Omega 3 and Omega 6 Fatty Acids

Authored by: Ken D. Stark

Handbook of Analysis of Active Compounds in Functional Foods

Print publication date:  January  2012
Online publication date:  January  2012

Print ISBN: 9781439815885
eBook ISBN: 9781439815908
Adobe ISBN:

10.1201/b11653-33

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Abstract

Omega 3 and omega 6 fatty acids are chemically classified as polyunsaturated fatty acids As is common to fatty acids, they consist of a hydrocarbon chain with a hydrophilic carboxylic acid group at the “alpha” terminus and a hydrophobic methyl group at the “omega” terminus. As a polyunsaturated fatty acid, omega 3 and omega 6 fatty acids have more than one carbon-carbon methylene-interrupted cis double bonds in the hydrocarbon chain. The “omega 3” designates that the carbon-carbon double bond located closest to the omega terminus is in the third position, whereas the double bond is in the sixth position for the “omega 6” fatty acids (Figure 32.1). This terminus labeling reflects a bias of mammalian fatty acid metabolism and biochemistry as typical mammalian enzymology is not capable of introducing carbon- carbon double bonds in the omega 3 and omega 6 positions Chemical-based nomenclature would locate the carbon-carbon double bonds using the “alpha” carboxy terminus as the reference point, and given that the “alpha” end of the molecule is the site of carbon addition (elongation) and removal (?-oxidation), an omega-3 bond in an 18-carbon fatty acid would be in the ?15 position, in a 20-carbon fatty acid it. would be in the ?17, and in a 22-carbon fatty acid it would be in the ?19 position. Using the “omega” methyl terminology, distinct and important biological fatty acid classes are established and, therefore, in humans, an omega 3 fatty acid remains an omega 3 fatty acid and an omega 6 fatty acid remains an omega 6 fatty acid despite various metabolic changes. In biological applications and the literature, fatty acid nomenclature is typically a mix of modified systematic and trivial naming systems. A common approach is a numerical abbreviation where digits preceding a colon represent the number of carbons in the fatty acid and the number following indicates the number of carbon-carbon double bonds. For unsaturated fatty acids, the number of double bonds is also followed by a locant number from the methyl end. For example, all-cis-9,12 octadecadienoic acid or linoleic acid is 18:2n-6. Generally, for biological fatty acids, one assumes that carbon-carbon double bonds are cis and methylene interrupted unless otherwise identified would be in the ?17, and in a 22-carbon fatty acid it would be in the ?19 position. Using the “omega” methyl terminology, distinct and important biological fatty acid classes are established and, therefore, in humans, an omega 3 fatty acid remains an omega 3 fatty acid and an omega 6 fatty acid remains an omega 6 fatty acid despite various metabolic changes. In biological applications and the literature, fatty acid nomenclature is typically a mix of modified systematic and trivial naming systems. A common approach is a numerical abbreviation where digits preceding a colon represent the number of carbons in the fatty acid and the number following indicates the number of carbon-carbon double bonds. For unsaturated fatty acids, the number of double bonds is also followed by a locant number from the methyl end. For example, all-cis-9,12 octadecadienoic acid or linoleic acid is 18:2n-6. Generally, for biological fatty acids, one assumes that carbon-carbon double bonds are cis and methylene interrupted unless otherwise identified.

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