Drying kinetics, colour, total phenolic content and antioxidant capacity properties of kiwi dried by different methods

Abstract

This study analysed the convective (60, 70 and 80 degrees C), microwave (120 and 350 W) and freeze drying methods in terms of their effects on the drying characteristics, colour, total phenolic content (TPC) and antioxidant capacity of kiwi slices. Nine different mathematical models were applied to experimental data to achieve the most accurate calculation for drying curves. The Midilli et al. and Wang and Singh models proved to be the most suitable at explaining the drying kinetics of kiwi samples as compared to other models according to the statistical tests. Each drying method was significantly affected by colour parameters (L*, a*, b*, C, alpha and Delta E). The dried samples exhibited respectively 5-49 % and 10-47 % less TPC and antioxidant capacity compared to the fresh sample. According to the correlation analysis conducted between TPC and antioxidant capacity for kiwi slices, there is a positive correlation (R (2) = 0.7796). Microwave dried samples at 120 W particularly had the lowest TPC and antioxidant capacity. Freeze drying method yielded the closest values with respect to colour values, total phenol content and antioxidant capacity to those of fresh samples when compared to the other methods.