Interaction of environmental moisture with powdered green tea formulations: relationship between catechin stability and moisture-induced phase transformations.

This study investigated the effect of phase transformations of amorphous and deliquescent ingredients on catechin stability in green tea powder formulations. Blends of amorphous green tea and crystalline sucrose, citric acid, and/or ascorbic acid were analyzed by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), dynamic water vapor sorption, water activity measurements, and high-performance liquid chromatography (HPLC) after storage for up to 12 weeks at 0-75% relative humidity (RH) and 22 degrees C. The glass transition temperature (T(g)) of green tea was reduced to below room temperature (<22 degrees C) at 68% RH. Dissolution of deliquescent ingredients commenced at RH values below deliquescence points in blends with amorphous green tea, and these blends had greater water uptake than predicted by an additive model of individual ingredient moisture sorption. Catechin degradation was affected by T(g) of green tea powder and both dissolution and deliquescence of citric and ascorbic acids.