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1.
The effects of β-glucan (BG) prepared from spent brewer’s yeast on gelatinization and retrogradation of rice starch (RS) were investigated as functions of mixing ratio and of storage time. Results of rapid visco-analysis (RVA) indicated that addition of BG increased the peak, breakdown, setback, and final viscosities, but decreased the pasting temperatures of the rice starch/β-glucan (RS/BG) mixtures. Differential scanning calorimetry (DSC) data demonstrated an increase in onset (To), peak (Tp), and conclusion (Tc) temperatures and a decrease in gelatinization enthalpy (ΔH1) with increasing BG concentration. Storage of the mixed gels at 4 °C resulted in a decrease in To, Tp, Tc, and melting enthalpy (ΔH2). The retrogradation ratio (ΔH2H1) and the phase transition temperature range (Tc − To) of the mixed gels increased with storage time, but this effect was reduced by the addition of BG. BG addition also slowed the syneresis of the mixed gels. Results of dynamic viscoelasticity measurement indicated that the addition of BG promoted RS retrogradation at the beginning and then retarded it during longer storage times. The added BG also retarded the development of gel hardness during refrigerated storage of the RS/BG mixed gels.  相似文献   

2.
The long-term dynamics of an amoeboid cell shape were studied using Physarum polycephalum plasmodia with various sizes. Cell shape varied oscillatorily in a multiple periodic manner. The organism periodically elongated with period of T7 = 10 h, branched with T6 = 4 h, became uneven with T5 = 30 min and T4 = 10 min, and blew up with T3 = 1.5 min. Tiny plasmodia changed shape much faster with T3 = 1.3 min, T2 = 24 s and T1 = 3.3 s simultaneously. The plasmodial cytoskeleton also showed periodic pattern formation with T6, T5 and T3. Periods of all known oscillatory phenomena in this organism correspond to some of the periods for the above seven rhythms, and the following geometric progression holds among the periods: Ti + 1/Ti = 7 and Ti + 2/Ti + 1 = 3, where i = 1, 3, 5. Thus, multiple oscillations in the plasmodium are organized globally.  相似文献   

3.

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C Thy (F40), local temperature coefficients (Δ/ΔT) and Q10.

2. 2.|Q10 and either F40 or ΔFT were little or not related.

3. 3.|A positive correlation between F40 and ΔFT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q10 of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Author Keywords: Neuronal thermosensitivity; hypothalamic thermosensory function; Temperature and synaptic transmission; avian thermoregulation; mammalian thermoregulation  相似文献   


4.
Gay Goodman  John S. Leigh  Jr. 《BBA》1987,890(3):360-367
The electron-spin relaxation rates of the two species of cytochrome a3+3-azide found in the azide compound of bovine-heart cytochrome oxidase were measured by progressive microwave saturation at T = 10 K. It has been shown previously that Cyt a+33-azide gives rise to two distinct EPR resonances, depending upon the oxidation state of Cyt a. When Cyt a is ferrous, Cyt a3+3-azide has g = 2.88, 2.19 and 1.64; upon oxidation of Cyt a, the a3+3-azide g-values become g = 2.77, 2.18, and 1.74 (Goodman, G. (1984) J. Biol. Chem. 259, 15094–15099). The relaxation effect of Cyt a on Cyt a3 could be measured as the difference in microwave field saturation parameter H1/2 between the g = 2.77 and g = 2.88 species. For each signal the spin-lattice relaxation time T1 was determined from H1/2 using the transverse relaxation time T2. The value of T2 at 10 K was extrapolated from a plot of line-width vs. temperature at higher temperature. The dipolar contribution to T1 was related to the Cyt a-Cyt a3 spin-spin distance utilizing available information on the relative orientation of Cyt a3-azide and Cyt a (Erecinska, M., Wilson, D.F. and Blasie, J.K. (1979) Biochim. Biophys. Acta 545, 352–364). By taking into account the relaxation parameters for both gx and gz components of the Cyt a3-azide g-tensor, the angle between the gz components of the Cyt a and Cyt a3g-tensors was determined to be between 0 and 18°, and the Cyt a-Cyt a3 spin-spin distance was found to be 19 ± 8 Å.  相似文献   

5.
The effects of starch/water ratio, amylose content, degree of phosphorylation, and added KI on water mobility in maize starch-water dispersions were studied by oxygen-17 spin-spin relaxation time measurements over a range of temperatures. The results demonstrate that: (i) the changes in spin-spin relaxation time (ΔT2) reflect the degree of starch-water interaction at different stages of the heating process; (ii) the amount of added water affects the initial T2 and ΔT2 during gelatinization; (iii) higher amylose contents result in lower water mobility in starch-water systems; (iv) higher degrees of phosphorylation lead to a decrease in water mobility, accompanied by a decrease in gelatinization temperature; and (v) added KI effectively decreases water mobility and gelatinization temperature in the starch-water systems studied.  相似文献   

6.
The formation of ordered structure, such as crystallites, in starch was studied by means of differential scanning calorimetry (DSC). The influence of time/temperature treatment and additives such as polyethylene glycol (PEG), bovine serum albumin (BSA) and a carbonate buffer on the formation was investigated. The experiments were planned with a CCC (Central Composite Circumscribed) design. For all three investigated systems it could be concluded that the incubation time at 6 °C was the decisive factor for the amount of ordered structure obtained during the incubation, while the incubation time at 37 °C was the decisive factor for the thermal stability of the crystallites as expressed by Ton, Tm and Tc. The additives seemed to mainly affect the nucleation phase of crystallization process. The additives decreased the time required in order to obtain a certain level of ordering in the incubated starch samples. The carbonate buffer decreased the amount of ordered structure in starch as judged by DSC enthalpy values, while increasing the melting temperature of these structures. The additives PEG and BSA lowered the melting temperatures of the starch in the systems but increased the enthalpy values. By optimization procedure a specific amount of ordered structure with desired thermal characteristics could be predicted.  相似文献   

7.
Keith A. Rose  Alan Bearden 《BBA》1980,593(2):342-352
Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T1, and spin-spin, T2, relaxation times of P-700+ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K T 100 K. T1 was 200 μs at 100 K and increased to 900 μs at 10 K. T2 was 40 ns at 40 K and increased to 100 ns at 10 K. T1 for 40 K T 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T1 deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T1 of P-700+ were examined: T1 of P-700+ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700+ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700+ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700+ due to either the iron-sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700+ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of the P-700+ signal. The absence of diplolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700+ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.  相似文献   

8.
Two simple experiments measuring the 13C linewidths ν1/2 and spin–lattice relaxation times T1 of each of the signals in the spectrum of trilinolein indicate that the ν1/2 and T1 values are consistent with the different degrees of motional freedom expected for the various 13C nuclei. However, for each chain, the ν1/2 and T1 measurements indicate a small reversal in mobility at C-10 relative to C-9 before motional freedom again steadily increases on each chain starting at C-11. The T1 experiment allows unambiguous assignments of the C-8 signal and C-14 signal, which differ by only 0.010 ppm. Measurements of 13C ν1/2 and T1 values on tripalmitin provide secure assignments for the C-5 and C-6 signals, for which conflicting assignments have been reported. The T1 measurements also show that among the tightly clustered C-8 through C-12 signals, the C-11 signals are the most downfield, while the C-12 signals are the most upfield, again contrary to a previous report. Similar measurements of 13C ν1/2 and T1 values on other triacylglycerols or related compounds may prove equally useful in making chemical shift assignments and detecting any discontinuities in motional freedom along a chain. The benefits and possible limitations of ultrahigh field NMR for studying triacylglycerols and related compounds are discussed.  相似文献   

9.
Deuterium magnetic resonance (2H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16-d3, 16′-d3 dipalmitoylphosphatidylcholine (16-d6 DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5–10°C below the gel-liquid crystal phase transition temperature (Tm). The phase transition is sensed in the 2H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to 3 kHz. In contrast, the Raman parameter used to characterize the CD3 vibrations is quite insensitive to the melting process, although an analogous parameter does sense disordering at Tm at the 10 and 10′ position in 10-d2, 10′-d2 DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD3 group is inhomogenously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD2 group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated.  相似文献   

10.
This paper describes a 13C solid state NMR study of hydrated powders and gels of locust bean gum galactomannan-LBG and Konjac glucomannan-KGM. Changes in relative spectral intensities, cross-polarization dynamics (TCH, T1ρH) and relaxation times (T1C, T1H, T2H) show that hydration (0–90%) of LBG powders increases the 108 Hz frequency molecular motions, probably reflecting the enhanced motion of non-aggregating segments and chain ends. Slower motions (104–105 Hz) are enhanced only slightly at 90% hydration. LBG gel shows higher spatial distinction between aggregated and non-aggregated segments than the hydrated powder and relaxation times indicate higher mobility for galactose-ramified segments, compared to linear mannose segments. While the dynamics of KGM hydration is similar to that of LBG, i.e. mainly affecting fast 108 Hz motions, the gel is significantly more rigid. Both spectra and relaxation times show that glucose residues in KGM gel are particularly hindered, probably due to their preferential involvement in chain aggregation.  相似文献   

11.
The effect of hydration on the molecular dynamics of soft wheat gluten was investigated by solid state NMR. For this purpose, we recorded static and MAS 1H spectra and SPE, CP, and other selective 13C spectra under MAS and dipolar decoupling conditions on samples of dry and H2O and D2O hydrated gluten. Measurements of carbon-proton CP times and several relaxation times (proton T1, T and T2, and carbon T1) were also performed. The combination of these techniques allowed both site-specific and domain-averaged motional information to be obtained in different characteristic frequency ranges. Domains with different structural and dynamic behaviour were identified and the changes induced by hydration on the dynamics of different domains could be monitored. The proton spin diffusion process was exploited to get information on the degree of mixing among different gluten domains. The results are consistent with the “loop and train” model proposed for hydrated gluten.  相似文献   

12.
Cyclodextrin glucanotransferase (CGTase) activity was observed when the bacterium was grown in the medium at various initial pH values, containing carbon, nitrogen, phosphorus and mineral salt sources at 50 °C for 24 h in the shake flasks. The optimisation of this growth medium was carried out using response surface methodology. The design contains a total of 32 experimental trials involving 10 star points and 6 replicates at the centre points. The design was employed by selecting sago starch, peptone from casein, K2HPO4, CaCl2 and initial pH as five independent variables in this study. The optimal calculated values of tested variables for maximal production of CGTase were found to be comprised of: sago starch, 16.02 g/l; peptone from casein, 20 g/l; K2HPO4, 1.4 g/l; CaCl2, 0.2 g/l and initial pH, 7.54 with a predicted CGTase activity of 14.20 U/ml. These predicted optimal parameters were tested in the laboratory and the final CGTase activity obtained was very close to the predicted value at 14.80 U/ml.  相似文献   

13.
Daily circadian rhythms of body temperature (Tb) and oxygen consumption (VO2) were measured in two murid species, which occupy extremely different habitats in Israel. The golden spiny mouse (Acomys mssalus) is a diurnal murid distributed in arid and hot parts of the great Syrio-African Rift Valley, while the broad-toothed field mouse (Apodeinns mystacinus) is a nocturnal species that inhabits the Mediterranean woodlands. In both species, the daily rhythms of Tb and VO2 are entrained by the photoperiod. Under laboratory experimental conditions (ambient temperature Ta = 33oC and photoperiod regime of 12L: 12D), Acomys russatus exhibits a tendency towards a nocturnal activity pattern, compared to the diurnal activity displayed by this species under natural conditions. Under the same photoperiod regime and at Ta = 28oC, Apodemus mystacinus displays nocturnal activity, as observed under natural conditions. The maximal values of Tb were recorded in Acomys russatus at midnight (23:50 h), while the maximal values of VO2 were recorded at the beginning of the dark period (18:20 h). In Apodemus mystacinus, the maximal values of Tb and VO2 were recorded at 23:40 and 20:00 h, respectively. The ecophysiological significance of these results is discussed further.  相似文献   

14.

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo).

2. 2. A thermal mannikin was also used to determine the exact operative temperature, T0.

3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms−1), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms−1).

4. 4. Local skin temperatures and answers to questionnaires were obtained.

5. 5. Skin temperature variations were affected by conditions and slight T0 changes.

6. 6. Comfort judgments were fairly well related to T0, especially when expressed as differences between actual non-uniform environment and the uniform one.

7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.

Author Keywords: Skin temperature; thermal sensation; comfort; climate heterogeneity  相似文献   


15.
Yield stress of 6% (w/w) waxy maize (WXM), cross-linked waxy maize (CLWM), and cold water swelling (CWS) starches in xanthan gum dispersions: 0%, 0.35%, 0.50%, 0.70%, and 1.0% was measured with the vane method at an apparent shear rate of 0.05 s−1. The intrinsic viscosity of the xanthan gum was determined to be: 112.3 dL/g in distilled water at 25 °C. Values of the static (σ0s) and dynamic (σ0d) yield stress of each dispersion were measured before and after breaking down its structure under continuous shear, respectively. The WXM and CWS starches exhibited synergistic behavior, whereas the CLWM starch showed antagonistic effect with xanthan gum. The difference (σ0s − σ0d) was the stress required to break the inter-particle bonding (σb). The contributions of the viscous (σv) and network (σn) components were estimated from an energy balance model. In general, values of σb of the starch–xanthan gum dispersions decreased and those of σn increased with increase in xanthan gum concentration.  相似文献   

16.
Physico-chemical characterisation of sago starch   总被引:3,自引:0,他引:3  
The physico-chemical characteristics of various sago starch samples from South East Asia were determined and compared to starches from other sources. X-ray diffraction studies showed that all the sago starches exhibited a C-type diffraction pattern. Scanning electron microscopy showed that they consist of oval granules with an average diameter around 30 μm. Proximate composition studies showed that the moisture content in the sago samples varied between 10.6% and 20.0%, ash between 0.06% and 0.43%, crude fat between 0.10% and 0.13%, fiber between 0.26% and 0.32% and crude protein between 0.19% and 0.25%. The amylose content varied between 24% and 31%. The percentage of amylose obtained by colourimetric determination agreed well with the values obtained by fractionation procedures and potentiometric titration. Intrinsic viscosities and weight average molecular weight were determined in 1M KOH. Intrinsic viscosity for amylose from sago starches varied between 310 and 460 ml/g while for amylopectin the values varied between 210 and 250 ml/g. The molecular weight for amylose was found to be in the range of 1.41×106 to 2.23×106 while for amylopectin it was in the range of 6.70×106 to 9.23×106. The gelatinisation temperature for the sago starches studied varied between 69.4°C and 70.1°C. The exponent ‘a’ in the Mark–Houwink equation and the exponent ‘’ in the equation Rg=kM was found to be 0.80 and 0.58, respectively for amylose separated from sago starch and these are indicative of a random coil conformation. Two types of pasting properties were observed. The first was characterised by a maximum consistency immediately followed by sharp decrease in consistency while the second type was characterised by a plateau when the maximum consistency was reached.  相似文献   

17.
Two new spin-crossover complexes, [Fe(Medpq)(py)2(NCS)2] · py · 0.5H2O (1) and [Fe(Medpq)(py)2(NCSe)2] · py (2) (Medpq = 2-methyldipyrido[3,2-f:2′,3′-h]-quinoxaline, py = pyridine), have been synthesized. The crystal structures were determined at both room temperature (298 K) and low temperature (110 K). Complexes 1 and 2 crystallize in the orthorhombic space group Pbca and monoclinic space group P21/n, respectively. In both complexes, the distorted [FeN6] octahedron is formed by six nitrogen atoms from Medpq, the trans pyridine molecules and the cis NCX groups. The thermal spin transition is accompanied by the shortening of the mean Fe–N distances by 0.194 Å for 2. The mononuclear [Fe(Medpq)(py)2(NCS)2] and [Fe(Medpq)(py)2(NCSe)2] neutral species interact each other via π-stacking, resulting in a one-dimensional extended structure for both 1 and 2. There exist C–HX (X = S, Se) hydrogen bonds for both complexes. Variable-temperature magnetic susceptibility measurements and Mössbauer spectroscopy reveal the occurrence of a gradual spin transition. The transitions are centered at T1/2 = 120 K for 1 and T1/2 = 180 K for 2, respectively.  相似文献   

18.
张晓龙  沈冰  权全  董樑  田开迪 《生态学杂志》2016,27(8):2551-2560
基于对半湿润易旱区的渭河平原农田2013—2014年冬小麦生长期土壤呼吸(SR)及环境因子和生物因子的观测,研究了冬小麦土壤呼吸日变化、季节变化特征,综合分析了温度(T)、土壤含水量(W)、总初级生产力(GPP)和叶面积指数(LAI)对土壤呼吸的影响.结果表明: 冬小麦土壤呼吸日变化呈单峰型,呼吸速率变化范围为1.5~6.94 μmol CO2·m-2·s-1,最大值出现在12:00—14:00;温度是影响土壤呼吸日变化的驱动因子,其中地表温度(Ts)能解释土壤呼吸时间变异的80.9%;土壤呼吸速率与温度的昼夜变化对应关系呈顺时针近椭圆曲线.冬小麦土壤呼吸速率从出苗后到冬季呈下降趋势,在冬季时保持较低水平,进入返青期后迅速增加,在抽穗期和灌浆期达到最大,成熟期后有所下降,变化范围为0.65~4.85 μmol CO2·m-2·s-1;土壤呼吸季节变化与温度、土壤含水量、GPP、LAI均呈显著(P<0.01)正相关关系;土壤温度和水分是影响土壤呼吸季节变化的关键因素,使用复合模型SR=e(a+bT5 cm+cW10 cm+dW10 cm2),可以解释土壤呼吸时间变异的82.6%,比单因子模型(不超过65.7%)的解释能力显著提高.经模型计算,该区域2013—2014年冬小麦生长期平均土壤呼吸速率为1.67 μmol CO2·m-2·s-1.  相似文献   

19.
The N,N-diethylcarbamato derivative of zirconium(IV), Zr(O2CNEt2)4 has been studied by X-ray crystallography. Crystal data: C20H40Na4O8Zr, monoclinic, space group C2/c, a = 14.057(1), b = 12.168(1), c = 16.746(2) Å, β = 108.071(4)°, Z = 4, Dc = 1.356, F(000) = 1168, T = 213 K. The compound is isotypic with the corresponding niobium(IV) derivative with a dodecahedral coordination at the zirconium atom. By reaction of NbCl4(THF)2 with Tl(hfacac), the hexafluoroacetylacetonato derivative of niobium (IV), Nb(hfacac)4, has been prepared and structurally characterized. The compound crystallizes in the orthorhombic space group Pna21 with the following cell constants: a = 10.399(4), b = 15.852(9), c = 119.073(1) Å. It is not isotypic with the corresponding zirconium(IV) derivative, Zr(hfacac)4. Crystal data: C20H4F24O8Zr, monoclinic, space group P21/n, a = 11.974(4), b = 20.451(6), c = 13.140(3) Å, β = 104.487(11)°, Z = 4, Dc = 1.960, F(000) = 1776, T = 223 K. Although in both compounds the central metal atom shows a square antiprismatic coordination, the coordination mode of the ligands is different and slight deviations from the D4(llll) and C2(llss) ideal geometries have been observed in the case of niobium and zirconium, respectively. An EPR study has been performed on the Nb(IV) derivatives as diluted solid solutions in frozen organic solvents or in the diamagnetic matrix of the corresponding zirconium(IV) compound. The EPR spectra have confirmed the presence of non-interacting paramagnets in the solid solutions and, in the case of Nb(O2CNEt2)4, the point symmetry of the paramagnetic centre has been found to be in agreement with the results of the X-ray investigation. An EPR spectrum of rhombic symmetry has been observed for the hexafluoroacetylacetonato derivative of Nb(IV) when diluted in frozen THF solution or in Zr(hfacac)4.  相似文献   

20.
NMR relaxation studies of intracellular Na in red blood cells   总被引:2,自引:0,他引:2  
The state of intracellular Na+ in human and dog erythrocytes was characterized by 23Na-NMR using dysprosium complexes as shift reagents. Intracellular Na+ concentrations were determined using integration of the inner Na+ NMR signals and measurements of the intracellular volume using 59Co-NMR of extracellular Co(CN)3−6. T2 was found to be significantly shorter than T1, indicating some binding to macromolecules. While the longitudinal magnetization decay follows a single exponential the transverse magnetization could be fitted with a double-exponential function. It was shown that neither the binding to the inner side of the membrane nor binding to hemoglobin contributes to the relaxation enhancement.  相似文献   

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