The aim of this study is to explore the
relationship between temperature and electrical conductivity of soya milk under
ohmic heating in tofu making. The soya milk of 10 Brix was heated to a steady temperature
of 90?C. The applied voltage was increased and the temperature rising rate was investigated
for adequate heating profiles in tofu making. Experimental results showed that
the electrical conductivity of soya milk is proportional to the heating time.
The temperature rising rate was increased from 1.46?C to 3.82?C/min as a result
of increased voltage. Hence ohmic heating could be an efficient, convenient
heating measure in tofu making.
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.