Effect of varying high-pressure treatment conditions on acceleration of ripening of cheddar cheese

The effects of high-pressure (HP) treatment conditions on proteolysis in Cheddar cheese ripening were investigated by response surface analysis. A second-order central composite rotatable design (CCRD) was used to study the influences of pressure and processing time in the range 70-400 MPa and 3.5-81.5 h, respectively, at 25 °C. Separate control samples were maintained for equivalent times at 25 or 8 °C at atmospheric pressure. Urea-PAGE analysis indicated that breakdown of α_s1-casein, and concomitant production of α_s1-I-casein (f 24-199), was increased by treatment at 100 MPa for 70 h at 25 °C. Accumulation of α_s1-I-casein did not increase at >225 MPa and, at 350-400 MPa, decreased accumulation of α_s1-I-casein was observed. Response surface models indicated that treatment at pressures <150 MPa gave greatest increases in levels of pH 4.6-soluble N (SN), expressed as a percentage of total N (TN) in cheese, relative to control samples. As pressurisation time increased at <150 MPa, levels of pH 4.6-SN/TN in cheese increased. However, in general, HP reduced the production of free amino acids. Confocal laser scanning microscopy showed structural differences between Cheddar cheese treated at 350-400 MPa and control cheese stored at 25 °C or 8 °C. In summary, the application of relatively low pressures increased levels of primary proteolysis in Cheddar cheese. However, the temperature of pressurisation was a significant determinant of the overall effect of HP on proteolysis in Cheddar cheese.