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 mm CaCl2 or 100 mm 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.