GC Separation of cis-Eicosenoic Acid Positional Isomers on an Ionic Liquid SLB-IL100 Stationary Phase

Gas chromatography (GC) of cis-eicosenoic acid (20:1) positional isomers has been investigated on a capillary column of ionic liquid 1,9-di(3-vinyl-imidazolium)nonane bis(trifluoromethyl)sulfonylimidate stationary phase (SLB-IL100). A test mixture of isomeric 20:1 methyl esters was prepared from flathead flounder flesh lipids. On a 60-m column operated at 150-180 °C, six peaks appeared in the elution order of 20:ln-15 → 20:ln-13 → 20:ln-11 → 20:ln-9 → 20:ln-7 → 20:ln-5. These peaks were baseline resolved within 20 min at 180 °C. The 20:ln-13 and 20:ln-11 isomers, poorly resolved on conventional polar polysiloxane stationary phases, were completely separated from each other with separation factor α = 1.02 and peak resolution (Rs) >- 1.57. When equivalent chain length (ECL) values were compared between the SLB-IL100 and CP-Sil 88 (biscyanopropyl polysiloxane), those of 20:ln-15 and 20:ln-13 exceptionally tended to be lower on the SLB-IL100. The excellent separation of 20:1 isomers seems due to less retention of 20:ln-15 and 20:ln-13 on SLB-IL100 rather than simply due to its high polarity. Analysis of herring oil 20:1 revealed the occurrence of 20:ln-13 in the Pacific herring but not in the Atlantic herring. The ionic liquid stationary phase, SLB-IL100, is effective for analyzing 20:1 isomers occurring in fish and other natural oils

Evaluation of Rhizopus oryzae Lipase for the Determination of Regiodistribution in Triacylglycerols with Medium Chain Fatty Acids

International audienceThe nutritional profile and rheological behaviors of lipids is both due to fatty acid composition and regiodistribution on external and internal positions of triacylglycerol. Actual methods for regiodistribution analysis having some restrictions, there is still a need for investigating a safe, simple and environmentally friendly method for the sn-2 position analysis that could especially be used for the analysis of fats containing medium and short chain fatty acids. The objective of this study was to evaluate the 1,3-selectivity and typoselectivity of Rhizopus oryzae lipase in the presence of short/medium chain fatty acids in partial hydrolysis conditions used for regiodistribution analysis. Structured triacylglycerols containing eight-carbon-chain length fatty acids in the sn-2 position were chemically synthesized using DCC/DMAP coupling agent and purification steps by flash-chromatography. The final product showed very high purity and was used as the substrate for 1,3-selectivity evaluation. Typoselectivity was assessed by investigating partial hydrolysis of equimolar blends of homogeneous TAG. This study confirmed the 1,3-selectivity of Rhizopus oryzae lipase in the hydrolysis conditions used, and revealed that this lipase was less influenced by fatty acids chain length than pancreatic lipase. Considering this, Rhizopus oryzae lipase appeared to be a good candidate for regiodistribution analysis of fats containing medium and short chain fatty acids