Research Note: Comparison of water-soluble metabolites in egg yolk, yolk granules, and yolk plasma based on quantitative metabolomic analysis.

Egg yolk (EY) can be divided into yolk granules (EYG) and yolk plasma (EYP) after water dilution and centrifugation. EYP had a significantly higher lipid content and is predominantly in the form of low-density lipoprotein (LDL) while EYG has a higher protein content. In order to explore the nutritional differences between EY, EYP and EYG, quantitative metabolomic analysis was carried out by ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC-MS/MS). The results showed that a total of 588 small molecule metabolites were identified, mainly glycerol phospholipids (51.59-66.46%), coenzymes, and vitamins (1.21-1.84%). A quantitative comparison showed that amino acids and their metabolites were the most representative metabolites of differential abundance in the contrast of EY and EYG, EYP and EYG. Carbohydrates and their metabolites were the representative metabolites of differential abundance between EY and EYP. The study provided important information for understanding the metabolic composition of EY, EYG, and EYP, as well as providing a reference for utilizing the whole egg.