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Experimental and predicted viscosities of model solutions at temperatures above the glass transition
No full textEvaluation of viscosities of amorphous phases in frozen systems by WLF kinetics and glass transition temperatures
No full textThe viscosities of concentrated solutions of glucose, fructose, sorbitol and xylitiol were measured by a falling sphere method. The measured viscosities
were compared with those predicted by WLF kinetics from glass transition temperatures.
Discrepancies between measured and predicted viscosities were found
to be within an order of magnitude of 0.3 on log E. Experimental data on
sucrose solutions obtained from literature sources were also compared with
WLF predicted values. The viscosities of the amorphous phases in frozen or
partially frozen sucrose-, glucose-, fructose-, citric acid-, dimethyl sulfoxide-,
polyvinylpyrrolidone- and glycerol-water systems were estimated by WLF
kinetics and freezing temperatures. At equal sub-freezing temperature, the
viscosities increased with the increasing of molecular weight. In addition,
viscosity changes during devitrification and recrystallization of 60-70% sucrose
solutions, which do not freeze upon cooling, were evaluated
Some thermal and physical changes in a glucose-glycine solution undergoing Maillard reaction
No full textRelazioni cinetiche e loro valutazione nei sistemi alimentari. L'esempio della reazione di Maillard
No full textStructure and Water Relations of Melanoidins Investigated by Thermal, Rheological and Microscopic Analysis
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Changes of some thermal and physical properties in model systems simulating an alcoholic fermentation
No full textHighly simplified model systems, simulating the fermentation of 25.00% sugar-water mixture into a 12.78% ethanol-water mixture, were considered in order to study their thermo-physical properties. Calorimetric data, viscosity and water activity determinations showed that important thermal and physical changes are associated with the steps of a fermentation process. Besides the increase in ethanol content, other concomitant changes are a strong increase in ethanol vapor pressure and a decrease in water activity and viscosity. DSC measurements of the models during scanning from -140C to 25C showed three peaks: peak I (exotherm) covered a temperature range from -110C to -80C and was attributed to the recrystallization of the ethanol monohydrate; peak 2 (endotherm), with peak temperature around -70C, was attributed to the melting of the alcoholic monohydrate; peak 3 (endotherm) in the higher temperature range from -30C to OC, was due to ice melting. The alcoholic monohydrate appeared only in the final simulated step of the fermentation, where only ethanol and water were present. The inhibitory effect of even small amounts of sugars on the formation of the monohydrate might be related to the increase in viscosity. This would confirm the formation of the ethanol hydrate as kinetically hindered, as it is reported in the literature
Determination of the glass transition temperatures of "solution A" and high molecular weight melanoidins and estimation of viscosities by the WLF equation: a preliminary study
No full textMaillard reaction in glucose-glycine systems studied by differential scanning calorimetry
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