Bound Water Content Research Articles

Developing a universal equation to estimate the mass of dewatered wastewater sludge during biological digestion at mesophilic and thermophilic temperatures

ABSTRACT A series of dewaterability tests were conducted on various types of sludges to establish a wholistic relationship between sludge water fractions. Sludge samples were obtained from batch and continuous sludge digesters, which were operated anaerobically and aerobically under mesophilic and thermophilic conditions. Dewaterability of the sludge samples and the distribution of water fractions were studied using centrifugation and thermal drying. Thickened waste activated sludge (T-WAS) contained 10–11 g bound water (BW)/g of total solids (TS), and it was more hydrophilic than primary and digested sludges. During anaerobic digestion, BW content fluctuated between and 2.14.24 g BW/g TS. However, aerobic digestion at 55 °C reduced the BW content of the mixed T-WAS + primary sludges from 3.7 to 2.14 g BW/g TS. A linear function was developed to correlate supernatant and BW mass fractions (R2 = 0.995). An equation was derived from the linear function to estimate the mass of dewatered sludge based on the TS concentration of the initial wet sludge. The developed expression is applicable to different kinds of wastewater sludges. It would be helpful for the designers and operators of sludge thickening and dewatering systems to use centrifugal separation.

Influence of further hydration on UHPC matrix properties

To investigate the evolution laws governing the macroscopic properties of ultra-high-performance concrete (UHPC) matrices under further hydration effect, a further hydration test was performed by varying the cement fineness and slag powder content. The influence mechanism of further hydration on strength was analyzed. The results revealed that the bound water content for further hydration and expansion strain for UHPC matrix with medium fineness cement achieved the minimum values, and the compressive strength reached the lowest value after 21 d of further hydration. Both the bound water content for further hydration and expansion strain showed a tendency to increase with increasing slag powder content, and the higher the slag powder content, the earlier was the peak strength achieved. The volume expansion of further hydration products caused the matrix to crack, and further hydration was manifested as damage effect, resulting in a decrease in strength.

Enhancing whipped cream anti-freeze properties: A dual plant system with aquafaba and mung bean protein

The objective of this study was to substitute sodium caseinate (SC) with a dual plant-based alternative to produce a refreshing sour whipped cream at pH 3.0, which could maintain stability when paired with low-pH foods. Aquafaba (AQ) was utilized as a novel foam booster, enhancing the whipped properties of the whipped cream, while pH12-shifting treated mung bean protein (BMBP) functioned as an interfacing stabilizer, improving its stability. Freeze-thaw stability of the aerated emulsion and the protein-protein interactions in the emulsion were characterized by analyzing water distribution, thermodynamics, serum loss, and protein retention rates. The high bound water content and dense bubble distribution of whipped cream prepared by AQ and native mung bean protein (NMBP) delivered superior freeze-thaw stability, shown as reduced serum loss, higher protein retention, and increased hardness. In addition, the internal fat network of the whipped cream made from a 1:1 combination of NMBP and BMBP showed moderate agglomeration with a comparable γmax value as SC-based whipped cream, indicating enhanced resistance to deformation and improved short-term shape retention. In conclusion, the combination of AQ and MBP provided viable options for the replacement of SC in commercial whipped cream.

Quantitative investigation of temperature-dependent bound water degeneration in bentonite clays

Temperature increases in saturated clay alter the physicochemical clay-water interactions and may lead to the conversion of bound water into free water. These changes significantly influence the physical, chemical, and engineering properties of clays, which are critical for geotechnical and geological engineering and minimizing risks in areas with expansive clay soils. However, quantifying this phenomenon remains challenging in the literature. This study presents a robust experimental approach for quantifying the thermal-induced conversion of bound water in clays, providing valuable insights into the mechanisms governing their thermo-mechanical behavior. A novel experimental method is proposed to quantify the degenerated bound water content in a clay system subjected to temperatures ranging from 20 to 50 °C. The research employs the siphon principle to examine volume changes in a clay system at elevated temperatures, focusing on measuring the conversion of bound water to free water. This method accounts for thermal expansion of both the soil constituents and the confining glass cylinder, as well as potential evaporation losses. To validate the setup's accuracy, a calibration test using standard Ottawa sand with negligible bound water was performed. After measuring system error, the primary outcome was calibrated. Results showed that at 30 °C, 40 °C, and 50 °C, 3 %, 9 %, and 15 % of the initial bound water, respectively, converted to free water.

Uncovering the mechanism controlling strength and microstructural evolution of belite-rich cement-based materials at different temperatures

The effect of temperature on the properties of belite-rich cement-based (BRC) materials is different from that on Portland cement (PC). This study provides a comprehensive understanding of the mechanisms controlling strength and microstructural evolution at different temperatures, especially C-S-H characteristics, of BRC materials. Phase assemblage, pore structure, and microscopic morphology of BRC paste, as well as phase composition and structure, chemically bound water, and bulk density of C-S-H were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), 1H and 29Si nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The strength of BRC mortar increased with temperature is because of the higher hydration degree of β-C2S, lower porosity (except for 60 °C), and increased main chain length (MCL) of C-S-H. Hydration degrees of 28-d β-C2S and C3S increased by 202.5% and 16.3%, respectively, while MCL increased by 39.4% from 5 to 60 °C. The higher temperature sensitivity of β-C2S is due to its activation energy being 12.4% greater than that of C3S in BRC paste. Additionally, gel porosity decreased with temperature due to decreased bound water content and increased 16.7% bulk density of C-S-H from 5 to 60 °C. Finally, the CaO/SiO2 was inversely proportional to MCL and bulk density, but positively to H2O/SiO2. The findings deepen the mechanistic understandings of the hydration kinetics and microstructural evolution for temperature-affected BRC material.

Impacts of alkaline washing pretreatment on municipal solid waste incineration fly ash (MSWI FA) and resulting geopolymers

The safe disposal and utilization of municipal solid waste incineration fly ash (MSWI FA) has emerged as a crucial challenge, primarily due to elevated levels of heavy metals and chlorides. In this study, the influence of key factors in different pretreatment methods on the physicochemical properties of MSWI FA was analyzed, and the effects and mechanism of different pretreatment methods on the resulting geopolymers were studied. Under the conditions of a liquid-solid ratio (L/S) of 7 mL/g, a rotational speed of 500 r/min, and a stirring time of 20 min, the alkali washing with 1 mol/L NaOH solution exhibited better effect than water washing. The total content of chlorides and the content of soluble chloride in AFA (MSWI FA with alkali washing) were 1.53 % and 0.85 %, respectively. Alkali washing had a greater influence on the migration of heavy metals from MSWI FA to filtrate than water washing. Meanwhile, alkaline washing exhibited better effect in calcium retention and sulfur removal. The pretreatment process enhanced the gel formation in geopolymers, subsequently exerting a significant influence on the compressive strength and leaching concentration of heavy metals. Thermogravimetric analysis showed the bound water content in AG (8.46 %) was the greatest in all simples, indicating that exerted the most pronounced impact on the gel formation during geopolymerization. And, the lower ratio of Si-O-Na to Si-O-T in AG (0.20) indicated a longer geopolymeric chains, which explained the higher compressive strength of geopolymers during the initial curing period. This article provides a new pretreatment method to promote the resource utilization of MSWI FA.

Insight into the relationship between the starch crystalline structure and textural quality and physicochemical properties of reconstituted rice: Influence of feed moisture content

Reconstituted rice was prepared by extrusion with different feed moistures (30 %, 33 %, 36 %, 39 % and 42 %), and the relationship between the crystalline structure, physicochemical properties, and textual quality of reconstituted rice was studied. The results revealed that, with the feed moisture increased (33 %–36 %), the gelatinization degree reached 97.28 % and the bound water content increased by 23.58 %. The water absorption index and swelling power index reached 8.35 g/g and 9.46 g/g, respectively, and the texture properties were close to those of native rice. Higher extrusion feed moisture (39 %–42 %) increased the setback value (206.00 cP) and breakdown value (721.33 cP) of starch, and the hardness and gumminess of reconstituted rice were also increased (p < 0.05). The starch crystalline structure was disrupted by extrusion and changed to a surface fractal structure, the relative crystallinity decreased from 26.87 % to 6.68 %, and the degree of order decreased from 1.680 to 1.006. Correlation analysis revealed that the crystalline structure of starch and water distribution would affect the textural and hydration properties of reconstituted rice. The results provide theoretical references and data support for improving the edibility and quality of reconstituted rice and enhancing the utilization rate of broken rice.

Nondestructive detection of saline-alkali stress in wheat (Triticum aestivum L.) seedlings via fusion technology

BackgroundWheat (Triticum aestivum L.) is an important grain crops in the world, and its growth and development in different stages is seriously affected by saline-alkali stress, especially in seedling stage. Therefore, nondestructive detection of wheat seedlings under saline-alkali stress can provide more comprehensive technical support for wheat breeding, cultivation and management.ResultsThis research focused on moisture signal prediction and classification of saline-alkali stress in wheat seedlings using fusion techniques. After collecting and analyzing transverse relaxation time and Multispectral imaging (MSI) information of wheat seedlings, four regression models were used to predict the moisture signal. K-Nearest Neighbor (KNN) and Gaussian-Naïve Bayes (GNB) models were combined with fivefold cross validation to classify the prediction of wheat seedling stress. The results showed that wheat seedlings would increase the bound water content through a certain mechanism to enhance their saline-alkali stress. Under the same Na concentration, the effect of alkali stress on moisture, growth and spectrum of wheat seedlings is stronger than salt stress. The Gradient Boosting Decision Regression Tree model performs the best in predicting wheat moisture signals, with a coefficient of determination (R2P) of 0.98 and a root mean square error of 109.60. It also had a short training time (1.48 s) and an efficient prediction speed (1300 obs/s). The KNN and GNB demonstrated significantly enhanced predictive performance when classifying the fused dataset, compared to using single datasets individually. In particular, the GNB model performing best on the fused dataset, with Precision, Recall, Accuracy, and F1-score of 90.30, 88.89%, 88.90%, and 0.90, respectively.ConclusionsUnder the same Na concentration, the effects of alkali stress on water content, spectrum, and growth of wheat were stronger than that of salt stress, which was more unfavorable to the growth of wheat. The fusion of low-field nuclear magnetic resonance and MSI technology can improve the classification of wheat stress, and provide an effective technical method for rapid and accurate monitoring of wheat seedlings under saline-alkali stress.Graphical

Enhancing structural strength and water retention of crosslinked polyacrylamide gel with the T-ZnOw

Crosslinked polyacrylamide gel serves as an effective plugging material, crucial for preventing water/gas channeling in reservoirs and enhancing the swept volume and oil recovery. However, its practical application encounters a significant challenge in maintaining long-term stability of strength and volume, particularly under high temperatures. This study investigates the reinforcement of polyacrylamide gel with three-dimensional (3D) nanomaterials, specifically tetra-needle-like zinc oxide whiskers (T-ZnOw), to enhance its structural stability and bound water content. The stress sweep tests showed that the addition of 0.15 wt% T-ZnOw increased the maximum elastic modulus of the gel to 28.5 Pa, representing a 51.2 % improvement compared to before the addition. After 60 days of high-temperature aging at 130 °C, the T-ZnOw strengthened gel still maintained an elastic modulus of 21.8 Pa. With increasing T-ZnOw concentration, the yield point of the gel increased from 4.74 Pa to 9.57 Pa, the anti-deformation of the gel has significantly increased. The stability test results in high salinity water indicate that at a salinity of 150,000 mg/L, the dehydration rate of the strengthened gel is less than 5 %, with an elastic modulus retention rate exceeding 88 %. Furthermore, thermodynamic testing confirms the enhanced thermal degradation resistance and water retention capacity of the gel. Under reservoir temperature conditions, the T-ZnOw strengthened gel exhibits a weight loss of less than 3 %. Additionally, the inclusion of T-ZnOw results in an increase in the bound water capacity index from 4.65 to 12.28. In conclusion, the integration of T-ZnOw into the polyacrylamide gel network not only enhances its mechanical performance and water retention under high-temperature conditions but also demonstrates superior stability in high-salinity environments. This innovative material shows significant potential for improving oil recovery rates in high-temperature reservoirs and can be applied to other high-temperature underground scenarios such as geothermal development and CO2 utilization and storage.

Utilization of biochar as a green additive in supersulfated cement: Properties, mechanisms, and environmental impacts

To promote the green development of building materials, this study develops a novel and sustainable method for incorporating coconut-derived biochar (BC) in supersulfated cement (SSC). Moreover, the solid waste desulfurized gypsum is used as a sulfate activator. The macroscopic experimental results show that the addition of 2 % biochar can reduce the fluidity of composites by 12.5 % but increase the 28-day compressive and flexural strength by 10.3 % and 19.1 %, respectively. Hydration heat analysis show that biochar can increase the maximum heat release of SSC. XRD patterns and TGA analysis indicate that 2 % biochar can improve the hydration degree of cement where the bound water content is increased by 8.9 %. SEM observations and 1H NMR spectrum suggest that although biochar can compact the microstructure, it increases the harmful and multiple harmful pores ratio. Furthermore, a comprehensive analysis considering greenhouse gas emissions, energy consumption, cost, fluidity, and mechanical properties is performed to evaluate the BC-SSC composites. The results prove that BC-modified SSC has significantly lower environmental pollution and resource consumption than ordinary Portland cement, but the cost may be increased.

An Integrated Hydration and Property Evaluation Model for Coral Powder–Cement Binary Blends

With the rise in the marine industry and marine tourism, coral powder is increasingly used to make concrete for marine islands. This study proposes a three-parameter hydration model and a hydration kinetic model to predict the performance of coral powder concrete based on previous experimental data. The process of the proposed prediction model is as follows: 1. The input parameters of the three-parameter hydration model are calibrated for the first 7 days using the cumulative hydration heat per gram of cement. The maximum cumulative hydration heat (455.87 J/g cement) and the shape coefficient (−0.87) remain constant. In this study, the hydration rate coefficients for 0%, 10%, and 20% coral powder were 6.91, 6.19, and 5.55, respectively, showing decreases of 10.41% and 19.68% compared with the specimens without coral powder. 2. At 28 days, the cumulative heat release values per gram of cement for 0%, 10%, and 20% coral powder were 389.77, 395.69, and 401.62 J/g, showing increases of 1.52% and 3.04% for the specimens containing 10% and 20% coral powder, respectively. Meanwhile, the hydration degrees for 0%, 10%, and 20% coral powder were 0.855, 0.868, and 0.881, respectively, showing increases of 1.52% and 3.04%. Furthermore, the cumulative heat release values per gram of binder were 389.77, 356.12, and 321.29 J/g, showing decreases of 8.63% and 17.56% for specimens containing 10% and 20% coral powder, respectively. 3. Properties such as compressive strength, ultrasonic pulse velocity (UPV), and surface electrical resistivity were evaluated using the power function and the cumulative hydration heat per gram of binder. 4. At 28 days, the chemically bound water contents for samples with 0%, 10%, and 20% coral powder were 0.2402, 0.2197, and 0.1981 g/g binder, respectively. Moreover, the calcium hydroxide contents were 0.1848, 0.1690, and 0.1524 g/g binder, showing reductions of 8.53% and 17.52% in bound water and 8.54% and 17.53% in calcium hydroxide. 5. A hydration kinetic model is proposed, which can distinguish between the dilution effect and the nucleation effect of coral powder, unlike the three-parameter model, which cannot distinguish between the two effects. Furthermore, the input parameters of the hydration kinetic model remain unchanged for different mixtures, while the input parameters of the three-parameter model must be varied among mixtures. Parameter analysis of the hydration kinetic model indicated that a low water–binder ratio and a high coral powder substitution rate significantly improve the relative reaction level of cement.

Effects of various acids on physical stability, rheological characteristics and curcumin encapsulation of whey protein isolate Pickering emulsion gels

Acid treatment can alter the functional properties of whey protein isolate (WPI), but the effect of different acids on properties of WPI‐stabilised Pickering emulsion gel (PE) is unknown. Compared with WPI‐PE, droplet size of the acid‐treated WPI‐PE decreased but its zeta potential, apparent viscosity, binding water capacity and curcumin encapsulation were enhanced. Due to the formation of the tightest gel structure of malic acid‐Pickering emulsion gel, it showed the highest viscoelastic modulus, bound water content and gel stability. This work would introduce a novel method for the development of PEs with good gelatinisation and curcumin delivery system for food processing.

Effect of heating treatment on processing characteristics of rice dough

Rice dough is a good source of digestible protein due to its advantages of being gluten-free and hypoallergenic compared to wheat dough, but the poor elasticity, low elongation and adhesion of rice dough limit its application. The effect of heating treatment with different temperature (40–100 °C) on processing characteristics of rice dough was explored. The results of fermentation characteristics showed that the best gas production and gas retention properties of rice dough were achieved at 70 °C. The rheological properties demonstrated a certain degree of deformation resistance at 85 °C, which resulted in the rice dough system exhibiting a tendency to flow at this temperature. Consequently, the blanching dough below 85 °C was deemed preferable for blanching. In addition, with the increase of temperature during blanching., the strength of the rice dough gel network increased. The results of proton distribution showed some of the emi-bound and free water in the rice dough was bound to bound water by exposed hydroxyl groups, leading to an increased bound water content, a decreased adsorbed and free water content. The degree of gelatinization of the rice dough increased gradually with increased blanching temperature, and the stability and resilience of rice dough reached the best at 70 °C. The thermal stability demonstrated that the ungelatinized portion of the rice dough exhibited enhanced structural stability, with the optimal thermal stability attained at 70 °C. It can therefore be concluded that the scalded dough made at 70 °C exhibits superior performance in all aspects and is suitable for subsequent processing of rice dough, which suggests a novel approach to the utilisation of rice dough in the future.

Preparation and Mechanism of Shale Inhibitor TIL-NH2 for Shale Gas Horizontal Wells.

In this study, a new polyionic polymer inhibitor, TIL-NH2, was developed to address the instability of shale gas horizontal wells caused by water-based drilling fluids. The structural characteristics and inhibition effects of TIL-NH2 on mud shale were comprehensively analyzed using infrared spectroscopy, NMR spectroscopy, contact angle measurements, particle size distribution, zeta potential, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results demonstrated that TIL-NH2 significantly enhances the thermal stability of shale, with a decomposition temperature exceeding 300 °C, indicating excellent high-temperature resistance. At a concentration of 0.9%, TIL-NH2 increased the median particle size of shale powder from 5.2871 μm to over 320 μm, effectively inhibiting hydration expansion and dispersion. The zeta potential measurements showed a reduction in the absolute value of illite's zeta potential from -38.2 mV to 22.1 mV at 0.6% concentration, highlighting a significant decrease in surface charge density. Infrared spectroscopy and X-ray diffraction confirmed the formation of a close adsorption layer between TIL-NH2 and the illite surface through electrostatic and hydrogen bonding, which reduced the weakly bound water content to 0.0951% and maintained layer spacing of 1.032 nm and 1.354 nm in dry and wet states, respectively. Thermogravimetric analysis indicated a marked reduction in heat loss, particularly in the strongly bound water content. Scanning electron microscopy revealed that shale powder treated with TIL-NH2 exhibited an irregular bulk shape with strong inter-particle bonding and low hydration degree. These findings suggest that TIL-NH2 effectively inhibits hydration swelling and dispersion of shale through the synergistic effects of cationic imidazole rings and primary amine groups, offering excellent temperature and salt resistance. This provides a technical foundation for the low-cost and efficient extraction of shale gas in horizontal wells.

Effect of electrohydrodynamic (EHD) drying on active ingredients, textural properties and moisture distribution of yam (Dioscorea opposita)

This paper systematically investigates the changes in material properties during electrohydrodynamic (EHD) drying, the discharge characteristics of the EHD system as well as the active ingredients, textural properties (hardness, adhesiveness, etc.) and moisture distribution of yam under EHD, air drying and hot air drying were investigated. The results showed that the active particles and the ionized wind generated during the discharge process of the electrohydrodynamic drying device had a significant effect on the drying. Compared to thermal drying, 21 kV drying resulted in the most complete cellular structure, the best internal bound water content as well as textural properties of yam. It played a positive role in the retention of internal nutrients in yam, and the total phenol and allantoin contents were increased by 25.74% and 81.99%, respectively. These results elucidate the advantages of electrohydrodynamic drying in yam drying and provide a reference for the application of EHD in drying.

A Numerical Hydration Model to Predict the Macro and Micro Properties of Cement–Eggshell Powder Binary Blends

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment.

Hydration, phase assemblage and microstructure of cementitious blends with low-grade limestone

Limestone of the purity mandated by the standards for use in cement manufacture (as raw material or as performance improver) is only a fraction of the mined material. Sometimes, limestone contains impurities like silica, clay, dolomite etc. beyond the levels specified for use as an additive or for cement production. This limestone, commonly known as low-grade limestone, also may have a potential to be used as a supplementary cementitious material. This paper reports a study conducted to understand the hydration behaviour of ordinary Portland cement in combination with low-grade limestone. Low-grade limestone samples with dolomite, silica and clay impurities were collected from various limestone mines in India and used in cementitious blends at various replacement levels after suitable processing. Reaction kinetics was studied using calorimetry and phase assemblage using techniques like X-ray diffraction and thermogravimetry. Mercury intrusion porosimetry was employed to study the microstructure of cementitious blends. Dilution effect of low-grade limestone was studied by measuring compressive strength of cement mortar cubes for various replacement levels. Shortening of induction period, increased peak heat rate and reduced time to peak were observed in the blends of ordinary Portland cement with low-grade limestone. Carboaluminate formation, ettringite stabilisation and higher bound water content were also seen. The studies showed that low-grade limestone also can be used as a partial replacement for ordinary Portland cement without compromising the strength up to 15% replacement. Higher replacement levels, although showing a reduction in strength due to dilution effect, could still be considered for non-structural applications.

Soybean protein isolate-sodium alginate double network emulsion gels: Mechanism of formation and improved freeze-thaw stability

Soybean protein isolate (SPI) is widely used in the food industry. However, SPI-based emulsion gels tend to aggregate and undergo oiling-off during freeze-thawing. In this study, emulsion gels were prepared by a combination of heat treatment and ionic cross-linking using SPI and sodium alginate (SA) as raw materials. The focus was on exploring the mechanistic effects of the SPI-SA double network structure on the freeze-thaw stability of emulsion gels. The results showed that the addition of SA could form different types of network structures with SPI, due to different degrees of phase separation. In addition, SA appearing on the SPI network indicated that the addition of Ca2+ shielded the electrostatic repulsion between SPI and SA to form SPI-SA complexes. The disappearance of the characteristic peaks of SA and SPI in Fourier transform infrared spectroscopy analysis also confirmed this view. Low-field nuclear magnetic resonance data revealed that SA played a role in restricting water migration within the emulsion gels, increasing bound water content, and thereby improving the water-holding capacity of the emulsion gels. Therefore, the incorporation of SA improved the freeze-thaw stability of SPI emulsion gels. These findings offer a theoretical basis and technical support for SPI application in frozen products.

Quality analysis of dough and steamed bread under various freezing conditions.

Freezing is a crucial step in the process of frozen foods. In this study, the effects of different freezing methods, including liquid nitrogen immersion freezing (LF), quick-freezing machine freezing (QF), packaging immersion freezing (PF), and ultralow temperature refrigerator freezing (UF), and freezing time (0, 15, 30, and 60 days) on the textural properties, dynamic rheological properties, water distribution, and structure of dough and the quality of end steamed bread were evaluated. Freezing resulted in a decline in the physicochemical properties of dough. UF- and QF-doughs had higher storage modulus and loss modulus, compared with PF- and LF-doughs. LF enhanced the textural attributes of the dough, resulting in reduced hardness and increased springiness. At 15 days of freezing, QF- and LF-doughs exhibited a compact and continuous structure with a smooth surface. Additionally, the correlation analysis elucidated that the weight loss rate and the bound water content of the dough had discernible impacts on the texture of both the dough and the resulting steamed bread. Overall, LF demonstrated a relatively high freezing efficiency and effectively maintained the quality of the dough for up to 15 days of freezing. These results offer valuable insights for the applications of freezing methods and time in frozen foods.

Effect and mechanism of biochar-based hydrogel to alleviate drought stress in tobacco

Drought is an important abiotic stressor that adversely affects agricultural production, resulting in decreased crop yields and food insecurity. The objective of this study was to develop a novel hydrogel-based composite (S-B-AA) by incorporating biochar into hydrogel (S-AA) and evaluating its effects on tobacco plants under drought stress. The S-B-AA hydrogel exhibited enhanced water absorption and retention capabilities compared to the S-AA hydrogel. Under drought stress conditions, the S-B-AA hydrogel effectively increased the total water content, relative water content, and free water content of tobacco leaves, while reducing the bound water content and water saturation deficit. Additionally, it improved the stomatal status of tobacco leaves, significantly enhanced the photosynthetic capacity of tobacco seedlings, and promoted biomass accumulation. Moreover, the S-B-AA hydrogel alleviated the excessive accumulation of reactive oxygen species (ROS) induced by drought stress in tobacco seedlings, thereby alleviating ROS damage to cell membranes. It also reduced antioxidant enzyme activity and the levels of the signaling molecule H2S, while minimizing the impact of drought stress on tobacco osmotic regulation. Transcriptome analysis revealed that S-B-AA up-regulated 2826 DEGs and down-regulated 5225 DEGs compared to the control group. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis demonstrated that the differentially expressed genes were predominantly enriched in the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signaling pathway, and photosynthesis pathway. This study provides a theoretical basis and practical guidance for the application of S-B-AA hydrogel in agriculture and environmental protection.