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1.
Pseudomonas fluorescens strain GRS1, PRS9 and their cold tolerant mutants were examined for their tricalcium phosphate (TCP) solubilizing activity in NBRIP (broth) media at 10°C and 25°C. Invariably, all the cold tolerant mutants of GRS1 and PRS9 were found more efficient than their respective wild type counterparts for ‘P’ solubilization activity at 10°C as compared to 25°C. ‘P’ solubilization potential of CRM was found maximum among all the strains followed by CRPF6 and CRPF4. To the best of out knowledge, this is the first report regarding low temperature ‘P’ solubilization activity.  相似文献   

2.
Pumpkin pectin: gel formation at unusually low concentration   总被引:2,自引:0,他引:2  
The gel properties of high-methoxy pectin from pumpkins have been investigated to assess the potential of this material as a hard-currency export from the former Soviet Union. Comparison was made with commercial slow-set, medium-set and rapid-set pectins from citrus peel. Gels were formed by cooling pectin solutions (pH 3·0; 60% (w/w) sucrose; 5% (w/w) corn syrup) from 95°C to 25°C, and the time-temperature course of network formation was monitored by small-deformation oscillatory measurements of storage modulus (G′). At concentrations above 1% (w/w) the pumpkin pectin gave weaker gels than the other three samples, but its minimum critical gelling concentration (c0) was found to be much lower (by at least a factor of five). Compression testing gave similar results, with pumpkin pectin giving useful breaking-stress (‘hardness’) at concentrations down to 0·5% (w/w), about a factor of two lower than for the citrus samples. Its gelation was also less rapid, giving G′ values below those of the other three samples at temperatures down to 60°C, but then setting sharply; this behaviour could be useful in avoiding ‘pregelation’ in commercial processing. The commercial slow-set pectin showed typical ‘weak gel’ properties in the solution state at 95°C, with systematic reduction in gel-like character with increasing ester content in the other samples. The rigidity of the final gels also decreased systematically through the series: rapid-set < medium-set < slow-set. These observations are tentatively ascribed to stable association of unesterified galacturonate chain segments at low pH, where electrostatic repulsion is suppressed.  相似文献   

3.
This short paper presents preliminary results on the ‘zero-shear’ specific viscosity ηsp0 of a commercial hydroxyethylmethylcellulose (Tylose MH-4000) in water, at the temperatures 10, 25 and 40·5°C, over a wide range of concentrations. At the two higher temperatures, two regions are found in the plot of logC[η]0 against logηsp0 with a C*[η]0 value of about 2·5. This is consistent with the behaviour of other random-coil polymers. At 10°C however, there is an interesting ‘upward shift’ in this plot in the dilute region. It is suggested that this is related to the different degree of hydration of the oligo(ethyleneoxide) side chains at this temperature.  相似文献   

4.
Differential scanning calorimetry (DSC), rheological measurements and granule size analyses were performed to characterize the influence of phosphorylation substitution levels on the properties of cross-linked potato starch. Phosphorus oxychloride (POCl3) was used to produce the cross-linked potato starch. The levels of the reagent used for the reaction ranged between 40 and 5000 ppm (dwb). Storage (G′) and loss (G″) moduli were measured for a 5% (w/w) gelatinized starch dispersion stored at 20 °C for 24 h after heating at 85 °C for 30 min. The samples from 80 to 500 ppm were recognized as ‘strong gel'systems, whereas native potato starch showed ‘weak gel'behavior. Steady shear and dynamic viscoelastic properties of gelatinized starch dispersion were compared. Furthermore, granule mean diameter was measured by laser scattering for a 1% (w/w) dispersion heated at 85 °C for 30 min. The granules in the 100 ppm sample swelled to a maximum of about 2.6 times the native starch granule mean diameter.  相似文献   

5.
A new room-temperature molten salt, 1:2 LiCl-ethylaluminum dichloride (LiCl-EtAlCl2, f.p. about 178 K), is examined using 13C relaxation methods at 7.05 T (−25 to + 80 °C). The methylene carbon undergoes scalar relaxation of the ‘second kind’ as it is coupled to a faster relaxing (quadrupolar) nucleus. LiCl-EtAlCl2 undergoes a significant liquid-state phase change between 5 and 15 °C as evidenced by observed changes in the relaxation properties of the methylene and methyl carbons and J(13C−27Al). The J(13C−27Al) coupling constants are 75 (− 10 to + 5 °C) and 11 Hz (15–65 °C), indicating a change in structure between 5 and 15 °C. Chemical shift anisotropies of 56 and 48 ppm are obtained for the methylene and methyl carbons in the EtAlCl2 dimer part of the 1:2 LiCl-EtAlCl2 solution.  相似文献   

6.
Differential UV spectroscopy and thermal denaturation were used to study the Mg2+ ion effect on the conformational equilibrium in poly A · 2 poly U (A2U) and poly A · poly U (AU) solutions at low (0.01 M Na+) and high (0.1 M Na+) ionic strengths. Four complete phase diagrams were obtained for Mg2+–polynucleotide complexes in ranges of temperatures 20–96 °C and concentrations (10−5–10−2) M Mg2+. Three of them have a ‘critical’ point at which the type of the conformational transition changes. The value of the ‘critical’ concentration ([Mgt2+]cr=(4.5±1.0)×10−5 M) is nearly independent of the initial conformation of polynucleotides (AU, A2U) and of Na+ contents in the solution. Such a value is observed for Ni2+ ions too. The phase diagram of the (A2U+Mg2+) complex with 0.01 M Na+ has no ‘critical’ point: temperatures of (3→2) and (2→1) transitions increase in the whole Mg2+ range. In (AU+Mg2+) phase diagram at 0.01 M Na+ the temperature interval in which triple helices are formed and destroyed is several times larger than at 0.1 M Na+. Using the ligand theory, a qualitative thermodynamic analysis of the phase diagrams was performed.  相似文献   

7.
A simple in-vitro ‘wet-plate’ method for mass-producing Phytophthora nicotianae zoospores at ≥ 1.0 × 106 zoospores/ml is described. Temperature critically affected zoospore production; 22 °C was optimum, while 36 °C was completely inhibitory. Zoospores being the most important propagule of P. nicotianae, temperature of recycled irrigation water may be manipulated to reduce diseases in irrigated nursery crops.  相似文献   

8.
The effect of constant and changing temperatures on both high and low lethal temperatures of Lymnaea peregra and the time course of acclimation were investigated. Snails acclimated to 6.5°, 11.5° and 16.5°C showed paradoxical ‘adaptation’ of their high letal temperature and reasonable ‘adaptation’ of the lowlethal temperature. This combination is thus observed for the first time in molluscs. Seasonal variation in the upper lethal temperature showed parallel changes and the snails became less resistant to heat during spring and summer. Acclimation to changing temperature conditions did not extend their temperature tolerance range. During the course of acclimation of 6.5°C snails to 16.5°C, about 70% of the acclimation was completed within the first 24 h and the rest was completed within 360 h at 16.5°C.  相似文献   

9.
Xanthan gum fermentation represents a good model for the study of the mixing of rheologically complex culture broths. Most of the previous work on power consumption dealt with ‘standard’, single impellers and used model fluids to simulate xanthan broths. This work describes the characterization of three dual-impeller combinations (D/T = 0·53) for the mixing of dehydrated—reconstituted fermentation broths of Xanthomonas campestris that had matched rheology to the actual broths. The bottom impeller was a Rushton turbine (RT) and the top impeller was another RT, a 45° pitched blade turbine (PT) or an A-310 Lightnin mixer (A310). The experiments were carried out in a tank of 0·0094 m3 working volume equipped with an air bearing dynamometer. The power was measured in a wide range of xanthan concentrations (5–40 kg m−3) in aerated (0·25, 0·5 and 1·0 vvm) and unaerated conditions. Unaerated power number (Po) vs. Reynolds number (Re) curves showed similar trends for the three combinations. Exponents close to −1 were obtained in the laminar region. A minimum in Po (Pomin) occurred at Re = 30–40, then increasing to a plateau value which was evident at Re> 200. In the transition region Pomin values were 4·3 (RT and RT), 3·6 (RT and PT) and 2·4 (RT and A310). The aerated power data for (RT and PT) and (RT and A-310) showed higher torque instabilities than the dual RT combinations at higher xanthan concentrations. The higher the xanthan concentrations, the higher the drop in power and the less important the effect of the aeration rate. Among the combinations tested, when using Rushton turbines, the well-mixed ‘cavern’ reached the tank wall (i.e., fluid motion was observed) at the lowest volumetric power input. High  相似文献   

10.
Size exclusion chromatography and low-angle laser light scattering have been used for studying the evolution of schizophyllan polysaccharide during a thermal treatment (t > 100°C) in aerated solution. Thermal denaturation of the native triple helices into single chains is initiated above 135°C and is complete in 10 min at 160°C. Both conformations can coexist in the 130–140°C temperature range. In the presence of oxygen, both forms of the biopolymer undergo severe thermal degradation. The rate of degradation was found to be independent of chain length and conformation. An activation energy of 104 kJ mol−1 was determined. The reaction was base-catalyzed. Analysis of chromatographic patterns indicate that the degradation probably occurs through an ‘all-or-none’ process.  相似文献   

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