Thermal effect of carbohydrate dissolution in aqueous-organic media

This work is devoted to the theoretical substantiation of connection of temperature dependence of the solubility of carbohydrates with thermal effect of their dissolution in the water-containing organic solvents that is of great importance for optimization of the technology of their extraction from plant raw materials and further purification and separation by recrystallization. The dependence of the solubility of fructose, glucose, sucrose, and maltose in aqueous isopropanol and acetone at temperatures of 298 К (25 ^оС) and 275 К (2 ^оС) from water content in a solvent was studied. The constancy of the mechanism of solubility of carbohydrates in these environments in the given temperature interval is experimentally proved. For the first time based on the equation of Vant-Goff the logical connection of temperature dependence of solubility and thermal effect of solubility of carbohydrates is strictly grounded. The values of the thermal effect that are determined by the experimental data allow calculating the solubility of the studied carbohydrates in the aqueous–organic solvent of different concentration in the temperature range from 2^оС to 25 ^оС.  It has been established that the main contribution to the thermal effect of dissolving carbohydrates is the hydration process. Solvation by molecules of organic solvent practically does not change the value of the specified thermal effect. The significance of determined temperature dependences of the solubility of fructose, glucose and maltose is shown to optimize the technological conditions for the separation of glucose-fructose and glucose-maltose syrups by selective crystallization. 

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