Thin Layer Drying Characteristics of Tomato Slices in A Hot Air Dryer

Abstract

The drying process of tomato slices were studied using a hot air dryer under five different levels of air temperature ranging from 50 to 70°C, at constant thickness of 5 ±0.2 mm, and a constant drying air flow rate of 0.07 m/sec. Tomato slices were sprayed before drying with 5% sodium chloride and left for 2 h to facilitate the release of moisture and preserve tomatoes during drying. Both the effective moisture diffusivity and activation energy were calculated. To find the best model for describing the drying curves, eight different thin-layer drying models were tested. The quality of dried tomato slices was assessed by estimating lycopene and ascorbic acid content. The results showed that the drying process of tomato slices took place during the falling rate period at all levels of temperature. Moisture content (MC) of tomato slices reduced from 751.79 %(d.b.) to 10% ±0.6 (d.b.) during a period of time ranging from 170 to 310minutes. The average values of effective moisture diffusivity varied from 9.9801×10 to 1.8871×10 ms and the activation energy was found to be 32.94 kJ.mol. The statistical analysis of fit tests revealed that Diamante et al. model provided a satisfactory fit for the experimental data, and followed by Page model. Lycopene content in dried tomato slices is higher than that of fresh tomatoes. While ascorbic acid content decreased by increasing air temperature.