Three-Dimensional Printing of Protein/Polysaccharide Mixed Gel Systems for Food Applications

With the improvement of living standards, there is a growing demand for personalized ingredients and desi gn in food. The serious aging situation has further expanded peoples’ requirements for tailored meal compositions and nutrition. Moreover, dysphagia diet has attracted more attention due to the expected double increase in the number of elderly people above 65 and older in the next three decades . However, the unattractive appearance of common dysphagia – oriented diet (usually in mashed or pureed state) causes a loss of appetite, which is directly related to malnutrition and weight loss for the swallowing -impaired patient. Additive manufacturing (AM), also known as 3D printing, is becoming an emerging technology in food application in recent years. It enables food fabrication with less material loss, more flexible shapes and precise content control, showing great potential to enter the home kitchen and clinics. Proteins and polysaccharides are two main types of macromolecules in food systems. They play a vital role in complementary nutritional, structural and textural functions, making the system based on prote in and polysaccharide a good model candidate for 3D food printing. This thesis aims to develop ink formulations based on protein/polysaccharide mixed gels for additive manufacturing towards food application. Firstly, an aqueous protein/polysaccharide food ink using gelatin B (GB) and xanthan gum (XG) was developed for direct -ink writing (DIW) printing. GB and XG were chosen as ink materials because they are low cost and commonly consumed food ingredients. The GB/XG mixed gel ink shows suitable properties during and after the 3D printing process, which endows a 40 -layer 3D printed object with clear pattern at room temperature. The addition of calcium ions (Ca2+), a daily required micronutrient, improves the rheologica l properties of the ink, giving rise to a higher shape fidelity. Furthermore, it was also found that the texture profile can be tuned by the infill percentage of the printed samples. Secondly, the DIW performance of protein/polysaccharide inks was further investigated. Besides the GB/XG pair discussed previously, another frequently used plant -based protein, soy protein acid hydrolysate (SP), was also studied in combination with XG. A processing map was established showing the effects of nozzle diameter and XG concentration on various type of printed geometries including one -dimensional (1D) filaments, two -dimensional (2D) arrays and 3D structures for both GB/XG and SP/XG systems. Rheological results showed that not only the flow behavior, but also the shape retention after printing could be affected by XG concentrations. In addition, a shape fidelity map was generated for the post -deposition assessment of printed 3D structures based on the viscoelastic properties of ink formulations and a defined shape fideli ty index of printed scaffolds. Furthermore, it has been proved that both protein type and XG concentrations are critical to textural properties of printed samples. Finally, based on the established processing and shape fidelity maps, an 18-layer 3D complex dolphin shape composed of two different mixed gels (i.e. 3GB/11XG and 8SP/15XG) was successfully printed by a multi – material DIW printing technique. Finally, a comparative study on cellulose nanocrystal (CNC)-enhanced protein/polysaccharide aqueous food inks was undertaken with GB/XG and whey protein isolate (WPI)/XG for 3D printing towards dysphagia diet. CNC addition improved the rheological properties, which resulted in a high shape fidelity right aft er printing and a ~90% retention of its original shape after 96 h for both GB/XG and WPI/XG systems. Additionally, CNC addition also affected the thermal stability of GB/XG system with a 15% enhancement on side area retention after heating at 50℃. Besides the CNC concentration, the post -deposition temperature also had an important effect on the textural properties, especially for the GB/XG system. Finally, an original finding was observed on the transition from non -approved dysphagia diet into level 5 -minced and moist dysphagia diet by holding at 4℃ on a GB/XG/1.5CNC printed sample.