Physical properties of simple and complex sugar systems.

Abstract

Honey, maple syrup and sugars during refining are examples of a complex solutions of concentrated sugars and other solutes. The physical properties of such systems are required for the design and optimization of processes and for the understanding of the behaviour of the final product. Literature shows limited data and even less rigorous analysis of the physical properties of concentrated sugar solutions. A fundamental thermodynamic approach provides an effective basis for the analysis and prediction of these properties. The main focus of this study was to consolidate physical property data for binary sugar systems, analyse the data using existing models, and propose newer models and equations to predict the physical properties of complex sugar solutions like honey.

In order to approach this, the physical properties density, viscosity, electrical conductivity, refractive index, mutarotation and water activity of binary solutions and sugar mixtures ranging from invert sugar solutions to model honey solutions with acid and salt were measured. Models that have been applied to sugar systems were reviewed. An equation for density based on the apparent densities of sugars in solution was validated. A viscosity equation that was extended from previous work with concentrated milk systems, was found to be very effective over the full concentration range of complex sugar solutions. Effects of viscosity on the electrical conductivity of sugar systems were analysed and a model was proposed for electrical conductivity in sugar systems. Hydration theory based on water activity measurements was applied to binary sugar systems and extended to model honey systems. Mixing theories were applied to the calculation of refractive index of solutions and also used as a tool to confirm the solid mass fraction in solutions.

The effect of mutarotation of sugars in viscous sugar solutions was studied using a new NMR technique that was validated using polarimetric measurements. In this study it was found that the mutarotation of glucose was not affected by the viscosity of the solution.

Past and new data and resulting equations provide a solid basis for future modelling and simulation of crystallization in these systems.