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Comparative studies on individual isomeric 18∶1 acids in cow, goat, and ewe milk fats by low‐temperature high‐resolution capillary gas‐liquid chromatography
Author(s) -
Precht Dietz,
Molkentin Joachim,
Destaillats Frédéric,
Wolff Robert L.
Publication year - 2001
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-001-0791-8
Subject(s) - vaccenic acid , chemistry , ozonolysis , cis–trans isomerism , gas chromatography , chromatography , fraction (chemistry) , double bond , resolution (logic) , barn , organic chemistry , fatty acid , linoleic acid , conjugated linoleic acid , artificial intelligence , computer science , civil engineering , engineering
The trans ‐ as well as the cis ‐18∶1 isomer profiles were established in cow, goat, and ewe cheese fats, with the assumption that these are representative of the corresponding milks. Argentation thin‐layer chromatography was combined with low‐temperature high‐resolution gas‐liquid chromatography on 100‐m highly polar capillary columns, thus adding precision to earlier data for these species. Despite differences in the absolute content of trans ‐18∶1 isomers between species, the relative profiles were essentially similar. Except for the minor trans Δ6–Δ8 group, all trans ‐18∶1 isomers with their ethylenic bonds between positions Δ4 and Δ16 (including the resolved critical pair Δ13/Δ14) were separated and quantitated individually. As expected, vaccenic ( trans Δ9−18∶1) acid was the main isomer, accounting for as much as 37 to 50% of the total fraction. It was observed that the goat trans ‐18∶1 isomer profile was usually rather close to that of cows in winter (barn feeding), whereas that of the ewe shows a seasonal dependence. The trans ‐18∶1 profile of ewe milk fats from this study resembles that of cows in the transition period between winter and summer (pasture) feeding. Regarding the cis ‐18∶1 acid fraction, two isomers (oleic and cis ‐vaccenic acids) accounted for ca . 97% of that fraction for the three species, with the cis ‐Δ12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative‐based procedures (generally ozonolysis), taking less time and alleviating some draw‐backs of the latter procedure.