α-Linolenic acid is an organic compound found in many common
vegetable oilsVegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
. In terms of its
structureThe IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry . Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be drawn. ...
, it is named
all-
cis-9,12,15-octadecatrienoic acid. In physiological literature, it is given the name 18:3 (
n−3).
α-Linolenic acid is a
carboxylic acidCarboxylic 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 three
cis double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the
n end. Thus, α-linolenic acid is a
polyunsaturatedPolyunsaturated fatty acids are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oils their characteristic property....
n−3N−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....
(omega-3) fatty acid. It is an
isomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
of
gamma-linolenic acidγ-Linolenic acid is a fatty acid found primarily in vegetable oils...
, a polyunsaturated
n−6n−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...
(omega-6) fatty acid.
History
Alpha-linolenic acid was first isolated by Rollett as cited in J. W. McCutcheon's synthesis in 1942, and referred to in Green and Hilditch's 1930's survey. It was first artificially synthesized in 1995 from C6 homologating agents. A Wittig reaction of the phosphonium salt of [(
Z-Z)-nona-3,6-dien-1-yl]triphenylphosphonium bromide with methyl 9-oxononanoate, followed by saponification, completed the synthesis.
Dietary sources
Seed oils are the richest sources of α-linolenic acid, notably those of
rapeseedRapeseed , also known as rape, oilseed rape, rapa, rappi, rapaseed is a bright yellow flowering member of the family Brassicaceae...
(
canolaCanola refers to a cultivar of either Rapeseed or Field Mustard . Its seeds are used to produce edible oil suitable for consumption by humans and livestock. The oil is also suitable for use as biodiesel.Originally, Canola was bred naturally from rapeseed in Canada by Keith Downey and Baldur R...
), soybeans, walnuts, flaxseed (
linseed oilLinseed 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...
),
perillaPerilla oil is obtained from the seeds of herbs of the genus Perilla, usually from the species Perilla frutescens. The seeds contain 35 to 45 percent oil which is obtained by pressing. Perilla oil is used along with synthetic resins in the production of varnishes...
, chia, and
hempHemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
. α-Linolenic acid is also obtained from the
thylakoid membranesA thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as...
of the green leaves of broadleaf plants (the membranes responsible for photosynthesis). The α-linolenic acid itself is suitable for many cooking purposes, at least as much as other minimally suitable cooking oils (such as butter, to which it is thermally superior), as it can withstand temperatures up to 350 degrees F (177 degrees Celsius) for 2 hours.
| Common name |
Alternate name |
Linnaean name |
% ALA† |
ref. |
| Chia |
chia sage |
Salvia hispanica |
64% |
|
KiwifruitThe kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia....
seeds |
Chinese gooseberry |
Actinidia chinensis |
62% |
|
PerillaPerilla is the common name of the herbs of the genus Perilla of the mint family, Lamiaceae. In mild climates, the plant reseeds itself. There are both green-leafed and purple-leafed varieties, which are generally recognized as separate species by botanists. The leaves resemble stinging nettle...
|
shiso |
Perilla frutescens |
58% |
|
FlaxFlax 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...
|
linseed |
Linum usatissimum |
55% |
|
| Lingonberry |
cowberry |
Vaccinium vitis-idaea |
49% |
|
PurslanePortulaca is the type genus of the flowering plant family Portulacaceae, comprising about 40-100 species found in the tropics and warm temperate regions. They are also sometimes known as Rose Moss or more commonly Moss Roses....
|
portulaca |
Portulaca oleracea |
35% |
|
| Sea buckthorn |
seaberry |
Hippophae rhamnoides L. |
32% |
|
HempHemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
|
cannabis |
Cannabis sativa |
20% |
|
RapeseedRapeseed , also known as rape, oilseed rape, rapa, rappi, rapaseed is a bright yellow flowering member of the family Brassicaceae...
|
canola |
Brassica napus |
10% |
|
| Soybean |
soya |
Glycine max |
8% |
|
| |
†average val |
Role in nutrition and health
α-Linolenic acid, an
n−3 fatty acid, is a member of the group of essential fatty acids (EFAs), so called because they cannot be produced within the body and must be acquired through diet. Most seeds and seed oils are much richer in an
n−6 fatty acid,
linoleic acidLinoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...
. Linoleic acid is also an EFA, but it, and the other
n−6 fatty acids, compete with
n−3s for positions in cell membranes and have very different effects on human health.
(See Essential fatty acid interactionsThe 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...
.)
α-Linolenic acid can only be obtained by humans through their diets because the absence of the required 12- and 15-desaturase enzymes makes
de novo synthesis from
stearic acidStearic acid is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH316CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates...
impossible.
Eicosapentaenoic acidEicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...
(EPA; 20:5,
n−3) and
docosahexaenoic acidDocosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...
(DHA; 22:6,
n−3) are readily available from fish oil and play a vital role in many metabolic processes. These can also be synthesized by humans from dietary α-linolenic acid, but with an efficiency of only a few percent.
Because the efficacy of
n−3 long-chain polyunsaturated fatty acid (LC-PUFA) synthesis decreases down the cascade of α-linolenic acid conversion, DHA synthesis from α-linolenic acid is even more restricted than that of EPA.
Linoleic acid (LA; 18:2,
n−6) is generally assumed to reduce EPA synthesis because of the competition between α-linolenic acid and LA for common desaturation and elongation enzymes.
Studies have found evidence α-linolenic acid is related to a lower risk of cardiovascular disease.
A 2005 study found that daily administration of α-linolenic acid significantly reduced both self-reported anxiety, stress levels, and objective measured cortisol levels in college age students.
A large 2006 study found no association between total α-linolenic acid intake and overall risk of prostate cancer.
Multiple studies have shown a relationship between alpha-linolenic acid (ALA), which is abundant in linseed oil, and an increased risk of prostate cancer. This risk was found to be irrespective of source of origin (e.g. meat, vegetable oil). A recent (2009) metastudy, however, found evidence of publication bias in earlier studies, and concluded that if ALA contributes to increased prostate cancer risk, the increase in risk is quite small.
Research has also suggested a major neuroprotective effect of α-linolenic acid in
in vivo models of both global
ischemiaIn medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
and KA-induced
epilepsyEpilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
; however, if sourced from flax seed oil, residues may have adverse effect due to its content of neurotoxic cyanogen glycosides and immunosuppressive cyclic nonapeptides.
A 2011 longitudinal study of over 50,000 women, conducted at Harvard University, over a period of ten years, found that a higher intake of α-Linolenic acid (combined with a lower intake of
linoleic acidLinoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...
) was positively associated with a significant reduction in depression in the same group (the same study also found that by contrast an intake of EPA and DPA found in fish oils did not reduce depression).
Hydrogenation
For manufacturers to achieve desirable traits, such as texture, spreadability and mouth feel, as well as to increase shelf life of products, unsaturated vegetable oils are often hydrogenated. Hydrogenation involves reacting the oils with hydrogen gas under pressure and high heat with the aid of a catalyst such as platinum oxide. Fully hydrogenated fatty acids become saturated fatty acids, although as fats they are not suitable for use in food, as they are as hard as wax due to the chain lengths of the original unsaturated fatty acids in the vegetable oils. Instead, oils are often only partially hydrogenated. When partially
hydrogenatedHydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
, part of the unsaturated fatty acids become unhealthy trans fats.
SoybeanThe soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
s are the largest source of
edible oilsVegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
in the U.S., and 40% of soy oil production is partially hydrogenated. The low
oxidative stabilityRancidification is the chemical decomposition of fats, oils and other lipids . When these processes occur in food, undesirable odors and flavors can result. In some cases, however, the flavors can be desirable . In processed meats, these flavors are collectively known as "warmed over flavor"...
of α-linolenic acid is one reason for producers deciding to partially hydrogenate
soybean oilSoybean 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...
.
Regulations forcing the listing or banning of trans fats have spurred the development of low-α-linolenic acid soybeans. These yield a more stable oil requiring hydrogenation in fewer products, and therefore providing trans fat-free alternatives for many applications, such as frying oil.
Several consortia are bringing low-α-linolenic acid soy to market.
DuPontE. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
's effort involves
silencingGene silencing is a general term describing epigenetic processes of gene regulation. The term gene silencing is generally used to describe the "switching off" of a gene by a mechanism other than genetic modification...
the FAD2 gene that codes for
Δ6-desaturaseA fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond. These desaturases are classified as...
, giving a soy oil with very low levels of both α-linolenic acid and LA. Monsanto Company has introduced to the market
VistiveVistive is the brand name for a family of genetically engineered soybeans developed by Monsanto. Currently the only Vistive seed on the market is a low-linolenic soybean that reduces or eliminates the need for addition of trans-fatty acids...
, their brand of low α-linolenic acid soybeans, which is less controversial than most
GMOA genetically modified organism or genetically engineered organism is an organism whose genetic material has been altered using genetic engineering techniques. These techniques, generally known as recombinant DNA technology, use DNA molecules from different sources, which are combined into one...
Monsanto offerings, as it was created via conventional breeding techniques.
Cardiovascular
Dietary α-linolenic acid has been assessed for its role in cardiovascular health. Clinical benefits have been seen in some, but not all, studies. Still, a review in 2005 concluded "The weight of the evidence favors recommendations for modest dietary consumption of α-linolenic acid (2 to 3 g per day) for the primary and secondary prevention of
coronary heart diseaseCoronary artery disease is the end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium with oxygen and nutrients. It is sometimes also called coronary heart disease...
."
Drying oils
α-Linolenic acid is the most abundant unsaturated component of several
drying oilA 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 (e.g.
perillaPerilla oil is obtained from the seeds of herbs of the genus Perilla, usually from the species Perilla frutescens. The seeds contain 35 to 45 percent oil which is obtained by pressing. Perilla oil is used along with synthetic resins in the production of varnishes...
,
walnutJuglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall , with pinnate leaves 200–900 millimetres long , with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts , but not the hickories...
and
linseed oilLinseed 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...
s.)
See also
- Essential fatty acid
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...
- List of n−3 fatty acids
- 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...
- 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...