Читать книгу 3D Printing of Foods - C. Anandharamakrishnan - Страница 43

Hydrogel‐forming extrusion (HFE) is the process of the extrusion of hydrocolloid solutions/ dispersions into a polymeric/ hardening/ gel setting bath using a syringe‐based extrusion mechanism through a moving printing nozzle (Kuo et al. 2021). Here, the solution temperature is a key criterion that determines the stability of droplets. The gel droplet’s diameter ranges about 0.2–5 mm that forms a smooth distinct layer on deposition (Sun et al. 2018a). The rheological property and the gelation characteristics of the polymeric solution have significant implications on the successful printing of hydrogels. During the printing process, the polymer solution in the liquid state gets transformed into a stable gel state upon deposition. Research works on the fabrication of edible hydrogels are quite increased due to the advantage of the development of soft foods for aged people with swallowing disorders (Serizawa et al. 2014). Commercially available hydrogel printers are equipped with advanced dispensing units for the precise deposition of material. A 3D fruit printer developed by a UK firm, Dovetailed combined strawberry fruit flavour with the sodium gel for 3D printing of little spheres into a cold solution of calcium chloride bath to resemble a raspberry fruit (Molitch‐Hou 2014).

Figure 2.8 3D printed wheat starch hydrogels.

Source: From Maniglia et al. (2020a) / With permission of Elsevier.

Recently the effect of dry heat treatment (DHT) on the 3D printing of cassava starch hydrogels has been reported (Maniglia et al. 2020b). The effect of pre‐processing and the post‐stability of printed cassava hydrogels were analyzed. The starch was chemically modified with prolonged exposure to DHT (4 hours at 130 °C) that resulted in higher carbonyl content and larger granule size. Thus, DHT was proved to have a significant implication on rheological properties that in turn aids in printability. Further, it was reported that the longest storage period increases the firmness of hydrogel preserves the structural integrity of printed 3D constructs. Similar results were obtained for DHT of wheat starches (Figure 2.8) (Maniglia et al. 2020a). During DHT, the molecular depolymerization was evident with a reduction in starch crystallinity. Thus, studies on starch‐based hydrogels would extend the possibilities of fabrication of novel soft foods with altered textures. Hence, more research studies on the impact of pre‐treatments on the chemical modification of macro components of food systems would explore the range of potential opportunities in 3D printing. In another study, the fabrication of bio‐scaffold with hybrid gels of gelatin and alginate (1 : 2) at 7% resulted in a stable 3D printed matrix with the highest hardness and adhesiveness (Kuo et al. 2021). Subsequent post‐processing freeze‐drying of 3D printed hydrogels enhanced the mechanical properties and shelf‐life of the product. Also, the microstructural analysis revealed the porous structure of the 3D printed scaffolds that has a great scope for encapsulation of bioactive compounds such as probiotics, enzymes, vitamins, minerals, enzymes, and antioxidants (Pérez‐Luna and González‐Reynoso 2018). However, only a few studies reported on the scope of integration of 3D printing and encapsulation. More research works are required in improving design modification of 3D printers suitable for micro‐ and nano‐encapsulation; software integration with a high power source; material characterization and method for improving the bioavailability of micronutrients.