3D food printing is a novel food processing technology that uses 3D printers to pile raw materials layer-by-layer to fabricate products with complex structures and shapes. Based on this technology, novel products with personalized shapes, colors, textures, nutritional profiles and flavors can be produced (Yang, Zhang, & Bhandari, 2017; Zhang, Pandya, McClements, Lu, & Kinchla, 2021). Among various 3D food printing technologies, extrusion 3D printing is the most commonly used method, which has some requirements on the printability of food bioinks. The bioinks should be “extrudable” to facilitate printing. They are expected to have adequate “self-supporting" capacity to maintain printed objects' desired structure and shape during or after printing (Sun, Zhou, Huang, Fuh, & Hong, 2015). However, most reported food bioinks used for extrusion 3D printing have poor printability (Jiang et al., 2019; Jiang, Zhang, & Mujumdar, 2021).

Egg yolk is a nutritious food ingredient that contains a wide range of macro- and micro-nutrients such as protein (16–18%, w/w), fat (30–33%, w/w), vitamins, minerals, and antioxidants (Anton, 2013). However, fresh egg yolk is highly perishable due to its high water activity, so it is usually dried into powder to extend the shelf life for food applications. Several recent studies reported the application of egg yolk powder for 3D printing (Liu, Liang, Saeed, Lan, & Qin, 2019). For example, (Anukiruthika, Moses, & Anandharamakrishnan, 2020) investigated the effect of incorporating egg yolk or white powder on the printability of rice flour-based food bioink. The result suggested that bioink with egg yolk powder exhibited better self-supporting capacity than the one containing egg white powder.

Starch is a common polysaccharide compound used to produce the gel for 3D food printing. It comprises many glucose molecules linked by α-1,4- and α-1,6-glycosidic bonds (Rong et al., 2023). Starch undergoes gelatinization at high temperatures, and the pasted starch have viscoelastic properties that can quickly respond to the applied shear strain and exhibit shear-thinning behavior. The regeneration of starch after pasting improves the mechanical strength of the starch gel, which is beneficial for maintaining the stability of the printed product (Chen et al., 2022; Zheng et al., 2019). In general, the printability of bioinks was significantly affected by the physicochemical properties of starch, such as amylose-to-amylopectin ratio, molecular structure and size, as well as regeneration rate. The ratio of amylose to amylopectin is an important factor affecting the performance of 3D printing. Amylose is a linear molecule that forms gels in water more tightly than amylopectin, resulting in stronger gels. Amylopectin, on the other hand, because of the presence of branches, makes its gel formation in water faster, and the gel structure is relatively relaxed. Recent studies reported the success of using starch-based bioinks for 3D food printing (Chen et al., 2022; Chen, Xie, Chen, & Zheng, 2019; Kim, Patel, & BeMiller, 2013). However, the gels solely produced using common starches such as potato or corn starches usually exhibit high viscosity and poor extrudability (Rong et al., 2023). Zheng et al. (2019) found that due to the existence of phospholipid bonds in the starch molecule, it is hard to regenerate resulting in samples printed from potato starch not being well stabilized. This is because too low a regeneration rate would inhibit the precipitation of water from the starch polymer network. To date, researchers have tried to improve the printability of starch-based bioinks by incorporating other food compounds. For example, Cui et al. (2022) added xanthan gum and sodium alginate to potato starch gels to develop novel bioinks with improved printability and structure retention properties of the printed 3D object. In addition, these reported starch-based gels were composed of limited types of food compounds, which resulted in a compromised nutritional value (Zeng, Chen, Chen, & Zheng, 2021). There is a research demand to develop novel nutritious bioinks with promising printability for 3D printing purposes (Jiang et al., 2019; Li et al., 2022).

In this study, we incorporated egg yolk powder into potato and corn starch to develop novel gel bioinks for food 3D printing. The rheological properties of gels were determined in terms of small amplitude oscillatory shear (SAOS), apparent viscosity measurement, and large amplitude oscillatory shear measurements. Subsequently, the microstructure, functional groups, textural profile, and printability of the different gels were investigated. International Dysphagia Diet Standardization Initiative (IDDSI) tests were conducted to assess the swallowing properties of the produced gels. This work aimed to provide insights on developing egg yolk powder-starch gel as novel bioinks for food 3D printing.