Gas chromatography of non-conjugated cis/trans 18:2 isomers using 100 m biscyanopropyl-polysiloxane and SLB-IL111 columns

Vahmani, P., Rolland, D.C., Gzyl, K.E. and Dugan M.E.R. 2017. Gas chromatography of non-conjugated cis/trans 18:2 isomers using 100 m biscyanopropyl-polysiloxane and SLB-IL111 columns. AOCS, April, Orlando.

Abstract

Several positional trans(t)-18:1 isomers (t4-t16-18:1) are formed during ruminal biohydrogenation of dietary unsaturated fatty acids and get incorporated into ruminant fats (e.g. beef and dairy). In the present study, liver cells were cultured with individual t-18:1 isomers and GC chromatograms of their triacylglycerol fatty acid methyl esters (FAME) were compared to beef fat chromatograms, and objectives included either confirming the presence of t-18:1 Δ-9 desaturase products in beef fat or tentatively identifying novel 18:2 isomers and their retention times. Individual t-18:1 isomers including t12-, t13-, t14-, t15- and t16-18:1 were isolated from beef fat using a combination of Ag+SPE and Ag+-HPLC, while t6-18:1 was sourced commercially. HepG2cells were cultured with individual t-18:1 isomers, and retention times of their Δ-9 desaturation products were determined using 100 m biscyanopropyl-polysiloxane and SLB-IL111 columns. Corresponding peaks were found in beef adipose tissues (i.e. subcutaneous fat and perirenal fat) known to have different delta-9 desaturase activities. Further lines of evidence indicating the presence of Δ-9 desaturation products of t-18:1 isomers in beef fat were developed by analysis of FAME fractionated using Ag+-TLC, and by GC/MS. Some of the Δ-9 desaturation products of t-18:1 have been previously identified in ruminant fat including cis(c)9,t12-18:2 and c9,t13-18:2. Some of the Δ-9 desaturation products of t-18:1 (c9,t14-18:2 and c9,t15-18:2) have been previously tentatively identified as different fatty acids, and for the first time we provide evidence of the presence of c9,t16-18:2, and where t6,c9-18:2 may elute during analysis of FAME from beef fat.

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