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

Abstract The influence of various reaction conditions on the gelation of whey protein 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°C, 1% BLP, no salt added). The enzyme-induced gelation process was significantly enhanced by increasing protein and enzyme concentration and by increasing temperature. The presence of salt, up to 15 m m CaCl 2 or 100 m m NaCl, decreased the gel time for the enzyme-induced gelation process. Higher salt concentrations, however, led to a more coagulum-like gel. The gelation properties of the enzyme-induced gels varied with pH, due to a combination of effects on 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 strength than the gels from untreated WPI solution.