教学课程资源库 更多>>

关键词： deforestation   microbial activity   microbial biomass   PLFA   soil organic carbon   Yungas  

摘要： Tropical and subtropical ecosystems are widely affected by the expansion of agriculture over pristine lands. Despite research efforts, knowledge of the impact of land-use change on soil is still limited by intrinsic variability, inconsistent results and inadequate replication. This study aimed to better understand the consequences of land-use change by focusing on long-term effects on both soil biotic and abiotic parameters. For this purpose, we selected three productive farms under similar management, each of them with pristine forest sites and agricultural sites that had been deforested for similar to 15 and similar to 30 years. In each site, we analysed soil microbiological (phospholipid fatty acids [PLFAs], biomass and activity) and physicochemical parameters. Long-term land-use change caused a detriment in soil microbial biomass, activity and fungal abundance, but only small changes in PLFA composition. In fact, PLFA composition was more affected by soil physicochemical properties such as carbon-to-nutrient ratios and labile carbon than by land use. Some physicochemical parameters (e.g., organic carbon and nutrients) were also negatively affected by land-use change and were more sensitive to time under agricultural use than microbiological parameters. The lower sensitivity of microbiological parameters could be the result of severe drought conditions at sampling, which may have affected soil microbial communities in both land uses. We were also able to detect associations between specific microbiological and physicochemical parameters. Among these, we identified some that seemed to result from their co-variation in response to land-use change and others that seemed to be independent of land use. Overall, our results show that soils can suffer further deterioration several years after deforestation. In order to restore soil health in these degraded lands, we need to keep on investigating the physical, chemical and biological mechanisms responsible for this deter

关键词： Fermentation-induced gelation   Soy protein isolate   Characterization  

摘要： Influence of lactic acid bacteria (LAB) on gel characteristics of fermentation-induced soy protein isolate (SPI) gel, including hardness, water holding capacity (WHC), pH, solubility, turbidity, particle size, zeta potential, surface hydrophobicity, free sulfhydryl, microstructure, rheological properties and in vitro gastrointestinal digestion was evaluated. First, fermentation increased the turbidity and average particle size, which was supported by a lower degree of solubility and zeta potential absolute value. The surface hydrophobicity was reduced after lactic acid bacteria fermentation, and a similar phenomenon occurred on the free sulfhydryl groups. It was found that fermentation resulted in SPI denaturation, structural changes, and aggregates formation, which were the foundation of gel formation. Subsequently, fermentation-induced SPI gels depended on the lactic acid bacteria used for fermentation, showing the specificity of gel characteristics. Among them, Lactobacillus acidophilus (L. acidophilus), Lactobacillus plantarum (L. plantarum), Lactobacillus casei (L. casei), and mixed strains of Lactobacillus bulgaricus (L. bulgaricus), and Streptococcus thermophilus (S. thermophilus) (1:1) exhibited the high coagulation ability, which could enhance the hardness and water holding capacity of the gels. L. plantarum-G had the lowest solubility and free sulfhydryl content and the highest turbidity, particle size, and zeta potential. Scanning electron microscope (SEM) results showed that L. casei-G and L. plantarum-G exhibited a dense and uniform three-dimensional network. The rheological properties showed that the earliest gel point and the highest storage modulus (G') and loss modulus (G") were acquired by L. casei-G, whereas the G' curve of L. lactis-G was still in the growth stage, and no platform was found in the growth curve. The ability of L. lactis to form gels was weaker. At the same time, the G' and G" of all LAB fermentation-induced gels showed strong freq

关键词： Homogenization pressures   Flour   Rice   Starch   Physico-chemical   Functional   Structural   Thermal   Rheological properties  

摘要： Research was conducted to explore the use of low pressure homogenization for extending functionality of rice flours. The impact of low pressure homogenization (0, 30, 50 MPa and 0, 1, 2, 3 passes) on the particle size distribution of long (LRF) and medium (MRF) rice grain flour was evaluated. The pressure level and the number of passes resulted in a lower particle size in both rice flours. Higher pressures and 3 passes led to an increase in the particle size due to aggregation of smaller particles. The effect of low pressure homogenization (0, 30 or 50 MPa 3 passes) on the physicochemical (composition, bulk density, thiol groups, hydration, emulsifying properties, hydrophobicity, crystallinity) thermal and pasting properties was analyzed. Homogenization increased swelling, oil absorption capacity and surface hydrophobicity of LRF and MRF samples even at 30 MPa. The bulk density and the emulsion stability of samples decreased by pressure. However, the emulsifying activity and thiol groups did not change in LRF, while increased in MRF particularly at 30 MPa. SEM micrographs revealed the microstructure changes, but no significant differences were observed in starch crystallinity. FTIR spectra suggested the modification of the flour constituents, particularly in MRF, reaching higher intensities. The disintegration and modification of the large molecules, increasing availability of binding sites, and partial gelatinization of starch granules, led to flours with different pasting performances. Correlation analysis confirmed that the particle size reduction played a determinant role in the structural and physicochemical changes of both rice flour varieties used.

关键词： Thermal conductivity   Transformer oil   Liquid insulation   Breakdown strength  

摘要： This century is undergoing a wave of knowledge and inventions making use of exceptional properties of nanofluids (NFs) in applications such as manufacturing and process heating, air conditioning and refrigeration systems, solar energy, heat pipes, electrical cooling systems and many others. Research investigations about NFs are on the increase due to growing attention and demand for NFs as heat transfer fluids. This can be observed from the number of articles published. To endorse the field further, the objective of this study is threefold. First, it presents the literature that specifies the preparation of NFs which are developed by the suspending of solid nanoparticles (NPs) in conventional working liquids. Secondly, it offers contemporary research on thermophysical features results of NFs. In this review, which primarily emphasizes research carried out in the last couple of decades, experimental inquiries from the latest developments of NFs applications and performance as a heat transfer system are summarized. Moreover, heat transfer mechanisms, challenges and impeding trends associated with NFs regarding heat transfer improvement are deliberated;which must motivate additional exploration. This analysis also deliberates numerous dynamics affecting the thermophysical features;comprising of synthesis techniques, the stability of NFs, various base fluids, type, size, shape, surface modification and volume fraction of nanoparticles (NPs). Though, there are inconsistent findings have been observed in the literature on the effect of factors on the thermophysical traits of NFs. The study also discovers that appropriate characterization of NFs may result in superior heat transfer fluids compared to conventional base fluids. Nevertheless, more extreme exploration is required towards the suitable selection of NPs, their synthesis, characterization and long-term stability of NF is essential to exploit their full potential along with the application of these innovative fluid

关键词： Achyranthes aspera   CuO nanoparticles   Physicochemical and morphological properties   Renewable application  

摘要： The present study was reported with synthesize of copper oxide nanoparticles by ethno botanical species. Bio convivial and compatible approaches were made to utilize the renewable source of leaves extract of Achyranthes aspera Linn as efficient capping and stabilizing agent as well. Also, natural A. aspera was functioned as reductant in the formation of CuO NPs. The phytosynthesized CuO nanoparticles were extensively characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, Scanning electron microscopy, Energy dispersive X-ray diffraction, High resolution tunnelling electron microscopy and also comprehensively examined their biological applications like antibacterial and antifungal susceptibility against E. lenta, E. aerogenes and C. albicans strains. An XRD result of prepared CuO nanoparticles reveals the monoclinic crystalline structure and average crystallite size of 11-16 nm. The morphology variations for different concentrations of precursor material were noticed by SEM image. Furthermore, the crystalline planes found in SAED pattern of synthesized CuO NPs were coincide to the analysed XRD spectra. In the present study, a novel green approach was used to synthesize of CuO NPs for the antibacterial activity of poorly characterized and emerging pathogens of E. lenta and E. aerogenes. Further, the physicochemical, morphological and biological properties of CuO NPs are discussed.

关键词： Dehydrogenase activity   Spatial cross-correlation   Lithogenic radionuclides   Cs-137   Soil water content  

摘要： Best soil management practices can be achieved by evaluating the spatial cross-correlation variability of soil microbiological and physicochemical indicators, in order to comprehend the underlying relations between these mutually dependent properties, being valuable indicators for prospective evaluation of soil resources. The purposes of this study were to measure microbiological and physicochemical variables in superficial soil, spatially cross-correlate and determine spatial causalities between these two families of variables. The spatial variability of pH, gravimetric soil water content, U-238, Th-232, K-40, Cs-137, acid phosphatase, dehydrogenase activity, microbial biomass carbon, mesophilic aerobic bacteria and filamentous fungi was studied at a 13 ha field located in Uruguay. U-238 and Th-232 were both negatively lineally correlated with gravimetric soil water content (-0.42), Cs-137 (-0.45 and -0.48 respectively) and dehydrogenase activity (-0.44 and -0.48 respectively). A semivariogram analysis revealed that the best fit model for soil variables was spherical, with moderate to strong spatial dependence. Cross-correlation results suggest that there is an influence factor from spatial interaction. In this sense, gravimetric soil water content connects physicochemical variables with soil biodiversity. Spatially, soil water content is inversely influenced by Th-232 and U-238 (as indicators of sub-superficial soil), and directly influenced by dehydrogenase activity (indicator of soil microbial activity), revealing soil microbial activity as a possible indicator of water retention in drying soils. The combination of spatial patterns of environmental radionuclides with microbiological indicators of soil quality could represent a valuable integrated approach to assess soil conservation status and further explain the impact of anthropogenic disturbance.

关键词： Lactococcus   Pediococcus   Volatile compounds   Free amino acids   Biogenic amines   Correlation  

摘要： The quality and flavor formation in fermented fish sausages are based on the complex metabolism of microbial community. In this study, the dynamic changes of physicochemical characteristics, volatile compounds, and microbial communities in the naturally fermented tilapia sausage were studied during the fermentation process. The main physical indexes (gel strength, whiteness, and hardness), dominant flavor free amino acids (glycine, alanine, and glutamic acid) and characteristic volatile flavor compounds (hexanal, heptanal, octanal, benzaldehyde, (E)-2-octenal, 4-ethylbenzaldehyde, (E)-2-heptenal, (E,E)-2,4-decadienal, 1-octen-3-ol, 2-pentylfuran, and 2-ethyl-furan) were significantly enhanced after fermentation, and were positively correlated with Lactococcus, Pediococcus, Enterococcus, and Lactobacillus. The microbial metabolic network showed that Lactococcus, Pediococcus, and Enterococcus played a significant role in the formation of physicochemical and flavor characteristics, while the accumulation of biogenic amines might result from the metabolism of Enterococcus, Enterobacter, and Citrobacter. Isolation of lactic acid bacteria in Lactococcus and Pediococcus might be suitable to improve the fermented tilapia sausage. Microbial metabolic network has revealed the physicochemical and flavor formation of tilapia sausage and can provide guidance for future research on screening of starters.

关键词： Amylose content   Colombian Andean region   Gelatinisation   Potato-starch   Viscosity  

摘要： We isolated and investigated the starch of six potato cultivars (Solanum tuberosum), grown in the Andean region in the south of Colombia, to determine their physicochemical properties. The potato cultivars are known by their common names asMambera,Ratona,Pastusa,Capiro,UnicaandRoja-huila. The minerals, amylose content, water absorption and water solubility of the starches were evaluated. Morphology, crystalline structure, gelatinisation, thermal degradation and viscosity were also determined. The results showed thatCapirostarch has a high mineral content. The apparent amylose and phosphorus contents in starch isolated fromMambera,RatonaandPastusawere higher than those fromUnicaandRoja-huila. The starches with higher amylose content and better-defined peak in X-ray diffraction (XRD) (Mambera,RatonaandCapiro) had higher gelatinisation temperatures and took more time to reach the viscosity peak. All starches have hexagonal crystalline structure (B-type). The final viscosity of starches isolated fromMamberaandRatonawas higher than that fromUnica,Roja-huilaandPastusadue to their higher apparent amylose content.

关键词： scandium   scandium oxide Sc2O3   scandium phosphate ScPO4   Delta G(f(298))(0) J/mol   Sc(OH)(3(aq))(0)   computer simulations   Selector   weathering profile  

摘要： The paper presents author's original and literature data on the standard free energy of 31 Sc ions and complexes in aqueous solution. Scandium behavior at the weathering of phyllite shales is physicochemically simulated with the Selector program package. The content of Sc in the shales is close to its average content in the Earth's crust: 10(-3) wt %. Solution in the weathering profile was determined to contain Sc practically only in the form of the hydroxocomplex. The dissolved Sc concentrations is controlled by the solubility of its oxide Sc2O3 and phosphate ScPO4 and is lower than 10(-9) mol/L.

关键词： Photosensitization   Curcumin   Strawberry   Preservation   Shelf life   Nutritional quality  

摘要： The effect of photosensitization mediated by curcumin on fungal growth, physicochemical properties and nutritional composition in Australian grown "Albion" strawberries was evaluated. Curcumin solution (1200, 1000 and 800 mu M) was sprayed on the strawberry surface, followed by illumination using blue light (420 nm) for 10 min at a dosage of 42 J/cm(2)and stored at 4 +/- 2 degrees C for 12 days. The fruit photosensitized with 1000-mu M curcumin (10 min, followed by storage at 4 +/- 2 degrees C) lasted up to 12 days with a fungal infection rate of 52%, whereas untreated control fruit developed 100% fungal infection and lasted for 8 days only under the same conditions. This treatment did not have an effect on colour, pH, moisture content, titratable acidity, ascorbic acid, total phenolic content and anthocyanins, whereas total soluble solids (9%) and total sugar (22%) were increased (p < 0.05). These initial results indicate that curcumin-based photosensitization could be an effective non-thermal technology to preserve the nutritional quality as well as to extend the postharvest life of fresh strawberry fruit.