In-situ aircraft observations of aerosol and cloud microphysical characteristics of mixed-phase clouds over the North China Plain.

Aerosol-cloud interactions play a vital role in climate change. This study leverages observations from the King-350 aircraft over the North China Plain on November 29, 2019, to examine aerosol and cloud microphysical characteristics of mixed-phase clouds. Through detailed vertical and spectral distributions, we investigate aerosol, cloud droplet, and ice crystal distributions in seeded clouds (SC) and natural precipitating clouds (NPC) within the same cloud system. From the vertical profile, SC and NPC have similar vertical distributions of aerosol and cloud droplets, with over 95 % of aerosols concentrated below 1600 m near the ground. Cloud droplets are more evenly distributed within the two clouds, cloud droplet number concentrations (Nc) in SC were three orders of magnitude higher than in NPC. Ice water content (IWC) and ice crystal number concentration (Ni) show distinct layer preferences-accumulating predominantly in SC's top layer and NPC's middle layer. From spectral distribution, a smaller proportion of cloud droplets (40-50 µm in diameter, the same hereafter) in SC compared to NPC. Rimed ice crystals and globular graupel (1325-1550 µm in diameter) were in SC, while plate and irregular ice crystals (300-450 µm) were in NPC with an order of magnitude higher than in SC. These microphysical differences highlight the complexity of cloud seeding efficacy, which varies based on cloud conditions and microphysical properties. In the first seeding, Ni increased by 1-2 orders of magnitude (125-300 µm) in the high Nc (Nc > 1.11 × 105 L-1) region. Seeding in low Nc (Nc < 1.11 × 105 L-1) regions was hard to be effective, especially in low Nc and low liquid water content (LWC) (LWC < 0.122 g/m3) regions. In the second seeding, ice crystals (125-250 µm) produced by the first seeding enhance the seeding efficiency. The responded regions were more sensitive to subsequent seeding, resulting in stronger reactions or longer duration.

Structure and mechanical properties of anisotropic agar gels obtained via unidirectional freezing.

The controllable formation of anisotropic gel structures is presently sought for the development of foods with novel textures. Here, we used unidirectional freezing to generate agar gels consisting of a honeycomb-like porous network of elongated and aligned pores. A custom-built Peltier system allowed for control of the freezing front velocity throughout the agar gels. A higher freezing velocity (10 µm/s) led to smaller pore sizes compared to the slower freezing velocity tested (2 µm/s). Texture analysis highlighted the significantly higher Young's modulus in the gels when compressed in the axial vs. radial direction - a direct consequence of the unidirectional freezing. The proton spin-spin relaxation time revealed greater water mobility in the unidirectionally frozen gel with larger pores. This study serves as the basis for the development of anisotropic hydrocolloid gels with a tunable microstructure and texture.

Effect of different freezing conditions on ice crystal formation behavior and ice-growth inhibition by cryoprotectants.

BACKGROUND: The formation of ice crystals will have adverse effects on aquatic products, and the key to ensure the long-term preservation and better quality preservations of the product is to evaluate the intercellular ice crystal formation to find suitable refrigeration conditions and cryoprotectants. RESULTS: The ice crystal formation was successfully captured by using an inverted microscope cryomicroscopic system equipped with a low-temperature stage, the ice crystals formed under different freezing methods between tuna muscle cells were observed directly, the deformation degree of muscle tissue pores during crystallization was evaluated, and the effect of freeze-thaw times on tuna samples was analyzed. The effects of the use of cryoprotectant such as cellobiose and carboxylated cellulose nanofibers on ice-growth inhibition were investigated, and the reliability of the ice crystal observation results was further verified by the determination of physical properties. The results showed that carboxylated cellulose nanofibers had the best ice-growth inhibition effect, they prevented about 50% cell deformation compared with the control group, and also reduced the minimum size of ice crystal formation. In addition, the addition of cellobiose and sodium tripolyphosphate gave the ice crystals a more uniform size and roundness. CONCLUSION: The experiment proposed a stable and clear observation method for the process of intercellular ice crystal formation, and the accuracy of the observation method was further verified by some physical indicators. This may help in the selection of suitable measurement methods to directly observe ice crystal formation behavior and screen cryoprotectants. © 2024 Society of Chemical Industry.

Higher molecular weight pectin inhibits ice crystal growth and its effect on the microstructural and physical properties of pectin cryogels.

Understanding the formation of ice crystals is essential for tailoring the microstructure and physical properties of cryogels. This study investigated the effects and mechanisms of pectin molecular weight (Mw) on impacting ice crystal formation. Pectin fractions various Mw (10.13-212.20 kDa) were prepared by hydrothermal method. The solution of high Mw pectin fractions exhibited higher contact angle, lower water freedom, and stronger adsorption of water molecules. The splat experiment and molecular dynamic (MD) results confirmed that higher Mw pectin have stronger ice crystal growth inhibition activity than lower Mw pectin. Furthermore, the pore size distribution of the cryogel increased from 98-203 µm to 105-267 µm as the molecular weight decreased from 212.2 kDa to 121.0 kDa. Additionally, in the higher Mw pectin cryogel, stronger mechanical strength was observed. These findings suggested that changing the molecular weight of pectin has the potential to regulate the ice crystal growth, microstructure and physical properties of frozen products.

Probing the Size Effect of Graphene Oxide Nanosheets on Ice Crystal Regulation and Laser-Assisted Rapid Rewarming.

Two-dimensional (2D) nanomaterials have attracted many researchers to explore the effect of ice control and rapid deicing due to their functional groups, large specific surface area, and excellent photothermal properties. However, the impact of size effects on ice crystal formation, growth, and photothermal performance has been rarely explored. Here, graphene oxide nanosheets (GO NSs) with controllable sizes were used as a representative of 2D nanomaterials to probe the effect of size on ice crystal regulation and rapid rewarming in cell cryopreservation. All sizes of GO NSs exhibited notable inhibitory effects on ice crystal size during the recrystallization process. Significantly, when the size of GO NSs was smaller than a certain size (<150 nm), they showed a more significant ice recrystallization suppression effects, which could reduce the ice crystal size to about 17% of that of pure water. Meanwhile, the photothermal experiments also indicated that smaller-sized GO NSs exhibited better photothermal behavior, with 90 nm GO NSs (GO-90) heating to 70 °C in just 1 min induced by an 808 nm laser (2 W/cm2). Furthermore, applying GO-90 (200 µg/mL) to cell cryopreservation, cell viability could reach 95.2% and 93% with a low amount of traditional cryoprotectant (2% v/v DMSO) for A549 cells and HeLa cells after recovery, respectively. With the assistance of a 808 nm laser, the rewarming time was also shortened to 20 s, greatly improving the rewarming rate. Our work associated specific sizes of 2D nanomaterials with their ice growth inhibition behaviors during recrystallization and photothermal properties to synergistically improve cell cryopreservation efficiency, providing guidance for effectively designing novel 2D nanomaterials for collaborative control of ice crystals in cell cryopreservation.

Multifunctional Laser-Induced Graphene-Based Microfluidic Chip for High-Performance Oocyte Cryopreservation with Low Concentration of Cryoprotectants.

Oocyte cryopreservation is essential in the field of assisted reproduction, but due to the large size and poor environmental tolerance of oocytes, cell freezing technology needs further improvement. Here, a Y-shaped microfluidic chip based on 3D graphene is ingeniously devised by combining laser-induced graphene (LIG) technology and fiber etching technology. The prepared LIG/PDMS microfluidic chip can effectively suppress ice crystal size and delay ice crystal freezing time by adjusting surface hydrophobicity. In addition, LIG endows the microfluidic chip with an outstanding photothermal effect, which allows to sharply increase its surface temperature from 25 to 71.8 °C with 10 s of low-power 808 nm laser irradiation (0.4 W cm-2). Notably, the LIG/PDMS microfluidic chip not only replaces the traditional cryopreservation carriers, but also effectively reduces the dosage of cryoprotectants (CPAs) needed in mouse oocyte cryopreservation. Even when the concentration of CPAs is cut in half (final concentration of 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO)), the survival rate of oocytes is still as high as 92.4%, significantly higher than the control group's 85.8%. Therefore, this work provides a novel design strategy to construct multifunctional microfluidic chips for high-performance oocytes cryopreservation.

Impact of frozen storage on physicochemical parameters and quality changes in cooked crayfish.

Customers are increasingly opting for ready-to-eat and easy-to-prepare food products, such as cooked crayfish. It is highly valued for its unique taste, tender meat, and nutritional properties. Therefore, we conducted an investigation into its quality parameters over an 8-week period at -20 °C. Parameters such as water distribution, oxidation reactions, color, microstructure, texture properties, and physicochemical parameters were examined. The physicochemical results indicated that as the storage time increased, the levels of pH and TVB-N (total volatile basic nitrogen) showed a significant increase, while the water holding capacity decreased significantly (P < 0.05). After two months of frozen storage, the carbonyl content and TBARS (thiobarbituric acid reactive substances) increased to 4.15 ± 0.16 nmol/mg protein and 1.6 ± 0.00 mg/kg, respectively. Additionally, the total sulfhydryl content decreased to 4.91 ± 0.10 mol/105 g protein, which had an impact on the quality of the crayfish. Electron microscopy revealed that with increasing storage time, the fiber structure gradually deteriorated due to water crystallization, leading to severe damage and breakage of muscle fibers. Interestingly, these changes related to storage affected color and texture parameters, thereby influencing the overall quality of the crayfish.

Effect of microbubbles on immersion freezing of grape tomato.

Microbubbles (MBs) were incorporated into calcium chloride solution as a novel freezing medium for immersion freezing of grape tomato. The effects of MB size (39, 43, 48 µm mean diameter), entrapped gas (air, N2, CO2) and freezing temperature (-10, -15, -20 °C) on the freezing behavior and quality attributes of tomato were investigated. MBs increased the nucleation temperature from -7.4 to -3.5 °C and reduced the onset time of nucleation from 5.8 to 2.9 min at freezing temperature of -20 °C, which facilitated the formation of small ice crystals within tomato. MB-assisted freezing reduced the drip loss by 13.7-17.0% and improved the firmness of tomato, particularly when MB size and freezing temperature decreased. Freezing tomato with air-MBs did not compromise its nutritional quality, using N2- and CO2-MBs even increased its lycopene content, by 31% and 23%, respectively. The results proved the preservation effect of MBs on fruit during immersion freezing. This study can benefit the fruit and vegetable industry by providing an efficient freezing technology for producing frozen products with high sensory and nutritional quality.

Effects of sanxan on water and ice crystal status of salt free frozen cooked noodles during freeze-thaw cycles.

This study compared four biocolloids (sanxan, xanthan gum, curdlan, and guar gum) in different concentrations to replace NaCl in improving the recooking quality of salt free frozen cooked noodles (SF-FCNs). Sanxan outperformed NaCl and other biocolloids significantly improving the firmness (21.0%), chewiness (63.5%), and toughness (15.4%) of SF-FCNs after 10 freeze-thaw (FT) cycles. The results of the freezing-thawing curves showed SF-FCNs had prior FT stability when sanxan was added at 1.2%. Subsequently, the result of differential scanning calorimetry and nuclear magnetic resonance revealed sanxan reduced the content and mobility of freezable water while increasing the content of bound water. The scanning electron microscope, mercury intrusion, and optical microscopy analyses indicated that sanxan reduced the size and volume of ice crystals and the structural damage of SF-FCNs by controlling the water. The work contributes to a theoretical framework for enhancing SF-FCNs quality through precise water and ice crystal control.

Reversible Stacking and Delamination-Regulation of MXene via Controlled Freezing.

MXene's configuration, whether it is aggregated or dispersed in a monolayer, determines the specific application areas and even greatly influences the intrinsic properties of MXene. However, how to desirably control MXene's configuration is challenging. Here, a simple, additive-free, chemical reaction-free, and scalable strategy to optionally and reversibly regulate MXene's ordered stacking and delamination of MXene aggregates (AM) is reported. Just by controlled freezing of MXene aqueous dispersions, the aggregation percentage, delamination percentage, and interlayer spacing of AM can be finely tuned. Experimental results reveal that the freezing-induced aggregation and delamination effects can be explained by the squeezing action of growing ice grains on the MXene excluded/concentrated between ice grains and the expanding action caused by the ice formation between AM lamellae, respectively. The dominance between them depends on the freezing parameter-influenced ice nucleation sites, numbers, and ice grain sizes. This work not only contributes to the preparation, storage, and practical applications of MXene, but also opens a new and green avenue for controlling materials' assembly structures.

Tailoring microstructure and mechanical properties of pectin cryogels by modulate intensity of ionic interconnection.

Porous morphology and mechanical properties determine the applications of cryogels. To understand the influence of the ionic network on the microstructure and mechanical properties of pectin cryogels, we prepared low-methoxyl pectin (LMP) cryogels with different Ca2+ concentrations (measured as R-value, ranging from 0 to 2) through freeze-drying (FD). Results showed that the R-values appeared to be crucial parameters that impact the pore morphology and mechanical characteristics of cryogels. It is achieved by altering the network stability and water state properties of the cryogel precursor. Cryogel precursors with a saturated R-value (R = 1) produced a low pore diameter (0.12 mm) microstructure, obtaining the highest crispness (15.00 ± 1.85) and hardness (maximum positive force and area measuring 2.36 ± 0.31 N and 12.30 ± 1.57 N·s respectively). Hardness showed a negative correlation with Ca2+ concentration when R ≤ 1 (-0.89), and a similar correlation with the porosity of the gel network when R ≥ 1 (-0.80). Given the impacts of crosslinking on the pore structure, it is confirmed that the pore diameter can be designed between 56.24 and 153.58 µm by controlling R-value in the range of 0-2.

Yeast-Raised Polyamidoxime Hydrogel Prepared by Ice Crystal Dispersion for Efficient Uranium Extraction from Seawater.

Uranium extraction from seawater has attracted worldwide attention due to the massive reserves of uranium. Due to the straightforward synthesis and strong affinity toward uranyl ions (UO2 2+), the amidoxime group shows promise for use in highly efficient uranium capture.  However, the low mass transfer efficiency within traditional amidoxime-based adsorbents severely limits the adsorption rate and the utilization of adsorption sites. In this work, a macroporous polyamidoxime (PAO) hydrogel is prepared by yeast-based biological foaming combined with ice crystal dispersion that effectively maintained the yeast activity. The yeast-raised PAO (Y-PAO) adsorbent has numerous bubble-like holes with an average pore diameter >100 µm. These macropores connected with the intrinsic micropores of PAO to construct efficient diffusion channels for UO2 2+ provided fast mass transporting channels, leading to the sufficient exposure of hidden binding sites. The maximum adsorption capacity of Y-PAO membrane reached 10.07 mg-U/g-ads, ≈1.54 times higher than that of the control sample. It took only eight days for Y-PAO to reach the saturation adsorption capacity of the control PAO (6.47 mg-U/g-ads, 28 days). Meanwhile, Y-PAO possessed excellent ion selectivity, good reusability, and low cost. Overall, the Y-PAO membrane is a highly promising adsorbent for use in industrial-scale uranium extraction from seawater.

To What Extent Do Low-Voltage Electrostatic Fields Play a Role in the Physicochemical Properties of Pork during Freezing and Storage?

Low-voltage electrostatic fields (LVEF) are recognized as a new technology that can improve the quality of frozen meat. To determine the extent to which LVEF assistance affects the quality of frozen pork for long-term storage, pork was frozen and stored at -18 and -38 °C for up to 5 months. Water-holding capacity, muscle microstructure, and protein properties were investigated after up to 5 months of frozen storage with and without LVEF assistance. In comparison to traditional -18 and -38 °C frozen storage, LVEF treatment inhibited water migration during frozen storage and thawing. As a result, thawing losses were reduced by 15.97% (-18 °C) and 3.38% (-38 °C) in LVEF-assisted compared to conventional freezing methods. LVEF helped to maintain the muscle fiber microstructure and reduce muscle protein denaturation by miniaturizing ice crystal formation by freezing. As a result of this study, LVEF is more suitable for freezing or short-term frozen storage, while a lower temperature plays a more significant role in long-term frozen storage.

Effect of Liquid Nitrogen Freezing Temperature on the Muscle Quality of Litopenaeus vannamei.

The implications of different liquid nitrogen freezing (LNF) temperatures (-35 °C, -65 °C, -95 °C, and -125 °C) on the ice crystal and muscle quality of white shrimp (Litopenaeus vannamei) were investigated in this essay. The results showed that better muscle quality was maintained after LNF treatment compared to that after air blast freezing (AF) treatment. As the freezing temperature of liquid nitrogen decrease, the freezing speed accelerated, with the freezing speed of LNF at -125 °C being the fastest. However, an excessively fast freezing speed was not conducive to maintaining the quality of shrimp. Among all the freezing treatments, LNF at -95 °C led to the lowest thawing losses and cooking losses, and the highest L* values, indicating that LNF at -95 °C could keep the water holding capacity of frozen shrimp better than that with other freezing methods. At the same time, LNF at -95 °C resulted in higher water holding capacity, and hardness values for shrimps than those with other frozen treatments (p < 0.05). In addition, the results of the water distribution of shrimps showed that treatment with a -95 °C LNF reduced the migration rate of bound and free water. Meanwhile, the microstructural pores of shrimps in the -95 °C LNF group were smaller, indicating that the ice crystals generated during -95 °C LNF were relatively smaller than those generated via other frozen treatments. In conclusion, an appropriate LNF temperature (-95 °C) was beneficial for improving the quality of frozen shrimp, and avoiding freezing breakage.

Observation and Measurement of Ice Morphology in Foods: A Review.

Freezing is an effective technology with which to maintain food quality. However, the formation of ice crystals during this process can cause damage to the cellular structure, leading to food deterioration. A good understanding of the relationship between food microstructure and ice morphology, as well as the ability to effectively measure and control ice crystals, is very useful to achieve high-quality frozen foods. Hence, a brief discussion is presented on the fundamentals/principles of optical microscopic techniques (light microscopy), electronic microscopic techniques (transmission electron microscopy (TEM) and scanning electron microscopy (SEM)), as well as other non-invasive techniques (X-rays, spectroscopy, and magnetic resonance) and their application to measuring ice formation rates and characterizing ice crystals, providing insight into the freezing mechanisms as well as direct monitoring of the entire process. And, in addition, this review compares (the negative and positive aspects of) the use of simple and cheap but destructive technologies (optical microscopy) with detailed microscopic technologies at the micro/nanometer scale but with pretreatments that alter the original sample (SEM and TEM), and non-destructive technologies that do not require sample preparation but which have high acquisition and operational costs. Also included are images and examples which demonstrate how useful an analysis using these techniques can be.

The Influences of Cryopreservation Methods on RNA, Protein, Microstructure and Cell Viability of Skeletal Muscle Tissue.

Background: Different experiments require different sample storage methods. The commonly used preservation methods in biobank practice cannot fully meet the multifarious requirements of experimental techniques. Programmable controlled slow freezing (PCSF) can maintain the viability of tissue. In this study, we hypothesized that PCSF-preserved samples have potential advantages in matching subsequent experiments compared with existing methods. Methods: We compared the differences on skeletal muscle tissue RNA integrity, protein integrity, microstructure integrity, and cell viability between four existing cryopreservation methods: liquid nitrogen (LN2) snap-freezing, LN2-cooled isopentane snap-freezing, RNAlater®-based freezing, and PCSF. RNA integrity was evaluated using agarose gel electrophoresis and RNA integrity number. Freezing-related microstructural damage in the muscle tissue was evaluated using ice crystal diameter and muscle fiber cross-sectional area. Protein integrity was evaluated using immunofluorescence staining. Cell viability was evaluated using trypan blue staining after primary muscle cell isolation. Results: PCSF preserved RNA integrity better than LN2 and isopentane, with a statistically significant difference. RNAlater preserved RNA integrity best. PCSF best controlled ice crystal size in myofibers, with a significant difference compared with LN2. The PCSF method best preserved the integrity of protein epitopes according to the mean fluorescence intensity results, with a significant difference. Cell viability was best preserved in the PCSF method compared with the other three methods, with a significant difference. Conclusion: PCSF protected the RNA integrity, microstructural integrity, protein integrity, and cell viability of skeletal muscle tissue. The application of PCSF in biobank practice is recommended as a multi-experiment-compatible cryopreservation method.

Observation on the ice crystal formation process of large yellow croaker (Pseudosciaena crocea) and the effect of multiple cryoprotectants pre-soaking treatments on frozen quality.

By observing the formation behavior of ice crystals, the quality of food products under different freezing conditions can be intuitively judged. In this paper, large yellow croaker was taken as the research object, and a novel cryomicroscopic system was developed to directly observe the structure of ice crystals during the freezing process. The cryoprotective effects of 4% sucrose +4% sorbitol (SU + SO), 4% xylo-oligosaccharide (XO), 4% xylo-oligosaccharide + 0.3% tetrasodium pyrophosphate (XO + TSPP) and 0.2% antifreeze protein (AFP) at different freezing temperatures were investigated. And the evaluation indicators, such as cell deformation degree, equivalent diameters, roundness, elongation and fractal dimension were introduced to quantify the damage of ice crystals to muscle tissues and fibers. The results indicate that reducing the freezing temperature and adding cryoprotectants can improve the quality of large yellow croaker. AFP has the best cryoprotective effect, with a reduction in cell deformation degree of 54.78% and 67.83% compared to the Control group at -5 °C and -20 °C, respectively. SU + SO and XO have the equivalent antifreeze effect, which is slightly inferior to XO + TSPP. In addition, physical parameters of large yellow croaker samples were measured to verify the influence of ice crystal structure on product quality. Therefore, direct observation of the ice crystal formation process and evaluation of ice crystal structure can accurately reflect the quality of frozen products, which is of great significance for the development of refrigeration and preservation technology.

Starch nanoparticles as a new ice crystal nucleator in Lactobacillus bulgaricus CICC 6097 cryoprotection.

This work aimed at studying the cryoprotective effect of starch nanoparticles (SNPs) as ice nucleators on Lactobacillus bulgaricus CICC 6097 and exploring the protective mechanism. SNPs with a diameter of 363 nm were obtained, which possessed special properties to enhance ice nucleation and blunt ice crystals edges, and can be wrapped around the surface of bacteria form a protective barrier, thus maintaining the integrity of cell membranes and improving the survivability of L. bulgaricus CICC 6097 from 36.09% to 75.56%. However, SNCs solution formed ice crystals with obvious spikes during freezing, which was harmful to bacteria survival. Therefore, SNPs addition is a possible strategy for increasing viable cell counts during freezing. To the best of our knowledge, this report is the first to demonstrate the cryoprotective effect of ice nucleator on lactic acid bacteria.

Study on the ice crystals growth under pectin gels with different crosslinking strengths by modulating the degree of amidation in HG domain.

The ice crystal morphology formed under a series of amidated pectin gels with various crosslink strengths were investigated. The results showed that as the degree of amidation (DA) increased, pectin chains exhibited shorter homogalacturonan (HG) regions. Highly amidated pectin exhibited a faster gelation rate and a stronger gel micro-network via hydrogen bonds. Based on cryogenic scanning electron microscopy (cryo-SEM), smaller ice crystals were formed in frozen gel with low DA, suggesting that a weaker cross-linked gel micro-network was more effective at inhibiting crystallization. After sublimation, lyophilized gel scaffolds with high crosslink strength displayed less number of pores, high porosity, lower specific surface area, and greater mechanical strength. This study is expected to confirm that the microstructure and mechanical properties of freeze-dried pectin porous materials could be regulated by changing the crosslink strength of pectin chains, which is achieved by increasing the degree of amidation in the HG domains.

Effect of water change on quality deterioration of Pacific white shrimp (Litopenaeus vannamei) during partial freezing storage.

The correlation between water changes and quality deterioration of Litopenaeus vannamei during partial freezing storage was evaluated in this study. Significant increases in cross-sectional area and equivalent diameter are detected, but the roundness and longiness of the ice crystals show irregular growth. Within the extension of storage, the bound water (T2b) and immobilized water (T21) decreased significantly. However, the free water (T22) increased significantly. Quality determination showed significant decrease in total sulfhydryl and Ca2+-ATPase, but significant increase in disulfide bonds during storage. Correlation analysis revealed that cross-sectional area showed significant negative correlation with total sulfhydryl and Ca2+-ATPase, while significant positive correlation with disulfide bonds, respectively. The correlation between water distribution index and Ca2+-ATPase, disulfide bonds was significant, respectively. Predicted models for the growth of ice crystals with respect to cross-sectional area and equivalent diameter size have been developed with the help of the Arrhenius model.