Effect of drying temperature on the rheological characteristics of dried seedless grapes

The grape is the second most widely cultivated fruit in the world after the orange; it is of great commercial interest. The Sultana variety is grown in large quantities in Tunisia and in the Mediterranean countries. The product is easily deformable; the thermo physical properties depend on the water content. By using the static gravimetric method, the sorption isotherms for sultana grapes were determined. By using the experimental drying kinetics and adopting a numerical procedure for solving the Fick's diffusion equation, the mass diffusion coefficient was determined as a function of the temperature and water content of the product. Using the constraint relaxation test, with a texture analysis machine, the mechanical properties of grains of dried grapes were measured. The relaxation function and the Young's modulus were then deduced. These characteristics are key parameters in running simulation models addressing the thermo hydro mechanical behavior and allow the appropriate process and drying time to be subsequently determined in order to avoid unnecessary energy consumption. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.