Determination of water content of dried fruits by drying kinetics

The aim of this work was to identify the kinetics of drying of dehydrated a gricultural products, such as high-sugar containing fruits, as well as the kinetics of a decomposition reaction of the constituents of the fruits, suc h as sugars. The knowledge of the kinetics may lead to an identification of the exact drying time of agricultural products and elimination of severe d iscrepancies from using different moisture content methodologies. The dryin g of currants at temperatures 65-97 degrees C for elongated times showed th at the weight did not reach equilibrium even after drying for several days, due to the decomposition of solids in addition to the water evaporation. F ructose was the primary source of decomposing material. Using the method of successive residuals, three simple first order of reaction equations were found appropriate models describing the dual water evaporation/decompositio n reaction phenomenon of dried fruits. By identification of the three simul taneously occurring mechanisms, an algorithm for determination of the appro priate drying time of agricultural products was proposed, according to whic h there is a separation of the effect of weight reduction due to sugar deco mposition, from the effect of weight reduction due to water evaporation. Th e proposed drying times for currants varied from 71 h at 65 degrees C to 4. 8 h at 97 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.