Frozen State Research Articles

The effect of freezing rate, frozen storage time and thawing methods on the concentration of thymosin proteins in pork meat

Proteins are the most important ingredients in meat. They are found in meat in different forms and with different functions. Thymosins are small proteins present in many animal tissues, with molecular weights of 1000–15000 Da. The technological processing of meat causes changes in the amount and shape of the basic ingredients. During the freezing of meat and its storage in the frozen state, various chemical reactions take place causing changes in the proteins. The aim of this paper was to examine the influence of the freezing rate and thawing methods on the changes and behaviour of thymosin proteins in pork meat (M. longissimus thoracis et lumborum) during storage. Protein analyses were performed using capillary gel electrophoresis (CGE) and the SDS-MW Analysis Kit (Beckman Coulter). The meat samples were frozen at 10 different rates (from 0.23 cm/h to 1.43 cm/h). The samples were tested at different times during 60 days of storage at -20oC (after 1, 15, 30, 45, 60 days). Before the analysis, the samples were thawed in the refrigerator, at room temperature and in the microwave. After one day of storing frozen meat samples, the relative concentration of thymosin was less than 1% in all tested samples. During 60 days of storage, most samples had a slight increase in the relative concentration of thymosin. The highest relative concentration of thymosin after 60 days of storage (1.67%) was recorded in a meat sample that was frozen at a rate of 1.10 cm/h and thawed in a microwave oven.

An experimental bench for studying the processes of freezing-thawing of soil in the laboratory

In the article, the authors consider the problem of building buildings and structures on permafrost soils, provides a brief overview of ways to preserve the frozen state of base soils. The analysis of scientific works devoted to the thermal interaction of an engineering structure with permafrost soils is given. Conducting full-scale experiments in the conditions of the spread of permafrost soils is a laborious and expensive undertaking, therefore, as part of the research, an experimental stand was developed that allows one to study the processes of freezing and thawing soils in laboratory conditions. The experimental stand is a soil tray with rigid walls and a bottom with overall dimensions in the plan of 1000x1000 mm and a height of 1000 mm. The open system was modeled by placing perforated pipes at the bottom of the tray with a heating cable installed inside the pipes, maintaining a positive water temperature. To ensure one-sided and plane-parallel freezing, the side surfaces and the bottom of the tray were glued with a heater. To fix the temperature of the soil in the experimental bench and the air temperature in the freezer, the TEREM 4-1 measuring complex with DTS 1-1 soil temperature sensors is used. To fix the movements of the soil base in the experimental bench, ICH-50 dial indicators with a division price of 0.01 mm on a telescopic magnetic stand are used. To study the processes of freezing thawing of soils, the authors propose a series of experimental studies on water-saturated loams in laboratory conditions. A description is given of an experimental bench with a model of a thermostabilizer for studying the processes of freezing-thawing of base soils in laboratory conditions, and a methodology for conducting experimental studies is described.

Investigation of zeranol in beef of Ukrainian production and its reduction with various technological processing

Synthetic growth stimulants are widely used to get high productivity of animals. These preparations can accumulate in the meat and their residual quantities will adversely affect the health of consumers. The purpose of the work was to monitor the content of zeranol, growth stimulant of ruminants in beef which goes to meat processing enterprises of the Western region of Ukraine and to determine the effect of heat treatment on its quantity. It was found out that 29.8% of beef samples taken at meat processing enterprises contained a stimulant for the growth of ruminant zeranol. It was found that during the storage of beef samples frozen at a temperature of -18 °C with different content of zeranol there is a decrease in its number. The most intense process of destruction of zeranol occurred during the first month of storage, during this period of time the amount of zeranol is reduced by an average of 20%, regardless of the initial content. Within two months of storage of frozen beef, the content of zeranol decreases by 28.2 ±0.17%, and at the end of the sixth month its quantity decreases to 33.2 ±0.58%. It was also found that the dynamics of zeranol reducing in beef samples with large quantities (22.5 μg.kg-1) and small (2.3 μg.kg-1) were the same. It was set up that during 30 min of meat cooking there was a decrease in the content of zeranol 24.7 ±0.23% and 32.0 ±0.35% for 60 min, compared to its content in fresh meat. At the same time, when stored in the frozen state and subsequent cooking, the reduction of zeranol content in meat was 39.3 ±0.3%. Therefore, it is proposed to revise and amendments into the regulatory documents of Ukraine regarding the control and supervision of the presence of hormone (zeranol) residues in meat and meat products in order to prevent their sale and consumption by humans.

The role of ink-bottle pores in freeze-thaw damage of oolithic limestone

Many natural building stones are altered when subjected to freeze-thaw (FT) cycles. On the one hand, the sensitivity of a material to FT damage has been quantified in the past by the existence of a material-specific critical water saturation. On the other hand, it was noticed that natural stones with a high volume of ink-bottle pores, normally hold a relatively large FT resistance. The relationship between the pore structure, the saturation and the FT resistance is however not well understood. In this paper, the influence of water content and the porosity on FT behaviour is investigated macroscopically with temperature and strain measurements, established techniques in FT related research, and X-ray computed micro-tomography (µCT). Strain measurements performed on Savonnières limestone samples clearly show an increasing expansion with increasing water content, with the existence of a critical water saturation level between 70 and 80%. Differential X-ray imaging on differently saturated limestone samples in an unfrozen and frozen state then aided in explaining the origin of this critical saturation degree. By draining water from surrounding micro-pores through cryo-suction, ink-bottle ooid voids served as expansion reservoirs. When the majority of the ooid voids is water saturated prior to freezing, these voids lose their expansion reservoir ability and damaging pressures arise when water freezes inside undrained micro-pores. These findings not only help to understand the FT resistance of this limestone, but also give insight in the general FT behaviour of materials with bi- or multimodal pore-size distributions.

Use of a temperature ramp approach (TRA) to design an optimum and robust freeze-drying process for pharmaceutical formulations.

Freeze-drying, until now, has been a process that was designed using a trial and error experimental approach. This approach is often material and time consuming, and the resulting freeze-drying processes are neither optimum nor robust. Accordingly, the objective of this study was to develop a simple-to-use and experimental-based approach to design an optimum and robust freeze-drying process for any given formulation. The temperature ramp approach (TRA) detailed in this study involves the implementation of a customized design of experiments (DoE) to perform few (three or four) experiments using a given drug formulation. The DoE results are analyzed to define optimum processing conditions (i.e., shelf temperature and chamber pressure) based on a predefined range of target product temperature for primary drying, which could be defined from formulation characterization at its frozen state. In this study, a successful freeze-drying process of two model formulations using the TRA was designed. Verification experiments at the optimum processing conditions showed excellent agreement in both product temperature and sublimation rate with the values obtained using the TRA. Thus, the TRA detailed in this study offers a significant advantage to reduce development time and material, and enhance the efficiency and robustness of the resulting freeze-drying process.

On the Determination of the Influence of Low Negative Temperatures on Deformability and the Development of the Microcracks Forming Process in Concrete Elements under Axial Compression

Diagrams of axial, lateral and volumetric strains of concrete elements under axial compression in the conditions of low negative temperatures (in the frozen state) are built. It has been established that concrete specimens in the frozen state have increased strength and increased limits of axial, lateral and volumetric strains under axial compression. The diagrams of lateral strains coefficient are built. The dependencies connecting the changes in the values of coefficient of lateral strains of the concrete with variable parameters of its stress-strain state under negative temperatures action are investigated. Based on the analysis of change patterns in lateral, axial and volumetric strains, patterns of microcracks forming in concrete elements in a frozen state are established. The influence of low negative temperatures on the change of parametric points (levels) of stress-strain state of concrete, characterizing the lower and upper boundaries of microcracks forming regions is established. The results of these investigations are used for the development for the diagram method calculating of reinforced concrete structures, designed for use in conditions of low negative temperatures.

Preservation of Epididymal Stallion Sperm in Liquid and Frozen States: Effects of Seminal Plasma on Sperm Function and Fertility

Three separate experiments were conducted to improve preservation of stallion epididymal sperm. In the first one, two different cooling extenders (Kenney and Gent) were compared. Sperm viability and motility patterns were assessed in 10 different epididymal sperm samples after 0 hours, 24 hours, 48 hours, 72 hours, and 96 hours of preservation at 4°C. No significant differences were observed in any of the evaluated parameters either between extenders or throughout the storage period. The second set of experiments was designed to determine whether supplementing thawing medium (INRA Freeze) with seminal plasma had any impact on the quality of frozen-thawed epididymal sperm. Ten epididymal frozen-thawed sperm samples coming from separate stallions were used and different functional parameters (sperm membrane integrity and lipid disorder, motility, intracellular Ca2+ levels, and intracellular concentrations of peroxides and superoxides) were evaluated after incubation with or without 50% seminal plasma. Supplementing thawing medium with seminal plasma had no impact on sperm function and survival. The third experiment was an in vivo study. Twenty-five mares were inseminated with epididymal frozen-thawed sperm and seminal plasma, and 21 were bred with epididymal frozen-thawed sperm only. Pregnancy rates obtained for mares artificially inseminated with epididymal frozen-thawed sperm and seminal plasma were significantly (P < .05) higher than those observed when seminal plasma was not infused (64% vs. 19%). Taken together, our data indicate that the quality of epididymal stallion sperm can be maintained at 4°C for up to 96 hours. In addition, not only does supplementing frozen-thawed epididymal sperm with seminal plasma have any damaging effect on their quality but it may also improve pregnancy rates after artificial insemination.

Resilience to Freezing in the Vegetative Cells of the Microalga Lobosphaera incisa (Trebouxiophyceae, Chlorophyta).

The chlorophyte microalga Lobosphaera incisa was isolated from the snowy slopes of Mt. Tateyama in Japan. This microalga stores exceptionally high amounts of the omega-6 LC-PUFA arachidonic acid in triacylglycerols, and therefore represents a potent photosynthetic source for this essential LC-PUFA. Assuming that freezing tolerance may play a role in adaptation of L.incisa to specific ecological niches, we examined the capability of L.incisa to tolerate extreme sub-zero temperatures. We report here, that the vegetative cells of L.incisa survived freezing at -20°C and -80°C (over 1month), without cryoprotective agents or prior treatments. Cells successfully recovered upon thawing and proliferated under optimal growth conditions (25°C). However, cells frozen at -80°C showed better recovery and lower cellular ROS generation upon thawing, compared to those preserved at -20°C. Photosynthetic yield of PSII, estimated by Fv /Fm , temporarily decreased at day 1 post freezing and resumed to the original level at day 3. Interestingly, the thawed algal cultures produced a higher level of chlorophylls, exceeding the control culture. The polar metabolome of the vegetative cells comprised a range of compatible solutes, dominated by glutamate, sucrose, and proline. We posit that the presence of endogenous cryoprotectants, a rigid multilayer cell wall, the high LC-PUFA content in membrane lipids, and putative cold-responsive proteins may contribute to the retention of functionality upon recovery from the frozen state, and therefore for the survival under cryospheric conditions. From the applied perspective, this beneficial property holds promise for the cryopreservation of starter cultures for research and commercial purposes.

Strength and deformation characteristics of silty clay under frozen and unfrozen states

Frost damage of soil foundations of engineering structures is controlled by mechanical properties of soil under frozen and unfrozen states, existing widely in cold regions such as Genhe area that is termed as the “pole of cold” in China. For investigating engineering properties of soil in cold regions, a series of triaxial compressive tests were carried out on both frozen and unfrozen Genhe silty clay with different degrees of compaction under different confining pressures. The test results show that the stress-strain curves gradually change from softening to hardening with increasing confining pressure, temperature and decreasing compaction degree. Additionally, both axial and radial deformation is more sensitive to lower confining pressures. An accurate method was proposed for determining the elastic modulus. The elastic modulus and strength decrease significantly as the state of soil changes from frozen to unfrozen. The effect of compaction degree on radial deformation, strength and failure strain is gradually eliminated with the increase of confining pressure, which can be observed in both frozen and unfrozen soil. The isotropic tensile strength and the cohesion were obtained in the stress spaces of p-q and σ-τ respectively, and the ice cementing force was identified by adopting the difference of the two strength parameters between frozen state and unfrozen state. The results indicate that the ice cementing force calculated by two strength parameters is consistent, which increases with increasing compaction degree.

Determination of the optimal step of installation between the evaporator pipes and the number of condenser units of the system of temperature stabilization of soils HET

Interest in developing the resource base of the Arctic and subarctic regions has recently increased thanks to the efforts of the media, oil corporations and the government, however, it must be understood that during the construction on the soils of these regions, in which ice acts as a cementing material, their natural temperature regime is violated. leading to the melting of the ice phase. It is known that when thawing frozen soil it loses its strength properties, as a result of which the foundations of the structures on which they are built are at risk of deformation and destruction. To solve this problem, special devices have been developed - seasonally acting cooling devices (SOU), which cool the soil in the cold season and "lock up" in the warm. For this reason, these devices are also called "thermal diodes." In this work, we consider the system of temperature stabilization of soils HET (horizontal naturally acting tubular system) installed at the base of a vertical steel tank (PBC) filled with hot oil-water mixture. A system is considered, in which ammonia acts as a coolant. In addition, the article carried out calculations of various design solutions of the HET system, expressed in variations of such parameters as the length of the evaporator, the number of condensers, and the installation step between the pipes of the evaporator. The work raises the question of justifying the laying step between the pipes of the HET system evaporator and the number of condenser blocks that will be sufficient for the effective functioning of the system, i.e., to maintain the soil in a frozen state. It is shown that for the effective functioning of the system it is not necessary to use a standard paving step equal to 0.5 m, but it can be increased without the risk of losing the bearing capacity of frozen soil. One of the results of the work is the fact that the system is overdetermined by the temperature of stabilization of soils of the HET type at small distances of the laying step relative to the increased distance, which is expressed in a decrease in the number of working days during a calendar year, all other things being equal.

Pressure-induced rapid solidification of polyphenylene sulfide melt

In this work, pressure-induced rapid solidification of polyphenylene sulfide (PPS) melt is studied on a pressure-jump apparatus. Five PPS samples under a pressure of 0.1 GPa are heated to 563 K, 573 K, 583 K, 603 K and 613 K, respectively. These samples are rapidly compressed to 2.4 GPa in about 20 ms. The solidified samples are quenched to room temperature and then depressured to ambient pressure. The X-ray diffraction (XRD) analyses of the recovered samples indicate that three PPS samples, prepared at 563 K, 573 K and 583 K, contain crystal phases but their crystallinity is lower than that of the original PPS powder. The remaining two PPS samples, prepared at 603 K and 613 K, are in amorphous state but do not sharp crystal diffraction peaks in the XRD patterns. Differential scanning calorimetry curves of the five PPS samples each display an endothermic step of glass transition at about 325 K and an exothermic peak of recrystallization around 360 K. The glass transition temperature decreases roughly with the increase of preparation temperature. The thermal enthalpy of recrystallization process increases with the increase of preparation temperature, indicating that the content of amorphous phase increases. We speculate that the recovered samples are in a “frozen state” of their parent liquid. At 563 K, 573 K and 583 K, the crystalline phases partially melt. More crystal phases melt with the increase of preparation temperature. The molten part is rapidly solidified into amorphous phase. At a temperature higher than 603 K, the crystalline phase fully melts, and after being rapidly compressed, amorphous PPS sample is obtained. For the amorphous PPS sample prepared at 613 K, we investigate whether the interior of this amorphous PPS sample is also in amorphous state. Micro XRD analysis indicates that the central part of the PPS sample is also in amorphous state, which suggests that this PPS sample is of a fully amorphous bulk. For the amorphous PPS sample prepared at 613 K, we investigate its recrystallization product. After being annealed at 425 K for 2 h, the amorphous phase, which is solidified from the melt of crystal phase, is recrystallized into the orthorhombic crystal phase. The results in this work indicate that the rapid compression can inhibit the PPS melt from being crystalized, so, it is a way to prepare amorphous PPS bulk. Since the solidification of polymer melt is realized by increasing pressure instead of quenching and is not limited by polymer thermal conductivity, it is a promising way to prepare amorphous polymer bulks with large size.

Особливості біохімічного складу плодів сортів обліпихи крушиноподібної (Hippophae rhamnoides L.) селекції Інституту садівництва НААН України

The analytical researches of sea buckthorn 3 cultivar ad 11 hybrid forms showed that it was cv Oliana that had the larg-est fruit mass (0,7). The berries of the variety Osoblyva and hybrid 1-15-3 had the maximum part of non-soluble organic substances (at a levil of 24.7 and 25.6 % respecti vely). The largest amount of dry soluble substances (13.1 %) during the growth and development period was accumulated by the fruits of the hydrid forms 1-15-8c and 1-15-2a and 1-15-2. The berries of the cultivars Osoblyva and Adaptyvna contained the largest (6.2 and 5.8 % respectively) number of sugar while those of most of studied forms had 3.0 %. The organic acid content in the ‘Oliana’ fruits was 2.77 %. That is less than the hybrids by 1.53 %. The pectins amount in the berries did not exceed 0.51 % of the total number and 0.44 % of the pro-topectine content/ The ascorbic acid maximum (over 15 mg/100 g) was accumulated by the fruits of the variety Adaptyvna and hybrid 1-5-30 and 1-5-15, The mentioned cultivar included the largest polyphenols amount (379 mg/100 g). According to the organoleptic physical and biochemical indicators the ‘Oliana’ fruits were recognized the most favoura-ble for freezing and storage in the frozen state among the studied cvs.

Cryoprotective characteristics of different sugar alcohols on peeled Pacific white shrimp (Litopenaeus vannamei) during frozen storage and their possible mechanisms of action

ABSTRACT Sugar alcohols, also known as polyols, have been widely applied in food products for their unique properties. In this work, the effect of soaking treatments composed of the sugar alcohols xylitol, sorbitol, erythritol, lactitol, mannitol, maltitol, and isomaltitol on the quality properties of peeled Pacific white shrimp during frozen storage were evaluated. Samples treated with water and sodium pyrophosphate (Na4P2O7) were designated as the negative and positive controls, respectively. The results indicated that significant improvements were found in thawing, pressing, and cooking loss, myofibrillar protein content, myofibrillar Ca2+-ATPase activity, and textural variables in xylitol- and mannitol-treated shrimp as compared to that of control samples. Water mobility analyses showed that xylitol and mannitol effectively increased the relaxation times T 21 and T 22 and the percentage of A 21 (trapped water) but decreased the percentage of A 22 (free water) in muscle tissue. Additionally, the microstructural results indicated that soaking in xylitol and mannitol significantly slowed the damage caused to muscle tissues by large ice crystals. Here, the incorporated xylitol and mannitol molecules presumably replaced water molecules by forming large hydrogen bonds with the muscle proteins, thereby stabilizing their structures in the absence of water while in the frozen state and suppressing the destruction of tissue structure. To note, the lactitol, isomaltitol, and maltitol used in this study did not seem to significantly contribute to cryoprotective effects on shrimp muscle during the experimental period.

Back to life from frozen state

Back to life from frozen state

Effects of deboning time and thawing method interaction on sensory descriptive profiles of cooked chicken breast and thigh meat

Effects of deboning time and thawing method interaction on sensory quality of cooked chicken meat were evaluated using factorial experiments with factors muscle type (breast and thighs), deboning time (45 min, 2 h, or 24 h), and thawing method (fresh/never freezing/thawing, directly from frozen state, and thawing for 2 or 24 h before cooking). Broiler meat was deboned at three different postmortem times and cooked from four states. Sensory quality of cooked meat was profiled by a trained descriptive panel. Statistical results show that there were no significant deboning and thawing interaction effects (P > 0.05) for sensory descriptive profiles regardless of muscle type. Intensity scores (5.6–7.1) of sensory texture attributes cohesiveness, hardness, rate of break down, and chewiness of early-deboned fillets (≤2 h) was greater than those (4.4–5.5) of 24 h-deboned fillets; however, there were no differences between three deboning times for cooked thighs. Cooking directly from frozen state caused harder thigh meat (5.7) than the other thawing treatments (<5.0); however, there were no difference in cooked fillets between thawing methods. Results indicate that deboning-time effects on sensory profiles are not altered by thawing methods, and vice versa. Deboning time more affects sensory quality of breast fillets, but thawing methods more influence thigh meat.

Seminal Plasma Cytokines Are Predictive of the Outcome of Boar Sperm Preservation.

Background: Boar seminal plasma is rich in cytokines, which could influence the capability of spermatozoa to tolerate preservation.Objectives: To evaluate the involvement of boar seminal plasma cytokines in the changes experienced by boar spermatozoa during their storage, either in liquid or frozen state.Materials and Methods: In two separated experiments, semen samples from healthy and fertile boars were split in two aliquots, one centrifuged twice (1,500 ×g for 10 min) to harvest seminal plasma, whereas the other was either commercially extended (3 × 107 sperm/mL) and liquid-stored at 17°C during 144 h (n = 28, Experiment 1) or frozen-thawed using a standard 0.5 mL protocol (n = 27, Experiment 2). Sixteen cytokines were quantified using Luminex xMAP®. Sperm attributes (CASA-evaluated total and progressive motility; flow cytometry-evaluated sperm viability, production of intracellular H2O2 and and levels of lipid peroxidation in viable spermatozoa) were evaluated either at 0, 72, or 144 h of liquid storage (Experiment 1) or before freezing and at 30- and 150-min post-thawing (Experiment 2).Results: Multiple linear regression models, with Bayesian approach for variable selection, revealed that the anti-inflammatory TGF-β2, TGF-β3, IL-1Ra, and IL-4 and the pro-inflammatory IL-8 and IL-18, predicted changes in sperm motility for liquid-stored semen while the anti-inflammatory IFN-γ was included in the models predicting changes in all sperm attributes for cryopreserved semen.Conclusion: Specific boar seminal plasma cytokines would contribute to modulate the structural and metabolic changes shown by spermatozoa during preservation, either in liquid or frozen state.

Generalized regimes for the formation of stratified regions during freezing of multi-component mixtures

Stratified double-diffusive layers (DDLs) in fluidic mixtures such as oceans, magma, and latte typically contain alternating low gradient mixing regions separated by high gradient interfaces. The prior knowledge is restricted to the formation of layers, but the existence of DDLs, under prolonged freezing conditions, as well as in multicomponent mixtures, is not yet understood well. In this work, a new observation depicting the existence of a life-cycle for a double-diffusive layer is revealed with the help of real-time observations of unidirectional freezing of multicomponent mixtures. The observations showed a systematic occurrence of the onset, formation, disappearance, and recurrence of the DDLs when freezing conditions prevailed for longer durations of time. The results also include first-ever observations of compositional stratification in a ternary mixture, which depends on the regimes and nature of buoyant convection. The ternary experiments also demonstrated the formation of DDLs much closer to the solidifying mush, which shed light on retaining the stratified layers in the frozen state. Furthermore, the hypothesized life-cycle of the DDL was mapped to the regimes of occurrence and the nonexistence of DDLs in the mixture phase diagrams of binary and ternary systems, with a threshold composition difference and the corresponding critical Rayleigh number. This distinction of the regimes on the phase diagram shows a striking correlation with a reduced ternary phase diagram of igneous rocks, thus providing a suitable basis for explaining the formation of layered rocks.

Magnetization dynamics of weakly interacting sub-100\u2009nm square artificial spin ices

Artificial Spin Ice (ASI), consisting of a two dimensional array of nanoscale magnetic elements, provides a fascinating opportunity to observe the physics of out-of-equilibrium systems. Initial studies concentrated on the static, frozen state, whilst more recent studies have accessed the out-of-equilibrium dynamic, fluctuating state. This opens up exciting possibilities such as the observation of systems exploring their energy landscape through monopole quasiparticle creation, potentially leading to ASI magnetricity, and to directly observe unconventional phase transitions. In this work we have measured and analysed the magnetic relaxation of thermally active ASI systems by means of SQUID magnetometry. We have investigated the effect of the interaction strength on the magnetization dynamics at different temperatures in the range where the nanomagnets are thermally active. We have observed that they follow an Arrhenius-type Néel-Brown behaviour. An unexpected negative correlation of the average blocking temperature with the interaction strength is also observed, which is supported by Monte Carlo simulations. The magnetization relaxation measurements show faster relaxation for more strongly coupled nanoelements with similar dimensions. The analysis of the stretching exponents obtained from the measurements suggest 1-D chain-like magnetization dynamics. This indicates that the nature of the interactions between nanoelements lowers the dimensionality of the ASI from 2-D to 1-D. Finally, we present a way to quantify the effective interaction energy of a square ASI system, and compare it to the interaction energy computed with micromagnetic simulations.

Freezing of Biologicals Revisited: Scale, Stability, Excipients, and Degradation Stresses.

Although many biotech products are successfully stored in the frozen state, there are cases of degradation of biologicals during freeze storage. These examples are discussed in the Perspective to emphasize the fact that stability of frozen biologicals should not be taken for granted. Frozen-state degradation (predominantly, aggregation) has been linked to crystallization of a cryoprotector in many cases. Other factors, for example, protein unfolding (either due to cold denaturation or interaction of protein molecules with ice crystals), could also contribute to the instability. As a hypothesis, additional freezing-related destabilization pathways are introduced in the paper, that is, air bubbles formed on the ice crystallization front, and local pressure and mechanical stresses due to volume expansion during water-to-ice transformation. Furthermore, stability of frozen biologicals can depend on the sample size, via its impact on the freezing kinetics (i.e., cooling rates and freezing time) and cryoconcentration effects, as well as on the mechanical stresses associated with freezing. We conclude that, although fundamentals of freezing processes are fairly well described in the current literature, there are important gaps to be addressed in both scientific foundations of the freezing-related manufacturing processes and implementation of the available knowledge in practice.

Mathematical Modeling of Heat-Exchange Processes in Outdoor Storage of Frozen Coal

The modeling procedure is developed to describe heat-exchange processes in outdoor summer storage piles of frozen coal produced in winter. This procedure takes into account thermophysical properties of coal and the pile bottom soil, pile structure, climatic factors and the presence of a heat-insulating coating over the pile. In terms of central Yakutia, it is shown that maximum transition of coal from frozen state (piling in January-March) to thawed condition at the pile height more than 5 m will make 25-35% by the end of the warm season (beginning of October). Application of simple and available heat-insulating materials can reduce thawing intensity by up to 2 times. Natural cold weakens the aggravating effect of oxidizing processes on coal quality in long-term storage of coal and its shipment to remote and hard-to-reach places.