Amorphous Sucrose Research Articles

Effect of Starch on the Molecular Mobility of Amorphous Sucrose

Molecular mobility in amorphous solid biomaterials is modulated by the composition and environment (primarily temperature). Phosphorescence of the triplet probe erythrosin B was used to generate a mobility map within amorphous sucrose films doped with starch ranging from 0.001 to 0.1 g starch/g sucrose. Data on the emission energy and lifetime of erythrosin B in sucrose and sucrose-starch films over the temperature range from 5 to 100 °C indicates that starch influences the molecular mobility as well as dynamic site heterogeneity of amorphous sucrose in a dose-dependent manner. At a starch/sucrose weight (wt) ratio below 0.005, both emission energy and lifetime decreased, and both the dipolar relaxation rate and nonradiative quenching rate k(TS0) increased, indicating that starch increased the matrix molecular mobility. At a ratio above 0.005, both emission energy and lifetime increased, and the dipolar relaxation rate and nonradiative quenching rate decreased, indicating that starch decreased the matrix mobility both in the glass and in the melt. The mobility showed a minimum value at a ratio of 0.01. The interactions existing in the sucrose-starch matrix are considered as the determining factor to influence the molecular mobility of sucrose-starch mixtures. Changes in the distribution of emission energies (emission bandwidth) and lifetimes indicated that starch increased the spectral heterogeneity at high contents while showing insignificant change or a slight decrease in the heterogeneity at low starch contents. These data illustrate the complex effects of a polymer with mainly linear structure and flexible conformation on the mobility of an amorphous, hydrogen bonded sugar matrix.

Pharmaceutical micro-particles give amorphous sucrose higher physical stability

The aim of this study was to explore how pharmaceutical micro-sized filler particles affect the amorphous stability of sucrose in sucrose/filler particle composites produced by freeze-drying. Focus was put on the filler particles’ properties crystallinity, hygroscopicity, hydrophobicity, and surface area, and their influence on physical stability of the amorphous phase. The micro-sized filler particles were examined with Blaine permeametry, gas adsorption, pycnometry, gravimetric vapour sorption, X-ray diffraction, and light microscopy before composites of sucrose and micro-sized filler particles were prepared by freeze-drying. The stability of the composites was examined with X-ray diffraction, differential scanning calorimetry (DSC), and microcalorimetry. All composites were amorphous and showed higher stability compared to pure amorphous sucrose, which was evident from a delay in heat and moisture-induced crystallization. However, calcium carbonate and oxazepam micro-sized filler particles lost their ability to stabilize the amorphous sucrose when exposed to humidity. The dry glass transition temperature ( T g ) was higher for the composites, indicating the stabilization was mediated by a reduced molecular mobility of the amorphous phase.

Dynamic and sub-ambient thermal transition relationships in water–sucrose solutions

This work was undertaken to investigate thermal and dynamic transitions observed in the temperature range close to the bulk ice melting temperature in sucrose solutions. Measurements of thermal (differential calorimetry) and dynamic (neutron scattering) properties were compared in order to give a physical interpretation of the thermal transitions observed during the thawing of amorphous sucrose solutions. In fact, the freezing of biological material leads to the distinction between different pools of water: bulk water which becomes ice after freezing, unfrozen water trapped in the glassy matrix or close to the interface of solutes can be considered, and finally freezable confined water with a lower melting point than bulk water and with properties depending on both the ice presence and the microstructure of the material. The transition temperatures such as glass transition or melting are dependent on the freezing protocol used and examples of annealing effects are presented, in order to underline the necessity of a good temperature control during freezing for the study of biological material with freezable water.

Water Sorption Glass Transition Protein-Stabilizing Behavior of an Amorphous Sucrose Matrix Combined With Various Materials

The effects of various additives on the physical properties of an amorphous sugar matrix were compared. Amorphous, sugar-additive mixtures were prepared by freeze-drying and then rehumidified at given RHs. Sucrose and eighteen types of substances were used as the sugar and the additive, respectively, and water sorption, glass-to-rubber transition, and protein stabilization during freeze-drying for the various sucrose-additive mixtures were examined. The additives were categorized into two groups according to their effects on T(g) and water sorption. Presence of polysaccharides, cyclodextrins, and polymers (large-sized additives) resulted in a decrease in equilibrium water content from the ideal value calculated from individual water contents for sucrose and additive, and in contrast, low MW substances containing ionizable groups (small-ionized additives) resulted in an increase. The increase in T(g) by the addition of large-sized additives was significant at the additive contents >50 wt.% whereas the T(g) was markedly increased in the lower additive content by the addition of small-ionized additives. The addition of small-ionized additives enhanced the decrease in T(g) with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives.

The effect of protein types and low molecular weight surfactants on spray drying of sugar-rich foods

The effect of protein types and low molecular weight surfactants (LMS) on spray drying of sugar-rich foods has been studied using sucrose as a model sugar and sodium caseinate (NaCas) and pea protein isolate (PPI) as model proteins. Sodium stearoyl lactylate (SSL) and Polysorbate 80 (Tween-80) were chosen as model ionic and non-ionic LMS. The sucrose:NaCas and sucrose:PPI solid ratios were maintained at (99.5:0.5) and (99:1), respectively and spray-dried maintaining 25% solids in feed solutions. It was found that the proteins preferentially migrated to the air–water interface reasonably swiftly and the addition of LMS resulted into partial or complete displacement of the proteins from the air–water interface. More than 80% of amorphous sucrose powder was produced with the addition of 0.13% (w/w) of NaCas in feed solution. PPI was not as effective and produced less than 50% recovery even at 0.26% (w/w) in feed. Addition of 0.01–0.05% SSL displaced 2.0% and 29.3% of proteins from the surface of sucrose–NaCas–SSL droplet, respectively, resulting in a 6.5 ± 1.2% to 51.9 ± 1.9% reduction in powder recovery. The extent of protein displacement was higher when SSL was added into sucrose–PPI solution; however, the powder recovery was not much affected. The addition of 0.01% Tween-80 in sucrose–NaCas solution resulted in a 48.2 ± 1.5% reduction in powder recovery and at 0.05% concentration, it displaced a substantial amount or all the NaCas from the droplet surface and no powder was recovered. The addition of 0.01% and 0.05% Tween-80 into sucrose–PPI solution resulted into very low powder recoveries (24.9 ± 0.4% and 29.5 ± 1.8%, respectively). The glass transition temperature (T g) results revealed that the amount of protein required for successful spray drying of sucrose–protein solutions depends on the amount of proteins present on the droplet surface but not on the bulk concentration. X-ray diffraction and scanning electron microscopy results showed that the powders of sucrose–NaCas/PPI and sucrose–NaCas/PPI with 0.01% SSL were mostly amorphous while those with sucrose–NaCas/PPI–Tween-80 (0.01%), sucrose–PPI–Tween-80 (0.05%) and sucrose–NaCas/PPI–SSL (0.05%) were crystalline.

Systematic investigation of the effect of lyophilizate collapse on pharmaceutically relevant proteins I: Stability after freeze‐drying

The objective of this work was to investigate the effect of cake collapse during freeze‐drying on the stability of protein lyophilizates containing a monoclonal IgG1‐antibody or a second pharmaceutically relevant protein, referred to as PA01. In addition, L‐lactic dehydrogenase was investigated because of its well‐documented sensitivity towards freeze‐drying stresses. Collapse was induced by two different means. First, by varying the ratio of the crystalline bulking agent mannitol to the amorphous stabilizer sucrose, different extents of collapsed cakes were generated. Second, formulations were freeze‐dried using an aggressive collapse‐cycle and a conventional freeze‐drying protocol and collapsed and noncollapsed cakes of identical formulation were produced. Lyophilizates were analyzed using a comprehensive set of analytical techniques to monitor protein stability in terms of formation of soluble and insoluble aggregates, the biological activity and the conformational stability. The stability of excipients, namely the glass transition temperature, crystallinity, reconstitution behavior, and the residual moisture content was analyzed as well. In addition, the extent of collapse was quantified using the decrease of the specific surface area (SSA). Collapsed cakes had comparable residual moisture levels to noncollapsed lyophilizates. Reconstitution times were not increased. Protein stability was not relevantly different between collapsed and noncollapsed cakes. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2256–2278, 2010

Implications of Global and Local Mobility in Amorphous Excipients as Determined by DSC and TM DSC

The paper explores the use of differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TM DSC) to study α- and β- processes in amorphous sucrose and trehalose. The real part of the complex heat capacity is evaluated at the frequencies, f, from 5 to 20mHz. β-relaxations were studied by annealing glassy samples at different temperatures and subsequently heating at different rates in a differential scanning calorimeter.

Vanillin Phosphorescence as a Probe of Molecular Mobility in Amorphous Sucrose

Changes in molecular mobility are important in defining the stability and quality of amorphous solid foods, pharmaceuticals, and other solid biomaterials. Predictions of stability must consider matrix mobility below and above T(g) (the glass transition temperature); measurement of molecular mobility in amorphous solids over time scales ranging from <10(-9) s to >10(8) s requires specialized methods. This research investigated how the steady-state and time-resolved emission and intensity of phosphorescence from vanillin (4-hydroxy-3-methoxy benzaldehyde), a common flavor compound, can be used to probe molecular mobility when dispersed within amorphous pure sucrose films. Phosphorescence emission spectra and time-resolved intensity decays, measured in sucrose as a function of temperature in the absence of oxygen, were strongly modulated by matrix molecular mobility. Temperature had a significant effect on vanillin phosphorescence peak frequency and bandwidth, intensity, and lifetime both in the glass and in the melt. Time-resolved phosphorescence intensity decays from vanillin were multiexponential both below and above the glass transition temperature, indicating that the pure (single component) amorphous matrix was dynamically heterogeneous on the molecular level. These data show that vanillin is a promising intrinsic probe of molecular mobility and dynamic heterogeneity in amorphous solid foods and perhaps pharmaceuticals.

Interaction of Environmental Moisture with Powdered Green Tea Formulations: Relationship between Catechin Stability and Moisture-Induced Phase Transformations

This study investigated the effect of phase transformations of amorphous and deliquescent ingredients on catechin stability in green tea powder formulations. Blends of amorphous green tea and crystalline sucrose, citric acid, and/or ascorbic acid were analyzed by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), dynamic water vapor sorption, water activity measurements, and high-performance liquid chromatography (HPLC) after storage for up to 12 weeks at 0-75% relative humidity (RH) and 22 degrees C. The glass transition temperature (T(g)) of green tea was reduced to below room temperature (<22 degrees C) at 68% RH. Dissolution of deliquescent ingredients commenced at RH values below deliquescence points in blends with amorphous green tea, and these blends had greater water uptake than predicted by an additive model of individual ingredient moisture sorption. Catechin degradation was affected by T(g) of green tea powder and both dissolution and deliquescence of citric and ascorbic acids.

Crystallization Rates for Amorphous Sucrose and Lactose Powders from Spray Drying: A Comparison

Sorption tests have been used to assess the effects of temperature, relative humidity, and molecular structure on the crystallization process within spray-dried lactose and sucrose at both room temperature and 40°C. Increasing the temperature by 10°C more than doubled the crystallization rate, up to three times for the case of lactose. Below a threshold value of the relative humidity, little to no crystallization was found, with this threshold being 51% for sucrose, at room temperature, which was lowered to 32% at 40°C. These results are consistent with the picture of the process as an activated rate one. Lactose and sucrose, which have the same molecular weight of 342 g/mol but different molecular structures and thus glass transition temperatures, showed similar overall crystallization rates for the same material temperatures, in contrast with the overall predictions of the Williams-Landel-Ferry (WLF) equation. The WLF equation suggests that the crystallization rate is a function of the difference between the material and the glass transition temperatures, but it is still possible that this equation may predict the effect of changing material temperature and relative humidity for a particular material.

Effect of addition of proteins on the production of amorphous sucrose powder through spray drying

Spray drying trials were carried out to produce amorphous sucrose powder. Firstly, pure sucrose solutions were prepared and spray dried at inlet and outlet temperatures of 160 °C and 70 °C, respectively. No amorphous powder was obtained and only 18% of the feed solids were recovered in a crystalline form, with the remaining solids lost as wall deposits. Secondly, sodium caseinate (Na–C) and hydrolyzed whey protein isolate (WPI) were added in sucrose:protein solid ratios of (99.5:0.5) and (99.0:1.0) and drying trials were conducted maintaining the initial drying conditions. In both these cases, greater than 80% of the feed solids were recovered in an amorphous form. The increase in protein concentration from 0.5% to 1% on dry solid basis did not further improve the recovery. The remarkable increase in recovery from a small addition of protein is attributed to preferential migration of protein molecules to the droplet-air interface, and the subsequent transformation of the thin, protein-rich film into a non-sticky glassy state upon drying. This film overcomes both the particle-to-particle and particle-to-wall stickiness. The measured bulk glass rubber transition temperature ( T g–r) values of the bulk mixtures at various moisture contents were very close to the corresponding mean glass transition temperature ( T g) of the pure sucrose indicating that surface layer T g rather than the bulk T g is responsible for this. Electron spectroscopy for chemical analysis (ESCA) studies revealed that the particle surface was covered by 50–58% (by mass) proteins. The calculated glass transition temperature of the surface layer ( T g,surface layer), based on the surface elemental compositions, showed that the T g,surface layer has increased to the extent that it remained within the safe drying envelope of spray drying.

Implications of Global and Local Mobility in Amorphous Sucrose and Trehalose as Determined by Differential Scanning Calorimetry

To investigate the local and global mobility in amorphous sucrose and trehalose and their potential implications on physical stability. Amorphous sucrose was prepared by lyophilization while amorphous trehalose was prepared by dehydration of trehalose dihydrate. The variation in the effective activation energy of alpha-relaxation through glass transition has been determined by applying an isoconversional method. Beta-relaxations were detected as shallow peaks, at temperatures below the glass transition temperature, caused by annealing glassy samples at different temperatures and subsequently heating at different rates in a differential scanning calorimeter. The effect of heating rate on the beta-relaxation peak temperature formed the basis for the calculation of the activation energy. alpha-Relaxations in glassy trehalose were characterized by larger activation energy barrier compared to sucrose, attributable to a more compact molecular structure of trehalose. The effect of temperature on viscous flow was greater in trehalose which can have implications on lyophile collapse. The size of the cooperatively rearranging regions was about the same for sucrose and trehalose suggesting similar dynamic heterogeneity at their respective glass transition temperatures. The activation energy of beta-relaxations increased with annealing temperature due to increasing cooperative motions and the increase was larger in sucrose. The temperature at which beta-relaxation was detected for a given annealing time was much less in sucrose implying that progression of local motions to cooperative motions occurred at lower temperatures in sucrose. Trehalose, having a lower free volume in the glassy state due to a more tightly packed molecular structure, is characterized by larger activation energies of alpha-relaxation and experiences a greater effect of temperature on the reduction in the activation energy barrier for viscous flow. The pronounced increase in cooperative motions in sucrose upon annealing at temperatures below (T(g) -50) suggest that even a small excursion in temperature could result in a significant increase in mobility.

Effect of Xanthan on the Molecular Mobility of Amorphous Sucrose Detected by Erythrosin B Phosphorescence

Molecular mobility in amorphous solids is modulated by composition and environmental conditions such as temperature. Phosphorescence of erythrosin B was used to generate a mobility map of amorphous sucrose film doped with xanthan gum at weight ratios of xanthan/sucrose ranging from 0.0001 to 0.01. On the basis of analysis of the emission energy and lifetime of erythrosin B in pure sucrose and sucrose-xanthan films over the temperature range from 5 to 100 degrees C, we conclude that xanthan influences the molecular mobility as well as the dynamic site heterogeneity of amorphous sucrose in a dose-dependent fashion. At xanthan/sucrose weight ratios below approximately 0.0005, both emission energy and lifetime decreased and k(TS0) (the nonradiative decay rate of the triplet state) increased, indicating that xanthan increased the matrix molecular mobility. At weight ratios above 0.001, both emission energy and lifetime increased and k(TS0) decreased, indicating that xanthan decreased matrix mobility, reaching a plateau at weight ratios between 0.005 and 0.01. The concentration at which the effect of xanthan switched from increasing to decreasing mobility was similar to the concentration at which polymer chains overlapped in solution, suggesting that the dynamic changeover reflected the onset of chain overlap in the amorphous solid. Systematic trends in the emission bandwidth and lifetime heterogeneity and variations in the emission lifetime vs wavelength indicated that xanthan reduced the matrix dynamic site heterogeneity except at a weight ratio of 0.01. These data illustrate the complex effects of a polymer with a rigid structure and large side chains on the mobility of an amorphous, hydrogen-bonded sugar matrix.

Effect of gelatin on molecular mobility in amorphous sucrose detected by erythrosin B phosphorescence

We have used phosphorescence from the triplet probe erythrosin B (Ery B) to evaluate the effect of gelatin on the molecular mobility of the amorphous sucrose matrix as a function of temperature. Ery B was dispersed in amorphous sucrose and sucrose–gelatin films at ratios of ∼1:10 4 (probe/sucrose), and delayed emission spectra and emission decay transients were measured over the temperature range from 5 to 100 °C. Analysis of spectra using a lognormal function provided the peak energy and bandwidth of the emission. The emission peak frequency decreased at low (0.00022–0.0007) gelatin concentrations and increased at high (above 0.0022) gelatin concentrations, indicating that gelatin increased the extent, and thus the rate, of dipolar relaxation at low gelatin content and decreased the extent at higher gelatin content. Decay transients were well fit to a stretched exponential function at all gelatin contents and temperatures. Analysis of the emission lifetimes provided a measure of the rate of non-radiative decay to the ground state, an indicator of matrix molecular mobility. This rate increased at low (0.00022–0.0022) and decreased at high (>0.0073) gelatin wt ratios. Analysis of the effect of gelatin on the emission bandwidth, the stretching exponent β, and the variation of lifetime across the emission band indicated that matrix dynamic site heterogeneity increased at low and decreased at high gelatin wt ratios. These results provide a novel insight into the complex dynamic effects of the gelatin polymer on the molecular mobility of the amorphous sucrose matrix.

The effect of salts on molecular mobility in amorphous sucrose monitored by erythrosin B phosphorescence

Salts are present in most amorphous biomaterials such as dried or frozen solid foods, plant seeds, and bacterial spores, and in some pharmaceutical formulations. However, knowledge of how salts modulate the physical properties of amorphous solid sugars, a major component in these systems, is lacking. We have used phosphorescence of the triplet probe erythrosin B (Ery B) to monitor molecular mobility in amorphous sucrose films (dried against P 2O 5) containing the salts NaCl, MgCl 2, CaCl 2, NaAcetate, Na 3Citrate, NaH 2PO 4, or Na 2HPO 4 at a mole ratio of 0.2:1 (salt/sucrose). All the salts examined, except NaH 2PO 4, significantly increased the phosphorescence lifetime of Ery B over the temperature range from 5 to 100 °C. This increase is due to a reduction in the rate of collisional quenching of the triplet state due to interactions with the matrix, indicating that these salts decreased the matrix molecular mobility. NaAcetate, Na 3Citrate, and Na 2HPO 4 decreased mobility more than NaCl, CaCl 2, or MgCl 2, perhaps due to specific hydrogen bonding interactions between the anion and sucrose. Systematic variations in the probe emission lifetime across the excitation and emission bands at 25 °C indicate that there are sites of different mobilities within amorphous solid sucrose; this dynamic site heterogeneity was enhanced in the presence of the divalent cationic salts MgCl 2 and CaCl 2. These results suggest that salts may play a significant role in modulating the mobility, and thus the long-term stability, of amorphous biological matrixes.

Physicochemical Characteristics of Sonazoid™, A New Contrast Agent for Ultrasound Imaging

The objective of the current work is to describe the physicochemical characteristics of Sonazoid™, a new ultrasound contrast agent for detection and characterisation of focal liver lesions. It has been demonstrated that Sonazoid™ powder for injection consists of microspheres of perfluorobutane (PFB) stabilised by a monomolecular membrane of hydrogenated egg phosphatidyl serine, embedded in an amorphous sucrose structure. Upon reconstitution with sterile water, stabilised microspheres of PFB are released in a predefined amount and size into a low viscosity, isotonic sucrose solution with a neutral pH. Sonazoid™ reconstituted product contains approximately 8 μl microspheres/ml with volume median diameter of approximately 2.6 μm. The product contains approximately 1.2 billion microspheres/ml of which less than 0.1% are larger than 7 μm. The acoustic properties of Sonazoid™ such as attenuation efficacy, fundamental and second harmonic backscatter efficacy are all well correlated to the microsphere volume concentration. The stability of Sonazoid™ after reconstitution is good, with no significant changes in physicochemical properties 2 h after reconstitution. Pressure stress is well tolerated by both concentrated and diluted Sonazoid™ with no permanent effects of pressures up to 300 mm Hg. The level and consistency of the investigated physicochemical properties demonstrate that Sonazoid™ should be well suited as a contrast agent for medical imaging with ultrasound. (E-mail: per.sontum@ge.com)

Investigating the Moisture Sorption Behavior of Amorphous Sucrose Using a Dynamic Humidity Generating Instrument

The moisture sorption behavior of freeze-dried amorphous sucrose was investigated using a dynamic humidity generating instrument, the Dynamic Vapor Sorption (DVS) instrument. The kinetic moisture sorption profiles of freeze-dried amorphous sucrose samples with 29% crystalline content were obtained using the DVS instrument at 9 relative humidity (RH) values, ranging from 10% to 90%, at 25 degrees C. Moisture-induced crystallization was observed for %RH values between 40% and 80%, where the crystallization onset time decreased as %RH increased. The moisture sorption behavior of freeze-dried amorphous sucrose with 3 crystalline contents, 23%, 29%, and 80%, was also compared, revealing that the crystalline content had a significant impact on the pseudo-sorption isotherm of freeze-dried amorphous sucrose. In general, for %RH values below 90%, samples that had a lower percent crystalline content had a higher pseudo-equilibrium moisture content, with the difference becoming most pronounced for the 60% to 80% RH values. The moisture-induced crystallization results as a function of %RH obtained in this study were compared to those previously reported in the literature, leading to an extensive discussion of both the experimental protocols used and the hypothesized mechanisms governing the long-term stability of amorphous materials. The hypothesized mechanisms discussed included the glass transition temperature boundary, the zero mobility temperature, and the hydration limit. Based on the dissimilarity in these hypothesized mechanisms, additional theoretical and experimental exploration is still merited in order to adequately predict the conditions (for example, moisture content, %RH, and temperature) required to ensure long-term stability of amorphous solids.

The effect of sodium chloride on molecular mobility in amorphous sucrose detected by phosphorescence from the triplet probe erythrosin B

Phosphorescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime that are specifically sensitive to molecular mobility of the local environment. This study used phosphorescence of erythrosin B to investigate how variation in NaCl content modulated the mobility of the amorphous sucrose matrix over the temperature range from 5 to 100 °C. Addition of NaCl increased the emission energy and the energy difference with excitation at the absorption maximum and the red edge, and increased the lifetime by reducing the non-radiative decay rate in the glass as well as in the undercooled liquid in a concentration dependent manner, indicating that NaCl decreased the matrix molecular mobility. Emission energy and lifetime increased with increasing NaCl content up to a maximum at NaCl/sucrose mole ratio of ∼0.5; above 0.5 mole ratio, the effect of NaCl was less significant and appeared to be opposed by increasing plasticization by residual water. Changes in the width of the distribution of the emission energy and lifetime and variation in the lifetime with excitation and emission wavelength indicated that NaCl increased the spectral heterogeneity and thus increased the extent of dynamic site heterogeneity. These results are consistent with a physical model in which sodium and chloride ions interact with sucrose OH by ion–dipole interactions, forming clusters of less mobile molecules within the matrix.

Effects of Vial Packing Density on Drying Rate during Freeze-drying of Carbohydrates or a Model Protein Measured using a Vial-weighing Technique

To determine the effects of vial packing density in a laboratory freeze dryer on drying rate profiles of crystalline and amorphous formulations. The Christ freeze-drying balance measured cumulative water loss, m(t), and instantaneous drying rate, m(t), of water, mannitol, sucrose and sucrose/BSA formulations in commercial vials. Crystalline mannitol shows drying rate behaviour indicative of a largely homogeneous dried-product layer. The drying rate behaviour of amorphous sucrose indicates structural heterogeneity, postulated to come from shrinkage or microcollapse. Trehalose dries more slowly than sucrose. Addition of BSA to either disaccharide decreases primary drying time. Higher vial packing density greatly reduces drying rate because of effects of radiation heat transfer from chamber walls to test vial. Plots of m(t) versus radical t and m(t) versus layer thickness (either ice or dried-product) allow interpretation of changes in internal cake morphology during drying. Vial packing density greatly influences these profiles.

The Effect of Glycerol on Molecular Mobility in Amorphous Sucrose Detected by Phosphorescence of Erythrosin B

Luminescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime that are sensitive to molecular mobility of the local solvent environment. This study investigated how variation in glycerol content influences the properties of an amorphous sucrose matrix by monitoring phosphorescence of erythrosin B over the temperature range from 5 to 100°C. Emission energy, lifetime, and red-edge excitation data revealed that glycerol affected the mobility of amorphous sucrose matrix primarily through plasticization when the mole ratio of glycerol/sucrose was above 0.27, resulting in a decrease in emission energy (ν p), lifetime (τ) and energy difference (Δν P) with excitation at the absorption peak and red edge and an increase in the nonradiative, collisional quenching rate k TS0. At mole ratios ≤0.27 and at temperatures below the matrix T g, glycerol exhibited an “antiplasticization” effect, as indicated by higher values of emission energy, lifetime, and energy difference and lower values of the matrix collisional quenching rate. Changes in the distribution of emission energy (emission bandwidth) and lifetime, and variation in the emission lifetime vs wavelength showed that glycerol reduced the spectral heterogeneity. These data illustrate the complex effect of a hydrogen bonding solute on the mobility of an amorphous, hydrogen bonded sugar matrix.