Stability of cyclopropane and conjugated linoleic acids during fatty acid quantification in lactic acid bacteria

Seven methods commonly used for fatty acid analysis of microrganisms and fo ods were compared to establish the best for the analysis of lyophilized lac tic acid bacteria. One of these methods involves fat extraction followed by methylation of fatty acids, while the other methods use a direct methylati on of the samples, under different operating conditions (e.g., reaction tem perature and time, reagents, and pH). Fatty acid methyl esters were identif ied by gas chromatography-mass spectrometry and quantified by on-column cap illary gas chromatography. Two reliable methods for the analysis of fatty a cids in bacteria were selected and further improved. They guarantee high re covery of classes of fragile fatty acids, such as cyclopropane and conjugat ed acids, and a high degree of methylation for all types of fatty acid este rs. These two direct methylation methods have already been successfully app lied to the analysis of fatty acids in foods. They represent a rapid and hi ghly reliable alternative to classical time- and solvent-consuming methods and they give the fatty acid profile and the amount of each fatty acid. Usi ng these methods, conjugated linoleic acids were identified and quantified in lactic acid bacteria.