Alpha-Linolenic acid

α-Linolenic acid
Other names	ALA; Linolenic acid; cis,cis,cis-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-9,12,15-Octadecatrienoic acid; (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid[1]; Industrene 120
Identifiers
CAS number	463-40-1 Y
Properties
Molecular formula	C18H30O2
Molar mass	278.43 g//mol
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

α-Linolenic acid is an organic compound found in many common vegetable oils. Systematically, it is named all-cis-9,12,15-octadecatrienoic acid.^[2] In physiological literature, it is given the name 18:3 (n−3).

α-Linolenic acid is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the n end. Thus, α-linolenic acid is a polyunsaturated n−3 (omega-3) fatty acid. It is an isomer of γ-linolenic acid, a polyunsaturated n−6 (omega-6) fatty acid.

History

Alpha-linolenic acid was first isolated by Rollett^[3]as cited in J. W. McCutcheon's synthesis in 1942^[4] and referred to in Green and Hilditch's 1930's survey^[5].

Alpha-linolenic 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.^[6]

Dietary sources

Seed oils are the richest sources of α-linolenic acid, notably those of rapeseed (canola), soybeans, walnuts, flaxseed (Linseed oil), perilla, chia, and hemp. α-Linolenic acid is also obtained from the thylakoid membranes of the green leaves of broadleaf plants (the membranes responsible for photosynthesis).^[7] Greens, therefore, and animals that eat greens, are often a good source of α-linolenic acid.^{[citation needed]}

Role in nutrition and health

Flax is a rich source of α-linolenic acid.

α-Linolenic acid, an n−3 fatty acid, is a member of the group of essential fatty acids, 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 acid. Linoleic acid is also an essential fat, but it, and the other n−6 fats, compete with n−3s for positions in cell membranes and have very different effects on human health. (See Essential fatty acid interactions.)

Eicosapentaenoic acid (EPA; 20:5, n−3) and docosahexaenoic acid (DHA; 22:6, n−3) play a vital role in many metabolic processes. Although these two fatty acids are readily available from fish, these marine-derived fatty acids can also be synthesized by humans from α-linolenic acid. Humans, however, can obtain α-linolenic acid only through their diets, because the absence of the required 12- and 15-desaturase enzymes makes de novo synthesis from stearic acid impossible. Furthermore, conversion of dietary α-linolenic acid into EPA is limited. 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.^[10]

It is generally assumed that linoleic acid (LA; 18:2, n−6) reduces EPA synthesis because of the competition between α-linolenic acid and LA for common desaturation and elongation enzymes.^{[citation needed]}

Studies have found evidence that α-linolenic acid is related to a lower risk of cardiovascular disease.^[11][12] However, the mechanism is still unclear: The body converts α-linolenic acid into the longer chain fatty acids EPA and DHA, and it is unknown whether the protective effect against cardiac arrhythmia is exerted by α-linolenic acid itself, or by these metabolic products.

A large 2006 study found no association between total α-linolenic acid intake and overall risk of prostate cancer.^[13]

Research has also suggested a major neuroprotective effect of α-linolenic acid in in-vivo models of both global ischemia and KA-induced epilepsy.^[14]

Hydrogenation

In order 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 orkel. Fully hydrogenated fatty acids become saturated fatty acids, although as fats they are not suitable for using 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 hydrogenated, all unsaturated fatty acids form trans fats. Soybeans are the largest source of edible oils in the U.S., and 40% of soy oil production is partially hydrogenated.^[15][16] The low oxidative stability of α-linolenic acid is one reason for producers deciding to partially hydrogenate soybean oil.^[17]

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 less often, and therefore providing trans-free alternatives into many applications such as frying oil.^[18] Several consortia are bringing low-α-linolenic acid soy to market. DuPont's effort involves silencing the FAD2 gene that codes for Δ⁶-desaturase, giving a soy oil with very low levels of both α-linolenic acid and LA.^[19] Monsanto Company has introduced to the market Vistive their brand of low α-linolenic acid soybeans.

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 disease."^[20]

Drying oils

α-Linolenic acid is the most abundant unsaturated component of several drying oils (e.g. perilla, walnut and linseed oils.)

See also

• Essential fatty acid
• List of n−3 fatty acids
• Essential nutrient

References