ANTONIASSI, R.

BIZZO, H. R.

GAMA, M. A. S.

LOPES, F. C. F.

SILVA, P. S.

SOUZA, A. M.

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SEPARATION OF CRITICAL PAIRS OF C18:1 ISOMERS AND CONJUGATEDLINOLEIC ACIDS IN MILK FATHumberto R. Bizzo1, Andressa M. Souza1, Priscila S. Silva1, Rosemar Antoniassi1, Marco AntonioS. Gama2, Fernando Cesar F. Lopes21 Embrapa Food Technology, Avenida das Americas, 29501, 23020-470 Rio de Janeiro, Brazil2 Embrapa Dairy Cattle, Rua Eugenio do Nascimento, 610, 36038-330 Juiz de Fora, BrazilThe analysis of fatty acids (as methyl esters, FAME) from milk fat is usually performed in highpolarity 100 m capillary columns. Due to sample complexity, however, sometimes properresolution between C18:1 cis/trans isomers, as well as conjugated linoleic acid (CLA) isomers,is not achieved. As part of an ongoing project on CLA, herein we report a study on a set ofchromatographic conditions towards the separation of these compounds in a single run, usinga CP-Sil 88 column (88% cianopropyl-aryl-polysiloxane, 100 m x 0.25 mm x 0.2 μm). All testswere performed in an Agilent 6890N gas chromatograph fitted with a flame ionization detector(kept at 280ºC). Separation of critical pairs of C18:1 and of CLA were carried out at constanttemperature (160ºC, 170ºC and 175ºC), as well as at temperature gradient from 160ºC to either175ºC, 210ºC or 215ºC. Carrier gas (hydrogen) flows ranging from 0.5 to 2.5 mL/min weretested. FAME and CLA standard solutions were injected (1.0 μL) at 250ºC and split 1:50. Fora given constant carrier gas flow, best separation was obtained with the 160ºC constanttemperature analysis. With temperature gradient analysis, flows between 1.0 and 2.0 mL/minled to better resolution. Best overall separation conditions were at 160ºC and variable carriergas flow: 2.0 mL/min (32 min), then 1.5 mL/min (32 min) and 2.5 mL/min (28 min), leading toa total analysis time of 92 min. Complete separation of the critical pair C18:1 cis/trans andCLA isomers was observed. It was also important to note that the signal corresponding to C21:0,which usually lies among CLA peaks, leading to miscalculations of this group, was observed ina chromatographic region well separated from CLA. The optimized method was applied to milkfat samples, six from bovines and six from ovines, fed with a diet rich in unsaturated fatty acids.The CLA yield varied from 0.5 to 2.0% in the milk from bovines, and from 0.6 to 0.9% in themilk from ovines.  Acknowledgements: Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq).P.37.517

Separation of critical pairs of C18:1 isomers and conjugated linoleic acids in milk fat.

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