Physicochemical Characterization of Lemongrass Essential Oil-Alginate Nanoemulsions: Effect of Ultrasound Processing Parameters

The formation of lemongrass oil (1 % v/v) nanoemulsions in aqueous sodium alginate solution (1 % w/v) containing Tween 80 (1 % v/v) as nonionic surfactant was studied in terms of droplet size, electrical charge, viscosity, and whiteness index considering different ultrasonication times (0, 30, 60, 120, and 180 s) and amplitudes (30, 60, and 100 mu m). The droplet size and size distribution of the emulsions decreased at increasing treatment time and amplitude. The minimum average droplet size observed in nanoemulsions was 4.31 +/- 0.18 nm with a narrow size distribution. The interface electrical charge of the coarse emulsion was -18.0 +/- 2.9 mV, whereas in ultrasonicated nanoemulsions, it diminished up to -55.8 +/- 6.4 mV when the sonication time was extended for 180 s. The viscosity of nanoemulsions also decreased at increasing treatment time and amplitude. Moreover, nanoemulsions became translucent after sonicating for 180 s at 30, 60, or 100 mu m with whiteness indices of 28.61 +/- 0.17, 27.93 +/- 0.21, and 27.86 +/- 0.33, respectively. Therefore, it can be stated that ultrasound processing might be a feasible technology to produce highly translucent lemongrass oil-alginate nanoemulsions, with extremely small droplet sizes and high stability to be used as delivery systems of essential oils in food products. However, it is necessary to investigate the effect of ultrasound processing parameters on the antimicrobial potential of essential oils incorporated to nanoemulsions.