Coagulation of Soymilk by Proteolytic Enzyme Treatment

Abstract

Soymilk was treated with proteolytic enzymes, including ficin, bromelain, papain, rennet and pepsin to investigate their digestibility and coagulability. Coagulation of soymilk occured within a short time after addition of ficin and bromelain, but papain treated soymilk required too long time for coagulation. Rennet and pepsin had no coagulability. It was clear that heat treatment of soymilk at the temperature above 70°C, corresponding to the denaturation of soy protein, was essential for coagulation of soymilk by proteolytic enzymes. The coagulability of ficin and bromelain for soymilk rapidly decreased by heat treatment of each enzyme solution at temperature above 65°C. As the coagulation of soymilk resulted in proteolysis of soy protein, the recovery of protein in coagulants from soymilk was comparatively low at reaction temperature in the rangeof 40°-60°C. To improve the protein recovery, 1.0×10^-5 or 1.0×10^-6 mol calcium was added to soymilk with enzymes. Addition of calcium, however, had no effect on the coagulability and protein recovery. The lactic fermentation of soymilk by Streptococcus thermophilus considerably reduced coagulation time and increasd the protein recovery. In the manufacturing process of cheese like product with application of curd formation by lactic fermentation and addition of ficin or bromelain, the curds obtained had no bitterness and the percentage of protein recovery reached approximately 80%.