Correlating 3D printing performance with sol-gel transition based on thermo-responsive k-carrageenan affected by fructose

Thermo-responsive food inks occupy an important part of 3D food printing materials. A great challenge of their accurate 3D printing is to ensure sol-gel transition is adapted to 3D printing process. In this study, k-carrageenan (KG) incorporated with fructose (0–30%, w/v) was selected as a representation of thermo-responsive inks, and their interactive mechanism was investigated. Sol-gel transition and rheology were correlated with 3D printing process in terms of extrusion stage, formation stage, and self-supporting stage. Results indicated that fructose addition increased ink's gelation temperature (Tg) and affected printing temperature selection. During extrusion stage, ink in sol-state with a low viscosity was desirable to enable proper extrudability. While, during formation stage, sol-gel transition speed (gelation time) was important for extruded ink to solidify to avoid continuous spreading. Increased elastic modulus (G′) with fructose addition was beneficial for printed structures to be self-supportable during self-supporting stage. Low field nuclear magnetic resonance (LF-NMR) indicated that water mobility was increasingly restricted with addition of fructose. Hydrogen bond, hydrophobic and electrostatic interactions all significantly affected the KG/fructose ink. Scanning electron microscopy (SEM) suggested that fructose addition resulted in a denser network structure. This study would provide insights on 3D printing of thermo-responsive food inks by correlating with sol-gel transition.