Interfacial freeze-thaw stability of Pickering emulsions stabilized by sodium Caseinate-modified solid lipid particles: Influence of lipid crystalline structure and polymorphic transitions.

This study investigated the freeze-thaw stability of Pickering emulsions stabilized by two high thermal stability lipids, palm stearin (PS, 46.9 °C) and fully hydrogenated soybean oil (HSO, 69.5 °C), in combination with sodium caseinate-modified solid lipid particles (SLPs). SLPs with distinct structural characteristics were prepared via temperature-controlled crystallization at 4 °C and 25 °C, and their effects on emulsion stability were analyzed in terms of crystallization behavior, particle size, zeta potential, interfacial adsorption, and rheological properties. At 4 °C, PS-SLPs exhibited an irregular morphology with larger particle size (532.0 ± 78.8 nm) and primarily β' crystal structure, showing rapid interfacial adsorption within 1500 s. Conversely, HSO-SLPs exhibited uniform spherical morphology, smaller size (375.4 ± 7.4 nm), an α-crystal form, higher elastic (G') and viscous (G'') moduli, and lower viscosity. Crystallization at 25 °C led to significant particle growth and slower interfacial tension reduction in all SLPs. PS-SLPs transitioned to α (98.27 %) and β (1.73 %) forms with reduced viscosity, whereas HSO-SLPs formed α (89.57 %), β (1.36 %), and β' (9.07 %) crystals with higher viscosity. Furthermore, the contact angle of SLPs increased significantly with elevated temperatures, though the zeta potential remained unaffected. Under freeze-thaw conditions, PS-SLPs exhibited reduced electrostatic repulsion, particle aggregation, and increased viscosity, especially at 25 °C, resulting in droplet instability. Conversely, HSO-SLPs formed at 4 °C maintained smaller particle size, greater electronegativity, and more robust interfacial films, minimizing droplet aggregation and oil precipitation. Interestingly, compared to PS, the α-crystal form of HSO-SLPs exhibits the best freeze-thaw stability in emulsions. These findings reveal mechanisms linking SLP properties to emulsion freeze-thaw stability and offer potential strategies for enhancing the stability of Pickering emulsions in food applications.