Читать книгу 3D Printing of Foods - C. Anandharamakrishnan - Страница 38

3D food printing is a digitalized process of fabrication of edible 3D construct in a layered manner. The subsequent layers of materials are bonded together through appropriate chemical transitions that alter the state of the material upon deposition. In contrast to the robotic manufacturing process, 3D printing of foods not only allows for automation of process but also helps in customization and personalization of diet (Sun et al. 2018b). More complex food geometries with intricate designs can be fabricated using 3D printing with accurate precision that is nearly impossible with conventional food processing techniques. Interestingly, 3D printing as a single standalone technology can integrate multiple unit operations of conventional processing into a single step (Nachal et al. 2019). Food printing follows a sequence of steps that starts with the development of 3D CAD design or scanned 3D model. The 3D model in its STL format is fed to the slicing software for retrieving the design information in machine‐readable G and M codes. These computer codes are applied to the 3D food printers that assist in the printing process. A typical 3D food printer consists of the coordinate movement axes, printing platform, motor assembly, feed supply, print head, and microprocessor controller unit (Anukiruthika et al. 2020) (Figure 2.2).

In a broader sense, food printing technologies are categorized based on the nature and state of raw materials used (Feng et al. 2018). It includes 3D printing of flowable liquids, solid powders, semi‐solid paste, and cell cultures. Accordingly, the AM processes that are adapted for 3D printing of liquid‐based semi‐solid food materials include extrusion printing, material jetting, and binder jetting. While the powder materials are 3D printed based on the sintering process. As a variant of existing 3D printing techniques, bioprinting involves the culturing of live cell cultures and tissue scaffolds (Godoi et al. 2016). Extrusion‐based food printing is the most common technique used for a wide range of food materials such as starch (Theagarajan et al. 2020), proteins (Liu et al. 2019a), dietary fibre (Lille et al. 2018), and myofibrillar tissues (Dick et al. 2019b). This is because of its simplicity, flexibility, and ease of operations. However, these types of food materials require appropriate pre‐processing for enhancing printability and post‐processing for its edibility (Feng et al. 2020). Next to the extrusion, the sintering technique is widely used for the fabrication of sugar and starch‐based 3D constructs. In the process of sintering, the solid particulates get compacted into a solid mass of material upon external stimuli such as either heat or pressure. Materials such as plastics, ceramics, and metals are commonly used in the sintering process. Considering food printing, sintering is used to fabricate 3D constructs from low melting powders such as sugars, fat, cocoa powder, and Nesquik without melting the material to the point of liquefaction (Sun et al. 2018a). Another powder‐based technique is inkjet printing. It involves the controlled deposition and accumulation of droplets of food inks either in a continuous or DoD manner. The solid powder particles are bonded together with the printed liquid material. Commercial 3D food printers such as De Grood Innovations™ and Foodjet™ are based on inkjet printing mechanisms that are used for 2D decorations and surface filling of cakes, pastries, and biscuits (Godoi et al. 2016). Although inkjet printing can produce fine and appealing 3D constructs than extrusion‐based printing, this technology is not suitable for high viscous food materials. In case of liquid binding, the printing involves the accumulation of powder layers through direct fusion with droplets of liquid binder as opposed to printing material as in case of material jetting (Holland et al. 2019). Commercial 3D printer Chef Jet™ are based on this technique and are used for printing of sugar fondants, confectioneries, and candies.

Figure 2.2 Schematic view of CARK food 3D printer.

Source: Anukiruthika et al. (2020) / With permission of Elsevier.

Another variant of the 3D printing technique used for printing live cell cultures is bioprinting. It involves the process of fabrication of living structures from a cell‐laden bio‐ink. Nowadays, scientists are more interested in the development of in‐vitro cultured meat that has a minimal environmental impact (Post et al. 2020). 3D bioprinting is an ideal means for the construction of cell tissues, scaffolds, and organs. Various AM approaches that are used for 3D bioprinting are extrusion‐based, droplet‐based, and photocuring‐based bioprinting. Among which extrusion‐based 3D printing is widely used for the printing of turkey (Lipton et al. 2010), fish (Chen et al. 2020), beef (Dick et al. 2019b), and pork‐based food products (Dick et al. 2020). Apart from extrusion‐based bioprinting, other approaches like droplet‐based and photocuring must be explored and studied in detail for a better understanding of the state‐of-the‐art of printing of in‐vitro meat. Some of the commercial 3D printers available for bioprinting include 3D Bioplotter, NovoGen MMX Bioprinter™, and Biobot™ (Gu et al. 2019). Advancements in bioprinting for food applications would open up a new dimension of research and remains to offer a promising solution for the shortage of animal‐based meat. Further, 3D printing has a less environmental impact with reduced carbon footprints and overall product life cycles.

Printability refers to the dimensional stability of the material to withstand its own weight (Kim et al. 2018a). So, the success of printability greatly depends on the material composition and printing variables. Food is a complex mixture of macro and micro constituents with varied physiochemical properties (Pérez et al. 2019). The selection of the 3D printing technique is greatly influenced by the type and state of the printing material supply. Some of the material properties are considered specifically based on the type of the printing technique. Properties such as glass transition temperature, powder characteristics, wettability, compressibility, melting and solidification behaviour, viscosity, and crystallinity highly influence the end‐quality and stability of the 3D printed constructs (Nachal et al. 2019). Similar to the product characteristics, process variables such as nozzle size, nozzle height, printing speed, flow rate, motor speed, laser power, and printing temperature must be optimized for the fabrication of seamless 3D construct (Liu and Zhang 2019). Consideration of the material properties and the process variables would vary based on the 3D printing technique used. Some of the common 3D printing technologies that are widely used for food applications have been discussed in the following sections.