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Study of individual trans ‐ and cis ‐16∶1 isomers in cow, goat, and ewe cheese fats by gas‐liquid chromatography with emphasis on the trans ‐Δ3 isomer
Author(s) -
Destaillats Frédéric,
Wolff Robert L.,
Precht Dietz,
Molkentin Joachim
Publication year - 2000
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/s11745-000-0614-y
Subject(s) - gas chromatography , chemistry , clinical chemistry , lipidology , chromatography , cis–trans isomerism , food science , organic chemistry , biochemistry
Low‐temperature gas‐liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans ‐and cis ‐hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin‐layer chromatography (Ag‐TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans ‐16∶1 isomer is palmitelaidic acid (the Δ9 isomer), but it does not exceed one‐third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans ‐Δ3 16∶1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca . 10% of the trans ‐16∶1 acid group. Otherwise, all isomers with their ethylenic bond between positions Δ4 and Δ14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans ‐16∶1 isomers only represent ca. 5% of the sum of the trans ‐16∶1 plus trans ‐18∶1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso‐17∶0 acid, which was confused with (and added to) trans ‐Δ9 (palmitelaidic) acid; consequently, these results were large overestimates. Regarding the cis ‐16∶1 acids, the Δ9 isomer is the prominent constituent as expected, but the second‐most important isomer is the Δ13 isomer. It does not appear that trans ‐16∶1 isomers are from ruminant milk fats of great nutritional importance as compared with trans ‐18∶1 isomeric acids. As for trans ‐18∶1 isomers, the combination Ag‐TLC/GLC is a necessary procedure to quantitate trans ‐16∶1 acids accurately and reliably. Ag‐TLC allows removal of interfering branched 17∶0 acids and cis ‐16∶1 acids, and low‐temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.