Unfrozen Phase Research Articles

On the frozen F-theory landscape

We study 6d \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal{N}$$\\end{document} = (1, 0) supergravity theories arising in the frozen phase of F-theory. For each of the known global models, we construct an F-theory compactification in the unfrozen phase with an identical non-abelian gauge algebra and massless matter content. Two such low energy effective theories are then distinguished through gauge enhancements in moduli space. We study potentially new global models obtained via compact embeddings of a plethora of 6d \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal{N}$$\\end{document} = (1, 0) superconformal field theories and little string theories constructed using frozen 7-branes. In some cases, these provably do not exist, and in other cases, we explicitly construct a compact embedding, yielding 6d supergravity theories with new massless spectra. Finally, by using gravitational anomaly cancellation, we conjecture the existence of localized neutral hypermultiplets along frozen 7-brane loci.

Quantification of Residual Water in Pharmaceutical Frozen Solutions Via 1H Solid-State NMR

Freezing is essential for the stability of biological drug substances and products, particularly in frozen solution formulations and during the primary drying of lyophilized preparations. However, the unfrozen segment within the frozen matrix can alter solute concentration, ionic strength, and stabilizer crystallization, posing risks of increased biophysical instability and faster chemical degradation. While quantifying the unfrozen water content is important for designing stable biopharmaceuticals, there is a lack of analytical techniques for in situ quantitative measurements. In this study, we introduce a 1H magic angle spinning NMR technique to identify the freezing point (Tice) and quantify mobile water content in frozen biologics, applying this method to analyze the freezing of a commercial high-concentration drug product, Dupixent®. Our results demonstrate that water freezing is influenced by buffer salt properties and formulation composition, including the presence of sugar cryoprotectants and protein concentration. Additionally, the 1H chemical shift can probe pH in the unfrozen phase, potentially predicting the microenvironmental acidity in the frozen state. Our proposed methodology provides fresh insights into the analysis of freeze-concentrated solutions, enhancing our understanding of the stability of frozen and lyophilized biopharmaceuticals.

Molecular structure and properties of cassava-based resistant maltodextrins

In-depth molecular structure and properties of cassava-derived resistant maltodextrins (RMDs) were determined. Cassava starch was dextrinized with 0.04% or 0.06% HCl at 120 °C for 60–180 min to obtain resistant dextrins (RDs), which were further hydrolyzed by α-amylase to produce RMDs. Prolonging dextrinization duration decreased proportion of α-1,4 linkages and α-/β-reducing ends but increased fraction of indigestible α-/β-1,6, β-1,4, β-1,2 linkages, degree of branching (DB), degree of polymerization, relative molecular weight, and total dietary fiber (TDF) content of the RMDs. Moreover, RMDs had greater proportion of β-glycosidic linkages, α-/β-reducing end, DB, TDF, and low molecular weight dietary fiber (LMWDF) content than their RD counterparts. Potential prebiotic activity score was higher in RMDs with abundant LMWDF fraction but low DB. Slight difference in the glass transition temperature of maximally freeze-concentrated unfrozen phase (Tg’) and unfrozen water content was found among RMDs. However, RMDs had lower Tg’ than their RD counterparts.

Ice recrystallization inhibition effect of cellulose nanocrystals: Influence of sucrose concentration

Stabilizers are commonly used to inhibit the ice recrystallization process that leads to the formation of large ice crystals, decreasing consumer acceptance of ice cream. However, the ice recrystallization inhibition (IRI) effect of stabilizers is very dependent on measurement conditions. The cause of this dependence is not clear, which imposes problems in comparing the IRI activity and understanding the IRI mechanism of stabilizers. This study investigated the influence of sucrose concentration on the IRI effect of cellulose nanocrystals (CNCs), which are newly identified IRI active materials. A splat assay and a sandwich assay were used to determine IRI activities of CNCs at sucrose concentrations from 2.0% to 49.0% w/w and incubation temperature of −8 °C for 30 min. The IRI activities of CNCs were higher at low sucrose concentrations, almost disappeared at medium sucrose concentrations, and restored slightly at high sucrose concentrations. The IRI effect of CNCs is correlated with the ratio between CNCs concentration in the unfrozen phase and total surface area of ice crystals. This surface area-related IRI effect was also observed with guar gum, locust bean gum, and poly(vinyl alcohol). It is a strong evidence of an ice-binding mechanism for the IRI effect of stabilizers. These research findings offer a new perspective in comparing and understanding the measurement condition-dependent IRI effect of stabilizers, which could potentially benefit the ice cream industry in developing new materials and recipes to control ice recrystallization.

Revisiting the classifications of 6d SCFTs and LSTs

Gauge-theoretic anomaly cancellation predicts the existence of many 6d SCFTs and little string theories (LSTs) that have not been given a string theory construction so far. In this paper, we provide an explicit construction of all such “missing” 6d SCFTs and LSTs by using the frozen phase of F-theory. We conjecture that the full set of 6d SCFTs and LSTs is obtained by combining the set of theories constructed in this paper with the set of theories that have been constructed in earlier literature using the unfrozen phase of F-theory. Along the way, we demonstrate that there exist SCFTs that do not descend from LSTs via an RG flow.

Rheological properties of stabilizers at low temperatures in concentrated sucrose solutions

During the freezing of sorbets, the concentration of sucrose and stabilizing macromolecules increases in the unfrozen phase. Rheological properties of this unfrozen phase were studied, depending on nature and concentration of hydrocolloids in sucrose solutions at temperatures below zero. Three stabilizers were tested individually in sucrose-rich solutions: locust bean gum (LBG), hydroxypropylmethylcellulose (HPMC) and carboxymethylcellulose (CMC). The parameters of the Ostwald-de Waele model were determined and apparent viscosities of solutions were calculated at shear rates encountered during the process. Intrinsic viscosities and critical concentrations of entanglement were determined to evaluate the expansion of polymers in solutions and the transition of concentration regimes according to process conditions. Viscoelastic properties were also tested to study the possible cryogelation. For HPMC and LBG, the shear thinning behavior increased quite linearly with the concentration in stabilizer whereas CMC was highly shear thinning. Increasing sugar did not reveal large effect on these properties. The increase in apparent viscosity of the unfrozen matrix in process conditions was dependent on stabilizers; solutions containing LBG were less viscous than the others. Intrinsic viscosities revealed that HPMC and LBG became progressively less expanded as the concentration of sucrose increased whereas CMC tended to aggregate. Measurements of viscoelastic properties evidenced a dominant viscous behavior for HPMC and LBG systems whereas CMC systems showed dominant elastic behavior at frequencies higher than 0.1 Hz. The next challenge will be to better understand the potential link between the particular rheological behavior of hydrocolloids in process conditions and their possible influence on crystallization mechanisms.

Freeze-Concentrated Phase and State Transition Temperatures of Mixtures of Low and High Molecular Weight Cryoprotectants

Although numerous studies have been conducted on the use of cryoprotectants to prevent the deterioration of food during freezing and frozen storage, scarce reports exist on the thermal transition properties of aqueous cryoprotectant solutions at frozen temperatures. The selection of a suitable cryoprotective medium for the long-term preservation of food requires knowledge of the effects of cryoprotectants and their concentration on the freeze-concentrated unfrozen phase and state transition temperatures known asTg′,Tm′, andTm. Calorimetric measurements were conducted to determine theTg′,Tm′, andTmvalues of thirty frozen aqueous solutions containing maltodextrin, polydextrose, and glucose, in which a distance-based experimental design was used for mixtures of four components to establish their corresponding mass fractions in the mixtures. Thermograms, measured during heating/rewarming from –70 to 20°C, were used to identify the glass transition and freezing temperatures. Mathematical expressions forTg′,Tm′, andTmas a function of the mass fractions of cryoprotectants and water and their interactions (p< 0.05) were developed to aid the formulation of cryoprotective media involving more than two cryoprotectants for adequate frozen conservation of high and intermediate moisture foodstuffs.

Fermentation time and fiber effects on recrystallization of starch components and staling of bread from frozen part-baked bread

Staling of white wheat bread produced from frozen part-baked bread (PBB) of different fermentation times (90–120–420min) and fiber contents (6% wheat bran and 6% wheat bran +2% inulin) was studied. Volume, texture, crumb and crust water content, water activity and crumb thermal properties (including Tm′ and Tg′) were measured after thawing and final baking. The results confirmed that typical freezing temperatures may not ensure the glassy state of the unfrozen phase of PBB, which may accelerate staling of final breads. The evolution of starch retrogradation, quantified by DSC, and of the crust and crumb water contents were analysed and related to the aging of bread. Firmness and cohesiveness values were used to quantify the extent of staling. Avrami equation was fitted to staling data with R2 coefficients above 0.9 in all cases. Bread characteristics and staling kinetics were significantly affected by fermentation time and fiber, particularly inulin. Inulin promoted amylopectin recrystallization and delayed the water movement from crumb to crust during staling. The combined effects of recrystallization and water loss in the starch fraction explained firming and cohesiveness loss kinetics.

Lyotropic behavior of a mono-tailed glycolipid assembly during solidification and melting of electrolyte/ice eutectic systems.

The properties of low molecular weight glycolipids at subzero temperatures have been paid much attention due to their great potential for applications in cryopreservation. In this study, the ability of glycolipids to maintain their lyotropic properties was investigated by analyzing the aggregation behavior of octyl-β-D-glucoside (β-OGlu) during solidification and melting of electrolyte/ice eutectic mixtures using a simultaneous X-ray diffraction-differential scanning calorimetry measurement and cryomicroscopic observation. During the freezing process, eutectic formation increased the concentration of the β-OGlu micelle solution in the unfrozen phase, leading to ordering of the molecular assembly. The molecular assembly exhibited a reversible phase transformation between liquid crystalline phases (e.g., lamellar (Lα) and hexagonal (H) phases) and an isotropic micelle solution (I), depending on the degree of eutectic formation, which was regulated by temperature. Because the coexistence of electrolyte/ice eutectic often induces the dehydration of lipids, the persistence of lyotropic properties under such arid conditions demonstrates an attractive performance of glycolipids for use in low temperature applications, such as the cryopreservation of poorly water-soluble drugs or proteins.

Sugar Crystallization and Glass Transition as Destabilizing Factors of Protein-Stabilized Emulsions

Temperature cycling across the glass transition of the aqueous phase of oil-in-water emulsions stabilized by whey protein isolate was considered as a possible factor affecting stability. Emulsions were formulated with an aqueous phase containing 80% (w/w) fructose, fructose:glucose 1:1 or glucose, in order to prepare a glass forming aqueous phase with sugar concentration corresponding to that of the unfrozen phase of the maximally freeze-concentrated solutions. This allowed thermal cycling across the glass transition in the absence of the formation of ice crystals. Emulsion stability was studied using differential scanning calorimetry, dynamic light scattering and by visual analysis of the morphology of the systems. Emulsified systems undergoing glass transition cycles of the aqueous phase did not show destabilization of the dispersed (crystallized) lipid phase. Sugar crystallization in the aqueous phase, which occurred when glucose systems were stored above the Tg, led to emulsion breakdown. In this study, the formation of a glassy structure in the continuous aqueous phase preserved the interfacial structure of WPI, thus protecting the dispersed lipid phase from destabilization. On the contrary, glucose crystallization caused disruption of the interfacial membrane structure and loss of integrity of the interface which resulted in extensive lipid phase destabilization.

Physical State Study of (Sugar Mixture)-Polymer Model Systems

The physical state of components in the unfrozen solute phase of frozen solutions was determined by using differential scanning calorimetry (DSC) for mixtures of lactose, sucrose, and trehalose with albumin, gelatine, or cornstarch. An equal weight ratio (1:1) of lactose-sucrose, lactose-trehalose and sucrose-trehalose mixtures with polymer systems (sugar mixture-albumen (1:1:1), gelatine (1:1:1), and cornstarch (1:1:1), as well as cornstarch-gelatine (1:1:1:1) was used. Mixed sugar mixture (lactose/sucrose)-polymer systems were further studied for maximum freeze-concentration in complex systems. A comparative thermal study between sugar-polymer and mixed sugar-polymer systems was conducted. The sugar-polymer and mixed sugar-polymer systems showed similarities and differences in thermal behaviour. The similarities included maximum freeze-concentration of a frozen system at an annealing temperature (Tm´-1) °C, constant initial concentration independent onset of glass transition Tg´, and onset of ice melting temperature Tm´, and increased in temperature difference between Tg´ and Tm´ or increase in broadness of transition with the addition of polymeric compound.

Effect of Calcium Chloride Addition on Ice Cream Structure and Quality

The influence of calcium fortification by the addition of calcium chloride on quality parameters of ice cream based on physical properties was investigated, as was the effect of κ-carrageenan at modifying the effects of this calcium fortification. Four ice cream mixes of conventional composition, with added κ-carrageenan (0 or 0.025%) and added calcium chloride (0 or 4.4g L−1 = 40mM of added Ca2+), were prepared. Modulated temperature-differential scanning calorimetry was used to investigate the effect of calcium chloride on the nucleation temperature, enthalpy of melting, and freezing point depression. The protein composition of 15.4% (wt/wt) reconstituted skim milk powder solutions with or without 4.4g L−1 added CaCl2 and in the supernatant after ultracentrifugation was determined. Fat particle size distributions in ice cream were characterized by light scattering. Ice crystal sizes before and after temperature cycling were determined by cold-stage light microscopy. The results demonstrated that the addition of calcium chloride led to a substantial increase in ice crystal sizes and in fat partial coalescence, which were exacerbated by the addition of κ-carrageenan. These results can be explained by the interaction between Ca2+ ions and casein micelles, rather than any effects on freezing point depression. The calcium ions led to a more compact micelle, less serum β-casein, and high fat destabilization, all of which would be expected to reduce macromolecular structure and volume occupancy in the unfrozen phase, which led to increased rates of ice recrystallization.

Factors affecting the freeze–thaw stability of emulsions

Many food emulsions are frozen to provide long-term stability to the product or as a necessary part of the food itself (e.g., ice cream), but very often the thawed emulsion is significantly destabilized and sometimes completely broken down into an oily and an aqueous phase. The phase behaviour of the frozen emulsion and hence the potential stresses can be calculated from the composition of the aqueous phase. For example, a 20% o/w emulsion prepared with 10% sucrose in the aqueous phase when frozen to −20 °C about 85% of the aqueous phase has frozen to ice leaving the unfrozen phase concentrated to about 62% with respect to droplets and 67% with respect to sucrose. The high-volume fraction and expanding ice press the droplets together and the high sugar (and other solute) concentration can affect the interdroplet forces. A combination of these effects can lead to the membrane separating the droplets rupturing and is responsible for the coalescence seen on thawing. The published studies on freeze–thaw stability of emulsions are reviewed within the framework provided by the phase diagram calculations.

Effect of additives on the thermo-mechanical behaviour of dough systems at sub-freezing temperatures

The aim of this study was to examine the effects of different additives, ascorbic acid, α-amylase, protease, hemicellulase, gluten, and gum guar, on thermo-mechanical dough properties at sub-freezing temperatures as measured by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). The DSC thermograms showed that dough with a combination of ascorbic acid and hemicellulase had greater amount of water unable to crystallize and a lower co-operativity in ice-melting transition, indicating more polymer–water interactions. DMA studies permitted identification of three peaks, which were related to the ice melting, α-relaxation and β-relaxation. α-transition occurred over a temperature range of ∼40 °C and the ascorbic acid and their combination with hemicellulase, amylase, protease and gum guar increased temperature transition. An increment of the matrix viscosity due to higher number of inter- and intra-molecular interaction caused by oxidation of gluten proteins (ascorbic acid), and the increment of aggregated solid or generated molecules in the unfrozen phase could explain the increment in this transition.

Ultrasonic monitoring of food freezing

The time of flight of an ultrasonic pulse moving parallel to the direction of heat flux was measured in blocks of food (gelatin, chicken, beef) during freezing. Echoes were recorded from the food surfaces and from the moving ice front within the food. The changing return times of these echoes were used to calculate the percentage of the food frozen as a function of time either from the measured position of the ice front or by assuming the overall time of flight of the acoustic pulse was the sum of times spent traveling through a frozen and unfrozen phase. Both methods are predicated on the observation that for foods the change in speed of sound on freezing is much greater than the changes with respect to temperature in the absence of a phase change. Both methods gave reasonable prediction of the time for complete freezing as measured by thermocouples but the latter was more practical as the ice front was difficult to measure as the muscle foods became increasingly frozen.

Dielectric Relaxations of Frozen Wheat Doughs Containing Sucrose, NaCl, Ascorbic Acid and Their Mixtures

The effects of sucrose, NaCl, and ascorbic acid on dielectric relaxations of frozen wheat doughs were investigated using dielectric analysis (DEA). All ingredients were dissolved in distilled water used to prepare wheat flour doughs to optimum consistency using a 10 g bowl Micro-Mixer. DEA measurements were made at a heating rate of 1 °C/min from −150 to 10 °C. Before the measurements, samples were equilibrated at −30 °C for 15 min to allow maximum ice formation, and then cooled at 1 °C/min to −150 °C. The frequencies used were 0·1, 0·5, 1, 5, 10, 20, 50, 100 and 1000 Hz. The dissipation factor (tan δ) of DEA showed an α-relaxation (glass transition), two low temperature relaxations (β and γ) and ice dissolution. Added NaCl had a markedly depressed the glass transition temperature (Tg′) and onset of melting of ice temperature (Tm′), probably because of the higher conductivity of the frozen material, and the decreased transition temperatures of the unfrozen solute phase. At the higher frequencies, the α-relaxation coincided with melting of ice, and all relaxation temperatures (α, β and γ) increased with increasing frequencies.

Fluorescence microscopy to study galactomannan structure in frozen sucrose and milk protein solutions

Locust bean gum (LBG) and guar were labeled with rhodamine isothiocyanate, and their location within a solution of sucrose or sucrose plus skim milk powder after freezing and during temperature cycling between −18 and −10°C was visualized with fluorescence and brightfield microscopy. LBG was observed to produce a structured gel-like network around the ice crystals, which became more distinct with repeated temperature cycling. Such a network was not evident with guar gum. Image analysis of the ice crystal size distributions showed that LBG had provided much greater resistance to ice recrystallization under these conditions than guar. The same trends were evident in sucrose plus skim milk powder solutions, but the overall increase in ice crystal size was less than it was without skim milk powder. Both the LBG and guar promoted the formation of a phase-separated protein region. Carrageenan successfully reduced the extent of protein/galactomannan phase separation, but solutions containing carrageenan recrystallized to a greater extent than those without carrageenan. It was suggested that a reduction in recrystallization resulted from the formation of a continuous polymer network and structural heterogeneity in the unfrozen phase.

Freeze Concentration with Supersonic Radiation under Constant Freezing Rate. Effect of Kind and Concentration of Solutes.

In freezing water which contains solutes, the solutes are removed from the frozen phase and concentrated in the unfrozen liquid phase, and strong agitation of the freezing interface is very effective. We used a supersonic radiation method instead of propeller agitation.The experiments of freeze concentration with/without supersonic radiation were carried out under a constant freezing rate (40 mm/h), using two concentrations (0.5, 5.0 kg/m3) of three aqueous solutions (sodium chloride, L-phenyl alanine and saccharose). Under this freezing rate, freezing without supersonic radiation could not concentrate solutes, but freezing with supersonic radiation could greatly do, and decreased the average distribution factor under 0.4. The distribution factors at a late stage of freezing are much smaller than those at an early stage, because the turbulence of solution by supersonic cavitation and the agitating intensity per unit unfrozen volume increases. Therefore the solutes are not easily caught on the freezing interface as the freezing interface approaches the supersonic radiation horn. The low mass concentration solution is concentrated more than high concentration solution. For a constant mass concentration solution, the solutes of large molecular weight are more easily separated and concentrated than those of small molecular weight.

Diffusion and relaxation in interface layers of crystals in nanoporous glass

Water and tetradecane confined in porous glass of a mean pore diameter of 10 nm were investigated both above and below their freezing points with respect to their relaxation as well as diffusion behavior. Below the freezing point, experimental data provide evidence for the existence of a non-frozen interface layer (NFL) between the crystal in the pore and the pore walls. The molecules in this layer are effectively confined in a quasi-two-dimensional space that forces them to reorient when moving along the curved pore surface. Through this relaxation mechanism, the translational mobility in the unfrozen phase reveals itself in a pronounced frequency dependence of the spin-lattice relaxation time. The experimentally observed drop of the self-diffusion coefficients by more than one order of magnitude below the phase transition can be interpreted in terms of geometric restrictions as well as interactions with the surface.

Influence of stabilizers and freezing rate on the stress relaxation behaviour of freeze-concentrated sucrose solutions at different temperatures

Stress relaxation behaviour of frozen sucrose solutions in the presence of xanthan gum, gelatin and guar gum was investigated using a thermomechanical analyzer. Freezing rate and stabilizer type had a significant influence on the calculated relaxation time (τ) and asymptotic modulus (E a) values at temperatures within and above the glassy state. Following slow (2°C min −1) and rapid freezing (liquid nitrogen) the temperature corresponding to a large reduction in τ was found to correlate well with previously reported T g onset of annealed and non-annealed systems, respectively (−48°C, rapid; −41°C, slow). At −20°C stabilized systems appeared to alter significantly the mechanism of structural relaxation leading to increased τ and short-term viscoelasticity properties determined from E a values, xanthan and gelatin exerting the greatest effect. It is postulated that above the critical concentration stabilizer action may evolve from modification of the kinetics of the unfrozen phase facilitated by changes in free volume distribution specifically altering the rheological and viscoelastic response of systems at sub-zero temperatures.