Effect of citric acid and blanching pre-treatments on drying and rehydration of Amasya red apples

Drying behaviour of red apples was experimentally examined in a laboratory dryer at drying temperatures of 55, 65 and 75 °C and a constant air velocity of 2.0 m/s. Two pre-treatments (blanching and 0.5% citric acid) were applied to prior to drying process. It was observed that both the drying temperature and pre-treatment affected the drying time. The shortest drying times were obtained from pre-treated samples with citric acid solution. Blanched samples have higher rehydration ratios than other samples. Five mathematical models namely, Newton, Henderson and Pabis, Page, Logarithmic and Parabolic models were evaluated in the kinetics research. The fit quality of the proposed models was evaluated by using the determination of coefficient (R2), reduced chi-square (χ2), root means square error (RMSE) and mean relative percent error (P). The Parabolic model provided the best representation of data. Effective moisture diffusivity (Deff) computed on the basis of Fick's second law. Deff value of pre-treated samples with citric acid solution was higher than the other samples.