Trans mono- and polyunsaturated fatty acids in human milk.

OBJECTIVE: The aim of the present study was to identify the trans isomers of C18 fatty acids in some human milk samples.
SUBJECTS: Ten human milk samples from French women were collected in a local milk bank in order to assess their trans mono and polyunsaturated fatty acids (PUFA) content. INTERVENTION: The fatty acid profile was examined using methyl and isopropyl ester derivatives. The combination of gas-liquid chromatography, high-performance liquid chromatography and silver nitrate thin-layer chromatography was needed to describe the detailed fatty acid compositions, including the trans isomers of unsaturated C18 fatty acids.
RESULTS: All the samples contained trans isomers of C18:1 acid (mean level 1.9 +/- 0.2% of total fatty acids), with trans vaccenic acid being the major isomer. The samples also contained various isomers of linoleic and alpha-linolenic acid, but at lower levels. Trans isomers of PUFA are the same as those present in deodorised or deep-fried oils. One sample presented an abnormally high degree of isomerisation of alpha-linolenic acid (almost 50%). This was related to the dietary habit or consuming foods that were deep-fried in rapeseed oil. This milk sample also contained some cyclic fatty acid monomers.
CONCLUSION: The human milk samples collected in this study contained some trans fatty acids, including isomers of essential fatty acids. This should be taken into account in the dietary intake of the newborn.