Modelling shrinkage and porosity during vacuum dehydration
(EN)
Krokida, MK
(EN)
Maroulis, ZB
(EN)
Zogzas, NP
(EN)
Apparent density, true density, specific volume and internal porosity were investigated during vacuum dehydration of banana, apple, carrot and potato, at various moisture contents and pressures. The pressure was found to effect significantly the apparent density and porosity of the materials examined, while for the true density, this effect was practically negligible. In all four materials the development of porosity was favoured by the decrease of pressure. At the lowest pressure used (30 mbars) banana and apple developed the highest porosity values (similar to 75%), followed by those of carrot (similar to 50%) and potato (similar to 25%). A simple mathematical model was proposed to predict the above properties as functions of material moisture content and pressure. The parameters incorporated into the model were: the enclosed water density, the dry solids density, the apparent density of the dry material, and a transformed volume-shrinkage coefficient. Among these parameters, only the apparent density of the dry material was found to be strongly affected by the pressure and a suitable exponential equation was proposed to express this influence. The proposed model was fitted to the experimental data satisfactorily, and the required parameters were estimated through a regression analysis procedure.
(EN)
