Activity and stability of castor oil-based microemulsions with cellulose nanocrystals as a carrier for astaxanthin

Microemulsions (MEs) are explored for its use in various food and drug formulations and applications. It is an amphiphilic material, consisting of oil phase, surfactant mixture, and aqueous phase. Castor oil (CO), which has anti-inflammatory and analgesic activities, was used as the oil-phase in the ME formulations. Stability and activity of CO-based ME were investigated along with the influence of encapsulating astaxanthin as lipophilic drug and the use of cellulose nanocrystals (CNC) as pickering agent. Regression model for predicting hydrodynamic diameter of astaxanthin-load (400 ppm) was explored with predictors being the weight fraction of CO, surfactant mixture, and CNC amount in the ME. Microemulation size is dependent on the oil-phase and amount of drug loaded, with CNC potentially improving the stability of ME with high CO fraction. The concentration at IC50 was reduced from 494.47 to 52.25 mu l/ml as the fraction of CO in ME formulation increased between 5 and 28 wt.% for free-radical scavenging activity. The same phenomenon was observed for anti-microbial assay, allowing 94.9% and 93.9% inhibition of Escherichia coli and Staphylococcus aureus growth, respectively. These results confirmed that CO-based MEs are promising as the topical drug delivery, especially as the carrier for the hydrophobic compound.