Читать книгу 3D Printing of Foods - C. Anandharamakrishnan - Страница 41

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 °C printing temperature and rice starch with 15–20% concentration (w/w) at 75 to 80 °C was suitable for HME (Zeng et al. 2020). A similar study on comparative analysis of printability of potato, corn, and rice starch gels has been reported (Chen et al. 2019). Nowadays, potato starch is widely used as a thickening and gelling agent in processed foods. In addition, the characteristic high degree of polymerization imparts viscosity and expansion behaviour to potato starch gels making it a suitable ingredient for the fabrication of personalized 3D printed food using HME. It was reported that potato starch of 15–25% concentration at 70 °C exhibits optimal printability. The hot‐melt extruded layers of potato starch result in a uniform extrusion with a compact gel network and possess greater structural integrity (Liu et al. 2020). Likewise, detailed studies on the gelation and gelatinization of millets and pseudo‐cereals would lead to the delivery of nutritious and personalized 3D printed foods that reduces the emergence of lifestyle disorders such as diabetes and obesity.

Figure 2.7 Hot‐melt extrusion of complex 3D geometry bunny using chocolate.

Source: From Lanaro et al. (2017), [p.30] / With permission of Elsevier. DOI‐https://doi.org/10.1016/j.jfoodeng.2017.06.029.