Drying model of sliced apple and effect of vacuum impregnation on its physiochemical properties

Abstract

This study presents the effects of convective (50 and 75 degrees C), microwave (90 and 160 W) and combined microwave-convective (90 W-50 degrees C, 90 W-75 degrees C, 160 W-50 degrees C and 160 W-75 degrees C) drying methods and vacuum impregnation pretreatment on the drying characteristics, titratable acidity, ash, total sugar, color, total phenolic content and antioxidant activity of sliced apple samples. The experiments were conducted with sliced apple samples, with and without vacuum impregnation pretreatment. To select the best thin-layer drying models for the drying treatments, nine mathematical models were fitted to the experimental data and based on the statistical tests used for evaluation, the Midilli et al. model was found to be the best fitted model to describe the drying behaviors of the apple samples. While L* and b* values decreased, a* value increased in dried sliced apple samples compared with fresh samples. In addition, the highest total sugar and antioxidant activity values were obtained when the samples were dried using 90 W microwave power and vacuum impregnation pretreatment.