Experiments and Modeling on Lyophilization of Fruits

Lyophilization or freeze-drying is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport. Freeze drying works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublime directly from the solid phase to gas. The greatly reduced water contents inhibit the action of microorganisms and enzymes that would normally spoil or degrade the substance. We used this technique to determine experimentally the reduction of the moisture content of sliced pineapples (Anana Comosus) with a specific thickness. The initial and final moisture contents are measure by the loss-on-drying (LOD) technique. Moisture removal percents are then correlated to the slice thickness and drying time. A mathematical model is proposed and used to correlate the experimental results. This model is based on the Biot number, a dimensionless number used in unsteady-state (or transient) heat transfer calculations. We proposed an alternative method utilizing MathCAD, to make this model-based prediction and compare it with others methods previously used. Furthermore, this model may help determine the value of the thermal conductivity of the sliced pineapple and other materials that can be analyzed via lyophilization if a proper estimate of the radiation heat-transfer coefficient is made a priori based only on the measured temperatures.