Influence of compression on water sorption, glass transition, and enthalpy relaxation behavior of freeze-dried amorphous sugar matrices

Impact of compression, physical aging, and freezing rate on the crystallization characteristics of an amorphous sugar matrix

“…These observations are quite typical for the crystallization of an amorphous sugar matrix (Aso et al, 1993;Karavas et al, 2005). However, our previous study (Imamura et al, 2011) demonstrated that the equilibrium water content of the compressed amorphous sucrose samples were ca. 40% lower than that of the control (uncompressed) samples, as shown in Table 3.…”

“…The deviations in the T g and T cry values for three independent experiments were within ±1.5°C of the average. Data reported in our previous study indicated that the temperature scanning rate had no effect on the T g and T cry values in the tested range between 1 and 10°C/min (Imamura et al, 2011).…”

“…In a typical experiment, the thoroughly dehydrated sample was gently ground into a powder using an agate mortar and pestle and then compressed using a hand-operated hydraulic compactor (SSP-10A, Shimadzu Rika Co., Tokyo, Japan). The compression was conducted at the compression pressure of 74 or 443 MPa for 5 min, under which conditions the changes in the T cry and hygroscopicity of freeze-dried sugar samples due to the compression have been found to be significant (Imamura et al, 2010(Imamura et al, , 2011. All procedures for the compression were done in an atmosphere of dry nitrogen at room temperature (25 ± 2°C).…”

“…All procedures for the compression were done in an atmosphere of dry nitrogen at room temperature (25 ± 2°C). Alternatively, the thoroughly dehydrated sample was stored at 50°C for 30 days (Imamura et al, 2011) so that the structural enthalpy of the sample matrix was fully relaxed (physically aged sample). The resulting samples, including the slowly-frozen and the compressed samples, were then rehumidified at 25 ± 1°C over saturated LiCl (RH 11%), CH 3 COOK (RH 23%), and MgCl 2 solutions (RH 33%).…”

“…The resulting samples, including the slowly-frozen and the compressed samples, were then rehumidified at 25 ± 1°C over saturated LiCl (RH 11%), CH 3 COOK (RH 23%), and MgCl 2 solutions (RH 33%). The water contents of the samples were determined by the gravimetric method (Imamura et al, 2011). The rehumidification was continued until the water content reached a constant level, the duration of which was only a single day for the uncompressed samples or several days for the samples compressed at 443 MPa (Imamura et al, 2011).…”