Effective Parameters in Hot Air Drying Process on Qualitative Properties of Grapefruit (Citrus paradise L.) and Selection of a Suitable Mathematical Thin-Layer Drying Model

The thin-layer drying behavior of Grapefruit slices is experimentally investigated in a convective dryer and the mathematical modeling by using thin-layer drying models is performed. In the present study, tests were conducted using three air temperatures (45, 55, 65 °C), two hot air velocities (1 and 2 ms-1), two-bed depth (1 and 2 cm) and three replications for each treatment. Based on the results, the best drying time was measured at 65 °C, hot air velocity of 2 ms-1 and bed depth of 1cm for 73 min. The calculated maximum value of effective moisture diffusivity coefficient was 7.44 × 10-8 m2s-1, and the minimum activation energy was 16.09 kJ.mol-1, at 65 °C, hot air velocity of 2 ms-1 and bed depth of 1cm. In the same vein, the maximum value of vitamin C (32.03 mg. (100 g)-1) was obtained at 55 °C, hot air velocity of 2 ms-1 and bed depth of 1cm. In addition, the page equation was found to give better predictions than the others. It is worth to note that the minimum value of change color (23.76) was measured at 45 °C, hot air velocity of 2 ms-1 and bed depth of 1cm.