Oleic acid is a
fatty acid that occurs naturally in various
animal
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
and
vegetable fats and oils. It is an odorless, colorless oil, although commercial samples may be yellowish. 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 CH
3(CH
2)
7CH=CH(CH
2)
7COOH.
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.
Occurrence
Fatty acids (or their salts) often do not occur as such in biological systems. Instead fatty acids such as oleic acid occur as their
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
s, commonly
triglycerides, which are the greasy materials in many natural oils. Oleic acid is the most common monounsaturated fatty acid in nature. It is found in fats (triglycerides), the phospholipids that make membranes,
cholesterol esters, and
wax esters.
Triglycerides of oleic acid comprise the majority of
olive oil (about 70%). Olive oil exceeding 2%
free oleic acid is graded unfit for human consumption. It also makes up 59–75% of
pecan oil, 61% of
canola oil,
36–67% of
peanut oil
Peanut oil, also known as groundnut oil or arachis oil, is a vegetable oil derived from peanuts. The oil usually has a mild or neutral flavor but, if made with roasted peanuts, has a stronger peanut flavor and aroma. It is often used in Americ ...
,
60% of
macadamia oil, 20–80% of
sunflower oil,
[(NDB ID: 04678, 04584)] 15–20% of
grape seed oil,
sea buckthorn oil, 40% of
sesame oil,
and 14% of
poppyseed oil. High oleic variants of plant sources such as sunflower (~80%) and canola oil (70%) also have been developed.
Karuka
The karuka (''Pandanus julianettii'', also called karuka nut and ''Pandanus'' nut) is a species of tree in the family Pandanaceae and an important regional food crop in New Guinea. The nuts are more nutritious than coconuts, and are so popul ...
contains 52.39% oleic acid.
It is abundantly present in many animal fats, constituting 37 to 56% of chicken and turkey fat, and 44 to 47% of
lard.
Oleic acid is the most abundant fatty acid in human
adipose tissue, and second in abundance in human tissues overall, following
palmitic acid
Palmitic acid (hexadecanoic acid in IUPAC nomenclature) is a fatty acid with a 16-carbon chain. It is the most common saturated fatty acid found in animals, plants and microorganisms.Gunstone, F. D., John L. Harwood, and Albert J. Dijkstra. The ...
.
Production and chemical behavior
The
biosynthesis of oleic acid involves the action of the enzyme
stearoyl-CoA 9-desaturase acting on stearoyl-CoA. In effect,
stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means ta ...
is
dehydrogenated to give the monounsaturated derivative, oleic acid.
Oleic acid undergoes the reactions of carboxylic acids and
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s. It is soluble in
aqueous base to give
soap
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...
s called
oleates. Iodine adds across the double bond. Hydrogenation of the double bond yields the
saturated derivative
stearic acid
Stearic acid ( , ) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a waxy solid and its chemical formula is C17H35CO2H. Its name comes from the Greek word στέαρ "''stéar''", which means ta ...
.
Oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
at the
double bond occurs slowly in air, and is known as
rancidification in foodstuffs and as
drying
Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be consid ...
in coatings.
Reduction of the
carboxylic acid group yields
oleyl alcohol.
Ozonolysis of oleic acid is an important route to
azelaic acid
Azelaic acid (AzA) is an organic compound with the formula HOOC(CH2)7 COOH. This saturated dicarboxylic acid exists as a white powder. It is found in wheat, rye, and barley. It is a precursor to diverse industrial products including polymers a ...
. The coproduct is nonanoic acid:
:H
17C
8CH=CHC
7H
14CO
2H + 4"O" → HO
2CC
7H
14CO
2H + H
17C
8CO
2H
Esters of azelaic acid find applications in lubrications and plasticizer.
Related compounds
The
trans isomer of oleic acid is called
elaidic acid or ''trans''-9-octadecenoic acid. These isomers have distinct physical properties and biochemical properties. Elaidic acid, the most abundant trans fatty acid in diet, appears to have an adverse effect on health. A reaction that converts oleic acid to elaidic acid is called
elaidinization Elaidinization is any chemical reaction which convert a cis- olefin to a trans- olefin in unsaturated fatty acids. This is often performed on fats and oils to increase both the melting point and the shelf life without reducing the degree of unsa ...
.
Another naturally occurring isomer of oleic acid is
petroselinic acid.
In chemical analysis, fatty acids are separated by gas chromatography of their methyl ester derivatives. Alternatively, separation of unsaturated isomers is possible by
argentation thin-layer chromatography.
In
ethenolysis, methyl oleate, the ''methyl ester'' of the acid, converts to
1-decene and methyl 9-
decenoate:
:
CH2=CH2 → CH
3(CH
2)
7CH=
CH2 + MeO
2C(CH
2)
7CH=
CH2
Dietary sources
Uses
Oleic acid is used as a component in many foods, in the form of its triglycerides. It is a component of the normal human diet, being a part of animal fats and vegetable oils.
Oleic acid as its sodium salt is a major component of soap as an
emulsifying agent
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...
. It is also used as an
emollient
A moisturizer, or emollient, is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin. The word "emollient" is derived from the Latin verb ''m ...
.
Small amounts of oleic acid are used as an
excipient in pharmaceuticals, and it is used as an emulsifying or solubilizing agent in aerosol products.
Niche uses
Oleic acid is used to induce lung damage in certain types of animals for the purpose of testing new drugs and other means to treat lung diseases. Specifically in sheep, intravenous administration of oleic acid causes acute lung injury with corresponding
pulmonary edema
Pulmonary edema, also known as pulmonary congestion, is excessive liquid accumulation in the tissue and air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia and respiratory failure. It is due ...
.
Oleic acid is used as a soldering flux in stained glass work for joining
lead came.
Nanoparticles
Oleic acid is widely used in the solution phase synthesis of
nanoparticles, functioning as a to control the size and morphology of nanoparticles.
Health effects
Oleic acid is the topmost
monounsaturated fat in the human diet. Monounsaturated fat consumption has been associated with decreased
low-density lipoprotein
Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densi ...
(LDL) cholesterol, and possibly with increased
high-density lipoprotein (HDL) cholesterol. Oleic acid may be responsible for the
hypotensive
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...
(
blood pressure reducing) effects of
olive oil that is considered a health benefit. A 2017 review found that diets enriched in oleic acid are beneficial for regulating body weight.
The United States
FDA has approved a health claim on reduced risk of coronary heart disease for high oleic (> 70% oleic acid) oils. Some oil plants have cultivars bred to increase the amount of oleic acid in the oils. In addition to providing a health claim, the heat stability and shelf life may also be improved, but only if the increase in monounsaturated oleic acid levels correspond to a substantial reduction in polyunsaturated fatty acid (especially
α-Linolenic acid) content. When the saturated fat or trans fat in a
fried food
Frying is the cooking of food in oil or another fat. Similar to sautéing, pan-fried foods are generally turned over once or twice during cooking to make sure that the food is well-made, using tongs or a spatula, while sautéed foods are cooked ...
is replaced with a stable high oleic oil, consumers may be able to avoid certain
health risks associated with consuming saturated fat and
trans fat.
See also
*
Oleylamine – the corresponding amine
*
Oleamide
Oleamide is an organic compound with the formula CH3(CH2)7CH=CH(CH2)7CONH2(. It is the amide derived from the fatty acid oleic acid. It is a colorless waxy solid and occurs in nature. Sometimes labeled as a fatty acid primary amide (FAPA), it ...
– the corresponding amide
References
External links
FATTY ACIDS: STRAIGHT-CHAIN MONOENOIC(The AOCS Lipid Library)
9-octadecenoic acid(NIST Chemistry Webbook)
{{Authority control
5α-Reductase inhibitors
Fatty acids
Excipients
Insect pheromones
Insect ecology
Insect repellents
Alkenoic acids