Crystal Properties and Hydrate Formation of Phytostanols and Phytosterols

Phytosterols, and their saturated analogs phytostanols, exist in different hydrated forms known as monohydrate (ca. 4 wt % water), hemihydrate (ca. 2 wt % water), and anhydrate (0 wt % water), all having different properties. In the current research, the solid-state characteristics of phytosterols and phytostanols were studied, with a focus on the hydrate formation and stability. The solid-state analysis was conducted using powder XRD, TGA, DSC, elemental analysis, and SEM. To the best of our knowledge, this is the first time that crystal lattice and unit cell parameters of β-sitostanol have been investigated. Surprisingly, we observed that different hydrate forms can be modified solely by adjusting the drying and storage conditions of the crystals. This implies that the crystallization conditions themselves, especially the solvent system, can be chosen based purely on crystal purity, preferred particle specifications and yield obtained. Anhydrous phytosterols are more stable against atmospheric moisture when stored at ambient conditions compared to anhydrous phytostanols, which absorb moisture remarkably quickly, within as little as an hour. The findings regarding the differences in stability and hygroscopicity tendencies are important aspects for storage and usage of the material in further applications.