Determination of optimal ultrasound conditions for preparation of O/W emulsions with encapsulated juniper berry essential oil (Juniperus communis L.)

Abstract

The microencapsulation of essential oils can provide their evaporation and oxidation protection, flavor retention or/and masking of unpleasant taste. The microencapsulation process involves emulsions preparation and drying of the obtained emulsion droplets. The aim of this study is the determination of optimal conditions for preparation of the stable O/W emulsions containing juniper berry essential oil with minimal droplet size, as a preparatory stage for microcapsule formation. As the first step for pre-emulsions preparation, homogenization at 10000 rpm for 5 min. was chosen, which gave emulsions with droplet size between 1.82 and 2.51?m, depending on concentrations of the surfactant (Tween 20) and encapsulated essential oil. The second step was ultrasound emulsification during 5 minutes at a frequency of 99%, using pulsed 10:10 s (ON/OFF) ultrasound treatment, which was chosen as an optimal, creating emulsions of droplet sizes of 320 nm in diameter (for 5% essential oil and 1% Tween 20). The addition of wall material changed the size and stability of emulsions, which depends on type of biopolymer and its surface competition with used surfactant. The maltodextrin (MD), gum arabic (GA) and their mixture in equal ratio were used. GA emulsions can be singled out as the most stable without used surfactant, with D4,3 = 1.11 ? 0.003 ?m. Using MD as a wall material requires addition of surfactant (1% w/v) to form stable emulsions. The mixture of MD/GA can be used with or without surfactant. The addition of Tween 20 (1% w/v) decreases droplet size from 14.86 to 0.99 ?m, while utilization of the ultrasound contributes to the droplet size decrease and emulsions stability.