Influence of Oil Phase and Emulsifier on Single and Double Emulsions: Formation, Stability, Encapsulation Efficiency, and Antioxidant Activity

Water-in-oil-in-water (W₁/O/W₂) emulsions consist of the internal aqueous droplets inside the lipid droplets (W₁/O emulsions), which are dispersed within the outer aqueous phase. The double emulsions exhibit structural complexity of multiple phases and two contradictory interfaces, necessitating improved stability through strategic modification of the oil phase as well as both the inner and outer aqueous phases. In this study, gel-in-oil (G/O) emulsions were formulated using sunflower oil, palm oil, or a tristearin–palm oil blend and achieved by gelation of the inner aqueous phase consisting of whey protein and blueberry extract. The primary emulsions were characterized in terms of size distribution and viscoelastic properties. Subsequently, gel-in-oil-in-water (G/O/W) emulsions were prepared using either Tween 80 or a combination of whey protein isolate (WPI) and xanthan gum (XG) in the outer aqueous phase. The formation and physical stability of the resulting double emulsions were evaluated based on microstructure, yield, viscoelastic properties, anthocyanin encapsulation, and antioxidant activity. It is noted that the encapsulation of anthocyanins and water retention were not consistent in the inner gelled phase. Encapsulation efficiency of anthocyanins ranged from 75% to 92% within the inner gelled phase, while a yield of double emulsions increased from 5.88% in Tween 80 and sunflower oil formulations to 77.09% in WPI/XG and tristearin–palm oil formulations. Moreover, the WPI/XG combination with structured lipids demonstrated superior viscoelastic strength and improved resistance to creaming and centrifugal stress. In WPI/XG-stabilized double emulsions, the inclusion of tristearin into palm oil resulted in a sustained increase in the antioxidant activity within the outer aqueous phase. These findings highlight the synergistic roles of oil structuring and biopolymer interfacial engineering in the design of double emulsions for potential applications in food preservation.