The quality of a dried product is affected by the drying process
employed. Heat-sensitive materials such as food and agricultural
products must be maintained at a low temperature during drying.
The drying methods that are generally applied to agricultural
products include low-temperature hot-air drying and freezedrying.
Although low-temperature hot-air drying is a low cost
process, a long drying time is required, and rotting or oxidation
during drying are serious issues in the case of foodstuffs and sensitive
chemical components. Freeze-drying induces porosity in the
dried material, and some components of the drying medium
remain in the dried material; moreover, the cost is very high and a
long drying time is required (Kudra and Mujumdar, 2009). The
development of drying technology employing a low drying temperature
combined with a high drying rate and high energy
efficiency (low cost) is required for drying heat-sensitive materials.
Fluidized-bed drying under reduced pressure is expected to be an
appropriate drying method for such materials. Fluidized-bed drying
under reduced pressure is a lower cost technique with a
significantly shorter drying time than required for freeze-drying,
although the properties of the dried product obtained by using
the former drying method are different from those of the same
products obtained by freeze-drying (Tatemoto and Michikoshi,
2014).