High pressure effects on proteolytic and glycolytic enzymes involved in cheese manufacturing

Abstract

The activity of chymosin, plasmin, and Lactococcus lactis enzymes (cell envelope proteinase, intracellular peptidases, and glycolytic enzymes) were determined after 5-min exposures to pressures up to 800 MPa. Plasmin was unaffected by any pressure treatment. Chymosin activity was unaffected up to 400 MPa and decreased at 500 to 800 MPa. Fifty percent of control chymosin activity remained after the 800 MPa treatment. The lactococcal cell envelope proteinase (CEP) and intracellular peptidase activities were monitored in cell extracts of pressure-treated cells. A pressure of 100 MPa increased the CEP activity, whereas 200 MPa had no effect. At 300 MPa, CEP activity was reduced, and 400 to 800 MPa inactivated the enzyme. X-Prolyl-dipeptidyl aminopeptidase was insensitive to 5-min pressure treatments of 100 to 300 MPa, but was inactivated at 400 to 800 MPa. Aminopeptidase N was unaffected by 100 and 200 MPa. However, 300 MPa significantly reduced its activity, and 400 to 800 MPa inactivated it. Aminopeptidase C activity increased with increasing pressures up to 700 MPa. High pressure did not affect aminopeptidase A activity at any level. Hydrolysis of Lys-Ala-p-NA doubled after 300-MPa exposure, and was eliminated at 400 to 800 MPa. Glycolytic enzyme activities of pressure-treated cells were evaluated collectively by determining the titratable acidity as lactic acid produced by cell extracts in the presence of glucose. The titratable acidities produced by the 100 and 200 MPa samples were slightly increased compared to the control. At 300 to 800 MPa, no significant acid production was observed. These data demonstrate that high pressure causes no effect, activation, or inactivation of proteolytic and glycolytic enzymes depending on the pressure level and enzyme. Pressure treatment of cheese may alter enzymes involved in ripening, and pressure-treating L. lactis may provide a means to generate attenuated starters with altered enzyme profiles.