title: A new conjugated linoleic acid isomer, 7 trans, 9 cis-octadecadienoic acid, in cow milk, cheese, beef and human milk and adipose tissue.
abstract: 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 investigated 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 delta7 and delta9 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 BF3 in methanol.
authors.affiliation: U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Washington, DC 20204, USA. mpy@cfsan.fda.gov
authors.forename: M P
authors.initials: MP
authors.lastname: Yurawecz
authors.forename: J A
authors.initials: JA
authors.lastname: Roach
authors.forename: N
authors.initials: N
authors.lastname: Sehat
authors.forename: M M
authors.initials: MM
authors.lastname: Mossoba
authors.forename: J K
authors.initials: JK
authors.lastname: Kramer
authors.forename: J
authors.initials: J
authors.lastname: Fritsche
authors.forename: H
authors.initials: H
authors.lastname: Steinhart
authors.forename: Y
authors.initials: Y
authors.lastname: Ku
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry*; D000293:Adolescent; D000818:Animals; D002417:Cattle; D002611:Cheese / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid; D005231:Fatty Acids, Unsaturated / Q000302:isolation & purification*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007223:Infant; D008041:Linoleic Acids / Q000302:isolation & purification*; D008461:Meat Products / Q000032:analysis*; D008892:Milk / Q000737:chemistry*; D010080:Oxazoles; D012834:Silver; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism
chemical_list: D005231:Fatty Acids, Unsaturated; D008041:Linoleic Acids; D010080:Oxazoles; C027369:octadecadienoic acid; C057549:4,4-dimethyloxazoline; D012834:Silver