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A heat and mass transfer model was proposed for the superheated steam drying, focusing on phenomena which occur during the initial stage of drying, i.e., condensation of superheated steam on material surfaces and subsequent shift from condensation to evaporation leading to the beginning of the actual drying (Reverse Process Model). Next, drying equations considering the reverse process were formulated for a shrinking/swelling infinite flat plate to calculate moisture content and temperature distributions in a material, changes in mass of a material with time, and a characteristic drying curve. Then, the influence of the initial thickness of a material and the heat transfer coefficient were investigated. In addition, calculation results were compared with experimental ones with regard to the change in mass of material with time and 1425 ORDER REPRINTS 1426 IYOTA ET AL.the characteristic drying curve, and good conformance was obtained for the initial stage of drying.

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The effect of the initial moisture content (X(0)) of amaranth seeds on expansion volume after popping was examined in hot air and superheated steam (SHS), using a fluidized bed system (FBS). The moisturized seeds were prepared under various vapor pressures due to various saturated salt solutions. In hot air, the maximum expansion volume was shown by seeds having X(0) of 0.16 at 260 degrees C for 15 sec, reaching 8.7-fold of the pre-popped seeds. Heating by SHS decreased the volume slightly. Thus, popping of amaranth seeds is influenced not only by the moisture content of the seeds, but also by moisture in the heat media.

Amaranth seeds can be popped by heating. The traditional method of popping in a skillet is simple, but it is difficult to control the heating time and temperature. To overcome these disadvantages, we developed a fluidized bed continuous processing system based on hot air heating for producing popped amaranth seeds in bulk. Using this system, we evaluated the effects of heat treatment at 260 °C for 15 s on the contents of B-group vitamins and essential and trace elements in amaranth seeds. The results showed that the treatment did not affect the content of B-group vitamins, and the recovery for essential and trace elements was 97-196%. This popping system is useful for processing amaranth seeds in terms of the product quality and nutrition.