The effect of storage temperature on recrystallization and
glass transition temperature (T
g)
of
nonwaxy and waxy rice starch gel systems containing 60% moisture
content was investigated by
differential scanning calorimetry to understand the relationship
between them. The nucleation
and propagation for the recrystallization process were determined by
recrystallization degree
obtained from crystallite melting enthalpy changes during storage.
The recrystallization rate for
both rice starch gels within 3 days of storage and its temperature
dependence were analyzed by
Avrami and Arrhenius equations. The maximum nucleation and
propagation for recrystallization
of both rice starch gel systems occurred at 4 °C and 30 °C,
respectively. The T
g slightly
increased
with increasing recrystallization degree, and the highest
T
g was observed in the maximum
recrystallization temperature ranges. The
T
g and recrystallization rate of nonwaxy rice
starch gel
were changed more than those of the waxy one, while the higher
activation energy and Q
10 value
were shown in waxy rice starch gel.
Keywords: Recrystallization; glass transition; rice starch gel; nucleation;
propagation; Avrami
equation; Arrhenius equation
A cooling crystallization process with pH control was proposed to produce L-methionine (L-Met) agglomerates with improved bulk densities. L-Met was crystallized upon increasing the pH of an acidic L-Met solution by the injection of an electrolyte aqueous solution. Considering factors including the salting-out effect of the cation and hydrogen ion acceptability of the anion, sodium acetate was selected as an electrolyte. When acetate ions were added to the acidic L-Met solution, supersaturation was generated by the pH increase owing to the protonation of acetate ions. It was found that, as the decreasing rate of hydrogen ion concentration was faster, the metastable zone width, represented as a function of hydrogen ion concentration, increased and denser agglomerates were formed. Furthermore, when the suspension was cooled subsequently, L-Met agglomerates with the bulk density of 760 g/L were obtained, which was about 4-fold higher than that of hollow-structured agglomerates produced from a neutral L-Met solution by only the slow cooling process.
A reactive
crystallization process induced by acidification of
azilsartan disodium salt was proposed to produce sub-micron-sized
crystals. In the present work, azilsartan crystals were obtained by
mixing two aqueous solutions of azilsartan disodium salt (ADS solution)
and acetic acid (AA solution). When ADS solution was injected into
AA solution, the crystalline azilsartan (type I), the thermodynamically
stable form, could be obtained by the phase transformation of amorphous
intermediates of azilsartan initially precipitated. Azilsartan crystals
transformed from amorphous phase were found to be much smaller than
those obtained directly with no transformation by addition of AA solution
into ADS solution. The spectra of ATR-FTIR and particle counts from
the focused beam reflectance measurement (FBRM) were utilized to investigate
the effect of temperature on the transformation process. Final crystal
size of azilsartan was found to be influenced by the relative scale
of dissolution time for amorphous intermediates. Furthermore, the
recovery of azilsartan crystals was found to be strongly affected
by the final pH of mixed suspension. Finally, azilsartan crystals
with size of about 500 nm and the recovery of higher than 90% were
successfully produced from the proposed process with pH 5 mixed suspension
at 20 °C.
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