Effect of soaking treatment in hot water on thermal and electrical properties of tubers and Japanese Radish

Abstract

Taro, potato, yam and Japanese radish samples were cut into cylindrical shapes (diameter=29mm; length= 40mm (taro and potato), 120mm (yam and Japanese radish), and were used to examine changes in gelatinization enthalpy, electrical impedance, moisture content and thermal conductivity during hot water treatment (100). The gelatinization enthalpy was measured with a differential scanning calorimeter (DSC). The onset temperatures of gelatinization of taro, potato and yam were 83. 2±0. 1, 62. 7±0. 4, 56. 2±1.0 respectively. To reach these temperatures, hot water immersion for 6min on taro and 3-4min on potato and yam were required. The circular arcs, which are the vector profiles of the electrical impedance and are known as Cole-Cole plots, disappeared after 5min from the beginning of soaking in hot water in all samples. It is supposed that the cell membrane of the sample was disrupted at the time. The transient heat probe method using twin probe was used for the determination of the thermal conductivity. Thermal conductivity of Japanese radish increased at first, and then kept constant. That of taro, potato and yam increased and decreased with the changes in moisture content at the earlier stage of the hot water treatment.