Soymilk Viscosity as Influenced by Heating Methods and Soybean Varieties

In the two-step heating experiments, soymilk with 5% protein was first heated at 55, 60, 65, 70, 75 or 80C for 10 min, and then heated at 97C for another 10 min. As a control, the soymilk was heated at 97C for 10 to 60 min by continuous one-step heating. The viscosity of the heated soymilk was measured after cooling to room temperature. Results showed that the two-step heating increased the soymilk viscosity by up to six times the viscosity of the control. The maximal viscosity was reached when the first-step heating temperature was 70C. Differential scanning calorimetry showed separate denaturation of soy 7S and 11S proteins was related to the viscosity increase. Soymilk protein content and soybean variety also influenced the viscosity. Three heat transfer methods, including ohmic heating, steam injection and water bath heating, produced different viscosities of soymilk.