Stability and release properties of double emulsions for food applications

Water-in-oil-in-water (W₁/O/W₂) double emulsions (DEs) containing gelatin and sodium chloride (NaCl) in the inner aqueous phase were developed for controlled release applications. Emulsions were prepared with water and canola oil, as well as with polyglycerol polyricinoleate and polysorbate 80 as emulsifiers for the primary water-in-oil (W₁/O) emulsion and secondary W₁/O/W₂ emulsions, respectively. All DEs containing both NaCl and gelatin were stable against sedimentation for the month-long study whereas control emulsions (with either no NaCl or gelatin) showed visual phase separation. The average oil globule size in freshly-prepared DEs grew from ∼45 to 70 μm with an increase in salt load from 2 to 8% (w/w), and changed little after 1 month. Besides its role in stabilization, NaCl was also used as a marker to evaluate DE release behaviour. The salt diffusion coefficient obtained using Fujita’s model rose from 4.7 to 6.0 × 10⁻¹¹ cm²/s with increasing NaCl concentration in the DEs from 2 to 8% (w/w). All stable DEs showed a high salt retention in the inner aqueous phase (>94%) after 1 month of storage at 4 °C. These results demonstrated the synergistic action of a gelling agent and electrolyte in stabilizing and modulating the release behaviour of NaCl from W₁/O/W₂ DEs.