THERMAL DEHYDRATION OF SOME FOOD-PRODUCTS AND KINETIC-PARAMETERS OF THIS PROCESS

The derivatographic method was used for the quantitative determination of water content in selected flour and fat products. Weight losses and thermal effects taking place in the examined products under the influence of heat were read from the obtained derivatograms. Percentage water contents were calculated from TG curves within the range from 5.6% (rice cereal) to 16.0% (potato flour), based on the diagrams recorded within the temperature range 20-1000 degrees C, narrower temperature ranges of dehydration and decomposition processes were determined. In addition, the number of stages of thermal decomposition of the examined products was determined and appropriate kinetic parameters were calculated. The values of the activation energy (E(a)) of dehydration, frequency factor (A) and reaction order (n) were calculated from TG, DTG and T curves within the temperature range from 20 to 90 degrees C. For potato flour the following values were obtained: E(a)=27.825 kJ/mol, A =1.05x10(5) 1/s and n=2.97x10(-3), for the remaining samples under investigation the activation energy E,is several dozen kJ/mol and the reaction order n is very low. The obtained data show that the dehydration process under study is mainly associated with evaporation of water adsorbed on products and to less extent with chemical processes.