14 research outputs found
Effect of addition of different hydrocolloids on pasting, thermal, and rheological properties of cassava starch
The Simon effect and handedness: Evidence for a dominant-hand attentional bias in spatial coding
Air-drying of fresh and osmotically pre-treated pineapple slices: Fixed air temperature versus fixed slice temperature drying kinetics
In this investigation, the air drying characteristics of fresh and osmotically pre-treated pineapple slices in a tray dryer were studied under different operating conditions. The air velocity varied from 1.5 to 2.5 m/s and the air temperature from 40 to 70 degreesC. The analytical solution of the second Fick's law for an infinite slab was used to calculate effective diffusion coefficients and their temperature dependence could be well represented by an Arrhenius-type equation. Comparison of the results showed that the diffusion coefficients were lower for the pre-treated fruit. By means of automatic control, it was possible to obtain drying curves under conditions of constant product temperature, which showed to be an alternative to reduce the drying time of pineapple slices
Viscoelastic and Thermal Properties of Collagen-Xanthan Gum and Collagen-Maltodextrin Suspensions During Heating and Cooling
The purpose of this work was to investigate the viscoelastic properties of aqueous suspensions of crude collagen powder extracted from bovine hides and nonsubmitted to the hydrolysis reaction that leads to gelatin. The studied variables included the collagen concentration and the addition of xanthan gum or maltodextrin at varied concentrations during heating/cooling of the mixtures. Differential scanning calorimetry thermograms showed that the addition of polysaccharides decreased the endothermic peak areas observed at the denaturation temperature of collagen. The rheological properties of the pure collagen suspensions were highly dependent on concentration: 4% and 6% collagen suspensions presented a great increase in the storage modulus after heating/cooling, whereas for concentrations of 8% and 10% G' decreased during heating and did not recover its original value after heating/cooling. The frequency sweeps showed that the thermal treatment was responsible by the strengthening of the interactions that formed the polymer network. Addition of 0.1% xanthan gum to collagen suspensions increased the gel strength, especially after heating/cooling of the system, whereas increasing gum concentration to 0.3% resulted in a weaker gel, which could indicate thermodynamic incompatibility between the biopolymers. Mixtures of collagen and maltodextrin resulted in more fluid structures than those obtained with pure collagen at the same collagen concentration and the range of temperatures in which these mixtures behaved as a gel decreased with increasing concentrations of both collagen and maltodextrin, suggesting incompatibilities between the biopolymers
Rehydration and shrinkage behaviour of dried pineapple
The shrinking behavior, apparent densities and rehydration indexes of fresh and osmotically pre-treated pineapple slices during air-drying were obtained. The air drying velocity varied from 1.5 to 2.5 m/s and the air temperature from 40 to 70 degreesC. By means of automatic control, it was possible to obtain drying curves under conditions of constant product temperature. Volumetric shrinkage of fresh samples was temperature independent for drying at high air velocities but, at lower velocities, increased with decreasing drying temperature. Osmotically pre-treating the material resulted in reduced shrinkage, as well as drying with product temperature controlled, due to lower drying times needed that led to shorter high temperature exposition. Moisture dependence of apparent density was highly non-linear and could be fitted by an empirical model. Fresh sample rehydration indexes were higher than osmosed ones and increased with increasing temperature, except for pre-treated samples dried at 70 degreesC, probably due to superficial sugar caramelization, which reduced surface water permeability
Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR Cascade Inhibitors: How Mutations Can Result in Therapy Resistance and How to Overcome Resistance
Synthesis and Solvatochromism of Substituted 4â(Nitrostyryl)phenolate Dyes
4-(Nitrostyryl)Âphenols <b>2a</b>â<b>9a</b> were
synthesized, and by deprotonation in solution, the solvatochromic
phenolates <b>2b</b>â<b>9b</b> were formed. Their
absorption bands in the vis region of the spectra are due to ÏâÏ*
electronic transitions, of an intramolecular charge-transfer nature,
from the electron-donor phenolate toward the electron-acceptor nitroarene
moiety. The frontier molecular orbitals and natural bond orbitals
were analyzed for the protonated and deprotonated forms. The calculated
geometries are in agreement with X-ray structures observed for <b>4a</b>, <b>6a</b>, and <b>8a</b>. The HOMOâLUMO
energy gaps suggest that, after their deprotonation, an increase in
the electron delocalization is observed. In the protonated compounds,
the HOMO is primarily localized over the phenol ring and the Cî»C
bridge. After deprotonation, it extends toward the entire molecule,
including the NO<sub>2</sub> groups. The solvatochromism of each dye
was studied in 28 organic solvents, and it was found that all compounds
exhibit a reversal in solvatochromism, which is interpreted in terms
of the ability of the media to stabilize their electronic ground and
excited states to different extents. The CatalaÌn multiparameter
equation is used in the interpretation of the solvatochromic data,
revealing that the most important contribution to the solute/solvent
interaction is the hydrogen-bond donor acidity of the solvent