Lutein-loaded soybean protein isolate-guar gum nano-emulsion delivery system: structure, characterization and environmental stability evaluation

Abstract Lutein possesses various functional activities and is widely used in food and pharmaceuticals. However, lutein is sensitive to environmental factors, processing and storage conditions, resulting in low bioaccessibility. In this study, a nano-emulsion system based on soybean protein isolate (SPI) and guar gum (GG) was developed to enhance the stability and delivery efficiency of lutein. The lutein-loaded nano-emulsion was successfully prepared using corn oil as the oil phase and an SPI-GG complex as the aqueous phase via high-speed shearing combined with ultrasonication. The optimized nano-emulsion exhibited uniform particle size (225.73 ± 4.61 nm), high zeta potential (−43.87 ± 0.67 mV), and stability primarily maintained by hydrogen bonding and intermolecular interactions. In vitro simulated digestion experiments indicated that the nano-emulsion significantly improved free fatty acid (FFA) release (80.00 %) and lutein bioaccessibility (78.71 %), outperforming the water–oil mixture system (48.24 %). Environmental stability tests demonstrated that the nano-emulsion remained stable under weak acidic to alkaline conditions (pH 6–12), low salt concentrations (20–80 mM Na + ), potassium sorbate (0.2–0.8 g/kg), and sucrose (7–9 g/mL). Storage stability analysis revealed that the nano-emulsion effectively delayed lutein degradation for 14 days under dark conditions at 4 °C. This study provides theoretical support for the development of efficient delivery systems for hydrophobic bioactive compounds, with potential applications in functional foods and oral drug delivery systems.