Conjugated linoleic acid (CLA) isomers in heat-treated vegetable oils

The aim of this study was to quantify the conjugated linoleic acids (CLA) i somers present in frying oils and to elucidate their structures. For this p urpose, used frying oils were collected in restaurants by the laboratoire I nterregional de la Repression des Fraudes. Three samples of sunflower oils, one of peanut oil and one of rapeseed oil containing different levels of t otal polar compounds were analysed. The samples were converted to methyl es ters using sodium methoxide and the CLA content was determinated by a combi nation of gas chromatography analysis on a 100 m CP Sil88 column and of sil ver-ion-high pressure liquid chromatography. The identification of the CLA isomers was carried out by gas chromatography coupled with mass spectrometr y of the 4-methyl- 1,2,4-triazoline-3,5-dione adducts. The amount of polar compounds in the frying oils ranged from 30 to 53%. The quantities of CIA f rom 0.4 to 0.5%. The 9, 11 and 70, 12-18:2 were the major CIA isomers. Amon g them, the di-trans isomers represent about 50% of the total CLA.