In previous experiment, drying efficiency of infrared and hot air dryers was investigated. On this study, drying rate of sweet potato according to different infrared interval was performed to find the optimal interval range. Steamed sweet potato was cut to a thickness of 0.5cm, the width and length were 1.5*3cm. The condition of infrared drying was 60 to 40°C, which range of interval was adjusted 5 to 20°C. Moisture content, brix, color, and texture were estimated as quality parameters. Drying rate was increased with decreasing temperature range and soluble solid contents were increased as drying time was increased, but there was no difference after 4 hours. Hardness was resulted in highest value at small temperature range and hard texture was affected by drying time. However, there were no significant differences in L, a, b value. In conclusion, small interval range of infrared was indicated highest drying efficiency and the optimal condition of drying time was 4 to 6.

Recently, additive-free sweet potato has been commercialized as a healthier snack food. However, these products are producing by semi-dried form to extend shelf-life, hence the products also possesses hard texture during chewing. To produce crispy sweet potato snack, this study was attempted to dry the semi-dried sweet potato instantly by a hot-press (HP) process. Mashed sweet potato was reformed and semi-dried at 65°C for varying time to provide various final moisture contents. The semi-dried samples were subjected to HP at the process temperature of 175-180°C for 2 seconds. As quality parameters, moisture content, brix, color, texture and sensorial test of the products were evaluated. Based on the results, optimal quality of the product was obtained by the semi-dried sample with 15~18% moisture at which the products exhibited good crispiness with bright yellow color. When the moisture content of the sample before HP was lower than 15%, the final products were normally broken during the HP process. In addition, extreme browning appearance was generated in this condition. Conversely, the sample with more than 18% of moisture was not completely dried by HP and the final product did not possess the crispy texture, although this product showed bright yellow appearance. Consequently, this study demonstrated the potential application of HP in sweet potato processing and the best condition was greatly affected by moisture content of sample prior to HP process.