GC Analysis of Seven Seed Oils Containing Conjugated Fatty Acids

Robert Goldschmidt,William Byrdwell

doi:10.3390/separations8040051

Abstract

The fatty acid compositions, including isomer compositions, of seven seed oils containing conjugated fatty acids (CFA) were determined. Seed oils were extracted using a modified Folch extraction, converted to fatty acid methyl esters, and analyzed by gas chromatography (GC) with mass spectrometry and flame ionization detection. The MS detector was operated in positive-ion chemical ionization mode using methane reagent gas. GC was performed using two columns providing different retention characteristics: a poly(ethylene glycol) column and a more polar biscyanopropyl column. The complimentary information provided by the two columns was crucial to peak identification in several cases. The major CFA species in the samples are well known but all contained lesser amounts of additional CFA that have not been widely reported. All samples contained multiple species of conjugated linolenic acid, and two samples also contained small amounts of conjugated linoleic acid. The seed oils of Jacaranda mimosifolia and Calendula officinalis were found to contain 8c,10t,12t-18:3, the natural occurrence of which has only been recently reported in some other samples. The seed oil of Impatiens balsamina has been reported to contain four conjugated 18:4 species, and we present evidence for a fifth conjugated 18:4 isomer.

Highlights

Conjugated fatty acids (CFA) are polyunsaturated fatty acids (PUFA) with two or more carbon-carbon double bonds that are separated by a carbon–carbon single bond.CFA usually include a mixture of cis (c) and trans (t) double bonds
Diconjugated FA are often referred to as conjugated linoleic acids (CLA), and triconjugated FA are often referred to as conjugated linolenic acids (CLNA)
Identification supported by MS (peaks observed in extracted ion chromatograms (EIC)

Summary

Introduction

Conjugated fatty acids (CFA) are polyunsaturated fatty acids (PUFA) with two or more carbon-carbon double bonds that are separated by a carbon–carbon single bond. In the preparation of the fatty acid methyl esters (FAME) of CFA, a common approach for analysis is gas chromatography (GC), where the choices of methylating reagent, temperature, and time of reaction are relevant factors Basic reagents such as NaOCH3 and tetramethylguanidine (TMG) are recognized as preserving the endogenous distributions of CFA when present as triacylglycerols (TAG) and in some other forms, but they are not effective in converting FA to FAME in all types of lipids [7,13,14]. Tung oil from the seeds of the tung tree, Vernicia fordii, is an example of a plant source having two prominent CLNA isomers, α-eleostearic acid (9c,11t, 13t-18:3) and β-eleostearic acid (9t,11t,13t-18:3) [16]. The identification or partial identification of certain other peaks was helped by comparison among the samples, as later described for specific cases

Materials and Methods

Results and Discussion

Chromatograms theOmegawax

Punicic acidacid

The temperatures at the time of time elution

Conclusions