Curcumin and mangostin compounds contained in turmeric root and mangosteen rind are widely known as active compounds that have antioxidant activity. These two active compounds are also known to have low solubility in aqueous solutions, so mixing them in nanoemulsions is expected to increase their solubility in body fluids. This study aims to formulate and characterize nanoemulsions containing mangosteen peel extract in natural eutectic solvent (NADES) and turmeric extract in virgin coconut oil (VCO), as a healthy herbal drink. In this study, NADES consisted of 1,2-propanediol, and betaine was applied to increase the solubility of α-mangostin in the aqueous phase, while curcumin from turmeric extract was dissolved in the VCO. The oil-in-water nanoemulsion has variations in the mass ratio of the aqueous phase to the oily phase, and variations in the content of xanthan gum as a thickener about 0.50 g - 0.15 g. Stability test using accelerated centrifugation method and freeze-thaw method showed the nanoemulsion was stable for more than one year. The pH values of various nanoemulsions were constant in the range of 6.4 - 6.8 which is a good criterion for a healthy drink. The emulsion droplet size ranged from 300 nm to 600 nm and the zeta potential value ranged from -19 mV to -44 mV, these results also indicated a stable nanoemulsion. The results of the freeze-thaw test showed that the nanoemulsion could maintain its stability under extreme conditions. The phenolic content and antioxidant activity of the nanoemulsion showed values ranging from 22 to 38 mg Gallic Acid Equivalent (GAE) /100 g sample and 30 - 55 µmol Fe (II)/100 g sample, respectively. From the antioxidant test using 2,2-diphenyl-1-picrylhydrazyl (DPPH), the nanoemulsion had an inhibition percentage close to 80% at a concentration of about 500,000 ppm. The stability of nanoemulsions in simulated gastrointestinal fluids showed that nanoemulsions were stable in them, thus potentially increasing the bioavailability of herbal extracts in gastrointestinal fluids. However, further research on the number of bioactive extracts in nanoemulsions needs to be reviewed by taking into account the safe limits of phenolic compounds from plants that can be consumed daily.
