The influence of thermal treatment and operational conditions on xanthan produced by X. arboricola pv pruni strain 106

The influence of thermal treatment and operational conditions (pH and stirrer speed) used in the process of xanthan production by Xanthomonas arboricola pv pruni strain 106 were evaluated through yield of xanthan, aqueous solution and fermentation broth viscosity, sodium content, pyruvate and acetyl content and molar mass. Different conditions used during the fermentation affected the xanthan characteristics. Thermal treatment decreased the final yield and pyruvate and acetyl content, and increased the xanthan aqueous solution and fermentation broth viscosities, as well as molar mass. In this study the best combination of yield and viscosity was obtained with the use of pH 7 and 400 rpm during fermentation and post-fermentation thermal treatment. Aggregation of xanthan molecules promoted by heating and detected through an increase of molar mass was apparently affected by the sodium content. As a result, a correlation between molar mass and xanthan solution viscosity could be observed.     

外源水溶性有机物及温度对红壤铜形态的影响

利用模拟培养试验研究了外源水溶性有机物（DOM）添加量和培养温度对红壤中Cu形态的影响. 结果表明: 与不添加DOM比较, 添加不同量的DOM均可提高土壤中交换态Cu的含量、降低铁锰结合态Cu含量; 随着培养时间的延长,不同DOM添加量下土壤交换态Cu含量呈逐渐下降趋势;至试验结束时,DOM添加量为250 mg·L^-1时土壤交换态和碳酸盐结合态Cu含量最高, 添加量为500 mg·L^-1时铁锰结合态Cu含量最高;不同DOM添加量下, 土壤中有机结合态Cu含量较CK增加10.67%～23.66%. 在25 ℃和45 ℃温度条件下, 添加DOM后土壤交换态和铁锰结合态Cu含量均随培养时间的延长呈下降趋势, 但在5 ℃下变化趋势相反; 3种温度下添加DOM后土壤碳酸盐结合态Cu含量有随培养时间延长而增加的趋势. 随着培养温度的升高,土壤有机结合态Cu含量增加, 但在温度较低(5 ℃)时土壤残渣态Cu含量下降.     

Anti-juvenile Hormone Effects of an Imidazole Compound (KK-42) in Different Larval Instars of Bombyx mori

The non-Newtonian behavior and dynamic viscoelasticity of solutions of the Ca salt of xanthan were measured with a rheogoniometer. The Ca salt of xanthan showed pseudoplastic behavior < 0.1 % but was plastic >0.3%. Compared with native, Na, and K salts of xanthan, the Ca salt had higher dynamic viscoelasticity at high concentrations. The apparent viscosity of Ca salt of xanthan was very large at low temperatures and decreased with increasing temperature. These suggest very strong intermolecular association of the xanthan (Ca salt) molecules, probably due to the formation of ionic force between adjacent charged trisaccharide side-chains via Ca²⁺ on different molecules. Possible structures for quaternary association including intramolecular association of xanthan molecules (Ca and K salts) in aqueous solution were proposed.     

Synthesis and Fungicidal Activity of Diaryl 1,1 -Dichloroethyl-phosphonates

Non-Newtonian behavior and dynamic viscoelasticity of a series of aqueous mixed solutions of xanthan and locust bean gum were measured using a rheogoniometer, and the rheological properties were analysed. A gelation occurred in the mixture at the concentration of 0.2% total gums at room temperature. The flow curves of the mixture solutions showed a yield value and approximated to plastic behavior at 50°C. The maximum dynamic modulus was obtained when the mixing ratio of xanthan to locust bean gum was 1:2, while comparable high moduli were also obtained in the mixing ratio of 1: 3 or 1:4. A mixture of deacetylated xanthan and locust bean gum showed the highest dynamic modulus, about two times that of the mixture of native or Na-form xanthan. The dynamic modulus of the mixtures decreased rapidly with increasing temperature. In contrast, the dynamic viscosity was scarcely changed during increasing temperature in the mixing ratio of 2: 1. The dynamic modulus was decreased by addition of urea (4.0 M), NaCl (0.1%) and MgCl₂. We concluded that the intermolecular interaction between xanthan and locust bean gum might occur between the side chains of the former and backbone of the latter, as in a lock-and-key effect.     

改性黄原胶酯化条件的优化及结构的表征

为了提高黄原胶的速溶性和粘度,将黄原胶进行改性处理。将黄原胶与马来酸酐进行酯化反应,探讨了黄原胶与马来酸酐摩尔比、反应时间和反应温度等因素的影响,以取代度为指标,利用响应面方法确定,该酯化反应的最优条件为:黄原胶与马来酸酐摩尔比1∶11.5、反应时间24.4 h、反应温度66℃。对改性黄原胶进行红外光谱、光散射和X-射线衍射等结构表征,表明酯化改性成功,且进一步解释了速溶性和粘度提高的原因。改性黄原胶细胞毒性实验,显示无毒性。结果表明,改性黄原胶的速溶性和粘度有很大提高,0.2%改性黄原胶的速溶性和粘度较对照提高了近3倍,在食品、药品等领域具有潜在的应用价值。     

Variation in Heat-shock Proteins and Photosynthetic Thermotolerance among Natural Populations of Chenopodium album L. from Contrasting Thermal Environments: Implications for Plant Responses to Global Warming

Production of heat-shock proteins (Hsps) is a key adaptation to acute heat stress and will be Important in determining plant responses to climate change. Further, intraspecifc variation in Hsps, which will influence species-level response to global warming, has rarely been examined in naturally occurring plants. To understand intraspeciflc variation in plant Hsps and its relevance to global warming, we examined Hsp content and thermotolerance in five naturally occurring populations of Chenopodium album L. from contrasting thermal environments grown at low and high temperatures. As expected,Hsp accumulation varied between populations, but this was related more to habitat variability than to mean temperature.Unexpectedly, Hsp accumulation decreased with increasing variability of habitat temperatures. Hsp accumulation also decreased with increased experimental growth temperatures. Physiological thermotolerance was partitioned into basal and induced components. As with Hsps, induced thermotolerance decreased with increasing temperature variability. Thus,populations native to the more stressful habitats, or grown at higher temperatures, had lower Hsp levels and induced thermotolerance, suggesting a greater reliance on basal mechanisms for thermotolerance. These results suggest that future global climate change will differentially impact ecotypes within species, possibly by selecting for increased basal versus inducible thermotolerance.     

Effect of corn steep liquor on xanthan production by Xanthomonas campestris

Summary The addition of corn steep liquor (CSL) to batch cultures of Xanthomonas campestris using sucrose as carbon source stimulated cell growth rate, viscosity and xanthan production as compared to non-supplemented cultures. The addition of CSL to a basal medium at a dose of 1 g/l, increased xanthan production and viscosity by 22% and 44% respectively. CSL also shortened the cultivation time and promoted a more efficient sucrose utilization for polymer synthesis. After 72 h of incubation the xanthan yield per sucrose consumed in the CSL-amended culture was 0.63 g/g, this is, 15% higher than without CSL addition. At higher doses of CSL cell growth rate was also increased but not polymer production.     

Rheology of concentrated isotropic and anisotropic xanthan solutions: 3. Temperature dependence

The oscillatory rheology of one rodlike and one semiflexible xanthan sample has been investigated as a function of temperature in the range of xanthan concentrations where the polymer forms a lyotropic liquid crystalline phase in aqueous NaCl solutions. Readily observed changes in the rheological observables at temperatures corresponding to phase boundaries permit construction of the biphasic chimney region of the temperature-composition phase diagram. The chimney region leans toward larger values of the polymer concentration with increasing temperature, presumably as a consequence of a reduction in the effective axial ratio of the helical polymer with increasing temperature. The results permit construction of plots of the rheological observables as a function of polymer concentration at temperatures T in the range 20 相似文献   

Relationships between Binding Quality of Meat and Myofibrillar Proteins

The viscosity change of myosin A concentrated solution with or without other components was measured as the incubation time elapsed at 30°C.

The viscosity of myosin A solution increased, but that of F-actin solution did not. The shear stress at 0.04 sec^?1 was not increased to 1.0 dyne/cm² in the former, but in the latter was below 0.5 dyne/cm².

The viscosity of myosin B solution increased slightly, but that of native tropomyosin-free myosin B solution decreased remarkably. In both the shear stress at 0.04 sec^?1 was greater than or equal to 15 dynes/cm².

The speed of the viscosity increase in the presence of 3 mm pyrophosphate and 3 mm MgCl₂ was higher in concentrated solution of myosin B than in that of native tropomysin-free myosin B. The shear stress at 0.04 sec^?1 after 6 hr at 30°C was 11.5 and 8.2 dynes/cm², respectively.

The effect of native tropomyosin and actin on the viscosity change was discussed.     

Salt-induced extension and dissociation of a native double-stranded xanthan

This study shows that xanthan molecules at room temperature may assume at least three different conformations in 0.1 m NaCl aqueous solutions in which the local structure is ordered: (1) the native compact double helix, (2) the extended double helix, and (3) the extended single helix. Experiments including viscosity, low-angle light scattering and optical rotation measurements have been carried out with a fully pyruvated and fully acetylated native laboratory sample supplied as fermentation broth. Two major conformation changes of the native double helix which were found irreversible in our experimental conditions can be induced by treatments at low ionic strength. After treatment in 10⁻⁴m NaCl, xanthan is still a double helix in 10⁻¹m NaCl, but the backbone of each strand has been extended. After the sample has been in 10⁻⁵m NaCl, the double helix has been dissociated and a single helix sample is obtained. Thus, the denaturing of xanthan is a two-step process. The first step consists of the extension of the two chains inside the double helix, and the second is a dissociation of the native double strand.     

E.s.r. study of the conformational transition of spin-labelled xanthan gum in aqueous solution

The order to disorder transition of xanthan molecules in aqueous solutions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutions at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attributed to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions at increasing ionic strength. The spectra gradually changed with rising temperature and the proportion of anisotropic component decreased. This spectral change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting that chain aggregation occurred.     

Modified xanthan—its preparation and viscosity

Xanthan with various pyruvic acid and acetate contents has been prepared from a single commercial polysaccharide sample using optimised chemical conditions (acid and alkali hydrolysis, respectively) for removal of acetal and acyl groups. The only significant change found on analysis of the modified xanthans was loss of pyruvic acid and/or acetate; no low moleculur weight carbohydrate-containing material was released. Contrary to some previous reports, evidence is presented to show that the pyruvic acid acetal and o-acetyl contents of xanthan do not affect solution viscosity. The viscosities of native, pyruvate-free and pyruvate/acetate-free xanthan solutions (0·3% w/v) were similar at shear rates 8·8–88·3 s^?1 in both distilled water and 1% KCl. Over the concentration range 0·2-1·5%, the viscosities of native and pyruvate-free xanthan at 10 s^?1 were similar. The viscosity increase on addition of 1% KCl to salt-free xanthan solutions was independent of pyruvic acid acetal substitution. Our results suggest that xanthan samples with various pyruvic acid acetal and o-acetal contents, prepared under different fermentation conditions of Xanthomonas campestri should not normally be used for assessing the contribution of these groups to solution viscosity.     

Effects of temperature on cell growth and xanthan production in batch cultures of Xanthomonas campestris

Batch xanthan fermentations by Xanthomonas campestris NRRL B-1459 at various temperatures ranging between 22 degrees C and 35 degrees C were studied. At 24 degrees C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27 degrees C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35 degrees C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h(-1) at temperatures between 27 degrees C and 31 degrees C. Cell yield decreased from 0.53 g/g glucose at 22 degrees C to 0.28 g/g glucose at 33 degrees C, whereas xanthan yield increased from 54% at 22 degrees C to 90% at 33 degrees C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27 degrees C and 30 degrees C. These results suggest that the optimal temperatures for cell growth are between 24 degrees C and 27 degrees C, whereas those for xanthan formation are between 30 degrees C and 33 degrees C. For single-stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two-stage fermentation process with temperature shift-up from 27 degrees C to 32 degrees C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.     

Improvement in bioreactor productivities using free radicals: HOCl-induced overproduction of xanthan gum from Xanthomonas campestris and its mechanism

Free-radical induction has been employed as a novel strategy to improve bioreactor productivity and, more specifically, the quality and productivity of xanthan gum from Xanthomonas campestris cultures. A 210% increase in xanthan yield and a 20% increase in viscosity (quality) resulted from HOCl (oxidant) treatment. The acetate mass fraction in xanthan gum decreased by 42% and its pyruvate mass fraction increased by 63% as a result of HOCl treatment. The growth rate was almost unaffected by HOCl treatment. A hypothesis to explain the mechanism of xanthan gum overproduction by free-radical induction has been formulated. The significant aspects of the hypothesis, such as SoxS protein binding to the promoter region of the gum gene and the consequent increase in mRNA concentrations, have been experimentally verified.     

Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch

Native new cocoyam starch (nNCS) was subjected to annealing (aNCS) and heat moisture treatment at 18% moisture level (h₁₈NCS), 21% moisture level (h₂₁NCS), 24% moisture level (h₂₄NCS) and 27% moisture level (h₂₇NCS) as hydrothermal treatments. Scanning electron and light microscopy revealed round and polygonal shapes with sizes ranging from 15 to 40 μm for native and modified starches. nNCS showed “A” pattern X-ray diffraction and no significant differences were observed in the X-ray pattern of the modified starches. Swelling power and solubility reduced following heat moisture treatment. At all pH studied (2–12), unmodified new cocoyam starch exhibited higher swelling capacity and solubility than the modified derivatives. Hydrothermal modifications improved water absorption capacity but reduced oil absorption capacity. Pasting temperature of native starch shifted to higher values following annealing and heat moisture treatment. Hot paste viscosity (Hv), viscosity after 30 min holding at 95 °C (Hv₃₀) and cold paste viscosity (Cv) reduced after annealing and heat moisture treatment. The result also indicates that hydrothermal treatments reduced the tendency for setback. As the number of days of storage of starch paste increased from 1 to 10, light transmittance of all the starches reduced but marked reduction of light transmittance was observed in native starch. DSC studies revealed increase in gelatinization temperature following annealing and heat moisture treatment. Starch hydrothermal modifications reduced retrogradation as enthalpies of regelatinization reduced following modifications. The regelatinization peak in the second day scanning shifted to lower temperature than the gelatinization peak in first run heating DSC curve for all samples. The regelatinization peak also became larger and shifted to higher temperature range when the storage days increased from 2 to 7.     

Biosorption of phenol and 2-chlorophenol by Funaliatrogii pellets

The removal of phenol (Ph) and 2-chlorophenol (2-CPh) from aqueous solution by native and heat inactivated fungus Funaliatrogii pellets were investigated. The effects of contact time, solid/liquid ratio, optimum pH and temperature on the phenols removal capacity by the pellets were established. The removal efficiency of phenols increased significantly with increasing biomass dose. The optimum pH was detected to be 8.0. The second-order equations are described and evaluated on the basis of a comparative estimation of the corresponding coefficients. The phenol removal equilibrium isotherm was modeled by the Langmuir equations. The enthalpy change values were obtained between −7.62 and −10.64 kJ/mol. This indicated that the uptake of phenols either on native or heat inactivated fungal pellets was based on a physical adsorption process.     

A novel globular protein electrospun fiber mat with the addition of polysilsesquioxane

The aim of this work has been to elaborate well defined gliadin nanofibers with incorporation of inorganic molecules, such as polyhedral oligomeric silsesquioxane (POSS). Nanofibers were obtained by electrospinning processing, controlling the relevant parameters such as tip-to-collector distance, voltage and feed rate. The fiber mats were characterized by SEM, confocal images, DSC, viscosity, FTIR and conductivimetry analysis. FTIR spectra showed characteristic absorption bands related to the presence of POSS-NH₂ within the matrices. SEM micrographs showed that gliadin fibers decreased their dimensions as the amount of POSS-NH₂ increased in the spinning solution. The electrical conductivity of gliadin solutions diminished as the concentration of POSS-NH₂ was increased. Besides, confocal micrographs revealed that POSS-NH₂ might be dispersed as nanocrystals into gliadin and gluten fibers. The dimension of gluten nanofibers was also affected by the POSS-NH₂ concentration, but conversely, this dependence was not proportional to the POSS-NH₂ amount. Somehow, the interaction between gliadin and POSS-NH₂ in aqueous TFE affected the solution viscosity and, as a consequence, higher jet instabilities and thinner fiber dimensions were obtained.     

Electron microscopy of native xanthan and xanthan exposed to low ionic strength

Optical rotation data indicate that xanthan can exist both in an ordered and a disordered conformation. Using molecular weights obtained from light scattering measurements and contour length distributions obtained from electron micrographs, we find that a native, filtered xanthan exposed to low salinity (< 10^?4M NaCl) and subsequently returned to 0.1M NaCl has a highly elongated structure with a mass per unit length of 1950 ± 200 Dalton/nm. Our data thus suggest that the ordered conformation of this xanthan is double stranded. We find that native, filtered xanthan in 0.1M NH₄Ac has a nearly similar structure, but exists in part as aggregates of varying shape and size. Electron micrographs of these xanthans in 10^?4M NH₄Ac (the disordered conformation) display a mixture of species ranging from unaggregated single- or perfectly matched double-stranded species, to double-stranded chains branching into its two subunits as well as double-stranded chains with different degrees of mismatching. This study suggests that the perfectly matched antiparallel or parallel double-stranded chain constitutes the lowest free energy state of the ordered conformation of xanthan in dilute aqueous solution.     

不同温度条件下杉木、桤木和火力楠细根分解对土壤活性有机碳的影响

通过室内培养试验,研究了不同温度(9 ℃、14 ℃、24 ℃和28 ℃)条件下桤木、杉木和火力楠细根分解对土壤活性有机碳的影响.结果表明,不同树种细根的分解率不同,树种间差异显著,大小依次为火力楠>桤木>杉木.细根分解率随着培养温度的增加而增大,随着培养时间的延长而降低.添加细根的种类、培养温度和培养时间均对实验系统中土壤微生物碳和水溶性有机碳的含量产生影响.3个树种细根分解使土壤微生物碳和水溶性有机碳含量显著高于对照,大小依次为火力楠>桤木>杉木>对照; 培养中期以及中等培养温度条件下细根分解对应着较高的土壤微生物碳和水溶性有机碳含量.细根分解对土壤易氧化碳含量无显著影响.     

青海油田微生物采油技术研究

从青海油田地层水中分离培养出4株微生物菌种,对其进行了耐温性、耐盐性等进行了探讨,分析了微生物处理前后原油组份及物性变化情况,并采用岩芯流动试验探讨了微生物的驱油效果。结果表明,这几种微生物菌种均能适应青海油田温度及高矿化度地层环境,作用于原油后对原油中的长链饱和烃类物质有较好的降解作用,能使其分子链变短,并产生有机酸或石油羧酸盐类表面活性剂等低分子物质,使原油的粘度、凝点及蜡含量均出现明显的下降,改善原油的流动性能。提高石油采收率。2口井的现场试验证明,微生物采油具有良好的提高石油采收率的效果和清蜡减阻效果。