3D Printing of Foods. C. Anandharamakrishnan

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Figure 2.6 3D printing of material supply using multi‐head 3D food printer MultiCARK™ (unpublished).

Another variant of the 3D printing system is the applicability of a multi‐head printing unit for the simultaneous printing of food materials (Nachal et al. 2019). The printing process using an in‐house designed multi‐head 3D food printer is presented in Figure 2.6 (MultiCARK™ unpublished). The lower printing speed of the single head system is the major disadvantage that results in lesser production and consumes more time. The incorporation of the multiple heads eventually overcomes the above‐mentioned limitations. However, the printing of multi‐scale ingredients with multi‐head systems adds to the complexity involved in the fabrication of 3D constructs. Hence, appropriate design modifications are required for ensuring the homogeneity of the ingredient mixtures. Conventionally, static‐ and agitating‐mixer units are used for the mixing of food materials (Millen 2012). So, the appropriate integration of the conventional processing units with a multi‐head 3D printing system would result in a homogeneous material supply. Thus, the system design of 3D printers for food applications remains a void research area that must be addressed for exploring the potential benefits of 3D food printing. Also, concerns related to operational safety and system cleanliness are the critical factors that must be considered for the safe delivery of the foods. Some of the available commercial 3D printers based on extrusion mechanism are Choc creator, Foodini, and BeeHex robot pizza printer (Sun et al. 2018a).

2.4.2 Classification of the Extrusion‐Based 3D Printing System

      2.4.2.1 Hot‐Melt Extrusion

HME also known as FDM, was first used for the 3D fabrication of polymers and ceramics. Considering food applications, HME is used for those materials considering their melting and solidification behaviour. The process involves the deposition of melted semi‐solid food from a moveable FDM print head through the hot‐end nozzle tip (Mantihal et al. 2019). The deposited layers will solidify immediately after extrusion and bonded together with the previous layers upon cooling. The temperature is precisely controlled and determined based on the melting point of the food materials used. HME is mostly applied for the fabrication of 3D constructs using chocolates, starch, and protein gels (Chen et al. 2019; Hao et al. 2010; Liu et al. 2019a). Understanding the material properties is crucial for the fabrication of 3D constructs in a well‐defined quality. In the case of chocolate printing, the combination of sugar with cocoa fat assists in the easy flow of the material through the extruder. The self‐supported layers of chocolate rely on the thermal properties such as glass transition temperature (T _g) and melting point that are critical for the successful solidification of the material (Mantihal et al. 2017). The chocolate ink with pseudoplastic behaviour imparts conducive printability that in turn depends on the temperature used. It is essential to play around the six crystal polymorphs of the cocoa butter for achieving a stable 3D‐oriented product with better texture and glossy appearance (Figure 2.7) (Lanaro et al. 2017). Some of the commercial 3D printers specific to chocolate printing are Choc Creator, ChefJet, and CocoJet. Researchers from the Massachusetts Institute of Technology (MIT) printed the melted chocolate using the direct ink writing (DIW) method using the developed 3D printer ‘Digital Chocolatier’ (Zoran and Coelho 2011). A similar approach has been used by 3D Food‐Inks Printer for the printing of 3D‐colored images on the extruded base (Golding et al. 2011). However, a post‐processing step is required for the fusion of printed layers. More recently, Rando and Ramaioli (2020) studied the effect of heat transfer on the print stability of chocolate. The study investigated the correlation between the rheological and thermal properties for achieving a well‐stable 3D structure. The stability criterion based on the developed yield stress during extrusion explained the stability or deformation of the printed materials.

Starch being an integral macro component of food grains that has a great scope for 3D printing. Recently, research on the fabrication of starch‐based 3D constructs using HME is gaining attention. When the starch suspensions are subjected to heat treatment, the starch granules will swell with the absorption of a large amount of water and results in a thicker gel matrix through the process of gelatinization. This resulted in a starch gel that possesses characteristic viscoelastic, shear‐thinning, and thixotropic behaviour that aids in the smooth continuous flow of material during extrusion and structural stability to printed layers during and after the extrusion process (Maniglia et al. 2020b). The mechanical strength and the extrudability of the starch gels explained its printability. Results showed that corn starch with 20% concentration (w/w) at 70–75 СКАЧАТЬ