Preparation, stability, and in vitro transport of soybean protein-based diosgenin nanoemulsions

•SPI NEs improve the bioavailability of DIO.•DIO-SPI NEs exhibit better physicochemical properties.•DIO-SPI NEs showed good stability under proper conditions.•The NEs encapsulation reduced the toxicity of DIO to cells.•The transport efficiency of DIO-SPI NEs was greater than that of free DIO. Soybean protein isolate (SPI)-stabilized nanoemulsions (NEs) were formulated to encapsulate diosgenin (DIO) to enhance its water solubility and bioavailability. The influence of DIO concentrations on NEs’ properties was investigated, and their environmental stability and cell permeability were also assessed. Results demonstrated that DIO significantly affected all the physicochemical properties of NEs. NEs with 1.0 mg/mL of DIO exhibited smaller droplet size (209 nm), lower polydispersity index (0.17), and higher stability coefficient (95.8 %). Furthermore, DIO-SPI NEs displayed better stability under appropriate pH ( 5), NaCl concentrations (≤0.3 M), temperatures (≤60 °C), and freeze–thaw cycles (≤2), as well as storage at 4 °C. Moreover, encapsulating DIO in NEs reduced its toxicity towards cells and enhanced its transport efficiency, which reached 3.16 ∼ 4.87 × 10−6. These findings highlight the potential of SPI-based NEs as a promising carrier for the efficient delivery of DIO.