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

Abstract

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. Industrial relevance Heat treatment and high pressure (HP) treatment have received considerable research attention as a means for increasing the yield of cheese curd. However, neither is attractive on its own; in the case of heating because it impairs other cheese-making properties of milk, whereas increases in curd yield by HP treatment of milk can be achieved only at economically unattractive long treatment times. However, when milk is heat-treated (10 min at 90 °C) and subsequently HP-treated at a pressure ≥ 250 MPa, an increase in the yield of cheese curd by ∼ 15% can be obtained, while the strength of the renneted milk gel is increased and the rennet coagulation time is reduced. These effects can even be obtained when the pressure is released immediately after the desired level is reached.