Investigating the drying parameters of Fijou fruit in a freeze dryer

Freeze drying is one of the best methods for the removal of water in temperature sensitive agricultural products. In the present study was investigated the process of drying the Fijou fruit in a freeze dryer under the influence of different pretreatments and were calculated the moisture diffusion coefficients (mass transfer coefficient) by using of Dincer and Dost models and Fick’s model, drying rate constant, convective mass transfer coefficient, specific energy consumption and specific moisture extraction ratio. Various pre-treatments applied to the samples are ascorbic acid (with 1% concentration and 1, 2 and 3 min), microwave (with 90 W for 10 min, 180 W for 5 min and 360 W for 2.5 min), blanching with hot water and steam (with 1, 2 and 3 min), potassium carbonate (with 2.5% concentration and 1, 2 and 3 min), osmotic (with 45% sucrose concentration and 10, 20 and 30 min), and ultrasound (with 10, 20 and 30 min). The highest drying rate constant and convective mass coefficient were obtained in microwave pre-treatment to 0.0073 (s-1) and 2.900×10-5 (m2/s), respectively. The range of moisture diffusion coefficients was variable in Fick’s model from 0.7404×10-8 to 1.3996×10-8 (m2/s) and for Dincer and Dost model from 4.5318×10-7 to 9.2149×10-7 (m2/s). The highest and lowest specific energy requirements were 47.23 and 23.61 kWh/kg in osmotic and microwave pre-treatment, respectively. Also the highest and lowest specific moisture extraction ratio were 0.0423 and 0.0212 kg/kWh in microwave and osmotic pre-treatment, respectively.