Thermodynamics of Isomers and Solubility Prediction in Multicomponent Sugar Solutions

A rigorous thermodynamic modeling framework for a system of isomers in chemical equilibrium is developed and applied to the lactose-water system. Through the knowledge of the water activity and of the liquid phase composition, thermodynamically consistent expressions for the activity coefficients of lactose isomers have been derived and used in the context of solid-liquid equilibria to predict the dependence of the saturation concentration of α-lactose on the dissolved β-lactose concentration. We also developed a comprehensive first-principles model that accurately describes the dissolution dynamics of α-lactose monohydrate. The data support the hypothesis that the sugar activity coefficients are a stronger function of the total sugar content rather than of the sugar solution composition. The activity coefficient expressions have been used to quantitatively predict the effect of glucose, galactose, and sucrose on the solubility of α-lactose monohydrate.