Subcritical Temperatures Research Articles

Metastable and unstable hydrodynamics in multiphase lattice Boltzmann.

Metastability in liquids is at the foundation of complex phase transformation dynamics such as nucleation and cavitation. Intermolecular interaction details, beyond the equationof state, and thermal hydrodynamic fluctuations play a crucial role. However, most numerical approaches suffer from a slow time and space convergence, thus hindering the convergence to the hydrodynamic limit. This work shows that the Shan-Chen lattice Boltzmann model has the unique capability of simulating the hydrodynamics of the metastable state. The structure factor of density fluctuations is theoretically obtained and numerically verified to a high precision, for all simulated wave vectors, reduced temperatures, and pressures, deep into the metastable region. Such remarkable agreement between the theory and simulations leverages the exact implementation at the lattice level of the mechanical equilibrium condition. The static structure factor is found to consistently diverge as the temperature approaches the critical point or the density approaches the spinodal line at a subcritical temperature. Theoretically predicted critical exponents are observed in both cases. Finally, the phase separation in the unstable branch follows the same pattern, i.e., the generation of interfaces with different topology, as observed in molecular dynamics simulations.

Study on the Rule of Change of Reservoir Rocks under Subcritical Steam Effect

This paper examines the lithology, pore throat, and fluid characteristics of the reservoir in Liaohe Oilfield Block 3624, using group V rocks as an example, combining a high-temperature and high-pressure reaction still with other equipment such as a rock mechanics tester and a scanning electron microscope. This study also designs and develops three controlled variable experiments, including the subcritical steam reservoir rock dissolution experiment, the subcritical steam reservoir rock mineral composition transformation experiment, and the subcritical steam reservoir rock mineral mechanical property experiment, also making clear the rule of change on the part of the rocks in the deep and heavy oil reservoirs after the injection of subcritical steam. Experimental results reveal the following: (1) Steam causes the dissolution of rocks, and when the steam temperature is in the subcritical region, dissolution is visible. After a 350 °C subcritical steam treatment, the relative melting temperatures of the components of rock materials are substantially greater than the melting point of the cement holding them together, causing the cement to significantly dissolve and a secondary crack network to emerge. (2) The mineral composition of the rocks changes as a result of elevated temperatures, with various mineral transformation trajectories being recorded after various steam treatments. Montmorillonite in reservoir rocks is converted into minerals like illite and chlorite in the subcritical steam temperature range. Another element influencing the creation of secondary cracks on rock surfaces is the reciprocal transformation of minerals, which alters the cohesiveness among mineral components. (3) Rocks suffer thermal damage and changes to their mechanical characteristics as a result of high-temperature steam dissolution and mineral transformations; the severity of these changes increases with the steam temperature.

Sub-Supercritical Hydrothermal Liquefaction of Lignocellulose and Protein-Containing Biomass

Hydrothermal liquefaction (HTL) is an emerging technology for bio-crude production but faces challenges in determining the optimal temperature for feedstocks depending on the process mode. In this study, three feedstocks—wood, microalgae spirulina (Algae Sp.), and hydrolysis lignin were tested for sub-supercritical HTL at 350 and 400 °C through six batch-scale experiments. An alkali catalyst (K2CO3) was used with wood and hydrolysis lignin, while e (Algae Sp.) was liquefied without catalyst. Further, two experiments were conducted on wood in a Continuous Stirred Tank Reactor (CSTR) at 350 and 400 °C which provided a batch versus continuous comparison. Results showed Algae Sp. had higher bio-crude yields, followed by wood and lignin. The subcritical temperature of 350 °C yielded more biocrude from all feedstocks than the supercritical range. At 400 °C, a significant change occurred in lignin, with the maximum percentage of solids. Additionally, the supercritical state gave higher values for Higher Heating Values (HHVs) and a greater amount of volatile matter in bio-crude. Gas Chromatography and Mass Spectrometry (GCMS) analysis revealed that phenols dominated the composition of bio-crude derived from wood and hydrolysis lignin, whereas Algae Sp. bio-crude exhibited higher percentages of N-heterocycles and amides. The aqueous phase analysis showed a Total Organic Carbon (TOC) range from 7 to 22 g/L, with Algae Sp. displaying a higher Total Nitrogen (TN) content, ranging from 11 to 13 g/L. The pH levels of all samples were consistently within the alkaline range, except for Wood Cont. 350. In a broader perspective, the subcritical temperature range proved to be advantageous for enhancing bio-crude yield, while the supercritical state improved the quality of the bio-crude.

Effect of subcritical water temperature on the structure, antioxidant activity and immune activity of polysaccharides from Glycyrrhiza inflata Batalin

In this study, the polysaccharide from Glycyrrhiza inflata Batalin extracted by hot water (HW-GP) was further physically modified with subcritical water to obtain novel polysaccharides (SW-GP). Comparative analysis was conducted to examine the disparities in conformation and bioactivity between HW-GP and SW-GP, aiming to precisely regulate the structure of the polysaccharides and enhance their bioactivity by controlling subcritical water temperature. The results showed that, compared with HW-GP, subcritical water modification (100–160 °C) not only significantly reduced the molecular weight of polysaccharides (from 5.586 × 105 g/mol to 1.484 × 105 g/mol), but also modulated the intermolecular interaction forces, which maintain the conformation of the polysaccharides, including electrostatic and hydrophobic interactions, thereby dynamically transforming the polysaccharide chain conformation from triple helix to random coil, and the strength of the chain conformation shifted from rigid to flexible. In addition, the modification of the SW-GP structure by subcritical water also enhanced its biological activity. SW-GP (140 °C) with low molecular weight and semi-rigid triple helix conformation showed the best scavenging effect on the DPPH, ABTS, and hydroxyl radicals, and exhibited excellent antioxidant activity. SW-GP (130 °C) with medium molecular weight and semi-rigid triple helix conformation significantly promoted the proliferation and phagocytosis of RAW264.7 cells, as well as increased the release levels of NO, TNF-α, IL-6, and IL-1β, and the immunomodulatory activity was much higher than that of other polysaccharides. These findings confirmed the feasibility of using subcritical water temperature as a regulatory feature for the structure and bioactivity of glycyrrhiza polysaccharides, which may have reference significance for the modification of polysaccharides with heightened bioactivity.

The influence of rolling at subcritical temperatures on the low-carbon steel structure and properties formation

Problem. In practice, the rolling of a low-carbon steel sheet due to significant heat losses ends in the austenite – ferrite two-phase structure region, which leads to the metal heterogeneous structure formation, that decreases the sheet steel properties of the and its ability to be drawn.
 Adverse temperature conditions characteristic of traditional hot rolling technology can be prevented by metal processing in the single-phase ferrite structure region below the critical point Ar1. Rolling of a thin sheet in the subcritical temperature range will ensure obtaining a uniform metal structure, which determines the level of its mechanical properties, as well as the quality of stamped parts
 Goal. The purpose of the work is study the rolling modes influence at subcritical temperatures on the low-carbon steel structure and properties formation.Methodology. The microstructure of 08ps steel samples was studied using a metallographic and electron microscope JSM-840 with a "Link-860/|500" microanalysis system, the 08ps steel samples cross-section fine structure was studied using an electron microscope JEM - 200Сx. The metal mechanical properties complex was determined by standard tensile test methods.Results. The 08ps steel structure and properties after rolling at subcritical temperatures were studied. The comparative analysis of the fine structure of the initial blank and deformed samples of low-carbon steel was carried out. It was established that changes are observed in the structure of the deformed samples and the initial blank, which indicate the polygonization and recrystallization processes implementation and do not provide the of metal mechanical properties level provided for by DSTU 2834-94.Originality. Тhe thin structure of a 08ps steel sheet deformed in the subcritical temperature range with air cooling was studied. The development differs in the temperatures of the beginning and end of rolling, as well as the cooling rate in the post-deformation period. It allows to expand theoretical ideas about the patterns of 08ps deformed steel structure formation and to use them in practice. Practical value. The results of the work can be applied in determining rational processing modes, which involve rolling at subcritical temperatures, to increase the complex metal properties and obtain high-quality parts by cold stamping.

The influence of temperature and pressure technological parameters on the characteristics of ZnO nanostructures synthesized by sol-gel process in isopropanol

The sol-gel process was employed to successfully synthesize ZnO nanostructures in isopropanol, employing various subcritical temperature and pressure conditions: (90°C, 2 bar), (120°C, 6 bar), (160°C, 14 bar), and (200°C, 30 bar). The resulting products were subsequently annealed at 500°C for 2 hours and subjected to characterization using different analytical techniques, including X-ray diffraction (DRX), infrared (ATR), UV-Visible, and photoluminescence (PL) spectroscopies. The DRX measurements confirmed that the ZnO nanostructures exhibited a polycrystalline structure of the hexagonal wurtzite type. The cell parameters and stresses within the crystallites were found to be influenced by the synthesis conditions (temperature and pressure), in contrast to the particle size. ATR spectra indicated high purity of the produced nanostructures, and it was observed that the position of the absorption band associated with the Zn-O vibrational bond of ZnO shifted towards lower wavenumbers as the temperature increased. UV-Visible spectra demonstrated that the absorption band shifted towards shorter wavelengths with increasing temperature and pressure. The optical gap displayed a similar trend to the lattice parameters and strain within the nanoparticles. PL measurements revealed that the processing temperature and pressure resulted in increased UV emission and decreased visible emission. However, the positions of the UV emission bands were independent of the synthesis parameters.

Rapid hydrothermal synthesis of mesoporous NiS2 and NiSe2 nanostructures for wastewater treatment

In the present study, single phase nickel based disulphide (NiS2) and diselenide (NiSe2) nanostructures were prepared hydrothermally in a short time span (4 h) under subcritical temperature (160 °C). The nanostructures grow in cubic crystal phases. Average crystallite sizes and intrinsic microstrains were determined using Williamson–Hall (W–H) plot analysis. Hollow NiS2 nanospheres and bipyramidal NiSe2 nanostructures are reported that are suitable for surface related applications. Thermal gravimetric analysis (TGA) indicated high stability of the nanostructures at elevated temperatures. Optical studies indicated visible light activeness of the nanostructures exhibiting sharp band edges. The nanostructures are mesoporous in nature with NiS2 and NiSe2 having respectively a large specific surface area of 310 m2/g and 177 m2/g. A primarily work done to determine the electrochemical nature of the nanostructures showed the materials are pseudo-capacitive in nature with specific capacitances of 1022 F/g and 480 F/g respectively for NiS2 and NiSe2. The photo-catalytic activity of the nanostructures was explored against a colourless pollutant; phenol. The nanostructures degraded most of the phenol (>90 %) under visible light illumination and the reusability experiments performed determined industrial value of the photocatalysts.

Critical behavior in a chiral molecular model.

Understanding the condensed-phase behavior of chiral molecules is important in biology as well as in a range of technological applications, such as the manufacture of pharmaceuticals. Here, we use molecular dynamics simulations to study a chiral four-site molecular model that exhibits a second-order symmetry-breaking phase transition from a supercritical racemic liquid into subcritical D-rich and L-rich liquids. We determine the infinite-size critical temperature using the fourth-order Binder cumulant, and we show that the finite-size scaling behavior of the order parameter is compatible with the 3D Ising universality class. We also study the spontaneous D-rich to L-rich transition at a slightly subcritical temperature of T = 0.985Tc, and our findings indicate that the free energy barrier for this transformation increases with system size as N2/3, where N is the number of molecules, consistent with a surface-dominated phenomenon. The critical behavior observed herein suggests a mechanism for chirality selection in which a liquid of chiral molecules spontaneously forms a phase enriched in one of the two enantiomers as the temperature is lowered below the critical point. Furthermore, the increasing free energy barrier with system size indicates that fluctuations between the L-rich and D-rich phases are suppressed as the size of the system increases, trapping it in one of the two enantiomerically enriched phases. Such a process could provide the basis for an alternative explanation for the origin of biological homochirality. We also conjecture the possibility of observing nucleation at subcritical temperatures under the action of a suitable chiral external field.

Modeling aqueous association constants and mineral solubilities at subcritical and supercritical temperatures

The need for sustainable power generation has increased interest in the use of hydrothermal fluids for industrial applications. New high-enthalpy geothermal systems and biowaste-to-fuel processes are two relevant examples that employ supercritical fluids which require an in-depth understanding of complex chemical reactions occurring near the supercritical temperature of water (374 °C). As these processes operate in thermodynamic regimes that are not currently covered by a standard molar Gibbs energy of formation model, only empirical fits for single reaction systems are available which limit the use of multi-component phase equilibria calculations that are standard practice for less extreme environments. Here, we advance a standard molar Gibbs energy of formation model able to operate in these otherwise inaccessible thermodynamic states to include species needed for key mineral solubility systems and ion association reactions. This work extends a model based on molecular statistical thermodynamics (MST) into four new systems (Na3PO4-H2O, LiOH-H2O, KOH-H2O, and BaSO4-H2O) by extending the model to cover 10 new species. For each of these systems, model predictions were consistently within the experimental uncertainties for the new systems covered. A breakdown of MST contributions to the model revealed that electrostatic and hard sphere contributions were key to reproducing density dependencies of standard molar Gibbs energy of formation values around the critical point of water.

AN APPLICATION OF COMPUTER SIMULATION OF AUSTENITE DECOMPOSITION IN OPTIMIZATION OF HOT ROLLING OF LOW ALLOYED STEEL BARS

Modern technologies need more and more precise computer design of manufacturing processes. Especially it is visible in thermal processing of steel, such as hot rolling, hot forging, casting, welding, 3D printing, and so on. An application of computer simulation of austenite decomposition in optimization of manufacturing of low alloyed steel bars by hot rolling was studied. For this purpose the mathematical model and computer software for very precise anticipation of TTT diagrams data was developed. The calculation of TTT diagrams data was based on chemical composition of low alloyed steels. The study started with definition mechanisms of austenite decomposition at constant subcritical temperatures. The mechanism of γ→α phase change in steel is not yet been adequately clarified. Methods for calibration of kinetic equations of austenite phase transition at constant subcritical temperatures were developed in this paper. Mathematical modeling of TTT diagrams data consists both, prediction of kinetic of phase transformations and anticipation of steel hardness. It was found out that the hardness of both, microstructural constituents and total hardness of steel mostly depends on the carbon content and temperature of γ→α phase transformation. The model of TTT diagrams data of low alloyed steel was verified in purpose to apply the model of isothermal decomposition of austenite in very precise method for prediction of microstructure composition and hardness of hot rolled steel bars. The verification of developed model was done by comparison of the calculated results of TTT diagrams data with experimentally estimated TTT diagrams data. By the simulation of hardness and microstructural composition of hot rolled steel bar the optimal cooling regime in cooling beds can be designed.

Green extraction of active ingredients from finger citron using subcritical water and assessment of antioxidant activity

In this study, subcritical water extraction (SWE) was used to extract active compounds, such as total phenols, total flavonoids, and essential oil, from finger citron. Response surface methodology (RSM) was applied to determine the optimal extraction conditions (total phenols: liquid-to-solid ratio (LSR) 40.9 mL/g, extraction time (ET) 2.7 h, subcritical water temperature (SWT) 183 °C; total flavonoids: LSR 38.8 mL/g, ET 2.4 h, SWT 176 °C; essential oil: LSR 42.3 mL/g, ET 2.5 h, SWT 182 °C). Under these conditions, the extraction yields of total phenols, total flavonoids, and essential oil were 45.65 ± 0.21 mg/g, 33.12 ± 0.19 mg/g, and 4.36 %, respectively. The extracts had remarkable antioxidant activity in vitro, especially those from SWE, which outperformed other methods. For the extracts, the IC50 values for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonat) (ABTS) radical scavenging, and (2-Phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) (PTIO) radical scavenging were 0.32 mg/mL, 0.05 mg/mL, and 6.14 mg/mL, respectively. Finger citron essential oil (FCEO) was also analyzed by GC-MS and 37 constituents were identified. The major component was D-limonene at 23.59 %. The essential oil extracted by subcritical water also showed notable antioxidant activity, with IC50 values of 0.97 mg/mL, 0.08 mg/mL, and 5.35 mg/mL for DPPH radical scavenging, ABTS radical scavenging, and PTIO radical scavenging, respectively. These findings show that SWE has a promising potential to extract active compounds from natural products and enhance their biological activity.

Non Catalytic Transesterification of Vegetables Oil to Biodiesel in Sub-and Supercritical Methanol: A Kinetic’s Study

Non catalytic transesterification in sub and supercritical methanol have been used to produce biodiesel from palm oil and soybean oil. A kinetic study was done under reaction condition with temperature and time control. The experiments were carried out in a batch type reactor at reaction temperatures from 210 °C (subcritical condition) to 290 °C (the supercritical state) in the interval ranges of temperature of 20 °C and at various molar ratios of oil to methanol. The rate constants of the reaction were determined by employing a simple method, with the overall chemical reaction followed the pseudo-first–order reaction. Based on the results, the rate constants of vegetables oil were significantly influenced by reaction temperature, which were gradually increased at subcritical temperature, but sharply increased in the supercritical state. However, the rate constants of soybean oil were slightly higher than that of palm oil. The activation energy for transesterification of soybean oil was 89.32 and 79.05 kJ/mole for palm oil. Meanwhile, the frequency factor values of both oils were 72462892 and 391210 min-1, respectively. The rate reaction for both of oil were expressed as -rTG = 72462892 exp(-89.32/RT)CTG for soybean oil and -rTG = 391210 exp(-79.05/RT)CTG for palm oil. © 2013 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Comment on “Computation of Isobaric Thermal Expansivity from Liquid Density Measurements. Application to Toluene”

We comment on work by Daridon et al., who proposed a novel method for computing the isobaric thermal expansion coefficient with the use of Mosteller–Tukey linearization of the density as a function of temperature. Since the mentioned work was primarily focused on the data at the standard atmospheric pressure and temperatures below the boiling point, we explore the range of validity of this approach in a more wide range of pressures and temperatures with special attention to the reproducibility of the zero temperature derivative of the expansivity at high pressures. It was found that the Daridon et al.’s method provides an accurate representation of the thermal expansion isobars in the subcritical temperature region up to the temperature where the real dependence has an inflection point. This means that the respective functional form can neither reproduce a finite maximum in the expansivity at supercritical pressures nor the divergence at the critical point. At the same time, within the method’s range of applicability, it allows detecting accurately the location of the points corresponding to the crossing of the thermal expansion isotherms that is demonstrated using the density data as well as the direct measurement of the expansivity through scanning transitiometry.

Subcritical Water Extraction of Onosma mutabilis: Process Optimization and Chemical Profile of the Extracts.

The aboveground and root parts of Onosma mutabilis were extracted using subcritical water and the process was optimized with response surface methodology. The composition of the extracts was determined by chromatographic methods and compared to that of conventional maceration of the plant. The optimum total phenolic contents for the aboveground part and the roots were 193.9 and 174.4 μg/g, respectively. These results were achieved at a subcritical water temperature of 150 °C, an extraction time of 180 min, and a water/plant ratio of 0.1, for both parts of the plant. Principal component analysis revealed that the roots contained mainly phenols, ketones, and diols, with the aboveground part mostly alkenes and pyrazines, whereas the extract from maceration contained mainly terpenes, esters, furans, and organic acids. The quantification of selected phenolic substances showed that subcritical water extraction compared favorably to maceration, especially with respect to pyrocatechol (1062 as compared to 10.2 μg/g) and epicatechin (1109 as compared to 23.4 μg/g). Furthermore, the roots of the plant contained twice as much of these two phenolics compared to the aboveground part. Subcritical water extraction of O. mutabilis is an environmentally friendly method that can extract selected phenolics at higher concentrations compared to maceration.

Heat hardening of a larval amphibian is dependent on acclimation period and temperature.

Plasticity in heat tolerance provides ectotherms the ability to reduce overheating risk during thermal extremes. However, the tolerance-plasticity trade-off hypothesis states that individuals acclimated to warmer environments have a reduced plastic response, including hardening, limiting their ability to further adjust their thermal tolerance. Heat hardening describes the short-term increase in heat tolerance following a heat shock that remains understudied in larval amphibians. We sought to examine the potential trade-off between basal heat tolerance and hardening plasticity of a larval amphibian, Lithobates sylvaticus, in response to differing acclimation temperatures and periods. Lab-reared larvae were exposed to one of two acclimation temperatures (15°C and 25°C) for either 3 or 7 days, at which time heat tolerance was measured as critical thermal maximum (CTmax ). A hardening treatment (sub-critical temperature exposure) was applied 2 h before the CTmax assay for comparison to control groups. We found that heat-hardening effects were most pronounced in 15°C acclimated larvae, particularly after 7 days of acclimation. By contrast, larvae acclimated to 25°C exhibited only minor hardening responses, while basal heat tolerance was significantly increased as shown by elevated CTmax temperatures. These results are in line with the tolerance-plasticity trade-off hypothesis. Specifically, while exposure to elevated temperatures inducesacclimation in basal heat tolerance, shifts towards upper thermal tolerance limits constrain the capacity for ectotherms to further respond to acute thermal stress.

Influence of Long-Term Subcritical Annealing on the Unalloyed Steel Welded Joint Microstructure

The article presents changes in the microstructure of hot-rolled unalloyed structural steel after the arc welding process and in the state after long-term exposure to 600 °C during operation. These studies enable a clear assessment of the effects of long-term exposure to elevated temperature relative to the as-welded condition, which has not been reported. The microstructure examination was carried out on welded joints in eight different zones of the joint. Studies have shown that the welding thermal cycle causes significant changes in the microstructure in the area of the base material heated above the A1 temperature-the heat-affected zone (HAZ)-and in the weld area in the case of multi-pass welding. The long-term exposure of the subcritical temperature of 600 °C on the welded joint leads to the phenomenon of cementite spheroidization in the pearlite in all zones of the joint, while preserving the band structure of the steel after rolling and the structural structure. In the case of the weld, acicular and side-plate ferrite disappearance was observed.

Molecular dynamics study of liquid–vapor transition in underwater electrical wire explosion

During underwater electrical wire explosion, liquid–vapor transitions are crucial to the energy deposition and the generation of shock waves. To explore the characteristics of liquid–vapor transition during electrical explosions in water, a large-scale molecular simulation method was designed. The modeling scales experimental exploding wires to nano-size and then tracks the motion of each atom. The surrounding water medium was simplified as an expanding wall, whose velocity was determined by experimental steak images. Using this model, the phase transition processes at different energy deposition rates were compared. The results show that high energy deposition rates can make the discontinuous liquid–vapor phase transition disappear, forming an axially uniform vapor column, while slow energy injection will change the exploding wire into a foamlike liquid–vapor mixture at a subcritical temperature. The different shapes of wire–water interfaces in the experimental shadowgraphs can be explained by these features of liquid–vapor transition.

COMBINED MICROWAVE-ASSISTED SUBCRITICAL LIQUID EXTRACTION OF CHITOSAN FROM CRAB SHELL WASTE

Current chitosan extraction methods require a highly concentrated alkaline solvent that is costly and environmentally unfriendly. This study aimed to assess the potential of using subcritical liquid deproteination to produce amorphous chitin to reduce the alkaline concentration during the deacetylation step to obtain high-quality chitosan. A combination of microwave-assisted demineralisation, subcritical liquid (SL) deproteination, and conventional deacetylation was employed for chitosan production. Distilled water and 2% and 4% sodium hydroxide (NaOH) were used at subcritical liquid treatment temperatures of 100 to 250°C. Meanwhile, deacetylation using 20%-50% NaOH was attempted on the deproteinised chitin. 1.8 M hydrochloric acid at a 1:10 solid-to-liquid solvent ratio produced chitin with acceptable quality during microwave-assisted demineralisation. Demineralised chitin subjected to SL treatment at 150°C and 4% NaOH had the best protein removal (84.6%). Chitosan with a high degree of deacetylation (80.68%) was obtained at a lower alkalinity of 30% NaOH, derived from SL-deproteinised chitin (4% NaOH at 100°C). The crystallinity of chitin after SL treatment was reduced significantly from 72.4% to 59.4%, which allows easier access for the solvent to hydrolyse the acetamide bond. This study confirms that good quality chitosan can be produced by utilising SL treatment of demineralised chitin at a significantly short time and lower deacetylation solvent concentration.

Correlation of conformational changes and immunomodulatory activity of lentinan under different subcritical water temperature

In order to reveal the intrinsic nature of the reduction or disappearance of biological activity in the processing and preparation of polysaccharides, and realize the effective control of highly active polysaccharides, the correlation between conformation and immunomodulatory activity of lentinan under different subcritical water temperatures was investigated. The results showed that, compared with the lentinan extracted by hot water (HW-L), with the increase of temperature (100–160 °C), the molecular weight of lentinans decreased (5.041 × 105–1.754 × 106 g/mol) and the rigidity of the chain weakened. The chains gradually loosened and a rigid-flexible transition occurred. At 160 °C, the conformation of lentinan completely changed from triple helix to random coil. In-vitro cell experiments showed that, lentinan at 120 °C could more efficiently promote the proliferation and phagocytosis of RAW264.7 cells, and significantly promote the secretion of NO, TNF-α, IL-6 and IL-1β, exhibiting stronger immunomodulatory activity. But the activity of lentinan decreased sharply at 150–160 °C. These results suggest a significant correlation between polysaccharide chain conformation and immunomodulatory activity under different subcritical water temperature conditions. By adjusting the temperature of subcritical water, the chain conformation of polysaccharides can be controlled, resulting in more efficient extraction of highly active polysaccharides.

Extraction of bioactive compounds from black‐footed abalone (Haliotis iris) using subcritical water extraction

AbstractBACKGROUNDOwing to their biodiversity, many valuable natural compounds have been extracted from marine resources and used in the development of pharmaceutical, nutraceutical and cosmeceutical products. The New Zealand black‐footed abalone (Haliotis iris) is known to host a variety of bioactive compounds in its flesh.RESULTSWater‐soluble bioactive compounds were extracted from H. iris by subcritical water extraction technique, and the effect of subcritical water temperature (110–280 °C) on the extraction performance was studied. The highest antioxidant activity and subsequently glycogen and phenolic content, as well as concentration of bioactives, were found at temperatures between 220 and 250 °C. The carbohydrate content of the extracts peaked at 110 °C, which was then degraded at higher temperatures. Protein and amino acid contents of H. iris extracts were also decreased as the temperature increased above 160 °C. Furthermore, the H. iris extracts were found to be non‐toxic.CONCLUSIONThe results indicate that extraction temperature has a significant impact on the bioactivity of H. iris extracts. Subcritical water extraction can be used in place of more traditional techniques to create high‐quality abalone extracts. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).