Initial Freezing Research Articles

Patterns of Ice Formation and Movement in Blackcurrant

Ice formation and movement in stems, leaves, and flowers of blackcurrant were observed by infrared video thermography. Stem sections bearing leaves and racemes were cooled slowly to as low as -6.4 °C and allowed to freeze without artificial nucleation. Ice formed in stems first, then moved from stems into leaves and racemes. Patterns of ice movement were complex and depended upon the temperature of the initial nucleation event. Individual flowers froze between -1.6 and -5.5 °C. Survival of flowers after a cooling treatment depended upon whether they froze and the amount of freezing that occurred in the peduncles to which they were attached. Some flowers survived the initial freezing treatments but later died because of peduncle damage. Movement of ice from stems into peduncles sometimes was observed to occur in discrete steps, separated by time and temperature. Several independent freezing events were often observed in a peduncle, rather than one continuous event. Pedicels attached to frozen peduncles often remained supercooled for several minutes to over an hour before freezing. No consistent pattern was evident during freezing of individual flowers in an inflorescence. The range of temperature over which flowers in a single inflorescence froze was in some instances over 4 °C. Both mature and immature flowers supercooled. Barriers to movement of ice appeared to exist at certain anatomical junctions within the plant, notably where the peduncle of an inflorescence attaches to a stem and where a flower pedicel joins a peduncle. The time required for ice to pass through these barriers was inversely related to the degree of supercooling that had occurred prior to freezing.

Study of cryostructuration of polymer systems. XX. Foamed poly(vinyl alcohol) cryogels

AbstractFoamed poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of whipped PVA water solutions (polymer with MW of 69,000 Da and DD ∼99 mol % was used), were obtained and their properties were studied. The rheological characteristics and macrostructure of these gel materials were controlled by the same factors as for the ordinary nonfoamed PVA cryogels (initial polymer concentration and freezing–thawing regimes) and also by the conditions of generation of fluid PVA foams. The study of the kinetics of the freeze–thaw‐induced gel formation of these foams revealed that the temperature dependence of the efficiency of cryotropic gelation showed a maximum at about −1.5°C. The presence of low molecular weight admixtures in the initial polymer solution appears to be a rather important factor because the admixtures were capable of decreasing the stability of fluid PVA foams and weakening both foamed and nonfoamed cryogel samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1609–1619, 2001

Phase transitions of hard disks in external periodic potentials: a Monte Carlo study.

The nature of freezing and melting transitions for a system of hard disks in a spatially periodic external potential is studied using extensive Monte Carlo simulations. Detailed finite size scaling analysis of various thermodynamic quantities like the order parameter, its cumulants, etc., are used to map the phase diagram of the system for various values of the density and the amplitude of the external potential. We find clear indication of a reentrant liquid phase over a significant region of the parameter space. Our simulations therefore show that the system of hard disks behaves in a fashion similar to charge-stabilized colloids that are known to undergo an initial freezing, followed by a remelting transition as the amplitude of the imposed, modulating field produced by crossed laser beams is steadily increased. Detailed analysis of our data shows several features consistent with a recent dislocation unbinding theory of laser induced melting.

EFFECT OF k -CARRAGEENAN AND NaCl ON INITIAL FREEZING POINT OF EGG AND SURIMI

Initial freezing points Ti of egg samples (melange of egg yolk and white, egg yolk, egg white) and surimi mixed with different mass fractions of . -carrageenan (w = 1O10%), NaCl (w = 1O10%), and mixtures of NaCl and . -carrageenan in mass ratio of 4:1 (w = 1O10%) were determined by use of differential thermal analysis (DTA). Samples of surimi were prepeared in laboratory conditions from Sardina pilchardus. Water content in surimi was 81.50%, in egg yolk 47.65%, in egg white 88.1%, and in melange it was 64.41% before mixing with the added substances. Relations between decrease of the initial freezing point Ti as function of mass fractions w of the added substances were determined by linear regression. Coefficients of determination in range of R 2 = 0.94O0.98 for samples of surimi, and R 2 = 0.92O0.98 for samples of egg were obtained. The largest effect of cryoscopic depression on initial freezing point Ti were exhibited by the samples of surimi with added: a) NaCl in the temperature range from O0.19 to O11.11 °C, b) mixtures of NaCl and . -carrageenan (from O0.19 to O9.08 °C), and c) . -carrageenan (from O0.19 to O0.72 °C). For the samples with pure NaCl the largest decrease of Ti was obtained for: a) egg yolk (from O0.59 to O20.77 °C), b) melange (from O0.59 to O8.74 °C), and c) egg white (from O0.50 to O7.37 °C). The results are compared and discussed with Chang-Tao model for prediction of Ti for meat.

MECHANISMS OF ICE CRYSTALLIZATION AND RECRYSTALLIZATION IN ICE CREAM: A REVIEW

This review article focuses on the mechanisms of ice crystallization and recrystallization and factors that influence them in ice creams. Ice crystallization is an important factor that determines ice cream's final quality. The smaller the ice crystal size is in the final product, the better the quality is. Large ice crystals cause a coarse, grainy, and icy texture in ice cream. The initial ice crystals are formed in the freezer barrel and then grow in size during hardening and storage. Recrystallization during storage is influenced by various factors, including total solids, initial freezing temperature, unfrozen water, stabilizer type, sweetener type, and storage temperature. The roles of these factors, especially stabilizers, are discussed.

Frost-induced reversible shrinkage of bark of mature subalpine conifers

Temporal and spatial patterns of stem and root radius changes were continuously measured on mature, subalpine Norway spruce ( Picea abies (L .) Karst.) over 2 years. In addition, freezing experiments with stem segments of saplings were carried out in a climate chamber. The dynamics of the radius fluctuations were analyzed in relation to temperature profiles of air, bark, and soil. We found that bark thickness sharply decreases by 1 mm and more within 2–3 days when the air temperature falls below −5°C. In contrast to the elastic tissues of the bark, the rigid xylem remains largely unaffected. This frost-induced shrinkage of the bark is up to 10 times larger than the measured amplitude of diurnal stem radius fluctuations in summer. During periods of rising air temperatures (>−12°C), the radius suddenly returns to its original size. We conclude, that the large stem and root radius changes in winter are related to changing bark water content, as is also the case during size fluctuations in summer. For a mature tree with a height of 25 m, the shrinkage of the entire stem bark is equivalent to approximately 20 l of water. A hypothesis is discussed which suggests a frost-induced transport of this water between bark and wood. It is based on the initial freezing of water in the xylem resulting in a water potential gradient between bark (solution) and wood (ice). The hypothesis suggests that the water transport between bark and wood is mainly determined by physical changes and that no biochemical transport energy or physiological control mechanisms are involved. As long as ice is initially formed in the xylem and not in the bark, this mechanism of bark dehydration comes into play and protects the living cells from frost damage.

The use of view angle tilting to reduce distortions in magnetic resonance imaging of cryosurgery☆

Susceptibility artifacts from magnetic resonance (MR)-compatible cryoprobes can distort MR images of iceballs. In this work, we investigate the ability of view angle tilting (VAT) to correct susceptibility induced distortions in MR images of cryosurgery. The efficacy of VAT was tested in an ex vivo bovine liver model of cryosurgery using MR-compatible cryoprobes. Artifacts on high bandwidth fast spin echo images of freezing obtained with and without VAT were compared with photographs of the actual iceball shape and size. In vivo imaging with VAT was demonstrated during percutaneous MR-guided cryosurgery of pig liver and brain. VAT was most successful in reducing probe and iceball distortions when the imaging plane was normal to the cryoprobe, and the cryoprobe was perpendicular to the main magnetic field of the scanner. VAT had the greatest benefit when used to correct MR images of freezing when the surface of the iceball was relatively near to the cryoprobe. For large iceballs, the artifact was small so the VAT correction was less important. We conclude that VAT significantly reduced distortions in the shape of the signal void corresponding to the extent of freezing visualized during MR-guided cryosurgery. This improved ability to visualize the exact location of the cryoprobe, as well as the precise shape of the iceball, particularly during initial freezing when the iceball is small, has potential to significantly improve the accuracy of MR-guided cryosurgery of small lesions, and the accuracy of MR-assisted temperature calculations that are based on precise imaging of the probe location, and boundary geometry of the iceball.

CRYOGENIC RAMAN SPECTROSCOPIC STUDIES IN THE SYSTEM NaCl-CaCl2-H2O AND IMPLICATIONS FOR LOW TEMPERATURE PHASE BEHAVIOR IN AQUEOUS FLUID INCLUSIONS

The character of Raman spectra in the O–H stretching region collected at low temperatures (~−180°C) from fine-grained aggregates of ice and salt hydrate (hydrohalite or antarcticite or both) in the system H2O–NaCl–CaCl2 reflects the composition of the parent solution and can be used to estimate the ratio of NaCl to CaCl2 in the system. Comparison of these spectra with spectra collected from moderate-salinity natural fluid inclusions from the Oregon 3 granitic pegmatite, Colorado, allows non-destructive testing, and confirmation that these inclusions contain CaCl2, as inferred from microthermometry. In both synthetic solutions in the H2O–NaCl–CaCl2 system and in natural fluid inclusions, Raman spectra collected after initial freezing indicate the presence of ice, but not salt hydrates. Upon warming, a phase change is observed at temperatures of between −70 and −50°C that appears as a darkening of the inclusion and that, during routine microthermometry, could be interpreted as a eutectic melting event. Raman spectra collected after this event indicate that it represents the crystallization of salt hydrates (hydrohalite and antarcticite), which we suggest occurs from an interstitial, hypersaline liquid. Many of the low “eutectic” temperatures reported in the literature may thus not represent first melting (stable or metastable), and inferences made about the composition of fluid inclusions from such measurements may be erroneous.

Motility, fertility and ultrastructural changes of ocean pout ( Macrozoarces americanus L.) sperm after cryopreservation

The present study examined the possibility of long term storage, by cryopreservation in liquid N 2, of the sperm of ocean pout ( Macrozoarces americanus L.), an internally fertilizing marine fish, and the changes in motility, fertility and ultrastructure of the sperm after freeze and thaw. Four cryoprotectants, including dimethyl sulfoxide (DMSO), and three semen diluents (A, B and C) were tested for their influence on sperm motility. Since the fresh sperm displayed the highest motility in diluent C, which had the closest chemical composition to that of the seminal plasma of ocean pout, with DMSO, this solution (C-DMSO) was chosen as a diluent for the present study of ocean pout semen cryopreservation. Fresh semen was diluted in three volumes of C-DMSO and filled in 0.25- or 1.7-ml straws, then frozen in liquid N 2 vapor. When the internal temperature of the straws had dropped to −95°C, the straws were plunged into the liquid N 2. To recover the sperm motility, the frozen semen was thawed in 1 or 30°C water bath for 30 and 7 s, respectively. It was demonstrated that the presence of DMSO in semen extender was essential for protecting the sperm from dying during freeze and thaw, and 20% of DMSO (v/v) yielded the highest post-thawed sperm motility (20–25% of the total cells). A freezing rate of average 9°C/min during the initial freezing phase (in liquid N 2 vapor) produced a higher post-thawed sperm motility than that produced by faster (18°C/min) and slower (6°C/min) freezing rates. Thawing the frozen semen in 30 or 1°C water did not cause any difference in terms of sperm motility. The loss of sperm motility during freeze and thaw might be due to the ultrastructural changes of sperm, e.g., severe swelling of the mitochondria or dehydration of cytoplasm at the midpiece, revealed by scanning electron microscope. The motile sperm in the post-thawed semen possessed fertility because in vitro artificial insemination of fresh eggs using the post-thawed semen yielded a fertilization rate of 33% vs. 48–58% from fresh semen.

Physico-Chemical Properties of Illite Suspensions after Cycles of Freezing and Thawing

AbstractThe effect of freezing and thawing on the rheological behavior of illite suspensions was studied by examining viscosity and plasticity. Stability of suspensions was characterized by a hysteresis loop of thixotropy. Thermal gravimetric and differential scanning calorimetry analysis were also used. After initial freezing and thawing, the flow curves of the suspensions show an increased viscosity, an “irregular up line”, and a greater hysteresis loop of thixotropy. The ratios of mean viscosity of previously frozen (F) and control (O) samples (ηF/ηO) for non-expandable 2:1 phyllosilicates ranges from 1.3 to 2.1. Addition of monovalent (0.1% Na2SiO3) and divalent cations (0.3% CaCl2 or BaCl2) increase and decrease the shear-stress difference between F and O samples, respectively. Prior freezing of clay samples results in an increase of plasticity by ∼20–30%. The thermal analysis data of F samples show an increase in weight loss, and a decrease in enthalpy of dehydration. The changes of physico-chemical properties from cycles of freezing and thawing are long lasting. The freezing memory effect of illite-type clays is expected to play an important role in ceramic processing, i.e., casting processes, plastic formation, and sintering.

Freezing and thawing rate effects on drip loss from samples of pork

The effects of six freezing rates, two storage times and three thawing rates on the drip loss from small samples (approximately 6 g) of pork were studied. Drip was collected by centrifugal extraction. Protein denaturation of the meat sample was analysed by differential scanning calorimetry. At fast freezing rates, drip losses obtained were not significantly different from that of fresh samples. At the slower freezing rates studied, drip losses were greater than that from fresh samples. After four weeks storage, drip losses were significantly greater at the slow freezing rates compared to the samples without storage. However, for the stored samples, there were no differences in drip losses with respect to the initial freezing rates. Furthermore, the drip losses from stored samples were not significantly different from drip losses of samples at the slow freezing rates without storage. No differences in denaturation profiles of the meat samples, composition of drip or total protein concentrations in the drip samples were observed.

Bifidobacterium longum Survival During Frozen and Refrigerated Storage as Related to pH during Growth

ABSTRACTFour strains of Bifidobacterium longum were grown at pH 5.5, 6.0, 6.5 and 7.0 and evaluated for survival and bile tolerance during frozen and subsequent refrigerated storage in milk. There were no reductions in cell numbers following initial freezing. There were effects for strain, pH and storage for three of the four strains of B. longum du ring storage at 5°C in milk. Bifidobacterium longum S9 was more stable than other strains in that no losses occurred, regardless of pH during growth. Results were variable for strains II, III, and ATCC 15707 grown at the various pH levels. Bifidobacterium longum S9 did not lose bile resistance during refrigerated storage as the other three strains did.

THERMAL FRACTURE IN A BIOMATERIAL DURING RAPID FREEZING

Thermal stresses leading to fracture during rapid freezing of a biomaterial are studied using potato tissues as an example. The thermal model includes the gradual freezing of the tissue, that is, the presence of a mushy zone. Water in the biomaterial expands almost 9% during freezing and develops transient stresses when the material is frozen from all sides. A viscoelastic model for the tissue is used with mechanical properties changing continuously during freezing. A comparison of stresses developed during freezing, with experimentally measured failure strength, is used as a criterion for initiation of a crack. The strain energy release rate G is calculated using the J integral. Experimental evidence of a catastrophic fracture during very rapid freezing (boundary temperature of 200 C) suggests that the G value is likely to exceed the critical rate (G) at this temperature but not so for slow freezing at a boundary temperature of c.40 C, for which no experimental fractures are observed. A multistep freezing process consisting of initial slow freezing followed by fast freezing to reach the final temperature of 200 C reduces the strain energy release rate, and experiments show that catastrophic failure can be avoided with this protocol.

Intracellular concentration of exogenous glycerol inSaccharomyces cerevisiaeprovides for improved leavening of frozen sweet doughs

Addition of glycerol to baker's yeast coupled with an incubation period under conditions of refrigeration to allow equilibration of the polyol across the yeast membrane, resulted in improved frozen sweet (10% sugar) dough leavening and keeping, relative to doughs made with yeast containing no added glycerol. Glycerol-loaded yeast showed smaller proof time increases after initial freezing and thawing. Also, glycerol treatment led to slower deterioration of the frozen sweet doughs during storage at −21°C for up to 8 weeks (proof time increases were significantly lower in stored frozen doughs made with glycerol-added yeast). Benefits of glycerol loading of yeast for the purpose of production of frozen plain (unsugared) doughs were less significant. The glycerol treatment effects became more significant as the yeast was stored refrigerated prior to mixing and freezing of doughs, i.e. shelf-life of yeast for use in frozen dough manufacture was improved by addition of glycerol. The improvements were dependent on glycerol concentration.

Impaired short- and long-term memory in Ts65Dn mice, a model for Down syndrome

Ts65Dn (TS), control littermates (CO) and Swiss (SW) male mice were tested in the elevated plus-maze and in the Morris water maze (MWM) for memory evaluation. In the plus-maze, each mouse was placed at the end of an open arm and initial freezing and the time to enter into an enclosed arm (transfer latency) were measured. SW mice decreased both measures over repeated trials, whereas no decrease of freezing was observed in CO mice, thus suggesting increased emotionality in this group. Compared to CO mice, TS mice showed less initial freezing, shorter transfer latencies, and spent less time in enclosed arms, suggesting a reduced ability to habituate or to inhibit behaviour. Animals were also submitted to a learning-set paradigm consisting of reaching a new platform position each day in the MWM. Two training phases (separated by a resting period of 6 weeks), each including eight acquisition and four cued sessions, were performed (each session consisting of four pairs of trials). CO and SW mice already reached an asymptotic performance by the second day of the first phase whereas TS mice did not achieve that level until the second training phase. The progression over trials indicated that CO and SW animals learned the new platform position between trials 1 and 2 of each session, whereas TS animals failed to do it and had more difficulties to find the platform when it was placed in the centre of the pool as compared to the other positions (SW, NE, E). The results suggest that TS mice show working memory impairments in addition to long-term memory deficits, although extensive training appeared to facilitate TS mice to achieve a level of performance similar to their control littermates. This represents another aspect of the cognitive deficits shown by TS mice: a mouse model of the human Down syndrome.

Bacterial Extracellular Ice Nucleator Effects on Freezing of Foods

ABSTRACTExtracellular ice nucleators (ECINs) were incorporated into foods and subjected to subzero freezing. Time‐temperature profiles, ice‐formation patterns and textures were examined by thermocouple, microscopy and texture analyzer. Onset temperatures (initial freezing), enthalpies and freezing rates were measured by DSC. Addition of ECINs to liquid foods elevated ice nucleation temperatures and promoted freezing. Solid or semisolid products frozen with ECINs resulted in a fiber‐like texture. These effects were more apparent at –10°C or higher. Differential scanning calorimetry revealed onset temperatures were increased 11°C by addition of ECINs, but length of time to complete the phase transition was extended at constant cooling rates. Results indicated that ECINs can be used instead of whole bacterial cells for efficient freezing and textural modification.

Experimental and theoretical study of model food freezing. Part I. Heat transfer modelling

Textural or organoleptic quality of frozen foods is strongly related to freezing operating conditions which govern the ice crystal size. During this work, gelatin gel was used as a model food and was frozen in a freezing device which ensured a unidirectional heat transfer. The temperature profiles recorded inside the material determined the position of the initial freezing front versus time and the initial freezing temperature. Temperature profiles were obtained for several gelatin gel compositions, cooling temperatures and initial temperature values. The heat transfer could be approximately fitted by the Neumann model. Relationships between gel composition and initial freezing temperature value were also discussed.

Optimal assay conditions for aspartate transcarbamylase (ATCase) activity in mesozooplankton

The optimal conditions for storing and assaying mesozooplankton aspartate transcarbamylase (ATCase) (EC 2.1.3.1.) are defined in order to enable the specific activity of this enzyme to be used as an index of mesozooplankton productivity. ATCase activity was found to be stable for more than 2 weeks when stored in liquid nitrogen, with a negligible loss of activity. whatever the state of frozen material (cell-free homogenate or whole cells). As an alternative, -20 degrees C,-90 degrees C freezers and dry ice (-80 degrees C) can give more flexibility for storing and transporting material, provided initial freezing has been carried out at -196 degrees C. ATCase specific activity was stable over a large range of total protein concentrations (2-55 mg ml(-1)) for most mesozooplankton samples, and the enzyme activity was linear between 0.8 and 80 nmol carbamyl aspartate min(-1) mg(-1) of total protein. The optimal incubation time (30 min), temperature (35 degrees C) and pH range (9-9.5) for assay of ATCase were similar for Calanus helgolandicus (Crustacea: Copepoda) (G.O.Sars) and three mesozooplankton assemblages sampled off Plymouth (UK) in May, August and November. However, the K-m values for both substrates were variable: from 3.9 to 79.1 for aspartate, and from 0.83 to 3.46 for carbamyl phosphate. Such variations are likely to be due to the presence of different ATCase catalytic potential, rather I:han changes in ATCase assemblage.

Relationship between memory and fear: Developmental and pharmacological studies

Habituation of the acoustic startle response (ASR) and freezing responses were assessed simultaneously in rats of different ages. Results showed that until 30 days of age rats were not able to express long-term habituation of the ASR, whereas irrespective of age, all rats exhibited the increased freezing responses as a result of fear conditioning. In addition, the interaction between fear and memory was studied using the same behavioral model in adult rats treated intraperitoneally with diazepam at doses 1.2 and 2.5 mg/kg. Diazepam administration did not result in a significant change in initial startle responsiveness but elicited a profound suppression of startle amplitude over trials. Furthermore, animals given diazepam showed more initial freezing than the vehicle-treated controls, while fear-conditioned freezing was decreased by diazepam. The pattern of results is discussed in relation to developmental and pharmacological dissociations between the different behavioral components of responses to aversive and stressful cues.

Short-time stability of markers of coagulation and fibrinolysis in frozen plasma

We studied the stability of three markers of coagulation (prothrombin fragment 1+2 (F1+2), thrombin-antithrombin III complexes (TAT), and soluble fibrin (SF)) in stored frozen plasma, in addition to one marker of fibrinolysis (total fibrinogen degradation products and fibrin degradation products (TDP)). All markers were measured using enzyme linked immunosorbent assays (ELISA). None of the markers changed significantly after initial freezing. F1+2 in plasma was stable following storage at −80° C for 3 months. In plasma containing high SF levels stored at −80° C, an insignificant time dependent trend towards decreasing plasma values was observed. TAT levels in plasma decreased significantly following 3 months at −80° C. TDP levels in plasma showed some fluctuation when stored in freezer. Our results suggest that careful observation of the long time storage stability of protein components is demanded in clinical research.