教学课程资源库 更多>>

关键词： Myrciaria dubia   Amazonian fruit   Degree of polymerization   Carrier agents   Anthocyanins release   Ascorbic acid release   Storage stability   Fickian diffusion  

摘要： Camu-camu (Myrciaria dubia [H.B.K] McVaugh) is a Amazonian fruit rich in ascorbic acid and phenolic compounds, and has been attracting great interest from the food, pharmaceutical and nutraceutical industries due to its potential health benefits. The bioactive compounds from camu-camu are considered sensitive and unstable, resulting in nutritional losses and impairment of its commercialization and export. For this reason, the camu-camu extract (pulp and peel) was subjected to microencapsulation by spray drying process using maltodextrin (MD), inulin (IN), and oligofructose (OL) as carrier agents. Lyophilized in natura camu-camu extract (CEL) was also evaluated. Thus, physicochemical and thermal properties and controlled release at different temperatures (25 degrees C and 35 degrees C) were investigated. In contrast with the IN and OL microparticles, the MD microparticles showed lower density and hygroscopicity, besides greater thermal stability, antioxidant activity, and retention of ascorbic acid and anthocyanins. FTIR spectra allowed the qualitative evidence of encapsulation of the bioactive compounds from the camu-camu extract. The highest percentage of volatile compounds was observed in IN microparticles, followed by OL and MD microparticles. The major group of compounds identified in CEL were terpenes (88%). The Korsmeyer-Peppas mathematical model allowed to describe the controlled release behavior of ascorbic acid and anthocyanins in the powder extracts. The controlled release followed a Fickian diffusion mechanism (n <= 0.43). The increase of temperature from 25 degrees C to 35 degrees C influenced on the release of bioactive compounds in all treatments, showing greater release for MD microparticles. The encapsulating materials were considered effective for the production of camu-camu extract powder, contributing to the better use of this Amazonian fruit. In addition, the encapsulation process increased the stability of its bioactive compounds, representing a

关键词： cassava starch   crystallinity   cultivars   physicochemical properties   root growth  

摘要： Wide variability exists in starch properties even among the same botanical source depending on climatic factors, genotypic differences, harvesting period, etc. The present study is an attempt to understand changes in structure, composition and physicochemical properties of cassava starch with root development. Starch is isolated from five cultivars of cassava at different root harvesting periods starting from root initiation stage, that is, 2-12 months after planting. The cultivars are selected in such a way that they represent different growing duration (short and normal), ploidy level (diploid and triploid), and end use (industrial and edible). Amylose/amylopectin ratio varies in a narrow range (0.24-0.28) for the starch from different varieties. Starch granule morphology does not show any significant variation with root growth and cultivar, but the average granule size varies significantly. All the starches show A-type X-ray diffraction pattern and the percentage crystallinity ranges from 37% to 48%. Average chain length and molecular weight of the starch show varietal differences. Even though the swelling power, solubility, water binding capacity and paste clarity are not significantly affected by the root harvesting period, the cultivar differences are evident for these parameters. Significant differences in the physicochemical and functional properties of starch with ploidy of the plant are not observed.

关键词： Qinghai-Tibet plateau   Soil degradation   Mattic epipedon   Soil micromorphology   Soil classification   Soil porosity  

摘要： The Qinghai-Tibet Plateau is currently suffering from severe ecological problems. Soil degradation is a major environmental problem, and there is strong evidence that such processes present an immediate threat to both biomass and economic yields. The aim of the present study is to clarify the response mechanism of mattic epipedon during soil degradation process in alpine meadow, we investigated (1) morphological characteristics and physicochemical properties of soils, (2) soil micromorphology under different degradation stage. According to plant and land use coverage, three sites were chosen from the Hequ horse farm: lightly degraded meadow (HQ1-L);moderately degraded meadow (HQ2-M);and heavily degraded meadow (HQ3-H). A vegetation survey and soil profile morphology showed that Kobresia kansuensis was the dominant species in HQ1-L and HQ2-M, featuring in topsoil horizons rich in rhizogenic organic matter which creates turfs. There are strong relationships between the presence of the mattic epipedon (OA horizon) and soil physicochemical properties. Thus, exchangeable cations, cation exchangeable capacity (CEC), total nitrogen (TN), and organic carbon (OC) decrease during the degradation of grassland;however, the pH value shows an opposite trend. Exchangeable cations, CEC, TN, and OC provide an index of soil fertility to measure the degree of grassland degeneration. Soils were classified as Luvic Phaeozems, Haplic Phaeozems, and Calcaric Phaeozems. From the micromorphology of soils in thin section, considering soil degradation, the porosity and fractal dimension decrease, and the soil microstructure evolves to an intergrain micro-aggregate structure. Also, by counting the number of excrements in the soil thin sections, and combining this with the fractal dimension of the porosity, we found the HQ1-L is more conducive to soil fauna survival, by comparison to HQ2-M, and HQ3-H which follow HQ1-L in condicivity. These results suggest that the existence of the OA horizon (

关键词： molybdenum disulfide   nanoparticles   fate   physicochemical composition   toxicity   oxidative stress   cell viability  

摘要： The physicochemical properties and the toxicological potential of commercially available MoS(2)nanoparticles with different lateral size and degradation stage were studied in the present research work. To achieve this, the structure and stoichiometry of fresh and old aqueous suspensions of micro-MoS(2)and nano-MoS(2)was analyzed by Raman, while x-ray photoelectron spectroscopy allowed to identify more quantitatively the nature of the formed oxidized species. A, the toxicological impact of the nanomaterials under analysis was studied using adenocarcinomic human alveolar basal epithelial cells (A549 cells) and the unicellular fungusS. cerevisiaeas biological models. Cell viability assays and reactive oxygen species (ROS) determinations demonstrated different toxicity levels depending on the cellular model used and in function of the degradation state of the selected commercial nanoproducts. Both MoS(2)nanoparticle types induced sublethal damage on the A549 cells though the increase of intracellular ROS levels, while comparable concentrations reduced the viability of yeast cells. In addition, the old MoS(2)nanoparticles suspensions exhibited a higher toxicity for both human and yeast cells than the fresh ones. Our findings demonstrate that the fate assessment of nanomaterials is a critical aspect to increase the understanding on their characteristics and on their potential impact on biological systems along their life cycle.

关键词： Carbon black (CB)   Silica fume (SF)   Cementitious composite   Piezoresistivity   Physicochemical properties   Electrical resistivity   Microstructure  

摘要： Carbon black (CB) filled cementitious composites as cement-based sensors with intrinsic piezoresistivity have the potential applications for structural health monitoring (SHM). Effect of silica fume (SF) replacement ratio on the physicochemical, mechanical and piezoresistive properties, and microstructure of CB-cementitious composite were experimentally investigated in this study. The results show that 5% or 10% replacement ratio of SF can improve the water impermeability, setting time and electrical conductivity, but decrease the fresh flowability. Cementitious composite with 10% SF exhibiteds excellent compressive and flexural strengths. Moreover, cement hydration in the acceleration stage decreased with the increase of SF content in the early stage, but the phase analysis after 28 days curing demonstrates that with the addition of SF, there are more hydrated products and less ettringite. In addition, the microstructures of cementitious composites without SF present more porous structures and CB agglomerations. In contrast, the amount of micropores or voids was significantly reduced by the addition of SF due to the physical filling effect and less CB agglomerations. In terms of piezoresistivity, SF can obviously improve the fractional changes of resistivity (FCR) under cyclic compression. With 10% SF, CB-cementitious composites as cement-based sensors exhibited excellent FCR and electrical stability, which will promote their development and application in the SHM for smart infrastructures. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： One-step vapor-phase assisted hydrothermal carbonization   Functionalized carbon   Functional groups   Adsorption   Hexavalent chromium  

摘要： Amino-, carboxyl- and thiol-functionalized carbons (denoted as HT-N, HT-AA and HT-SCY, respectively) were successfully prepared via a facile one-step vapor-phase assisted hydrothermal carbonization process from glucose in the presence of ethylenediamine, acrylic acid and thioglycolic acid, respectively. Their physiochemical properties and static adsorption performance for Cr(VI) were comparatively studied by the Raman, FT-IR, XPS, Elemental analysis, SEM, N-2 adsorption/desorption, Zeta potential and UV-vis spectrophotometer. Their adsorption data fitted the pseudo-second order kinetic and the Langmuir model models well suggesting their chemical and single-layer adsorption processes. The maximum adsorption capacities obtained by the Langmuir model are as follows: HT-N (171.23 mg/g) > HT-AA (94.25 mg/g) > HT-SCY (15.41 mg/g) > HT without functionalization (13.00 mg/g). The XPS and FT-IR results showed that Cr(VI) was enriched on the surfaces of the HT-N and HT-AA indicating that type of the functional group is a key factor to affect their adsorption performance. Their main adsorption mechanism involved electrostatic interaction and complexation between the functionalized groups and Cr(VI), and then the adsorbed Cr(VI) was partly reduced to Cr (III) with the help of electron donors. This simple vapor-phase assisted hydrothermal carbonization method could be extended to prepare diverse functionalized carbons for efficient treatment of heavy metal wastewater.

关键词： Wheat bran   Fomitopsis pinicola   Solid state fermentation   Physicochemical and functional properties   Flavor   Textural properties  

摘要： Wheat bran was solid state fermented by Fomitopsis pinicola. The results showed that the processing properties were increased by fermentation and the content of total phenol and alkylresorcinols was 5.91 and 1.55 times of the unfermented bran respectively by the 6th day. The total antioxidant capacity was 5.73 times of the unfermented sample by the 4th day. Electronic nose analysis showed that the fermented wheat bran had a special flavor. GC-MS analysis found that 4-ethyl-2-methoxy-phenol was the main flavor substance, which was sharply increased during the fermentation. Furthermore, the textural properties of the dough and bread containing fermented bran were significantly improved. The content of phytic acid in the bread was significantly decreased, while the protein, total phenol and alkylresorcinols contents were significantly increased. Results suggest that solid state fermentation by Fomitopsis pinicola is a promising way to improve wheat bran to a nutritious and flavorful cereal food ingredient.

关键词： Chemical structure   Glass transition   Organic polymers   Materials   Molecules  

摘要： The glass transition temperature (T-g) is a fundamental property of polymers that strongly influences both mechanical and flow characteristics of the material. In many important polymers, configurational entropy of side chains is a dominant factor determining it. In contrast, the thermal transition in polyurethanes is thought to be determined by a combination of steric and electronic factors from the dispersed hard segments within the soft segment medium. Her;we present a machine learning model for the T-g in linear polyurethanes and aim to uncover the underlying physicochemical parameters that determine this. The model was trained on literature data from 43 industrially relevant combinations of polyols and isocyanates using descriptors derived from quantum chemistry, cheminformatics, and solution thermodynamics forming the feature space. Random forest and regularized regression were then compared to build a sparse linear model from six descriptors. Consistent with empirical understanding of polyurethane chemistry, this study indicates the characteristics of isocyanate monomers strongly determine the increase in T-g. Accurate predictions of T-g from the model are demonstrated, and the significance of the features is discussed. The results suggest that the tools of machine learning can provide both physical insights as well as accurate predictions of complex material properties.

关键词： Selenium  

摘要： Although the material hydroxyapatite (HAP) has excellent porous, biocompatible, and biodegradable properties, its mechanical strength and microbial inhibition rate are not adequate for its direct use in bone tissue engineering or in constructing artificial teeth. To overcome some of its limitations, in the present study, we have formed an organic-inorganic composite with an altered internal structureviadoping selenium (Se) cations into the lattice of HAP. We have synthesized Se-substituted HAP (Se-HAP) composites with different Se/P ratios (0.01, 0.05, and 0.1 M)viaa wet chemical route in which two different sets of samples were collected (1) after only precipitation (referred to as the precipitation method) and (2) after precipitation followed by sonication (referred to as the sonochemical method). FTIR and Raman spectroscopic analyses confirmed the successful doping of Se into the HAP matrices, while powder XRD studies indicated their highly crystalline nature, which was significantly influenced by Se doping. The XRD data also showed that the Se-HAP particles formed by the precipitation method have a size of 56 nm and those formed by the sonochemical method have a size of 29 nm. Morphological analysis by means of SEM and TEM indicated that the sonochemical method produces well-defined rod-shaped particles, while the precipitation method produces particles with agglomerated structures. Hemolytic studies confirmed that the Se-HAP particles are biocompatible, and that the hemolytic ratio increases with the Se content. In addition, antibacterial studies indicated that Se-HAP responds quite well against a Gram-positive strain (S. aureus), on a par with the response to a Gram-negative strain (P. aeruginosa). Finally,in vitrocell viability and proliferation studies indicated an increase in the proliferation capacity of non-cancer cells (NIH-3T3 fibroblasts) and a considerable reduction in the viability of cancer cells (MG-63 osteosarcoma). Based on the overall analysis,

关键词： Negative ions  

摘要： While there have been many studies on the physicochemical characterisation of ILs, little work has previously been reported on the properties unique to the trifluoroborate anion. Here we have characterised the thermal properties, viscosity, liquid nanostructure and intramolecular interactions of 15 novel aryltrifluoroborate ILs. These ILs all contained a tetrabutylammonium cation paired with either meta- or para-substituted aryltrifluoroborate anions, or di-anionic substituted aryltrifluroborate anions. It was found that of the 15 samples analysed, 4 would technically be considered molten salts as they have melting points greater than 100 degrees C. Overall the structure-property relationship trends of these samples are similar to those previously reported for alkyl and perfluoroalkyltrifluoroborate ILs which contained K+ or Cs+ cations, with the big difference being the ILs in this study having considerably lower melting points.