Frozen tubers were washed and sliced into 5-mm thick pieces and blanched in boiling water. Then, the slices were dried for 5 h at either 60 or 70 °C in a drying oven with aeration (DSR-133, Isuzu, Niigata, Japan). After cooling, chips were milled in a grinder (model 650 D; Iwatani Sangyo, Osaka, Japan) to produce a fine powder with particles less than 1.0 mm in diameter.