Effect of fat hardness on large deformation rheology of emulsion-filled gels

The aim of this work was to investigate the impact on the texture properties of emulsion-filled gels when saturated solid fat is replaced by unsaturated liquid oil. Whey protein aggregate, gelatin and micellar casein, were chosen to form different types of gel matrices and the fat hardness was varied by selection of the fat type and variation of the temperature. As emulsifier, either whey protein aggregates, whey protein or sodium caseinate was used. Texture properties of the filled gels were investigated by uniaxial compression. The fracture properties were affected by the presence of emulsion droplets, however the effect of fat hardness was small. The presence of emulsion droplets (either liquid or solid) increases the gel stiffness as compared to the emulsion-free gel, indicating that the droplets are an active part of the gel. An increase in solid fat content led to a moderate increase in gel stiffness for whey protein aggregate gels, which was in agreement with predictions according to the Palierne model for the effect of fat hardness on the stiffness of the filled gels. For the gelatin and micellar casein gels, the magnitude by which the gel stiffness increased as a function of the solid fat content was much larger than expected on the basis of this model. Microscopical observation suggested that this was caused by an inhomogeneous distribution of the fat droplets, due to droplet aggregation or/and concentration of the droplets in gel strands, which increases the effective volume fraction of the droplets in the matrix.