Fabrication and characterization of gel-in-oil-water (G/O/W) double emulsion stabilized by flaxseed gum/whey protein isolate complexes

The aim of this study was to fabricate stable water-in-oil-in-water double emulsions with gelled internal water phase (G/O/W emulsion). The polyglycerol polyricinoleate (PGPR) was used as the lipophilic emulsifier and flaxseed gum (FG) /whey protein isolate (WPI) electrostatic complexes were used as the hydrophilic emulsifier. The rheological results showed that W1 became gelled when the FG concentration reached 0.4 wt%. Increased concentrations of FG in W1 significantly enhanced the stability of W1/O/W2 emulsions, accompanied with the diminution in droplet size and increased viscosity. It could be attributed to the strong interfacial activity and thickening effect of FG. Optical and confocal microscopy confirmed the formation of W/O/W emulsion structure and supported the particle size results. The maximum complex formation between FG and WPI occurred at pH 3.8, with the mass ratio of 1:1. In comparison to WPI, the complex of FG/WPI exhibited a significant improvement in the stability of G/O/W double emulsions. The storage stability test showed that the G/O/W emulsion fabricated with 0.8 wt% FG and 0.5 wt% FG/WPI complexes showed the highest stability without phase separation or oil-off phenomenon within 28 days. Consequently, the incorporation of FG (≥0.4 wt%) in W1 and utilization of FG/WPI complexes could be considered as a new strategy for obtaining W/O/W emulsions with long-term storage stability.