Influence of matrix inhomogeneity on the rheological properties of emulsion-filled gels

The aim of this work was to determine the effect and magnitude of matrix inhomogeneity on the rheological properties of emulsion-filled gels. To this end, we have investigated the rheological properties in casein gels containing different volume fractions of dispersed fat droplets with varying hardness. Rheological properties of the filled gels were investigated by uniaxial compression. Matrix inhomogeneity was controlled by changing the casein concentration, and was quantified by confocal laser scanning microscopy (CLSM) and image analysis. CLSM images showed that the matrix becomes more inhomogeneous when the protein concentration decreases and image analysis was used to quantify this inhomogeneity. As the dispersed fat droplets bind to the proteins (active droplets), the droplets are located more in the casein-rich areas. The inhomogeneous distribution of the casein micelles led to an accumulation of the dispersed fat droplets in the gelled micellar casein regions, thereby increasing the effective volume fraction of the droplets. This increase in the effective volume fraction of the droplets was higher for lower casein concentrations, due to a higher degree of inhomogeneity, resulting in a larger effect in reinforcing the gel compared to more homogeneous systems. These results may be used for designing structures to decrease the fat content or replace solid fat by liquid oil.