Effect of pretreatments on solar dehydration of different varieties of apple (Malus domestica)

In this study, four different apple varieties were dried in a solar tunnel dryer using four different methods. Apple slices were immersed in a solution consisting of 0.5% ascorbic acid, 0.5% sodium metabisulphite, and 0.5% citric acid for 3 min. Constant measurements were performed in various parts of the dryer for drying air temperature, solar irradiation, air velocity, and relative humidity during drying. The change in the mass of apples was measured on a daily basis. Furthermore, ten mathematical models were used to study the drying process, which were Newton, Page, Henderson and Pabis, logarithmic, diffusion, two-term, two-term exponential, Midilli, Alibas, and logistic equation. Then, these models were compared in terms of their performance levels based on correlation coefficient (R2), chi-square value (χ2), and root mean square error (RMSE) between moisture ratios (MR) that were observed and predicted. Furthermore, we observed that the Alibas model and the two-term model revealed the ratio of drying in a satisfactory way for all drying methods.