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

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Abstract
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.