The evaluation of proteases as coagulants for soy protein dispersions

The ability of different proteases to induce the gelation of soy protein isolate dispersions (5.33% w/w) was studied. The coagulation time and gel firmness were determined using dynamic viscoelastic measurements. Among the six protease tested, papain was the most effective coagulant in terms of gel strength and coagulation speed; the second was alcalase. Degree of hydrolysis (DH), pH and viscosity profiles of soy proteins were tested during the coagulation with different proteases. The result suggested that strong interactions, other than electrostatic interaction, existed between peptides in papain and alcalase induced coagulation. Thermal and pH stability tests indicated that papain was more stable than alcalase in the temperature (60–90 °C) and pH (5.8–7.0) ranges studied. Higher papain dosages within the range of 5–13.3 U/ml resulted in firmer soy protein gels, but concentrations higher than 13.3 U/ml produced weaker gels. With the addition of 0.625 mM cysteine, the soy protein coagulation ability of papain was improved. A soy protein gel formed with 0.025% papain in the presence of 0.625 mM cysteine had about the same strength as that induced by 0.133% papain without cysteine.