Spearmint essential oil (SEO) has been widely recognized for its therapeutic properties in treating gastrointestinal, respiratory, carminative, diuretic, antispasmodic, and sedative ailments. Moreover, it is commonly utilized as a flavoring agent in various food and beverage products. However, the effectiveness of SEO for medicinal purposes is hindered by its limited water solubility. Hence, the objective of this research was to determine the optimal conditions for producing a nanoemulsion of SEO by measuring turbidity through a mixture experimental design. The study aimed to investigate the impact of different formulation variables on turbidity as the response variable. These variables included PEG-40 hydrogenated castor oil (HCO) (1%-2% w/w), Tween 80 (1%-3% w/w), Tween 20 (1%-3% w/w), propylene glycol (PG) (5%-20% w/w), and polyethylene glycol 400 (5%-20% w/w). The results of the experimental design showed that the obtained data could be adequately fitted in a second-order polynomial model for the prediction of nanoemulsion turbidity with a multiple regression coefficient of 0.9704. The particle size value at the optimum condition was 81.28 nm, which was matched with the result of transmission electron microscopy (TEM). The thermodynamic and long-term stability of the prepared nanoemulsion were investigated. Furthermore, the developed nanoemulsion exhibited better antimicrobial activity against E. coli. In vitro release testing showed that the release of the optimized nanoemulsion was significantly increased. This study demonstrated that SEO is capable of forming stable nanoemulsions for use in delivery systems of flavoring agents in the food industry.
