Characterization of gluten-free bread crumb baked at atmospheric and reduced pressures using TD-NMR

This research aimed to study the effects of using a partial vacuum for bread baking on macromolecules and water distribution in gluten-free bread. Bread baking under partial vacuum results in greater oven rise and a larger gas fraction in the crumb. Because water's boiling point decreases under reduced pressure, it was expected that its distribution within the dough and its interactions with the others dough's constituents (mainly starch) would differ from those in bread baked under atmospheric pressure. Time-domain nuclear magnetic resonance was used, as it has the rare capacity to quantify both gelatinization and retrogradation of starch. Complementary rheological measurements made it possible to show that crumb Young's modulus was mostly influenced by the gas fraction whereas there was little change in starch gelatinization and retrogradation when dough was baked under partial vacuum. When insufficiently hydrated (48%), the volume of breads was practically the same whatever the baking process. Meanwhile, the nuclear magnetic resonance results suggested that amylose short-term crystallization (on cooling) is dependent on water content. In addition, crumb Young's modulus during storage at room temperature correlated with an increase in free induction decay signal intensity.     

A DSC study of the effect of bread making methods on bound water content and redistribution in chitosan enriched bread

The effect of bread making methods on bound water migration from crumb to crust and moisture redistribution during bread storage at room temperature was studied. Comparative analysis of water behavior in bread crusts and crumbs was performed using differential scanning calorimetry method. Water vaporization enthalpies and temperatures of water vaporization peaks were determined and compared for bread produced by a single stage, straight dough method and bread produced by a two stage, sponge-and-dough method. The effect of chitosan on the crust and the crumb properties was analyzed for the breads produced by both methods.     

Impact of the state of water on the dispersion stability of a skin cream formulation elucidated by magnetic resonance techniques

This study investigated the relationship between the state of water and the dispersion stability of a skin cream formulation. Hydrophilic ointments treated with a high-pressure wet-type jet mill were used as model formulations. Spin-lattice relaxation times (T(1)) were measured by magnetic resonance techniques to estimate the state of water in samples. A shorter T(1) relaxation time was obtained from samples with higher surfactant content, whereas the processing pressure of the jet mill and 1-week storage at 40 °C did not influence the T(1) relaxation time. Observations using scanning electron microscopy (SEM) showed that coalescence occurred in samples with lower surfactant contents (1.0% by weight) following 1-week storage at 40 °C. We also investigated samples prepared using a hydrophilic surfactant with a short polyethylene glycol (PEG) chain and with PEG-4000. From the change in T(1) relaxation times after removing the oil phase from samples by centrifugation, it was clarified that most of the surfactant was located on the surface of oil droplets. Furthermore, SEM observations showed that phase separation was facilitated as the PEG chain length of the surfactant shortened. Thus, a thin water layer over oil droplets is the most important factor for stabilizing their dispersion. This study provides proof-of-principle results on the contribution of the state of water to the dispersion stability of a skin cream formulation.     

A calorimetric study of the glass transition kinetics in polyisoprene

The connection between the dielectric and calorimetric relaxation behaviours of synthetic polyisoprene Cariflex IR 305 is studied. A similar comparison of dielectric and dilatometric results was described in [1]. The heat capacity was measured during heating of samples prepared with different thermal history. Experimental results were compared with the heat capacity curves calculated for a model based on the multiparameter theory of Kovacs et al. [4]. The model considers the relaxation system as being composed of a set of subsystems characterized by different relaxation times. The distribution of relaxation times and their temperature dependence were taken from the diclectric measurement. The relaxation time of a subsystem from posed to depend, not only on the actual, temperature of the sample, but also on the deviation of this subsystem from equilibrium, or alternatively, on the deviation of the system as a whole. The comparison between the measured and modeled curves shows that both influences must be taken into account in order to explain the experimental results.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday.     

Thermomechanical properties of glassy cereal foods

The main objective of this paper is to discuss the relationship between physical state, fracture mechanism, and texture for low moisture cereal-based foods. Experiments were also carried out to get a better understanding of the role of water. At room temperature, extruded bread and white bread (previously) dehydrated, then rehydrated in atmospheres with controlled humidities) exhibited a brittle behavior up to around 9% moisture. At 13.7% moisture, they were ductile. A significant loss in the crispness of extruded bread was observed between 8.5 and 10% moisture. The glass transition temperature (T _g) was measured, using dynamic mechanical thermal analysis (DMTA), for samples with up to 40% moisture. The resultingT _g curve showed that the important changes in fracture mechanisms and crispness occurred while the samples were still in the glassy state. The viscoelastic behavior of both extruded and white breads suggested that a secondary relaxation occurred around 10?C. Another event was observed around 70?C for low moisture sample, using DMTA. This event was attributed to disruption of low energy interactions.     

Cell culture arrays using magnetic force-based cell patterning for dynamic single cell analysis

In order to understand the behavior of individual cells, single cell analyses have attracted attention since most cell-based assays provide data with values averaged across a large number of cells. Techniques for the manipulation and analysis of single cells are crucial for understanding the behavior of individual cells. In the present study, we have developed single cell culture arrays using magnetic force and a pin holder, which enables the allocation of the magnetically labeled cells on arrays, and have analyzed their dynamics. The pin holder was made from magnetic soft iron and contained more than 6000 pillars on its surface. The pin holder was placed on a magnet to concentrate the magnetic flux density above the pillars. NIH/3T3 fibroblasts that were labeled with magnetite cationic liposomes (MCLs) were seeded into a culture dish, and the dish was placed over the pin holder with the magnet. The magnetically labeled cells were guided on the surface where the pillars were positioned and allocated on the arrays with a high resolution. Single-cell patterning was achieved by adjusting the number of cells seeded, and the target cell was collected by a micromanipulator after removing the pin holder with the magnet. Furthermore, change in the morphology of magnetically patterned cells was analyzed by microscopic observation, and cell spreading on the array was observed with time duration. Magnetic force-based cell patterning on cell culture arrays would be a suitable technique for the analysis of cell behavior in studies of cell-cell variation and cell-cell interactions.     

Clustering dynamics in water/methanol mixtures: a nuclear magnetic resonance study at 205 k<T<295 k

Proton nuclear magnetic resonance (1H NMR) experiments have been performed to measure the spin-lattice, T1, and spin-spin, T2, relaxation times of the three functional groups in water/methanol mixtures at different methanol molar fractions (XMeOH=0, 0.04, 0.1, 0.24, 0.5, 1) as a function of temperature in the range 205 K相似文献   

Development of heat capacity measurement system for single crystals of molecule-based compounds

We report on construction of a new low temperature heat capacity measurement system. This system was designed for performing thermodynamic investigation by thermal relaxation technique for small amount of samples at extremely low temperature region between 70 mK and 10 K. Two different calorimetry cells for this system were designed. One is a usual-type calorimetry cell consisting of tiny chip-type thermometer and strain gauge heater. The size of the sample stage has been reduced for measuring small samples. The other is designed for performing heat capacity measurements under magnetic fields of which magnitude and direction are accurately controlled. The calorimetry cells with heat capacity measurement unit can be mounted on a handy top-loading type dilution refrigerator of which outer diameter including the adiabatic space is 27 mm. We discuss basic performance and specification of the constructed cells and low temperature heat capacity data of an organic charge transfer salt obtained by this system.     

Magnetic properties of BiMnO3 studied with Dc and Ac magnetization and specific heat

Magnetic and specific heat measurements were performed in a single-phased powder BiMnO3 sample prepared at 6 GPa and 1383 K. The imaginary part of the ac susceptibilities showed strong frequency dependence below the ferromagnetic Curie temperature of 98 K. The relaxation measurements revealed time-dependent magnetic properties below 98 K. These data indicate the appearance of a "spin-glass-like" state in BiMnO3. Specific heat measurements showed the existence of ferromagnetic spin waves. However, no simple term Cm [directly proportional] T3/2 was found indicating an unconventional behavior of the magnetic specific heat. The Debye temperature was estimated to be 410 K using isostructural compounds BiScO3 and BiCrO3.     

Resolving the controversy on the glass transition temperature of water?

We consider experimental data on the dynamics of water (1) in glass-forming aqueous mixtures with glass transition temperature T(g) approaching the putative T(g) = 136 K of water from above and below, (2) in confined spaces of nanometer in size, and (3) in the bulk at temperatures above the homogeneous nucleation temperature. Altogether, the considered relaxation times from the data range nearly over 15 decades from 10(-12) to 10(3) s. Assisted by the various features in the isothermal spectra and theoretical interpretation, these considerations enable us to conclude that relaxation of un-crystallized water is highly non-cooperative. The exponent β(K) of its Kohlrausch stretched exponential correlation function is not far from having the value of one, and hence the deviation from exponential time decay is slight. Albeit the temperature dependence of its α-relaxation time being non-Arrhenius, the corresponding T(g)-scaled temperature dependence has small steepness index m, likely less than 44 at T(g), and hence water is not "'fragile" as a glassformer. The separation in time scale of the α- and the β-relaxations is small at T(g), becomes smaller at higher temperatures, and they merge together shortly above T(g). From all these properties and by inference, water is highly non-cooperative as a glass-former, it has short cooperative length-scale, and possibly smaller configurational entropy and change of heat capacity at T(g) compared with other organic glass-formers. This conclusion is perhaps unsurprising because water is the smallest molecule. Our deductions from the data rule out that the T(g) of water is higher than 160 K, and suggest that it is close to the traditional value of 136 K.     

Component dynamics in polyvinylpyrrolidone concentrated aqueous solutions

(2)H-nuclear magnetic resonance (NMR) and neutron scattering (NS) on isotopically labelled samples have been combined to investigate the structure and dynamics of polyvinylpyrrolidone (PVP) aqueous solutions (4 water molecules/monomeric unit). Neutron diffraction evidences the nanosegregation of polymer main-chains and water molecules leading to the presence of water clusters. NMR reveals the same characteristic times and spectral shape as those of the slower process observed by broadband dielectric spectroscopy in this system [S. Cerveny et al., J. Chem. Phys. 128, 044901 (2008)]. The temperature dependence of such relaxation time crosses over from a cooperative-like behavior at high temperatures to an Arrhenius behavior at lower temperatures. Below the crossover, NMR features the spectral shape as due to a symmetric distribution of relaxation times and the underlying motions as isotropic. NS results on the structural relaxation of both components-isolated via H/D labeling-show (i) anomalously stretched and non-Gaussian functional forms of the intermediate scattering functions and (ii) a strong dynamic asymmetry between the components that increases with decreasing temperature. Strong heterogeneities associated to the nanosegregated structure and the dynamic asymmetry are invoked to explain the observed anomalies. On the other hand, at short times the atomic displacements are strongly coupled for PVP and water, presumably due to H-bond formation and densification of the sample upon hydration.     

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

Nuclear magnetic resonance spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. (1)H and (7)Li spin-lattice relaxation times (T(1)) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T(1) values along with the presence of minima in T(1) as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and quasi-elastic neutron scattering experiments.     

Effect of Octenyl Succinic Anhydride (OSA) Modified Starches on the Rheological Properties of Dough and Characteristic of the Gluten-Free Bread

The study focused on the influence of starch modified by octenyl succinic anhydride (OSA) on the rheological and thermal properties of gluten-free dough containing corn and potato starch with the addition of pectin and guar gum as structure-forming substances. The starch blend used in the original dough recipe was partially (5% to 15%) replaced with OSA starch. The rheological properties of dough samples were determined, and the properties of the resulting bread were analyzed. It was found that the dough samples behaved as weak gels, and the values of storage and loss moduli (G′ and G″, respectively) significantly depended on angular frequency. Various shares of OSA starch in recipes modified dough in different ways, causing changes in its rheological characteristics. The introduction of OSA starch preparations resulted in changes in the bread volume and physical characteristics of the crumb. All the applied preparations caused an increase in bread porosity and the number of pores larger than 5 mm, and there was a parallel decrease in pore density. The presence of OSA starch preparations modified bread texture depending on the amount and type of the applied preparation. The introduction of OSA starches in gluten-free bread formulation caused a significant drop in the enthalpy of retrograded amylopectin decomposition, indicating a beneficial influence of such type of additive on staling retardation in gluten-free bread.     

Electron paramagnetic resonance investigation of the electron-doped manganite La(1-x)Te(x)MnO3 (0.1 ≤ x ≤ 0.2)

The electron paramagnetic resonance (EPR) properties of the electron-doped manganite La(1-x)Te(x)MnO(3) (0.1 ≤ x ≤ 0.2) are investigated based on the data of EPR spectra, resistivity, and magnetic susceptibility. With decreasing temperature from 400 K, the EPR linewidth ΔH(PP) decreases and passes through a minimum at T(min), then substantially increases with further decreasing temperature. The broadening of the EPR linewidth above T(min) can be understood in terms of the increase in the relaxation rate of spin of e(g) polarons to the lattice with increasing temperature due to the similarity between the temperature dependence of the linewidth ΔH(pp)(T) and the conductivity σ(T). For the samples with x = 0.1 and 0.15, the conductivity activation energy E(σ) is comparable with the activation energy E(a) deduced from the linewidth. Whereas for the x = 0.2 sample, there is a large difference between E(σ) (0.2206 eV) and E(a) (0.0874 eV).     

Water behavior in mesoporous materials as studied by NMR relaxometry

Water in mesoporous materials possessing a two-dimensional hexagonal structure has been studied by the variation of its NMR longitudinal relaxation time T(1) as a function of the static magnetic field value, or equivalently of the NMR measurement frequency. This technique, dubbed relaxometry, has been applied from 5 kHz (measurement frequency) up to 400 MHz with various instruments including a variable-field spectrometer operating between 8 and 90 MHz. Moreover, the range 0-5 kHz could be investigated by transverse relaxation, T(2) denoting the corresponding relaxation time, and relaxation in the rotating frame, T(1ρ) denoting the corresponding relaxation time. Measurements of proton relaxation rates (inverse of relaxation times) have been performed with H(2)O and HOD (residual protons of heavy water) at water volumes of 80%, 60%, and 40% relative to the porous volume. Comparison between H(2)O and HOD shows clearly that, above 1 MHz where both sets of data are superposed, relaxation is purely intermolecular and due to paramagnetic relaxation (dipolar interactions of water protons with unpaired electrons of paramagnetic entities). Below 1 MHz, it is possible to subtract the intermolecular contribution (given by HOD data) from H(2)O data so that one is left with intramolecular relaxation which is solely due to water reorientational motions. The analysis of these low-frequency data (in terms of Lorentzian functions) reveals two types of water within the pores: one interacting strongly with the surface and the other corresponding to a second layer. High-frequency data, which arise from paramagnetic relaxation, exhibit again two types of water. Due to their correlation times, one type is assigned to relatively free water within the pores while the other type corresponds to bulk (interparticular) water. Their proportions, given as a function of the volume fraction, are consistent with the above assignments.     

The Effect of α-, β- and γ-Cyclodextrin on Wheat Dough and Bread Properties

Cyclodextrins (CDs) are cyclic oligosaccharides that have found widespread application in numerous fields. CDs have revealed a number of various health benefits, making them potentially useful food supplements and nutraceuticals. In this study, the impact of α-, β-, and γ-CD at different concentrations (up to 8% of the flour weight) on the wheat dough and bread properties were investigated. The impact on dough properties was assessed by alveograph analysis, and it was found that especially β-CD affected the viscoelastic properties. This behavior correlates well with a direct interaction of the CDs with the proteins of the gluten network. The impact on bread volume and bread staling was also assessed. The bread volume was in general not significantly affected by the addition of up to 4% CD, except for 4% α-CD, which slightly increased the bread volume. Larger concentrations of CDs lead to decreasing bread volumes. Bread staling was investigated by texture analysis and low field nuclear magnetic resonance spectroscopy (LF-NMR) measurements, and no effect of the addition of CDs on the staling was observed. Up to 4% CD can, therefore, be added to wheat bread with only minor effects on the dough and bread properties.     

Construction of an Isoperibol Calorimeter to Measure the Specific Heat Capacity of Foods Between 20 and 90°C

A simple isoperibol calorimeter, using the modified method of mixtures, was developed to measure the average specific heat capacity of different dough types between 20 and 90°C. The method consisted of encapsulating the sample in a copper cylinder and immersing the capsule in water at a different temperature. The procedure was tested for reliability with distilled water and whole fat milk before applying it to five dough types of varying moisture and fat contents. Mean values of 4.176±0.008 kJ kg^-1 K^-1 and 3.942±0.034 kJ kg^-1 K^-1 were obtained for distilled water and milk respectively, which agree within 0.23 and 0.34% from reported values. The specific heat values for the five dough types were found to range between 2.15–2.68 kJ kg^-1 K^-1 between 2.35–3.10 kJ kg^-1 K^-1 and between 2.40–3.19 kJ kg^-1 K^-1 at the three temperature levels studied. The specific heat capacity was found to depend not only on the moisture level but also on the fat content, especially for dough types with a high percent of fat. Regression analysis was then used to correlate these values and develop a set of empirical equations. The results were used to assist in energy balance calculations in backing oven for industrial purposes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct screening of tetracyclines in water and bovine milk using room temperature phosphorescence detection

A fast and simple flow-through optosensor was designed and characterized for the direct screening of four tetracycline (TCC) antibiotics (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in water and bovine milk samples. The proposed optosensor provides rapid binary yes/no overall responses, being appropriate for the screening of this family of antibiotics above or below a pre-set concentration threshold.The experimental set-up is based on a flow-injection manifold coupled on-line to a phosphorescence detector. Aliquots of the samples are pretreated with Eu(III) to form room temperature phosphorescent metal chelates and injected in the flow manifold. Those chelates are then on-line retained on a conventional flow-cell (packed with polymeric Amberlite XAD-4 particles) which is placed inside the cell holder of the phosphorimeter. After the emission is registered, the antibiotic-metal complexes are eluted from the packed resin with 1 M HCl (for milk samples a second regeneration step, using methanol, should be performed). A sample throughput of about 20 samples per hour was obtained. Optimum experimental conditions include a pH 9, a Eu(III) concentration of 2 × 10⁻⁴ M and 8 mM sodium sulphite as chemical deoxygenant. The phosphorescence emitted by the europium-TCC complexes was measured at 394 and 617 nm for excitation and emission wavelengths, respectively.The unreliability region, given by the probability of false positives and false negatives, respectively (set at 5% in both cases) was in the range between 0.2 and 11.6 nМ for detection of tetracyclines in water samples (at a cut-off level of 4 nM) and in the range between 165 and 238 nM for detection of tetracyclines in milk (cut-off level fixed at the normative EU level of 200 nM). Finally, the applicability of the proposed screening optosensor was tested for the reliable control of tetracyclines in contaminated and uncontaminated water and milk samples.     

Magnetic properties of bulk BiCrO3 studied with dc and ac magnetization and specific heat

Single-phased powder BiCrO(3) sample was prepared at 6 GPa and 1653 K. Its magnetic properties were investigated by dc/ac magnetization, magnetic relaxation, and specific heat measurements. Four anomalies of magnetic origin were found near 40, 75, 109, and 111 K. The long-range antiferromagnetic order with weak ferromagnetism occurs at T(N) = 109 K. The ac susceptibilities showed that the transition near T(N) is a two-step transition. Additional frequency-independent broad anomalies were observed on the real part of the ac susceptibilities near 75 K, likely, caused by the change in the magnetic easy axis. The dc magnetic susceptibilities also had anomalies at 75 K, and the isothermal magnetization curves and relaxation curves changed their behavior below 75 K. Below 40 K, frequency-dependent anomalies with very large temperature shifts were observed on both the real and imaginary parts of the ac susceptibilities. The monoclinic-to-orthorhombic structural phase transition near 420 K was investigated by magnetization and differential scanning calorimetry measurements.     

Thermal history effects and methyl tunneling dynamics in a supramolecular complex of calixarene and para-xylene

The low-temperature structure and dynamics of guest molecules of p-xylene incorporated in the isopropyl-calix[4] arene(2:1) p-xylene complex have been investigated by solid state nuclear magnetic resonance (NMR). Using one-dimensional 1H-decoupled 13C cross-polarization magic-angle-spinning (MAS) NMR and two-dimensional 1H-13C correlation spectroscopy, a full assignment of the 13C and 1H chemical shifts has been made. Using 1H NMR relaxometry, the effects of thermal history on the structure of the system have been investigated. Rapidly cooled samples have 1H spin-lattice relaxation times T1, which at low temperature (T<60 K) are typically two orders of magnitude faster than those observed in annealed samples which have been cooled slowly over many hours. In both forms, the low-temperature relaxation is driven by the dynamics of the weakly hindered methyl rotors of the p-xylene guest. The substantial difference in T1 is attributed in the rapidly cooled sample to disorder in the structure of the complex leading to a wide distribution of correlation times and methyl barrier heights. A comparison of the linewidths and splittings in the high resolution 13C MAS spectra of the two forms provides structural insight into the nature of the disorder. Using 1H field-cycling NMR relaxometry, the methyl dynamics of the p-xylene guest in the annealed sample have been fully characterized. The B-field dependence of the 1H T1 maps out the spectral density from which the correlation times are directly measured. The methyl barrier heights are determined from an analysis of the temperature dependence.