Optimal coagulant concentration, soymilk and tofu quality as affected by a short-term model storage of proto soybeans

Soybeans were adjusted to water activities (A(w)) from 0.60 to 0.81, and stored at 30C for up to 3 months. At 1-month intervals, soybeans were retrieved from the storage and processed into 10.5 Brix soymilk. The optimal coagulant concentration (OCC)for making filled tofu was determined using a titration method. Other soymilk characteristics, including total solids, protein, 11 S/7 S protein ratio, phytate, titratable acidity, pH and color were also determined. Filled tofu was prepared from each stored soybeans with the respective OCC using MgCl2 or CaCl2. With increasing A(w) or storage time, the OCC decreased significantly. The decrease in OCC was significantly correlated to the difference in soymilk titratable acidity and the change in soymilk pH. Soybean storage time slightly decreased the breaking stress and apparent Young's modulus of the filled tofu, particularly the MgCl2 coagulated tofu. With increasing A(w) or storage time, the lightness and yellowness intensity of both soymilk and tofu decreased, whereas their redness intensity increased.