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 (PILN), and grinding in liquid nitrogen (PGLN) affect the structural and functional integrity of lyophilized EYGs. PILN 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 PILN'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 PILN had superior viscoelastic stability and gelation capacity, critical for emulsified systems. PILN achieved optimal color stability and thermal resilience (DSC, TGA), collectively indicating a well-preserved, homogeneous supramolecular structure. Structurally, PILN and PGLN 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.