Linoleic acid

Linoleic acid

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Linoleic acid is an unsaturated n-6 fatty acid
Omega-6 fatty acid
n−6 fatty acids are a family of unsaturated 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.The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids...

. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2(n-6). Chemically, linoleic acid is a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 with an 18-carbon chain and two cis double bonds; the first double bond is located at the sixth carbon from the methyl end.

Linoleic acid belongs to one of the two families of essential fatty acids that humans and animals must ingest for good health, because the body requires them for various biological processes, but cannot synthesize them from other food components.

The word "linoleic" comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word linon (flax
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...

). Oleic means "of, relating to, or derived from oil or olive" or "of or relating to oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...

" because saturating the n-6 double bond produces oleic acid.

In physiology


LA is a polyunsaturated fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 used in the biosynthesis of arachidonic acid
Arachidonic acid
Arachidonic acid is a polyunsaturated omega-6 fatty acid 20:4.It is the counterpart to the saturated arachidic acid found in peanut oil, Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6).It is the counterpart to the saturated arachidic acid found in peanut oil,...

 (AA) and thus some prostaglandin
Prostaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....

s. It is found in the lipids of cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

s. It is abundant in many vegetable oils, comprising over half (by weight) of poppy seed
Poppyseed oil
Poppyseed oil is an edible oil from poppy seeds . The oil has culinary and pharmaceutical uses, as well as long established uses in the making of paints, varnishes, and soaps.Poppy seeds yield 45–50% oil...

, safflower
Safflower
Safflower is a highly branched, herbaceous, thistle-like annual. It is commercially cultivated for vegetable oil extracted from the seeds. Plants are 30 to 150 cm tall with globular flower heads having yellow, orange or red flowers. Each branch will usually have from one to five flower heads...

, sunflower
Sunflower oil
Sunflower oil is the non-volatile oil expressed from sunflower seeds. Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. Sunflower oil was first industrially produced in 1835 in the Russian Empire.- Composition :Sunflower oil is mainly a...

, and corn oil
Corn oil
Corn oil is oil extracted from the germ of corn . 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. One bushel of corn...

s.

Linoleic acid is an essential fatty acid that must be consumed for proper health. A lack of LA and other n-6 fatty acids in the diet causes dry hair, hair loss,
and poor wound healing. However, achieving a deficiency in linoleic acid is nearly impossible consuming any normal diet and is thus not considered to be of clinical concern.

Along with oleic acid
Oleic acid
Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable fats. It has the formula CH37CH=CH7COOH. It is an odorless, colourless oil, although commercial samples may be yellowish. The trans isomer of oleic acid is called elaidic acid...

, linoleic acid is released by cockroaches
Cockroaches
A cockroach is an insect of the order Blattaria. "Cockroach" may also refer to:*Cockroach , a 2001 album by Danger Danger*Cockroach , a 2008 novel by Rawi Hage...

 upon death to deter other roaches from entering the area. This is similar to the mechanism found in ants and bees, in which oleic acid is released upon death.

Metabolism and eicosanoids


The first step in the metabolism of LA is performed by Δ6desaturase, which converts LA into gamma-linolenic acid
Gamma-Linolenic acid
γ-Linolenic acid is a fatty acid found primarily in vegetable oils...

 (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.

GLA is converted to Dihomo-gamma-linolenic acid
Dihomo-gamma-linolenic acid
Dihomo-γ-linolenic acid is a 20-carbon ω−6 fatty acid. In physiological literature, it is given the name 20:3 . DGLA is a carboxylic acid with a 20-carbon chain and three cis double bonds; the first double bond is located at the sixth carbon from the omega end. DGLA is the elongation product...

 (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. For example, both AA-derived thrombaxane and leukotrieneB4 are proaggretory and vasoconstrictive eicosanoids. The oxidized metabolic products of linolenic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1
TRPV1
The transient receptor potential cation channel subfamily V member 1 ', also known as the capsaicin receptor and the vanilloid receptor 1, is a protein that, in humans, is encoded by the TRPV1 gene...

, the capsaicin
Capsaicin
Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...

 receptor, and through this might play a major role in hyperalgesia
Hyperalgesia
Hyperalgesia is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.-Types:...

 and allodynia
Allodynia
Allodynia is a pain due to a stimulus which does not normally provoke pain. Temperature or physical stimuli can provoke allodynia, and it often occurs after injury to a site...

.

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

One study monitoring two groups of survivors of myocardial infarction concluded “the concentration of alpha-linolenic acid
Alpha-linolenic acid
α-Linolenic acid is an organic compound found in many common vegetable oils. In terms of its structure, it is named all-cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 ....

 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.”

Industrial uses


Linoleic acid is used in making quick-drying oil
Drying oil
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen . Drying oils are a key component of oil paint and some varnishes...

s, which are useful in oil paint
Oil paint
Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...

s and varnish
Varnish
Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...

es. 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
Linoleyl alcohol
Linoleyl alcohol is a fatty alcohol produced by the reduction of linoleic acid....

.

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.

Appendix: Dietary sources

Name % LA ref.
Safflower oil  78%
Grape seed oil
Grape seed oil
Not to be confused with Rapeseed oil.Grape seed oil is a vegetable oil pressed from the seeds of various varieties of Vitis vinifera grapes, an abundant by-product of winemaking.- Cooking :...

 
73%
Poppyseed oil
Poppyseed oil
Poppyseed oil is an edible oil from poppy seeds . The oil has culinary and pharmaceutical uses, as well as long established uses in the making of paints, varnishes, and soaps.Poppy seeds yield 45–50% oil...

 
70%
Sunflower oil
Sunflower oil
Sunflower oil is the non-volatile oil expressed from sunflower seeds. Sunflower oil is commonly used in food as a frying oil, and in cosmetic formulations as an emollient. Sunflower oil was first industrially produced in 1835 in the Russian Empire.- Composition :Sunflower oil is mainly a...

 
68%
Hemp oil
Hemp oil
Hempseed oil is pressed from the seed of the hemp plant irrespective of the strain of cannabis. Cold pressed, unrefined hemp oil is dark to clear light green in color, with a pleasant nutty flavor. The darker the color, the grassier the flavour....

 
60%
Corn oil
Corn oil
Corn oil is oil extracted from the germ of corn . 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. One bushel of corn...

 
59%
Wheat germ oil
Wheat germ oil
Wheat germ oil is extracted from the germ of the wheat kernel, which makes up only 2½% by weight of the kernel Wheat germ oil is particularly high in octacosanol - a 28 carbon long-chain saturated primary alcohol found in a number of different vegetable waxes. Octacosanol has been studied as an...

 
55%
Cottonseed oil
Cottonseed oil
Cottonseed oil is a cooking oil extracted from the seeds of cotton plant of various species, mainly Gossypium hirsutum and Gossypium herbaceum...

 
54%
Soybean oil
Soybean oil
Soybean oil is a vegetable oil extracted from the seeds of the soybean . It is one of the most widely consumed cooking oils. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints...

 
51%
Walnut oil
Walnut oil
Walnut oil is oil extracted from English walnuts . It is about 50% linoleic acid, an essential omega-6 fatty acid. Walnut oil is also a good source of omega-3 fatty acids which are also essential to human nutrition....

 
51%
Sesame oil
Sesame oil
Sesame oil is an edible vegetable oil derived from sesame seeds. Besides being used as a cooking oil in South India, it is often used as a flavor enhancer in Chinese, Japanese, Korean, and to a lesser extent Southeast Asian cuisine.The oil from the nutrient rich seed is popular in alternative...

 
45%
Rice bran oil
Rice bran oil
Rice bran oil is the oil extracted from the germ and inner husk of rice. It is notable for its very high smoke point of and its mild flavor, making it suitable for high-temperature cooking methods such as stir frying and deep frying...

 
39%
Pistachio oil
Pistachio oil
Pistachio oil is a pressed oil, extracted from the fruit of Pistacia vera, the pistachio nut.-Culinary uses:Compared to other nut oils, pistachio oil has a particularly strong flavor. Like other nut oils, it tastes similar to the nut from which it is extracted. Pistachio oil is high in Vitamin E,...

 
32.7%
Peanut oil
Peanut oil
Peanut oil is an organic material oil derived from peanuts, noted to have the aroma and taste of its parent legume....

 
32%
Canola oil  21%
Chicken fat
Chicken fat
Chicken fat is fat obtained from chicken rendering and processing. Of animal-sourced substances, chicken fat is noted for being high in linoleic acid, a beneficial omega-6 fatty acid. Linoleic acid levels are between 17.9% and 22.8%. It is often used in pet foods, and has also been used in the...

 
18-23%
Egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 
16%
Linseed oil
Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...

 
15%
Lard
Lard
Lard is pig fat in both its rendered and unrendered forms. Lard was commonly used in many cuisines as a cooking fat or shortening, or as a spread similar to butter. Its use in contemporary cuisine has diminished because of health concerns posed by its saturated-fat content and its often negative...

 
10%
Olive oil
Olive oil
Olive oil is an oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps...

 
10%
Palm oil
Palm oil
Palm oil, coconut oil and palm kernel oil are edible plant oils derived from the fruits of palm trees. Palm oil is extracted from the pulp of the fruit of the oil palm Elaeis guineensis; palm kernel oil is derived from the kernel of the oil palm and coconut oil is derived from the kernel of the...

 
10%
Cocoa butter
Cocoa butter
Cocoa butter, also called theobroma oil, is a pale-yellow, pure edible vegetable fat extracted from the cocoa bean. It is used to make chocolate, biscuits, and baked goods, as well as some pharmaceuticals, ointments, and toiletries...

 
3%
Macadamia oil
Macadamia oil
Macadamia oil is the non-volatile oil expressed from the nut meat of the macadamia tree, a native Australian nut...

 
2%
Butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...

 
2%
Coconut oil
Coconut oil
Coconut oil is an edible oil extracted from the kernel or meat of matured coconuts harvested from the coconut palm . Throughout the tropical world, it has provided the primary source of fat in the diets of millions of people for generations. It has various applications in food, medicine, and industry...

 
2%
  average val

See also

  • Conjugated linoleic acid
    Conjugated linoleic acid
    Conjugated linoleic acids are a family of at least 28 isomers of linoleic acid found mainly in the meat and dairy products derived from ruminants. As the name implies, the double bonds of CLAs are conjugated, with only one single bond between them....

  • Essential fatty acids
  • Essential fatty acid interactions
    Essential fatty acid interactions
    The actions of the ω-3 and ω-6 essential fatty acids are best characterized by their interactions; they cannot be understood separately.Arachidonic acid is a 20-carbon ω-6 conditionally essential fatty acid...

  • Eicosanoid
    Eicosanoid
    In biochemistry, eicosanoids are signaling molecules made by oxidation of twenty-carbon essential fatty acids, ....

    s
  • Essential nutrient
    Essential nutrient
    An essential nutrient is a nutrient required for normal body functioning that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health , and thus must be obtained from a dietary source...

    s
  • Linolein
    Linolein
    Linolein is a triglyceride, in which glycerol is esterified with linoleic acid. It is used in the manufacturing of biodiesel. Linolein is also used in making cosmetic products....


External links