Freeze-thaw Treatment Research Articles

Preparation of a nano aluminum phosphate enhanced hydroxyapatite coating for marble conservation

Open-air marble relics in Beijing are experiencing degradation due to sugaring, dissolution and other illnesses. Therefore, it is necessary to apply a protective and reinforcing coating to the weathered surface. Hydroxyapatite (HAP) has significantly lower solubility and dissolution rate compared to calcite. Additionally, HAP has similar lattice parameters with calcite, suggesting that a cohesive layer of HAP can be formed over calcite. In fact, HAP exhibits a lattice mismatch of 5 % with calcite, which might potentially lead to stress if the layer exceeds a few nanometre in thickness. On the other hand, aluminum phosphates (ideally, B-AlPO4) only exhibit a 1 % mismatch with calcite and have a solubility lower than that of calcite. In this study, in order to improve the property of HAP in marble conservation, sol–gel method was employed to synthesize nano AlPO4, which were then incorporated into the phosphate solution to produce protective coating on the stone surface. The coatingʼs morphology and the structure were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high capacity 3D X-ray microscopy (XRM), optical microscope, and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). Moreover, the color, the contact angle, the three-point bending strength measurements, as well as the simulated acid rain test and freeze–thaw treatment were performed to assess the chromatic aberration, hydrophilicity, reliability, and durability of the coating. Results indicated that the nano AlPO4, with its matched lattice parameters and nucleation site provision, facilitated the formation a coherent HAP layer of crystal flakes. Subsequently, the anti‑corrosion property, freeze-thaw resistance and consolidation property of the coating were improved, demonstrating the potential application the hybrid of HAP with nano AlPO4 in the preservation of marble.

Analysis of the impact of pluronic acid on the thermal stability and infectivity of AAV6.2FF

BackgroundThe advancement of AAV vectors into clinical testing has accelerated rapidly over the past two decades. While many of the AAV vectors being utilized in clinical trials are derived from natural serotypes, engineered serotypes are progressing toward clinical translation due to their enhanced tissue tropism and immune evasive properties. However, novel AAV vectors require formulation and stability testing to determine optimal storage conditions prior to their use in a clinical setting.ResultsHere, we evaluated the thermal stability of AAV6.2FF, a rationally engineered capsid with strong tropism for lung and muscle, in two different buffer formulations; phosphate buffered saline (PBS), or PBS supplemented with 0.001% non-ionic surfactant Pluronic F68 (PF-68). Aliquots of AAV6.2FF vector encoding the firefly luciferase reporter gene (AAV6.2FF-ffLuc) were incubated at temperatures ranging from -20°C to 55°C for varying periods of time and the impact on infectivity and particle integrity evaluated. Additionally, the impact of several rounds of freeze-thaw treatments on the infectivity of AAV6.2FF was investigated. Vector infectivity was measured by quantifying firefly luciferase expression in HEK 293 cells and AAV particle integrity was measured by qPCR quantification of encapsidated viral DNA.ConclusionsOur data demonstrate that formulating AAV6.2FF in PBS containing 0.001% PF-68 leads to increased stability and particle integrity at temperatures between -20℃ to 21℃ and protection against the destructive effects of freeze-thaw. Finally, AAV6.2FF-GFP formulated in PBS supplemented with 0.001% PF-68 displayed higher transduction efficiency in vivo in murine lung epithelial cells following intranasal administration than vector buffered in PBS alone further demonstrating the beneficial properties of PF-68.

Dietary salidroside supplementation improves meat quality and antioxidant capacity and regulates lipid metabolism in broilers

We aimed to explore the effect of salidroside (SAL) on meat quality, antioxidant capacity, and lipid metabolism in broilers. The results demonstrated that SAL significantly reduced the yellowness (b*), shear force, cooking loss, drip loss, MDA, TBARS, and carbonyl content in breast (P < 0.05), while increasing the pH value (P < 0.05), suggesting an improvement in meat quality. SAL lowered the lipid contents in liver and serum (P < 0.05), while increasing the proportion of unsaturated fatty acids in breast (P < 0.05), indicating effective regulation of lipid metabolism by SAL. SAL increased the activity of antioxidant enzymes and the expression of antioxidant genes in both liver and muscle (P < 0.05). Additionally, SAL improved the meat quality and antioxidant capacity of breast subjected to repeated freeze-thaw treatment. SAL may enhance meat quality by improving antioxidative stability and regulating lipid metabolism, potentially serving as a dietary supplement for broilers.

Effects of Freeze-Thaw Cycles on the Quality of a Novel Mixed Grain Composite Dough and Its Product (Potato-Oat Yu): Hybridization of Potatoes and Oats.

To provide a theoretical basis for the frozen storage of potato-oat composite dough and its products, this investigation examines changes in the quality of potato-oat composite dough and its resulting product during freeze-thaw cycles. The study measured key aspects such as moisture content, dynamic rheological properties, water state, protein secondary structure, color, and sensory assessment. The influence of these factors on the product's quality is analyzed. The findings revealed that the freeze-thaw treatment caused a reduction in water content, freezable water, and deeply bound water, as well as an increase in weakly bound water, β-sheet, random coil, and α-helix, and a decreased β-turn of the potato-oat composite dough. Additionally, the dough treated by freeze-thaw cycles resulted in darker color, and the sensory properties of the product were affected significantly after exceeding three freeze-thaw cycles. Moreover, an increase in the number of freeze-thaw cycles resulted in an upward trend of moisture content for the composite dough, whereas G' initially increased and then decreased. The G″ of the composite dough peaked after the third freeze-thaw cycle. Overall, the composite dough quality significantly deteriorated at the fourth freeze-thaw cycle. There was a significant increase in the freezable water content, the largest modulus of elasticity, and the smallest tan δ. Therefore, the usage of the potato-oat composite dough should not exceed three cycles.

Freeze-thaw effect on performance degradation of recycled glulam from structural members after cyclic loading

To achieve sustainable production with recycled glulam from after-service structural members, the physical and mechanical properties of the recycled glulam under different numbers of freeze-thaw cycles (60, 120, 180 times) were investigated. The results showed that the freeze-thaw cycle treatment had a serious damaging effect on the glue layer, rather than the laminates of the specimens, which showed the tackless phenomenon. The physical properties (color change, mass and dimensional variation) of the specimens changed most significantly after the first freeze-thaw cycles (60 cycles), and then showed slow growth. As the number of freeze-thaw cycles on the specimens increased, the strength, especially the shear strength of the specimens showed a significantly decreasing trend (45% for compressive strength and 100% for shear strength after 180 cycles), whilst the ductility shows an increasing trend. A strength prediction model of the recycled glulam under freeze-thaw cycles was established. Based on the shape characteristics of the tested stress-strain curves, the compression and shear performance models of recycled glulam influenced by the number of freeze-thaw cycles were proposed.

Effects of hypothermia–hypoxia pulping, high hydrostatic pressure processing, and repeat freeze–thaw cycles on the quality of raw kiwifruit puree

AbstractThis study evaluated the effects of the whole process of non‐thermal processing (hypothermia–hypoxia pulping and high hydrostatic pressure (HHP) pasteurization), different freezing methods, and repeat freeze–thaw cycles on physicochemical and nutritional quality of kiwifruit puree. Results showed that hypothermia–hypoxia treatment can retain the vitamin C, total phenol content, and antioxidant capacity of the puree better. Different pasteurization treatments can effectively kill microorganisms and improve the total phenol content and antioxidant capacity of the raw puree. Compared with thermal treatment, HHP can better retain the color, viscosity, and aroma components of the raw puree. The freezing methods have little impact on the quality of the raw puree, but peroxidase enzyme activity after quick freezing was significantly higher than that of slow freezing. Different freeze–thaw treatments had adverse effects on the quality of kiwifruit, and the damage of 25°C thawing conditions was more serious than that of 4°C thawing conditions. This research would provide new ideas for the production and storage of high‐quality kiwifruit puree and potential technical support for kiwifruit puree commercial production.Practical ApplicationsThe results of this study showed that non‐thermal processing can maintain the quality of kiwifruit puree better than traditional thermal processing, which provides a new idea for the production of high‐quality kiwifruit puree. In addition, this study suggests that temperature fluctuations should be minimized during storage to better maintain kiwifruit quality. This will provide potential technical support for the commercialization of kiwifruit puree.

Study of chondrogenesis of umbilical cord mesenchymal stem cells in curdlan- poly(vinyl alcohol) composite hydrogels and its mechanical properties of freezing-thawing treatments

The curdlan gel is a natural material produced by bacteria. It utilizes chemical cross-linking reactions to form a 3D porous composite hydrogel, increasing its porosity and water content, and improving its mechanical properties. It can be used in tissue repair and regenerative medicine. Curdlan-Poly(vinyl alcohol) (PVA) composite hydrogel can rapidly swell within 1 min due to its porous structure. Compression tests confirmed that it still maintains its original mechanical strength, even after five repeated freeze-thaw (FT) processes, making it suitable for long-term cryopreservation. The purpose of this study is to transplant umbilical cord mesenchymal stem cells (UC-MSCs) on Curdlan-PVA composite hydrogel and observe the chondrocytes on the material. The results of using 4′,6-diamidino-2-phenylindole (DAPI), hematoxylin and eosin (H&E), calcein-acetoxymethyl ester (calcein AM), and Collagen type II–Fluorescein isothiocyanate (FITC) staining, confirmed that UC-MSCs can attach and differentiate into chondrocytes on 3D Curdlan-PVA composite hydrogel.

Effects of whole wheat flour on frozen dough and steamed bread during freeze-thaw cycles

The research on Chinese steamed bread (CSB) with whole wheat flour (WWF) is limited and has not been discussed during freeze-thaw. This study investigated the effects of WWF addition on the dough and CSB quality during freeze-thaw cycles. The results of low-field nuclear magnetic resonance (LF-NMR) and dynamic rheological properties demonstrated that the WWF reduced the adverse changes of freeze-thaw treatment on the dough. Characteristics, texture, and cross section analysis of CSB showed that WWF (20%) could relatively maximize stability. To study the mechanism, arabinoxylan (AX) and water-extractable arabinoxylan (WEAX) from WWF were added to dough. Consistent with WWF, it was found that they could improve freeze-thaw tolerance of frozen dough and CSB. Meanwhile, WEAX (1.12%) could better increase quality and freeze-thaw tolerance of CSB. The results presented in the study indicate that the anti-freeze-thaw effects of WWF could be attributed to AX and WEAX.

Protective roles of highly conserved motif 1 in tardigrade cytosolic-abundant heat soluble protein in extreme environments.

Tardigrades are remarkable microscopic animals that survive harsh conditions such as desiccation and extreme temperatures. Tardigrade-specific intrinsically disordered proteins (TDPs) play an essential role in the survival of tardigrades in extreme environments. Cytosolic-abundant heat soluble (CAHS) protein, a key TDP, is known to increase desiccation tolerance and to protect the activity of several enzymes under dehydrated conditions. However, the function and properties of each CAHS domain have not yet been elucidated in detail. Here, we aimed to elucidate the protective role of highly conserved motif 1 of CAHS in extreme environmental conditions. To examine CAHS domains, three protein constructs, CAHS Full (1-229), CAHS ∆Core (1-120_184-229), and CAHS Core (121-183), were engineered. The highly conserved CAHS motif 1 (124-142) in the CAHS Core formed an amphiphilic α helix, reducing the aggregate formation and protecting lactate dehydrogenase activity during dehydration-rehydration and freeze-thaw treatments, indicating that CAHS motif 1 in the CAHS Core was essential for maintaining protein solubility and stability. Aggregation assays and confocal microscopy revealed that the intrinsically disordered N- and C-terminal domains were more prone to aggregation under our experimental conditions. By explicating the functions of each domain in CAHS, our study proposes the possibility of using engineered proteins or peptides derived from CAHS as a potential candidate for biological applications in extreme environmental stress responses.

Estimating dynamic compressive strength of rock subjected to freeze-thaw weathering by data-driven models and non-destructive rock properties

ABSTRACT The dynamic compressive strength (DCS) of frozen-thawed rock influences the stability of rock mass in cold regions, especially when rock masses are possibly disturbed by dynamic loads. Laboratory freeze-thaw weathering treatment is usually time-consuming, and the dynamic strength test is destructive. Therefore, this paper attempts to quickly predict the DCS of frozen-thawed sandstones using data-driven methods, non-destructive rock properties, and basic environmental parameters. The sparrow search algorithm (SSA), gorilla troops optimiser, and dung beetle optimiser were chosen to develop two hyperparameters in the random forest (RF). The classic RF, back propagation neural network, and support vector regression models were taken as the control group. These six models were developed to predict the DCS. Their prediction results were compared. Finally, the sensitivity analysis was carried out to assess the significance of all input variables. The results indicate that the SSA – RF model yields the best prediction result, and three optimised models have better performance than single machine-learning models. Strain rate, dry density, and wave velocity are found to be the three most important parameters in DCS prediction, which further indicates that there is also a strong correlation between the characteristic impedance of the rock and the DCS.

Inhibiting T-Cell-Mediated Rejection of the Porcine Meniscus Through Freeze-Thawing and Downregulating Porcine Xenoreactive Antigen Genes.

Immune rejection presents a significant challenge in xenogenic meniscal transplantation. Pigs are widely regarded as an advantageous tissue source for such transplants, with porcine GGTA1, CMAH, and B4GALNT2 being among the most common xenoreactive antigen (Ag) genes. While some studies have suggested that allogeneic meniscus (AM) transplants may exhibit immunoprivileged properties, our study observed slight immunological rejection has been observed following contact between human meniscal cells (HMCs) and human peripheral blood mononuclear cells (PBMCs). Given the limited systematic research on immune responses following xenograft meniscus transplantation, we established porcine meniscus transplantation (PMT) models to comprehensively assess the immunogenicity of porcine meniscus (PM) from both innate and adaptive immune perspectives. Our investigations confirmed that PMT beneath the epidermis led to innate cell infiltration into the xenografts and T-cell activation in local lymph nodes. T-cell activation upregulated the interleukin (IL)-17 signaling pathway, disrupting collagen organization and metabolic processes, thereby hindering PM regeneration. Using freeze-thaw treatment on PM alleviated T-cell activation post-transplantation by eliminating xenogenic DNA. In vitro findings demonstrated that gene editing in porcine meniscal cells (PMCs) suppressed human T-cell activation by downregulating the expression of xenoreactive Ag genes. These results suggest that GGTA1/CMAH/B4GALNT2 knockout (KO) pigs hold significant promise for advancing the field of meniscal transplantation.

Pickering emulsion with high freeze-thaw stability stabilized by xanthan gum/lysozyme nanoparticles and konjac glucomannan

In this study, freeze-thaw cycle experiments were conducted on food-grade Pickering emulsions co-stabilized with konjac glucomannan (KGM) and xanthan gum/lysozyme nanoparticles (XG/Ly NPs). The rheological properties, particle size, flocculation degree (FD), coalescence degree (CD), centrifugal stability, Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and microstructure of Pickering emulsion stabilized by KGM before and after freeze-thaw were characterized. It was found that as the concentration of KGM increased, the flocculation degree (FD) and coalescence degree (CD) of the emulsion decreased after the freeze-thaw cycle compared to the control sample, and the microscopic images showed that the droplets became smaller and less affected by the freeze-thaw cycles. The rheological and water-holding properties also confirmed that the KGM-added emulsions still had a strong gel network structure and prevented the separation of the continuous and dispersed phases of the droplets after freezing and thawing. Freeze-thaw treatments had a negative effect on the stable emulsion of XG/Ly NPs, while the addition of KGM improved the freeze-thaw stability of the emulsion, which provided a theoretical basis for the development of emulsion products with high freeze-thaw stability.

Impact of polyamide microplastics on riparian sediment structures and Cd(II) adsorption: A comparison of natural exposure, dry-wet cycles, and freeze-thaw cycles

Microplastics (MPs) accumulation in sediments has posed a huge threat to freshwater ecosystems. However, it is still unclear the effect of MPs on riparian sediment structures and contaminant adsorption under different hydrological processes. In this study, three concentrations of polyamide (PA) MPs-treated sediments (0.1%, 1%, and 10%, w/w) were subjected to natural (NA) exposure, dry-wet (DW) cycles, and freeze-thaw (FT) cycles. The results indicated that PA MPs-added sediment increased the micro-aggregates by 10.1%−18.6% after FT cycles, leading to a decrease in aggregate stability. The pH, OM, and DOC of sediments were significantly increased in DW and FT treatments. In addition, the increasing concentration of PA MPs showed an obvious decrease in aromaticity, humification, and molecular weight of sediment DOM in FT treatments. Also, high level of MPs was more likely to inhibit the formation of humic-like substances and tryptophan-like proteins. For DW and FT cycles, 0.1% and 1% PA MPs-treated sediments slightly increased the adsorption capacity of Cd(II), which may be ascribed to the aging of MPs. Further correlation analysis found that DW and FT altered the link between DOM indicators, and aggregate stability was directly related to the changes in sediment organic carbon. Our findings revealed the ecological risk of MPs accumulating in riparian sediments under typical hydrological processes.

Tailoring an egg white protein double network emulsion gel as a novel fat substitute for improving freeze-thaw stability of minced meat gel

This work aimed to investigate the effect of double network emulsion gel (DNEG) as a substitute for pork back fat (PBF) on the freeze-thaw stability of minced meat gel (MMG). We used slow acidification with glucono-δ-lactone (GDL) to induce egg white protein (EWP) gelation, while CaCO3 was affected by acidification to release Ca2+ to cross-link sodium alginate (SA), resulting in the gradual formation of DNEG networks. The MMG prepared using DNEG substitute for PBF had fine hardness and color after 5 freeze-thaw cycles (FTCs). This was due to the excellent plasticity of DNEG, which made it more capable of filling the voids of minced meat products, thus reducing the space for ice crystal growth. As a result, MMG prepared with DNEG could pass through the maximum ice crystal formation zone faster and avoid damage due to the formation of larger ice crystals. Notably, DNEG provided a barrier for the migration of immobilized water to bulk water in the sample. After several freeze-thaw treatments, the water holding capacity of samples prepared with DNEG decreased significantly slower, which slowed down the oxidation and decomposition of meat proteins. In summary, this study revealed the role of fat substitute DNEG as a favorable filling material for improving the freeze-thaw stability of minced meat products, and provided a technical reference for the development of healthy and storable meat products.

Experimental study of the effect of ultralow temperature on the fracture toughness of sandstone

Fractures are widely present in subsurface formations, and fracture extension under ultralow temperature conditions is important for tasks such as liquid nitrogen fracturing and underground storage of liquid natural gas or liquid air. Therefore, the fracture toughness of sandstone under ultralow-temperature conditions was investigated using three-point bending tests of the NSCB specimens. The specimen damage processes were monitored using the DIC technique, and the changes in the pore microscopic characteristics after ultralow-temperature treatment were observed using CT and SEM. The results show that fracture toughness of dry sandstone was insensitive to the variations of the ultralow temperature (-30 to −120 ℃), whereas that of saturated sandstone increased gradually with the decrease of temperature due to the cementing effect of ice. DIC analysis showed that the peak strain around the fracture tip increased, and the fracture extension time was shortened with a decrease in temperature for both dry and saturated sandstone samples. The minerals shrank and the samples became more compacted with a decrease in temperature for the dry samples, resulting in their brittle characteristics under ultralow temperatures. The enhanced cementation effects of ice under ultralow temperatures induced high internal stress and rapid energy release upon failure of the saturated samples. Large pores shrank owing to pore collapse and filling after the one-cycle ultralow-temperature freeze–thaw treatment.

Maize residue retention shapes soil microbial communities and co-occurrence networks upon freeze-thawing cycles.

Maize residue retention is an effective agricultural practice for improving soil fertility in black soil region, where suffered from long freezing-thawing periods and intense freeze-thawing (FT) cycles. However, very few studies have examined the influence of maize residue retention on soil microbial communities under FT cycles. We investigated the response of soil microbial communities and co-occurrence networks to maize residue retention at different FT intensities over 12 cycles using a microcosm experiment conditioned in a temperature incubator. Our results indicated that maize residue retention induced dramatic shifts in soil archaeal, bacterial and fungal communities towards copiotroph-dominated communities. Maize residue retention consistently reduced soil fungal richness across all cycles, but this effect was weaker for archaea and bacteria. Normalized stochastic ratio analysis revealed that maize residue retention significantly enhanced the deterministic process of archaeal, bacterial and fungal communities. Although FT intensity significantly impacted soil respiration, it did not induce profound changes in soil microbial diversity and community composition. Co-occurrence network analysis revealed that maize residue retention simplified prokaryotic network, while did not impact fungal network complexity. The network robustness index suggested that maize residue retention enhanced the fungal network stability, but reduced prokaryotic network stability. Moreover, the fungal network in severe FT treatment harbored the most abundant keystone taxa, mainly being cold-adapted fungi. By identifying modules in networks, we observed that prokaryotic Module #1 and fungal Module #3 were enhanced by maize residue retention and contributed greatly to soil quality. Together, our results showed that maize residue retention exerted stronger influence on soil microbial communities and co-occurrence network patterns than FT intensity and highlighted the potential of microbial interactions in improving soil functionality.

Elastic and conductive gellan gum/polyvinyl alcohol physical hydrogels with low swelling potential for sustainable flexible electronics

Conductive hydrogels are considered to be promising materials for flexible electronics, but those nondegradable are bound to produce substantial undesirable electronic wastes once widely applied, inconsistent with the long-term sustainable development goals. To develop biodegradable conductive hydrogels for sustainable flexible electronics, a green chemical reaction-free strategy was developed to manufacture a novel type of composite hydrogels, exploiting biodegradable gellan gum and polyvinyl alcohol as the matrices and natural-derived tannic acid as the crosslinking agent. The technique involves successive cool-induced sol−gel transition, freeze-thawing and Na2SO4 solution treatment. A universal electronic testing machine, scanning electronic microscope, X-ray diffractometer, thermogravimetric analyzer, and electrochemical work station were employed to study the mechanics, structure and morphology, swelling and conductivity of the hydrogels. The results indicate strong, elastic and tough hydrogels were achieved owing to the multi-crosslinked multiple-network structure. The maximum compressive stress (90% strain), tensile strength, breakage elongation and fracture energy reach 10.7 MPa, 1.2 MPa, 890% and 480 kJ/m3 respectively. The stress recovery rate still remains 86% after 10 consecutive loading-unloading under 200% strain. The highest conductivity reaches 3.27 S/m, which along with the excellent mechanics confers them good strain-sensing behavior. Moreover, the final hydrogels show low swelling in both water (the equilibrium swelling ratio (ESR) < 300%) and physiological saline (ESR < 90%). The excellent mechanical performance, high conductivity and good strain sensing, low swelling and inherent biodegradability as well as the ecofriendly manufacturing process imply potential prospect in sustainable flexible electronics.

Mechanical properties and damage modeling of unloaded marble under freezing and thawing with different temperature ranges

The seasonal freeze-thaw environment is a primary factor contributing to the deterioration of manually excavated disturbed rock masses on reservoir bank slopes in highland alpine areas. To investigate the mechanical properties and damage deterioration mechanism of excavation-unloading rock under seasonal freeze-thaw environment in cold region, the freeze-thaw cycle tests with different temperature difference levels (−10–10 °C, −15–25 °C, −20–40 °C) and different cycle times (0,10,20,30) were simulated for the triaxial unloading damaged marble. Then, the mechanical parameters of unloaded marble after freezing and thawing were obtained by uniaxial compression and triaxial compression tests, and the influence laws of temperature ranges, number of freezing and thawing cycles and confining pressure on the mechanical properties of unloaded marble were analyzed. Finally, the damage model of unloaded marble considering freeze-thaw action was established. The results show that the strength of unloaded marble is significantly weakened under the combined effect of F-T (freezing and thawing) and loading, and that the deterioration effect of the number of F-T cycles is stronger than that of the temperature ranges. The increase in the confining pressure increased the compressive strength and elastic modulus of the unloaded marble, and suppressed the damage of the unloaded marble after the freeze-thaw treatment. The porosity of the unloaded marble developed gradually and increased exponentially with the increase of the number of freeze-thaw cycles, the compressive strength and elastic modulus had a negative exponential relationship with the number of freeze-thaw cycles, and the shear strength parameter had a quadratic polynomial relationship with the number of freeze-thaw cycles. In addition, the softening mechanism of unloaded marble by natural water plays a key role in the process of freeze-thaw cycle, and the damage model considering freeze-thaw is established, and the theoretical curves are well matched with the experimental results. The outcomes of this study hold significant theoretical and engineering importance for evaluating the stability of excavated unloaded rock in highland alpine regions.

N-rich chitosan-derived porous carbon materials for efficient CO2 adsorption and gas separation.

Capturing and separating carbon dioxide, particularly using porous carbon adsorption separation technology, has received considerable research attention due to its advantages such as low cost and ease of regeneration. In this study, we successfully developed a one-step carbonization activation method using freeze-thaw pre-mix treatment to prepare high-nitrogen-content microporous nitrogen-doped carbon materials. These materials hold promise for capturing and separating CO2 from complex gas mixtures, such as biogas. The nitrogen content of the prepared carbon adsorbents reaches as high as 13.08wt%, and they exhibit excellent CO2 adsorption performance under standard conditions (1 bar, 273K/298K), achieving 6.97mmol/g and 3.77mmol/g, respectively. Furthermore, according to Ideal Adsorption Solution Theory (IAST) analysis, these materials demonstrate material selectivity for CO2/CH4 (10 v:90 v) and CO2/CH4 (50 v:50 v) of 33.3 and 21.8, respectively, at 1 bar and 298K. This study provides a promising CO2 adsorption and separation adsorbent that can be used in the efficient purification process for carbon dioxide, potentially reducing greenhouse gas emissions in industrial and energy production, thus offering robust support for addressing climate change and achieving more environmentally friendly energy production and carbon capture goals.

Efficient production of γ-aminobutyric acid using engineered Escherichia coli whole-cell catalyst

γ-Aminobutyric acid (GABA) has been widely used in the food, feed, pharmaceutical, and chemical industry fields. Previously, we developed a whole-cell catalyst capable of converting L-glutamate (L-Glu) into GABA by overexpressing the glutamate decarboxylase gene (gadz11) from Bacillus sp. Z11 in Escherichia coli BL21(DE3). However, to enhance cell permeability, a freeze-thaw treatment is required, and to enhance GADZ11 activity, pyridoxal 5′-phosphate (PLP) must be added to the reaction system. The aim of this study is to provide a more efficient approach for GABA production by engineering the recombinant E. coli above. First, the inducible expression conditions of the gadz11 in E. coli were optimized to 37 °C for 6 h. Next, an ideal engineered strain was produced via increasing cell permeability by overexpressing sulA and eliminating PLP dependence by constructing a self-sufficient system. Furthermore, an efficient whole-cell biocatalytic process was optimized. The optimal substrate concentration, cell density, and reaction temperature were 1.0 mol/L (the molecular ratio of L-Glu to L-monosodium glutamate (L-MSG) was 4:1), 15 and 37 °C, respectively. Finally, a whole-cell bioconversion procedure was performed in a 3-L bioreactor under optimal conditions. The strain could be reused for at least two cycles with GABA yield, productivity and conversion ratio of 206.2 g/L, 117.8 g/L/h and 100.0%, respectively. This is currently the highest GABA productivity from a mixture of L-Glu and L-MSG reported without the addition of cofactors or additional treatment of cells. This work demonstrates that the novel engineered E. coli strain has the potential for application in large-scale industrial GABA production.