Abstract
Traditional and state-of-the-art techniques were combined to probe for various lipid classes from egg yolk and avocado qualitatively and quantitatively. A total lipid extract was isolated using liquid–liquid extraction. An aliquot of the total lipid extract was subjected to transesterification to form volatile fatty acid methyl esters suitable for gas chromatography to quantify fatty acyl residues in both food samples. Another total lipid aliquot was separated into two lipid fractions of higher and lower polarity using silicic acid column chromatography. All fractions were analyzed using thin-layer chromatography and were checked for cholesterol using the Liebermann-Burchard test. In addition, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using 2,5-dihydroxybenzoic acid and 4-chloro-α-cyanocinnamic acid matrixes was performed to analyze the composition of separated lipid fractions. Egg yolk exhibited phosphatidylcholines and phosphatidylethanolamines in the more polar fraction and cholesterol in the less polar one. Avocado contained detectable amounts of the nonpolar triglyceride triolein. The experiments can be split between three 3-h laboratory periods to allow upper-division students to gain exposure to both lipid theory and hands-on experimental lipid analysis.
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