Direct comparison of the tofu-like precipitate formation by adding different coagulants: magnesium chloride and glucono-δ-lactone

Tofu is produced by adding a coagulant such as MgCl(2) and glucono-δ-lactone (GDL) in soymilk. However, the molecular mechanism of tofu formation by adding these coagulants has been compared between the results obtained under different conditions. In this study, the formation of a tofu-like precipitate (TLP) by adding GDL was directly compared with that formed by adding MgCl(2) under the same conditions except for the coagulants. The effects of both the coagulants were almost the same on the changes in the precipitate weight, supernatant protein concentration, and urea-soluble protein concentration, indicating that a common contributing factor induces TLP formation. However, the effects of the coagulants on pH were largely different, suggesting that pH reduction is not an absolute requirement in TLP formation induced by adding MgCl(2). Moreover, the findings of this study revealed that the decrease in the surface charge of soymilk proteins is a common initiation factor for TLP formation, whereas the intermolecular hydrophobic interaction is an important factor for the formation of urea-insoluble precipitates. Overall, these findings will be useful in discovering new coagulants to enhance the quality characteristics of tofu.