In tofu making by heat treatment, the addition of coagulant ionizes the proteins as a result of heat dissolution and the ionized proteins aggregate with the coagulant to form protein clusters. The electrical conductivity (EC) of the soya milk emulsion varies in response to the progress of gelation. By ohmic heating, the applied current and voltage directly indicate the electrical conductivity of the soya milk emulsion and then indirectly the progress of tofu gelation. In this paper, ultrasonic measurement is adopted to explore the feasibility of using EC as an indicator of tofu gelation. Experiments showed a strong correlation between EC and ultrasonic measurement in characterisation of tofu gelation.
[1] Kohyama, K., Sano, Y. and Doi, E. (1995) Rheological Characteristics and Gelation Mechanism of Tofu (Soybean Crud). Journal of Agricultural and Food Chemistry, 43, 1808-1812. http://dx.doi.org/10.1021/jf00055a011
[2] Jackson,C.-J., Dini, J.P., Lavandier, C., Rupasinghe, H.P.V., Faulkner, H., Poysa, V., Buzzell, D. and DeGrandis, S. (2002) Effects of Processing on the Content and Composition of Isoflavones during Manufacturing of Soy Beverage and Tofu. Seminars in Food Analysis, 37, 1117-1123.
[3] Ting, C.H., Kuo, F.J., Lien, C.C. and Sheng, C.T. (2009) Use of Ultrasound for Characterising the Gelation Process in Heat Induced CaSO4-2H2O Tofu Curd. Journal of Food Engineering, 93, 101-107. http://dx.doi.org/10.1016/j.jfoodeng.2009.01.015
[4] Saowapark, S., Apichartsrangkoon, A. and Bell, A.E. (2008) Viscoelastic Properties of High Pressure and Heat Induced Tofu Gels. Food Chemistry, 107, 984-989.
[5] Kuo, F.J., Lien, C.C., Huang, Y.Y., and Ting, C.H. (2011) Use of Ultrasound for Measuring Tofu Texture. Journal of Engineering in Agriculture, Environment and Food, 4, 83-89. http://dx.doi.org/10.1016/S1881-8366(11)80017-0
[6] Awad, T.S., Moharram, H.A., Shaltout, O.E., Asker, D. and Youssef, M.M. (2012) Applications of Ultrasound in Analysis, Processing and Quality Control of Food: A Review. Food Research International, 48, 410-427. http://dx.doi.org/10.1016/j.foodres.2012.05.004
[7] Vicente, A.A. (2007) Ohmic Heating as an Alternative to Con-ventional Thermal Treatment. Dissertation for PhD Degree in Chemical and Biological Engineering, Universidade do Minho Escola de Engenharia.
[8] Lien, C.C., Shen, Y.C. and Ting, C.H. (2014) Ohmic Heating for Tofu Making—A Pilot Study. Journal of Agricultural Chemistry and Environment, 3, 7-13. http://dx.doi.org/10.4236/jacen.2014.32B002
[9] Amatore, C., Berthou, M. and Héert, S. (1998) Fundamental Principles of Electrochemical Ohmic Heating of Solutions. Journal of Electroanalytical Chemistry, 457, 191-203. http://dx.doi.org/10.1016/S0022-0728(98)00306-4
[10] Stanc, J. and Zitny, R. (2010) Milk Fouling at Direct Ohmic Heating. Journal of Food Engineering, 99, 437-444. http://dx.doi.org/10.1016/j.jfoodeng.2009.11.019
[11] Ono, T., Tezuka, M., Taira, H., Igarashi, Y. and Yagasaki, K. (2000) Properties of Tofus and Soy Milks Prepared from Soybeans Having Different Subunits of Glycinin. Journal of Agricultural and Food Chemistry, 48, 1111-1117. http://dx.doi.org/10.1021/jf990560l
[12] Guo, S.T., and Ono, T. (2005) The Role of Composition and Content of Protein Particles in Soymilk on Tofu Curding by Glucono-δ-Lactone or Calcium Sulfate. Journal of Food Science, 70, C258-C262. http://dx.doi.org/10.1111/j.1365-2621.2005.tb07170.x
[13] Li, X., Toyoda, K. and Ihara, I. (2011) Coagulation Process of Soymilk Characterized by Electrical Impedance Spectroscopy. Journal of Food Engineering, 105, 563-568. http://dx.doi.org/10.1016/j.jfoodeng.2011.03.023
[14] Sastry, S.K., Sarang, S. and Knipe, L. (2008) Electrical Conductivity of Fruits and Meats during Ohmic Heating. Journal of Food Engineering, 87, 351-356. http://dx.doi.org/10.1016/j.jfoodeng.2007.12.012