Dosage des acides gras trans et linoleique conjugues dans la matiere grasse du lait par chromatographie gaz-liquide: Comparaison des methodes et etude de la variation des teneurs en fonction des saisons et de l'altitude

摘要

This work presents the results of trans and conjugated linoleic fatty acids (CLA) in 40 milk fats produced in winter and at three altitudes in summer using three complementary gas chromatographic methods. The levels of the trans and CLA fatty acids in 40 milk fat samples were significantly higher in summer samples compared to the winter ones and increased during the summer time as a function of the altitude. The methods used were complementary: The general method using a direct separation of the fatty acid on a 100 m CP Sil 88 column allows the determination of the main trans and conjugated fatty acids. However, an other method based on a pre-separation of the trans-C18 : 1 isomers on silver-impregnated thin layer plate is necessary for the determination of all these isomers and particularly of the trans-vaccenic acid in view of the importance of this latter acid for the fodder fat metabolism of the cow rumen. For the determination of the CLA, the gas chromatographic method used in this work can be now advantageously replaced by a method using liquid liquid chromatography with columns impregnated with silver nitrate.