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Abstract: This study shows that controlled aggregation of acidic whey protein microspheres in water-in-oil (W/O) emulsions can be used to create semi-solid lipids. An acidic aqueous phase (10 g/100 g whey protein isolate, 100 mmol/L NaCl, pH 3.5) was homogenized with an oil phase (8 g/100 g polyglycerol polyricinoleate in soybean oil) to form a W/O emulsion. These emulsions were then heated (90 °C, 30 min) to induce thermal denaturation and gelation of the globular proteins in the internal aqueous phase, which promoted irreversible gelation of the overall W/O emulsion. Rheology measurements indicated that the resulting materials had paste-like properties: they were solid-like below a critical yield stress and fluid-like (shear-thinning) above this value. The apparent shear viscosity of the W/O emulsions increased with thermal treatment, aqueous phase content, and decreasing shear rate. W/O emulsion gels containing acidic aqueous phases were considerably weaker than those containing neutral aqueous phases due to the pH dependence of whey protein gelation. Controlled aggregation of whey protein microspheres within W/O emulsions may be a useful means of producing highly viscous or semi-solid lipids with low saturated and trans-fat contents for use in the food and other industries. [Copyright &y& Elsevier]

Abstract: The effect of heteroaggregation of oppositely charged protein microspheres dispersed within a liquid oil phase on the microstructure and rheological properties of water-in-oil (W/O) emulsions was evaluated. The aqueous phase of the initial W/O emulsions contained either 10% β-lactoglobulin or 10% lactoferrin (pH 7, 100mM NaCl). At this pH, β-lactoglobulin (BLG) is negatively charged while lactoferrin (LF) is positively charged. The oil phase consisted of a lipophilic non-ionic surfactant (8% polyglycerol polyricinoleate, PGPR) dispersed within soybean oil. Three 40% W/O emulsions were formed containing different types of protein microspheres: (i) BLG: 100% BLG droplets; (ii) LF: 100% LF droplets; and (iii) Mixed: 50% BLG droplets and 50% LF droplets. Prior to heating, the mixed emulsions had a higher shear viscosity, yield stress, and shear modulus than the BLG or LF emulsions, which suggested that electrostatic attraction led to the formation of a three-dimensional network of aggregated droplets. All three W/O emulsions underwent an irreversible fluid-to-solid transition when they were heated above ≈70°C. This phenomenon was attributed to thermal denaturation of the globular BLG and LF molecules within the aqueous phase promoting aggregation and network formation of the protein microspheres. After heating, the mixed emulsions had a higher shear viscosity, yield stress and shear modulus than the BLG or LF emulsions, suggesting that a stronger droplet network was formed due to electrostatic attraction. Shear rheology measurements of the W/O emulsions showed that the lipid phases formed after heating were non-ideal plastics characterized by a yield stress and shear thinning behavior. These results may facilitate the design of semi-solid or solid foods with reduced saturated- or trans-fat contents suitable for use in commercial 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]