Abstract
A mathematical model has been developed to determine the thermal conductivity and permeability for the dried layer of food samples undergoing sublimation dehydration. An automatic measurement system has developed for the data acquisition as well as determination of these transport properties by applying the drying data to the model. The values of transport property were presented for several food materials indicating the critical processing factors for the drying rate of each material. Some structural models were developed for predicting the permeability of water vapor flowing through the dried layer. In a cellular food model, the resistance of a cell membrane to the molecular transfer of water vapor was determined from both value of permeability and microscopic observation of the dried layer. The model was considered to play an important role in predicting optimum heating program for the surface temperature of materials. A micro-slicer image processing system (MSIPS) has been developed for measuring the three-dimensional (3-D) structure and distribution of ice crystals formed in frozen food materials. The system has functions to reconstruct the 3-D image based on the image data of exposed cross sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1 μm and display the internal structure as well as an arbitrary cross section of the sample choosing observation angles. The effects of freezing conditions on the morphology and distribution of ice crystals were demonstrated quantitatively from the observations of raw beef and model solution systems stained by fluorescent indicator. A technical cooperation project has been carried out between university and industries for optimizing the design and operation of industrial freeze-dryer to produce egg soups. In the project a new heating program was developed to shorten the drying time for the batch-type freeze dryers in industrial scale.
