vacuum drying characteristics of some vegetables

in this research the drying of four kinds of vegetables was investigated in a vacuum dryer. the effect of temperature on drying rate of samples at various temperatures (30, 35 and 45 °c) was studied. six thin-layer drying models were fitted to drying data and suitable model was selected from them. then effective moisture diffusivity and activation energy of samples were calculated. the diffusion approximation model gave excellent fit forfenugreek and mint leaves and vegetative parts of leek and the page model was considered adequateto describe the thin-layer drying behavior of parsley leaves. the effective diffusivity values changed from 2.92×10-10 to 9.81×10-10, 1.77×10-10 to 5.99×10-10, 9.3×10-11 to 1.7×10-10 and 1.27×10-9 to 3.4×10-9 for fenugreek, mint and parsley leaves and vegetative parts of leek, respectively. an arrhenius type of equation was used to evaluate the effect of temperature on the effective diffusivity and the activation energy values was found 66.36, 66.34, 32.27 and 51.16 kj/ mol for fenugreek, mint and parsley leaves and vegetative parts of leek, respectively.