EFFECTS OF LIMITED PROTEOLYSIS ON THE MICROSTRUCTURE OF HEAT-INDUCED WHEY-PROTEIN GELS AT VARYING PH

Whey protein solutions, reconstituted 12% commercial whey protein isol ate, were hydrolyzed at pH 7.0 by one of three proteases: trypsin, Neu trase(R) (from Bacillus subtilis), and a Bacillus licheniformis protea se. Heat-induced gels were made from the hydrolysates after pH adjustm ent, and their microstructure was examined by transmission electron mi croscopy and compared with the structure of control gels made from unh ydrolyzed whey protein solutions. The gels formed from the unhydrolyze d whey protein solutions, as expected, were fine-stranded when set at pH 3-0 and 7.0 and particulate when set at pH 5.2. The enzymatic treat ments caused alterations in the microstructure of the heat-induced gel s. The changes were small at pH 3.0, marked at pH 5.2, and strongest a t pH 7.0. Of special interest was the dramatic change in the microstru cture of the gels set after treatment with Bacillus licheniformis prot ease. The Bacillus licheniformis protease gels consisted of small aggr egates (similar to 0.1 mu m) arranged in open clusters (pH 5.2) or tig htly packed in a regular pattern (pH 7.0), corresponding to a high gel strength. Limited hydrolysis is thus a way to change the microstructu re and properties of gels at weakly acidic and neutral pH, a range tha t is suitable for the production of many foods.