Simultaneous interaction of pH, CaCl2 addition, temperature and enzyme concentration on milk coagulation properties / Interacción simultánea del pH, CaCl 2 añadido, temperatura y concentración enzimática sobre la coagulación de la leche

Abstract

The simultaneous interaction, of the pH (5.6-6.8), CaCl2 addition (100-300 mg/L milk), tempera ture (30-40 °C) and enzyme concentration (0.02-0.05 rennet units/ml milk) on curd firmness (CF) and clotting time (CT) during milk coagulation were followed. The coagulation was performed in the specially designed vessel which was coupled to a rheometer. Whole milk was coagulated by the addition of two types of enzyme, one of microbial and another of bovine origin. The effect of the four variables on CT and CF was evaluated using the response surface design by Box and Wilson, consisting of 30 combinations of factors on four levels, grouped into three blocks. Surface response analysis lead to a polynomial function that describes CT and CF as a function of pH, temperature, added CaCl2 and enzyme concentration. The simultaneous interaction demonstrated that for curd firmness development the main factors were a decrease in pH and an increase in temperature. The firmness of the gel produced with microbial enzyme depended on temperature; conversely, the pH affected the curd firmness achieved with bovine rennet. Under the test conditions, maximum firm ness values were obtained over a small range of pH and temperature. Experimental tests on firm ness showed a better fit for the microbial model than for the bovine one.