Liquid fragility and the glass transition in water and aqueous solutions

Thermomechanical transitions of meat-analog based fried foods batter coating

This study aimed to characterize the thermomechanical transitions of meat-analog (MA) based coated fried foods. Wheat and rice flour-based batters were used to coat the MA and fried at 180 °C in canola oil for 2, 4 and 6 min. Glass-transition-temperature (Tg) of the coatings were assessed by differential scanning calorimetry, directly after frying or after post-fry holding. Mechanical texture analyzer and X-ray microtomography were employed to assess textural attributes and internal microstructure, respectively. Batter-formulation substantially impacted the Tg of fried foods coating i.e., crust. Tg of fried foods crust were ranged between -20 °C to -24 °C. Tg was positively correlated with frying time and internal microporosity (%), whereas negatively correlated with moisture content. Internal microstructure greatly influenced the textural attributes (hardness, brittleness, crispiness). Post-fry textural stability considerably impacted by Tg. Negative Tg value explains post-fry textural changes (hard-to-soft, brittle-to-ductile, crispy-to-soggy) of MA-based coated products at room-temperature (25 °C) and under IR-heating (65 °C).

On the universality of viscosity in supersaturated binary aqueous sugar solutions: Cryopreservation by vitrification

Nowadays, the physical nature of supersaturated binary aqueous sugar solutions in the vicinity of the glass transition represents a very important issue due to their biological applications in cryopreservation of cells and tissues, food science and stabilization and storage of nano genetic drugs. We present the construction of the Supplemented Phase Diagram and the non-equilibrium nature of the undersaturated-supersaturated kinetic transition. The description of its thermodynamic nature is achieved through the study of behavior of their viscosity as temperature is lowered and concentration increased. In this work, we find a universal character for the viscosities of several sugar water solutions.

Glass transition phenomena and dielectric relaxations in supercooled d-lyxose aqueous solutions

Differential scanning calorimeter and broadband dielectric spectroscopy in a broad range of temperatures (150-300 K) were employed to study the d-lyxose aqueous mixture at different hydration levels. Two relaxation processes were observed in all investigated d-lyxose aqueous mixtures. A relaxation process (process-I) usually known as the primary relaxation mode which is accountable for the collective motion of d-lyxose aqueous solution, was observed above the glass transition temperature (Tg). Below Tg, another process designated as process-II was found which is mainly related to the water molecule relaxation inside the d-lyxose matrix. The average relaxation times as a function of temperature and dielectric strengths of both observed relaxation processes (I & II) were analyzed for all hydration levels in d-lyxose. It was identified that the relaxation amplitude of process-II in the d-lyxose aqueous mixture was increased drastically and their activation energies were found to be approximately independent of the content of water above critical concentration, xc = 0.28. This suggests that the dynamical process observed above xc was dominated by the presence of water clusters. In the current aqueous mixture, the critical content of water (xc) is slightly higher as compared to previously reported aqueous mixtures, indicating a more cooperative nature of water molecules with a d-lyxose matrix. Additionally, the Tg of pure water was estimated at 128 ± 5.8 K from the extrapolation of DSC Tg data of the d-lyxose aqueous solution by using the well-known Gordon-Taylor equation. Our current result gives further support to the well-accepted glass transition (Tg) of pure water.

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria

The purpose of this study was to clarify the glass-transition behavior of bacteria (Cronobacter sakazakii) as a function of water activity (aw). From the water sorption isotherm (298 K) for C. sakazakii, monolayer water content and monolayer aw were determined to be 0.0724 g/g-dry matter and 0.252, respectively. Mechanical relaxation was investigated at 298 K. In a higher aw range of over 0.529, the degree of mechanical relaxation increased with an increase in aw. From the effect of aw on the degree of mechanical relaxation, the mechanical awc (aw at which mechanical glass transition occurs at 298 K) was determined to be 0.667. Mean-square displacement of atoms in the bacteria was investigated by incoherent elastic neutron scattering. The mean-square displacement increased gradually with an increase in temperature depending on the aw of samples. From the linear fitting, two or three dynamical transition temperatures (low, middle, and high Tds) were determined at each aw. The low-Td values (142-158 K) were almost independent from aw. There was a minor effect of aw on the middle Td (214-234 K) except for the anhydrous sample (261 K). The high Td (252-322 K) largely increased with the decrease in aw. From the aw dependence of the high Td, the dynamical awc was determined to be 0.675, which was almost equivalent to the mechanical awc. The high Td was assumed to be the glass-transition temperature (Tg), and anhydrous Tg was estimated to be 409 K. In addition, molecular relaxation time (τ) of the bacteria was calculated as a function of aw. From the result, it is suggested that the progress of metabolism in the bacterial system requires a lower τ than approximately 6 × 10-5 s.

Curled cation structures accelerate the dynamics of ionic liquids

Ionic liquids are modern liquid materials with potential and actual implementation in many advanced technologies. They combine many favourable and modifiable properties but have a major inherent drawback compared to molecular liquids - slower dynamics. In previous studies we found that the dynamics of ionic liquids are significantly accelerated by the introduction of multiple ether side chains into the cations. However, the origin of the improved transport properties, whether as a result of the altered cation conformation or due to the absence of nanostructuring within the liquid as a result of the higher polarity of the ether chains, remained to be clarified. Therefore, we prepared two novel sets of methylammonium based ionic liquids; one set with three ether substituents and another set with three butyl side chains, in order to compare their dynamic properties and liquid structures. Using a range of anions, we show that the dynamics of the ether-substituted cations are systematically and distinctly accelerated. Liquefaction temperatures are lowered and fragilities increased, while at the same time cation-anion distances are slightly larger for the alkylated samples. Furthermore, pronounced liquid nanostructures were not observed. Molecular dynamics simulations demonstrate that the origin of the altered properties of the ether substituted ionic liquids is primarily due to a curled ether chain conformation, in contrast to the alkylated cations where the alkyl chains retain a linear conformation. Thus, the observed structure-property relations can be explained by changes in the geometric shape of the cations, rather than by the absence of a liquid nanostructure. Application of quantum chemical calculations to a simplified model system revealed that intramolecular hydrogen-bonding is responsible for approximately half of the stabilisation of the curled ether-cations, whereas the other half stems from non-specific long-range interactions. These findings give more detailed insights into the structure-property relations of ionic liquids and will guide the development of ionic liquids that do not suffer from slow dynamics.

Effects of glass transition and hydration on the biological stability of dry yeast

The purpose of this study was to determine the effects of glass transition and hydration on the storage stability of baker's dry yeast (Saccharomyces cerevisiae). The glass transition temperature (T_g ) of the yeast decreased with increase in water activity (a_w ), and a_w at which glass transition occurs at 25 °C was determined as the critical a_w (a_wc ). From mechanical relaxation measurements at 25 °C, the yeast exhibited a large mechanical relaxation above the a_wc , and the degree of mechanical relaxation increased gradually with increasing a_w . This behavior corresponded to a gradual increase in molecular mobility with increasing a_w in the rubbery liquid state. Freezable water was observed from a_w ≥0.810, and the proportion of freezable water increased with increasing a_w . Examination of the effect of a_w on the residual biological activity of yeast samples stored at 25 °C for 30 days revealed maximum residual biological activity at a_w  = 0.225 to 0.432. In the lower a_w range, the residual biological activity decreased because of oxidation of lipids. In the higher a_w range, the residual biological activity decreased gradually with increasing a_w . The yeast samples maintained a relatively high residual biological activity, because they could maintain relatively low molecular mobility even in the rubbery liquid state, as suggested by their mechanical relaxation behavior. At a_w ≥0.809, residual activity decreased to a negligible value. This could be explained by the appearance of secondary hydrate water (freezable water). Hydrate water protects yeast cells from lipid oxidation but reduces the T_g . As a result, the yeast cells are stabilized maximally only at the a_wc . PRACTICAL APPLICATION: Although the growth rate of yeast cells becomes negligible below a certain a_w , the biological activity of dry yeast decreases gradually during storage. The fact that dry yeast can be maximally stabilized at the a_wc is practically useful as a criterion for controlling storage stability. In addition, it was found that a remarkable reduction in the molecular mobility, which is otherwise ordinarily increased due to the glass-to-rubber transition, is prevented in yeast. It is possible that the crystallization of amorphous sugar can be prevented by yeast extract. The suggested effect is expected to result in enhanced quality of carbohydrate-based foods.

Physical and structural characteristics of starch-based and conventional cookies: Water sorption, mechanical glass transition, and texture properties of their crust and crumb

The physical properties of starch-based cookie (gluten free and low fat) were compared with those of conventional cookie in consideration for the difference between crust and crumb parts. The internal porosity of the samples was measured by X-ray computed tomography. The starch-based cookie had a higher porosity (0.61) than the conventional cookie (0.42). The mechanical glass-transition temperature (T_g ) of the samples was evaluated by the thermal rheological analysis. The anhydrous mechanical T_g of the starch-based cookie was much lower than that of the conventional cookie. The T_g -depression of the starch-based cookie induced by water sorption was more gradual than that of the conventional cookie. For both types of cookie, the crust components were more resistant to water plasticizing than crumb components because of the difference of the equilibrium water contents at each water activity. For the texture analysis of crust components, the whole samples were fractured. The starch-based cookie had a lower fracture force, distance, and energy than the conventional cookie at each water activity point. For the texture analysis of crumb components, a portion of the crust was removed from the whole samples, and the exposed crumb was compressed by a plunger. From the texture profile, a normalized linear length was evaluated. The normalized linear length for the starch-based cookie was higher than that for the conventional cookie. These results were corresponded to the differences in the undeveloped gluten and fat contents.

Physical Ageing of Amorphous Indapamide Characterised by Differential Scanning Calorimetry

The objective of this study was to characterise amorphous indapamide (IND) subjected to the physical ageing process by differential scanning calorimetry (DSC). The amorphous indapamide was annealed at different temperatures below the glass transition, i.e., 35, 40, 45, 65, 75 and 85 °C for different lengths of time, from 30 min up to a maximum of 32 h. DSC was used to characterise both the crystalline and the freshly prepared glass and to monitor the extent of relaxation at temperatures below the glass transition (T_g). No ageing occurred at 35, 40 and 45 °C at the measured lengths of times. Molecular relaxation time constants (τ^KWW) for samples aged at 65, 75 and 85 °C were determined by the Kohlrausch-Williams-Watts (KWW) equation. The fragility parameter m (a measure of the stability below the glass transition) was determined from the T_g dependence from the cooling and heating rates, and IND was found to be relatively stable ("moderately fragile") in the amorphous state. Temperature-modulated DSC was used to separate reversing and nonreversing processes for unaged amorphous IND. The enthalpy relaxation peak was clearly observed as a part of the nonreversing signal. Heat capacities data for unaged and physically aged IND were fitted to C_p baselines of solid and liquid states of IND, were integrated and enthalpy was presented as a function of temperature.

Extension and Limits of Cryoscopy for Nanoconfined Solutions

This work investigates the phase behavior of aqueous solutions of glycerol confined in MCM-41 and SBA-15 nanoporous matrixes by calorimetry. Limitations due to overfilling and eutectic freezing are prevented by the absence of an external liquid reservoir and by the glass-forming property of glycerol. Consequently, the stability of nanoconfined ice in equilibrium with aqueous solutions is studied over a wide range of compositions. In confinement, a large temperature depression of the liquidus line is observed. A thermodynamic model accounting simultaneously for the cryoscopic and the Gibbs-Thomson effects gives a consistent view of the phase diagram for large pores (R_p = 4.15 nm). For smaller pores (R_p = 1.8 nm), it reveals that the water activity strongly deviates from the bulk solution with the same composition, indicating the possible role of concentration heterogeneities in determining the onset of ice freezing in strongly nanoconfined solutions.

Ionic liquid based battery electrolytes using lithium and sodium pseudo-delocalized pyridinium anion salts

The electrolyte salt plays an important role for the overall performance and safety of lithium- and sodium-ion batteries (LIBs and SIBs, respectively). Here, two new lithium and sodium pseudo-delocalized pyridinium anion based salts were used to prepare ionic liquid (IL) based electrolytes. The Li and Na salts of the 1-methylpyridinum 2,6-dicarboxylate anion (MM26py) were synthesized and dissolved in an IL matrix (Pyr14TFSI) - hence creating mixed anion electrolytes. The obtained electrolytes are stable up to 150 and 200 °C and show ion conductivities of 2.8 and 3.2 mS cm-1 at room temperature, for the LIB and SIB electrolytes, respectively. A competitive effect between the MM26py and the TFSI anions to coordinate the alkali metal cations is observed. Finally, the electrochemical stability windows of 2.3 and 2.5 V, respectively, confirm that these electrolytes can be used practically in medium-voltage LIBs and SIBs.

Control of Physical Changes in Food Products

Food is a multicomponent system that mainly comprises protein, carbohydrate, fat, and water. During food processing and preservation, various physical changes (e.g., melting, crystallization, glass transition) occur in food products, affecting their quality. This chapter specifically examines the effect of physical changes on the quality of dry and frozen food products. Dry food products are commonly in an amorphous state. Therefore, glass transition occurs during their dehydration-rehydration processing. To control their texture and physical stability, it is important to elucidate the effects of water contents on the glass transition temperature of dry food products. Frozen foods consist of ice crystals and freeze-concentrated matrix. The formation of ice crystal and the dynamics of ice crystal evolution affect food quality. Therefore control of ice crystals is important for high-quality frozen food. Moreover, because freeze-concentrated matrix consists of solute that are plasticized by the unfrozen water and is in an amorphous state, it can undergo glass transition by freeze concentration. The physical state of freeze-concentrated matrix also strongly affects the stability of food quality during frozen storage.

Accelerated Physical Stability Testing of Amorphous Dispersions

The goal was to develop an accelerated physical stability testing method of amorphous dispersions. Water sorption is known to cause plasticization and may accelerate drug crystallization. In an earlier investigation, it was observed that both the increase in mobility and decrease in stability in amorphous dispersions was explained by the "plasticization" effect of water (Mehta et al. Mol. Pharmaceutics 2016, 13 (4), 1339-1346). In this work, the influence of water concentration (up to 1.8% w/w) on the correlation between mobility and crystallization in felodipine dispersions was investigated. With an increase in water content, the α-relaxation time as well as the time for 1% w/w felodipine crystallization decreased. The relaxation times of the systems, obtained with different water concentration, overlapped when the temperature was scaled (Tg/T). The temperature dependencies of the α-relaxation time as well as the crystallization time were unaffected by the water concentration. Thus, the value of the coupling coefficient, up to a water concentration of 1.8% w/w, was approximately constant. Based on these findings, the use of "water sorption" is proposed to build predictive models for crystallization in slow crystallizing dispersions.

Computational fluid dynamics approaches in quality and hygienic production of semisolid low-moisture foods: a review of critical factors

Low-moisture foods have been responsible for a number of salmonellosis outbreaks worldwide over the last few decades, with cross contamination from contaminated equipment being the most predominant source. To date, actions have been focused on stringent hygienic practices prior to production, namely periodical sanitization of the processing equipment and lines. Not only does optimum sanitization require in-depth knowledge on the type and source of contaminants, but also the heat resistance of microorganisms is unique and often dependent on the heat transfer characteristics of the low-moisture foods. Rheological properties, including viscosity, degree of turbulence, and flow characteristics (for example, Newtonian or non-Newtonian) of both liquid and semisolid foods are critical factors impacting the flow behavior that consequently interferes heat transfer and related control elements. The demand for progressively more accurate prediction of complex fluid phenomena has called for the employment of computational fluid dynamics (CFD) to model mass and heat transfer during processing of various food products, ranging from drying to baking. With the aim of improving the quality and safety of low-moisture foods, this article critically reviewed the published literature concerning microbial survival in semisolid low-moisture foods, including chocolate, honey, and peanut butter. Critical rheological properties and state-of-the-art CFD application relevant to quality production of those products were also addressed. It is anticipated that adequate prediction of specific transport properties during optimum sanitization through CFD could be used to solve current and future food safety challenges.

Effects of salt on the expansion of starchy snacks: a multiscale analysis

We investigate the effect of salt on the expansion of starchy snacks during frying by means of a multiscale simulation model.

Broadband dielectric spectroscopic, calorimetric, and FTIR-ATR investigations of D-arabinose aqueous solutions

The dielectric relaxation behavior of D-arabinose aqueous solutions at different water concentrations is examined by broadband dielectric spectroscopy in the frequency range of 10(-2) -10(7) Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (T(g)). In addition, the same solutions are analyzed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) method at the same temperature interval and in the frequency range of 3800-2800 cm(-1). The temperature dependence of the relaxation times is examined for the different weight fractions (x(w)) of water along with the temperature dependence of dielectric strength. Two relaxation processes are observed in the aqueous solutions for all concentrations of water. The slower process, the so-called primary relaxation process (process-I), is responsible for the T(g) whereas the faster one (designated as process-II) is due to the reorientational motion of the water molecules. As for other hydrophilic water solutions, dielectric data for process-II indicate the existence of a critical water concentration above which water mobility is less restricted. Accordingly, FTIR-ATR measurements on aqueous solutions show an increment in the intensity (area) of the O-H stretching sub-band close to 3200 cm(-1) as the water concentration increases.

Relationship between the phase diagram, the glass-forming ability, and the fragility of a water/salt mixture

Water is known to be an exceptionally poor glass former, which is a significant drawback in the low-temperature storage of food and biomatter. This is one of the characteristic features of water, but its link to the thermodynamic and kinetic anomalies of water remains elusive. Recently, we showed that the glass-forming ability and the fragility of a water/salt mixture are closely related to its equilibrium phase diagram [Kobayashi, M.; Tanaka, H. Phys. Rev. Lett.2011, 106, 125703]. Here we propose that frustration between local and global orderings controls both the glass-forming ability and fragility on the basis of experimental evidence. Relying on the same role of salt and pressure, which commonly breaks tetrahedral order, we apply this idea to pure water under pressure. This scenario not only explains unusual behavior of water-type liquids such as water, Si, and Ge but also provides a general explanation on the link between the equilibrium phase diagram, the glass-forming ability, and the fragility of various materials including oxides, chalcogenides, and metallic glasses.

Possible link of the V-shaped phase diagram to the glass-forming ability and fragility in a water-salt mixture

Water is a very poor glass former, but its link to the thermodynamic and kinetic anomalies remains elusive. We experimentally reveal that the glass-forming ability and fragility of a water-salt mixture are closely related to its equilibrium phase diagram. We propose that frustration between local and global orderings controls both the glass-forming ability and the fragility. Relying on the same role of salt and pressure, which commonly break tetrahedral order, we apply this idea to pure water under pressure. This scenario not only explains unusual behavior of water-type liquids such as water, Si, and Ge but also provides a mechanism for a link between the equilibrium phase diagram, glass-forming ability, and fragility for various materials including oxides, chalcogenides, and metallic glasses.

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

Supplemented temperature/composition phase diagrams include the non-equilibrium glass-transition temperature (Tg) curve and equilibrium ice-melting and solubility curves. The inclusion of the non-equilibrium curve allows one to establish relationships with the time coordinate and, thus, with the dynamic behavior of systems, provided that the thermal history of such systems is known. The objective of this report is to contribute to the potential applications of supplemented state diagrams for aqueous glass-formers, in order to describe the influence of water content, nature of vitrifying agents, and temperature on the physico-chemical properties of foods and biological and pharmaceutical products. These data are helpful to develop formulations, processing strategies, or storage procedures in order to optimize the stability of food ingredients and pharmaceutical formulations. Reported experimental data on phase and state transitions for several food and pharmaceutical systems were analyzed. Some methodological aspects and the effect of phase and state transitions on the main potential chemical reactions that can alter those systems during processing and/or storage are discussed.

Osmo-air drying of aloe vera gel cubes

Aloe vera (Aloe barbadensis Miller) cubes of 12.5 × 12.5 × 12.5 mm thick were osmosed for 4 h in sugar syrup of 30, 40 and 50°Brix concentration and temperatures of 30 and 50°C at constant syrup to fruit ratio of 5:1. Osmosed and unosmosed aloe vera samples were hot air dried at 50, 60, 70 and 80°C with constant air velocity of 1.5 m/s. The water loss, solid gain and convective drying behaviour were recorded during experiments. It was observed that water loss and solid gain ranged from 39.2 to 71.3 and 2.7 to 6.3%, respectively during osmo-drying. The moisture diffusivity varied from 2.9 to 8.0 × 10⁻⁹ m²/s and 2.7 to 4.6 × 10⁻⁹ m²/s during air drying of osmosed and unosmosed aloe vera samples, respectively. Drying air temperature and osmosis as pre-treatment affected the water loss, solid gain, diffusivity at −p ≤ 0.01

Drying and rehydration of DLPC/DSPC symmetric and asymmetric supported lipid bilayers: a combined AFM and fluorescence microscopy study

This work characterizes the impact of lipid symmetry/asymmetry on drying/rehydration reorganization in phase-separated dilauroylphosphatidylcholine (DLPC)/distearoylphosphatidylcholine (DSPC) supported lipid bilayers (SLBs) at the submicron and micron-scale. In addition the prevention of major drying/rehydration reorganization by the use of trehalose is demonstrated. Even though it was found using fluorescence microscopy that micrometer scale structure is preserved in the presence and absence of trehalose upon drying/rehydration, AFM and FRAP experiments successfully revealed major changes in the phase-separated structure such as defects, obstructions, lipid condensation, collapse structures, and complex incomplete DLPC-DSPC mixing/exchange in the absence of trehalose. In the presence of trehalose the membrane preserves its structure at the nanometer scale and mobility. We found that SLBs with asymmetric domain configurations underwent major rearrangements during drying and rehydration, whereas the symmetric domain configuration mainly rearranged during rehydration, that we hypothesize is related to lower transmembrane cohesiveness or lack of anchoring to the substrate in the case of the asymmetric domains.

Modelling Viscosity Temperature Dependence of Supercooled Sucrose SolutionsThe Random-Walk Approach

Sucrose and its supersaturated or supercooled solutions are of the utmost importance in areas as different as food and pharmaceutical industries or cryopreservation of biological systems. In the supercooled "state", such amorphous solutions are fragile systems, presenting extremely high viscosity with decreased mobility of molecules, impairing experimental determinations at low temperatures (below critical temperature, Tc). This work proposes the random walk (RW) approach to study relaxation behavior in the supercooled melt, using only viscosity data at temperatures above Tc. For comparison purposes, the Vogel-Fulcher-Tamman (VFT) model was fitted to th data. The random walk approach is based on the distribution of molecular energies, thus having a theoretical support not found in the VFT model. The RW estimated parameters can be correlated with system characteristics, showing their dependence on water content or sucrose concentration. RW and VFT model description was evaluated from the mathematical and physical points of view, but the random walk model led to more consistent regression results and parameter estimates with improved precision.