Development of a pH-responsive system based on starch and alginate-pectin hydrogels using coaxial 3D food printing

This study developed and optimized a 3D food printing (3DFOODP) process of a complex hydrogel system, consisting of a starch core and a pH-responsive alginate-pectin (Al–P) shell for potential encapsulation purposes. A coaxial nozzle setup was employed to print such a complex hydrogel structure. The 3D printability of inks (i.e., starch and Al–P) was first optimized for the best shape retention. By varying the concentrations of these biopolymers (i.e., 10–12 wt% for starch and 2–4 wt% for Al–P) in the ink solutions, it was found that a 2 wt% Al–P and an 11 wt% starch concentration provided the best printability. The printability of Al–P was significantly enhanced with the use of 0.02 M calcium chloride solution during the ink formation. The rheological properties of the inks were characterized in detail, where the shear experienced by the inks in the coaxial nozzle was also calculated. XRD and FTIR analyses of the 3D-printed hydrogel system showed a reduction in crystallinity and no covalent chemical interactions, respectively. Finally, SEM images displayed a porous structure ideal for encapsulation purposes.