Estimation of Electrical Conductivity of Soymilk with Varied TSS Levels using Ohmic Heating

Experiments were conducted to study the effects of electric field strengths (EFS) and the concentrations of total soluble solids (TSS) on the electrical conductivity, pH and ohmic heating behaviour of soymilk. Soymilk of different TSS (6, 7, 8, 9 and 10°Brix) were ohmically heated by using three different electric field strengths (10, 11.5 and 13 V/cm). For determining the effect of time and temperature on electrical conductivity, temperature, current and voltage were recorded at regular intervals. It was observed that with increasing of EFS and TSS, time required to reach the target temperature was decreasing. Uniformity of ohmically heated sample was also checked and found that at all TSS levels, soymilk was uniformly heated. The minimum time required to reach target temperature is 4 min when TSS is 10 and EFS is 13 V/cm and the maximum time required to reach target temperature is 15 min when TSS is 6 and EFS is 10 V/cm. Also, the electrical conductivity-temperature relationships were observed to be linear below 95°C for all electric field strengths applied. The observed ohmic heating behaviour of soymilk corresponded well with their electrical conductivity values. There was a slight change in pH of soymilk at varied levels of total soluble solids and applied electric field strengths. The range of pH of soymilk varied from 6.5 to 7.23 while the pH of soymilk without ohmic heating treatment was 7. This indicates that the pH of soymilk after ohmic treatment was decreasing.