In this thesis, the macroscopic phase separation of milk proteins and high molecular weight oat beta-glucan was investigated. A better knowledge of this model system will improve our ability to control structure in dairy gels containing nutritionally significant concentrations of dietary fiber. A phase behaviour diagram was obtained experimentally, and the results were then modelled using theoretical models based on thermodynamic incompatibility between casein micelles and beta-glucan and demonstrated that casein micelles are the main contributors to the instability of these mixtures. Water in water emulsion systems formed at high concentrations of protein and beta-glucan upon mixing, and were visualized using confocal scanning laser microscopy. For the first time, the dynamics of phase separation of these mixtures were followed using diffusing wave and ultrasonic spectroscopy, as well as with rheological methods. The work explored the formation of different bi-continuous networks by controlling the gelation of the protein phase using chymosin. This enzymatic reaction specifically destabilizes the casein micelles, allowing for a kinetic control of protein gelation within or between phase separated domains. The addition of -carrageenan and the effect of shear on the mixtures were evaluated as possible strategies for controlling the growth of the phase separated domains in dairy gels containing concentrations of beta-glucan high enough to be nutritionally significant. Results indicated that different structures could be obtained depending on the processing conditions, for example, the mode of addition of the polysaccharides or the pre-shearing conditions. This work represents a novel approach for incorporating nutritionally significant concentrations of beta-glucan in dairy foods, and serves as proof of concept for further development of an important application area linked to the development of reduced fat dairy products with additional health benefits. / Canadian Dairy Commission (CDC) and Natural Sciences and Engineering Research Council (NSERC)

This thesis describes the development and applications of an extension of DWS which enables the recovery of ‘localized’ mechanical properties, in a specified region of a complex jelly-like object which is inhomogeneous, marked out by the focal volume of an ultrasound transducer, also called the region-of-interest (ROI). Introduction of the sinusoidal forcing creates a sinusoidal phase variation in the detected light in a DWS experiment which modulates the measured intensity autocorrelation, g2 (τ ). Decay in the modulation depth with τ is used to recover the visco-elastic spectrum of the material in the ROI. En route to this, growth of the mean-squared dis- placement (MSD) with time is extracted from the modulation depth decay, which was verified first by the usual DWS experimental data from an homogeneous object with properties matching those in the ROI of the inhomogeneous object and then those obtained by solving the generalized Langevin equation (GLE) modelling the dynamics of a typical scattering centre in the ROI. A region-specific visco-elastic spectral map was obtained by scanning the inhomogeneous object by the ultrasound focal volume. Further, the resonant modes of the vibrating ROI were measured by locating the peaks of the modulation depth variation in g2(τ ) with respect to the ultrasound frequency. These resonant modes were made use of to recover elasticity of the material of the object in the ROI. Using a similar strategy, it was also shown that flow in pipe can be detected and flow rate computed by ‘tagging’ the photons passing through the pipe with a focussed ultrasound beam. It is demonstrated, both through experiments and simulations that the ultrasound-assisted technique devel- oped is better suited to both detect and quantitatively assess flow in a background of Brownian dynamics than the usual DWS. In particular, the MSD of particles in the flow, which shows forth a super-diffusive dynamics with MSD growing following τ α with α < 2, is captured over larger intervals of τ than was possible using existing methods. On the theoretical front, the main contribution is the derivation of the GLE, with multiplicative noise modulating the interaction ‘spring constant’. The noise is derived as an average effect of the micropolar rotations suffered by the ‘bath’ particles on the ‘system’ particle modelled. It has been shown that the ‘local’ dynamics of the system particle is nontrivially influenced by the dynamics, both translation and rotation, of ‘nonlocal’ bath particles.