RH-temperature phase diagrams of hydrate forming deliquescent crystalline ingredients

•Created RH-temperature phase diagrams of sodium sulfate, glucose, and citric acid.•Developed water activity method to measure the anhydrate-hydrate phase boundary.•Determined the peritectic temperature of sodium sulfate, glucose, and citric acid.•Anhydrates can deliquesce prior to forming hydrates at some RH-temperature conditions.

Several common deliquescent crystalline food ingredients (including glucose and citric acid) are capable of forming crystal hydrate structures. The propensity of such crystals to hydrate/dehydrate or deliquesce is dependent on the environmental temperature and relative humidity (RH). As an anhydrous crystal converts to a crystal hydrate, water molecules internalize into the crystal structure resulting in different physical properties. Deliquescence is a solid-to-solution phase transformation. RH-temperature phase diagrams of the food ingredients alpha-d-glucose and citric acid, along with sodium sulfate, were produced using established and newly developed methods. Each phase diagram included hydrate and anhydrate deliquescence boundaries, the anhydrate-hydrate phase boundary, and the peritectic temperature (above which the hydrate was no longer stable). This is the first report of RH-temperature phase diagrams of glucose and citric acid, information which is beneficial for selecting storage and processing conditions to promote or avoid hydrate formation or loss and/or deliquescence.