Phase behavior and moisture sorption of deliquescent powders

Deliquescence lowering was investigated in powder blends of different particle sizes. Deliquescent compounds, widely used in edible products, were used to prepare two model blends: fructose–citric acid anhydrous (M1) and sucrose–sodium chloride (M2). The relationship between the water activity and the composition of each system was measured and used to build phase diagrams, from which information about the eutonic composition (EC) was extracted. Data were evaluated using five models (Raoult’s law, and the Ross, Ferro Fontán–Chirife–Benmergui, Zdanovskii–Stokes–Robinson, and extended Zdanovskii–Stokes–Robinson equations), and the extended Zdanovskii–Stokes–Robinson equation provided the best fit. The effects of formulation, compound ratio, particle size, degree of compaction, and storage RH on moisture sorption profiles were determined and varied for M1 and M2. The EC was 33:67 wt% citric acid:fructose for M1 and 16:84 wt% NaCl:sucrose for M2. Blending powders created sufficient particle intimacy to enable deliquescence lowering in both systems (the mutual deliquescence RH was 44.1% for M1 and 63.6% for M2), and the eutonic composition was the most susceptible to moisture-induced changes. The results of this study show that powder behavior in the presence of moisture can be largely predicted from equilibrium phase diagrams.