Formation Of Large Pores Research Articles

Features of synthesis of ZnSe ceramics from nanopowders obtained using a high-power laser

The reasons for the occurrence of optical inhomogeneities in ZnSe or Fe:ZnSe ceramics, which were made from nanoparticles, obtained using a continuous wave ytterbium fiber laser, were investigated. Evaporation of ZnSe at T ≤ 900 ˚С results in formation of large pores (0.5 - 10µm) in the ceramics. When the material is oxidized by means of oxygen adsorbed from air onto the surface of nanoparticles, such refractory phases as ZnO and ZnSeO3 are formed. Even a low content of these phases ( < 1wt. %) results in formation of accumulations of small crystallites ( 0.2 - 3 μm) in the ceramics. Numerous pores and extended accumulations of small crystallites are optical non-uniformities that scatter and absorb light. Changes in the chemical composition and contamination of ZnSe during the production of nanopowders and ceramics turned out to be too small for such inhomogeneities to form.

Comparative study of silica-based porous materials in the purification of radioactive wastewater

A significant challenge in the treatment of low-level radioactive wastewater is the effective purification of low-concentration radionuclides. Silica-based adsorbents are advantageous for the deep-purification of low-concentration metal ions. This study investigates three primary types of silica-based adsorbents: functionalized mesoporous silica, various modified zeolites, and mesoporous calcium silicate hydrate (C-S-H). These adsorbents were synthesized and their deep-purification effects on heavy metals and radionuclides were compared. The results indicated that mesoporous silica showed relatively poor adsorption for most metal ions. Zeolites outperformed mesoporous silica, with Zn framework-modified zeolites showing enhanced adsorption for several metal ions. Notably, C-S-H displayed superior adsorption performance, achieving high adsorption capacities for various metal ions and radionuclides. Specifically, at a dose of 0.5 g/L, the adsorption efficiency of C-S-H for numerous radionuclides in nuclear power plant wastewater exceeded 92–99 %, highlighting its potential for practical applications. An in-depth analysis of the physical and chemical structure and the adsorption mechanisms of C-S-H revealed its large mesoporous structure and electrostatic attraction to cations across a wide pH range. Multivalent cations were removed through exchange with Ca2+ in C-S-H, whereas monovalent cations were removed through exchange with Na+ in C-S-H. The cyclic structure of silica-oxygen tetrahedra in C-S-H, which promotes large pore formation and provides abundant ion exchange sites, underpins its excellent adsorption properties. This study offers valuable insights for the selection and application of silica-based materials in radioactive wastewater treatment.

Durability Performance of CGF Stone Waste Road Base Materials under Dry-Wet and Freeze-Thaw Cycles.

The disposal of stone waste derived from the stone industry is a worldwide problem. The shortage of landfills, as well as transport costs and environmental pollution, pose a crucial problem. Additionally, as a substitute for cement that has high carbon emissions, energy consumption, and pollution, the disposal of stone wastes by utilizing solid waste-based binders as road base materials can achieve the goal of "waste for waste". However, the mechanical properties and deterioration mechanism of solid waste-based binder solidified stone waste as a road base material under complex environments remains incompletely understood. This paper reveals the durability performance of CGF all-solid waste binder (consisting of calcium carbide residue, ground granulated blast furnace slag, and fly ash) solidified stone waste through the macro and micro properties under dry-wet and freeze-thaw cycling conditions. The results showed that the dry-wet and freeze-thaw cycles have similar patterns of impacts on the CGF and cement stone waste road base materials, i.e., the stress-strain curves and damage forms were similar in exhibiting the strain-softening type, and the unconfined compressive strengths all decreased with the number of cycles and then tended to stabilize. However, the influence of dry-wet and freeze-thaw cycles on the deterioration degree was significantly different; CGF showed excellent resistance to dry-wet cycles, whereas cement was superior in freeze-thaw resistance. The deterioration grade of CGF and cement ranged from 36.15 to 47.72% and 39.38 to 47.64%, respectively, after 12 dry-wet cycles, whereas it ranged from 57.91 to 64.48% and 36.61 to 40.00% after 12 freeze-thaw cycles, respectively. The combined use of MIP and SEM confirmed that the deterioration was due to the increase in the porosity and cracks induced by dry-wet and freeze-thaw cycles, which in turn enhanced the deterioration phenomenon. This can be ascribed to the fact that small pores occupy the largest proportion and contribute to the deterioration process, and the deterioration caused by dry-wet cycles is associated with the formation of large pores through the connection of small pores, while the freeze-thaw damage is due to the increase in medium pores that are more susceptible to water intrusion. The findings provide theoretical instruction and technical support for utilizing solid waste-based binders for solidified stone waste in road base engineering.

Effect of microwave vacuum drying time on the quality profiles, microstructures and in vitro digestibility of pork chip snacks

In present study, the quality profiles, microstructures and in vitro digestibility of pork chip snacks (PCS) prepared by microwave vacuum drying (MVD) under different drying times (20, 21, 22, 23, and 24 min) were investigated. The results revealed significant decreases in the moisture content and L*-value of PCS, while the protein/ash contents, a*-value, and b*-value of PCS markedly increased with prolonged MVD time (P < 0.05). Additionally, as MVD time extended from 20 to 24 min, the textural characteristics of PCS, particularly brittleness and crunchiness, initially increased and then gradually decreased (P < 0.05). Scanning electron microscopy (SEM) images showed that a moderate MVD time (22 min) resulted in the formation of larger pores in PCS, enhancing brittleness and crunchiness. However, excessive MVD time (24 min) led to the melting of these pores, subsequently reducing the brittleness and crunchiness of PCS. Furthermore, in vitro protein digestibility of PCS gradually decreased with increasing MVD time, primarily attributed to increased protein aggregation, as indicated by changes in sulfhydryl contents. In summary, our findings highlight that PCS subjected to 22 min of MVD exhibited the highest overall acceptability. This study provides a novel strategy for the application of MVD in the processing of meat snacks.

Effects of PEF pretreatment, combined with different drying methods, on the physicochemical properties, bioactive components, antioxidant potential as well as structural and thermal properties of dried yams

This work investigated the effects of pulsed electric field (PEF) pretreatment, combined with different drying methods, on the quality of dried yams. The results showed that the pretreatment resulted in the formation of large pores in the yam tissues, thereby affecting the rehydration capability and hardness of the dried yam slices. The type of drying method after treatment did not alter the free radical stretching bands of yam. Additionally, the pretreated samples had a higher peak viscosity, through viscosity, final viscosity and break down, alongside lower pasting temperatures, To, Tp, Tc, and △H. Rheological measurements further indicated that all doughs exhibited solid-like behavior to different extents. The pretreatment also decreased the amount of allantoin and polysaccharides in dried yam slices, while negatively influencing their antioxidant activity. Finally, the choice of drying methods significantly affected the quality of the dried yams. In highlighting the effects of PEF pretreatment, combined with different drying methods, on dried yam, the results can help to expand their application within the food industry.

Enhanced high temperature ablation resistance of dense ZrB2–Al2TiO5 composite coating by very low-pressure plasma spraying

ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.

Enhancing mechanical properties of Al-6Mg-0.3Sc-0.15Zr alloy through high cooling rate oil quench investment casting

This article investigates the profound impact of cooling rate on the mechanical properties of Scandium (Sc)-bearing aluminum alloys produced through oil quench investment casting (QIC). Conventional investment casting (CIC) often yields materials with suboptimal mechanical properties due to the formation of large pores and a lack of density in the alloy. QIC at higher cooling rates results in a substantial improvement in mechanical properties. This leads to a duplex grain size distribution with minor changes in average grain size compared to conventional casting. Additionally, the increased cooling rate promotes the formation of nanosize precipitates of Al3(Sc, Zr) during the aging process, significantly enhancing age hardness. Furthermore, tensile and wear properties experience a remarkable enhancement in QIC after aging. The higher cooling rate minimizes Sc segregation, resulting in a supersaturated solution. Specifically, an increase of 17% in UTS and 28% in yield strength is observed in the QIC process compared to the CIC. QIC demonstrates potential as a viable method for enhancing the mechanical characteristics of Sc-bearing aluminum alloys, especially in situations when a distinct solutionizing treatment is not possible. This research underscores the potential of high cooling rate QIC as a viable method for enhancing performance in various engineering applications.

Effect of poly(styrene sulfonate) treatment on the structural evolution and sonodynamic performance of PCN-224 nanoparticles

Porphyrin based nanosize metal-organic frameworks (MOFs), such as PCN-224, are promising sonosensitizers for the sonodynamic therapy (SDT) due to their high porphyrin loading capacity and excellent water dispersity. However, the limited pore size of PCN-224 and the close proximity between porphyrins may impede the generation and diffusion of reactive oxygen species (ROS). In this study, a facile ligand exchange method is developed to regulate the structure and the content of tetrakis(carboxyphenyl)-porphyrin (TCPP) in the treated PCN-224 nanoparticles (NPs). Through simple incubation of PCN-224 NPs in poly(styrene sulfonate) (PSS) solution, the ligand exchange between PSS and TCPP happens and a part of TCPP is released to the solution. The ligand exchange results in the transformation of the crystalline structure to amorphous structure of PCN-224, the formation of larger pores and the decrease of surface area. The increased pore size can enhance the generation ability of 1O2 due to the favorable diffusion of substances. This effect can compensate the decreased amount of TCPP in the NPs until the incubation time reaches 8 h in a 2 mg/mL PSS. After balancing the two factors of structure change and TCPP content in the treated PCN-224 NPs, one can achieve their optimal SDT performance. Through a ligand exchange process, this work provides a facile method to regulate the structure of MOFs-based sonosensitizers and their SDT performance.

Synthesis of xylan and lignin based hydrogels and their use as growth media for rice (Oryza sativa)

Different hydrogels were synthesised using lignin and xylan (extracted from rice straw) as the raw material, PVA as matrix template, citric acid, and succinic acid as crosslinkers and were structurally characterised by FT-IR and SEM analysis. Citric acid cross-linked hydrogels caused loose bonding between polymers and resulted in formation of large pores whereas succinic acid cross-linked hydrogels were observed to have less porosity and tight bonding network. The swelling ratio and reswelling capacity of hydrogels revealed that lignin hydrogels outperformed all other hydrogels. All the synthesised hydrogels were tested for their use as soil culture media ingredient for the germination of rice seedlings. All the hydrogels performed well in stress conditions as compared to normal conditions. Xylan/lignin hydrogel and lignin hydrogels performed best under stress conditions. These hydrogels could be used effectively as an ingredient of soil culture media owing to their tendency to absorb and retain water properly.

Antibacterial Marinopyrroles and Pseudilins Act as Protonophores.

Elucidating the mechanism of action (MoA) of antibacterial natural products is crucial to evaluating their potential as novel antibiotics. Marinopyrroles, pentachloropseudilin, and pentabromopseudilin are densely halogenated, hybrid pyrrole-phenol natural products with potent activity against Gram-positive bacterial pathogens like Staphylococcus aureus. However, the exact way they exert this antibacterial activity has not been established. In this study, we explore their structure-activity relationship, determine their spatial location in bacterial cells, and investigate their MoA. We show that the natural products share a common MoA based on membrane depolarization and dissipation of the proton motive force (PMF) that is essential for cell viability. The compounds show potent protonophore activity but do not appear to destroy the integrity of the cytoplasmic membrane via the formation of larger pores or interfere with the stability of the peptidoglycan sacculus. Thus, our current model for the antibacterial MoA of marinopyrrole, pentachloropseudilin, and pentabromopseudilin stipulates that the acidic compounds insert into the membrane and transport protons inside the cell. This MoA may explain many of the deleterious biological effects in mammalian cells, plants, phytoplankton, viruses, and protozoans that have been reported for these compounds.

Effect of high humidity on the initial mechanical properties and failure modes of thin spray-on liners (TSLs)

Thin Spray-on Liners (TSLs) are a novel rock support technology used in underground projects, which often encounter harsh environments such as high humidity. The mechanical properties of TSLs are affected by the high humidity environment. This study aims to summarize the support mechanisms of TSLs and evaluate the effects of humidity on their performance. Two cement-based TSLs were prepared. They used vinyl acetate-ethylene copolymer emulsion (VAE emulsion) and polyacrylate emulsion as modifying materials, respectively. Specimens were subjected to four different humidity environments for 7 days. The mechanical properties of the specimens were evaluated through compressive, flexural and pull-out tests. The impermeability test was utilized to test the sealing of TSLs. Microscopic observation was conducted using a Lecia microscope. The study also analyzed the interfacial failure modes observed in the pull-out test. The results indicated that increasing humidity hindered the film formation reaction of TSLs, preventing the formation of a continuous three-dimensional spatial polymer mesh structure. Instead, cohesive large particles were formed, negatively impacting the mechanical properties. Additionally, increasing humidity led to the formation of large pores and crack lines within TSLs, further decreasing their mechanical and sealing properties. The increase in humidity also weakened the dry shrinkage effect of TSLs, resulting in increased bond strength. Therefore, analyzing the initial mechanical properties of TSLs under high humidity conditions is crucial for guiding their application in underground projects.

Enhancing corrosion resistance in Mg[sbnd]Li alloy through plasma electrolytic oxidation coatings — Exploring the impact of ionic liquids (BmimBF4)

The wide application of MgLi alloys is limited by the poor corrosion resistance, which needs to be improved by surface treatment. Plasma electrolytic oxidation (PEO) method is one of the most promising methods for the formation of oxide coatings on MgLi alloys. However, the conventional PEO technique with high energy consumption causes poor coating compactness and hampers efforts to enhance corrosion resistance. In this study, various concentrations of ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, BmimBF4) are introduced into the concentrated alkaline electrolyte to facilitate the formation of a PEO coating on the surface of LA91 magnesium‑lithium (MgLi) alloy. The influence of BmimBF4 on PEO coatings has been investigated. The results indicate that a concentrated electrolyte significantly lowers the working voltage of PEO, thereby enhancing energy efficiency. Uneven adsorption on the substrate surface, resulting from the low concentration of BmimBF4 (≤20 mL/L) in the electrolyte, induces partial discharge, leading to high surface roughness and the formation of large pores. However, when an excessive amount of BmimBF4 (>20 mL/L) is present, it uniformly adsorbed onto the substrate surface during the initial stage of PEO process, forming a corrosion inhibitor layer. This leads to a consistent discharge on the surface of substrate throughout the entire PEO process, resulting in a reduction in both surface roughness and micropore size. Among these coatings, the one prepared in an electrolyte containing 20 mL/L BmimBF4 exhibits the highest contact angle (66.8° ± 3.8°) and the best long-term corrosion resistance (hydrogen evolution rates <0.02 mL·cm−2·h−1). These properties can be attributed to the physical and chemical adsorption of BmimBF4, which contains hydrophobic long alkyl chains, as well as the maximum thickness with extended discharging channels. This study offers a guiding strategy for further reducing energy consumption and enhancing the corrosion resistance of PEO coatings.

The influence of welding speed on nanosecond laser welding of AZ31B magnesium alloy and 304 stainless steel

Nanosecond pulse laser welding was performed on AZ31B magnesium alloy and 304 stainless steel to investigate the impact of welding speed on the joining process. The temperature field of the magnesium/steel laser welding process was simulated using COMSOL software. The findings revealed that a welding speed of 10 mm/s resulted in significant spattering and larger porosity defects in the joint due to excessive heat input. However, when the welding speed was increased to 30 mm/s, these defects disappeared, and the porosity decreased to a minimum, leading to an increased bonding area at the interface. As the speed increased, the heat input decreased, making it more challenging for the porosity to escape from the molten pool and resulting in the formation of larger pores. The shear force test results indicated that the highest shear force was 298.7 N at a welding speed of 30 mm/s. The reduction in porosity and greater penetration depth of the magnesium alloy contributed to the desired mechanical performance. Additionally, the fracture modes were classified as button pullout failure (BPF), base material tearing failure (BTF), and interface failure (IF). The outermost weld seam served as the initial fracture path for both BPF and BTF modes, with BTF ultimately fracturing in the steel base material during tearing. Oxide inclusions, porosity, and the angle of distortion contributed to the fracture path of IF.

Experimental Study on Pore Structure and Soil-Water Characteristic Curve of Ionic Rare Earth Ore under Seepage

The ionic rare earth (RE) ore body undergoes particle transport and pore structure change during the leaching process, resulting in "uneven percolation, preferential channel, leaching blind area," and other problems, leading to structural changes in the ore body, low leaching efficiency, and waste of resources. The unsaturated infiltration process is also the key stage that causes these problems. The initial pore structure evolution of the ore body plays a decisive role in the permeability coefficient of the ore body, and the direct influencing factor of the permeability coefficient is the distribution of the pore radius. We carried out research through indoor simulated leaching, the filter paper method for determining matrix suction, and nuclear magnetic resonance (NMR) testing. An ionic rare earth ore soil-water characteristic curve within a large matrix suction range was obtained by the filter paper method. With the increase in volumetric water content, the matrix suction presents a sharp downward trend. When the volumetric water content is less than 20%, this rule is particularly obvious. With the increase in matrix suction, the thickness of the adsorbed water film on the particle surface and pore radius show a decreasing power function trend. Under percolation, the porosity of an ionic rare earth ore sample tends to increase linearly with the increase in volumetric water content during the process from non-saturation to saturation; the porosity of a saturated ore sample after seepage expanded by 17.5 times compared to that of an unsaturated ore sample before seepage. The change rule of the internal microstructure of the ore sample is reflected in the gradual disappearance of micro pores and the gradual formation of small, medium, large, and mega pores, which shows a gradual increase trend. In the pore radius distribution, the more large and medium pores, the larger the permeability coefficient; the more micro and small pores, the smaller the permeability coefficient. For some ore bodies with poor permeability, the ore body is infiltrated with clear water under small water pressure before leaching with a leaching solution, which can improve the permeability of the ore body, effectively improve the efficiency of rare earth leaching, and increase the economic benefits.

Effect of microwave drying on the brittleness quality of pork chip snacks: Perspectives on drying kinetics and microstructural traits

Ready-to-eat pork-based snacks have gained widespread popularity among consumers. The aim of this study was to investigate the brittleness quality of pork chip snacks (PCS) produced by microwave drying (MD) from the perspective of drying kinetics and microstructural traits. Changing microwave intensity and slice thickness significantly affected the colour and texture quality of the final PCS. The MD process of PCS presented a long heating-up phase and a short hindered drying phase, and the model of Midilli et al. described the drying kinetics well. The hindered drying phase dominated the ripening process and the formation of brittleness quality of PCS, and the temperature above 157.3 °C may cause an undesirable colour appearance. The microstructural characteristics showed that the formation of many large pores in PCS promoted the brittleness quality, while excessive temperature caused the tissue to melt with fewer pores to reduce brittleness. Overall, for fresh pork slices, it is recommended to produce PCS with a thickness of 3.5 mm at 4 W/g for 22 min to achieve a desirable brittleness quality. This study may provide a reference for the production of meat snacks such as PCS.

Improved Oxidation Resistance of Graphite Block by Introducing Curing Process of Phenolic Resin.

The purpose of this study is to improve the oxidation resistance of graphite blocks after graphitization at 2800 °C by introducing a curing process of phenolic resin, used as a binder to control the pore size. Using the methylene index obtained from FTIR, the curing temperature was set to 150 °C, the temperature at which cross-linking most highly occurs. Graphite blocks that had undergone curing, and were carbonized with a slow heating rate, showed increased mechanical and electrical properties. Microstructural observation confirmed that the curing process inhibited the formation of large pores in the graphite block. Therefore, the cured graphite block showed better oxidation resistance in air than a non-cured graphite block. Oxidation of the graphite block was caused by pores created by pyrolysis of the phenolic resin binder, which acted as active sites.

Study on the Soil Deterioration Mechanism in the Subsidence Zone of the Wildcat Landslide in the Three Gorges Reservoir Area

The stability of soil mass near the dam bank in the Three Gorges Reservoir is closely related to the periodic variation in the reservoir water level. In order to study the influence of water level variation on soil mass, the soil mass in the water level fluctuation zone of the Wildcat landslide was taken as the research object, and the mechanism of soil mass deterioration in this area was revealed by comparing the strength and mineral structure characteristics of soil mass at different elevations by means of macro- and meso-microscopic analysis. The results show the following: (1) With the increase in sampling elevation, the natural water content of the soil decreases, and the dry density of the soil is a minimum when the elevation is 155 m and at a maximum when the elevation is 175 m. (2) The soil mass in the water dissipation zone of the Wildcat landslide can be divided into three areas: When the elevation is 145–155 m, the fractal dimension increases, the soil fragmentation increases, the cohesion decreases, and the soil deterioration increases. When the elevation is 155–175 m, the fractal dimension decreases, the soil fragmentation decreases, the cohesion increases, and the soil deterioration weakens. When the elevation is greater than 175 m, there is no soil deterioration. (3) X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) were used to test the soil’s mineral composition and pore size at different elevations. It was found that the main reason for the severe deterioration of macro-strength parameters of the soil at the elevation of 155 m was that the proportion of clay minerals and quartz was at the lowest, and the proportion of medium pores and large pores was at the highest. (4) Through the combination of macro and mesoscopic testing and analysis, it was found that the rise and fall of the reservoir water level will lead to the strong chemical action of the skeleton and cemented mineral dissolution in the soil degradation-enhanced area, as well as the physical action of soil particles, resulting in the formation of more medium pores and large pores in the soil and eventually the formation of seepage channels.

Effects of alkali and alkaline-earth oxides on preparation of red mud based ultra-lightweight ceramsite

As the main alkali and alkaline-earth oxides in red mud, the effects of Na2O and CaO on the physical properties, crystalline phases and microstructure of red mud based ultra-lightweight ceramsite (RUC) were systematically investigated using XRD, FTIR and SEM-EDS methods. Na2O and CaO promote the generation of glass phase and reduce the viscosity of liquid phase. A proper Na2O content accelerates the formation of internal large size pores and the expansion of ceramsite, but excessive Na2O makes the pores grow and connect to each other and then reduces the compressive strength of RUC. The presence of CaO produces the glass phase with high fluidity that can fill the internal pores of RUC, thereby reducing the expansion property and water absorption. High contents of Na2O and CaO accelerate the crystallization of nepheline and anorthite respectively, and the formation of anorthite is contributed to improve the strength of RUC. The bulk density and compressive strength of RUC can reach 365–485 kg/cm3 and 1.05–1.53 MPa when the contents of Na2O and CaO in RUC are controlled within 3% and 3.5%, respectively, which meet the requirement of GB/T 17431.2–2010.

Experimental Study on the Dissolution Characteristics and Microstructure of Carbonate Rocks under the Action of Thermal-Hydraulic-Chemical Coupling.

Microdamage in a rock induces a change in the rock's internal structure, affecting the stability and strength of the rock mass. To determine the influence of dissolution on the pore structure of rocks, the latest continuous flow microreaction technology was used, and a rock hydrodynamic pressure dissolution test device simulating multifactor coupling conditions was independently developed. The micromorphology characteristics of carbonate rock samples before and after dissolution were explored using computed tomography (CT) scanning. To conduct the dissolution test on 64 rock samples under 16 groups of working conditions, 4 rock samples under 4 groups were scanned by CT under working conditions, twice before and after corrosion. Subsequently, the changes in the dissolution effect and pore structure before and after dissolution were quantitatively compared and analyzed. The results show that the dissolution results were directly proportional to the flow rate, temperature, dissolution time, and hydrodynamic pressure. However, the dissolution results were inversely proportional to the pH value. The characterization of the pore structure changes before and after sample erosion is challenging. After erosion, the porosity, pore volume, and aperture of rock samples increased; however, the number of pores decreased. Under acidic conditions near the surface, carbonate rock microstructure changes can directly reflect structural failure characteristics. Consequently, heterogeneity, the presence of unstable minerals, and a large initial pore size result in the formation of large pores and a new pore system. This research provides the foundation and assistance for predicting the dissolution effect and evolution law of dissolved pores in carbonate rocks under multifactor coupling, offering a crucial guide for engineering design and construction in karst areas.

The Profile of Exopolysaccharides Produced by Various Lactobacillus Species from Silage during Not-Fat Milk Fermentation

The exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) and released into fermented milk play a protective role from stress factors as well as improve emulsifying and thickening properties of the product, reduce syneresis, and increase elasticity. Here we report the relationship between the properties, composition, and microstructure of EPS produced by six different strains of lactobacilli (L. bulgaricus and five strains isolated from silage). The presence of fructose together with negative-charged uronic acid was found to play a significant role in changing the EPS properties. Thus, the increased fraction of rhamnose and arabinose and a decrease in xylose leads to compaction of the EPS, decreased porosity and increased both OH- and superoxide scavenging and Fe-chelating activities. By contrast, increased xylose and low rhamnose and arabinose apparently leads to loss of large aggregates and high DPPH activity and FRAP. The high content of glucose, however, provides the formation of large pores. The increased fructan fraction (69.9 mol%) with a high fraction of galacturonic (18.2 mol%) and glucuronic acids (6.7 mol%) apparently determines the highly porous spongy-folded EPS microstructure. Taken together, our results indicate that both the quantitative characteristics of the individual components of the fraction and the structural features of EPS are important for the antioxidant potential of fermented milk and depend on the strain used for milk fermentation, suggesting the advantage of a multicomponent starter to achieve the optimal beneficial properties of fermented milk.