Processo de nanoemulsificação de óleos essenciais assistido por ultrassom

Abstract

Essential oils are volatile oils obtained from plants by physico-chemical extraction processes. To overcome the hydrophobicity of essential oils, and allows their dispersion in an unfavorable environment, many researchers have proposed the emulsification process (eg. Nanoemulsions, NEs, with droplets size with less than 300 nm of diameter). Thus, this work aims to develop a process of nanoemulsification of essential oils by using ultrasound energy (US) to obtain oil-in-water NEs, without using organic solvents. US energy, applied using probes or baths systems, was compared with a conventional high-speed homogenizer shear method. The emulsions were obtained by batch processes. After careful evaluation of hydrophilic lipophilic balance (HLB) of the oil phase, and the appropriate surfactant, it was possible to produce a translucent NE with controlled viscosity, allowing obtaining liquid or pasty products. The NE was obtained by evaluating US probe geometry and amplitude, as well as the sonication time and the ration between oil and aqueous phase. The apparent hydrodynamic diameter (HD) analysis were performed for emulsions that remained stable for 30 days, or longer. When only ultrasound energy was used, NEs with HD of 41 nm, and with a polydispersion index (IPD) below 0.25 were obtained. On the other hand, when the conventional shear procedure (at 5000, 10000 and 15000 rpm) was evaluated, the emulsions with IPD higher than 0.25, and the HD ranging from 50 nm up to 1 μm were obtained. The higher values of IPD, associated with high values and non-uniform HD, resulted in an unstable NEs, with strong tendency to coalescence and phase separation. The obtained results corroborates that US energy is an efficient way for obtaining uniform, reduced drop size and kinetically stable NEs. The batch process using the US probe, as well as those using US bath, have shown promise alternatives for possible industrial applications. Among the evaluated ultrasonic systems, the most promising alternative for reducing the HD and IPD was the probe type device, with 750 W of nominal power, operating at 20 kHz, and 60% amplitude.