Synergistic Coagulation of Soy Milk by Glucono-δ-Lactone and Magnesium Chloride: A Model Study on the Physicochemical...

Tofu production relies on coagulants like magnesium chloride (MgCl₂) and glucono-δ-lactone (GDL), each imparting distinct textures and flavors. Understanding their synergistic effects is crucial for developing high-quality tofu that balances structural uniformity with enhanced nutritional value. In this study, we investigated the synergistic coagulation of soy milk using a mixed-coagulant system. Various concentrations of GDL (1-7 mM) and MgCl₂ (0-20 mM) were added to soy milk, and the resultant tofu-like precipitate (TLP) formation was analyzed by measuring pH changes, residual protein concentration (RPC), wet precipitate mass (m_wp), and urea solubility. Results showed that increasing GDL concentrations largely shifted the onset of TLP formation and the peaks of urea-soluble protein (USP) and urea-insoluble protein (UIP) toward lower MgCl₂ concentrations. A strong negative correlation was observed between GDL concentration and the midpoint concentrations for RPC and m_wp. Analysis of pH dynamics revealed that GDL-induced hydrogen ion (H⁺) release effectively lowered the threshold for magnesium ions (Mg²⁺) required for coagulation. This interaction suggests that both coagulants promote aggregation by reducing protein surface charges. We conclude that surface charge reduction is the primary driving factor for TLP formation in mixed systems. These findings provide a quantitative framework for optimizing tofu formulations, allowing manufacturers to control coagulation efficiency and texture more precisely. PRACTICAL APPLICATIONS: This research advances tofu development by combining glucono-δ-lactone (GDL) and magnesium chloride (MgCl₂) to achieve tailored texture, flavor, and nutritional value-overcoming limitations of single coagulants. The approach reduces the characteristic bitterness associated with MgCl₂ while bringing out the natural sweetness of soybeans. It also helps in the magnesium fortification of GDL tofu. It also supports processing conditions and minimizing batch-to-batch variations in industrial tofu production.