Adsorption isotherms and thermodynamic properties of dried pumpkin fruit slices

Effects of sulphite and slice thickness on adsorption isotherms and isosteric heat of sorption of pumpkin fruit slices were investigated. Pumpkin fruits were used to obtain 4mm thick samples (P0, 4; P1, 4) and 5 mm (P0, 5; P2, 5) sulphited at 0, 1.0 and 0, 2.0 % respectively. Samples were dried at 75 ⁰C at a velocity of 1.53 m/s. The equilibrium moisture content (EMC) were generated using moisture sorption studies at 10, 20, 30 and 40 ⁰C within water activity (aw) range of 0.15 to 0.95. Sorption data was fitted with BET and GAB models. Sorption thermodynamics were determined. The moisture sorption isotherms of pumpkin slices were sigmoidal in shape (type II). BET monolayer ranged from 5.35 to 10.31 gH2O/100 g solid. The apparent surface area of sorption (So) decreased as temperature increased from 10 to 40 ⁰C. GAB monolayer ranged from 6.05 to 17.56 gH2O/100 g solid. Molar enthalpies of vaporization were highest for monolayer, followed by multilayer and pure water. The isosteric heat of sorption decreased with increase in moisture content.