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Abstract  

Water states and displacements can be investigated with thermogravimetry (TG) either in its classical or in the Knudsen version (where standard pans are replaced with Knudsen cells). The case of wheat flour dough is considered in various steps of bread making, namely, mixing, proofing, baking, staling. The split of DTG signals into various components (gaussian functions) support the assumption that the overall dough water is partitioned into various fractions. Few comments are devoted to water displacements during freezing.

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Polymorphous transitions in cocoa butter

A quantitative DSC study

Journal of Thermal Analysis and Calorimetry
Authors: D. Fessas, M. Signorelli, and A. Schiraldi

Summary  

Large experimental evidence was collected on polymorphous transitions of triacyl glycerols (TAG) in cocoa butter by means of DSC investigations. The cooling treatment (in conditions close to those of the industrial practice) and the annealing temperature significantly affect the overall crystal fraction and the distribution of the various polymorphs. These data allowed a quantitative, although purely phenomenological, kinetic parameterization of polymorphous transitions of cocoa butter. The evaluation of the relevant kinetic constants and their dependence on the temperature allowed prediction of the yield in every polymorph after a given thermal history. Similar evidences were attained for cocoa liquor and dark chocolate where TAG are sided by other ingredients. These results can be the basis for an industrial exploitation.</o:p>

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Abstract  

It is presented a study concerning the influence of guanidinium chloride (GuHCl) and urea on thermal stability of Bovine Pancreatic Ribonuclease A (RNAase A) at differentpH values. As expected, at increasing the denaturant concentration, the protein thermostability decreases. This is shown by a decrease of both the thermodynamic parameters, temperature and heat effect, characterising the denaturation process. In order to analyse the calorimetric curves we adopt a statistical thermodynamic approach. The individual one-dimensional DSC profiles have been expanded into another dimension by varying the GuHCl concentration, so that a heat capacity surface is defined for eachpH. By means of the ICARUS program, developed in our laboratory, we accomplish a two dimensional deconvolution of the experimental data linking the binding equilibrium to the denaturation process. This analysis provides a well founded and complete statistical thermodynamic characterisation of denaturation process of RNAase A in the presence of GuHCl and allows to calculate the thermodynamic parameters associated to the binding of denaturant molecule.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Barone, F. Catanzano, P. Del Vecchio, D. Fessas, C. Giancola, and G. Graziano

Abstract  

In this study we try to re-analyze thepH dependence of thermal stability of small globular proteins. From the thermodynamic point of view a long series of calorimetric and spectroscopic investigations has shown that the decreased stability in very acidic conditions can be ascribed to entropic effects. The same conclusion is reached, from a microscopic point of view, by assuming that a binding of protons on equal and noninteracting sites takes place as a consequence of unfolding process. By linking the conformational unfolding equilibrium to the proton binding equilibrium, a model is developed that is able to describe the dependence on thepH of the thermal denaturation processes of small globular protiens. The application of the model to hen lysozyme and T4 lysozyme correctly accounts for the experimental results.

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A new software package (THESEUS) has been assembled for the analysis of the DSC data, Concerning the thermal denaturation of biological macromolecules. The system is useful to obtain accurate physico-chemical information, bypassing the casual and systematic errors, very common in these experiments. It can also be used for handling data from other instruments and methodologies giving thermodynamic, spectroscopic or other kind of data as a function of temperature. Because many of the researches in this field are of exploratory nature and continuously new unfolding mechanisms are described or hypothesized in the current literature, we have written and assembled this powerful and flexible program of general applicability, in order to put the operator in a position to control each step of the calculation procedure and use his own experience for choosing the better way to solve unexpected problems.

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Preparation ofwheat resistant starch

Treatment of gels and DSC characterization

Journal of Thermal Analysis and Calorimetry
Authors: L. Wasserman, M. Signorelli, A. Schiraldi, V. Yuryev, G. Boggini, S. Bertini, and D. Fessas

Abstract  

A suitable thermal treatment of gels of various starch varieties was assessed to achieve the formation of resistant starch (i.e. amylose crystals). On the basis of DSC data, the yield of amylose crystals and their thermal stability did not seem correlated with the amylose content of the starch. This last parameter may not therefore be referred to as the only factor that defines a resistant starch promising starch variety.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Barone, P. Del Vecchio, D. Fessas, C. Giancola, G. Graziano, and A. Riccio

Abstract  

DSC measurements have been accomplished in aqueous solutions of bovine pancreatic ribonuclease A (RNAase A) in the presence of subsaturating amounts of 3′ cytidine monophosphate (3′ CMP) and 2′ cytidine monophosphate (2′ CMP) atpH 5.0 and 5.5. In these conditions the experimental profiles do not conform to a one-step unfolding process. It can be emphasized, as a general phenomenon, that a strong linkage between the temperature-induced protein unfolding and the ligand binding, when the ligand is less than the saturation level, causes marked distortions from a two-state transition. A purely equilibrium thermodynamic analysis gives a correct account of this behaviour and allows to simulate calorimetric curves. It is thus possible to obtain, in an indirect manner, information about the thermodynamic parameters concerning the binding process, namely the association constant and the binding enthalpy. The values ofKb and Δb H for 3′CMP and 2′CMP, so determined, are consistent with the literature data.

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