Intensification and optimization of the process for thyme oil in water nanoemulsions preparation using subcritical water and xanthan gum

Intensified process based on subcritical water conditions (120 degrees C and 1.5 atm, for 2 h) was utilized to prepare thyme oil in water (O/W) nanoemulsions. In this technique, water and xanthan gum, as green solvent and natural microbial emulsifier, were utilized. Results of gas chromatography revealed that Thymol and Carvacrol were two main bioactive compounds of the extracted thyme oil. Effects of amounts of xanthan gum(0.05-0.25 g) and thyme essential oil (0.2-0.8 mL) on size of oil nanodroplets and polydispersity index (PDI) of the resulted nanoemulsions were evaluated using response surface methodology. Results demonstrated that the produced thyme O/W nanoemulsion by 0.242 mL thyme oil and 0.140 g xanthan gum had smallest average nanodroplet size (150 nm) and PDI (0.088). Furthermore, monodispersed and spherical in shape thyme oil nanodroplets were provided in the nanoemulsion using these optimal conditions with zeta potential value of -10.1 mV and antioxidant activity of 17.4%. Results also indicated that this prepared nanoemulsion had high fungicidal and bactericidal activities toward Penicillium digitatum and Escherichia coli, respectively.