Impact of citric acid on the drying characteristics of kiwifruit slices

Kiwifruit slices were dried at four different air drying temperatures of 50, 55, 60 and 70 degrees C and at 2 m s(-1) air velocity by using a cabinet dryer in this study. The drying, rehydration and colour characteristics were significantly influenced by pretreatment and drying temperature. The drying time decreased with the increase in drying temperature. The drying rate curves showed that the entire drying process took place in the falling rate period. Five well-known thin-layer models were evaluated for moisture ratios using nonlinear regression analysis. The results of regression analysis indicated that the Midilli & Kucuk model the best to describe the drying behaviour with the lowest chi(2) and RMSE values, and highest R-2 value. The effective moisture diffusivity of the dried kiwifruit slices was calculated with Fick's diffusion model, in which their values varied from 4.19x10(-10) to 6.99x10(-10) m(2) s(-1) over the mentioned temperature range. The dependence of effective diffusivity coefficient on temperature was expressed by an Arrhenius type equation. The calculated values of the activation energy of moisture diffusion were 10.37 and 19.08 kJ mol(-1) for citric acid and control samples, respectively.