Characterization and structural analysis of egg yolk plasma

Egg yolk plasma is the main contributor to the emulsifying and gelling properties of egg yolk. Despite its functional importance, and although extensive physicochemical studies have been conducted, further in-depth characterization of its colloidal components, namely the low-density lipoproteins (LDLs), is needed. In this study, egg yolk plasma was prepared at two ionic strengths (0.1 and 0.2 M NaCl) and centrifuged at 10,000 or 40,000 × g to investigate the influence of extraction conditions on composition, structure, and functionality. Increasing NaCl reduced plasma lipid content and increased the relative abundance of LDL apoproteins. Increasing centrifugal force increased the proportion of neutral lipids and decreased the proportion of polar lipids. Despite these compositional differences, dynamic light scattering and small-angle X-ray scattering (SAXS) consistently showed a dominant LDL population centered at 40-50 nm across all conditions, indicating structural robustness. The SAXS data were successfully described using a core-shell model, supporting a low-electron-density lipid core surrounded by a protein- and phospholipid-rich shell, with dimensions consistent across treatments. Temperature-dependent SAXS showed that LDL particles remained structurally stable up to ∼65 °C, above which they showed increased interparticle aggregation, followed by pronounced anisotropy and restructuring above ∼70 °C. Plasma prepared at 40,000 × g formed the stiffest heat-induced gels, whereas plasma prepared at 10,000 × g reached lower equilibrium interfacial tension and higher interfacial viscoelastic moduli at equal protein concentration. Overall, moderate variations in extraction conditions did not alter LDL structure but induced compositional changes that modulated interparticle interactions and functionality, supporting the view of egg yolk plasma as a structurally robust yet functionally tunable colloidal system.