Textural properties of firm tofu as affected by calcium coagulants

This research was aimed to evaluate the effects of calcium coagulants (10-40 mmol/L in soymilk) including calcium chloride, calcium lactate, and calcium gluconate on the textural properties (microstructures, large deformation behaviors under uniaxial compression) and some relevant chemical properties of firm tofu. The results showed that the stress-strain behaviors of tofu could be modelled very well with the first order Ogden model (R-2 = 0.992-0.998), and the effects of three coagulants on the textural properties of tofu followed similar trends. Firstly, the failure strain (0.66-0.73, indicating deformability) of tofu was not significantly affected by the type (P = 0.056) and the concentration (P = 0.399) of calcium added. In addition, as the calcium level increased from 10 to 30 mmol/L, the failure stress (from 5.27-5.38 kPa to 17.09-19.73 kPa) and rigidity (from 3.18-3.36 kPa to 10.16-12.96 kPa) of tofu continuously increased, but a further increase of calcium level to 40 mmol/L led to decreases in both failure stress (14.17-15.51 kPa) and rigidity (9.37-11.39 kPa). Furthermore, the effects of calcium levels on the strength of tofu were consistent with that on the microstructure features, moisture levels, and water holding capacity of tofu. Tofu prepared with all three coagulants were good sources of calcium (123-311 mg/100 g tofu), which may be used to meet consumer needs for diversified products of calcium-rich tofu.