Controlling the rheological properties of W₁/O/W₂ multiple emulsions using osmotic swelling: Impact of WPI-pectin gelation in the internal and external aqueous phases

The purpose of this study was to create W₁/O/W₂ Multiple Emulsions by controlled osmotic swelling, and gelation of whey protein isolate (WPI) and high methoxy pectin (HMP) microspheres in internal and external acidic aqueous phases. Three different kinds of W₁/O/W₂ multiple emulsions (ME) were prepared, with 8 wt.% Polyglycerol polyricinoleate (PGPR) in their oil phases, with WPI and HMP in internal and external aqueous phases (250 mM NaCl, pH 3.5): (i) ME1: The inner aqueous phase (W₁) contained 40% buffer solution, while W₂ consisted of 10% WPI and 2% HMP; (ii) ME2: W₁ contained 10% WPI, with 2% HMP (250 mM NaCl) in W₂; (iii) ME3: 10% WPI and 2% HMP in W₁, while W₂ contained 1% Tween 80. The original multiple emulsions were diluted by different factors (1:0 to 1:5 with citrate buffer solution), and subject to thermal treatment from 25 to 90 °C to compare their microstructural and rheological properties. It was observed that the ME1 emulsion had higher viscosity and shear modulus than for other emulsions. After dilution however, the shear viscosity of ME3 was higher than ME1 and ME 2 at intermediate shear rates, which showed that the emulsions were osmotically well controlled in internal aqueous phases. Optical and confocal microscopy also supported our rheological measurements with evidence of WPI-HMP gelation, and osmotic swelling, in original and in swollen multiple emulsions. The results of this work may provide useful information about the encapsulation of bioactive compounds, in internal and external aqueous phases, for the development of healthier reduced-fat products in food industry.