Читать книгу 3D Printing of Foods - C. Anandharamakrishnan - Страница 42

The cold extrusion also known as room temperature extrusion (RTE) refers to the process of extrusion and deposition of materials without phase change. Most of the natively printable materials and pre‐processed non‐natively printable, as well as alternative ingredients, can be printed using RTE (Nachal et al. 2019). This type of extrusion is applied for the fabrication of 3D printed products that are difficult to produce by conventional food processing methods. Adoption of 3D printing would result in the production of foods with higher repeatability and smooth finish making them suitable for mass production and customization. Ready to cook (RTC) pasta products with novel 3D designs can be printed from a mixture of wheat semolina and water without the influence of temperature using RTE. Similarly, surface filling and graphical decorations of confectioneries are done using RTE (Van der Linden 2015). The semi‐solid paste‐like food materials are more appropriate for RTE; hence it is also referred to as soft material extrusion. The process involves the continuous extrusion of material from the moving print head that results in layered deposition of materials adhered to the preceding layers upon cooling without phase transition. The printing material supplies not only possess the adequate yield stress and elastic modulus but also shear‐thinning tendency to withstand the desired shape after printing (Huang 2018). Although the temperature is less significant during RTE, the temperature must be fine‐tuned that has a direct influence over the material consistency (K) and flow behaviour (n) (Hamilton et al. 2018). The printability of vegemite and marmite has been determined based on the K and n values in achieving a proper extrusion rate. Apart from the rheological properties, the particle size, crystallinity, and material composition would greatly affect the printability and quality of the 3D constructs.

Cereal and millet‐based doughs, cheese, creamy peanut butter, cake frostings, jam, jelly, hummus, and Nutella are some of the common food materials that are suitable for RTE (Cohen et al. 2009; Millen 2012; Periard et al. 2007). Among the food printing technologies, extrusion‐based 3D printing is widely used for a diverse range of food materials. More recently, the non‐printable surimi (Scomberomorus niphonius) paste was printed with the addition of microbial transglutaminase as an additive (Dong et al. 2020). Results showed that the addition of transglutaminase in the range of 0.2–0.3% (w/w) enhanced the printability of surimi paste. Further, the textural properties such as hardness, cohesiveness, and resilience of the surimi gel were gradually increased with an increase in the concentration of transglutaminase up to 1.4%. The entire printing process was performed using an extrusion‐based 3D printer at room temperature (20 °C). In a similar approach, the printability of the microalgae was assessed for the development of nutritious 3D printed snacks from pastry wheat flour. In this study, a dual printhead system was employed for the coaxial extrusion of microalgae‐enriched snacks. Results showed that the material supplies with 3 and 4% Chlorella resulted in desired 3D construct with accurate precision (Uribe‐Wandurraga et al. 2020). Other than pre‐processing of the materials to enhance printability, post‐processing is another significant step that ensures the safety and edibility of the 3D printed foods. Few of the commercial 3D food printers integrate the post‐processing cooking step along with the printing process. However, most of the lab‐scale 3D printers reported in the literature are at their initial stage that assists in the printing process alone. Hence, additional post‐processing must be followed immediately after the printing process (Yang et al. 2019a). It is crucial to ensure the shape stability and structural integrity of the 3D printed layers during post‐processing without any deformations. Post‐processing methods such as drying, frying, baking, and freezing are common food processing methods used for cooking 3D printed samples (Krishnaraj et al. 2019). A detailed discussion on the various post‐processing methods and its feasibility are presented in subsequent chapter of the present book.