Effect of Pretreatment Solution on Drying and Color Characteristics of Seedless Grapes

Drying and color characteristics of 'Sultana' seedless grapes were investigated in a cabinet dryer under different air drying temperatures (55, 65, and $75^{\circ}C$) and constant air velocity (2 m/s). Results indicated that the moisture content and drying rate were influenced by the pre-treatment solution and dying air temperature. The increase in drying air temperature resulted in a decrease in drying time. The drying data were fitted to the different mathematical models such as Lewis, Henderson and Pabis, and Parabolic models. The Parabolic model was found as the best model having the highest determination of coefficient ($R^2$) and lowest reduced chi-square ($X^2$) and root means square error (RMSE) values. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick's second law, and varied from 1.048 to $6.919{\times}10^{-10}m^2/s$ over the temperature range. The values of activation energy varied from 47.34 to 57.25 kJ/mol.