Air-drying characteristics of tomatoes

The drying characteristics of tomatoes were investigated at 55, 60, 65 and 70 degrees C with air flow rate of 1.5 m/s. Prior to drying, tomatoes were subjected to dipping in alkaline ethyl oleate solution (2% ethyl oleate + 4% potassium carbonate). Also, drying of raw tomatoes was taken as a control. During the experiments, tomatoes were dried to the final moisture content of 11% from 94.5% (w.b.) It has been found that pre-treatment and air temperature affect the course and rate of drying. The increase in the air temperature in the range 55-70 degrees C markedly increased the drying rate of tomatoes. The experimental data were fitted to two drying models: Henderson and Pabis, and Page models. The models were compared using the coefficient of determination and reduced chi-square. The Page model best described the drying curve of tomatoes. A diffusion model was used to describe the moisture transfer and the effective diffusivity at each temperature was determined. The effective diffusivity of pre-treated and untreated varied between 5.65-7.53 x 10(-10) and 3.91-6.65 x 10(-10) m(2)/s, respectively. The temperature dependence of the diffusivity coefficient was also described by the Arrhenius type relationship. The activation energy of tomatoes was in the range of 17.40-32.94 kJ/mol. (c) 2006 Elsevier Ltd. All rights reserved.