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Abstract: The objective of this work was to prepare novel microstructures and textures by controlled osmotic swelling and gelation of multiple (W1/O/W2) emulsions. Initially, multiple emulsions were prepared: internal aqueous phase (W1) containing 20wt.% whey protein isolate (WPI) in buffer solution (pH7, 250mM NaCl); oil phase (O) containing 6wt.% polyglycerol polyricinoleate (PGPR) in soybean oil; and external aqueous phase (W2) containing 250mM NaCl and 1wt.% Tween 80. These W1/O/W2 emulsions were then subjected to different degrees of dilution (1:0 to 1:5 with salt-free buffer) and thermal treatment (30 to 90°C) to induce swelling and/or gelation of the internal aqueous phase. W1/O/W2 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. [Copyright &y& Elsevier]

Abstract: Controlled aggregation of protein microspheres in water-in-oil (W/O) emulsions was used to form semi-solid lipid materials. The aqueous phase consisted of 10wt% whey protein isolate (WPI) in buffer solution (pH 7.0, 100mM NaCl). The oil phase consisted of a lipophilic nonionic surfactant (8 wt % polyglycerol polyricinoleate, PGPR) dispersed in a liquid oil (soybean oil). Lipid phases containing protein microspheres were formed by homogenization of the oil and aqueous phases to form a W/O emulsion followed by heating (90°C for 30min) to promote gelation of the WPI in the aqueous phase. Temperature-scanning dynamic shear measurements showed that the W/O emulsions underwent an irreversible liquid-to-solid transition when heated above the thermal denaturation temperature of WPI, which was attributed to protein gelation and microsphere aggregation. Optical microscopy indicated that a three-dimensional network of aggregated protein microspheres was formed at high aqueous phase contents (>30 wt %). Shear rheology measurements (shear stress versus shear rate) indicated that these structured emulsions were non-ideal plastic-like materials. The apparent shear viscosity increased with thermal treatment, increasing aqueous phase content, and decreasing shear rate. The structured W/O emulsions developed in this study may be useful materials for the development of foods with highly viscous or gel-like lipid phases, but low saturated or trans-fat contents. [Copyright &y& Elsevier]