Effect of pretreatments on drying characteristics of Thompson seedless grapes

The effect of various pretreatments on drying characteristics of Thompson seedless grapes were studied using a laboratory scale cabinet tray dryer with the controlled condition at air temperature 50°C and at air velocity of 1.2 m/s. In various pretreatments, lye treatment and potassium metabisulphite (KMS) were used with commercial dipping oil and citric acid. Variable thermal diffusivity was calculated from experimentally estimated values of thermo-physical properties at a given moisture contents. Studies of transport properties for all pretreatments were also conducted. These parameters were correlated with the corresponding moisture content in an empirical model using a non-linear regression method. Treatments with Citric acid found to be effective, thermal diffusivity significantly decreased with a decrease in the moisture content of the grapes. The pre-drying treatments had no significant effect on the thermo-physical properties of grapes.