Fatty acid and conjugated linoleic acid isomer profiles in human milk fat

The fatty acid composition of 39 mature human milk samples from four Spanish women collected between 2 and 18 weeks during lactation was studied by gas chromatography. The conjugated linoleic acid (CLA) isomer profile was also determined by silver-ion HPLC (Ag+-HPLC) with three columns in series. The major fatty acid fraction in milk lipids throughout lactation was represented by the monounsaturated fatty acids, with oleic acid being the predominant compound (36-49% of total fatty acids). The saturated fatty acid fraction represented more than 35% of the total fatty acids, and polyunsaturated fatty acids ranged on average between 10 and 13%. Mean values of total CLA varied from 0.12 to 0.15% of total fatty acids. The complex mixture of CLA isomers was separated by Ag+-HPLC. Rumenic acid (RA, cis-9 trans-11 C18:2) was the major isomer, representing more than 60% of total CLA. Trans-9 trans-11 and 7-9 (cis-trans + trans-cis) C18:2 were the main CLA isomers after RA. Very small amounts of 8-10 and 10-12 C18:2 (cis-trans + trans-cis) isomers were detected, as were different proportions of cis-11 trans-13 and trans-11 cis-13 C18:2. Although most of the isomers were present in all samples, their concentrations varied considerably.