Controlling W/O/W multiple emulsion microstructure by osmotic swelling and internal protein gelation

The objective of this work was to prepare novel microstructures and textures by controlled osmotic swelling and gelation of multiple (W-1/O/W-2) emulsions. Initially, multiple emulsions were prepared: internal aqueous phase (W-1) containing 20 wt.% whey protein isolate (WPI) in buffer solution (pH 7,250 mM NaCl); oil phase (O) containing 6 wt.% polyglycerol polyricinoleate (PGPR) in soybean oil; and external aqueous phase (W-2) containing 250 mM NaCl and 1 wt.% Tween 80. These W-1/O/W-2 emulsions were then subjected to different degrees of dilution (1:0 to 1:5 with salt-free buffer) and thermal treatment (30 to 90 degrees C) to induce swelling and/or gelation of the internal aqueous phase. W-1/O/W-2 emulsions had appreciably higher viscosities than O/W emulsions with similar fat contents, which was attributed to the increase in effective particle volume associated with the water droplets trapped inside the fat droplets. Heat treatment increased the apparent shear viscosity of the emulsions, which was attributed to thermal denaturation and aggregation of the globular proteins altering the structure and interactions in the system. The strategies used to alter the microstructure and rheology of the multiple emulsions utilized in this study may be useful for the production of foods with novel textures or reduced-fat products. (C) 2013 Elsevier Ltd. All rights reserved.