Preservation of supramolecular structure and technofunctionality in egg yolk granules via cryogenic processing

Egg yolk granules (EYGs), as bio-macromolecular assemblies rich in lipoproteins and phosvitin, are critical for food applications requiring emulsification, gelling, and thermal stability. This study investigates how slow freezing at -20 °C (PF₂₀), moderate freezing at -80 °C (PF₈₀), immersion in liquid nitrogen (PI_LN), and grinding in liquid nitrogen (PG_LN) affect the structural and functional integrity of lyophilized EYGs. PI_LN outperformed other methods, preserving macromolecular architecture through rapid vitrification, which minimized ice crystal damage, yielding small (d₄,₃ ≈ 110 μm vs. 380 μm in PF₂₀), porous particles with enhanced solubility (46 % vs. 15 %) and turbidity (0.54 vs. 0.11), attributed to retained phospholipid-protein interactions. SDS-PAGE analysis confirmed PI_LN's superiority, showing sharp protein bands with reduced SDS binding, indicating preserved native conformations, while PF₂₀ displayed diffuse bands and smearing, suggesting aggregation and denaturation. Rheological evaluations demonstrated that PI_LN had superior viscoelastic stability and gelation capacity, critical for emulsified systems. PI_LN achieved optimal color stability and thermal resilience (DSC, TGA), collectively indicating a well-preserved, homogeneous supramolecular structure. Structurally, PI_LN and PG_LN exhibited low bulk and tapped densities (≈ 0.16, 0.30 g/cm³), high porosity (≈ 93 %), and robust particle density (≈ 4.5 g/cm³), indicative of preserved supramolecular organization. PF₂₀, however, showed compromised porosity (72 %) and elevated bulk/tapped densities (0.33/0.49 g/cm³), reflecting structural collapse. These findings underscore liquid nitrogen immersion as a superior strategy for stabilizing EYGs' bio-macromolecular framework, enabling high-performance egg-derived ingredients for advanced food applications.