Tailoring the properties of egg white protein-based emulsion gels for 3D printing: Role of droplet size and matrix concentration.

Abstract

This study investigated the effects of oil droplet size and egg white protein concentration on the properties of emulsion gels to be applied in 3D printing ink. Droplets with distinct sizes were produced by a combination of homogenization and sonication. To tailor the properties of emulsion gels, discrepant sizes of droplets and gradient concentrations of egg white protein (EWP) were applied. With increasing EWP concentration, the gel strength increased from around 30 to 250 g, also the rheology properties were improved. Further analysis of relaxation time indicated that the water molecular mobility changed appreciably with EWP concentration and emulsion droplet size, a tighter binding was exhibited in the emulsion gel with small droplets and high matrix content. The incorporation of smaller droplets was prone to the formation of a denser network structure characterized by a finer mesh size (9.30 nm) and a higher cross-linking density (3.94 mol/m³). Moreover, with progressing EWP concentration, the 3D printing accuracy of emulsion gels firstly increased and then decreased, peaking at 8% EWP concentration, which attained 96.7% and 95.4% for emulsion gel containing small and large droplets. It was concluded that its stability was improved with rising EWP concentration and smaller emulsion droplets. This study highlights the important roles of protein concentration and droplet size in the design of emulsion gels with texture-tunable properties for 3D printing ink.