High shear cooking extrusion to create fibrous mozzarella cheese from renneted and cultured curd

To understand shearing on cheese curds during high shear extrusion, the controlable parameters of a twin-screw extruder were related with measured and calculated parameters that characterise the extrusion process effects on product properties. Curd properties were correlated with specific mechanical energy SME (23-390 kJ·kg^-1), T_exit (22-54 °C) and residence time RT (36-507 s); the wide experimental range studied provided new insights regarding extrusion of cheese curds. Longer and finer fibers were produced at low SME (23-27 kJ·kg^-1), high T_exit (50-54 °C) and short RT (55-60 s). Whereas extruded curds produced at high SME (166-390 kJ·kg^-1), low T_exit (22-23 °C) and long RT (371-396 s) tend to form a compact structure with less fiber formation. Temperature in the heating section, T_h, and temperature of the cooling die, T_c, were found to determine critical curd phase transitions during extrusion, from viscoelastic solid to viscoelastic liquid and vice versa, that are important for the creation of fibrous cheese curd structures. T_c was the most important factor influencing SME, indicating the considerable contribution of the cooling process in increasing the shear forces. Curd composition and textural properties were significantly influenced by T_h and T_c, showing that a higher T_h enhances curd elasticity and reduces melt strength while a higher T_c induces lower water content and increases melt strength. We concluded that a variety of structured mozzarella products with customized properties can be produced by controlling the extrusion parameters.