Self-assembly of plant polyphenols-grafted soy proteins to manufacture a highly stable antioxidative Pickering emulsion gel for direct-ink-write 3D printing

The practicable application of 3D printing in the pharmaceutical and food sectors directly relates to the preparation of highly stable bioactive printable inks. Here, three different polyphenols (rosemary polyphenols, thyme polyphenols, and basil polyphenols) were individually grafted onto soy protein isolate through a free-radical grafting method to produce a precursor printable ink to develop 3D printed plant-based cheese. The morphological features, emulsion rheology measurements, quartz crystal microbalance with dissipation monitoring techniques, and interfacial shear rheology were used to monitor emulsification features and interfacial rheology (i.e., adsorption kinetics, viscoelastic features, and interfacial adsorbed layers) of precursor inks. Compared to soy-based ink, polyphenols-grafted soy protein inks developed more stable emulsions against coalescence with finer droplets. Also, the interfacial adsorption properties of protein particles were improved after the grafting process, in which the surface dilatational viscoelastic moduli and interfacial pressure were boosted. The ink formulating by soy protein-g-rosemary polyphenols (with greater hydrophobicity) showed a emulsion droplets with smaller size, had a stiffer structure, and stronger surface activity than inks containing soy protein-g-thyme or soy protein-g-basil polyphenols, which displayed a 3D printed cheese analogue with improved lubrication property, higher creamy sensation and mouth-coating feature. Overall, this work suggests that compatibilization of the plant polyphenols and the soy proteins offers an opportunity for adopting plant-based inks in the 3D printing of advanced materials.