Characterization of frozen glucose solutions

Effects of Mono-, Di-, and Tri-Saccharides on the Stability and Crystallization of Amorphous Sucrose

Amorphous sucrose is a component of many food products but is prone to crystallize over time, thereby altering product quality and limiting shelf-life. A systematic investigation was conducted to determine the effects of two monosaccharides (glucose and fructose), five disaccharides (lactose, maltose, trehalose, isomaltulose, and cellobiose), and two trisaccharides (maltotriose and raffinose) on the stability of amorphous sucrose in lyophilized two-component sucrose-saccharide blends exposed to different relative humidity (RH) and temperature environmental conditions relevant for food product storage. Analyses included X-ray diffraction, differential scanning calorimetry, microscopy, and moisture content determination, as well as crystal structure overlays. All lyophiles were initially amorphous, but during storage the presence of an additional saccharide tended to delay sucrose crystallization. All samples remained amorphous when stored at 11% and 23% RH at 22 °C, but increasing the RH to 33% RH and/or increasing the temperature to 40 °C resulted in variations in crystallization onset times. Monosaccharide additives were less effective sucrose crystallization inhibitors relative to di- and tri-saccharides. Within the group of di- and tri-saccharides, effectiveness depended on the specific saccharide added, and no clear trends were observed with saccharide molecular weight and other commonly studied factors such as system glass transition temperature. Molecular level interactions, as evident in crystal structure overlays of the added saccharides and sucrose and morphological differences in crystals formed, appeared to contribute to the effectiveness of a di- or tri-saccharide in delaying sucrose crystallization. In conclusion, several di- and tri-saccharides show promise for use as additives to delay the crystallization kinetics of amorphous sucrose during storage at moderate temperatures and low RH conditions. PRACTICAL APPLICATION: Amorphous sucrose is desirable in a variety of food products, wherein crystallization can be problematic for texture and shelf-life. This study documents how different mono-, di-, and tri-saccharides influence the crystallization of sucrose. Monosaccharide additives were less effective sucrose crystallization inhibitors relative to di- and tri-saccharides. These findings increase the understanding of how different mono-, di-, and tri-saccharide structures and their solid-state properties influence the crystallization of amorphous sucrose and show that several di- and tri-saccharides have potential for use as sucrose crystallization inhibitors.

Controlled crystallization of the lipophilic drug fenofibrate during freeze-drying: elucidation of the mechanism by in-line Raman spectroscopy

We developed a novel process, "controlled crystallization during freeze-drying" to produce drug nanocrystals of poorly water-soluble drugs. This process involves freeze-drying at a relatively high temperature of a drug and a matrix material from a mixture of tertiary butyl alcohol and water, resulting in drug nanocrystals incorporated in a matrix. The aim of this study was to elucidate the mechanisms that determine the size of the drug crystals. Fenofibrate was used as a model lipophilic drug. To monitor the crystallization during freeze-drying, a Raman probe was placed just above the sample in the freeze-dryer. These in-line Raman spectroscopy measurements clearly revealed when the different components crystallized during freeze-drying. The solvents crystallized only during the freezing step, while the solutes only crystallized after the temperature was increased, but before drying started. Although the solutes crystallized only after the freezing step, both the freezing rate and the shelf temperature were critical parameters that determined the final crystal size. At a higher freezing rate, smaller interstitial spaces containing the freeze-concentrated fraction were formed, resulting in smaller drug crystals (based on dissolution data). On the other hand, when the solutes crystallized at a lower shelf temperature, the degree of supersaturation is higher, resulting in a higher nucleation rate and consequently more and therefore smaller crystals. In conclusion, for the model drug fenofibrate, a high freezing rate and a relatively low crystallization temperature resulted in the smallest crystals and therefore the highest dissolution rate.

Particle size dependent molecular rearrangements during the dehydration of trehalose dihydrate in situ FT-Raman spectroscopy

PURPOSE

(1) To characterise the different phases of trehalose using FT-Raman spectroscopy. (2) To monitor the changes in the structure of trehalose dihydrate on isothermal heating at 80 degrees C.

METHODS

Different phases of trehalose were prepared and FT-Raman spectra obtained. Trehalose dihydrate was sieved to < 45 microns and > 425 microns particle size fractions and FT-Raman spectra were obtained at various time intervals during heating at 80 degrees C.

RESULTS

During heating at this temperature, the spectra of a < 45 microns particle size fraction showed a loss of peak resolution with time and after 210 minutes resembled the spectrum of amorphous trehalose prepared by lyophilisation, indicating that the material was rendered amorphous by heating. In contrast, spectra obtained from a > 425 micron particle size fraction altered with time and became characteristic of the crystalline anhydrate. The approximate kinetics of this transformation to the anhydrate were monitored by analysis of peak intensity ratios with time. A two state rearrangement was indicated; some functional groups appeared to manoeuvre into the spatial arrangement found in the anhydrate initially before the rest of the ring structure relaxed into this conformation. This may be due to some parts of the molecule being immediately affected by the loss of the water molecules on dehydration prior to the subsequent reorientation of the entire molecule into the anhydrate crystal lattice.

CONCLUSIONS

The < 45 micron particle size fraction becomes disordered on dehydration induced by heating at 80 degrees C whilst the > 425 micron particle size fraction crystallises to the anhydrate under the same conditions.