Proteolysis of a high pressure-treated ewe's milk cheese

Ewe's milk cheeses at different stages of ripening (1 and 15 days) were subjected to high pressure (HP) in the range of 200-500 MPa at 12 degrees C for 10 min in order to study the possibility of cheese ripening acceleration. Microbiological counts (total counts, lactococci and lactobacilli) were reduced as pressure increased, specially those treatments carried out at :400 MPa. Water soluble nitrogen at pH 4.6 expressed as % total N (WSN/TN) and total free amino acids (FAA) were used as index of proteolysis. At the end of ripening, cheeses pressurized at 15 days of ripening had higher WSN/TN values than those treated at day 1, with cheeses treated at 300 MPa obtaining the highest values. The application of 300 MPa treatments led to an increase in the FAA content compared to control cheeses, particularly when HP treatment was applied at day 1. Treatments at 500 MPa resulted in lower FAA contents than control cheeses, suggesting that pressures > 400 MPa delay the FAA formation. Enhancement of proteolysis observed at 300 MPa may be attributed to HP-produced cell lysis and enzymes release, although HP-induced conformational changes in protein cheese matrix could play also a role.