Sweet potato chip making process
The process procedure of the sweet potato chips was modified according to Chen (1987) and Chen and Chiang (1985). Washed sweet potatoes were cut into 1 mm thick slices with a conventional food slicing machine. To prevent discoloration of sliced sweet potatoes during dehydration, the slices were soaked in 0.5% sodium bisulfite (NaHSO3) solution for 30 min, and then soaked in running water for 1 h. The prepared slices were dried in a tunnel drier (Si Dien Co., Taichung, Taiwan) at 80 °C for 1 h according to the commercial preparation procedure. The conditions of the tunnel drier were: total length 15 m, conveyor speed 0.25 m/min, air humidity less than 40% relative humidity, air speed 2.7 m/s, and water content of the final product less than 5%. The slices, without a NaHSO3 solution soaking treatment, were freeze-dried. All processing treatments were done in triplicate.