Enantioselective Analysis of Chiral Anteiso Fatty Acids in the Polar and Neutral Lipids of Food

Abstract

Anteiso fatty acids (aFA) are substituted with a methyl group on the antepenultimate carbon of the straight acyl chain. This feature leads to a stereogenic center. The 12-methyltetradecanoic acid (a15:0) and the 14-methylhexadecanoic acid (a17:0) are the most common aFA found in food, although they occur only in very small quantities. In this study we used gas chromatography in combination with a chiral stationary phase to determine the enantiomeric distribution of both a15:0 and a17:0 in the neutral and polar lipids of aquatic food samples and cheese. The best suited column was selected out of four custom-made combinations of heptakis(6-O-tert-butyldimethylsilyl-2,3-di-O-methyl)-beta-cyclodextrin (beta-TBDM) with different amount and polarity of an achiral polysiloxane. After separation of polar and neutral lipids of the food samples by solid phase extraction, fatty acid methyl esters were prepared and the fatty acid methyl esters were fractionated by reversed phase high performance liquid chromatography. Measurements of fractions high in aFA by enantioselective GC/MS in the selected ion monitoring mode verified the dominance of the (S)-enantiomers of a15:0 and a17:0 in both lipid fractions. However (R)-enantiomers were detectable in all samples. The relative proportion of the (R)-enantiomers was up to fivefold higher in the polar lipids than in the neutral lipids. The higher proportions in the polar lipids indicate that microorganisms might be involved in the formation of (R)-aFA.

Examining the Fish Microbiome: Vertebrate-Derived Bacteria as an Environmental Niche for the Discovery of Unique Marine Natural Products

“…[38], [39] Natural sebastenoic acid was reduced by hydrogenation over 10% palladium on carbon to give 2,3,4,5-tetrahydrosebastenoic acid ( 2 ). Comparison of the optical rotation for 2 ([α] D 24  = −7.21) with the reported literature value for ( R )-12-methyltetradecanoic acid ([α] D 22  = −5.84) defined the absolute configuration at C12 as R .…”

Exploring the fatty acids of vernix caseosa in form of their methyl esters by off-line coupling of non-aqueous reversed phase high performance liquid chromatography and gas chromatography coupled to mass spectrometry

“…Without the availability of reference standards it turned out difficult to assess the enantiomeric excess of the chiral fatty acids with the exception of the anteisofatty acids. Previously, it was found that the S-anteiso-fatty acids were dominant in food [16,17]. However, in most occasions the R-enantiomer was detected as well.…”

“…In this study, we used this off-line RP-HPLC and GC/EI-MS technique to determine the fatty acids of vernix caseosa after conversion into the corresponding methyl esters. In addition, samples of vernix caseosa are known to contain a number of chiral fatty acids including anteiso-fatty acids which can be resolved by application of modified cyclodextrins [16][17][18]. The HPLC method was also found suitable to gather fractions simple enough for the direct enantioselective analysis by GC/EI-MS [17].…”

“…In addition, samples of vernix caseosa are known to contain a number of chiral fatty acids including anteiso-fatty acids which can be resolved by application of modified cyclodextrins [16][17][18]. The HPLC method was also found suitable to gather fractions simple enough for the direct enantioselective analysis by GC/EI-MS [17]. Thus, left-overs from the GC/EI-MS analysis of RP-HPLC fractions were used to study the enantioseparation of anteiso-fatty acids.…”

Up to 21 Different Sulfur‐Heterocyclic Fatty Acids in Rapeseed and Mustard Oil

“…The two remaining stereoisomers are enantiomers. Derived from other chiral fatty acids-for instance anteiso-fatty acids are known to be strongly enriched in the S-enantiomer [15], 4-alkylbranched fatty acids were R-enantiopure [16], and ricinoleic acid being R-enantiopure [17]-it was very likely that the SHFA were also non-racemic and may be enantiopure. For this reason, we attempted a determination of the optical rotation of FAME enriched from the native rapeseed and mustard oil (mixture of 21 SHFA).…”