Analytical supercritical fluid extraction with lipase catalysis: Conversion of different lipids to methyl esters and effect of moisture

Abstract  The fat content of lipid-containing samples has been determined by extraction of the fat with supercritical carbon dioxide, followed by enzyme-catalyzed methylation of the fat under supercritical conditions, prior to gas chromatography (GC) analysis. This study was initiated to determine the effect of moisture content on the extraction and conversion of lipids in oilseed and meat samples to their fatty acid methyl ester (FAME) derivatives. These samples were freeze-dried or mixed with Hydromatrix and compared with untreated control samples by employing the above-described supercritical fluid extraction-reaction sequence. Particular attention was focused on minor constituents, such as phospholipids and cholesteryl esters, to see if they could be extracted and derivatized by the above technique. Recoveries and reaction conversions of the lipid species were determined with the aid of GC, high-performance liquid chromatography, and supercritical fluid chromatography for analyses of the extracted lipids. Total fat values were higher from the freeze-dried meat and oilseed samples than from samples mixed with Hydromatrix or left untreated. Extraction of cholesteryl esters was better than 90%, and conversion of the cholesteryl esters to FAME was 93% or higher. Extraction of phosphatidic acid was only 88% compared to more than 90% recoveries for the other phospholipid species. FAME conversion was better than 96% for all phospholipid samples in the study.