Rheological Properties and Cutting Time of Rennet Gels. Effect of pH and Enzyme Concentration

Abstract

Abstract The subjectively evaluated cutting time of rennet gels was compared to the rheological moduli measured by oscillation at different rennet concentrations and different milk pHs. We found no unique value of the rheological moduli at cutting time but a linear correlation between the cutting time and the time of the maximum rate of increase of G′ indicating that the properties evaluated empirically by the cheesemaker are related to fundamental rheological properties. G ∗ was 7–10 Pa at the cutting time at pH 6.7 and decreased with decreasing pH. Plotting the maximum rate of increase of G′ vs. the enzymatic reaction rate we found a linear relationship with a positive intercept at the y-axis. This shows that the rate of gelfirming is not determined by the enzymatic reaction rate alone. Both the slope and the intercept increased with decreasing pH, demonstrating that the effect of pH on the rate of gelfirming was not only caused by the change in the enzymatic reaction rate. The results indicated that the rate of structural rearrangements of the gel increased when the pH was lower.