Dynamic Rheological Properties of Soymilk during the Coagulation Process
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Abstract:
To achieve normalization and standardization of tofu production, the dynamic rheological properties of soymilk and related kinetics during the coagulation process were investigated. Dynamic time scanning was performed at 75 ℃, 80 ℃, and 85 ℃; coagulation of soymilk consisted of two first-order reactions and matched a consecutive first-order reaction model. The rate constant in the first stage was much higher than that in the second stage and the calculated activation energy values from elastic modulus and viscous modulus were 19.19 × 101 kJ/mol and 8.67 × 101 kJ/mol, respectively. Tofu gel could not be formed from soymilk at temperatures below 70 ℃. The elastic modulus G'-t and viscous modulus G"-t curves intersected at 75 ℃, which indicated that the coagulation temperature of soymilk was 75°C. Through dynamic temperature scanning, it was found that the coagulation process could be divided into three stages: induction stage (65 ℃~70 ℃), acceleration stage (70 ℃~92 ℃), and stabilization stage (above 92 ℃). The elastic modulus G' and viscous modulus G" increased slowly and a small amount of flocculent precipitate was generated in soymilk during induction; G' and G" increased rapidly during acceleration and tended to be stable during stabilization, indicating that the coagulation process was complete and tofu gel was formed.
