Abstract: In order to explore the effect of inorganic salts on papain-induced coagulation of soybean protein, the changes of clotting time, texture properties, pH and protein degradation were determined during or after the coagulation of soybean protein isolate (SPI) in the presence of one of five salts including NaCl, KCl, CaCl2, MgCl2 and MgSO4. The results showed that the clotting time was shortened and gel strength was increased; the pH of SPI was reduced after the addition of salts. After papain was added, the pH revealed a continuous decrease to a steady level upon a certain time of incubation. Ca2+ and Mg2+ revealed more effective than Na+ and K+ on both clotting time and gel strength under the same ionic strength. The gel strength revealed an increase by 60% when the amount of papain was reduced to 0.1% from 0.15% (m/m). Therefore, the presence of salts could shorten clotting time and gel strength, and the addition of calcium or magnesium salts is an effective way to enhance the strength of papain-induced SPI gel.

Key words: salts, papain, soybean protein isolate, gel