Optimization of Solvent Extraction and Direct Transmethylation Methods for the Analysis of Egg Yolk Lipids

The composition of egg yolk lipids differs greatly from most other food lipids, as it combines high contents of triglycerides and phospholipids, as well as a high proportion of cholesterol. The lipids are organized in lipoproteins and are dispersed in aqueous phase. Classical extraction methods using chloroform and methanol have not been optimized for such a matrix, therefore quantitative extraction yields of egg lipids can be inaccurate. In this study, the original method of Bligh and Dyer is evaluated and adapted for egg lipids. Furthermore, a direct extraction/derivatization method is presented. Solvent extraction resulted in a lipid yield of 31.8 ± 0.89% and total fatty acid yield was 257 ± 2 mg/g yolk whereas the direct method yielded 250 ± 7 mg/g yolk. Gas chromatographic analyses confirmed that lipid recovery was complete for triglycerides and phospholipids as well.