Construction and Properties of Tea Polyphenols-Egg White Protein Composite Gel in 3D Printing Systems

Tea polyphenols (TP) have biological activities such as scavenging free radicals. The TP-EWP complex formed by the combination of TP and egg white protein (EWP) can enhance the structural stability and gel properties of the protein. TP, EWP, corn starch, xanthan gum, and gelatin were used as raw materials in this paper. The rheological properties, textural and structural properties, secondary structure, microstructure, and 3D printing behaviours of 3D printed gel system with different TP-EWP additions were evaluated. The results showed that TP-EWP was able to bind to polysaccharides through intermolecular interactions (e.g., hydrogen bonding, hydrophobic interactions), which enhanced the network structure of the 3D printed gel system. The mobility of water molecules was reduced, with the result that some free water was gradually converted into immobile water. However, when TP-EWP was added in excess of 25%, it caused excessive cross-linking or network collapse, which increased porosity and improved water mobility. The inclusion of TP-EWP was enhanced the gels' rheological characteristics. The gels all showed pseudoplastic behavior and the G' of all samples increased with increasing frequency. With the increase of TP-EWP addition, the flowability of the gels improved and the G'' of the gels tended to decrease. When the amount of TP-EWP added was increased from 20% to 25%, the proportion of α-helices in the gel rose from 17.11% to 25.29%. However, when more than 25% of TP-EWP was added, the percentage of α-helices dropped. The strength, hardness, chewability, and viscosity of the gels were significantly impacted by the addition of various TP-EWP (P<0.05). This study provides a theoretical basis for the application of polyphenol-protein composite gel in the development of 3D printing ink for functional foods.