Rheometry of processed cheeses

The quality and especially the consistency of cheeses are connected with their rheologic properties. Rotary rheometry is a suitable method for studying the processed cheese rheometry. For measuring we used the rotary rheometer Rheotest 2 with a co-axial measuring cylinder arrangement. The research was aimed at rheological behaviour of processed cheeeses and processed cheese mix which was prepared by the processing of a corresponding mix directly in a rheometer measuring jar. We studied three cheeses with a different chemical composition by the measurement of a shear stress at different rotation frequencies. On an analogy with similar materials of a similar chemical composition (comminuted meat) we expected the correlation of a yield stress and viscose and plastic behaviour of the material. It was proved that a processed cheese reacts like non-Newtonian liquid with a characteristic power shape of yield curves. Shear stress values at the given shear rate as well as apparent viscosity values depend, at a constant temperature, on the chemical composition, i. e. on the content ratio of water, fat and proteins. Shear stress value raises with the increase of water phase content. Apparent viscosity at a constant temperature decreases with the rise of shear stress. The apparent viscosity also depends on the chemical composition in such a way that it is the highest one in a cheese with the highest water content. As the processed cheese mix temperature raises, the exponential value of shear stress decreases as well as the apparent viscosity does. Nevertheless the highest values are reached in the processed cheese mix with the highest fat content. It is evident that after overstepping about 70 degrees C a further decrease does not practically occur and the apparent viscosity decreases (for the given temperature and tangential stress) and since about the tenth day it already remains constant. This course of apparent viscosity correlates also with the most suitable cheese consistency, as to its sensory property, after 10 days