Tea saponins as natural emulsifiers and cryoprotectants to prepare silymarin nanoemulsion

Tea saponins (TS), a natural surfactant, are extracted from Camellia oleifera seed meal of Camellia plants. Silymarin (SM) is a flavonoid compound with hepatoprotective effect, and its clinical application is limited by its insoluble properties and low oral bioavailability. The objective of this study was to investigate the potential of TS as emulsifiers to prepare silymarin nanoemulsion (SM-NE) and as cryoprotectants to prevent the irreversible aggregation of SM-NE droplets during freeze-drying. The particle size and polydispersity index (PDI) of SM-NE decreased with the concentration of emulsifier-TS increased (particle size: 192–360 nm; PDI: 0.034–0.100). SM-NE freeze-dried powder (SM-NE-FDP) using 5% (w/v) TS as cryoprotectants had good redispersibility. TS effectively prevented the irreversible aggregation of SM-NE droplets during freeze-drying. P-XRD patterns indicated that SM was successfully encapsulated in TS-stabilized SM-NE. TEM and SEM images showed that TS-stabilized SM-NE droplets were spherical in uniform size. FT-IR analysis confirmed that the chemical structure of SM in TS-stabilized SM-NE had not significantly changed. In vitro cumulative release of SM from TS-stabilized SM-NE was sustained and affected by pH. The studies proved the ability of TS as natural emulsifiers to prepare SM-NE, and as cryoprotectants to reduce the damage of SM-NE during freeze-drying.