Extrusion-based 3D printing of food biopolymers: A highlight on the important rheological parameters to reach printability

The interest in 3D food printing has increased substantially over the years. One of the main challenges in this field is how foods can be made printable. Often, biopolymers are added to achieve printable consistency. The printability of biopolymers-based food materials is strongly affected by the rheological properties of the inks. This review focuses on identifying the important rheological parameters to achieve acceptable printability in 3D food printing. These parameters, describing viscoelasticity, yield stress, flow behaviour, die swell and extensional flow, are discussed across the different stages of extrusion-based type of printing; (a) the ink preparation, (b) the ink extrusion, (c) the ink deposition, and finally (d) the formation of the 3D structure. Temperature dependent rheological behaviour affecting the sol-gel behaviour of food inks is also described. Overall, more knowledge is still required, especially regarding the relationship between rheological properties of food inks and printing conditions, in order to widen the application of this technology within the food industry, particularly in the development of personalised diets.