Starch Gelatinization Kinetics in Bread Dough. DSC investigations on 'simulated' baking processes

Starch gelatinization in wheat flour dough of various moisture contents was quantitatively evaluated by means of DSC. The experimental records were worked out in the form of excess heat capacity vs. T traces which were deconvoluted to single out the contribution of starch gelatinization from that of the decomposition of amylose-lipid complexes. The quantitative procedure used put into evidence that a third endothermic process would take place in the dough with a poor moisture content. DSC runs carried out with sealed pans (i.e., at constant moisture level) and open pans (from which some water was free to evaporate) allow simulation of two extreme conditions of a real baking process, namely that relevant to the central core and to superficial layer of a dough loaf, respectively. The extent of starch gelatinization occurred in these conditions was quantitatively assessed. These data were collected at various heating rates and used to define temperature-time-transformation(TTT) diagrams which are useful tools to predict the progress of baking for any given thermal history of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Equilibrium desorption isotherms of water,ethanol, ethyl acetate,and toluene on a sodium smectite clay

Desorption isotherms for water, ethanol, ethyl acetate and toluene from a sodium smectite clay have been determined by both dynamic vapor sorption (DVS) measurements and Knudsen thermogravimetry (KTGA), at the exception of toluene that was measured only by the DVS method. The results obtained using these two methods were in satisfactory agreement, providing reliable insight into the desorption process, with certain lack of precision for ethyl acetate. The observed desorption behaviour suggests a liquid like phase at high volatile load, and a sorbed state in which molecules interact with the counter ions, at low volatile contents. However, the isotherms for water determined at various temperatures nearly superposed when plotted as a function of water activity, indicating the strength of the interactions in the clay–water system to remain of the same order of magnitude as that in bulk water, consistent with previous ab initio calculations.     

Rheological properties of doughs with buckwheat and quinoa additives

Rheological properties of doughs prepared from wheat flour with buckwheat and quinoa flour addition (2.5 mass %, 5.0 mass %, 7.5 mass %, and 10 mass %) were investigated using a farinograph and compared with those of standard dough (without addition of pseudocereals). The following characteristics were determined: water absorption capacity, water consumption, dough growth time, level of dough softening, dough stability, mechanical resistance, and dough elasticity. Dough stability showed a linear decrease with the increasing content of pseudocereals. Doughs containing quinoa flour were more stable than those with buckwheat flour addition. Dough growth time was reduced with increasing amounts of buckwheat flour but it was not affected in the case of quinoa flour addition. From the comparison of the studied characteristics it can be concluded that an addition of lower amounts of quinoa (up to 5.0 mass %) to wheat flour will not significantly impair rheological properties of the dough but provides for enhanced nutritional value of the prepared bakery products.     

Portable single-sided NMR measurements at variable temperatures: Implementation of a thermo-controlled device and application to the heating of bread dough

A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.     

Synthesis, vaporization, and thermodynamics of ultrafine Nd2Hf2O7 powders

Ultrafine Nd₂Hf₂O₇ powders with the pyrochlore structure are prepared by self-propagating hightemperature synthesis (in the Pechini version). The elemental and phase composition of the powder are studied. Microstructure is studied by scanning electron microscopy. BET specific surface areas are determined. Thermal behavior is studied by TGA/DSC/DTA up to 1473 K. The sintering kinetics of as-synthesized Nd₂Hf₂O₇ powder at various temperatures is studied. Nd₂Hf₂O₇ vaporization in the range 2400–2600 K is studied by Knudsen effusion/mass spectrometry, and the thermodynamic characteristics of this compound are determined.     

Diffusion and adsorption measurements in porous solids by inverse gas chromatography

The new inverse gas chromatography methodology of reversed-flow gas chromatography has been applied to measure diffusion and adsorption in porous solids. The theoretical analysis leads to equations describing the experimental data with very few approximations. From these, the total overall rate constant of transference (k = k(R) + k(2)), its probable error, the diffusion coefficient (D(1)) into porous solids (alpha-alumina and gamma-alumina), and its probable error are calculated by means of a simple PC program. The methodology was applied to pentane, hexane, and heptane diffusing into porous alpha- and gamma-alumina at various temperatures. A comparison of the results is made with those obtained by the Knudsen formula and with those of other researchers.     

Effects of Physical and Chemical Factors on the Structure of Gluten,Gliadins and Glutenins as Studied with Spectroscopic Methods

This review presents applications of spectroscopic methods, infrared and Raman spectroscopies in the studies of the structure of gluten network and gluten proteins (gliadins and glutenins). Both methods provide complimentary information on the secondary and tertiary structure of the proteins including analysis of amide I and III bands, conformation of disulphide bridges, behaviour of tyrosine and tryptophan residues, and water populations. Changes in the gluten structure can be studied as an effect of dough mixing in different conditions (e.g., hydration level, temperature), dough freezing and frozen storage as well as addition of different compounds to the dough (e.g., dough improvers, dietary fibre preparations, polysaccharides and polyphenols). Additionally, effect of above mentioned factors can be determined in a common wheat dough, model dough (prepared from reconstituted flour containing only wheat starch and wheat gluten), gluten dough (lack of starch), and in gliadins and glutenins. The samples were studied in the hydrated state, in the form of powder, film or in solution. Analysis of the studies presented in this review indicates that an adequate amount of water is a critical factor affecting gluten structure.     

Crystallization and Thermodynamic Properties of Titanium Stannides

Thermodynamic properties of pure titanium stannides obtained by crucible-less growth techniques under vacuum are determined by differential scanning calorimetry and Knudsen effusion. The enthalpy, specific heat capacity, entropy and Gibbs energy temperature dependence were simulated using Maier and Kelly equations. Standard enthalpies of evaporation, formation and atomization of titanium stannides were determined and compared with earlier-known data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theoretical modeling and experimental analysis of direct contact membrane distillation

A two-dimensional mathematical model was theoretically developed to predict the temperature polarization profile of direct contact membrane distillation (DCMD) processes. A concurrent flat-plate device was designed to verify the theoretical prediction of pure water productivity on saline water desalination. The numerical results from the temperature polarization profile were obtained using the finite difference technique to reduce the two-dimensional partial differential equations into an ordinary differential equations system. The resultant simultaneous linear equations system was solved with the fourth-order Runge-Kutta method. The results show theoretical prediction agreement with the measured values from the experimental runs. A combination of the Knudsen flow and Poiseuille flow models in the present mathematical formulation for membrane coefficient estimation was used to establish theoretical agreement. The influence of the inlet saline water temperature and volumetric flow rate on the pure water productivity as well as the hydraulic dissipated energy are also delineated.     

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.     

Knudsen effect on plasma-particle mass transfer. I. Formulation and application to self-diffusion

The Knudsen effect on mass transfer between a plasma gas and a small particle is investigated. A predictive model is developed by incorporating the Z-potential approach into the jump theory. The predictions of the model are explored through a case study. The results indicate that the Knudsen effect is significant and depends strongly on the particle size and the surface conditions. The plasma and the particle surface temperatures are also found to be determining factors. Under certain conditions, it is observed that the Knudsen effect can enhance the plasma-particle mass transfer, contrary to the predictions of the previous near-isothermal models.     

Kinetics of liquid annulus formation and capillary forces

The dependence of the capillary adhesion force F(cap) between a silica microsphere and a flat silica surface versus a time period t of the samples' contact (i.e., dwell-in time) is experimentally investigated using atomic force microscopy (AFM). F(cap) was found to be dependent on t if the humidity was >30-35%. This dependence is exponential, with decay (characteristic) times of ～10 s. It is suggested that the kinetics of the adhesion process are related to the growth of the water annulus between surfaces. Furthermore, we propose that the growth kinetics has two components: (1) water vapor diffusion from the surrounding humid media into the gap between samples and (2) water drainage from the gap. The theory of diffusion through thin pores (i.e., gaps) is developed, and analytical formulas are obtained for the dependence of the meniscus radius r versus time t. However, the experimental dependence of F(cap) versus t and, consequently, r versus t obtained in this article disagrees with the theoretical prediction by several orders of magnitude. Similar results were obtained from the literature data for capillary forces between an AFM cantilever tip and a flat surface. Possible reasons for the deviation from diffusion theory are suggested: surface and Knudsen regimes of vapor diffusion, nonsteady state vapor flow, and tortuosity. Taking into account the viscous drainage of water from the multilayer gap can explain the experimental kinetics of bridge formation, but only if the viscosity of the adjacent multilayer of water is several orders of magnitude larger than the bulk viscosity.     

Vapor Pressure Determination by Pressure DSC

A new pressure DSC module (Mettler DSC27HP) and its abilities for vapor pressure determination in the range of subambient pressure to 7 MPa are presented. To compare the new to an established method, vapor pressures of caffeine, naphthalene and o-phenacetin have been determined both by pressure DSC and the Knudsen effusion cell method. These results, including the derived heats of evaporation and heats of sublimation, are compared to literature values. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors affecting flux and ethanol separation performance in vacuum membrane distillation (VMD)

Membrane distillation (MD) has a great potential as a concentration process for temperature labile liquids such as fruit juices, etc. Besides water, also aroma compounds will permeate through the membrane depending on their volatility and how the MD process is operated on the permeate side.In this paper, an experimental and theoretical investigation of the influence of concentration polarisation and temperature polarisation on the flux and selectivity of binary aqueous mixtures of ethanol is presented for vacuum membrane distillation (VMD) processes. Experimental results include changes of the following parameters: nature of solutions, membrane material and pore size, feed temperature, recirculation flow rate. One method was proposed in order to evaluate the concentration polarisation effects from the fit of the experimental data. General models taking into account Knudsen and viscous flows were proposed, but viscous contribution resulted to be negligible under our operating conditions. Therefore, theoretical fluxes were estimated using Knudsen model and a good agreement between them and the experimental ones was found.     

Vapour Pressure and Thermoanalytical Study of Diethyldithiocarbamates of Platinum Metals

A thermoanalytical study of the diethyldithiocarbamates of the platinum metals Pt(II), Pd(II), Rh(III), Ir(III) and Ru(III) was carried out by means of DTA techniques in an inert atmosphere and in vacuum. Decomposition temperatures were determined and the mass loss curves were obtained for these compounds in helium and in vacuum. The X-ray diffraction patterns of the solid products of M(dtk)n thermolysis were studied. The temperature dependences of the saturated vapour pressures of the listed chelates were measured by flow and Knudsen methods, and the vaporization parameters were determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Ziziphus and Cordia Gums on Dough Properties and Baking Performance of Cookies

The influence of 2% and 5% Cordia (CG) and Ziziphus (ZG) gums on dough characteristics and cookie quality was investigated. Micro-DoughLab, a texture analyzer (TA), a rapid viscoanalyzer (RVA), and solvent retention capacity were used to examine the effect of CG and ZG gums on dough physicochemical parameters (SRC) and cookie quality. The diameter, thickness, spread, and sensory evaluation of cookies were evaluated. With the addition of CG and ZG, dough softness, mixing time, and mixing tolerance index (MTI) increased, whereas stability and water absorption decreased. TA data showed that adding gums resulted in softer and less sticky doughs than the control, whereas RVA data showed that adding CG resulted in a significant increase in peak viscosity, but no change in flour gel setback. In comparison to the control and CG samples, the ZG samples exhibited the most dough extensibility. The thickness and diameter of the cookies increased but the spread decreased, due to the added gums. The gum-containing cookies had a lower overall acceptability by panelists than the control, although only by a small margin. Gum-containing cookies, on the other hand, can deliver up to 5% soluble fiber.     

Thermal transitions of gluten-free doughs as affected by water, egg white and hydroxypropylmethylcellulose

The thermal performance of a gluten-free bread dough consisting of a blend of non allergenic corn and cassava starches (75:25) with hydroxypropylmethylcellulose (HPMC) as gluten mimetic hydrocolloid in conjunction with egg white (EW) was determined by differential scanning calorimetry. In order to analyse the effects of different levels of the components (water: 80-110%, HPMC: 0-2% and EW: 0-10% over the starch blend) on the thermal transitions of the dough, a Doehlert design and a response surface methodology were used.The analysis of variance showed that EW did not affect the onset temperature of gelatinisation and HPMC did not affect the peak and conclusion temperatures. HPMC-water interactions mainly controlled the onset temperature of starch gelatinisation. On the other hand, the peak and conclusion temperatures were determined by the additive and opposite effects of water and EW.     

Effect of apple pomace powder addition on farinographic properties of wheat dough and biscuits quality

In the present study, dietary fibre rich powders obtained from two apple cultivars (Gala, Golden Delicious) were analysed for their chemical composition and functional properties. Apple powders contained more than 50 mass % of total dietary fibre and showed high values of hydration properties such as water holding (11.73–18.34 g g^?1), water retention (11.31–11.68 g g^?1) and swelling capacity (7.19–8.03 cm³ g^?1). Incorporation of apple pomace powders (5 mass %, 10 mass %, and 15 mass %) to wheat dough resulted in a significant increase of water absorption (58.60–71.80 mass %), dough development time (from 3.43 min to 5.53 min) and dough stability (from 9.40 min to 10.90 min). The results also indicate that an addition of higher amounts (10 mass % and 15 mass %) of apple pomace powders negatively affects the volume, thickness, width, and spread ratio of biscuits and reduces their overall acceptance. Sensory analysis also showed that no significant differences between the control biscuits and biscuits containing 5 mass % of apple pomace powder from cultivar Gala were found.     

A gas-inlet system coupled with a Knudsen cell mass spectrometer for high-temperature studies

A gas-inlet system coupled with a Knudsen effusion mass spectrometer has been developed to study at high temperature the interaction of solids and vapors with reactive permanent gases, such as H(2) and O(2), directly introduced into the cell from external low-pressure reservoirs (pressure range: 10(-4) < p < 1 bar). By selecting the gas flow from the external reservoir the pressures of the gases inside the Knudsen cell can be quantitatively controlled over three orders of magnitude, approximately from 10(-8) to 5.10(-5) bar. Mixtures of two different gases can be introduced into the cell, controlling their partial pressures independently. The capabilities of the device have been tested with four gas-solid systems: PbO(s) + O(2)(g), GeO(2)(s) + O(2)(g), Ga(s) + H(2)(g) and Au(s) + H(2)(g), by studying the relevant high-temperature equilibria. The results obtained for the dissociation energies of the diatomic molecules PbO(g), GeO(g), GaH(g), and AuH(g) compare well with the literature data giving confidence in the reliability and versatility of the method. Preliminary experiments on the in situ formation of H(2)O(g) in the Knudsen cell by the introduction of controlled gaseous H(2)/O(2) mixtures are also presented.     

PHYSICAL STRUCTURE AND PHASE PROPERTIES OF AQUEOUS SYSTEMS OF LIPIDS FROM RYE AND TRITICALE IN RELATION TO WHEAT LIPIDS

In connection with studies of technical functionality of lipids in cereals, the aqueous systems of lipids from rye and tri-ticale flour are described and compared to different wheat culti-vars. Rye lipids give a lamellar liquid-crystalline phase with very small ordered regions, and this phase is continuously changed into an L2-phase with increasing water content. Triticale lipids exhibit phase equilibria in between lipids of wheat and of rye. Evidence is given for a significant role of the lamellar liquid--crystalline phase with regard to technical functionality when the cereal flour is worked in water to give a dough.