Analysis of Phospholipids in Eggs

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Introduction

Some portion of an egg, be it the yolk, white or whole egg, is found in countless finished food products. As with many precursor ingredients, the properties of the eggs must be verified prior to being added into the final product. Historically, the fat content of eggs has been analyzed by acid hydrolysis. The acid hydrolysis gravimetric method requires the use of expensive solvents along with dangerous acids. With the introduction of the ORACLE™, CEM has endeavored to replace these gravimetric methods.

The ORACLE has performed very well with a multitude of products and has proven to be as accurate, and in some cases, more precise than gravimetric techniques for triglyceridebased fat analysis. However, certain industries characterize fat differently than others. To better encapsulate what is globally defined as fat, CEM is expanding the use of the ORACLE to include the analysis of phospholipids. To better study phospholipids, we chose to study eggs, due to their relatively high phospholipid content.


Current Issue

When analyzing egg yolks, whole eggs, and egg yolk powders, the current ORACLE methodology results in a fat result that is slightly lower than the acid hydrolysis gravimetric method. It has been reported that dry egg yolk is approximately made of 62.5% lipids, 33.0% proteins, 1.2% carbohydrates and 3.5% minerals.1 Lipids in yolk are associated with lipoprotein assemblies. These lipoproteins are made up of 62% triglycerides, 33% phospholipids and less than 5% cholesterol. The ORACLE has had no difficulties in the analysis of triglycerides, so this led to the hypothesis that the discrepancy was due to phospholipid content. Phospholipids are amphiphilic, containing a hydrophilic phosphoric acid head group and a hydrophobic tail of two fatty acids. In egg yolk, phosphatidylcholine makes up 76% of the present phospholipids. Phosphatidylethanolamine represents 22% of the phospholipids while the other 2% is made up of other various phospholipids. Looking at the percentages of the components in egg yolk, phosphatidylcholine corresponds to approximately 23% of the total fat in the yolk.