Influences of Calcium and pH on Protein Solubility in Soybean Milk.

Tofu-curd is made by the flocculation of proteins in soybean milk with an addition of calcium. The proteins consist of soluble and particle fractions. The influences of calcium and pH on the protein solubility of these fractions were investigated. The protein particles precipitated at lower calcium concentrations than that of the soluble proteins. This precipitation of proteins took place at higher pH with calcium than that without calcium. Therefore, it is considered that the first step to tofu-curd is the formation of a network by the protein particles at low calcium concentration. The next step was seemed to be the binding of the soluble proteins to the network by further addition of calcium and decreasing pH.