Changes in creep behavior and microstructure of model Mozzarella cheese during working

- Shear work affects structure, fat particle size and creep behaviour of cheese.
- Excessive shear work causes loss of anisotropic nature of model Mozzarella cheese.
- Elastic response of model cheese increased with increase in shear work levels.

The effect of shear work input on the microstructure, fat particle size and creep behavior of model Mozzarella type cheeses was studied. Cheese samples were prepared in a twin screw cooker at 70 °C by mixing protein and fat phases together with different amounts of shear work input. Major changes in cheese structure were observed while working at 150 rpm and 250 rpm screw speeds. Confocal microstructures plus macroscopic observations showed systematic changes in structure with increased shear work inputs with unmixed buttery liquid observed at <5 kJ kg−1, typical Mozzarella type microstructures (elongated fat-serum channels) at 6-15 kJ kg−1 and homogeneously distributed, small size fat droplets at >58 kJ kg−1. At very high shear work inputs, > 75 kJ kg−1, striations or anisotropy in the microstructures had disappeared and small micro-cracks were evident. A 4-element Burger's model was found adequate for fitting the creep data of model cheese at 70 °C but a 6-element model was required at 20 °C. As shear work input increased retarded compliance decreased and zero shear viscosity increased indicating the more elastic behavior of the cheeses with higher shear work input. Changes in the protein matrix appear to be the main reason for increased elastic behavior.