Preparation, separation, and confirmation of the eight geometrical cis/trans conjugated linoleic acid isomers 8,10‐through 11,13–18∶2

Abstract

Conjugated linoleic acid (CLA) mixtures were isomerized with p-toluenesulfinic acid or I2 catalyst. The resultant mixtures of the eight cis/trans geometric isomers of 8,10-, 9,11-, 10,12-, and 11,13-octadecadienoic (18:2) acid methyl esters were separated by silver ion-high-performance liquid chromatography (Ag+-HPLC) and gas chromatography (GC). Ag+-HPLC allowed the separation of all positional CLA isomers and geometric cis/trans CLA isomers except 10,12-18:2. However, one of the 8,10 isomers (8cis, 10trans-18:2) coeluted with the 9trans,11cis-18:2 isomer. There were differences in the elution order of the pairs of geometric CLA isomers resolved by Ag+-HPLC. For the 8,10 and 9,11 CLA isomers, cis,trans eluted before trans,cis, whereas the opposite elution pattern was observed for the 11,13-18:2 geometric isomers (trans,cis before cis,trans). All eight cis/trans CLA isomers were separated by GC on long polar capillary columns only when their relative concentrations were about equal. Large differences in the relative concentration of the CLA isomers found in natural products obscured the resolution and identification of a number of minor CLA isomers. In such cases, GC-mass spectrometry of the dimethyloxazoline derivatives was used to identify and confirm coeluting CLA isomers. For the same positional isomer, the cis,trans consistently eluted before the trans,cis CLA isomers by GC. High resolution mass spectrometry (MS) selected ion recording (SIR) of the molecular ions of the 18:1, 18:2, and 18:3 fatty acid methyl esters served as an independent and highly sensitive method to confirm CLA methyl ester peak assignments in GC chromatograms obtained from food samples by flame-ionization detection. The high-resolution MS data were used to correct for the nonselectivity of the flame-ionization detector.

Effect of storage temperature on the quality of eggs from conjugated linoleic acid-fed laying hens

“…Conjugated linoleic acid, briefly known as CLA, is a mixture of geometrical and positional isomers of linoleic acid (C18:2 c-9, c-12) and involves a double bond at positions 8 and 10, 9 and 11, 10 and 12 or 11 and 13 (Eulitz et al, 1999). Each of these positional conjugated diene isomers can occur in cis-trans, transcis, cis-cis or trans-trans geometrical configurations.…”

CONCLUSION European Federation for the Science and Technology of Lipids: 2001, l’EFL prend ses marques dans l’espace européen des lipides…

“…Figure 2A shows the separation of CLA methyl esters prepared from sunflower oil, on a CP Sil88 column. The GC order of elution of the different CLA isomers is now well documented [3,29]. The GC analysis revealed that the 9,11-and the 10,12-18:2 were the major isomers.…”

Isomerization of 9c11t/10t12c CLA in Triacylglycerols

“…The temperature was held at 170°C for 40 min. The peak identification was carried out by comparing the reported conjugated linoleic acid profiles in references [10,11,13,14] and methyl esters prepared from the 9c11t and 10t12c triacylglycerols as described in the section ''Samples and methods''. The peaks in the chromatograms were then integrated, and their relative percentages were calculated using an excel spread sheet.…”

“…The two important CLAs namely 9c11t and 10t12c were prepared in large quantities by alkali isomerisation of 9c12c linoleic acid [14]. Eulitz et al [14] synthesised eight CLA isomers, 8,10 through 11,13, by isomerising CLA mixtures by p-toluene sulfinic acid or iodine catalyst.…”

“…The two important CLAs namely 9c11t and 10t12c were prepared in large quantities by alkali isomerisation of 9c12c linoleic acid [14]. Eulitz et al [14] synthesised eight CLA isomers, 8,10 through 11,13, by isomerising CLA mixtures by p-toluene sulfinic acid or iodine catalyst. Jain and Proctor [15] synthesised 9c11t, 9t11c, 10t12c and 10c12t CLA isomers in large quantities for the first time by UV photoirradiation of soya oil in the presence of iodine catalyst.…”