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A new conjugated linoleic acid isomer, 7 trans, 9 cis ‐octadecadienoic acid, in cow milk, cheese, beef and human milk and adipose tissue
Author(s) -
Yurawecz Martin P.,
Roach John A. G.,
Sehat Najibullah,
Mossoba Magdi M.,
Kramer John K. G.,
Fritsche Jan,
Steinhart Hans,
Ku Youh
Publication year - 1998
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/s11745-998-0273-z
Subject(s) - conjugated linoleic acid , food science , clinical chemistry , lipidology , linoleic acid , chemistry , adipose tissue , cow milk , milk fat , fatty acid , biochemistry , linseed oil
The identity of a previously unrecognized conjugated linoleic acid (CLA) isomer, 7 trans, 9 cis ‐octadecadienoic acid (18∶2) was confirmed in milk, cheese, beef, human milk, and human adipose tissue. The 7 trans, 9 cis ‐18∶2 isomer was resolved chromatographically as the methyl ester by silver ion‐high‐performance liquid chromatography (Ag + ‐HPLC); it eluted after the major 9 cis , 11 trans ‐18∶2 isomer (rumenic acid) in the natural products analyzed. In the biological matrices in‐vestigated by Ag + ‐HPLC, the 7 trans, 9 cis ‐18∶2 peak was generally due to the most abundant minor CLA isomer, ranging in concentration from 3 to 16% of total CLA. By gas chromatography (GC) with long polar capillary columns, the methyl ester of 7 trans, 9 cis ‐18∶2 was shown to elute near the leading edge of the major 9 cis , 11 trans ‐18∶2 peak, while the 4,4‐dimethyloxazoline (DMOX) derivative permitted partial resolution of these two CLA isomers. The DMOX derivative of this new CLA isomer was analyzed by gas chromatography‐electron ionization mass spectrometry (GC‐EIMS). The double bond positions were at Δ7 and Δ9 as indicated by the characteristic mass spectral fragment ions at m/z 168, 180, 194, and 206, and their allylic cleavages at m/z 154 and 234. The cis/trans double‐bond configuration was established by GC‐direct deposition‐Fourier transform infrared as evidenced from the doublet at 988 and 949 cm −1 and absorptions at 3020 and 3002 cm −1 . The 7 trans, 9 cis ‐18∶2 configuration was established by GC‐EIMS for the DMOX derivative of the natural products examined, and by comparison to a similar product obtained from treatment of a mixture of methyl 8‐hydroxy‐and 11‐hydroxyoctadec‐9 cis enoates with BF 3 , in methanol.