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 |
|
57557 | |
KEGG | |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
| |
| |
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 ] |
Acidity (pKa) | 4.77 at 25°C [4] |
Hazards | |
NFPA 704 (fire diamond) | |
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). |
Linoleic acid (LA) is an organic compound with the formula HOOC(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups (−CH=CH−) 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 Latin linum ' flax ',and oleum 'oil', reflecting the fact that it was first isolated from linseed oil.
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]
The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid. [13]
Linoleic acid (LA: C
18 H
32 O
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
37 NO
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
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
20H
37NO
2; 18:2,n-6), an N-acylethanolamine,[ clarification needed ] - 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]
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.[ 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. [25] [26] [27] [28]
Linoleic acid is also used in some bar of soap products.
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 oil | 75% | |
Safflower oil | 72-78% | [31] |
Evening Primrose oil | 65-80% | [32] |
Melon seed oil | 70% | |
Poppyseed oil | 70% | |
Grape seed oil | 69.6% | |
Prickly Pear seed oil | 63% | |
Artichoke oil | 60% | |
Hemp oil | 54.3% | [33] |
Wheat germ oil | 55% | |
Cottonseed oil | 54% | |
Corn oil | 51.9% | [34] |
Walnut oil | 51% | |
Soybean oil | 50.9% | [35] |
Sesame oil | 45% | |
Pumpkin seed oil | 42-59% | [36] |
Rice bran oil | 39% | |
Argan oil | 37% | |
Pistachio oil | 32.7% | |
Peach oil | 29% | [37] |
Almonds | 24% | |
Canola oil | 17.8% | [38] |
Sunflower oil | 20.5% | [39] |
Chicken fat | 18-23% | [40] |
Peanut oil | 19.6% | [41] |
Egg yolk | 16% | |
Linseed oil (flax), cold pressed | 14.2% | [42] |
Lard | 10% | |
Palm oil | 10% | |
Olive oil | 8.4% | [43] |
Cocoa butter | 3% | |
Macadamia oil | 2% | |
Butter | 2% | |
Coconut oil | 2% | |
†average val |
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]
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]
In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.
Omega−3 fatty acids, also called Omega−3 oils, ω−3 fatty acids, Ω-3 Fatty acids or n−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chemical structure. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA can be found in plants, while DHA and EPA are found in algae and fish. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. DHA and EPA accumulate in fish that eat these algae. Common sources of plant oils containing ALA include walnuts, edible seeds, and flaxseeds as well as hempseed oil, while sources of EPA and DHA include fish and fish oils, and algae oil.
Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health, but cannot synthesize them.
α-Linolenic acid, also known as alpha-linolenic acid (ALA), is an n−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, walnuts, chia, hemp, and many common vegetable oils.
A saturated fat is a type of fat in which the fatty acid chains have all single bonds between the carbon atoms. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branched chain of carbon (C) atoms. Along the chain, some carbon atoms are linked by single bonds (-C-C-) and others are linked by double bonds (-C=C-). A double bond along the carbon chain can react with a pair of hydrogen atoms to change into a single -C-C- bond, with each H atom now bonded to one of the two C atoms. Glyceride fats without any carbon chain double bonds are called saturated because they are "saturated with" hydrogen atoms, having no double bonds available to react with more hydrogen.
Linseed oil, also known as flaxseed oil or flax oil, is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant. The oil is obtained by pressing, sometimes followed by solvent extraction.
Hemp oil is oil obtained by pressing hemp seeds. Cold pressed, unrefined hemp oil is dark to clear light green in color, with a nutty flavor. The darker the color, the grassier the flavour. It should not be confused with hash oil, a tetrahydrocannabinol-containing oil made from the Cannabis flower.
Grape seed oil is a vegetable oil derived from the seeds of grapes. A by-product of the winemaking industry, it is typically used for edible applications.
Oleic acid is a fatty acid that occurs naturally in various animal and vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish due to the presence of impurities. In chemical terms, oleic acid is classified as a monounsaturated omega-9 fatty acid, abbreviated with a lipid number of 18:1 cis-9, and a main product of Δ9-desaturase. It has the formula CH3−(CH2)7−CH=CH−(CH2)7−COOH. The name derives from the Latin word oleum, which means oil. It is the most common fatty acid in nature. The salts and esters of oleic acid are called oleates. It is a common component of oils, and thus occurs in many types of food, as well as in soap.
Omega-6 fatty acids are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n-6 position, that is, the sixth bond, counting from the methyl end.
gamma-Linolenic acid or GLA is an n−6, or omega-6, fatty acid found primarily in seed oils. When acting on GLA, arachidonate 5-lipoxygenase produces no leukotrienes and the conversion by the enzyme of arachidonic acid to leukotrienes is inhibited.
Rice bran oil is the oil extracted from the hard outer brown layer of rice called bran. It is known for its high smoke point of 232 °C (450 °F) and mild flavor, making it suitable for high-temperature cooking methods such as stir frying and deep frying. It is popular as a cooking oil in East Asia, the Indian subcontinent, and Southeast Asia including India, Nepal, Bangladesh, Indonesia, Japan, Southern China and Malaysia.
Corn oil or maize oil (British) is oil extracted from the germ of corn (maize). Its main use is in cooking, where its high smoke point makes refined corn oil a valuable frying oil. It is also a key ingredient in some margarines. Corn oil is generally less expensive than most other types of vegetable oils.
Sunflower oil is the non-volatile oil pressed from the seeds of the sunflower. Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient.
In biochemistry and nutrition, a polyunsaturated fat is a fat that contains a polyunsaturated fatty acid, which is a subclass of fatty acid characterized by a backbone with two or more carbon–carbon double bonds. Some polyunsaturated fatty acids are essentials. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturated fats, which include drying oils.
Fatty acid desaturases are a family of enzymes that convert saturated fatty acids into unsaturated fatty acids and polyunsaturated fatty acids. For the common fatty acids of the C18 variety, desaturases convert stearic acid into oleic acid. Other desaturases convert oleic acid into linolenic acid, which is the precursor to alpha-linolenic acid, gamma-linolenic acid, and eicosatrienoic acid.
There are many fatty acids found in nature. Two types of fatty acids considered essential for human health are the omega-3 and omega-6 types. These two essential fatty acids are necessary for some cellular signalling pathways and are involved in mediating inflammation, protein synthesis, and metabolic pathways in the human body.
Avocado oil is an edible oil extracted from the pulp of avocados, the fruit of Persea americana. It is used as an edible oil both raw and for cooking, where it is noted for its high smoke point. It is also used for lubrication and in cosmetics.
Protein combining or protein complementing is a dietary theory for protein nutrition that purports to optimize the biological value of protein intake. According to the theory, vegetarian and vegan diets may provide an insufficient amount of some essential amino acids, making protein combining with multiple foods necessary to obtain a complete protein food. The terms complete and incomplete are outdated in relation to plant protein. In fact, all plant foods contain all 20 amino acids including the 9 essential amino acids in varying amounts.
Linoleoyl-CoA desaturase (also Delta 6 desaturase, EC 1.14.19.3) is an enzyme that converts between types of fatty acids, which are essential nutrients in the human body. The enzyme mainly catalyzes the chemical reaction
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