SIMULTANEOUS INTERACTION OF PH, CACL2 ADDITION, TEMPERATURE AND ENZYME CONCENTRATION ON MILK COAGULATION PROPERTIES

The simultaneous interaction, of the pH (5.6-6.8), CaCl2 addition (100 -300 mg/L milk), temperature (30-40 degrees C) and enzyme concentratio n (0.02-0.05 rennet units/ml milk) on curd firmness (CF) and clotting time (CT) during milk coagulation were followed. The coagulation was p erformed in the specially designed vessel which was coupled to a rheom eter. Whole milk was coagulated by the addition of two types of enzyme , one of microbial and another of bovine origin. The effect of the fou r variables on CT and CF was evaluated using the response surface desi gn 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, te mperature, added CaCl2 and enzyme concentration. The simultaneous inte raction demonstrated that for curd firmness development the main facto rs were a decrease in pH and an increase in temperature. The firmness of the gel produced with microbial enzyme depended on temperature; con versely, the pH affected the curd firmness achieved with bovine rennet . Under the test conditions, maximum firmness values were obtained ove r a small range of pH and temperature. Experimental tests on firmness showed a better fit for the microbial model than for the bovine one.