Protease-induced gelation of unheated and heated whey proteins: effects ofpH, temperature, and concentrations of protein, enzyme and salts

The influence of various reaction conditions on the gelation of whey protei n isolate (WPI) induced by a protease from Bacillus licheniformis (BLP) was investigated by following the gelation with a Formagraph and a controlled stress rheometer. As little as 0.5% of denatured WP, or 2% of untreated WP, was able to gel upon the enzymatic treatment (pH 7.0, 50 degrees C, 1 % BL P, no salt added). The enzyme-induced gelation process was significantly en hanced by increasing protein and enzyme concentration and by increasing tem perature. The presence of salt, up to 15 mM CaCl2 or 100 mM NaCl, decreased the gel time for the enzyme-induced gelation process. Higher salt concentr ations, however, led to a more coagulum-like gel. The gelation properties o f the enzyme-induced gels varied with pH, due to a combination of effects o n the net charge and on the enzyme activity. In all conditions tested, the denatured WPI solution had a higher rate of gelation and a higher gel stren gth than the gels from untreated WPI solution. (C) 2000 Elsevier Science Lt d. All rights reserved.