Characterising the influence of milk fat towards an application for extrusion-based 3D-printing of casein-whey protein suspensions via the pH-temperature-route

This study presents the design and characterisation of casein-whey protein suspensions (8.0/10.0% (w/w) casein and 2.0/2.5% (w/w) whey protein) mixed with dairy fat (1.0, 2.5 and 5.0% (w/w) total fat) processed via the pH-temperature-route in preparation for 3D-printing. Mechanical treatment was applied to significantly decrease the particle size of the milk fat globules and increase surface area, creating small fat globules (<1 mu m) covered with proteins, which could act as pseudo protein particles during gelation. Different proteins covered the fat globule surface after mechanical treatment, as a result of differences in the pH adjusted just prior to heating (6.55, 6.9 or 7.1). The protein-fat suspensions appeared similar by transmission electron cryogenic microscopy and the zeta-potential of all particles was unchanged by the heating pH, with a similar charge to the solution (similar to -20 mV) occurring after acidification (pH 4.8/5.0) at low temperatures (2 degrees C). A low heating pH (6.55) resulted in increased sol-gel transition temperatures (G' = 1 Pa) and a decreased rate of aggregation for protein-fat suspensions. A higher heating pH (6.9 and 7.1) caused an increased rate of aggregation (aggregation rate >= 250 Pa/10 K), resulting in materials more promising for application in extrusion-based printing. 3D-printing of formulations into small rectangles, inclusive of a sol-gel transition in a heated nozzle, was conducted to relate the aggregation rate towards printability.