Effect of outer water phase composition on oil droplet size and yield of (w₁/o/w₂) double emulsions

In this study the effect of various emulsifiers (whey protein isolate (WPI), Na-caseinate, and Tween 20) and thickeners (xanthan and pectin) present in the outer water phase, w₂, on oil droplet size and yield of the inner water phase, w₁, of (w₁/o/w₂) double emulsions was investigated. Double emulsions stabilized by Tween 20 had smaller oil droplet sizes and higher yields in comparison to emulsions stabilized by WPI and Na-caseinate. Gelation of the inner water droplets w₁ increased yield by 20% for all emulsifiers. Upon the addition of thickeners, the increasing viscosity of the outer water phase, w₂, facilitated oil droplet breakup. This resulted in smaller oil droplets and lower yields. When pectin was used as a thickener, in comparison to xanthan, an additional decrease in yield was observed. The yield decreased to values close to zero indicating that all inner water droplets w₁ were lost during emulsification. We conclude that type of hydrophilic emulsifier, properties of inner water droplets, viscosity ratio of continuous and dispersed phase, as well as type of thickener influence oil droplet size and yield of w₁ phase of double emulsions. This work provides a better understanding of how composition influences the properties of double emulsions and how this can be used to design double emulsions as fat replacers in more complex food systems.