Determination of CLA trans,trans Positional Isomerism in CLA-Rich Soy Oil by GC-MS and Silver Ion HPLC

A similar to 20% CLA-rich soy oil with low saturated fat and no cholesterol was produced by photoisomerizing soy oil linoleic acid. The oil is predominately trans,trans CLA, with the oil containing 17% trans, trans CLA. Recent studies have shown that trans, trans CLA-rich soy oil significantly reduces heart disease and diabetes risk factors in obese rats. However, the positional isomerism of these geometrical isomers has not been identified. The objectives of the study were to determine trans, trans CLA positional isomerism of CLA fatty acids in CLA-rich soy oil and determine the resolution of trans, trans CLA positional isomers by silver ion chromatography. GC-MS studies of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) derivatives of CLA-rich oil showed that 9,11 CLA and 10,12 CLA were the major positional isomers. These were hypothesized to be the trans, trans CLA isomers, which was confirmed by silver ion chromatography and subsequent GC-FID fatty acid and ATR-FTIR geometrical isomer analysis of the collected fractions. The identification of 9,11 trans, trans CLA and 10,12 trans, trans CLA as the major CLA isomers in CLA-rich oil then allowed the deduction of the synthetic mechanism of the photoisomerism of soy oil linoleic acid to trans, trans CLA.