查找使用阿拉丁产品的科研文献

Effect of osmotic dehydration combined with vacuum freeze-drying treatment on characteristic aroma components of peach slices

Jin-Ru Wang,Xin-Ye Wu,Cheng-Bi Cui,Jin-Feng Bi

Hot air drying (HD), vacuum freeze drying (FD), and pilot-scale freeze drying (PSFD) are extensively used to prepare peach slices. However, the aroma of hot air drying and vacuum freeze-drying is yet to be addressed. In this study, HS-SPME-GC–MS was used to characterize and quantify the volatile compounds in peach slices. First, 33, 36, and 46 volatile compounds were identified and quantified in the HD, FD, and PSFD groups, respectively. PSFD is preferable to HD and FD in terms of the volatile compound types, content, and aroma profiles. PSFD was selected for subsequent permeation and dehydration experiments. The key aroma compounds with an OAV ≥ 1 were found in the PSFD30 group. GC-O analysis was conducted on the PSFD30 group, leading to the preliminary identification of 2-methylbutanal, pentanal, hexanal, 2-hexenal, phenylacetaldehyde, ethyl acetate, 2-methylbutyl acetate, ethyl lactate, linalool, methyl heptenone, and γ-octalactone as distinctive aromas in dried peach slices.

Effect of Si3N4 solid contents on mechanical and dielectric properties of porous Si3N4 ceramics through freeze-drying

Ling Li,Qinggang Li,Juan Hong,Mengyong Sun,Jie Zhang,Shaoming Dong

Porous Si 3 N 4 ceramics with uniform pore distributions were fabricated by freeze drying with liquid N 2 as refrigerant, and then sintered at 1700 °C under an N 2 pressure of 0.3 MPa. The Si 3 N 4 dispersant slurries were prepared by ball milling for 12 h and casting into a mold using liquid nitrogen as a freezing medium with the top surface of the sample exposed to air at room temperature. The temperature gradient contributed to bimodal peaks of pore size distribution . Effects of solid concentration on the porosity, mechanical, and dielectric properties of the Si 3 N 4 sample were systematically investigated. As the solid content increased from 15 vol.% to 40 vol.%, the porosity decreased from 83.9% to 40.58%. Therefore, flexural strength and compressive strength increased from 0.1 MPa to 94.7 MPa, and 1.3 MPa–314 MPa, respectively. Moreover, the dielectric constant increased from 1.4 to 4.0. This study indicated that the freeze-drying process is a useful method for fabricating novel porous Si 3 N 4 ceramics with unidirectional channels.

A Facile Freeze-Drying Strategy To Prepare Hierarchically Porous Co/C Foams with Excellent Microwave Absorption Performance

Ting Huang,Zhengchen Wu,Jiawei Lin,Qi Yu,Donggui Tan,Lei Li

The hierarchically porous Co/C foam with low density has been successfully prepared by a facile sequential process of foaming–lyophilization–carbonization. In the hierarchical structure, the macro- and mesoscopic pores are created by surfactant-assisted foaming and lyophilization processes, while the nanoscale pores spring from the etching reaction between gelatin-derived carbon and metal oxides during the high-temperature carbonization. By adjustment of the carbonization temperature and loading of the as-prepared absorbent, a maximum reflection loss (RL) achieves −56.5 dB at the thickness of 2.49 mm, and a broad effective absorption bandwidth (EAB) of 6.0 GHz is reached. The corresponding mechanism demonstrates that such an outstanding performance is rooted in the synergetic loss capacities from dielectric and magnetic components. Therefore, it is believed that this work provides a significant guidance for exploring high-performance and lightweight microwave absorbents.

Ultra-porous cellulose nanofibril aerogel films as excellent triboelectric positive materials via direct freeze-drying of dispersion

Yiheng Song,Jiangkai Bao,Yang Hu,Menghan Xu,Zhibo Yang,Yating Liu,Quanling Yang,Chuanxi Xiong,Zhuqun Shi

Cellulose-based materials hold great promise for excellent triboelectric materials due to their fascinating attributes. However, few works have studied in a detail and systematic manner of the relationship between the cellulose structure and the output performance. Herein, we report the preparation of TEMPO-oxidized cellulose nanofibril s (TOCN) aerogel films with a high specific surface area of 134.1 m 2 /g as a high-performance inorganic filler-free triboelectric positive layer by a simple and controllable method. TOCN aerogel films with different structures were prepared in one-step by a direct freeze-drying process from quick freezing TOCN dispersions. The effects of four gradually increasing freezing rate methods on TOCN aerogels were proposed and studied. And the addition of TBA improved the freezing rate, reduced the volume expansion and decreased the surface tension, which were beneficial to the triboelectric properties of TOCN aerogel films. Effects of the nanofibril structures and device parameters on their triboelectric output performance were also discussed in detail. Without the addition of any fillers and chemical modification, the pure TOCN aerogel film based triboelectric nanogenerator (TENG) devices achieved a record power density of 156 mW/m 2 . Meanwhile, external influencing factors of the device and recyclability of the pure cellulose triboelectric material were systematically investigated. This work would provide a comprehensive guidance for the design and preparation of high-performance cellulose-based triboelectric positive materials.

Octadecyltrimethoxysilane modified freeze-drying magnesium silicate hydroxide towards high-performance wear-resistance: Synthesis, characterization, and tribological evaluation

Kai Wang,Qiuying Chang,Kai Gao,Bin Wang,Rongqin Gao,Qingqing Yan

Magnesium silicate hydroxide (MSH) has attracted much attention as lubricant additive for its environmental-friendly property. However, its hydrophilicity hindered the industrial application in lubricating oils. Here, we used octadecyltrimethoxysilane (ODTMS) to modify freeze-drying magnesium silicate hydroxide (F-MSH) to obtain ODTMS@F-MSH nanomaterial , which functions well in lubricants free of any dispersant . Tribological tests indicate that, compared with a fully formulated oil, the addition of ODTMS@F-MSH reduces wear effectively (∼25.8%). The magnesium, silicon , and oxygen-containing tribo-film formed on the worn surface. The tribo-film forming mechanism was investigated by atomic force microscope (AFM) experiments and Molecular dynamics (MD) simulations. The results indicate that the ODTMS@F-MSH nanoparticles are of much lower stiffness and higher adhesion than ball-milling MSH (B-MSH), thus reducing the possibility of scratching the rubbing surface and promoting nanoparticles’ adsorption on it. Then the solid tribo-film is formed due to sliding contact between moving parts, thereby enhancing the anti-wear performance.

Probe into the adaptability of local equilibrium/non-equilibrium assumptions in simulating freeze-drying of porous media

Wei Wang,Shuo Zhang,Yanqiu Pan,Yijia Ji,Xin Li,Guohua Chen,Xuewu Liu

A multiphase transport model was formulated to explore the adaptability of local thermal and mass equilibrium/non-equilibrium (LTE/LTNE and LME/LMNE) assumptions in simulating freeze-drying of porous media. Saturated and unsaturated samples with the same initial mass and moisture content but different initial saturations were used in freeze-drying experiments and numerical simulations. Four pairwise combinations between LTE/LTNE and LME/LMNE were tested using the commercial software of COMSOL Multiphysics based on the finite element method. Results showed that the LTE-LMNE assumption achieved excellent agreements between numerical and experimental drying curves with RMSEs being 1.81% for the saturated sample and all less than 1.00% for the unsaturated samples. Based on distributions of saturation and temperature, and variations of effective mass diffusivity and thermal conductivity, the rate-controlling factor was determined to be mass transfer for the saturated material and heat transfer for the unsaturated one. Convective heat transfer played an unimportant role in freeze-drying. The LTE-LMNE based model provided satisfactory predictive capabilities under different conditions. Appropriately increasing the operating temperature could boost the drying rate. Changing the chamber pressure had insignificant effects with drying time differences only below 3%. The smaller the initial saturation, the shorter the drying time. The initially unsaturated frozen material with preformed pores significantly enhanced the freeze-drying process and improved the process economy.

An effective strategy for improving the freeze-drying survival rate of Lactobacillus curvatus and its potential protective mechanism

Xiao-min Li,Lie-hua Che,Ying Wu,Cong Li,Bao-cai Xu

Freeze-drying is a common method to prepare dried starter cultures with high stability and a long storage time. However, the bacterial cells suffer varying degrees of damage during the freeze-drying process. This study aimed to provide an effective strategy to improve the survival rate of Lactobacillus curvatus and to explore its potential protective mechanisms. The survival rates of bacterial cells in different cryoprotectants before and after freeze-drying were measured using the plate count method. The protective effects of composite cryoprotectants on bacterial cells were investigated from multiple perspectives, including key enzyme activities, the internal morphology of bacterial cells, and cell membrane integrity. Results showed that the freeze-drying survival rate of bacterial cells in the composite cryoprotectants consisting of trehalose, oleic acid and skimmed milk (85.38%) was significantly improved compared to that in PBS solution (2.04%). The addition of composite cryoprotectants could reduce damage to the cell wall and cell membrane, maintain the normal morphology of bacterial cells and cell membrane integrity, and improve key enzyme activities (lactate dehydrogenase, pyruvate kinase and ATPases) during the freeze-drying process. The viability of freeze-dried cultures was also monitored at different temperatures during storage, and the cell survival of freeze-dried cultures at −20 °C was the highest, reaching 61.13%. The findings obtained in this work offer a new method to improve the viability of Lactobacillus curvatus after freeze-drying, and may promote the wide use of freeze-dried cultures in the food fermentation industry.

Preparation and properties of fiber-reinforced polybenzoxazine composite aerogels based on freeze drying and ambient pressure drying methods

Zhaorun Hou,Chunxia Zhao,Jinbo Cheng,Zhuo Chen,Jixuan Wei,Hui Li,Dong Xiang,Yuanpeng Wu

Polybenzoxazine aerogels have gained much attention as a new type of polymeric aerogels in the field of flame resistant materials. Herein, a unique method for the preparation of fiber-reinforced PBa composite aerogels has been reported using polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) as dispersion carriers through freeze-drying for surface modified basalt fibers (Z@BF). Bisphenol-A type benzoxazine (Ba) monomer was used as the matrix, which infiltrated into the carrier for dispersed fibers to obtain a PBa composite gel by sol-gel method. Solvent exchange and ambient drying techniques were used to obtain the final composite aerogel samples. Z@BF formed a double-network structure with the aerogel matrix, which resulted in 55.43% increase in compressive strength, a low volumetric shrinkage (27.46%), and density (0.19–0.21 g cm 3 ) of the prepared aerogel. The addition of Z@BF increased the residual carbon content (59.6% at 800 °C) in the aerogel, while reducing the total heat release rate by 36.9% and the peak heat release rate by 60.61%. Besides, the aerogels possessed excellent self-extinguishing property, and the self-extinguishing time was only 1.31 s after flame burning at 1200 ℃ for 10 s. The composite aerogels obtained by this combination of atmospheric pressure drying and freeze-drying techniques not only possessed high mechanical strength and excellent flame retardant properties, but also provided a new idea for the preparation of fiber-reinforced PBa aerogels. This would further expand the potential use of PBa aerogels in flame retardant materials.

Preparation and Properties of Basalt Fiber-Reinforced Aqueous Polybenzoxazine Composite Aerogels Based on One-Step Freeze-Drying Method

Peijiang Long,Zhaorun Hou,Jinbo Cheng,Hui Li,Chunxia Zhao,Jialin Liao,Yuanpeng Wu,Haibo Zhao,Haoran Huang,Yuxing Li

Polybenzoxazine (PBa) aerogels have gained much attention as a fire-retardant material because of their flexible molecular design and excellent mechanical properties. Incorporation of inorganic fibers into PBa aerogels using a simple and effective method seems attractive yet challenging. Herein, we report a unique method for the one-step preparation of basalt fiber (BF) reinforced PBa composite aerogels by freeze-drying using carboxymethyl cellulose (CMC) as a dispersion carrier. Aqueous benzoxazine (Ba) monomer was used as the matrix and phosphoric acid was used as the polymerization catalyst, while the uniform dispersion of BF was achieved by blending with CMC. The results indicate that the PBa/CMC/BF composite aerogel reveals a layered microstructure with BF dispersed between the layers. And the composite aerogel achieves a low volume shrinkage (1.11%), and strong mechanical strength (compressive stress of 1.73 MPa at 60% compressive strain). Additionally, TGA analysis reveals that the composite aerogel achieves a higher initial decomposition temperature (> 200°C) and residual mass (> 48 wt%) in a nitrogen atmosphere. Excellent flame retardancy of PBa/CMC/BF composite aerogel is achieved due to the introduction of nonflammable BF: as BF content rises, its peak heat release rate decreases by 92.5%, average heat release by 86.6%, and total smoke release by 76.7%. In combustion tests, the composite aerogel self-extinguishes within 0.5 s. After hydrophobic modification, the composite aerogel achieves a water contact angle greater than 135°, while PBa/CMC/BF 3 exhibits the typical “silver mirror phenomenon” in water. This study presents a straightforward and rapid method for constructing a lightweight, flame retardant, hydrophobic, and high-strength fiber-reinforced PBa composite aerogel, with promising applications in the aerospace sector.

Effects of complex cryoprotectant on the freeze-drying survival of Lactobacillus acidophilus FMNS-10 and its protective mechanisms

Xiangfei Li,Menghan Wang,Meng Ding,Xinyi Pang,Jing Sun,Yingjian Lu

Freeze-drying is a common method for preserving bacteria cells, but it can cause cell damage in the process of protection. Therefore, it is necessary to explore a cryoprotectant to improve cell survival during the process. This research aimed to explore the optimal cryoprotectant formulation of L. acidophilus FMNS-10 and its protection mechanism. The optimal cryoprotectant consisted of 10.7 % skim milk, 3 % sodium L-glutamate and 10 % D-trehalose, resulting in a survival rate of 91.69 % for L. acidophilus FMNS-10 after freeze-drying ( p  < 0.05). Under this condition, the integrity of cell wall and membrane of L. acidophilus FMNS-10 was close to that of the fresh strain, which could be attributed to preventing ice crystal formation. Cryoprotectants demonstrated a significant protective effect on enzymatic activities. In the cryoprotectant-free group, the activities of β-galactosidase, L-LDH, Na + /K + -ATPase and the concentration of Ca 2+ decreased by 36.19 %, 51.82 %, 89.40 %, and 41.90 %, respectively. However, the cryoprotectant group were only 7.10 %, 1.66 %, 7.41 %, and 4.10 % reductions compared to the cryoprotectant-free group ( p  < 0.05). These results indicated that the optimal cryoprotectant improved the survival rate of L. acidophilus FMNS- 10 by inhibiting the loss of enzyme activity. In addition, the optimal cryoprotectant significantly mitigated the DNA damage induced by freeze-drying. The reduction in enzyme and DNA damage may be attributed to complex cryoprotectants maintaining the stability of their three-dimensional structures and reducing structural disruption caused by freezing. Further analysis of storage stability revealed that the viable count of L. acidophilus FMNS-10 exceeded 10 7  CFU/mL when stored at −20 °C for 180 days. These findings provide a comprehensive theoretical foundation for how to freeze-dry Lactobacillus acidophilus.

Zn2+-loaded cellulose beads stabilized by chitosan and prepared via freeze-drying for removing human testosterone in plasma

Huibin Yu,Hongqin Ke,Tu Chen,Xing Li,Shenglong Tan,Lei Zhou,Shenqi Wang

Hemoperfusion using metal ion affinity adsorbent is a promising method to remove human testosterone in plasma. Due to the leakage of metal ion from the adsorbents, there is no metal ion affinity adsorbent for hemoperfusion. In this study, chitosan was used to coat the adsorbent for preventing the leakage of Zn2+ loaded. Meanwhile, freeze-drying method was used to enhance adsorption capacity of Zn2+-loaded cellulose beads for testosterone. The results indicate that after the adsorbent was coated by 0.02% chitosan solution, the highest adsorption percentage reached 48%, during adsorption, the Zn2+ concentration in plasma did not increase; the adsorption capacity of the adsorbent can be significantly enhanced by freeze-drying. The results may be caused by porosity of the adsorbent enlarged via freeze-drying and improved stability by coating with chitosan. In addition, the adsorbent shows better selectivity and storage stability and could be a potential adsorbent to treat prostate cancer.

Degradation kinetic of anthocyanins from rose (Rosa rugosa) as prepared by microencapsulation in freeze-drying and spray-drying

Yajing Yu,Yuanping Lv