Preparation of monodisperse water-in-oil-in-water emulsions using microfluidization and straight-through microchannel emulsification

Water-in-soybean oil-in-water (W/O/W) emulsions with an internal water phase content of 10-30% (vol/vol) were prepared by a two-step emulsification method using microfluidization and straight-through microchannel (MC) emulsification. A straight-through MC is a silicon array of micrometer-sized through-holes running through the plate. Microfluidization produced water-in-oil (W/O) emulsions with submicron water droplets :of 0.15-0.26 mu m in average diameter (d(av,w/o)) and 42-53% in CV (CVw/o) using tetraglycerin monolaurate condensed ricinoleic acid esters (TGCR) and polyglycerin polycondensed ricinoleic acid esters (PGPR) as surfactants dissolved in the oil phase. The d(av,w/o) and viscosity of the W/O emulsions increased with an increase in internal water phase content. Straight-through MC emulsification was performed using the W/O emulsions as the to-be-dispersed phase and polyoxyethylene (20) sorbitan monooleate (Tween((R)) 80) as a surfactant dissolved in the external water phase. Monodisperse W/O/W emulsions with d(av,w/o/w) of 39.0-41.0 mu m and CVw/o/w below 5% were successfully formed from a straight-through MC with an oblong section (42.8 x 13.3 mu m), using the TGCR-containing systems. The d(av,w/o/w) of the monodisperse W/O/W emulsions decreased as the internal water phase content increased because of the increase in viscosity of the to-be-dispersed phase. Little leakage of the internal water droplets and no droplet coalescence or droplet breakdown were observed during straight-through MC emulsification.