Modelling bulk density, porosity and shrinkage of quince during drying:: The effect of drying method

The effect of drying method on bulk density, substance density, porosity, and shrinkage of quinces at various moisture contents was investigated. Samples were dehydrated with four different drying methods: conventional drying in fluid bed and tray driers, infrared assisted air drying, osmotic dehydration combined with conventional air drying and freeze drying. All the properties except substance density were affected by drying method. Bulk density of freeze dried materials decreased with decreasing moisture content while for all other dehydration processes, bulk density and porosity increased with decreasing moisture content. Freeze dried materials developed the highest porosity whereas the lowest was obtained using osmotic dehydration. Freeze dried samples had limited shrinkage. Simple mathematical models were used to correlate the above properties with the material moisture content. For the substance density, a single non-linear equation gave accurate predictions irrespective of drying methods. Although differences in shrinkage with the drying method were detected, the same model as a function of moisture content could be used for all drying methods but with different coefficients. (c) 2007 Elsevier Ltd. All rights reserved.