IMPROVED GAS-CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF THE INDIVIDUAL FREE FATTY-ACIDS IN CHEESE USING A CAPILLARY COLUMN AND A PTV INJECTOR

A gas chromatographic method with a capillary column and a programmed temperature vaporizer injector has been used to analyze the individual free fatty acids in cheese. The lipids were extracted from an acidified cheese slurry with diethyl ether and treated with tetramethylammonium hydroxide (TMAH) to convert the free fatty acids to tetramethylammonium soaps (TMA-soaps), which were subsequently pyrolyzed to methyl esters in the injector. Carrying out injection at the initial column temperature resulted in lower dispersion of the results, but the solvent front prevented quantitative determination of butyric and caproic acids, and an injector temperature of 300-degrees-C was therefore employed. Under the conditions tested, trimethylamine (tma) flash-off did not affect the determinations. The accuracy of the method improved at higher free fatty acid contents (coefficient of variation of 0.53 % for a total free fatty acid content of 9000 mg/kg as opposed to 7.0 % for a total free fatty acid content of 1400 mg/kg). The recovery rate for individual free fatty acids ranged between 91 and 103 %.