More reasons to add less salt - NaCl's unfavourable impact on glass transition and moisture sorption of amorphous maltose-NaCl blends

摘要

Adding NaCl to maltose depressed the glass transition temperature (T-g) of freeze-dried maltose-(dissociated) NaCl powder (by up to 9.1 degrees C at 10%mol addition level) but did not impact sorption isotherm in the water activity (a(w)) range of 0.1-0.3. Above 2%mol NaCl, moisture and NaCl had an antagonistic effect on T-g depression of freeze-dried maltose-NaCl powder. According to linear and Flory-Fox models, T-g increased linearly with mixtures' molecular weight. T-g and sorption isotherm curves were then combined to determine the a(w) at which glass transition occurs at various storage temperatures (i.e. critical a(w)). From the combined curve, critical a(w) decreased linearly with increased NaCl concentration in the mixture. Furthermore, the critical a(w) depression was steeper at higher temperatures. Finally, neither processing (dry mixing versus freeze drying) nor NaCl concentration affected the crystallization kinetics of amorphous maltose during dynamic humidification (0 to over 90% relative humidity) at 25 degrees C.