Monitoring dynamics of phase separation in oat beta–glucan⁄milk mixtures with ultrasonic and diffusing wave spectroscopy

N Sharafbafi1, SM Tosh2, M Alexander1, and M Corredig1 

1Department of Food Science, University of Guelph, Guelph, Ontario, Canada
2Agriculture and Agri-Food Canada, Guelph Food Research Center, 93 Stone Road West, Guelph, Ontario, Canada

Thermodynamic incompatibility and consequent phase separation of proteins and polysaccharides is a challenge in enrichment of dairy food products with high concentrations of soluble fiber. This is while understanding the structures formation upon mixing and monitoring dynamics of phase separation represent the opportunity to control and create novel structures including high contents of soluble fiber. Beta-glucan extracted from cell wall of cereal grains is a non-interacting polysaccharide, promoting cholesterol lowering and glycemic response with an intake of 0.75g/serving1. This amount is shown to result in phase separation and instability when added to milk and dairy food products2.
Model systems containing milk and beta-glucan were studied to determine the effect of concentration of protein and polysaccharide on the dynamics of phase separation. Indeed, while most reports on phase separating systems are limited to the development of a phase separation diagram and microstructure imaging, the mixtures were studied using ultrasonic and diffusing wave spectroscopy, to describe the details of the phase separation dynamics. These spectroscopic techniques are ideal to the study of structure formation in milk mixtures, as they can be carried out in situ, without dilution. There was an initial decrease in turbidity parameter (1/l*) and diffusion coefficient of particles in the samples with increasing beta-glucan concentration. At high enough concentrations of beta-glucan micro domains rich in protein formed. An increase in turbidity was noted over time, which indicated the development of phase separated domains. At concentrations >0.3% beta-glucan, the mixtures showed less changes over time, revealing retardation of the dynamics due to high viscosity developed in the continuous phase. The attenuation and velocity parameters measured by ultrasonic spectroscopy revealed the changes in the domains at longer length scales, confirming the higher stability of the mixtures at high concentrations of beta-glucan. It could be concluded that with using these spectroscopic techniques it is possible to describe in detail the molecular changes occurring to these concentration dependent mixtures, and enable fine-tuning the structural changes occurring in milk containing polysaccharides. 

References
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