Structuring Properties of Beta-glucan in Dairy Gels: Control of Phase Separation
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.