Effects of high pressure treatment on the rennet coagulation and cheese-making properties of heated milk

In this study, the effect of high pressure (HP) treatment (0-30 min at 100-600 MPa at 20 °C, where treatment for 0 min implies the immediate release of pressure after reaching the desired level) on the rennet coagulation and cheese-making properties of milk heated at 90 °C for 10 min was investigated. Unpressurised heated milk or heated milk treated for 0 min at 100 MPa was not coagulable by rennet; however, heated milk treated at 250-600 MPa for 0-30 min had a rennet coagulation time (RCT) equal to, or lower than, that of unheated unpressurised milk; RCT decreased with increasing pressure and treatment time. The strength of the rennet-induced coagulum from heated milk treated at 250-600 MPa for 30 min or 400 or 600 MPa for 0 min was considerably higher than that of unheated unpressurised milk. Furthermore, the yield of cheese curd from HP-treated heated milk was ∼ 15% higher than that from unheated unpressurised milk and the protein content of the whey was ∼ 30% lower, regardless of pressure or treatment time, whereas the moisture content of the curd was not significantly influenced. These results indicate that by the application of a heat treatment, followed by a HP treatment, milk with superior rennet coagulation and cheese-making properties can be obtained.