Application of two-stage ohmic heating to tofu processing

Thermal denaturation of soybean proteins is a prerequisite for tofu gel formation. Soymilk is conventionally heated with a one-stage steam heating. Two-stage ohmic heating was applied to soymilk in this study. Optimizing the two-stage heating condition for making filled-tofu and the effect of the two-stage heating on soft-tofu were investigated. Our results show that the combination of 70 °C for 10 min and 100 °C for 5 min was the best condition of the two-stage heating for preparing filled-tofu. Compared to the one-stage heating, the two-stage heating increased the soft-tofu's apparent breaking strength by 12.2% and apparent Young's modulus by 16.2%, reduced the syneresis rate by 21.8%, and increased the yield and the solid recovery by 4.5% and 5.4%, respectively. Two-stage ohmic heating is a potential method for heating soymilk in tofu manufactures.