Monodisperse W/O/W emulsions encapsulating l-ascorbic acid: Insights on their formulation using microchannel emulsification and stability studies

Stabilizing l-ascorbic acid is a challenge for food industries. The present study aimed to formulate monodisperse food-grade water-in-oil-in-water (W/O/W) emulsions containing a high concentration of l-ascorbic acid in an inner aqueous phase using homogenization and subsequent microchannel emulsification (MCE). The microchannel (MC) array plate used here was a silicon asymmetric straight-through MC array that consists of numerous 10 μm × 100 μm microslots with a 30 μm depth, each connected to a 10 μm-diameter circular MC with a 70 μm depth. Water-in-oil (W/O) emulsions contained a soybean oil solution with 4–8% (w/w) tetraglycerin condensed ricinoleic acid ester as a continuous phase and an aqueous solution with 10–30% (w/v) l-ascorbic acid, 1% (w/w) magnesium sulfate, and 1% (w/v) gelatin as an inner aqueous phase. The W/O emulsion droplets formulated using a rotor-starter homogenizer had average droplet diameters of 2.6–2.9 μm and coefficients of variation (CVs) of 13–17%. MCE was performed using a dispersed W/O emulsion phase and a 5 mM phosphate buffer containing 1% (w/w) decaglycerol monolaurate and 10–30% (w/v) D(+)-glucose as an outer aqueous phase. Monodisperse W/O/W emulsions containing W/O droplets with average diameters of 26.0–31.5 μm and CVs below 10% were successfully formulated via an asymmetric straight-through MC array at a low hydrophobic emulsifier concentration, regardless of l-ascorbic acid concentration. The W/O droplets dispersed in these monodisperse W/O/W emulsions were physically stable in variation of average diameter and CV for more than 10d of storage at 4 °C. The monodisperse W/O/W emulsions also exhibited l-ascorbic acid retention exceeding 80% during storage.