Effect of high-pressure treatment on the activity of some polyphenoloxidases

The activity of a commercial polyphenoloxidase extracted from mushrooms was found to decrease steadily with increasing applied pressure (100-800 MPa) and time (1-20 min) in phosphate buffer at pH 6.5. Complete inactivation was only achieved on treatment at 800 MPa for at least 5 min. In contrast, relatively mild heat treatment (60 degrees C for 30 min) at atmospheric pressure led to total inactivation. The loss in activity was irreversible. Sephadex chromatography indicated that pressure treatment caused some aggregation of the enzyme. Polyphenoloxidases extracted (but not purified) from mushrooms and potatoes responded differently to pressure. The enzyme in potatoes steadily lost activity with increasing applied pressure although after 10 min at 800 MPa about 40% of the activity remained. The mushroom extract exhibited a marked increase in activity after treatment at 400 MPa for 10 min (about 140% of the value of the untreated sample) and even after 10 min at 800 MPa considerable activity remained (about 60% of the original value). Possible reasons for these differences are discusssed. When mushrooms were pressurized, considerable browning was observed immediately after pressurization, even at 200 MPa. Potatoes and apples browned to a limited degree on pressure treatment up to 600 MPa and browned still further on subsequent storage. Treatment at 800 MPa, of both potatoes and apples, caused litte browning but both foods took on a cooked appearance. It is concluded that high-pressure treatment alone is not a realistic means of inactivating these enzymes in food. (C) 1996 Elsevier Science Ltd.