QUANTITATIVE DETERMINATION OF CONJUGATED LINOLEIC ACID ISOMERS IN BEEF FAT

Authors: FRITSCHE, JAN - VISITING SCIENTIST; FRITSCHE, SONJA - VISITING SCIENTIST; Solomon, Morse; MOSSOBA, MAGDI - FDA; YURAWECZ, MARTIN - FDA; MOREHOUSE, KIM - FDA; KU, YUOH - FDA

Submitted to: European Journal of Fat Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: With the recent reports on the beneficial health effects of conjugated linoleic acid (CLA) on carcinogenesis, atherosclerosis, platelet aggregation, and body fat deposition in humans, there is a need for a rapid quantitative identification and determination procedure for CLA. CLA is a multiplicity of geometrical and positional isomers of linoleic acid (polyunsaturated fatty acid) with conjugated double bands and is predominantly found in ruminant-based products. The most advanced method to quantitate CLA to date is a combination of gas chromatography (GC) and multi-column high performance liquid chromatography (HPLC) with GC providing the total CLA and HPLC the isomeric distribution. This study evaluated a triple-column HPLC procedure for quantitating CLA in beef samples. Use of a triple-column HPLC was successful at differentiating the isomeric distribution of CLA in the meat samples but was less accurate at quantitating the total CLA content as compared to using the GC procedure. Results indicate that using a multi-column HPLC procedure, rapid separation and accurate isomeric distribution of CLA in meat samples can be obtained.

Technical Abstract: The amounts of 14 conjugated linoleic acid (CLA) isomers (t12t14, t11t13, t10t12, t9t11, t8t10, t7t9, t6t8; 12,14 c/t, t11c13, c11t13, t10c12, 9,11 c/t, t8c10, t7c9-18:2) in 20 beef samples were determined by triple-column silver-ion high performance liquid chromatography (Ag+ -HPLC). Quantitation was performed using an external CLA reference standard consisting of cis9,trans11-18:2, trans9,trans11-18:2 and cis9,cis 11-18:2. Linearity was checked as being r>0.9999 between 0.00002 to 2 mg/ml. The determination limit (5-fold signal/noise ratio) of the CLA reference was estimated to be 0.25, 0.50, 1.0 ng/injection for the cis/trans, trans,trans and cis,cis isomers, respectively. As expected, cis9,trans11-18:2 was the predominant isomer (1.95 mg/g fat) in beef, followed by trans7,cis9-18:2 (0.19 mg/g fat); cis,cis isomers were below the determination limit in most beef samples. Total CLA amounts determined by Ag+ -HPLC were compared to total CLA determined by gas chromatography (100 m CPSil 88 column). The amounts obtained by GC were generally higher than those determined by Ag+ -HPLC due to co-eluting compounds.