A review of the recent literature on crystallization of the commercial sugars (fructose, glucose, lactose, and sucrose) is presented. Topics include: NUCLEATION--The formation of the crystalline phase from supersaturated solutions can occur by either a spontaneous or a forced nucleation mechanism. Recent work on the mechanisms, kinetics, and impact of both heterogeneous and secondary (contact) nucleation is discussed. GROWTH--Recent studies on the mechanisms and kinetics of crystal growth will be reviewed. This discussion includes work on the growth rate dispersion exhibited by these sugars. EFFECTS OF IMPURITIES AND ADDITIVES--The presence of impurities and additives (including mixed sugar systems) affects both the nucleation and growth steps. A discussion of the recent work in this area is included. Emphasis is placed on the relationship between these crystallization phenomena and the solution structure for comparison purposes.
Sucrose crystallization in thin films (50-55 µm) was studied, using a videomicroscopy technique, at conditions encountered during hard panning processes. No nucleation occurred in unseeded films, while a linear increase in seeded crystals occurred during drying. Crystal growth rate increased with temperature (25-30ЊC) and with air velocity (2.4-12.5 m/sec), but did not change with varying sucrose concentrations (70-76% w/w) and relative humidities (0-66% at 30ЊC). FD&C Yellow No. 5 food coloring in the dye form (0.05-0.5 g/100 mL) showed no effects while similar concentrations in the lake form inhibited crystal growth rate.
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