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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 10Â wt% whey protein isolate (WPI) in buffer solution (pH 7.0, 100Â mM 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 (90Â Â°C for 30Â min) 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 (>Â 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.
âº Solid-like lipid phases can be formed by aggregation of protein microspheres. âº The gel strength increases with increasing water content and thermal processing. âº These systems may be useful for creating low transâfat and saturated fat lipids.
Journal: Food Research International - Volume 48, Issue 2, October 2012, Pages 544-550