Preparation, characterization, and functional properties of zein/gallic acid/sodium alginate ternary composite nanoparticles for enhancing stability and bioaccessibility of phytosterols.

Phytosterols, a class of phytochemicals exhibiting limited aqueous solubility and low oil solubility, possess diverse physiological functions that have attracted considerable research interest. However, their poor aqueous solubility significantly restricts practical applications in functional food systems. To address these limitations, we developed a novel core-shell nanoparticle system. This system features zein as the hydrophobic core, which encapsulates phytosterols through hydrophobic interactions and hydrogen bonding, while sodium alginate forms the hydrophilic outer protective layer via electrostatic interactions. Gallic acid, functioning as both a cross-linker and antioxidant, was adsorbed at the zein/sodium alginate interface via hydrogen bonding and electrostatic interactions. The phytosterol-loaded zein/gallic acid/sodium alginate (ZGSP) nanoparticles were synthesized using an anti-solvent precipitation technique and systematically characterized using dynamic light scattering (DLS), fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), differential scanning calorimetry (DSC), scanning electron microscope (SEM), and transmission electron microscopy (TEM). The resulting ZGSP nanoparticles exhibited greater structural compactness, higher encapsulation efficiency (81.1 ± 0.03 %), improved oxidative stability, and superior physicochemical stability compared to controls. Furthermore, the nanoparticles demonstrated excellent colloidal stability under diverse conditions, including a broad pH range (3.0-8.0), high ionic strength (50-500 mM NaCl), and simulated gastrointestinal environments. Notably, the ZGSP nanoparticles significantly enhanced phytosterol bioaccessibility compared to free phytosterol controls (P < 0.05). These findings demonstrate that the ZGSP nanoparticles provide an effective platform for phytosterol encapsulation, protection, and delivery; thereby expanding the potential applications of phytosterols in functional foods and nutraceuticals.