Effect of high-pressure treatment at various temperatures on activity of indigenous proteolytic enzymes and denaturation of whey proteins in ovine milk

The effect of high-pressure (HP) processing (200, 450 or 650 MPa) at various temperatures (20, 40 or 55 degrees C) on the total plasmin plus plasminogen-derived activity (PL), on plasminogen activators (PA), on protease activity (which seemed to be equivalent to cathepsin D), and on denaturation of major whey proteins in ovine milk was investigated. There were synergistic effects between pressure and temperature at 450 and 650 MPa for partial inactivation of PL, PA and cathepsin D. In contrast, processing at 200 MPa did not affect the activity of these enzymes. Treatment at 650 MPa was necessary for the denaturation of a-lactalbumin, and denaturation was enhanced with increasing temperature. In contrast, denaturation of P-lactoglobulin occurred at all combinations of HP and temperature studied. In conclusion, HP affected the activity of various indigenous proteolytic enzymes and the denaturation of major whey proteins of ovine milk, which may influence its behaviour during the manufacturing of dairy products. (c) 2008 Elsevier Ltd. All rights reserved.