Effects of gelation temperature on Mozzarella-type curd made from buffalo and cows' milk. 1: Rheology and microstructure

The rheology and microstructure of Mozzarella-type curds made from buffalo and cows' milk were measured at gelation temperatures of 28, 34 and 39 degrees C after chymosin addition. The maximum curd strength (G') was obtained at a gelation temperature of 34 degrees C in both types of bovine milk. The viscoelasticity (tan delta) of both curds was increased with increasing gelation temperature. The rennet coagulation time was reduced with increase of gelation temperature in both types of milk. Frequency sweep data (0.1-10Hz was recorded 90 min after chymosin addition, and both milk samples showed characteristics of weak viscoelastic gel systems. When both milk samples were subjected to shear stress to break the curd system at constant shear rate, 95 min after chymosin addition, the maximum yield stress was obtained at the gelation temperatures of 34 degrees C and 28 degrees C in buffalo and cows' curd respectively. The cryo-SEM and CLSM techniques were used to observe the microstructure of Mozzarella-type curd. The porosity was measured using image J software. The cryo-SEM and CLSM micrographs showed that minimum porosity was observed at the gelation temperature of 34 degrees C in both types of milk. Buffalo curd showed minimum porosity at similar gelation temperature when compared to cows' curd. This may be due to higher protein concentration in buffalo milk. (C) 2012 Elsevier Ltd. All rights reserved.