Effect of drying method on the adsorption isotherms and isosteric heat of passion fruit pulp powder

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Water adsorption isotherms and isosteric sorption heat of spray-dried and freeze-dried dehydrated passion fruit pulp with additives and skimmed milk

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Changes of density, thermal conductivity, thermal diffusivity, and specific heat of plums during drying

The thermal properties of plums (Prunus domestica) and prunes were investigated in the moisture content of 14.2-80.4% (wet basis) near room temperature (approximately 28 degrees C). The apparent density of the fruits increased from 1042.9 to 1460.0 kg/m(3), and the bulk density increased from 706.6 to 897.5 kg/m(3) as the plums were dried, following classical empirical models as a function of moisture content. It was found that specific heat, effective thermal diffusivity, and effective thermal conductivity of the prunes increased with the moisture content of the samples, which can be represented by using different empirical models.

The role of hydration on the mechanism of allosteric regulation: In situ measurements of the oxygen-linked kinetics of water binding to hemoglobin

We report here the first direct measurements of changes in protein hydration triggered by a functional binding. This task is achieved by weighing hemoglobin (Hb) and myoglobin films exposed to an atmosphere of 98%, relative humidity during oxygenation. The binding of the first oxygen molecules to Hb tetramer triggers a change in protein conformation, which increases binding affinity to the remaining empty sites giving rise to the appearance of cooperative phenomena. Although crystallographic data have evidenced that this structural change increases the protein water-accessible surface area, isobaric osmotic stress experiments in aqueous cosolutions have shown that water binding is linked to Hb oxygenation. Now we show that the differential hydration between fully oxygenated and fully deoxygenated states of these proteins, determined by weighing protein films with a quartz crystal microbalance, agree with the ones determined by osmotic stress in aqueous cosolutions, from the linkage between protein oxygen affinity and water activity. The agreements prove that the changes in water activity brought about by adding osmolytes to the buffer solution shift biochemical equilibrium in proportion to the number of water molecules associated with the reaction. The concomitant kinetics of oxygen and of water binding to Hb have been also determined. The data show that the binding of water molecules to the extra protein surface exposed on the transition from the low-affinity T to the high-affinity R conformations of hemoglobin is the rate-limiting step of Hb cooperative reaction. This evidences that water binding is a crucial step on the allosteric mechanism regulating cooperative interactions, and suggests the possibility that environmental water activity might be engaged in the kinetic control of some important reactions in vivo.

Effect of drying method on the sorption isotherms and isosteric heat of persimmon pulp powder

Moisture equilibrium data of persimmon pulp powders with 50% maltodextrin (dry basis) obtained with different drying methods were determined at 20, 30, 40 and 50 degrees C. The spray-dryer gave a dry product with a higher adsorption capacity than the other methods. The vacuum- and freeze-dried products had the same adsorption capacity. The highest isosteric heat of sorption was observed for powders produced by spray-drying. The isokinetic temperature (T(B)) calculated for persimmon pulp powder obtained by vacuum-, spray- and freeze-drying were 541.4 K, 616.3 K, 513.2 K, respectively. The sorption process was spontaneous and enthalpy controlled.

Magnetic field dependence of the magnetic susceptibility and the specific heat of the doped plasticized polyaniline (PANI-DB3EPSA)0.5

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of temperature and of the addition of accelerating and retarding agents on the kinetics of hydration of tricalcium silicate

The formation of calcium silicate hydrates (C-S-H) during the hydration of tricalcium silicate (C3S) in pure water and in water solutions containing 1% CaCl2 (accelerator) and 0.01% saccharose (retarder) was studied by small-angle X-ray scattering (SAXS). SAXS measurements were performed under isothermal conditions within the temperature range 25 °C T < 52 °C. The experimental results indicate that the time variation of the mass fraction of the C-S-H product phase, α(f), can be fitted, under all conditions of paste setting, by Avrami equation, α(t) = 1 -exp(-(kt)′), k being a rate parameter and n an exponent depending on the characteristics of the transformation. The parameter n is approximately equal to 2 for hydration of C^S in pure water. Depending on temperature, n varies from 2 to 2.65 for hydration in the presence of CaC^ and saccharose. The value n = 2 is theoretically expected for lateral growth of thin C-S-H plates of constant thickness. The time dependence of SAXS intensity indicates that the transformed phase (C-S-H) consists of colloidal particles in early stages of hydration, evolving by two-dimensional growth toward a disordered lamellar structure composed of very thin plates. The activation energy ΔE for the growth of C-S-H phase was determined from the time dependence of X-ray scattering intensity. These data were obtained by in situ measurements at different temperatures of hydration. The values of ΔE are 37.7, 49.4, and 44.3 kJ/mol for hydration in pure water and in water solutions containing CaCl2 and saccharose, respectively. © 2000 American Chemical Society.

Molecular properties of the PCO radical: heat of formation and the isomerization pathways

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparison of the Effects of Hydration with Water or Isotonic Solution on the Recovery of Cardiac Autonomic Modulation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The use of extruded feed in fish food

In our country, the intensive culture of fish has been making progress due to the availability of extruded rations, which are characterized by the way they have been formulated to assist the nutritional demands of the tropical species and for facilitating a better practice of alimentary handling. This process checks the extruded product density and the desirable physical/chemical aspects to a diet that should be handled in the water, the critical factor of this activity. It is important to emphasize that this product stays to the surface of the water, facilitates the consumption control and the observation of the general aspects of the school of fish, as well as guaranteeing that no deterioration of the physical/chemical characteristics of the water occurs. The floating characteristic of the extruded ration is preferable for farmers because most of the tropical species feed at the surface of the water. In some cases, in the function of the alimentary habit, the thermal conditions of the water and the handling system produce granules with different densities. This is due to the humidity and the applied cooking heat, which modifies the time of hydration, and consequently the ability to float. To establish the physical presentation idea for a ration for tropical fishes, it is necessary that the pellets come in sizes, textures, humidities and densities in order to allow for the different phases of the lives of the fishes. This ration should be the result of characteristics of the species, such as the anatomophysiologics particularities, alimentary habits, digestive capacity and alimentary behavior. Only in this way is it possible to offer to those fishes a ration whose nutritious value and physical presentation facilitate the best biological and economic answers.Those aspects need to be reviewed because the tropical species that are cultivated in our country present selective behavior in relation to the size of the pellet. Generally, this has access to the digestive system without waste; the digestibility, therefore, is dependent upon the size of the particles and the physical aspects of the pellets. They should still consider that those granules could be less abrasive and softer. The extruded rations available in the national market present a qualitative reference to its proteic level, whose consequence allows us to infer that those are overestimated for the final phase of those fishes. Thus, the final cost of production is made unfeasible. In this point of view of the development of the national fish culture, and the growing adoption of the intensive system of production, it can link that such progress is a function of the availability of the rations in the extruded form. Although this technique of processing of rations has revolutionized the market in such a way that has been seen as preferable for farmers, some feel that there is a lack of products best suited for the initial phases of fingerlings production.

Water regulation of actinomycin-D binding to DNA: the interplay among drug affinity, DNA long-range conformation, and hydration

Actiaomycin-D (actD) binds to natural DNA at two different classes of binding sites, weak and strong. The affinity for these sites is highly dependent on DNA se(sequence and solution conditions, and the interaction appears to be purely entropic driven Although the entropic character of this reaction has been attributed to the release of water molecules upon drug to DNA complex formation, the mechanism by which hydration regulates actD binding and discrimination between different classes of binding sites on natural DNA is still unknown. In this work, we investigate the role of hydration on this reaction using the osmotic stress method. We skew that the decrease of solution water activity, due to the addition of sucrose, glycerol ethylene glycol, and betaine, favors drug binding to the strong binding sites on DNA by increasing both the apparent binding affinity Delta G, and the number of DNA base pairs apparently occupied by the bound drug n(bp/actD). These binding parameters vary linearly with the logarithm of the molar fraction of water in solution log(X-w), which indicates the contribution of water binding to the energetic of the reaction. It is demonstrated that the hydration change measured upon binding increases proportionally to the apparent size of the binding site n(bp/uctD). This indicates that n(bp/actD) measured from the Scatchard plod is a measure of the size of the DNA molecule changing conformation due to ligand binding. We also find that the contribution of DNA deformation, gauged by n(bp/act) to the total free energy of binding Delta G, is given by Delta G = Delta G(local) + n(bp/actD) x delta G(DNA), where Delta G(local), = -8020 +/- 51 cal/mol of actD bound and delta G(DNa) = -24.1 +/- 1.7cal/mol of base pair at 25 degrees C. We interpret Delta G(local), as the energetic contribution due to the direct interactions of actD with the actual tetranucleotide binding site, and it n(bp/actB) X delta G(DNA) as that due to change inconformation, induced by binding, of it n(bp/actD) DNA base pairs flanking the local site. This interpretation is supported by the agreement found between the value of delta G(DNA) and the torsional free energy change measured independently. We conclude suggesting an allosteric model for ligand binding to DNA, such that the increase in binding affinity is achieved by increasing the relaxation of the unfavorable free energy of binding storage at the local site through a larger number of DNA base pairs. The new aspect on this model is that the size of the complex is not fixed but determined by solutions conditions, such as water activity, which modulate the energetic barrier to change helix conformation. These results may suggest that long-range allosteric transitions of duplex DNA are involved in the inhibition of RNA synthesis by actD, and more generally, in the regulation of transcription. (C) 2000 John Wiley & Sons, Inc.

Comparative study of resistance to heat in two species of leaf-cutting ants

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Thermal and Rheological Properties of a Family of Botryosphaerans Produced by Botryosphaeria rhodina MAMB-05

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dynamics of meso and thermo citrate synthases with implicit solvation

The dynamics of hydration of meso and thermo citrate synthases has been investigated using the EEF1 methodology implemented with the CHARNM program. The native enzymes are composed of two identical subunits, each divided into a small and large domain. The dynamics behavior of both enzymes at 30 degrees C and 60 degrees C has been compared. The results of simulations show that during the hydration process, each subunit follows a different pathway of hydration, in spite of the identical sequence. The hydrated structures were compared with the crystalline structure, and the root mean square deviation (RMSD) of each residue along the trajectory was calculated. The regions with larger and smaller mobility were identified. In particular, helices belonging to the small domain are more mobile than those of the large domain. In contrast, the residues that constitute the active site show a much lower displacement compared with the crystalline structure. Hydration free energy calculations point out that Thermoplasma acidophilum citrate synthase (TCS) is more stable than chicken citrate synthase (CCS), at high temperatures. Such result has been ascribed to the higher number of superficial charges in the thermophilic homologue, which stabilizes the enzyme, while the mesophilic homologue denatures. These results are in accord with the experimental found that TCS keeps activity at temperatures farther apart from the catalysis regular temperature than the CCS. (c) 2005 Wiley Periodicals, Inc.