GELATION OF BETA-LACTOGLOBULIN TREATED WITH LIMITED PROTEOLYSIS BY IMMOBILIZED TRYPSIN

The gelation of P-lactoglobulin treated by limited proteolysis with immobilized trypsin was studied by dynamic rheometry. Gelation conditions were (1) 80 degrees C for 3 h with 7% protein (w/v) in 20 mM CaCl2 at pH 7 and (2) 60 degrees C for 12 h with 7% (dr 15%) protein (w/v) in 20 mM CaCl2 (or 100 mM NaCl) at pH 7. Thermal transition temperatures of the different components in the limited proteolysis mixture were determined by differential scanning calorimetry to be 54.0, 58.8, 64.0, and 81.8 degrees C, which are believed to correspond to fragments of the beta-barrel domain and native beta-lactoglobulin. The partially hydrolyzed beta-lactoglobulin had a lower gel point and gelled more rapidly than native beta-lactoglobulin at 80 degrees C. Hydrolyzed beta-lactoglobulin, heated at 60 degrees C in 20 mM CaCl2, formed a weak gel at 7% (w/v) protein and a strong gel at 15%;(w/v). By comparison, very weak gels were formed with native beta-lactoglobulin at both 7% and 15% (w/v) protein at 60 degrees C.