Colloidal state-based studies on the chloride salts of magnesium- and calcium-induced coagulation of soymilks

Chloride salts (MgCl₂ and occasionally CaCl₂) coagulation of the heated soymilks is the key step in manufacturing traditional tofu. In this study, colloidal state diagrams were constructed first, and then the effects of processing parameters, including coagulant concentration, preheating intensity, protein concentration, and coagulation temperature as well as the intrinsic properties (phytate concentration) on the microstructure, protein coagulability, and water holding capacity (WHC) were investigated to gain an overall framework understanding of the Mg²⁺ and Ca²⁺ coagulated soymilk process. As the variables changed, the coagulated soymilks displayed one of the following states: colloidal suspension, flocs, weak gel, and strong gel. The microstructures of the coagulated systems also changed to different features with the variation in processing parameters and phytate concentrations. Several interesting results were obtained. It was found that the transformations from colloidal suspension to gel state were usually corresponding to the increase of particle size, the decrease of porosity, and a sharp increase in protein coagulability. The colloidal states of Mg²⁺ and Ca²⁺ coagulated soymilks were usually different, but their microstructures were similar. With the increase of protein concentration, the protein coagulability decreased but the WHC was enhanced. The presence of high phytate contents led to form small protein agglomerates, which resulted in worse protein coagulation and WHC. It is expected that this study will deepen the understanding of chloride salts coagulation process.