The effect of high pressure homogenization on emulsions containing oat β-glucan : a study of viscosity, stability and molecular weight

Abstract: This master thesis project has been conducted in cooperation with Lantmännen AB who are producers of PromOat® - an oat β-glucan powder concentrate. The main objective of this thesis was to investigate the properties of emulsions containing PromOat® oat β-glucan, focusing on the viscosity, stability, and molecular weight before and after high pressure homogenization (HPH) at pressures of 100, 150 and 200 bars. The viscosity of emulsions was measured on a shear rate range from 0.1 to 100/s and extrapolated to zero shear force. Results showed a significant decrease in viscosity with HPH and its increasing pressures in both research and control samples, indicating its disruptive character on β-glucan aggregates. Stability analysis of oat β-glucan emulsions through backscattering measurements indicated no significant differences among the research samples, suggesting that HPH did not affect the overall stability of the emulsions. Obtained results in light of documented loss of viscosity with HPH suggest stabilizing effect of oil droplet size reduction. Control samples showed variations in backscattering behavior, indicating the influence of HPH on stability. Light microscopy images revealed smaller oil droplet sizes in emulsions subjected to HPH pressures, confirming its well documented disruptive effect on oil droplets. Asymmetrical flow field-flow fractionation (AF4) analysis of oat β-glucan samples using multi-angle light scattering (MALS) and differential refractive index (dRI) detectors showed an increase in average molar mass and average root-meansquare radius with higher HPH pressures, suggesting that re-aggregation of oat β-glucan had occurred under different circumstances than in non-homogenized sample which manifests itself in increased average molar mass and root-meansquare radius. In conclusion, HPH was found to significantly decrease the viscosity and disrupt the aggregate structure of oat β-glucan in emulsions. The overall stability of the emulsions was not significantly affected. The molecular properties of βglucan, such as molar mass and root-mean-square radius, were influenced by HPH treatment. These findings may contribute to a better understanding of the HPH impact on oat β-glucan properties in emulsions.