THE EFFECT OF FREEZING AND PRESSURE OF 50 MPA AND 100 MPA ON THE PROTEOLYTIC ACTIVITY OF ENZYMES IN EDAM CHEESE

This study examined the effects of pressure treatment at 50 MPa / 0.5 h and 100 MPa / 0.5 h, at 18 ± 2oC, on the proteolytic activity of edam cheese subject to freezing after week 1, 4, 6 and 8 of ripening. The aim of the study was to test the utility of high pressures in cheese ripening under model conditions. Sensory and chemical analysis was performed on Edam cheeses after varied periods of ripening. The chemical analysis involved determination of active acidity of cheese, water and salt content and the content of different fractions of nitrogen compounds. Subsequently, the cheeses were frozen in a freezer (freezing rate 1 cm h –1 ) or in an alcohol bath (freezing rate 0.1 cm h –1 ), in order to speed up the lysis of starter cells. Extracts of frozen cheeses were subjected to high pressure treatment. Proteolytic activity of enzymes was determined by the Westhoff method in frozen, frozen and pressurised and control cheese samples after 1 and 2 weeks of incubation at 30 o C. The results of the sensory and chemical analysis displayed the normal course of the ripening process. The proteolytic activity of enzymes increased as the cheese ripened. No significant difference was found between the proteolytic activity in extracts from control cheese and in those from frozen and pressurised cheese. Freezing the cheese after 8 weeks of ripening lowered the activity of proteolytic enzymes. The proteolytic activity of enzymes in extracts from frozen cheeses after 8 weeks of ripening, pressurised at 50 MPa / 0.5 h was higher than in those subjected to the pressure of 100 MPa / 0.5 h. Pressure treatment of extracts from frozen cheeses at 50 MPa or 100 MPa did not result in expected acceleration of proteolysis.