Effect of high pressure processing on rennet coagulation properties of milk

Abstract

The effect of high pressure (HP) treatment of milk on rennet coagulation properties were evaluated. Three coagulation parameters—lag time, mean coagulation rate and inflexion time (time for reaching the point of maximum coagulation rate) were evaluated as a function of pressure (200–400 MPa), temperature (3–21 °C) and holding time (10–110 min) using a response surface methodology. A central composite rotatable design and a second order multiple response model were used to investigate the effect of process variables (pressure, temperature and holding time) and relate them to coagulation parameters. In general, with an increase in pressure or holding time, or a decrease in temperature, lag and inflexion times associated with the rennet coagulation showed a decreasing trend while the mean coagulation rate showed the opposite. Canonical analyses indicated that the stationary point was a saddle point for lag time and mean coagulation rate whereas a minimum for inflexion time. At the stationary point, the predicted values were: lag time, 7.7 min (85 min HP treatment at 296 MPa and 5 °C); inflexion time, 11.3 min (50 min treatment at 370 MPa and 6 °C) and mean coagulation rate, 0.0034 min −1 (72 min at 275 MPa and 14 °C).