EFFECTS OF LIMITED PROTEOLYSIS ON GELATION AND GEL PROPERTIES OF WHEY-PROTEIN ISOLATE

Whey protein isolate was hydrolyzed by three proteolytic enzymes, porcine trypsin, a Bacillus subtilis protease (Neutrase (R)), and a Bacillus licheniformis protease. The heat-induced gelation properties of the hydrolysates were investigated as a function of pH, whey protein concentration, and the degree of hydrolysis, which was determined by osmometry. At pH 5.2, all control solutions (not hydrolyzed) containing 3 to 12% whey protein formed gels on heating to 80 degrees C, but, at pH 3.0 and 7.0, only the most concentrated solution gelled. After hydrolysis by the B. licheniformis protease, all whey protein solutions at pH 7.0 formed gels, and the strength of the 12% whey protein gel was 10 times higher than that of the corresponding control gel. Trypsin hydrolysis prevented gelation of the 12% whey protein solution at pH 3.0 and 7.0 and caused a pronounced weakening of the gels formed at pH 5.2. Hydrolysis by Neutrase (R) did not change the ability to form a gel, but the gels formed at pH 5.2 and 7.0 were weaker and, at pH 3, were slightly stronger than the control gels. Gelation properties of whey proteins, thus, can be manipulated by limited proteolysis. Of special interest is the possibility of making very strong heat-set gels in the neutral pH range.