Gas chromatography of non-conjugated cis/trans 18:2 isomers using 100 m biscyanopropyl-polysiloxane and SLB-IL111 columns
Citation
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.
Plain language summary
Several trans fatty acids are formed during ruminal biohydrogenation of dietary unsaturated fatty acids and get incorporated into beef and dairy fats, but it is not known to what extent these are further metabolized (i.e. desaturated). In the present study, we isolated several trans fatty acids from beef fat and used liver cells to make their desaturation products. We then compared liver cell analysis to beef fat analysis to find the desaturation products. We discovered that several fatty acids in beef fat had been previously mis-identified (i.e. not as trans fatty acid desaturation products), and we found two previously uncharacterized trans fatty acid desaturation products in beef fat.
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.