Fatty acids isomers

Valenzuela A, Morgado N Trans fatty acid isomers in human health and the food industry. Biol Res 1999 32 273. 

Figure 13.13 Fatty acid isomers in partially hydrogenated rapeseed oil (a) all fatty acids, (b) C18 l cis fatty acids, (c) C18 l trans fatty acids, (d) structure of C18 l A 5 trans fatty acid, and (e) structure of C18 l A15 trans fatty acid. (Courtesy of A. Stolyhwo.)...

In a partially hydrogenated fat, the number of fatty acid isomers is dramatically increased by the appearance of geometrical isomers (i.e., cis and trans configurations) and various positional isomers (i.e., different positions of double bonds within the fatty acid chain). Thus the in-... 

The acetal ester does not trimerize and can be stored for years before hydrolysis and use34. The deuterium-labelled fats have been needed in multigram quantities for studies of the metabolism of configurational and positional fatty acid isomers in humans. 

Aungst, B.J. 1989. Structure-effects studies of fatty acid isomers as skin penetration enhancers and skin irritants. Pharm Res 6 244. 

Booyens et al. (1984) reported that unnatural dietary trans and cis unsaturated fatty acid isomers are a definite risk factor in the etiology of coronary disease, despite an early report about the hypocholesterolemic activity of unsaturated fatty acids from plant origin. 

Precht et al. (2001) found that the proportion of trans-18 1 fatty acid isomers was similar in the milk fat of the cow, goat and sheep vaccenic acid (llr-18 l) was the major isomer in all these milks, accounting for 51, 37 and 47% of the total, respectively. The isomers between 91 and 161, excluding the 111, made up most of the rest (4-10% each). 

The fatty acids present in fats and oils may be analyzed after their hydrolysis and subsequent conversion by methylation to volatile methyl esters. In this Process, different methylating agents may be used, and these are methanol/sulfuric acid (20) or methanol-BFs (21). The methyl esters so produced are then identified with gas chromatography. Standard fatty acids methyl esters are often used for tentative identification purposes. For determination of fatty acid isomers, including trans-fatty acids, it is necessary to use appropriate columns and conditions for analysis. 

TABLE 1. Principal n-3 Fatty Acids, Saturated, and Monoethylenic Fatty Acid Isomers (w/w%) in Triacylglycerols and Wax Esters of Copepods and Commercial Oils of Pelagic Species of North Atlantic Fish Likely to be Consuming Copepods. 

During the course of transformation of the unsaturated fatty acids to saturated fatty acids, positional isomers of unsaturated fatty acids are produced. These unsaturated fatty acid isomers are known as trans-fatty acids (62), as shown in Figure 6. 

Emken EA. Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils. Ann Rev Nutr 1984 4 339-376. 

As previously recalled, enzymatic CTI in eukaryotic cells is unknown and the presence of trans fatty acid isomers in humans has been generally attributed to exogenous sources. After a series of studies in several countries it was found that trans fatty acid isomers can give harmful effects on health, involving risk factors of heart attack and coronary artery disease, impairment of fetal and infant growth... 

There are other cases of inhibition of lipid enzymatic pathways by trans fatty acid isomers. The above reported mono-14 -trans isomer of arachidonic acid is inhibitor of the synthesis of thromboxane B2 and, therefore, can prevent rat platelet aggregation [52]. The transformation of mono-trans isomers of linoleic acid by rat liver microsomes showed that the 9-cis,12-trans isomer is better desaturated, whereas the 9-trans, 2-cis isomer (Scheme 6.1) is better elongated [53]. 

In summary, it appears that the positional isomers of docosenoic acid are equivalent in their cardiopathogenic properties, and to date there is no convincing evidence that real differences exist when fish oils or rapeseed oils, with the same concentration of docosenoic fatty acid isomers are fed to rats. 

Lipoxygenation of PUFA can result in a range of positional hydroxyl fatty acid isomers that have been shown to exhibit a range of bioactivities. When AA is the main PUFA substrate, a range of HETE are formed (Figure 3.3). 

Dutton, H. and Emken, E.A. (1979) Geometrical and Positional Fatty Acid Isomers, American Oil Chemists Society, Champaign. 

Duchateau GSMJE, van Oosten HJ, and Vasconcellos MA (1996) Analysis of cis- and trans-fatty acid isomers in hydrogenated and refined vegetable oils by capillary gas-liquid cbromatograpby. JAOCS 73(3) 275-282. 

Morris, L. J. (1962) Separation of higher fatty acid isomers and vinylogues by thin layer chromatography. Chem. Ind. (London) 1238-. ... 

Cyclopentyl and cyclohexyl fatty acid monomers are present in heated vegetable oils. Sebedio et al. (1989) have used GC/MS to identify the major products from heated linseed oil as a mixture of 1 1 cis and trans cyclopentyl and cyclohexyl isomers the products of heated sunflower oil were found to be mostly cyclopentyl isomers. The major cyclopentyl isomers were the cis and trans isomers of methyl 7-(2 -hexyl cyclopentyl)-heptanoates and methyl 10-(2 -propylcyclopentyl)-decanoates. The major cyclohexyl isomers were trans and cis methyl 9-(2 -propylcyclohexyl)-nonanoates and made up 50% of the cyclic fatty acid isomers of linseed oil. Dobson et al (1995) have used AgNOs and GC/MS for the structural analysis of cyclic diene fatty acids, and Mossoba et al (1996) have presented confirmatory MS data for cyclic fatty acid monomers by using deuteration. 

K. Nuernberg. Effect of Diet on the Deposition of n-3 Fatty Acids, Conjugated Linoleic and C18 l trans Fatty Acid Isomers in Muscle Lipids of German Holstein Bulls./. Agr. Food Chem. 52 6607-6615 (2004). 

Ramamurthi, S., V. Manohar, and V.V.S. Mani. Characterization of Fatty Acid Isomers in Dehydrated Caster Oil by Gas Chromatography and Gas Chromatography-Mass... 

Precht, D. and J. Molkentin. C18 l, C18 2 and C18 3 TransanA Cm Fatty Acid Isomers Including Conjugated Cis A9, Trans A11 Linoleic Acid (CLA) as Well as Total Fat Composition of German Human Milk Lipids. Nahrung43, 233—244 (1999). 

But where do all the other isomers come from Desaturation should not occur in the reducing environment of the rumen and thus could not explain the array of isomers observed as desaturation of rra r-monoenes. On the other hand, hydrogenation is efficiently accomplished when rumen pH is appropriate for the organisms involved in the isomerization and hydrogenation of PUFA (16). Several of the organisms appear to have specific selectivity for certain structures of the PUFA on which they act. Different microbes could have different preferences for PUFA isomers, rumen pH, or nutrients but there is insufficient information at this time to clearly describe the rumen flora in a way that would explain the plethora of fatty acid isomers observed in the rumen and milk of dairy cows. The following discussion may provide insights into possible mechanisms to explain the presence of the myriad of trans, cis, and CLA fatty acids in rumen and milk fat. 

---