide of linoleic acid (LA: C
    18    H
    32    O
    2    ; 18:2, n-6) and its metabolized incorporated ethanolamine (MEA: C
    2    H
    7    NO    ), is the first natural inhibitor of FAAH, discovered.

    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.

    Reduction of the carboxylic acid group 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, skin-lightening and moisture retentive properties when applied topically on the skin.

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

    Dietary sources

    See also: Vegetable oil § Composition of fats

    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.

    Name % LA† ref.
    Salicornia oil 75%
    Safflower oil 72-78%
    Evening Primrose oil 65-80%
    Melon seed oil 70%
    Poppyseed oil 70%
    Grape seed oil 69.6%
    Prickly Pear seed oil 63%
    Artichoke oil 60%
    Hemp oil 54.3%
    Wheat germ oil 55%
    Cottonseed oil 54%
    Corn oil 51.9%
    Walnut oil 51%
    Soybean oil 50.9%
    Sesame oil 45%
    Rice bran oil 39%
    Argan oil 37%
    Pistachio oil 32.7%
    Peach oil 29%
    Almonds 24%
    Canola oil 17.8%
    Sunflower oil 20.5%
    Chicken fat 18-23%
    Peanut oil 19.6%
    Egg yolk 16%
    Linseed oil (flax), cold pressed 14.2%
    Lard 10%
    Palm oil 10%
    Olive oil 8.4%
    Cocoa butter 3%
    Macadamia oil 2%
    Butter 2%
    Coconut oil 2%
      †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.

    Health effects

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

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

    See also

    Further reading

    External links


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