Additive layer manufacturing of semi-hard model cheese: Effect of calcium levels on thermo-rheological properties and shear behavior

Additive layer manufacturing (ALM) is an emerging technology for production of complex three-dimensional objects in the food sector. In this study, semi-hard model cheeses with different calcium levels (15.8 ± 0.9 to 31 ± 2 mg Ca g−1 protein) were produced to investigate thermo-rheological properties and shear behavior at large strain to set up process parameters for hot-melt extrusion based ALM. The gel-sol transition temperature (51.7 ± 0.2 to 60 ± 2 °C) significantly (P < 0.001) decreased with declining calcium levels. Hence, extrusion die temperature was set to 60 °C in capillary rheometer experiments to mimic hot-melt extrusion based ALM. The extrudate strands were evaluated visually and recorded pressure profiles were analyzed to determine critical shear rates. It was demonstrated that critical shear rate (10-30 s−1) increased significantly (P < 0.001) with decreasing calcium levels and with increasing flowability (tan δ60°C). By exceeding the critical shear rate, extrusion instabilities occurred indicating limitation of ALM processes.