IDENTIFICATION BY MASS-SPECTROMETRY OF TH E LINOLEIC-ACID AUTOXIDATION PRODUCTS IN HYDROALCOHOLIC SOLUTIONS

The unsaturated fatty acids and the complex lipids containing unsatura ted fatty acids, are very oxygen sensitive. These molecules are found in numerous alcoholic beverages and their autoxidation leads to the fo rmation of hydroperoxides, themselves transformed into volatile compou nds with a bad smell, thus contributing to the off flavour of hydroalc oholic beverages. The present study involves hydroperoxide formation f rom linoleic acid in hydroalcoholic media of wine like composition (12 % vol. asthanol, pH = 3.5), containing traces of iron and copper as ox idation promoters. First, a method to stabilize the hydroperoxide stru cture is proposed, consisting in reducing the OOH function to more sta ble alcohol function, followed by a methylation of the carboxylic func tion to the corresponding methyl ester. These derivatized molecules ar e more stable and more volatile than the initial hydroperoxides. By hi gh performance liquid chromatography coupled with liquid secondary ion mass spectrometry, four derivatives of molecular weight 310 are obser ved; they correspond to the four expected reduced and methylated hydro peroxides.