Acid-heat induced structural remodeling and gelation of egg yolk high-density lipoproteins: Insights into fibrillation pathways and rheological behavior.

Egg yolk high-density lipoprotein (HDL) is a protein-lipid macromolecular complex whose tightly packed architecture restricts its structural adaptability. In this work, an acid-heat treatment was employed to induce HDL disassembly and guide its reorganization into ordered fibrillar assemblies, ultimately forming hydrogels with tunable microstructures and rheological characteristics. Atomic force microscopy, fluorescence spectroscopy, and Fourier-transform infrared spectroscopy were used to elucidate the structural evolution of HDL during the treatment. The results showed that acidic heating triggered HDL fragmentation, followed by the formation of amyloid-like fibrils that progressively elongated during maturation, with heights increasing from 2.03 to 3.68 nm and lengths extending from 76.3 to 316.1 nm. This hierarchical transformation was accompanied by enhanced β-sheet content and stabilization through hydrophobic interactions and hydrogen bonding. These molecular changes coincided with substantial strengthening of gel viscoelasticity, reflected by an increase in storage modulus (G') from 0.2 to 164.3 Pa at 67.75 rad/s. Overall, acid-heat induction effectively reorganized HDL into fibrillar hydrogels with regulated structural and mechanical properties, providing mechanistic insights into protein fibrillation pathways relevant to macromolecular engineering and functional material design.