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Concept
Polyunsaturated fatty acid
Résumé
In biochemistry and nutrition, polyunsaturated fatty acids (abbreviated PUFAs) 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. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturated fats.
Polyunsaturated fatty acids are a subclass of fatty acids possessing two or more carbon–carbon double bonds.
The position of the carbon-carbon double bonds in carboxylic acid chains in fats is designated by Greek letters. The carbon atom closest to the carboxyl group is the alpha carbon, the next carbon is the beta carbon and so on. In fatty acids the carbon atom of the methyl group at the end of the hydrocarbon chain is called the omega carbon because omega is the last letter of the Greek alphabet. Omega-3 fatty acids have a double bond three carbons away from the methyl carbon, whereas omega-6 fatty acids have a double bond six carbons away from the methyl carbon. The illustration below shows the omega-6 fatty acid, linoleic acid.
Polyunsaturated fatty acids can be classified in various groups by their chemical structure:
methylene-interrupted polyenes
conjugated fatty acids
other PUFAs
Based on the length of their carbon backbone, they are sometimes classified in two groups:
short chain polyunsaturated fatty acids (SC-PUFA), with 18 carbon atoms
long-chain polyunsaturated fatty acids (LC-PUFA) with 20 or more carbon atoms
PUFAs with 18 carbon atoms, which are the most common variety, are not produced by mammals. Since they have important dietary functions, their biosynthesis has received much attention. Plants produce PUFAs from oleic acid. Key enzymes are called fatty acid desaturases, which introduce additional double bonds. Desaturases convert oleic acid into linolenic acid the precursor to alpha-linoenic acid, gamma-linolenic acid, and eicosatrienoic acid.
Industrial PUFAs are generally obtained by hydrolysis of fats that contain PUFAs.
Source officielle
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