Graeme Gillies

Influence of the Volume Fraction, Size and Surface Coating of Hard Spheres on the Microstructure and Rheological Properties of Model Mozzarella Cheese

This study investigated the influence of model filler particles (glass beads) on the microstructure and rheological properties of Mozzarella cheese. Model Mozzarella cheese composites with increasing volume fractions of glass beads of various sizes and surface properties were processed in a Rapid Visco Analyser (RVA). Confocal laser scanning microscope images showed that all the hard spheres were dispersed in the protein phase, rather than in the fat phase. Dynamic oscillatory rheology revealed that the volume fraction of the glass beads had a major influence on the complex modulus (G*) of the cheese composites, whereas the size and the coating of the glass beads had no influence. However, the zero shear viscosity (η0), measured using the creep-compliance test, was affected by both the size and the volume fraction of the glass beads. This indicated that there were some interactions between the glass beads and the cheese matrix. Filler–matrix interactions played a major role in the fracture properties of the cheese composites. The fracture stress (σf) was highly dependent on the coating and the size of the glass beads. Simple equations for filled gels from the literature fitted well with the experimental results and could be successfully applied for future predictions. According to this study, the transfer of knowledge from filled polymer composites to model cheese appears relevant. This can provide a good basis for designing new dairy product structures.

Simple transmission measurements discriminate instability processes in multiple emulsions

Water-in-oil-in-water double emulsions (W1/O/W2) consist of water droplets (W1) dispersed in oil globules (O), which are then redispersed in an external aqueous phase (W2). This paper reports multiple light scattering investigations on W1/O/W2 double emulsions, the inner W1/O emulsion being a concentrated micron sized inverse emulsion, and the outer O/W2 emulsion being a dense direct emulsion. Double emulsions are inherently unstable, and changes of structure can arise from many processes such as instability of both the W1/O and the O/W2 emulsions, and an exchange of water in between the two aqueous phases. Diffuse Transmission Spectroscopy (DTS) is used to follow the structural evolution of these complex systems. We show here that DTS can discriminate between some of the different instability processes of double emulsions. We design three different systems where one of the destabilization processes is dominating, and build different models accounting for the temporal evolution of the turbidity of the system. We find that these models scale well with the experimental data.